tyatmll ImoEtaitg Bhratg Jltlfara, N*w fork ALEXANDER GRAY MEMORIAL LIBRARY ELECTRICAL ENGINEERING THE GIFT OF Cornell University Library TK 145.H68 Heavy electrical engineering 3 1924 004 406 231 Cornell University Library The original of this book is in the Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924004406231 HEAVY ELECTRICAL ENGINEERING ELECTRIC RAILWAY ENGINEERING H. F. PARSHALL, M.Inst.C.E. AND H. M. HOBART, M.Inst.C.E., M.I.E.E. £2 2s. net. The Electrical Engineer. — "The book is thoroughly up to date, and deals with the most recent practice. It is one which we can heartily commend to all who are interested in the development of electric traction, although the names of the authors form perhaps the best commendation." The Times. — " Upon the bookshelf of technical literature this volume will be assigned a place amongst standard works." LONDON ARCHIBALD CONSTABLE & CO. LD. 10 ORANGE STREET LEICESTER SQUARE W.C. HEAVY ELECTRICAL ENGINEERING H. M. HOB ART, M.Inst.C.E., M.I.E.E., Mem. A.I.E.E. CONSULTING ENGINEER NEW YORK D. VAN NOSTRAND COMPANY 23 MURRAY AND 27 WARREN STREETS 1908 BRADBURY, ACJNEW, & CO. LI)., PRINTERS, LONDON AND TONERIDGE. THIS BOOK IS DEDICATED TO ERNST DANIELSON UNDER WHOSE GUIDANCE AND INFLUENCE THE AUTHOR ACQUIRED HIS FIRST ENTHUSIASM FOR ENGINEERING WORK. PREFACE Many text books have been published under the general title of " Electrical Engineering." An examination of these books reveals on the part of their authors a conception of the preferential scope of the subject which is at complete variance with my conception. Hence, beyond the similarity of title, there is nothing in common between the present treatise and these others. I have omitted routine descriptive material as well as the elementary generalities regarding electricity and magnetism, and I have directed my efforts to an attempt to familiarize the reader with various considerations and calculations of which a sound, knowledge should be acquired in order to enable him effectively] to engage in practical electrical engineering work. Eegrettable as it appears, it is nevertheless a fact that the real progress in electrical engineering is being made by too small a majority of those engaged in the electrical engineering profession. Many have not the remotest approach to broad knowledge of the subject ; often they have not the energy or the enterprise to exer- cise their own reasoning faculties. Such are hardly more than figure-heads desirous on the one hand of being on the side of the most fashionable engineering fad, so soon as there is no longer any doubt of its being fashionable, and on the other hand hesitating to depart from the cut-and-dried practice of years' standing, which makes the preparation of plans a mere matter of copying, and eliminates all risk and uncertainty. Swayed by these opposing tendencies, they soon become incapable of seeing any engineering question in its true aspects. Steam turbines are recommended, utterly regardless of whether condensing facilities are sufficient; single phase traction by commutator motors is heralded with a flourish of trumpets by the very engineers who had previously taken up the position that one of the chief objections to the continuous current motor is the necessity of employing a commutator ; electrical PREFACE ix survive ; the forced idea will go to the wall ; but it is only after extended experiments conducted on a large scale have been laboriously completed, that we realize that an idea has been followed out that could have lived only under particularly favourable conditions, such as are not usually found in practical operation." I am of opinion that were engineers to display greater frankness in dealing with current engineering questions as they arise, there could not fail to result a more general acquirement of true engineer- ing instincts and an avoidance, to a greater extent, of the wasteful method of only distinguishing " forced " ideas after the loss of much valuable time and the waste of vast sums of money. As a case in point the single phase railway mania may be cited. This has even now hardly run its course, although a thoughtful consideration of the case should have long since enabled engineers to see that it is a " forced " idea. Behrend points out that : " The very mueh reduced output of both generators and motors, if operated single phase ; the reduced efficiency ; the impaired regulation ; the increased heating and less stability of single phase motors and generators, connected with the increased cost resulting from the greater amount of material required ; these form the main reasons which induce me to call the recent attempts which have been made in the utilization of single phase currents a forced idea. . . . If single phase currents are to be used successfully, a new creative idea must be introduced which will do away with some of the dis- advantages peculiar to the present single phase apparatus." Another instance cited by Behrend on this same occasion is so remarkably pertinent that I should like to call attention to it : — " In the category of the forced ideas is to be placed the idea of transmitting large volumes of power by means of high potential continuous current. That such things can be done is unquestion- able, but to do them by means of high potential continuous current is unreasonable. The intuition of the experienced engineer, which is, as it were, the consolidated experience of many years, will guard him against becoming too deeply wrapt up in schemes of this sort." The means by which the true engineering instinct may best be acquired cannot be concisely set forth. In my opinion, however, one thing is very important, and that is, to be as frank as possible, not only when discussing engineering questions with others, but also, when working with such questions by ourselves ; equally important it is, and by no means easy, to be rigorously frank with ourselves and so not to delude ourselves into placing x PEEPACE confidence in premature conclusions. The first-mentioned relation is nowadays but little more than a farcical battle of " bluff," neither participant displaying much sincerity nor crediting others ■with more. In the second relation, our attitude towards our- selves, there is sometimes scarcely less deception. In an interesting contribution to the Times Engineering Supplement for January 8, 1908, Prof. Ayrton relates that Lord Kelvin once, in a spirit of mischief, had printed and sent out to various of his friends copies of a paper containing a number of complicated equations accom- panied by wholly meaningless and unintelligible text. The paper was reverentially received, and Lord Kelvin used to relate with a twinkle in his eye that " nobody has yet found any mistake in that paper." We aspire to employ mathematical or other complex methods which most of us are by nature or education utterly incompetent truly to comprehend, and we consider this latter circumstance to be so woefully humiliating that we have not the ' courage to admit it even to ourselves. Is it not far better, in such a plight, to throw away these complicated and, to us at any rate, useless tools, and turn to simple, if less elegant processes ? It is, however, useless to generalize even in such questions, and when reflecting on these lines, one is apt to come round to the point of view enunciated somewhat as follows by Buskin : — " Such, then, are a few of the great principles, by the enforce- ment of which you may hope to promote the success of the modern students of design ; but you should remember that none of these principles will be of any service whatsoever unless you fully recognize that they are in one profound and stern sense, useless. By this I mean that you must understand that neither you ijor anyone can, in the great ultimate sense, teach anybody how to make a good design. If designing could be taught, all the world would learn, as all the world reads or calculates. But designing is not to be spelled nor summed. My men continually come to me, in my drawing class in London, thinking I am to teach them what is instantly to enable them to gain their bread. ' Please, sir, show us how to design.' ' Make designers out of us.' And you, I doubt not, partly expect me to tell you to-night how to make designers of your Bradford youths. Alas ! I could as soon tell you how to make or manufacture an ear of wheat, as to make a good artist of any kind. I can analyse the wheat very learnedly for you, and tell you that there is starch in it, and carbon, and silex. I can give you starch and charcoal and flint, but you are as far from your ear PEEFAOE xi of wheat as you were before. All that can possibly be done for anyone who wants ears of wheat, is to show him where to find grains of wheat, and how to sow them, and then, with patience — ground and weather permitting — the ears will come. So in this matter of making artists — first you must find your artist in the grain ; then you must plant him ; fence and weed the field about him, and with patience — ground and weather permitting — you may get an artist out of him, not otherwise." If we substitute engineering students for Euskin's audience of young artists, the pertinence and soundness of the view is very striking. Before concluding this Preface I wish to acknowledge my indebtedness to the work of the late Prof. Lewicki, and of Mollier, for certain fundamental data relating to the phenomena of friction in steam and of the properties of superheated steam ; to Carter's investigations in the subject of electric traction, and to the Electrical Review, the Electrical Times, the Times Engineering Supplement, Electrical Engineering, the Railway Gazette, and the Tramway and Railway World, for the courteous permission to employ certain extracts from the columns of their publications. Messrs. Edward Arnold and Messrs. Whittaker & Co. have also kindly permitted certain brief extracts to be made from Wilson and Lydall's Electric Traction, and from Stevens and Hobart's Steam Turbine Engineering. Had not the preparation of the MS. preceded Lord Kelvin's death, I should, throughout the .treatise, have employed the kelvin for the unit of energy, instead of the kw hr, and I earnestly advocate the general use of the term " kelvin " in this sense. To Mr. J. B. Sparks I am indebted for much able technical assistance, particularly in the sections relating to the transmission of electrical energy. London, 1908. H. M. HOBART. CONTENTS Preface . . . . CHAP. PAGE Vll List of Illustrations ... . . . . xv i. introductory . .... . 1 ii. the overall efficiency of generating stations and the relation between coal consumption and outgoing elec- trical energy ... 18 hi. steam raising plant 57 tv. piston engines and steam turbines 73 v. condensing plant .... 92 vi. electric generating plant 105 vii. the design of generating stations 121 viii. high-tension power transmission lines 157 ix. the high-tension continuous current series system . 203 x. electric traction calculations 218 xi. traction motors and electrification of railways . . 240 Appendix 307 Index .... 309 LIST OF ILLUSTRATIONS FIG. _ PAGE 1. Relation between Heat and Temperature for Water and Steam at Atmospheric Pressure 3 2. Relation between Heat and Temperature for Water and Steam at Various Pressures 6 3. Curve showing Average Specific Heat for Steam Superheated from the Saturation Temperature to various Higher Temperatures . 12 4 — 7. Curves of Convertible Energy in One Ton of Steam . To face 17 8. Curve showing the Average Overall Efficiencies of Generating Stations of Various Capacities ....... 28 9. Efficiencies of Stations as given by Patchell 33 10. Efficiencies of Stations ......... 35 11 — 13. Analysis of Losses in Steam Generating Plant .... 38 14 — 15. Annual Output and Efficiency of Pour Continental Generating Stations 46 16. Average Efficiency of Continental Generating Stations of Various Outputs for Different Tears 48 17. Average Rated Amount of Connections to the Distributing Mains of Generating Stations of Towns with a Population of under 10,000 Inhabitants . . . . ... . . . . .49 18. Estimated Efficiencies of Stations of Various Capacities ... 54 19. Diagrammatic Section of a Typical Power Station, with Slow Speed Vertical Engines 58 20. Central London Railway Daily Load Curve, 1906 .... 60 21. General Outline of Preliminary Design for Large Steam Turbine Generating Station ......... 62 22. Curves of Water Heat, Latent Heat and Total Steam Heat . . 63 23. Curves showing Variation of Final Temperature of Steam with Absolute Pressure and for Various Numbers of Degrees of Superheat 66 24. Showing the Size of Steam Pipes required for different Weights of Steam "70 25. Representative Data of Steam Consumption of Steam Turbines and Piston Engines ... 74 26 — 28. Curves showing the effect of Admission Pressure, Superheat, and Exhaust Pressure on the Pull Load, i and i Load Steam Consumption To face 75 xvi LIST OF ILLUSTEATIONS FIG. PAGE 29. Curves of Steam Consumption of Piston Engines and Steam Turbines of Various Sizes operated under Various Conditions of Temperature and Pressure ...... To face 75 30. Diagrammatic Bepresentation of Transformation of Heat of Steam into Electrical Energy ......... 78 31. Showing how the Friction Losses due to the Potation of a 22 kw de Laval Turbine Wheel vary with the Density of the Surrounding Steam . 79 32. Showing how the Friction Losses in a 22 kw de Laval Turbine vary with the Speed 80 33. Friction Loss of Wheel Eevolving in Steam of Various Densities . 81 34. Riedler-Stnmpf 2,000 Horse Power Wheel 82 35. Belluzzo's Tests of Friction Losses of Wheels Eevolving in Dry Steam 83 36. Turbine Wheels and Blades with which the Curves of Fig. 35 were obtained 84 37 — 40. Showing the Speed of Steam emerging from a Correctly Pro- portioned and Frictionless Diverging Nozzle supplied at various Pressures and Temperatures .... To face 85 41 — 44. Showing the Steam Consumption of Steam Turbines and Piston Engines with 100 per cent. Thermodynamic Efficiency To face 85 45 — 46. Representative Curves for the Steam Consumption at Bated Load and Half Load of Modern Generating Sets employing Piston Engines and Steam Turbines operated at an Admission Pressure of 13 kg per sq cm, a Superheat of 50° C and an Exhaust Pressure of 0'15 kg per sq cm To face 87 47 — 48. Curves showing the Thermodynamic Efficiency of Bepresentative Piston Engines and Steam Turbines at Bated Load and Half Bated Load To face 87 49. Steam Consumption as Function of Admission Pressure ... 87 50 — 54. Variation of Steam Consumption and Efficiency with Admission Pressure, calculated for a 4,000 kw Parsons Type Steam Turbine, at Constant Steam Temperature of 250° C. . . . . .89 55. Showing the Thermal Efficiencies for various Steam Temperatures as a Function of the Admission Pressure ..... 91 56. Curves Showing the Quantity of Water required to condense One Ton of Steam 96 57 — 59. Belation between the Temperature of Condensing Water and the Exhaust Pressure (Curves based on tests by B. W. Allen) . 101 60. Belation between the Temperature of Condensing Water and the Exhaust Pressure (Curves based on tests by B. L. Weighton) . 102 61. Comparison between weights of High-Speed Engine-Driven Gene- rating Sets and Parson's Type Turbine-Driven Generating Sets . 118 62. Belation of Bated Speeds and Outputs of Direct- Connected Electric Generating Sets . . .119 63. Section of a Typical Power Station, with Slow Speed Vertical Engines 1 23 64. Central London Bailway. Sectional Elevation of Power Station . 124 65. Central London Bailway. Plan of Power Station . . . .125 LIST OF ILLUSTRATIONS xvii ^ 1 ^^* PAGE 66. Bristol Tramways. Cross-section of Power Station . . . .126 67. Cross-section of Chelsea Power Station of the London Underground Railways Co. ..... 127 68. Sectional Elevation of Thorn Hill Power Station of the Yorkshire Power Co. 129 69. Plan of Thorn Hill Power Station of the Yorkshire Power Co. . . 130 70. Plan of the Central Electric Supply Co.'s Marylebone Station . . 131 71. Cross-section of Engine and Boiler Rooms of Great Eastern Rail- way's Generating Station 132 72. Plan of Generating Station of Great Eastern Railway . . 133 73. The Overall Length of Parsons Turbo-Generating Sets . . .136 74. Floor Space occupied by Parsons Turbo -Generating Sets . . . 137 75—78. Alternative Arrangements of Boilers and Turbo-Generating Sets 138 79. Plan and Elevation of Power House proposed for supplying Electricity for Operating the Berlin Elevated Railways . . 139 80. London County Council Electricity Supply, 1907. General Arrange- ment of Proposed Generating Station at Barking . . . 140 81. Preliminary Outline of General Arrangement of 270 Million kw hr per annum Generating Station 141 82. Carves showing the Draught obtained from various Chimneys when the Temperature and the Height of the Shaft are varied . . 143 83. Connection Diagram for Steam Plant showing Steam and Water Circuits ..... 150 84. Showing Correct Location of Main Range . 152 85. Typical Arrangement of Steam Piping ... . . 153 86. Distance between Conductors, in Meters, for Different Working Voltages . 164 87. Minimum Height of Conductor above Ground for Different Voltages between Conductors 165 88. Weight of Steel Towers of Various Overall Lengths and for Various • Loads ... 168 89. Classification of Overhead Transmission Lines .... 170 90. Cost of Three-Phase Duplicate Circuit Transmission Line (Copper Line) 171 90A. Cost oE Three-Phase Duplicate Circuit Transmission Line with Aluminium Line Conductors . . . . . . .172 91. Cost of Three-Phase Duplicate Circuit Transmission Lines . . 173 92. Cost of Three-Phase Duplicate Circuit Transmission Lines with 0,3 per cent. Loss per km for various Voltages between Con- ductors 174 93. Sections of High Tension Cables 179 94. Section of Single-Core Cable to illustrate Fall of Potential in the Dielectric 181 95. Insulation Thickness for Homogeneous Cables from Jona's Formula 182 96. Thickness of Insulation of Graded Cables for Alternating Current . 183 97. Works Cost Constant for Three-Core Cable, as function of Copper Section and Voltage 187 h.e.e. b xviii LIST OF ILLUSTRATIONS FIG. PAGE 98. Cost of Three-Phase Three-Core High Tension Cables . . .189 99. Cost of Three-Phase Three-Core High Tension Cables . . .190 100. Cost of Three-Phase Three-Core Cables at different Voltages between Cores, with 0,3 per cent. Loss per km . . . 191 101. Curves showing most Economical Voltage for kw Transmitted per Cable at 0,3 per cent. Loss per km ...... 192 102. Cost of Cable per km per kw Transmitted with Increasing kw (for most economical Voltage) with 0,3 per cent, loss per km . . 193 103. Section through Underground Conduit 196 103a. Determination of most Economical Line Efficiency for Trans- mission of 50 Million kw hr per year over a distance of 25 km . 200 104. Curves showing the most Economical Efficiency for Transmission Lines To face 201 105. Curves showing most Economical Efficiency of Line for Annual Transmission of 50 Million kw hr at various Voltages . . . 202 106. Diagram of Typical Bulk Supply Area 205 107. Transmission Loss as a Percentage of Load for Continuous and Alternating Current Systems . . . . . • .211 108. Thury's Tests of Sparkling Voltages for Continuous Current and Alternating Current in the Air .213 109. Typical Speed-Time Diagram ... .... 218 110. Graphical Representation of the Degree of Importance of the Duration of Stop, and the Number of Stops, on the Schedule Speed, for an Average Speed of 36 km per hour and for various Distances between Stops ... . 220 111. Graphical Representation of the Degree of Importance of the Average Speed on the Schedule Speed for 1 Stop per km . .221 112. Speed-Time Diagrams for a 1 km Run at an average Speed of 36 km per hour 221 113. Modified Speed-Time Diagram 222 114. Simplified Speed-Time Diagram 222 115. Graphical Determination of the Value of the Mean Acceleration from the Speed-Time Curve 223 116. Simplest form of Speed-Time Diagram .... . 224 117. Simplified Speed-Time Diagrams for Different Rates of Acceleration 225 118. Curves for Tractive Resistance (from Aspinall's Formula) . . 226 119. Curves for Tractive Resistance (from Zossen Tests) .... 227 120. Tractive Resistance on Tube Railways .... . 227 121. Analysis of Tractive Resistance ..... . 228 122. Tractive Resistance Curves for Different Weights of Trains . . 229 123. Author's Curves for Tractive Resistance for a 200-Ton Train in Tube and in Open 231 124 — 127. Maximum Speeds necessary in order to obtain certain Schedule Speeds with various Rates of Acceleration ..... 232 128 — 131. Rates of Acceleration necessary to obtain certain Schedule Speeds 233 132 —133. Tractive Force for Accelerating 235 134 — 142. Curves showing the Watt-Hours per Ton Eilometer at Axles LIST OF ILLUSTRATIONS xix ™J. PAGE for a 200-Ton Train, also Average Input at Axles in Kilowatts per Ton To face 235 143. Speed, Tractive Force, Power and Energy at Axles for a 200-Ton Train operated at Average Speed of 51 kw per hour distance of 2 km between Stops To face 237 144. Energy expended at Axles and Maximum Instantaneous Power for Different Rates of Acceleration 237 145. Curves giving the Overall Efficiency of Equipment .... 238 146 — 154. Curves showing the Watt Hour Input to the Trolley per Ton Kilometer for a 200-Ton Train, and also- the Overall Efficiency of the Equipment To face 239 155 — 163. Curves showing the Average Input to the Trolley in Kilowatts per ton, and also the Watt Hours Input to the Trolley per Ton Kilometer (from Figs. 146—154) for a 200-Ton Train . To face 239 164. Outline Sketch of 240 hp. C Railway Motor 252 165. Outline Sketch of 115 hp Single-Phase Railway Motor . . . 253 166. Starting Curves of Siemens-Schuckert 175 hp Compensated Series Motor .264 167. Efficiency and Power Factor Curves of Siemens-Schuckert 175 hp Compensated Single-Phase Motor 265 168. Speed Time Diagram and Energy Input Curves for a 156-Ton Five- Coach Train provided with 6-175 hp motors ..... 266 169. Curves showing the Losses in the Motors during the Run. Separated from the Total Input Curves of Fig. 168 268 170. Speed Characteristic and Tractive Force Curves of Siemens-Schuckert Single-Phase Motor 269 171. Alternative Speed Time Diagram and Energy Input Curves for a 156-Ton Five-Coach Train provided with 6-175 hp Motors . . 270 172. Curves showing the Losses in the Motors at any instant during the run. Separated from Total Input Curves of Fig. 171 . . . 272 173. Speed Characteristic and Tractive Force Curves of 175 hp Compen- sated Siemens-Schuckert Single-Phase Motor .... 273 174. Alternative Speed Time Diagram for a 156-Ton Train (Five-Coach) showing the Impossibility of attaining the required Schedule Speed with Limited Acceleration 275 175 — 178. Performance Curves of Siemens-Schuckert 175 hp Compensated Series Single-Phase Motor at Pressures of 320 volts, 275 volts, 220 volts, and 150 volts To face 275 179. Speed, Ampere and Torque Curves of W E 51, 115 hp Single-Phase Compensated Repulsion Motor 277 180. Curves of Speed and Time and of Energy Input to Axles for 132-Ton Train 278 181 — 188. Data of Capital Costs and Operating Expenses corresponding to the Electric Railway Systems of Columns A, B, C & D of Tables 92, 93 and 94 To face 300 181A — 188A. Data of Capital Costs and Operating Expenses corresponding to the Electric Railway Systems of Columns A, B, C & D of Tables 92, 93 and 94 To face 300 LIST OF TABLES TABLE PAGE I. The Specific Heat of Water at Various Temperatures . 4 II. Table of the Internal, the External, and the Total Latent Heat of Vaporisation of Water 5 HI. Table of Energy in Kilowatt Hours, required to convert One Ton of Water at 0° 0. into Steam at various Pressures and Superheats .8 IV. Table of Specific Volume and Specific Weight of Saturated and Superheated Steam 9 V. Table of the Energy in Kilowatt Hours required to convert One Ton of Water at 0° C. into Steam at various Temperatures and Pressures .... .10 VI. Table of the Average Specific Heat of Steam, heated from the Temperature of Vaporisation to various Pinal Temperatures . 11 VII. Table of Specific Gravity and Specific Heat of various Materials 11 VIII. Heat, in Kilowatt Hours, rendered available for Con- version into Work by the Expansion of One Ton of Steam . .15 IX. Wetness Factors at Exhaust, for Steam Expanded Adiabatically from various Initial Temperatures and Pressures ......... 16 X. Calorific Values of a Number of Varieties of Coal . . 18 XI. Energy required to raise One Ton of Steam from Water at 50° C. to various Pressures and Degrees of Superheat . 21 XLT. Showing, for various Boiler Efficiencies and various Coal Qualities, the Tons of Steam raised per Ton of Coal burned, as a function of the Boiler Pressure and Super- heat 23 XIII. Cost of Coal in Pence per Kilowatt Hour for various Boiler Efficiencies 24 XIV. Cost and Calorific Value of Coal used in various Generating Stations 26 XV. Fuel Cost per Kilowatt Hour Output from Generating Stations given in Table XIV 27 XVI. Annual Outputs and Annual Overall Efficiencies of 26 Generating Stations 29 XVII. Further Details of the Twenty-six Generating Stations . 30 LIST OF TABLES TABLE PAGE XVIII. Average Overall Efficiencies of .Stations given in Table XVI 31 XIX. Particulars of Stations given by Patchell .... 34 XX. Average Eesults for Stations given by Patchell . . 36 XXI. Average Overall Efficiencies of Generating Stations for 30 per cent, and 50 per cent. Load Factor ... 36 XXII. Showing Losses during Transformation of Energy con- tained in Coal into Mechanical or Electrical Energy . 37 XXIII. Table of Exterior Lighting of various British Towns . 39 XXIV. Table. of Public Lighting Supply for Four Continental Towns, showing relation to Private Lighting ... 41 XXV. Table for Electric Tramways in various British Towns, showing Car Miles per Inhabitant and kw hr per Car km 41 XXVI. Table of Electricity Supply in Various Continental Towns, showing hp connected in Motors per 1000 Inhabitants and kw hr per year per hp connected .... 42 XXVn. To tal Electricity required for Hypothetical City of 1 000 000 Inhabitants 43 XXVIII. Showing the Growth of the Demand for Electricity in Nine Provincial Towns ....... 44 XXIX. Showing the Growth of the Population in Nine Provincial Towns .... 44 XXX. Showing the Demand for Electricity per Inhabitant in Nine Provincial. Towns for the Years 1896 and 1906 . 45 XXXI. The Demand for Electricity in 158 Continental Generating Stations ..... .... 45 XXXII. Electrical Output and Efficiency of the Generating Stations in Four Continental Towns for 1901 — 05 ... 47 XXXIII. Average Efficiency of Continental Generating Stations of various Outputs for different Years .... 47 XXXIV. Leading Particulars of three well-known Generating Stations 50 XXXV. Ultimate Capacities of various Stations for 50 per cent. Load Factor 51 XXXVI. Particulars of Generating Sets to be Installed ... 52 XXXVII. Eepresentative Values of Steam Consumption of Generating Sets 52 XXXVIII. Particulars of Steam Consumption for Stations of various capacities 52 XXXIX. Particulars of Energy contained in Steam used by Generating Sets installed in Stations in Table XXXVIII. 53 XL. Annual Overall Efficiencies of the Generating Stations given in Table XXXIX 54 XLI. Coal Consumption for Stations A, B, and D . . .55 XLII. Coal Consumption in Kg per Kw Hr for Stations A, B, C and D 55 XTiHI. Annual and Hourly Steam Consumption of Large Electric Generating Stations 57 LIST OF TABLES TABLE XLIV. XLV. XLVI. XLVII. XLvm. XLIX. L. LI. LIT. LHI. LIV. LV. LVI. LVIL LVIII. LIX. LX. LXI. LXII. LXIII. LXIV. LXV. LXVI. LXVII. LXVIIIa. LXvniB. LXIX. lxx. lxxi. Maximum Hourly Steam Consumption of Large Electric Generating Stations 57 Length of Steam Fiping in Large Electric Generating Stations . . 64 Absolute Temperatures of Steam at various Pressures and with various Degrees of Superheat 60 Absolute Pressure of Steam in Kg per Sq Om for various Final Temperatures and Degrees of Superheat . . 67 Data of Steam Piping .... . 68 Eough Values -of the Temperature of the Flue Gases in their Passage from Grate to Chimney . . . .71 Heat Conduction Values . . ^ . . 71 The Wetness Factor of the Exhaust Steam from a 1000 Kw Turbo Generator Working at Full Eated Load under various conditions . . . . . .77 The Heat absorbed by One Ton of Circulating Water . 93 Tons of Circulating Water required to Condense One Ton of Saturated Steam when the Temperature of the Water is raised to the Temperature of the Steam ... 95 Data of Engine Rooms of Generating Stations . To face 131 Average Values for Engine Room Space per Kw of Plant installed . . 134 Data of Boiler Rooms of Generating {Stations To face 135 Average Values for Boiler House Design .... 135 Particulars of Coal Storage for Generating Station . . 142 Particulars of some Typical Chimney Shafts . . . 144 Relation between Weight and Volume of Air at different Temperatures 145 Data of Economisers 148 Excitation Power required for Alternators . . . 154 Costs of Generating Stations ...... 155 Costs of Poles and Towers 160 Data constituting Basis of Transmission Line Investigation 161 Temperature Rise of Bright Copper and Aluminium Con- ductors in Still Air at 20° C 162 Sag. of Conductors of various Section on 143 Meter Span . 165 Dimensions, Weights and Costs of Three-Phase Duplicate Circuit Steel Tower Transmission Lines, Copper Lines . 166 Dimensions, Weights and Costs of Three-phase Duplicate Circuit Steel Tower Transmission Lines, Aluminium Lines .......... 167 Data of Overhead Transmission Lines — (a) Copper Lines . 176 ,, ,, ,, ,, (b) Aluminium ,, . 177 Sections of Core in Three-Core Cables to which the Investigation relates 180 Maximum Permissible Current for Three-Phase Three-Core High Tension Copper Core Cables giving a Final Temperature Rise of about 25° C. when laid underground 1 80 LIST OF TABLES TABLE PAGE LXXII. Showing suitable Thicknesses of Lead for Three-Core Cables 184 LXXIII. Dimensions, Weights and Costs of Three-Core Cables . 188 LXXIHa. Comparison of Costs of Copper and Aluminium Cables . 195 LXXP7. Estimates of Total Cost for Conduit Laying . . .198 LXXV. Approximate Total Cost of Laying Single-Duct Clay Conduit in Pounds Sterling per Duct per kw . . 199 LXXVI. Installations Employing the High Tension CO Series System 204 LXXVIL— LXXX. Estimates of Costs of Generating Stations To face 208 LXXXI. Highfield's Total Costs of Series System and Alternating System 120 LXXXII. Eevised Total Costs of Series System and Alternating System 210 LXXXIII. Showing for a 1 km run at an Average Speed of 36 km per hour, the serious effect on the Schedule Speed of Increasing the Duration of Stop 219 LXXXIV. Showing the Effect of the Duration of Stop for one Stop per 2 km and an Average Speed of 36 km per Hour . 219 LXXXV. Showing the Effect of the Duration of Stop for one Stop per km, and an Average Speed of 18 km per Hour . 220 LXXXVI. Boiling Stock Data 230 LXXXVII. Rated Outputs of Motors of Different Types but of Equal Weight and for Equal Speed of 500 rpm ; Ventilated, but not with Forced Draught . . . 247 LXXXVIII. Railway Motors . . ... . 248 LXXXIX. Rated Output of Motors of Different Types, but of Equal Weight and for Equal Speed (namely, 500 rpm), with Forced Draught 250 XC. Data of Modern Traction Motors and Equipments To face 254 XCI. Data of Weights of Standard Continuous Current Railway Motors and Equipments . . ... 258 XCII. Characteristics and Conditions of Carter's four Alternative Projects . . • . 295 XOIII. Capital Outlay with Carter's Four Alternative Projects . 296 XCIV. OperatingExpenseswithCarter'sFourAlternatingProjects 298 XCV. Considerations affecting the Commercial Success of Electric Railway Undertakings 303 XC VI. Considerations affecting the Commercial Success of Electric Railway Undertakings 304 HEAVY ELECTRICAL ENGINEERING CHAPTEE I Introductoby Scope of this Treatise. — Questions concerning the design of appa- ratus are throughout this treatise regarded as subsidiary to those relating to the design of the stations in which the apparatus is employed. The design of electrical machinery is in itself so broad a subject that a special course of study is necessary for any approach to adequate treatment, and it cannot be considered in the present treatise. In like manner, the design of steam boilers, super- heaters, piston engines, steam turbines, gas engines, pumps, condensers, cooling towers, and other apparatus employed at a generating station, constitute equally broad subjects. We shall in the earlier chapters aim to acquire familiarity with the results which can be obtained from the principal amongst these component pieces of apparatus, and to learn to correctly combine them for efficient service in aggregates which we shall denote as generating stations. Energy.— We are chiefly concerned in this treatise with three forms of energy, namely, heat energy; electrical energy; mechanical energy. When energy manifests itself in the form of heat energy, it is convenient to briefly call it " heat " ; when in the form of electrical energy, it may be called " electricity " ; finally, when in the form of mechanical energy, it may be called " work". Unit of Energy. — The quantity of energy when in any of these forms, may be expressed in kilowatt hours (kw hr). Kilowatt Hour. — The most frequently occurring occasions when we must express energy quantitatively, are those on which it is being transformed from one kind into another, as, for instance, from electricity into heat. The kilowatt hour is 1000 watt hours. The watt hour is the quantity of electricity which is h.b.b. b 2 HEAVY ELECTRICAL ENGINEERING transformed into heat in a wire of one ohm resistance when a current of one ampere flows through it for one hour. As a potential difference of one volt is required to produce a current of one ampere in a circuit of one ohm resistance, one watt hour is equal to one volt ampere hour for continuous current and for alternating current at unity power factor. It is, however, to be noted that in heavy electrical engineering the watt hour is an inconveniently small quantity, and the kilowatt hour is more convenient, and is thus taken as a unit of energy. In the following chapters it will appear that even the kilowatt hour is often an inconveniently small unit, for in some departments of heavy electrical engineering, undertakings requiring millions of kilowatt hours per annum are involved. It has been customary to denote this quantity of electrical energy as one Board of Trade unit since it is a unit which has been officially adopted by the Board of Trade, and it is still frequently expressed in this way. It is, however, more often expressed as one kilowatt hour. When no ambiguity is thereby introduced, it is often customary to briefly designate this quantity of energy as one "unit"; but this course is not to be recommended, as the word " unit " should be reserved for use in its more general sense. In this treatise the following terms are used in dealing with quantities of energy : — 1 watt hour . . . (1 w hr) 1 kilowatt hour . . (1 kw hr) = 1000 w hr. Weight and Volume. — One ton may be defined as the weight of one cubic meter of water at a temperature of 4 . 1 1 ton = weight of 1 cubic meter (1 cu m) of water = weight of 1000 cubic decimeters (1000 cu dm) of water = weight of 1000 liters (1000 1) of water = 1000 kilograms (1000 kg) = 1 000 000 grams (1 000 000 g). Pressure. — The unit of pressure is 1 kilogram per square centi- meter. 2 When not otherwise expressly stated, absolute pressures 1 4° is the temperature of maximum density of water. Throughout this treatise the Centigrade temperature scale is employed, and instead of by four deg. Cent, or 4° O. this temperature is often indicated by 4°. 2 A pressure of one kilogram per square centimeter is equivalent to the pressure of a mercury column with a height of 735,5 mm. It is almost equivalent to the normal atmospheric pressure. For this reason the unit of pressure is sometimes designated a "metric atmosphere." As a unit, it has the advantage over the ordinary " atmosphere " that it is independent of barometric variations. INTEODUCTOBY 3 are to be understood ; that is to say, pressures are referred to an absolute vacuum, and not to atmospheric pressure. Relation between Heat and Temperature. — The relation between heat and temperature for water and steam may be illustrated by means of the curve in Fig. 1, which represents the occurrences attending the absorption of energy by one ton of water, i.e., the "heating" of one ton of water. During the entire operation the v. W o , if. 3 ' S}L jej. 700 o— s. o ■ -u - £ 0,5- v> in u t: - 1 " i/.O-r < t: - Sabui -att^ dS team. 600 4 < Co to - n ■ t ' r ' s / i,iV e v? 100 ■fji vP C V\e£ ^ \l>' •y 50 100 150 ZOO 250 300 350 Temperature in Degrees' Centigrade. 400 Fig. 2.— Relation between Heat and Temperature eor Water and Steam at Various Pressures. has been absorbed, we shall have a mixture consisting of 0,5 ton of water and 0,5 ton of steam. To the diagram in Fig. 1 has been added a scale showing the " wetness " of the steam at various stages of the process of imparting 626 kw hr to the ton of water. At the commencement of the process the "wetness" is 100 per cent., or we may say that the steam has a wetness factor of 1,00. When 125 kw hr have been absorbed the wetness factor is 0,80, and when INTEODUCTOBY 7 the entire 626 kw hr have been absorbed the wetness factor is 0,00, and we have so-called " saturated " steam. Further additions of heat are accompanied by increase of tem- perature, and the steam is said to be " superheated ". This part of the process corresponds to the right-hand sloping portion of the diagram in Fig. 1. The angle at which this portion of the diagram slopes upward is dependent upon the specific heat of superheated steam. The specific heat of superheated steam varies considerably with the temperature and pressure. In Table VI. and Fig. 3 the at present most probable values are given. Physicists are occupied in obtaining more reliable data. For our purposes at the moment it is sufficient to state that the specific 'heat of steam is roughly about half of that of water. Hence a given quantity of energy imparted to a ton of steam will raise its temperature through about twice as many degrees as the same amount of energy imparted to one ton of water. These data are embodied in the diagrams in Fig. 2, where are drawn for various pressures, a set of lines corresponding to those already given for an absolute pressure of 1 kg per sq cm in Fig. 1. The leading properties of steam are entered up in Tables III., IV. and V. At the present time, considerable difference of opinion exists amongst physicists with regard to the values of the specific heat of superheated steam at various temperatures and pressures. The values employed in the construction of Tables III. to V. are in accord with those given by Mollier in his brochure entitled " Neue Tabellen und Diagramme fur Wasserdampf "K Mollier's values for the specific heat of steam are given in Table VI. The values given in this Table represent the average specific heat while the temperature of the steam is raised from the temperature of vaporisation to various final temperatures (100°, 150°, 200°, etc.). From these values the curves in Fig. 3 have been drawn. The specific heat and specific gravity 2 of some common materials are given, together with the kw hr per ton per deg. cent, tempera- ture rise, in Table VII. Examples of the amount of energy represented by 1 kw hr : — 1. 1 kw hr is sufficient to lift one ton through a height of 367 meters. 1 Published (1906) by Julius Springer, Berlin. 2 The specific gravity of a body may be defined as the density, or specific weight of the body in grams per cubic centimeter, kilograms per cubic decimeter, or tons per cubic meter. HEAVY ELECTEICAL ENGINEERING TABLE in. Table of the Energy, in Kilowatt Hours, required to convert One Ton of Water at 0° 0. into Steam at Various Pressures and Superheats. c la gp 3 fl Heat in Kilowatt Hours per Ton. Component Parts. Total Steam Heat. DQ a; rf 43 to TJ1A 43 GO 100° 150° 200° 250° 300° 850" 400° 450° A E c D E F G H K L M 0,02 17 700 747 775 803 831 859 885 913 940 0,04 29 704 11 J) 11 11 11 11 11 11 0,06 36 709 11 11 11 11 11 11 11 11 0,08 41 713 11 11 11 „ 11 11 11 0,10 46 716 746 774 802 830 858 884 912 11 0,12 49 717 11 11 11 11 ii 11 11 11 0,15 54 720 11 ,, 11 11 ii 11 11 11 0,20 60 724 773 11 ,, ii 11 11 „ 0,25 65 725 745 n 801 824 ii 11 11 11 0,30 69 727 11 11 ii ii 11 11 11 0,35 72 729 11 n 1) n ii 11 11 11 0,40 76 730 11 ii 11 ii „ 11 11 11 ' 0,50 . 81 733 744 hi 800 828 857 883 911 939 0,60 86 736 5) ii 11 11 n 11 11 11 0,70 90 737 1) ii 11 11 856 11 1) 11 0,80 93 739 11 771 11 827 11 11 11 11 0,90 96 740 ,, 11 „ ,, 11 11 11 11 1,0 99 741 742 770 799 826 855 882 11 938 1,1 102 743 11 ii 11 11 11 11 11 1,2 104 745 11 ii 11 11 11 11 11 1,4 109 746 11 ii 11 11 11 11 11 1,6 113 748 1) ii 11 11 11 11 11 1,8 116 750 ii 11 11 ,, 11 11 2,0 120 752 769 798 11 854 11 11 11 2,5 127 754 768 797 11 11 881 11 11 3,0 133 756 767 796 825 853 11 11 11 3,5 138 758 766 795 11 11 880 11 11 4,0 143 759 764 794 824 852 879 910 11 4,5 147 761 11 11 11 11 11 11 5,0 151 764 1) 11 11 11 11 „ 5,5 155 766 11 11 11 11 11 11 6,0 158 767 793 823 51 11 11 „ 6,5 161 767 792 822 11 11 909 11 7,0 164 768 791 1) 851 11 11 11 7,5 167 769 790 821 11 11 11 11 8,0 170 770 789 820 850 879 908 937 8,5 172 771 11 11 11 11 11 11 9,0 174 771 a 798 11 11 11 11 11 9,5 177 772 V 11 11 11 11 11 „ 10 179 773 w 787 819 849 878 11 936 11 183 775 -4-3 CD 786 11 11 11 ii 12 187 776 £ 785 818 848 11 907 ii 13 191 777 784 817 11 11 11 ii 14 194 778 782 816 847 877 11 ii 15 197 778 781 815 846 11 906 n 16 200 779 779 813 845 876 905 935 18 206 780 812 844 11 11 11 20 211 781 811 843 815 905 INTRODUCTORY TABLE VI. 11 Table of the Average Specific Heat of Steam, heated from the Temperature of Vaporisation to Various Final Temperatures. in Kg. perSq. Cm. 0,5 1 2 4 6 8 10 12 14 16 Temperature of Vaporisation in °C. 46 81 99 120 143 158 170 179 187 194 200 o 100 0,480 0,490 0,501 150 0,479 0,488 0,495 0,513 0,533 200 )) 0,486 0,491 0,505 0,523 0,538 0,558 0,573 0,588 0,601 &.s J 250 )) 0,484 0,489 0,500 0,514 0,528 0,543 0,556 0,569 0,578 0,588 sg 800 )1 0,483 0,487 0,496 0,508 0,519 0,531 0,541 0,551 0,562 0,569 S3 B50 „ 0,482 0,485 0,493 0,503 0,513 0,522 0,531 0,539 0,547 0,555 "rt 400 0,478 )) 0,484 0,491 0,500 0,508 0,517 0,523 0,531 0,538 0,545 s \ 150 ,, " 0,483 0,489 0,497 0,505 0,513 0,519 0,525 0,531 0,537 TABLE VII. Table of Specific Gravity and Specific Heat of Various Materials. Material. Specific Gravity (Tons per cum) Specific Heat. Kilowatt Hours required to raise the Tempera- ture of 1 Ton by 1°. Kilowatt Hours required to raise the Tempera- ture of 1 Cubic Meter by P. Water 1,0 1,0 1,16 1,16 lee ... 0,93 0,49 0,57 0,53 Coal 1.3 0,24 0,28 0,36 Wrought Iron 7,7 0,11 0,13 1,00 Cast Iron 7,2 0,13 0,15 1,08 Copper 8,9 0,10 0,12 1,07 Lead ... 11,4 0,03 0,035 0,40 Zinc ... 6,9 0,09 0,11 0,76 Aluminium ... 2,6 0,22 0,25 0,65 Transformer Oil 0,9 0,75 0,87 0,78 2. 1 kw hr is consumed at the trolley in propelling a 10-ton tram- car of good design on a good and level track for a distance of from 1 to 2 kilometers or thereabouts (according to the number of stops per kilometer), at a schedule speed of some 12 kilometers per hour. 3. 1 kw hr is absorbed in 84 hours by a 12-candle power lamp requiring 1 watt per candle power. If the lamp is only in circuit for an average period of two hours per day, 8,7 kw hr will be absorbed by the lamp in the course of one year, provided 12 HEAVY ELECTRICAL ENGINEERING that it survives for 730 hours in circuit, with an average efficiency of 1 watt per candle power and that its candle power does not alter. If the charge is M. per kw hr (i.e., per "unit"), the cost of /730 \ rgy for this lamp will amount to (^ X 3 = j 26^ for the year. eners 0.60 200 0,58 %0,5S ?0,54 & y y $0.52 u s S s* y* x y f S t ■»*2 ^0,50 ?/ ^s> ■r^. >" k v. §0,48 i& 0.46 2 4 6 8 10 12 Absolute Pressure in Kilograms per So, Cm . Ml' I ' I ' I' ' I ' I — 14 MO. 1150 T Critical or Saturation Temperature for Steam at above Pressure. 250 ZOO 350 400 450 16 2V0 Fig. 3. — Curve showing the Average Specific Heat for Steam Super- heated from the Saturation Temperature to various Higher Temperatures. (Note. — The above Curves are plotted from results given by Mollier.) Eeplacing the lamp once per year, at a cost of BOd, brings the total annual outlay per lamp to 26 + 30 = 56d. To this must also be added an equitable proportion of the meter rental. On these assumptions, the lamp thus costs a matter of some 5 shillings per year. 4. The latent heat of liquefaction of ice is 93 kw hr per ton; INTKODUCTOBY 13 that is to say, to convert one ton of ice at 0° into one ton of water at 0° requires the absorption of 93 kw hr. 5. The specific heat of ice is 0,49. Consequently to convert one ton of ice at — 8° into water at 0° requires the application of 97,6 kw hr, this amount being accounted for as follows : 4,6 kw hr are required to raise the temperature of the ice to 0°, and 93 kw hr are required to liquefy the ice. 6. To convert one ton of ice at — 8° into water at + 8° requires the expenditure of 107* kw hr, this amount being accounted for as follows : as in example (5), 97,6 kw hr are required to change the ice into water at 0°, and a further 9,3 kw hr to raise the temperature of the water to 8°. 7. The average specific heat of transformer oil is 0,75, of copper 0,10, of iron 0,11. In a certain transformer, the weight of the copper is 100 kg, the laminations 200 kg, the cast iron case 150 kg, and the oil 180 kg. The internal loss amounts to 1 kw, and it is required to find the time required to cause a rise of temperature of 40°, assuming that the heat is exclusively employed in causing a rise of temperature, and that none is radiated from the external surface of the frame. The oil requires 0,75 X 1,16 X 0,18 X 40 = 6,3 kw hr. Similarly, the copper requires 0,46 kw hr, the laminations 1,02 kw hr, and the frame 0,75 kw hr The total heat required is 8,5 kw hr, so that if the losses in the transformer are 1 kw, the time would be 8,5 hours, under the conditions set forth. Energy Transformations. — Electrical energy — or briefly — elec- tricity, can be transformed into work energy — or work, with an efficiency as high as 95-per cent, in large motors. Work may be trans- formed into electricity with equally high efficiency. The remaining 5 per cent, or thereabouts, is converted into heat energy or — briefly — into heat. Electricity and work may both be converted into heat with an efficiency of 100 per cent. Thus, if an electric current is sent through a resistance, the electrical energy may be entirely con- verted into heat in the resistance. If work is performed in stirring water, as in Joule's experiment, the work energy may be entirely transformed into heat energy. The so-called " generation " of electrical energy in generating stations should, strictly speak- ing, be described as the transformation of energy from heat to electricity. When we wish to convert heat into electricity or into work, no such high efficiencies are attainable. There are no known means of 14 HEAVY ELECTRICAL ENGINEERING transforming heat directly into electricity on a large commercial scale. Heat may, with a low efficiency, be transformed into work in a steam engine or a gas engine, and the work may, at high efficiency, be transformed into electricity. The large portion which, in the first step, is not transformed into work, remains heat; the small part which, in the second step, is not transformed into electricity, is converted into (or lost as) heat. Of the heat absorbed by a large steam engine or steam turbine, during the passage of the steam, only some 60 per cent, can, in the present state of the art, ultimately be converted into electricity. When we trace the process back to the calorific contents of the fuel, it may be stated that it is rarely practicable to convert more than some 8,0 per cent, into electricity. With gas engines some 25 per cent, of the calorific value of the fuel may be transformed into electricity in the circuits supplied from the dynamo driven by the gas engine. The greater efficiency of the gas engine is, however, in large units, offset by the greater cost, greater depreciation and greater space required, as also in many cases by the disadvantage of its less uniform turning moment and its less reliability at its present stage of development. Let us therefore direct our attention to the steam engine or steam turbine, which, as already stated, permits, in large sets, of con- verting into electrical energy some 60 per cent, of the energy abstracted from the steam in its passage through the engine. In accordance with this definition of the efficiency of an engine, the heat rejected to the condenser is not regarded as a loss. It may be for instance, and often is, employed in heating pro- cesses. Waste heat engines have also been devised for employing the lower temperature ranges. Whether or not it is expedient to further employ the heat energy rejected to the condenser, it is nevertheless heat energy. Subtracting this energy from that contained in the steam at admission, we have as remainder, the energy which has undergone transformation in the steam engine or turbine. A large proportion of this becomes converted from heat energy into useful work energy, and the remainder is ultimately wasted in heating the engine and the surroundings. The ratio of the energy delivered from the engine as work, to the energy which has been absorbed in the engine, i.e., to the "con- vertible energy", is designated the "thermodynamic" efficiency. In Table VIII. are set out the amounts of " convertible " energy per ton of steam when working between various admission «2 fi O « "fe» E? 1 s o ^ ff n C< £ e s 8 <. QQ «, t§ !§ % OCO(NOQ (M1NHHHHH o id CNOC0t*rHQ0a>0i H Oi CO CO W O O t> lO(MHOOll> CM t— 1 i— i i— 1 rH i— I CO HOCO««iCHON rH ^H rH rHi-H «> o o CO Tf^i>omooiH COHOOcD^CCHO (N(MtHtHi-1iHiHt-( o (MO!^CO(NOOlM (M O) t> Tt< CO (N H OJ (N iH iH rH i-l iH rH o o CM QCOlOOiCOHtMCO OOOCDCOtMrHOGO (M rH rH rH rH rH rH o c*©oocooot-i»© Oaotfscor-jooioo CQ *-H rH rH rH rH w o o o CO CNCTIX^COOOH THC^OSCDlO-^COrH (NtMHHHHHH o CM OCO!NI>IMOOIM COOCOiOtHCOIMO (MINHHHHHH o o cm t-t-^C0(NO(Ni< HO)I>^CO(MHOJ CM rH rH rH rH rH rH CD rHffiCO«*0$rH©0 CQHHHHriH CM o o CO OCO^cOHt-COO W CO O t- O tJI (N (N (N(NC>IHHHHH o CDlOOWOCOCOH COHO)COIOCO(NH (NlNHHHHHH o o CM co^oscoCiOOOicM (MOIMOCClNHO (MlMHHHHHH 00 rHOit*»OCO co th co (N CNOJlMHrt HHH O o 04 OOOCOCNECOCOCO^ C$T-'GOCO^COCMrH C^CMrHrHrHrHrHrH Exhaust Pressure in Kg per Sq Cm.- O rH N "* «0 COOO O" O" CD 0~ O O" rH iH s^ e-h M 1 H '-a "3 s OQ £ s s CQ <, £ * g ■sio^Otfit Bsau^eAV a o a* to t-l ft M W _d a) w M CD .2 in i «1 P ti CD 2 ft CD fl o 1 o o CO CO O t> t* rH r-l rH O O O o CM rH rH rH O O O O o o OOcDCOOOitr-CO-^ i— IrHrHrHOOOO o oo"o"o oo"o CO m gooCOCQrHOOi^ W iH 1-4 rH rH[rH O O oo ooo ooo CO o o CO W CO OS CO "^ CO CT iH iH O O O O O o" O o o o o" O OOTHcqOsOOCO^CO t-HtHtH OO OCDO o" do o~o~ d o" o" O o OODWINHOJCOiO (NrHrHrHrHOOO d d o~ o~ d o" d o" | C i r l r l H H rHOO d o" o"o~o" o*~ o" d o o (M C0(MO5CDlOC00qrH o o"d*d* d d do" COOJOiCDOCOOlrH Ol OJ rH rH rH r^i-i ^ oo""ooo"oo""o" r-i O O CO O5t*-^rHOS00t-irj ddo"o"ddo"d o OJ HOt>^C0(MOC0 ^1 ^ 1 ~i ^ ^ ■" ' ^ ° d d o"d o" do d" o o CM ^COrHQ0!>-CO^rH C40401rHrHTHrHrH^ ooo""o""oooo Exhaust Pressure in Kg per Sq Cm. O^tHC^-^CD 00 ow ddddo"dr-TiH •II -daovfnxl •KValg 3.0 &0& 3KQ SI XQS.'S.&'S. KiaiXliaAKOQ 30 SEAHflO •£ pun '9 '0 'f •sgjjj jaiatiJiquao ajenbs Jad swejBoiih u\ aunssajj uoissiwpy sqouap aessiosqy ?/ 1 7/ Zl 01 8 3 ? 13 O • 0> ' ' S7 07 8'0 9'0 Z'O 10 in'n 001 ■q qq£ gjnjgjadu]3± uoissiwpy OtrZ 'O c OSZ 3Jnqejadu/aj uotssiuipy o 00Z sjnqejadwaji uoissjwpv •pait INTRODUCTORY 1? pressures and temperatures and various exhaust pressures. With an engine of 60 per cent. " thermodynamic " efficiency, the work energy obtained per ton of steam is equal to 0,60 of the " convertible " energy set forth in the table. The values set forth in the table have been deduced on the assumption of expansion without loss or gain of energy by the steam. Its temperature during this process of so-called "adiabatic" expansion, decreases in accordance with definite thermodynamic laws into which it is not proposed to enter. Accompanying the decrease in temperature, there is, for certain ranges, a condensa- tion of a portion of the steam. The corresponding " wetness factors " are set forth in Table IX. The data in Table VIII. are plotted in the curves of Figs. 4 — 7. H.E.E. CHAPTEE II THE OVERALL EFFICIENCY OF GENERATING STATIONS AND THE RELATION BETWEEN COAL CONSUMPTION AND OUTGOING ELECTRICAL ENERGY In employing the customary expression " Generating Station " we must clearly recognise that a more exact expression would be " Transforming Station," since in such a station we transform a small part of the energy of combustion of the coal, or other fuel, into electrical energy, at the same time — unwillingly — transforming a much larger part of the energy of combustion of the coal into irrecoverable heat energy. We shall first ascertain how great a percentage of the energy of combustion of coal, engineers have learned to transform into electrical energy. The Calorific Values of Fuels. — Various kinds of coal contain widely different amounts of stored-up energy per ton. The heat energy obtained by burning one ton of coal in the presence of an ample supply of air and under other suitable conditions, may be expressed as the energy of combustion per ton, or the calorific value per ton. In Table X. are given representative conservative values for the TABLE X. Calorific Values of a Number of Varieties of Coal. Source. Nature. Calorific Value of Coal in Kilowatt Hours per Ton. Wales England ... Scotland ... United States of America 1 Germany Almost pure anthracite Bituminous Bituminous Anthracite Bituminous Anthracite Bituminous ' ' Braunkohle ' ' (hard lignite) " Braunkohle " (soft lignite) 9800 9000 8300 9000 8700 8300 8100 | 6300 I 4300 THE OVEBALL EFFICIENCY OF GENERATING STATIONS 19 energy of combustion of various coals, in kilowatt-hours per ton of coal. ■ We see from Table X. that the available qualities of coal, range in calorific value from 9800 kw hr per ton downwards. 1 8700 kw hr per ton is a readily obtainable value. This value represents tbe heat energy obtained by burning one ton of good bituminous coal in the presence of a suitable supply of air, and under otherwise suitable conditions. Examples of the Amount of Energy contained in One Ton of Coal of a Calorific Value of 8700 kw hr per ton, — (1.) Could we transform this heat energy at 100 per cent, efficiency, into electrical energy of suitable voltage, we could run sixty-two 16 c.p. incandescent lamps for one year with the energy yielded by the combustion of one ton of coal. 2 Owing to the losses in transformation, we rarely obtain from one ton of coal sufficient electrical energy for more than four lamp years. (2.) As another example of the energy contained in a ton of coal with a calorific value of 8700 kw hr, we may say that this energy is sufficient to lift a weight of one ton through a height of about 3200 km ; or 8200 tons through one kilometer. (3.) A further instance of the amount of energy contained in a ton of coal of a calorific value of 8700 kw hr, may be found in the statement that it is about equal to the amount of energy consumed by an ordinary urban tramcar of 12 tons weight, in traversing 10 000 km of average urban route at a schedule speed of 10 km per hour and with three stops (of five seconds duration each) per km, the equipment comprising ordinary continuous current series wound motors with series parallel control, and the tramcar 1 For the convenience of readers who may still be accustomed to deal with calorific values in British uuits we may state that 1 kwhr = 3411 British thermal units, and 10 000 kw hr per ton = 15 500 British thermal units per lb. The plan employed in the present treatise is to express all energy in kilowatt hours, so that the energy, whether in the coal, in the steam or in the electrical system, shall in all cases be expressed in the same unit. 2 This statement is based on an incandescent lamp consuming 1 watt per candle power. .". 1 candle power hour requires 1 watt hour. If the watt hours per ton of coal = 8 700 000 then the candle power hours per ton of coal = 8700000 = 8 700 000 1,0 m ^ ■, j, 8 700 000 Total candle power = ^ wz = "90 No. of 16 c.p. lamps =-^° = 62 02 .20 HEAVY ELECTEICAL ENGINEEEING being accelerated and braked in accordance with present approved practice. That in actual practice, a ton of coal is consumed at the generating station for every 800 car km or less, is due to the fact that some 92 per cent, to 95 per cent, of the energy of combus- tion of the coal, is transformed into irrecoverable heat energy in the course of the various transformations of energy occurring between the coal pile and the trolley wheel. (4.) As another example, let us take a 200 ton train, travelling on a level track at a uniform speed of 60 km per hour, and requir- ing a tractive force of 3 kg per ton. Suppose the locomotive has an efficiency from coal to axles, of 1,5 per cent, for this speed and tractive force. How many kilometers can the train travel while burning one ton of coal, having a calorific value of 8700 kw hr per ton ? Energy transmitted to axles per ton of coal burned = 0,015 X 8700 = 130 kw hr 1 kw hr = 0,367 ton km 130 kw hr = 47,6 ton km 47 6 Or, a 200 ton train could be lifted through ^- = 0,288 km. As the coefficient of friction is 0,003, this is equivalent to the 238 200 ton train running ' = 79 km on the level, with a coal UjUUo consumption of one ton. This is a consumption of 11,2 kg of coal per km. (5.) If 93 kw hr of energy are imparted to one ton of ice at 0° C, the ice is transformed into water at 0° C. .•. If the energy set free by the complete combustion of one ton of coal of a calorific value of 8700 kw hr were entirely transferred 8700 to ice at 0° C, then = 93,5 ton of ice would be melted. This would have a volume of about 93,5 cu m and corresponds to a cubical block of ice measuring 4,55 meters on each side. 1 kw hr raises one ton of water, by 0,86° 0. .■. The energy of combustion of one ton of coal of a calorific value of 8700 kw hr per ton, is sufficient to raise the temperature of 8700 X 0,86 = 7500 tons of water by 1° C. 7500 tons of water occupy a cubical space measuring 19,6 meters on each edge. Thus the energy of combustion of one ton of coal of a calorific value of 8700 kw hr per ton, will : 1. Melt 93,5 tons of ice at 0° C, THE OVERALL EFFICIENCY OF GENERATING STATIONS 21 or 2. Increase from 0° to 1° C, the temperature of 7500 tons of water. 7500 The latent heat of ice is 93,5 = 80. 93 While 93 kw hr is required to melt one ton of ice, ^ = 80 1,16 kw hr suffices to raise the temperature of one ton of water from 0° to 1° C. Consider one ton of water at a temperature of 100° C, and at atmospheric pressure. "We see from Table III. that 626 kw hr are required to evaporate this ton of water into steam at the same temperature ; hence the latent heat of steam at this pressure is 626 1,16 = 540. In burning one ton of good coal under a boiler, we may transfer to the contents of the boiler 75 per cent, or more of the energy of combustion. To calculate the effect, we may consult Table XL, in which are given values for the energy absorbed in kw hr in raising one ton of water from 50° C to the boiling point at various absolute pressures, and in evaporating it at those pressures and in super- heating it 50° C, or 100° C, as may be required. Table XI. has been derived from Table III. TABLE XL Energy required to raise One Ton of Steam from Water at 50° (J to various Pressures and Degrees of Superheat. Kilowatt Hours per Ton of Steam raised from Feed Water at a Temperature of 50° C. Boiler Pressure (abs.) in Kg per Sq Cm, i.e., in Metric Atmo- spheres. Amount of Superheat in Degrees Cent. 0"0. (Sat. Steam). 50° C. 100° c. 8 709 743 776 10 712 748 781 12 715 752 786 14 718 756 791 16 720 759 795 18 721 761 798 It is convenient to consider water at 0° as devoid of internal energy, and it is merely necessary to make the mental reservation 22 HEAVY ELECTEICAL ENGINEERING that this is not strictly the case. In Table XI. we have derived values for the kw hr required to raise one ton of steam from water at 50° C, and this has required deducting from the values in Table III. the kw hr absorbed in increasing the temperature of one ton of water from 0° C to 50° C. Thus from Table III. we find that at an absolute pressure of 10 kg per sq cm, one ton of water at 0° C requires 806 kw hr to convert it into steam with 50° C of superheat. But to raise the temperature of one ton of water from 0° C to 50° C requires 50 x 1,16 = 58 kw hr, and this amount must be deducted. 806 - 58 = 748 kw hr. Therefore 748 kw hr are necessary to raise one ton of steam at an absolute pressure of 10 kg per sq cm, and with 50° C of super- heat, from water at 50° C. The other values in Table XL are similarly derived. From the values in Table XI. we may readily deduce Table XII., in which are set forth the tons of water evaporated per ton of coal of various qualities, and for boiler efficiencies of 60 per cent., 65 per cent., 70 per cent., 75 per cent., and 80 per cent., and for various pressures and superheats. Since we may obtain from Table XII. the number of tons of steam raised per ton of coal burned, for boiler efficiencies of 60 per cent, to 80 per cent, for given pressures and amounts of superheat, it is a simple step to deduce the fuel cost for producing one ton of steam when burning coal of a given price per ton, and a given calorific value. Fuel costs thus derived are entered up in the second column of Table XIII. for steam raising plants of from 60 per cent, to 80 per cent, efficiency, burning coal of a calorific value of 8700 kw hr per ton and costing, delivered on site, from four shillings to sixteen shillings per ton. The stated boiler efficiencies must be understood to include the overall efficiency of boiler, superheater and steam piping. Steam driven generating sets consume, according to circumstances, from 6 to 20 kilograms (thousandths of a ton) of steam per kw hr of output from the dynamo. The circumstances affecting the steam consumption per kw hr delivered, excluding the question of type and design, relate mainly to the average percentage of rated load at which the plant operates during the period considered, and to the conditions of admission pressure, superheat and vacuum. We shall not at this stage enter upon the consideration of these points. Assuming that the mean steam consumption per kw hr delivered, *6 "S<5 fell ■si e fir-" ■2 ^ >> 5- M Hi m «"? O a, s « e s C CO s S ■3* 2 J i: e s 4^ •■o 1 7,91 7,50 7,17 8,57 8,14 7,76 9,23 8,74 8,36 9,S9 9,33 8,95 10,5 10,0 9,55 OS ' CM m o ^COinMS-HDOWOtDCOiO CO OS lO CM CO^CM CO CO_CO ■* OS "# o eo — <„co nTi>.n co" co*(> os" co"oo"os"os~oT o o or © in OS 00 (3 O H (NJr- inOr-HCOCDint-mr-IC© O OCFJr-mOlOJOliftOOH t-(NcO co j>Tj>T co co t-Tos co co ooToTcToor 9000 Kilowatt Hours. : ; to s as -w m o c o OHO.WHffiiOO.IMNO.CO co»rt Or-II--i-(Ir-CO(--CMOi=OCO'*0'* , j>Ti^'ffi"co t-TjOo^oo t-Tcu co"co o oToT CM r-1 "SC0!OC0COiflHtOH-*C0(O COCO iftrH CO >-'^J>-- t *l COCOO^ffiOHdH t^t^" o co" t>i-^ o6"co co oT co" co" o aTos" 00 CStOcOCNt--tOtDOOCMOSOO CO t— ' vOCTO)CNCOiOCO'*Hi'HNH(Dyi J>- t-^ CD CO t-^* t-^" CO CO CO a* oT co" o oT os" «s c= . .8 8 13 § oW o s CD a o 1=1 o NHHS(OiO©H03iDOH"#miO O N^f CO^tM CR (M 00 -*00 *0-*OiiO no co" j>Tj>r co"co" t-Ti>rco" oo"od"oTco"co CM (MCOOOCMlO^NHCOHt-OO'tf'* rH_t~ ^NinOMaiO©*HiOOtO t- co co Nt-rNocrNrN oo"co"co"os"orco* CO ±-COCOI~-CO-*C-Ol— COCiCOcD-^iCO HComi-i'HmoffifflowiC'Hc- b-COcOl>.t-.J^-COCOJt-COCOC00105CO 4-3 is - o g S l oM o o CO CO g eS 03 02 li O 01 1=1 O H !0(Tm o co os m co-* o ffiCO"©"^© tO~NTN^(>3 j>_'t»rco"co"co" OOOOCOCMC'l^^CMCOCOCM'^OCM t— CO iH CM OS_CO CO "^r-l CO OS CO CS «3 fH ffi(DffiNoVNVVooVVco'»"co" 00 OOOCMONCOtjICNICOW^IMOH ©"ffiCoVNVt-V'NOT'ooVoToDOo" 1 Is o o co l-H 6 r3 02 O to a o COCOCOCMOCMO^fOCSHOt-CO** COiOIMCOOC-l»tJ'HWO)ONmO »0"O'»OC0CO'O«C !D!ONO!Ot-NI> (M Na)-#CCHfl©inH«-i"CONCOTj(H co in co co o t~ co o cm co os co co *ch i-t in in" o" co" ^N c^" 00 OiO(NOO)K)OOHO.r-t-r-nH OiCO-*-*t- m cm_o tjh" co" co ■*" *** -^ ■** ■* ■*" io" Tf" -*jT o" m" o" .r;EH * » ■£ _- G rt j- 6 8 10 12 14 16 18 20 Is," 5 Kilograms per Kilowatt Hour. §r 4s. 0,57 0,041 0,055 0,069 0,083 0.097 0,110 0,124 0,100 5s. 0,71 0,052 0,069 0,086 0,103 0,121 0,138 0,155 0,175 to 6s. 0,86 0,062 0,083 0,104 0,124 0,145 0,166 0,186 0,207 o 7s. 1,01 0,072 0,097 0,121 0,145 0,169 0,193 0,217 0,242 p 8s. 1,15 0,083 0,110 0,138 0,166 0,193 0,221 0.24S 0,276 "3 9s. 1,30 0,093 0,124 0,155 0,187 0,217 0,248 0.2S0 0,310 1" 10s. 1,44 0,104 0,138 0,173 0,207 0,241 0,276 0,310 0,345 lis. 1,58 0,114 0,152 0,190 0,228 0,266 0,304 0,342 0,379 12s. 1,72 0,124 0,166 0,207 0,249 0,290 0,331 0,373 0,414 'S 13s. 1,87 0,184 0,1S0 0,224 0,269 0,314 0,359 0,404 0,44S to ffl 14s. 2,02 0,145 0,193 0,242 0,290 0,338 0,386 0,435 0,483 'ft cj 15s. 2,16 0,155 0,207 0,259 0,311 0,362 0,414 0,466 0,517 E O 16s. 2,30 0,165 0,221 0,276 0,331 0,386 0,441 0,497 0,552 >s r 4s. 0,53 0,039 0,051 0,064 0,077 0,090 0,103 0,115 0,128 ■S 5s. 0,66 0,048 0,064 0,080 0,096 0,112 0,128 0,144 0,162 OQ CD 6s. 0,81 0,058 0,077 0,096 0,116 0,135 0,154 0,173 0,193 PI O 7s. 0,94 0,067 0,090 0,112 0,135 0,157 0,1 SO 0,202 0,225 rt 5 8s. 1,07 0,077 0,103 0,128 0,154 0,180 0,206 0,231 0,257 05 '3 9s. 1,21 0,087 0,115 0,144 0,174 0,202 0,230 0,260 0,289 -u 10s. 1,34 0,097 0,128 0,160 0,193 0,224 0,256 0,288 0,320 j5 lis. 1,47 0,106 0,141 0,176 0,212 0,247 0,283 0,317 0,352 ■h ! 6s. 0,69 0,050 0,067 0,083 0,100 0,116 0,133 0,150 0,167 C 7s. 0,81 0,058 0,078 0,097 0,116 0,136 0,155 0,175 0,194 '5 • . 6s. 0,64 0,046 0,061 0,078 0,093 0,100 0,124 0,139 0,155 5 o Pi 7s. 0,75 0,054 0,072 0,091 0,109 0,127 0,145 0,162 0,182 8s. 0,86 0,062 0,083 0,104 0,124 0,145 0,166 0,186 0,206 9s. 0,96 0,070 0,093 0,117 0,140 0,163 0,186 0,210 0,233 10s. 1,08 0,078 0,103 0,130 0,155 0,181 0,206 0,234 0,260 w lis. 1,18 0,085 0,114 0,143 0,171 0,200 0,227 0,257 0,285 ^ 12s. 1,29 0,093 0,124 0,156 0,186 0,218 0,248 0,280 0,310 'o e3 13s. 1,40 0,101 0,135 0,169 0,203 0,236 0,269 0,304 0,337 14s. 1,50 0,109 0,145 0,182 0,218 0,254 0,290 0,327 0,364 p 15s. 1,61 0,116 0,K6 0,195 0,233 0,272 0,311 0,360 0,390 c 16s. 1,72 0,124 0,166 0,207 0,248 0,290 0,331 0,372 0,414 THE OVERALL EFFICIENCY OP GENERATING STATIONS 25 is known, we may, for the price and quality of coal, and for the boiler efficiencies considered, obtain from the right-hand section of Table XIII. the fuel cost in pence per kw hr delivered from the dynamo. For coal of any other calorific value, the fuel cost will be in the inverse ratio of the calorific values. Let us apply this to the following case : — Mean boiler efficiency = 70 per cent. Cost of coal = 10 shillings per ton. Mean steam consumption = 9 kg per kw hr. Calorific value of coal ~ 7000 kw hr per ton. From Table XII. in the section relating to 70 per cent, boiler efficiency and ten shillings per ton, we find for steam consump- tions of 8 and 10 kg per kw hr respectively, coal costs of 0,118 and 0,148 pence per kw hr. Thus for a steam consumption of 9 kg per kw hr we obtain a , . . 8700 0,118 + 0,148 fuel cost of ^jqq x 2 = 1,24 X 0,133 = 0,165 pence per kw hr. The Overall Efficiency of Generating Stations. — A very interesting example of the readiness with which electrical engineering calcula- tions may be carried out, may be found in the calculation of the efficiency of a generating station, this efficiency being defined as the ratio of the kilowatt-hours delivered from the generating station during a year, to the kilowatt-hours of calorific value of the coal burned during the year. Let us carry out this calculation for a representative generating station in Great Britain. During twelve months 1,5 million kw hr were delivered from this station, and this was employed for lighting and tramways. The load factor 1 was 22 per cent., and the station was run condensing. The coal burned had a calorific value of 7500 kw hr per ton. 6700 tons were burned during the year. Hence the total energy of combustion for the year, amounted to 7500 X 6700 = 50 million kw hr. Thus the overall efficiency of the generating station was 1 5 -^r = 3,0 per cent. While this is not a good result, it is nevertheless typical of the great majority of generating stations of this type and capacity. A 1 The load factor is the ratio of the average output taken oyer the 8750 hours of a year, to the maximum output at any time during the year. 26 HEAVY ELECTRICAL ENGINEERING condensing station of this output should, however, show at least 5 per cent, efficiency. With large modern stations, efficiencies of over 7 per cent, are often attained. Thus for the year ending June 30th, 1904, the efficiency of the Berlin Electricity Works, with an output of 113 million kw hr from a number of distributed generating stations, works out at 9,6 per cent., and the efficiency obtained by this company for the year ending June 30th, 1905, when the output had risen to 141 million kw hr, was 10 per cent. For the year ending June 30tb, 1906, the output of the Berlin Electricity Works was 167 million kw hr, and the overall efficiency was 10,3 per cent. The overall efficiency of the generating station of the- Glasgow Corporation Tramways, for the year ending May 31st, 1906, and with an output of 26 million kw hr, was 9,6 per cent. The Sheffield Corporation Tramways, for the same year, had an output of 14,5 million kw hr from the generating station, and an efficiency of 7,8 per cent. From the various sources from which this data was brought together, it appeared that the average price paid for coal, and the calorific value of the coal used in these plants, was as shown in Table XIV. TABLE XIV. Cost and Calorific Value of Coal used in various Generating Stations. Cost of Coal in Shillings per Ton. Calorific Value in Kilowatt Hours per Ton. Berlin Electricity Works (1905) Glasgow Corporation' Tramways (1906) Sheffield Corporation Tramways (1906) 16,0 6,4 8,2 8 100 8 100 7 700 From the data in Table XIV. we may deduce, as in Table XV., the fuel cost per kw hr of calorific value of the coal, and then, dividing by the efficiency, also the fuel cost per kw hr of output from the generating stations. Given the cost of coal in shillings per ton, its calorific value in kw hr per ton, and the efficiency of the generating station in per cent., then the fuel cost in pence per kw hr of annual output from generating station 1200 X Cost of coal ~ Calorific value X Efficiency THE OVEEALL EFFICIENCY OF GENEEATING STATIONS 27 TABLE XV. Fuel Cost per Kilowatt Hour Output from Generating Stations given in Table XIV, Cost per Kilowatt Hour of Calorific Value of Fuel in Pence. Efficiency of Generating Station or Stations. Fuel Cost per Kilo- watt Hour Output from. Generating Stations in Pence. Berlin Electricity Works (1905) ... Glasgow Corpora- tion Tramways (1906) Sheffield Corpora- tion Tramways (1906) 0,0245 0,0095 0,0127 10,0 9,6 7,8 0,245 0,099 0,164 Thus in the case of the Sheffield Corporation Tramways, we have — fuel cost per kw hr of annual output from the generating station, 1200 X 8,2 .... = 7700 x 7,8 = °' 164 penCe Let us suppose that the Sheffield Corporation Tramways had substituted a coal of a calorific value of 9000 kw hr per ton, for which a price of 11 shillings per ton was paid, and that the efficiency of the steam-raising plant was unaffected by this change in the quality of the coal burned. The fuel cost per kw hr of annual output from the generating station would have become 1200 x 11 . „_ 9000lT73 =0 ' 188penCe - - Instead, however, of burning 24 000 tons of coal per year, only 7700 9000 X 24 000 = 20 500 tons of the better coal should be required, and hence savings in other directions could be made as the result of the lesser weight of coal to be handled. Moreover, the efficiency of the steam plant would generally be affected by a change in the grade of fuel. Suppose the efficiency to have been increased to 8,2 per cent, (from 7,8 per cent.), then the fuel cost with the new fuel would have become »,„ir. X r> n = 0,179 pence per kw hr of annual output. 9000 x 8,2 * v It is a matter requiring considerable investigation to determine, '28 HEAVY ELECTRICAL ENGINEERING in any particular case, the most economical grade of coal to be burned. It involves also a consideration of the type and pro- portions of boiler, of grate, of stoking arrangements, as well as of the cost of modifying or replacing certain of these arrangements with others more suitable to other grades of fuel. It has already been pointed out that Works commonly designated C: kl CD 9 8 X 7 • 6 5 X 4 3 2 1 5 10 15 20 25 30 35 40 Output of Station in Mil/ions of Kw hr Pig. 8. — Curve Showing the Average Overall Efficiencies of Generating Stations of Various Capacities (see p. 31). x = Stations in Great Britain. • = Stations Abroad. " Generating Stations " should, strictly speaking, be termed " Transforming Stations," since in such stations we transform a small part of the energy of combustion of the coal or other fuel, into electrical energy. At the same time we — unwillingly — transform a far larger part of the energy of combustion of the coal into irrecoverable heat energy. T3 S B C( SQ c<2 & % 6? s g "« s c s I 3.9 ■ 3« g'.Sog'Sd "5" « °-j C a> £ w Q O >-l O (O ffliflCOtO CO CO cq_rf to tji" t)T «jjf ^T o co* ?o so j>T t-T co" 1-lr-li-lrHr-iCMCOCCCrjTti-^iO O O t~ O *- CO © ^ co" r-T i^" cc t> oT 00000000 ©OCMCMOOOO t-COOCOI— t-GOO iO (N O0J- J> CO OQ I* OOOOOOOOOOOO OOCOOCit— OOOO^OO WCQMOTM'*H'Ot-ODI-0 „.3fc».a [ - « zZ&au fS-gll '3.J5 'g £1 h3 O tf H £ fc CO P-< > F4 CQ OOOOOOOO ■*.— O O OCOCM O •*ooooco-*o W©tOOf HCOIM #r-ICN(M(NCSlCM 0^555^555555 id oi^odwf r-T ■4 o *£> coo csi _. N PJ rt 2 ,3 ,2,2 .2 ,2 3 0,3 ■H 'J " i 'J S ' 3 w ffi .- o ft s « la a* HHH*i0 1»M-*!0 CO -*H i-l ■T i-i" ih i-T i-T cn" eo co co" ** ■"*" iO &>-S< aj ^3 ^ rt £ a> j3 ;0 3 t ;? 5 ,d « « £ a> £ T q 3 eflP ^fflpjMflopcqMPg°ef O OMOO iO Oi lO CO cot- OS CM CN CO CO I- "* OOOOOO O 'O o •* ira CO 1— I £-- t— Ol iO 01 CO CO CO CO i^ OOOOOO O O O CO *o cn 00 ■* o m OHmnco CO CO ^ tH CO (D jo suotii;w 9T pUB i U89AV!).8a ^^ h-c c 'S S3 ^a^-d 5 rt 3 ^ * S HOtCCOON 5 5 ° C S3 « r. «S H> |>'5 •IE9X J9c[ sanoH WBAoijh jo 9aoin)]\[ 95 ptlB 81 niaa^a 30 HEAVY ELECTEICAL ENGINEERING The author has analysed the results of a number of generating stations with the object of determining the efficiency from the coal bunkers to the outgoing mains. We shall denote this efficiency as the "Annual Overall Efficiency " of the generating station. Twenty-six of these generating stations are classified in three groups in Table XVI. In each group, one-half represents British TABLE XVII. Further Details of the twenty-six Generating Stations. Reference Number. Results for Tear Ending Year o Working. Use of Energy ; L = Lighting P = Power T = Traction. Annual Load Factor. Steam Pressure in Kg per SqCm. Superheat in Deg Cent. Exhaust Pressure in Kg per Sq Cm. I. II. III. IV. V. VI. VII. VIII. IX. X. XI. xi r. 1905 1906 1905 1906 1905 1905 1906 1906 1905 1906 1905 1906 7th 7th 5th 9th 17th 6th 12th 12th 15th 13th 13th 13th L.P.T. L.T. L.P.T. L. L.P.T. L.P.T. L.P.T. L.P.T. L.P.T. L.T. L.P.T. L. 41 12,8 17 14,5 46,5 16,2 20,9 16,6 11,9 10 10,5 10 9,5 8,0 10 11 12 11 12 11 70° C. 80° C. 30° C. 50° C. 70° C. 0,17 to 0,2 0,03 0,13 0,50 XIII. XIV. XV. XVI. XVII. XVIII. XIX. XX. 1905 1905 1906 1906 1906 1905 1905 1906 13th 10th 9th 10th 6th 11th 14th 8th L.P. T. T. L.P.T. T. L.P.T. L.P.T. T. 35 16,5 28,5 37,5 12 12 11 11 11 12 12 9—13 50° C. 55 20—55 0,13 0,13 0,13 XXI. XXII. XXIII. XXIV. XXV. XXVI. 1905 1906 1904 1905 1906 1905 5th 7th 5th 17th 12th 4th T. T. L.P.T. L.P.T. L.P.T. L.P.T. 31,0 21,2 39,4 11 14 12 14 14 60° C. 0,12 0,07 stations, and one-half represents stations outside of Great Britain. None of the stations are situated in the United States, as the data studied did not comprise any such stations. Two considerations controlled the choice of stations for inclusion in the investigation. The first consideration was that the available data should comprise as many as possible of the conditions affecting the annual overall XiiJi uviiwALL EFFICIENCY OF GENERATING STATIONS 31 efficiency. The second consideration was that the range of capacities and the average capacity of the British stations should he about equal to the range of capacities and the average capacity of the stations located outside of Great Britain. The selection was made without any reference whatever to the value of the resulting average efficiencies. The stations are arranged in the order of their annual outputs, beginning with a small station with an annual output of about one million lew hr, and concluding with a station with an annual output of 55 million kw hr. In Table XVI. is also compiled the necessary data for determining the annual overall efficiency of each station. In Table XVII. are recorded various particulars of the stations which could be expected to have a bearing upon the efficiency. In Table XVIII. these results are averaged for the British stations, and for the stations situated outside of Great Britain. From this Table is plotted the curve shown in Fig. 8, which may be fairly said to represent modern practice for generating stations working under average conditions. TABLE XVIII. Average Overall Efficiencies of Stations given in Table XVI. Class. Great Britain (B)or Abroad (A). Average Output from Generating Station during Year in Millions of Kw Hr. Average Efficiency of Generating Station. Between 1,0 and 5,1 millions of kw hr per year. 1 J 3,6 2,5 4,9 6,0 Between 7 and 16 millions of kw hr per year. ! 5 13,6 11,7 8,2 7,1 Between 18 and 56 millions of kw hr per year. 1 5 31,7 38,5 7,7 9,0 It is a pity that the published returns from generating stations are not more complete. Thus we naturally ask ourselves whether 32 HEAVY ELECTEICAL ENGINEEEING it might not be possible to trace a connection between the overall efficiency and the extent to which electrical storage batteries are employed, but we find that the incompleteness of our data makes this impossible. It is fair to assume that all these stations were operated condensing, although this fact is recorded only in the case of the British stations. In fact, non-condensing stations, when known to be such, were purposely excluded from the comparison., In but few cases, however, have we records of the average exhaust pressure maintained, or of the average amount of superheat employed. The comparison of the capital cost and of the rate of depreciation would also have been impracticable, and hence one cannot say that the one or the other set of generating stations represents the better engineering. Analysis of Losses in Supply System. — Another important omission from the published returns of British generating stations, is the annual output from the station. The amount recorded is generally the amount of energy actually used by the consumers. The difference between the two amounts represents the energy lost in transmission. In Table XVI. the output entered for the British stations has been obtained by increasing the amount of energy sold during the year, by 25 per cent., or in other words, the transmission loss has been assumed to be 20 per cent, of the energy generated. That this value is a sufficiently fair approximation for the purpose, is indicated by the results of an analysis of twelve continental generating stations for the year 1904. For these cases the average transmission losses were as follows : — Loss in feeders . . 12 per cent.-i All expressed ,, ,, accumulators . 7 „ „ [ as percentage of „ ,, distributors . 6 „ ,, j energy generated. Total 25 per cent. Still higher values were obtained for five continental towns that included transformers in their transmission system : — Loss in Feeders ' - 3 per cent. ,, „ Accumulators 3 ,, „ ,, ,, Transformers .... 17 „ „ Distributors 8 . 31 per cent. THE OVEKALL EFFICIENCY OF GENERATING- STATIONS 33 Setting aside minor considerations, it is quite evident that the efficiency curve of Pig. 8- is very low. The efficiency of steam generating sets at full load, frequently exceeds 20 per cent, in larger sizes when operated under reasonably economic conditions of pressure, superheat and vacuum, and the efficiency of the steam raising plant when working at its rated capacity should not fall below 74 per cent. Taking the efficiency of the steam piping at 9 8 i 6 ft ■X 5 ^ 4 53 £ 3 2 / Fig. 9. 10 20 30 40 50 60 10 Annual Output in Millions of Kwhr Efficiencies of Stations as given by Patchell. 95 per cent., we obtain a practicable full load overall efficiency of the generating station of 0,20 X 0,74 X 0,95 = 14,0 per cent. The difference between this efficiency and that actually obtained in practice, is due chiefly to the circumstances that the plant is run for a large part of the time at considerably less than full load ; that fires must be kept up under one or more spare boilers; that the boilers and engines are not maintained in the condition H.B.B. d 34 HEAVY ELECTRICAL ENGINEERING of highest efficiency; that the supply of air to the fires is not suitably regulated ; that the coal is not uniformly of the calorific TABLE XIX. Particulars of Stations given by Patchell. W B ft a . CD O an (Qua P,3 ■+» Pi >» P. 5 Station. a * O ■* ft o eO § S2 SI 1 s o t3M I ■S o h3 Sheffield (Neepsend) . 3,5 1,83 8400 15,4 6,50 13,4 f Powell Duffryn Steam Goal Co. . 4,5 1,70 8400 14,3 7,00 37,0 City and South London Railway . 6,6 2,00 7400 14,8 6,75 35,0 1 St. James and Pall Mall Co. 6,7 2,51 9200 23,1 4,33 18,6 Charlottenburg, 1904 . 6,7 2,04 7340 15,0 6,66 24,6 1 I Central Electric Co. 7,1 1,00 9000 17,1 5,85 12,5 Elberfeld, 1904 .... 7,2 1,36 8000 10,9 9,17 27,2 Leeds 8,4 3,24 7100 23,0 4,35 14,5 Charing Cross Co. (Bow, 1904) . 10,3 1,56 9700 15,1 6,62 13,1 Salford 13,7 1,98 9250 18,3 5,46 28,0 County of London Co. . 11,4 2,50 7100 17,8 5,61 18,9 II. - Westminster .... 11,6 2,25 9300 21,0 4,76 27,0 Charing Cross Co. (Bow, 1905) . 12,2 1,65 9000 14,8 6,72 13,7 Hamburg (Zollverein), 1904 12,9 1,36 8700 11,8 8,47 38,6 Munich, 1904 .... 12,9 1,68 8200 13,8 7,25 24,2 \ Cologne, 1904 13,1 1,63 8300 13,5 7,40 37,8 / Copenhagen, 1904 13,3 1,77 8100 14,3 7,00 29,3 London Electric Supply Co. 14,2 2,08 7750 16,1 6,20 25,0 Newcastle (Carville for 6 Months) 14,6 1,42 7100 10,1 9,95 37,0 III. - Bradford 14,7 1,87 8400 15,7 6,37 28,0 Dresden, 1904, Power and Light . 18,0 3,07 5200 15,8 6,33 29,0 Frankfort, 1904 .... 18,5 1,53 8700 13,3 7,50 29,8 Glasgow Corporation . 20,6 2,04 6800 13,9 7,20 17,4 \ Metropolitan E. S. Co. . 22,7 2,10 7600 16,0 6,25 22,0 / Hamburg (Combined), 1904 27,2 1,54 8700 13,4 7,46 28,4 Oberschlesischer Industrie-Bezirk 27,3 2,18 7000 15,3 6,54 35,2 Manchester (Stuart St.) 28,2 1,62 8700 14,1 7,10 36,3 IV. - Vienna, 1904 45,9 1,22 7700 9,4 10,6 35,2 Boston (Mass., U.S.A.), Edison . 49,9 1,21 9500 11,5 8,70 28,2 Berlin, 1904 113,4 1,40 8100 11,4 8,77 31,1 Chicago (Fisk St.) Edison . 130,2 2,04 6500 13,3 7,52 33,0 Berlin, 1905 141,1 1,08 8000 8,64 11,6 30,4 value of the samples tested, and to various other detail circumstances. While improvement should be made in all these respects, it is not reasonable to expect that 14 per cent, efficiency should at present be THE OVERALL EFFICIENCY OF GENERATING STATIONS 35 obtained. In plants of large capacity, however, it should be more closely approached than is at present the case. As is shown in Table XVI., it is not unusual to find large stations with an annual overall efficiency of over 9 per cent. In a contribution to the Proceedings of the Institution of Elec- trical Engineers, 1 Patchell has published some tables of data giving the coal consumption, the calorific value, the load factor, and the annual output for quite a number of generating stations. The author has rearranged PatchelFs figures according to the units used in the present work, and they are given herewith in Table XIX. in •4-J B A _C_ ^ 8 1 f S* •*"■ / ^ . — — •* / Sfc Uj 4 £ 2 10 20 30 40 50 60 70 Annual Output in Millions of Kw hr Fig. 10. Efficiencies of Stations. Curve A from Fig. 8, on p. 28.— Author's investigation. Curve B from Fig. 18, on p. 54.— Attainable values. Curve C. from Fig. 9, on p. 33.— Patchell's investigation. arranged in the order of increasing annual outputs in millions of kilowatt hours. The author has divided these thirty-two results into four groups of eight stations each, and arranged in the order of increasing capacities of the stations. The averages for these four groups are given in Table XX., and they are plotted in the curve of Fig. 9. In Fig. 10 are repeated the curves of Figs. 8 and 9, and there is also added the curve of Fig. 18 on p. 54, which represents values which, it would appear, 1 Journal I. E. E. t vol. xxxvi., p 156. D2 36 ought to p. 53. HEAVY ELECTRICAL ENGINEERING attained. The derivation of Fig. 18 is discussed on TABLE XX. Average Results for Stations given by Patchell. Group. Average Output in Millions of Kw Hr per Annum. Average Load Factor. Average Efficiency. i. ii. in. IV. 6 12 17 70 23 25 27 32 6,3 6,5 7,1 8,5 It is evident from an examination of Fig. 10, that there is a fair agreement between the results of the author's own analysis of existing generating stations of various capacities and Patchell's results. The former curve shows somewhat higher values than the latter, partly owing to the fact that many of the results are more recent. In Table XXI. are set forth fair representative figures for the values at present obtained, and the values which ought to be readily obtained. These are roughly estimated for 30 per cent, and for 50 per cent, load factors. TABLE XXI. Average Overall Efficiencies of Generating Stations. 50 per Cent. Load Factor. For 30 per Cent, and Capacity of Station in Millions of Kw Hrs per Annum. Load Factor — 30 Per Cent. Load Factor = 50 Per Cent. Overall Efficiency now obtained. Overall Efficiency which should be Obtainable. Overall Efficiency now obtained. Overall Efficiency which should be Obtainable. 6 12 17 70 6,8 7,0 7,2 8,4 7,2 8,1 8,6 9,8 7,3 7,8 8,2 9,1 8,2 9,2 9,6 10,5 Analysis of Losses in Generating Station. — It is very instructive to note that of the total heat available from the combustion of coal or other fuel, only 11 per cent., under most favourable conditions, is transformed into useful work. It is interesting to examine where the remaining 89 per cent, is lost. The various losses which occur during the process of transformation from heat to electrical or THE OVERALL EFFICIENCY OF GENERATING STATIONS 37 mechanical energy are allocated by various authorities in the proportions shown in Table XXII., where the figures given by Professor Dalby, H. C. Stott (in a paper read before the American Institute of Electrical Engineers), 1 and by " Power " in a pamphlet published in 1904, are placed in parallel columns. It is seen that there is a very fair agreement between the figures. It is as well to remember when comparing the results that no economiser is used by Professor Dalby, or by " Power," although in the latter case a large amount of heat is returned by the feed-water heater. Pro- fessor Dalby's figures are less recent than the others, which are actual test results, made under working conditions. In Pigs. 11, 12- and 13, the figures given in Table XXII. are diagrammatically represented by a stream of energy, the various losses being represented by small branch streams. The energy ulti- mately available at the bus bars is represented by a thick black stream. This graphical method of showing the losses is due to Professor Dalby. It is interesting to note the large percentage of heat rejected to the condenser, due to the low thermal efficiency of all steam engines. TABLE XXII. Showing Losses during Transformation of Energy contained in Goal into Mechanical or Electrical Energy. Source of Loss. Percentage of Loss of Total Heat as given by the following : Prof. Dalby. H. C. Stott. "Power." Eadiation and ashes Chimney .... Bejeeted to condenser . Minor losses Total losses .... Heat returned by feed water Heat returned by economiser Net losses .... Total energy in coal . Efficiency .... 7 27 53 10,4 10,4 22,7 60,1 6,4 6,0 22,0 57,3 10,3 97,4 99,6 95,6 5,0 92,4 100,0 7,6 3,1 6,8 89,7 100,0 10,3 5,0 90,6 100,0 9,4 1 " Power Plant Economics," Trans. Am. Inst. Elec. Engrs., vol. xxv. (1906), p. 1. 38 HEAVY ELECTBICAL ENGINEEBING Demand for Electricity. It is a difficult matter to predetermine the demand for elec- tricity. Local conditions vary so widely that it is impossible to obtain a very accurate estimate either of the demand or of the Chimney 27% Radiation7\ & Ashes ■ Energy available at ' 'Engine Flywheel Fig. 11. Peof. Dalbt's Analysis of Losses. Condenser IQ3!! Energy available at Bus bar Fig. 12. Stott's Analysis of Losses. Chimney 22% Radiation 6% & Ashes 11/ 57 p" Condenser W., Energy available WZ at Bus bars Fig. 13. " Power" Analysis of Losses. Figs. 11, 12 and 13. Analysis of Losses in Steam Generating Plant. growth of the demand from year to year. Nevertheless, it is possible by analysis of a number of undertakings to make a rough estimate of the prospects of a power supply serving a large densely populated THE OVERALL EFFICIENCY OF GENERATING STATIONS 39 area such as a large manufacturing city. We have made such an analysis in the following pages, and, as an illustrative example, we have at the same time worked out rough estimates for a city of one million inhabitants. ' Interior Lighting. — Analysis of returns for twenty-two large towns in Great Britain, with populations ranging from 800 thou- sand down to 50 thousand, show that for every thousand inhabitants there are some 800 eight c p lamps (or the equivalent in larger candle power), connected, i.e., 0,8 lamp per person. The average number of kw hr per lamp per year works out at 17 at the customers' meters. The data on which these averages is based is set forth in Table XXIII. TABLE XXIII. Table of Interior Lighting of various British Towns. No. Place. Population. Thousands. No. of 8 c p Glow Lamps per Inhabitant. Kw hr per Lamp Year. 1 2 3 4 5 6 7 Newcastle-on-Tyne . Sheffield . Leeds Birmingham Manchester Liverpool . Glasgow . 400,0 413,0 450,1 522,2 698,3 702,2 800,0 2,1 0,82 0,8 0,5 1,05 0,83 1.0 Not obtainable 14,6 21,1 19,2 22,0 18,7 20,9 8 9 10 11 12 Cardiff . Newcastle District . Leicester . Hull .... West Ham 172,6 214,9 220,0 250,0 275,4 0,63 0,47 0,85 0,96 0,31 24,9 28,1 11,0 14,0 29,1 13 14 15 16 17 Huddersfield Bournemouth . East Ham Preston Oldham 95,0 106,0 104,0 120,0 137,2 1,4 1,1 0,32 0,83 0,42 12,6 11,8 16,0 13,7 15,4 18 19 20 21 22 Darlington Tynemouth Stockton . Ilford Wallasey . 49,0 51,6 51,5 55,0 56,5 0,67 0,62 0,48 0,96 0,59 13,1 17,1 15,6 23,3 13,7 Average . 0,805 17,1 40 HEAVY ELECTEICAL ENGINEERING The c p values are expressed in terms of the equivalent number of 8 c p incandescent lamps, when arc lamps or other types of incandescent lamps are employed. On the basis of 3,5 watts per c p an 8 c p lamp requires 3,5 X 8 = 28 watts i.e., 28 watt hours per hour. The average hours burning per year is therefore 17 X 1000 fi „ —28 = 61 ° or qeF" = 1>66 hours per day. The above figures are from stations which on the average have been running for about ten years. Of course the precise number of lamps per inhabitant varies widely according to local conditions, such as the amount of competition by gas lighting, the amount of lighting required during the daytime in consequence of fogs, and still more upon the enterprise of the conductors of the undertaking. Included in this last condition is the price per kw hr. For one million inhabitants we should expect, on the basis of eight-tenths of an eight candle-power lamp per inhabitant, a total of 800 000 eight candle-power lamps. A year or two ago we should have based our estimates on some such lamp efficiency as 3,5 watts per candle. With the rapid progress now being made in improving the incandescent lamp, as shown, for instance, by Tantalum, Osmium, Tungsten and Nernst lamps, we could greatly reduce this value. Although, however, these lamps have efficiencies better than two watts per candle, their introduction will necessarily be slow, and a large percentage of the lamps will for some years continue to be of the carbon filament type and of some such economy as 3,5 watts per candle. Hence for an average value, we should not, for the next two or three years, be safe in assuming less than 2,5 watts per candle. If the lamps burn on the average 1,7 hours per day, at 2,5 watts per candle, the consumption per lamp per day will be 2,5 X 8 X 1,7 = 34 watt hours. The consumption per lamp-year is thus 34 x 365 in . , , 1000 = 12 > 4 kwhr. For 800 000 lamps the total number of kw hr required will be 12,4 X 0,80 = ten million kw hr per year. THE OVERALL EFFICIENCY OF GENERATING STATIONS 41 Allowing 15 per cent, loss in transmission and distribution we must generate ^-^ = 11,7 million kw hr per year to provide for interior lighting. Street Lighting. — For four large continental cities for which the returns were examined, the ratio of the consumption for public arcs to that for private lighting is as set forth in Table XXIV. TABLE XXIV. Table of Public Lighting Supply for four Continental Towns, showing relation to Private Lighting. No. Town. Kw hr used for Total kw hr for Private Lighting. Public Arcs -f- Total Private Lighting. Public Arcs. Private Arcs. Private Glow Lamps. 1 2 6 7 Berlin Hamburg . Dusseldorf . Rotterdam. 1 940 000 213 000 161 500 61500 12 610 000 483 000 234 500 248 500 17 400 000 4 890 000 1 466 000 798 000 30 010 000 5 373 000 1 700 500 1 046 500 1 : 15 1 : 25 1 : 10 1 : 17 Let us estimate the street lighting at 25 per cent, of the interior lighting. Hence for our city of one million inhabitants, we shall require to deliver from the generating station for street lighting 11,7 X 0,25 = 2,9 million kw hr per year. TABLE XXV. Table for Electric Tramways in various British Towns, showing Gar Miles per Inhabitant and Kw Hr per Gar km. (See next page for text). No. Place. Population in Thousands. Car Miles per Inhabitant. Kw Hr per Car Mile. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 Sheffield Leeds Manchester . Liverpool Glasgow Sunderland . Cardiff . Nottingham . Potteries District Warrington . Cork . Oldham . Brighton Darwen . Carlisle . Burton . Rotherham . 425 446 750 760 1000 159 108 240 270 80 90 100 123 40 46 52 58 21,8 22,0 29,5 25,8 26,2 14,7 25,3 17,0 12,4 8,4 15,8 22,8 15,0 10,1 11,7 14,0 16,4 0,99 0,87 0,75 1,02 0,58 0,68 1,04 0,95 0,95 0,73 0,68 0,95 0,96 1,04 0,63 0,84 1,01 Average . 18,4 0,87 42 HEAVY ELECTRICAL ENGINEERING Surface Tramway Load. — By a similar process of averaging the tramway returns for seventeen cities in England, we find an average of 18,4 car km per year per inhabitant ; and an average consumption of 0,87 kw hr per car km. The data is set forth in Table XXV. For our town of one million persons we should expect about 18,4 million car km per year. On the basis of 0,87 kw hr per car km, we should require 18,4 X 10 8 X 0,87 = 16 million kw hr per year for surface tramways. Such a city would also require at least some 22 km of double track overhead or underground railway. Taking as a basis the Central London Eailway, which, with its 9,25 km, requires annually, including lifts and lighting, some eighteen million kw hr, we should, for our 22 km, require 22 „-pT X 18 = 43 million kw hr per year, for overhead or under- ground railway. Power. — From returns of eight large continental towns set forth in Table XXYI. with an average population of about half a million we find the average connection for power works out at 12,5 h p per 1000 inhabitants. Also the mean value for the kw hr consumed per year per connected h p of motive power is 244 kw hr per year for these towns. These figures will of course depend on the nature of the locality and the class of manufacture, but their probable values as set out in Table XXVI. indicate that for our typical town of one million people we shall not err very much during the first years of working in calculating on the mean values obtained. TABLE XXVI. Table of Electricity Supply in various Continental Towns showing hp connected, in Motors per 1000 Inhabitants, and lew hr per Year per hp connected. No. Place. H p in Motors connected per 1000 Inhabitants. Kw hr per year per h p connected. Population in Thousands. 1 2 3 4 5 6 7 8 Berlin . Hamburg Breslau . Bremen . Dusseldorf Rotterdam Karlsruhe Konigsberg 20,7 12,4 6,5 11,7 9,1 14,0 18,2 7,6 516 298 356 160 256 125 132 312 2835 830 446 201 237 370 106 195 Average . 12,5 244 THE OVERALL EFFICIENCY OP GENERATING STATIONS 43 Hence for our town of one million inhabitants, the power con- nection would, on this basis, amount to 12 500 h p of motors, causing 12 500 X 244 = 3 million kw hr per year at the customers' g meters, and requiring a supply of ~-~= = 3,5 million kw hr from the generating station. Summing up the various requirements we obtain Table XXVII. TABLE XXVII. Total Electricity required for Hypothetical City of 1 000 000 Inhabitants. Employed for Millions of kwhr required from Generating Station per Year. Interior Lighting .... Street Lighting Surface Tramways .... Elevated or Underground Eailways Power ...... Total 11,7 2,9 16,0 43,0 3,5 77,1 Statistics show, however, 1 that the use of electricity for lighting, traction and power, is growing rapidly, whereas the above deduced total is based upon present conditions. This consideration makes it necessary to make our plans with a view to increasing the above output by 50 per cent, in the course of, say, the next ten years. Hence we shall design our generating station for an ultimate capacity of 1,50> X 77,l w = 116 million kw hr per year, or say, some 120 million kw hr per year. At first, however, we shall only purchase generating apparatus sufficient for providingfor one-third of the above amount, or 40 million kw hr per year, and we shall thus save the interest on the capital outlay which would be required to install at first sufficient machinery to provide 120 million kw hr. If our expectations are realised, we shall have sufficient demand for power to justify installing machinery for another forty million kw hr at the end of four years of working and by the end of the eighth year of working, the remaining forty million kw hr will be called for and will justify installing sufficient machinery to bring the station up to the full capacity for which it was originally planned. This procedure also has the advantage that we can obtain, in the second and third groups of machinery, the advantage of 44 HEAVY ELECTEICAL ENGINEEEING improvements made in the design of generating apparatus during the coming eight years. Annual Increase in Output. — Table XXVIII. shows the output of nine important provincial towns for the years 1896 and 1906, and the average increase per annum. TABLE XXVIII. 1 Showing the Growth of the Demand for Electricity in Nine Provincial Towns. Town. Year of Working (1S96). Output in Millions of Kw Hr. Increase in 10 Years. Average Increase per Cent. Per Annum, 1896. 1906. Glasgow . Newcastle-on-Tyne Manchester . Liverpool Leeds Sheffield Bradford Edinburgh Salford . 4th 7th 2nd 13th 2nd 2nd 5th 1st 1st 1,1 0,9 1,8 1,2 0,5 0,3 0,7 0,9 0,05 43,9 42,2 40,0 31,5 21,9 16,7 14,0 12,9 10,9 42,8 41,3 38,2 30,3 21,4 16,4 13,3 12,0 10,8 44,7 % 46.7 % 36.8 % 38,8 % 45,3 % 50,2 % 35.5 % 30,7 % 70.6 % Table XXIX. gives the population of these towns for the same years, and the average rate of increase. In Table XXX. is com- pared the demand for electricity per inhabitant for the two years. TABLE XXIX. Showing the Growth of the Population in Nine Provincial Towns. Population in Town. Thousands. Increase in 10 Years. Average Increase per cent, per Annum. 1896. 1906. Glasgow 817 785 - 32 - 0,5 % Newcastle-on-Tyne. 197 377 + 180 + 7 % Manchester . 520 625 + 105 + 2 % Liverpool 518 704 + 186 + 3 % Leeds 390 463 + 73 + 2 % Sheffield 334 448 + 114 + 3 % Bradford 216 289 + 73 + 3 % Edinburgh 277 337 + 60 + 2 % Salford . 198 234 + 36 + 3 % ■ The first four columns of this Table are from page 436 of the Electrical Times of September 27th, 1906. THE OVERALL EFFICIENCY OF GENERATING STATIONS 45 TABLE XXX. Showing the Demand for Electricity per Inhabitant in Nine Provincial Towns for the Years 1896 and 1906. Town. Output in Kw Hr per Inhabitant. Increase in Average Increase per cent. 1806. 1906. per Annum. Glasgow . 1,4 56,0 54,6 15% Newcastle-on-Tyne . 4,6 . 92,3 87,7 7% Manchester 3,5 64,0 60,5 6% Liverpool 2,3 44,7 42,4 7% Leeds 1,3 47,4' 46,1 14% Sheffield . 0,9 37,3 36,4 37% Bradford . 3,2 48,5 45,3 4% Edinburgh 3,3 38,3 35,0 1,5% Salford . 2,5 46,5 44,0 6% Table XXXI. shows the demand for electricity per inhabitant for 158 continental generating stations. TABLE XXXI. The demand for Electricity in 158 Continental Generating Stations. Number of Output in kw hr Stations. per Inhabitant. 2 2 5 4 16 6 12 8 16 10 15 12 26 15 13 17 14 20 15 25 10 30 7 35 11 over 35 As to the growth of the demand for electricity in continental towns, Table XXXII shows the electrical output and efficiency of the generating stations in four continental towns for the years 1901, 1904 and 1905. The results are shown in graphical form in Figs. 14 and 15. 46 HEAVY ELECTKICAL ENGINEEBING ~W^ 10 1901 1904 1905 F>9 16 C •*■ ) c f 1901 1904 1905 Year of Operation, • = Stockholm o = Strassburg x = Stuttgart a = Breslau Figs. 14 and 15. Annual Output and Efficiency of Four Continental Genebating Stations. THE OVEBALL EFFICIENCY OF GENEBATING STATIONS 47 TABLE XXXII. Electrical Output and Efficiency of the Generating Stations in Four Continental Towns from 1901 — 1905. Town. 1901. 1904. 1905. Output. Efficiency. Output. Efficiency. Output. Efficiency. Stockholm . 2,6 6,1% 6,8 7,6 % 10,9 10,4 % Strassburg . 7,1 5,7% 9,4 8,6% 10,6 9,2% Stuttgart . 6,0 6,5% 8,5 6,1% 9,1 6,3% Breslau 1,7 4,5% 7,4 6,7% 8,1 7,6 %■ Average 4,4 5,7 % 8,0 7,3% 9,7 8,4% In laying down the plans for a generating station it should be borne in mind that as the output of the station increases, the TABLE XXXIII. Average Efficiency of Continental Generating Stations of various Outputs for different Years. Output in Millions of Kw Hr per Year. Nuniber of Stations. Efficiency. Year. Less than 1 1—5 6—10 11—20 100 24 30 3 5 1 4,1 5,6 6,1 6,5 9,8 -1901 Less than 1 1—5 6—10 11—20 21—50 51—100 over 100 63 40 15 8 3 1 1 6,5 6,1 7,0 7,8 7,5 5,9 11,1 1 ■ 1904 Less than 1 1—5 6—10 11—20 21—50 51—100 over 100 71 36 17 11 1 1 1 6,4 6,1 7,1 7,8 6,9 11,1 10,0 1 -1905 48 HEAVY ELECTRICAL ENGINEERING attainable efficiency will increase also. This has already been shown in the case of the four continental towns analysed in Figs. 14 and 15. That it has more general application is indicated by Table XXXIII. which is a summary of the workings of a large number of continental generating stations over a period of five years. Table XXXIII gives the average efficiency of a large number of continental generating stations of different outputs for 10 1-J <3 8 l / «£ *' S- ^* { 2 I 20 40 60 80 100 Output in Millions of Kw hr Symbols for Year of Operation-. • = 1901 o = 1904 * = 1905 Pig. 16. AVEBAGE EeEICIENCT OF CONTINENTAL GeNEEATING STATIONS OF Various Outputs fob Different Tears. various years, and the number of stations analysed. The results are given graphically in Fig. 16. Another method of investigating the growth of the demand for electricity is to consider the number of kilowatts of rated capacity of the apparatus connected to the distributing mains of the generating station. An investigation into this question has been made by Hoppe, and the present author has put the results into graphical form in Fig. 17. In this figure, the abscissae represent the rated number of kilowatts connected per 1000 THE OVERALL EFFICIENCY OF GENERATING STATIONS 49 inhabitants, and the ordinates the year of operation of the generating station. Considering the uppermost curve, we see that for eleven towns V. o . N Cl ps «•* M <* M ** •^ N v. ■o >0 '(-. o to K <=n Ol Ol -•. <») o> °1 0-) o> r-i O CJ 03 f) tf) th * 03 "i °1 <8 6 — ^ e <3 V 1 *_ / ^--i ^ * 4 \l 1 ^ ^ b>. \ V > * s zoei s b. ^ \ioei '0061 mi •SSSI c i LG81 S3 aesi t 1 i b *cw «9 • b a to Hi s£ »5 -C C3 IT, C3 2 "= E" 1 5 ffl w H g to o M H & & o FN I* o O £ ft P o o EH Eh P O o 3S Bh ^ O OX) UOIJBJpdg JO J83\ which started supplying electricity in the year 1893, the rated connections were 10 kw per 1000 inhabitants at the end of the second year of operation, and that they had risen to 36 kw at the end of the eleventh year of operation (1902). h.e.b. E 50 HEAVY ELECTRICAL ENGINEERING Comparing with this the fact that fifteen towns commenced supply in 1894, the rated kilowatts being seventeen at the end of the second year, and 39,5 at the end of the tenth year, the number of towns starting supply each year is given in the Table at the. side of Pig. 17. All the towns under consideration had a population of less than 10 000 inhabitants. Capacity of Single Generating Station.— As illustrations of the size of modern generating stations, some rough leading data of a number of such stations have been brought together in Table XXXIV. TABLE XXXIV. Leading Particulars of three well-known Generating Stations. Name of Generating Station. Millions of Kilo- watt-Hours delivered from Generating Station per Year during One Year or Half Year, Period con- sidered. Total Kilowatts rated capacity of Generating Sets, excluding Exciters and Sets for Lighting and Power in Generating Station. Average load during total period con- sidered (based on 24- hour day). Max. Load during Total Period con- sidered. Load Factor at outgoing Mains from Generat- ing Stations. Pinkston Station Glasgow Cor- poration Tram- ways 26 Year ending May 1906 11200 2980 9600 31% Shepherd's Bush Station (Central London Railway) 18,1 Half year ending June 30th 1905 5100 2060 4000 52% Eingsend Station (Dublin United Tramways) 8,2 Half year ending June 30th 1905 3600 936 In Table XXXV. are given rough estimates of the ultimate capacities for which these stations would be suitable with a 50 per cent, load factor. To the three stations in Table XXXIV. there have been added in Table XXXV. the Neasden Generating Station of the Metropolitan Eailway of London, and the Chelsea (Lofs THE OVERALL EFFICIENCY OF GENERATING STATIONS 51 Eoad) Power Station of the Underground Electric Bailways Com- pany of London; the estimates in these last two cases are, of course, only of the roughest nature, as although electrical power has now been delivered from these two stations for some consider- able time, a number of initial difficulties of various sorts have retarded developments, and have led the interested parties to suppress information. TABLE XXXV. Ultimate Capacities of Various Stations for 50 per cent. Load Factor. Name of Generating Station. Millions of Kilowatt Hours of An- nual Capa- city of Gene- rating Station for a 50 per cent. Load Factor. Total Kilowatts Rated Capacity of Generating Sets excluding Exciters and Sets for Light- ing and Power in Generating Station. Average Load based on a 24-Hours Day. Correspond- ing Maximum Load (based on 50 per cent. Load Factor). Rated capa- city of Gene- rating Sets Installed per Million KwHr Output per Annum. Dublin C.L.E. Glasgow Neasden Chelsea 13 19,5 44 58 200 3600 5100 11200 14 000 44 000 1480 2220 5000 6600 22 800 2960 4440 10 000 13 200 45 600 277 262 255 241 220 Systematic Procedure in the Design of Steam-Driven Electric Generating Stations. — Single generating stations may thus deliver hundreds of millions of kilowatt-hours of electrical energy per annum. Let us roughly work out some preliminary figures for stations of capacities for delivering 10, 30, 90 and 270 millions of kilowatt-hours per annum. By reference to Table XXXV. we see that while for the smaller of these stations we shall require to install generating sets having 280 kw rated capacity per million kw hr per annum, the largest station will require but 200 kw rated capacity per million kw hr per annum. The total rated capacity of generating sets to be installed, the number of sets and the rated capacity per set, are set forth in Table XXXVI. With steam generating sets, practically as low a rate of steam consumption has been obtained with 1800 kw sets as with any of larger capacity. Hence for all but the smallest one of these four stations, we can estimate on obtaining the same average steam consumption. Taking an absolute admission pressure of 13 kg per e 2 52 HEAVY ELECTRICAL ENGINEERING TABLE XXXVI. Particulars of Generating Sets to be Installed. Designation of Generating Station. Millions of Kw Hr per Annum. Rated Capacity of Generating Sets per Million Kw Hr per Annum, for 50 per cent. Load Factor. Kilowatts Total Rated Capacity of Generating Sets to be Installed. No. of Generating Sets to be Installed. Kilowatts Rated Capacity of each Generating Set. A B C D 10 30 90 270 280 240 210 200 2800 7200 18 900 54 000 4 4 4 8 700 1800 4700 6800 sq cm, 50° C of superheat, and an exhaust pressure of 0,15 kg per sq cm, a fair figure for the "all-day" steam consumption of the 700 kw sets will be 8,9 kg per kw hr, and for the larger sets, 8,4 kg per kw hr, as in Table XXXVII. TABLE XXXVII. Representative Values of Steam Consumption of Generating Sets. Rated Output in Kw. Steam Consumption at Rated Load. "All day" Steam Consumption. 700 1800 4700 6800 8,0 7,5 7,5 7,5 8,9 8,4 8,4 8,4 The next steps in the estimate are set forth in Table XXXVIII. TABLE XXXVIII. Particulars of Steam Consumption for Stations of Various Capacities. Designation of Generating Station. Capacity in Mil- lions of Kw Hr per annum. Steam Consump- tion in Kg per KwHr. Tons of Steam Con- sumed per annum. Average Tons of Steam per Hour during year. A B O D 10 30 90 270 8,9 8,4 8,4 8,4 89 000 252 000 756 000 2 268 000 10,2 28,8 86,4 259 The next step is to work back from the steam to the coal. Table III. sets forth the energy in kilowatt hours required to raise THE OVERALL EFFICIENCY OF GENERATING STATIONS 53 one ton of steam of various pressures and superheats. From this Table we find that for our standard conditions of pressure and superheat (13 kg per sq cm and 50° C superheat) 810 kw hr of energy are expended in raising one ton of steam from one ton of water at 0° C. But we may take the temperature of the feed water as 50° C since we are able to re-employ the heat in the condensed steam to raise the temperature of the feed water. From Table I. on p. 4 we find that 58 kw hr are required to raise one ton of water from 0° C to 50° C. Hence to obtain one ton of steam at our standard conditions of pressure and superheat, from feed water at 50° C, we shall require to impart to the steam — 810 - 58 = 752 kw hr. The average boiler efficiency will be to a considerable extent dependent upon the size of the station, because the larger the station the smaller is the percentage of boilers in operation at less than full load. Hence we shall for our four plants take the average boiler eCSciency for the year at 66, 68, 70, and 71 per cent, respectively. Taking 5 per cent, loss in the steam piping for all cases, we have for the combined efficiency of boilers and steam piping : 63, 65, 67, and 68 per cent. Thus we must burn under the boiler a fuel of such quality and amount as to provide during the year the energy of combustion shown in the last two columns of Table XXXIX. TABLE XXXIX. Particulars of Energy contained in Steam used by Generating Sets Installed in Stations in Table XXXVIII. Designation of Station. Capacity in Millions of KwHr per Annum. Tons of Steam Con- sumed by Generating Sets per Annum. Energy in Kw Hr to be given to each Ton of Steam. Total Energy to be Imparted to Steam per Year in Millions of Kw Hr. Combined Efficiency of Boilers and Steam Piping. Total Energy of Combus- tion in Millions of KwHr per Annum. Total Energy of Combus- tion per hour dur- ing Year in KwHr. A B C D 10 30 90 270 89 000 252 000 756 000 2 268 000 752 752 752 752 67 190 • 570 1710 63% 65% 67% 68% 105 292 850 2520 12 160 33 400 97 200 288 000 From the data in Table XXXIX., we may obtain the annual overall efficiency of these generating stations, as shown in Table XL. 54 HEAVY ELECTRICAL ENGINEERING TABLE XL. Annual Overall Efficiencies of the Generating Stations given m Table XXXIX. Designation of Generating Station. Capacity in Millions of Kw Hr Delivered from Station per Annum (S). Total Energy of Com- bustion of Coal Burned in Millions of Kw Hr per Annum (T). Annual Overall Efficiency of Generating Station 100 S T A B C D 10 30 90 270 105 292 850 2520 9,5% 10,3% 10,6% 10,7% // to s ^ — 1 9 1 7 I ■I 6 a *- 4 QJ H Q 3 — Fig. 18. 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 Output of Station in Millions of Kw hr Estimated Efficiencies of Stations of Various Capacities. From Table XL. THJii UVERALL EFFICIENCY OF GENERATING STATIONS 55 From the curves in Fig. 8 we have seen that the average annual overall efficiencies obtained in practice, on plants of 10 and 30 millions of kw hr of annual capacity, are 7,3 per cent, and 8,4 per cent, respectively, as against the above estimated figures of 9,5 and 10,3. H = w 10,3 _ V! As our assumptions in developing the estimates for these four stations have been very conservative, we may say that it would be reasonable to attempt to improve average present practice, as indicated by the curve in Fig. 8, by at least 30 per cent, in stations of 10 million kw hr of annual output, and by some 25 per cent, in stations of 30 million kw hr of annual output. The results for the annual overall efficiency as arrived at in the last column of Table XL. are plotted in Fig. 18. Eeturning to our estimates, let us assume that we employ a quality of coal with a calorific value of 8700 kw hr per ton. From this figure we at once obtain the number of tons of coal burned per year, as set forth in Table XLI. TABLE XLI. Coal Consumption for Stations A, B, C and D. Designation of Station. Capacity in Millions of Kw Hr per annum. A 10 B 30 C 90 D 270 Total energy of combus- tion per annum in Millions of Kw Hr. 105 292 850 2520 Energy of Com- bustion of one Ton of Coal. 8700 8700 8700 8700 Tons of Coal Con- sumed per year. 12 100 33 600 97 700 290 000 Do. per hour (Average for Year). 1,38 3,84 11,1 33,2 TABLE XLII. Coal Consumption in Kg per Kw Hr for Stations A, B, C and D. Designation of Station. Capacity in Millions of Kw Hr Delivered from Generating Station per Annum. Tons of Coal Burned per Annum. Kg of Coal Burned per Kw Hr Delivered. A B C D 10 30 90 270 12 100 33 600 97 700 290 000 1,21 1,12 1,08 1,07 56 HEAVY ELECTRICAL ENGINEERING In Table XLII. are derived results for the kilograms of coal burned (of a calorific value of 8700 kw hr per ton) per kw hr of electrical energy delivered from the generating station per annum. Following these rough preliminary estimates of the quantities involved, the design of coal bunkers, coal conveyors, boilers, super- heaters, condensing plant, piping, generating sets, cables and switchboard, all require detailed consideration. The purpose of the present chapter, however, has been to lay down a systematic plan of procedure in the choice of plant of the type indicated. CHAPTEE III STEAM KAISING PLANT In the preceding chapter we derived fair values for the steam consumption of generating stations of various sizes. For an absolute admission pressure of 13 kg per sq cm, 50° C of superheat- and an exhaust pressure of 0,15 kg per sq cm, we arrived at certain values for the steam consumption for stations with a 50 per cent, load factor. These values, which should be attainable in well-designed plants, are given again in Table XLIII. TABLE XLIII. Annual and Hourly Steam Consumption of Large Electric Generating Stations. Capacity of Station in Millions of Kilo- watt Hours per annum. "All Day" Steam Consumption in Kilograms per Kilo- watt Hour. Tons of Steam Consumed per annum. Average Tons of Steam per Hour during Year. (There are 365 x 24 = 8750 hours in one year.) 10 30 90 270 8,9 8,4 8,4 8,4 89 000 252 000 756 000 2 270 000 10,2 28,8 86,5 259 Thus, on the assumption that the maximum load is occasionally of one hour's duration, we have TABLE XLIV. Maximum Hourly Steam Consumption of Large Electric Generating Stations. Capacity of Station in Millions of Kilo- watt Hours per annum (50 per cent. Load Factor). Average Tons of Steam per hour during Year. Maximum Tons of Steam per hour. 10 30 90 270 10,2 28,8 86,5 259 20,4 57,6 173 518 58 HEAVY ELECTRICAL ENGINEERING Table XLIV. shows that, for a generating station of 270 million kw hr capacity per year, the aggregate boiler plant must have sufficient capacity,, including a reasonable provision for spare plant, to deal with 518 tons of steam per hour. For high speed generating sets,- whether reciprocating or turbine sets, the size of the required engine room is very small in com- parison with the size of the boiler house, and it becomes a serious problem to avoid great lengths of steam piping from the boilers to the generating sets. In Fig. 19 is shown a diagrammatic section of a typical electricity station with slow speed vertical engines. In this case the engine "77 ^777777777777 777777777777777. IT 71 Fig. 19. Diagrammatic Section oe a Typical Power Station, with Slow Speed Vertical Engines. room and the boiler house are of about the same size. This outline should be compared with the outline of the steam turbine station shown in Fig. 21, from which it will be seen that the space occupied by the boiler house is several times that occupied by the engine room. (This subject is further dealt with in Chapter VII.). Hence the space occupied by boilers is an important consideration, and is leading to the very general use of boilers of the water-tube type. One of the most notable features of this type of boiler is its economy in floor space as compared with other types. It may be said that for large generating stations, some type of water-tube boiler is generally preferable. In Table LVI. of Chapter VII. are given leading particulars of the boiler plant in a number of modern generating stations- For a ■STEAM RAISING PLANT 59 given required total boiler capacity, the greater the capacity of the individual boiler the less will be the total space occupied by the boiler installation. The manufacturers of the leading types of water-tube boilers are prepared to deliver as standard apparatus boilers with a normal evaporative capacity of 15 tons per hour " from and at " 100° C. Table III. on p. 8 shows that to evaporate one ton of water at atmospheric pressure and consequently at a temperature of 100° C into steam at the same temperature and pressure, requires the absorption by the ton of water, of 626 kw hr of energy. Hence this boiler, which the makers are rating at a normal capacity of 15 tons per hour " from and at " 100° C, is one capable, at normal load, of conveying to the interior of the boiler 15 X 626 = 9400 kw hr of energy per hour, i.e., at its normal rate of working, it is a 9400 kw boiler. In general, the better the quality of the coal the more may be gotten out of a boiler of a given rated capacity, although the variation in the steam raising capacity due to variations in the quality of the coal is of very limited range. Thus we may state that this standard boiler is a boiler with which energy may be conveyed to the contents at the rate of 9400 kw. If it is required in such a boiler to raise steam at an absolute pressure of 13 kg per sq cm from water at 50° C, and to superheat the steam by 50° C, then we find from Table III. (on p. 8) that 810 — 58 = 752 kw hr must be imparted to each ton of water in the boiler. Thus, under these conditions, we can, as normal load, only produce = 12,5 tons of steam per hour. With an absolute pressure of 18 kg per sq cm, and with 150° C of superheat, ^r- — 33 = 11,5 tons of steam per hour will be produced at normal load. This way of treating the matter is to a certain extent faulty, since the tubes devoted to superheating purposes are generally located at a remote part of the boiler only accessible to the hot products of combustion after these have already circulated amongst the tubes in which the water is evaporated, and the effect is more or less confined to reducing the temperature of the flue gases. "When, 60 HEAVY ELECTRICAL ENGINEERING however, the superheater is built into the boiler, it is difficult to establish any hard and fast line of demarcation, and we shall be on the safe side in handling the question as. above indicated. Now, in our 270 million kw hr per year station, we have arranged to employ eight main generating sets, each of a rated capacity of 6800 kw. "When running at rated load with a steam pressure of 13 kg per sq cm, and with 50° of superheat, the steam consump- tion (with an exhaust pressure of 0,15 kg per sq cm) is 7,5 kg per kw hr (see Fig. 45, Chapter IV.), or a total consumption of 6800 X 0,0075 = 51 tons of steam per hour. We have seen that under these conditions, one of the boilers, when working at its rated capacity, delivers 12,5 tons of steam per hour. ouuu 4500 j r ^ n r tP ar ' Cy [ nri w fT M r tul Load Rati w 4-000 ,1 .r \ i \ 1 3500 1 \ [ 1- V S \- *3000 (*■ ■-\ 1 \ V b 1 l> f %P500 i \s \ / \ S2000 i M ^-_s 1 M Kimum Kilowatts 4. JR< V V. "\ 1500 >~ over u 4 hr ■\ — i ' Plant toad Factor 93.5%. Stition do, __S5I% \ ; 1000 r> V — -i 500 ^ < 4 M 45 6 / 5 £ i ) / ; •>.„ on ip 12 J 4 5 5 7 8 s 10 1 M, It in 1 9" t U 12 3 1 Fig. 20. Central London Railway Daily Load Curve, 1906. Now, although the load factor of the whole station is 50 per cent, for the year, it is important to have each generating set and its group of boilers running as close as practicable to its rated capacity. When actually running at the rated capacity, we have 100 per cent. " plant " load factor. Above the rated capacity we may or may not have higher efficiency ; but we should, in any case, only consider running above rated capacity as in the nature of an overload, and only permissible for reasonably short periods, say, at the most, a couple of hours. The preferable adjustment is such that the average of the fluctuating load shall be approximately the rated load. Thus, in the case of the Central London Eailway, the load during the 24 hours varies as shown in Fig. 20, and, as indicated on the diagram, arrangements are made to vary the number of generating sets in service so as to obtain nearly 100 per cent. STEAM RAISING PLANT 61 "plant" load factor, although the "station" load factor for the year is only about 55 per cent. If we install four of these standard 9400 kw boilers for each generating set, we shall, at rated load, require to work each boiler at 51 -£-= 12,8 tons of steam per hour, which, for a boiler pressure of 13 kg and for 50° C of superheat, is only about 2 per cent, overload. Thus as we have eight generating sets we must install 4 X 8 = 32 boilers. The precise arrangement of the boilers is a matter of the design of the station as a whole, which is carried further in Chapter VII. Let us for the present consider a single 6800 kw generating set and its group of four 9400 kw boilers. It is of course desirable to arrange the boilers at as small a distance from the generating set as other conditions render practicable, in order to reduce both the cost and the length of the piping. In Table XLV. are brought together for Lot's Eoad, Neas- den, and Central London, the average length of the steam pipe connection from the boilers to the particular generating set which they are designed to supply when normally operated. TABLE XLV. Length of Steam Piping in Large Electric Generating Stations. Station. Average Length of Steam Piping to Engine or Turbine, in Meters. Lot's Ed., Chelsea . Neasden .... Central London Eailway . 43 37 55 Average value 45 meters We see that it is frequently necessary that this distance shall be some 45 meters. The distance is generally greater in large than in small plants. In Fig. 21 is indicated a general outline of the design for the 270 million kw hr per annum station, having eight 6800 kw turbo sets and four boilers for each set. This" drawing gives a good idea of the relative space required by engines and boilers, and the great 62 HEAVY ELEOTEIOAL ENGINEERING length of steam piping required between one turbine and its boilers. We shall shortly take up the question of the general design of the steam piping. First, however, let us take up certain questions relating to the boiler. Boilers of this type and capacity should have a heating sur- face of 7 sq dm per kw rated capacity of the boiler ; hence a total heating surface of 66 000 sq dm per boiler. ELEVATION _Q^ X ^T PLAN Pig. 21. General Outline of Preliminary Design for Large Steam Turbine Generating Station. When burning bituminous coal of a calorific value of 8700 kw hr per ton, suitably fired and with a suitable air supply, these boilers should show an efficiency of 70 per cent. Thus coal with a total calorific value of 9400 0,70 13 400 kw hr must be burned per hour under each boiler. STEAM KAISING PLANT 63 This amounts to 13 400 8700 1,54 tons per hour. For burning this grade of coal, the boilers should be provided with a grate surface of 0,09 sq dm per kw hr of calorific capacity. The total grate surface per boiler should thus be 0,09 X 18 400 = 1210 sq dm corresponding to 1,27 kg of coal per sq dm per hour. A grate for hand firing should be some 10 per cent, larger, thus running to 0,10 sq dm per kw hr of calorific capacity, and being 700 650 600 550 ik-500 taoo §;350 §300 $250 $200 ^150 ■5 100 50 3~~4 5 6 7 8 9 10 II 12 13 1* 15 16 17 18 19 20 Absolute Boiler Pressure in Kg per Sq.cm Fig. 22. Curves of Water Heat, Latent Heat and Total Steam Heat. suitable for burning only some 1,15 kg of coal per sq dm per hour. Present developments in boiler construction do not justify considering as standardised, boilers of larger rated capacity than the size here discussed, although it is to be hoped that progress will soon be made in the development of boilers of much larger capacity. Let us assume that this standard boiler is supplied with a chain grate stoker designed for burning a good quality of bituminous coal of an average calorific capacity of 8700 kw hr per ton. If we provide independently fired superheaters, and also preheating apparatus, required to •aisk one Ton of Saturated Steam from water at IQO'C •erature 64 HEAVY ELECTKICAL ENGINEEEING so that the function of the boiler shall be restricted chiefly to evaporating water already heated to the boiling point corresponding to the boiler pressure, the calculations for the boiler itself must be correspondingly modified. The first function, pre-heating, relieves the boiler of but a small percentage of its duty. Much the greater portion of the boiler's duty relates to converting the water into steam. The relative amounts required for these purposes when a boiler of this standard type is working at its rated capacity may, for various pressures, be taken at the values plotted in Fig. 22. The Economic Pressure. — One of the first questions to be decided in the design of a steam driven generating station relates to the economic steam pressure. When other considerations require that piston engines shall be employed, it will be necessary, in the interests of good economy, to install high pressure boilers, for the economy of piston engines increases markedly with increasing steam pressures. Out of consideration for this fact, steam pressures have gradually been increased, until, in recent installations, specific pressures of less than 12 kg have been very exceptional, and it has been considered good practice to employ considerably higher specific pressures, up to 16 kg or more. In a subsequent chapter dealing with piston engines and turbines, it will, however, be shown that while, as just stated, the economy of piston engines is distinctly improved with increasing steam pressures, there is, in the case of steam turbines, comparatively very slight improvement with increasing pressure, so slight indeed that it does not justify sacrificing other advantages. In fact, it becomes of distinct economic advantage, when turbines are employed, to adopt much lower boiler pressures. This largely rests upon the consideration that the lower the boiler pressure, the greater may be the number of degrees by which the steam may be heated above the temperature of dry saturated steam for a given pressure, without exceeding practicable limits of final temperature. The use of super- heated steam has only become at all customary during the last few years. Prior to that time, the temperatures associated with saturated steam had alone to be considered, and thus, even with the increasing boiler pressures which were becoming customary, no prohibitive steam temperatures were reached. When, however, it became apparent that further great economies were possible by the use of superheated steam, engineers were already so far committed and accustomed to the advocacy of high pressures, that they were STEAM KAISING PLANT 65 disinclined to revert to lower steam pressures. Consequently it became necessary to attack the problems associated with the use of very considerably higher steam temperatures than had heretofore been employed. To the already high temperatures associated with saturated steam of high pressure, it was necessary to add the 50° C or more of superheat which was known to be accompanied with considerable further economies. The construction of superheaters to withstand these high TABLE XLVI. Absolute Temperatures of Steam at various Pressures and with various Degrees of Superheat. Absolute Pressure in Kg per Sq Cm. Final Temperat are of Steam, in Degrees Centigrade, for following Amounts of Superheat. ro. HFC. 20" C. 30° C. d0°C. 50° O. 60" C. 80° O. 100" C. 125° O. 150° O. 200 °C. 1 100 110 120 130 140 150 160 180 200 225 250 300 2 120 130 140 150 160 170 180 200 220 245 270 320 3 133 143 153 163 173 183 193 213 233 258 283 333 4 143 153 163 173 183 193 203 223 243 268 293 343 5 151 161 171 181 191 201 211 231 251 276 301 351 6 158 168 178 188 198 208 218 238 258 283 308 358 7 164 174 184 194 204 214 224 244 264 289 314 364 8 169 179 189 199 209 219 229 249 269 294 319 369 9 174 184 194 204 214 224 234 254 274 299 324 374 10 179 189 199 209 219 229 239 259 279 304 329 379 11 183 193 203 213 223 233 243 263 283 308 333 383 12 187 197 207 217 227 237 247 267 287 312 337 387 13 191 201 211 221 231 241 251 271 291 316 341 391 14 194 204 214 224 234 244 254 274 294 319 344 394 15 197 207 217 227 237 247 257 277 297 322 317 397 16 200 210 220 230 240 250 260 280 300 325 350 400 17 203 213 223 233 243 253 263 283 303 328 353 403 18 206 216 226 236 246 256 266 286 306 331 356 406 19 209 219 229 239 249 259 269 289 309 334 359 409 20 212 222 232 242 252 262 272 292 312 337 362 412 temperatures, and the obtaining of cylinder oil which would not be deleteriously affected at these temperatures, presented very grave difficulties for a long time, and even at present these considerations play the major part in limiting the extent to which engineers are inclined to resort to superheating. It is highly improbable that it is even now at all widely realised that the economy of steam turbines is but very slightly improved with increasing steam pressure. It is, however, generally recognised that the economy of all types of engines is considerably improved with an increasing amount of superheat. H.E.E. F 66 HEAVY ELECTEICAL ENGINEERING When both these facts are clearly appreciated, engineers cannot logically do otherwise than revert to considerably lower steam pressures when turbines are employed as prime movers, for with lower boiler pressures a greater number of degrees of superheat will be associated with a given ultimate steam temperature than with high steam pressures. It is evident that from most stand- points it is the actual temperature of the steam which determines the practicability of employing a given number of degrees of •nju j0r~ 350 0. ^300 s£ h &250 fl .g S 150 g *x r^ £ ^ 8 inn 1 % 1 1 / i ? 1 Absolute Pressure in Kg per Sq, cm Fig. 23. Curves showing Variation of Final Temperature of Steam with Absolute Pressure and por Various Numbers oe Degrees of Superheat. superheat and of obtaining the corresponding decrease in steam consumption. These considerations will be better appreciated by a study of Tables XL VI. and XL VII. In Table XL VI. are given, for various pressures, the absolute temperatures of steam with various amounts of superheat. While but little interest attaches to Table XL VI., the values in Table XL VII., which is readily compiled from Table XL VI., are of very considerable importance. In Table XL VII. are recorded the absolute pressures corresponding to various amounts of superheat and various steam temperatures. The results in Table XL VI. have been plotted in the curves of Pig. 23. STEAM BAISING PLANT 67 The progress in the development of superheaters has reached such a point that there is no insurmountable difficulty in dealing with steam temperatures of, say, 300° C. Nevertheless much greater freedom from difficulties will be secured by limiting the steam temperature to 250° C. From Fig. 23 we see that if we employ so high a pressure as 16 kg per sq cm we may give the steam 50° of superheat for a steam temperature of 250° C. If, however, we were to reduce the steam pressure to 8 kg per sq cm, TABLE XLVII. Absolute Pressure of Steam in Kg per Sq Cm for various Final Temperatures and Degrees of Superheat. Final Tem- perature of Steam in Degrees Centigrade. Absolute Pressure in Kg per Sq Cm for following Amounts of Superlieat. 0° C. 10° C. 20° C. 30° C. 40° C. 50" C. 60° C. 80° C. ioo° c. 120° C. 150" 0. 200° C. 100 1 110 1,5 1 120 2 1,5 1 130 2,65 2 1,5 1 140 3,6 2,8 2 1,5 1 150 4,9 3,6 2,8 2 1,5 1 160 6,2 4,8 3,6 2,8 2 1,5 1 180 10,2 8,0 6,4 4,8 2,8 2 2 1 200 16 12,8 10,2 8,0 6,2 2,8 3,6 2 1 220 19,6 16 12,2 10,2 8,0 6,2 3,6 2 1 240 22 19,6 16 13 10,2 6,2 3,6 1,7 200 19,6 16 10,2 6,2 3,3 M 280 22 16 10,2 5,4 2,7 300 22 16 9,2 4,3 1 320 22 14,4 8,1 2 340 20,6 13,1 3,6 360 18,9 6,2 380 10,2 400 16 the curves of Fig. 23 show us that a superheat of 80° C gives the same steam temperature, namely 250° G. Thus to compare the relative advantages of using pressures of 16 or of 8 kg per sq cm, the relative economies at 16 kg per sq cm and a superheat of 50° C on the one hand, and 8 kg per sq cm and a superheat of 80° C on the other hand, must be compared. This comparison cannot properly be carried out until we have considered the laws controlling the variation of economy with the pressure and the superheat. These are taken up in Chapter IV. For our present purposes we must anticipate, and state that if it is a case of using F 2 68 HEAVY ELECTRICAL ENGINEERING steam turbines, the steam consumption is about the same in the two cases, when associated with the use of a reasonably low exhaust pressure, say a pressure of 0,15 kg per sq cm. This being the case, the next question to be considered relates to the relative costs of steam raising plant for these two pressures. It would appear that the cost of the boilers will be slightly less for the lower pressure, but probably not to a greater extent than to offset the cost of providing the increased superheater surface. To raise one ton of steam to a specific pressure of 16 kg and 50° C superheat on the one hand, and to 8 kg and 80° C superheat on the other hand, and in both cases from feed water at 50°, TABLE XLVIII. Data of Steam Piping. SSeo Bw„| S®S •- s 2 tf» . SB 0;§~ qj Is .2 6 fc-B 3 aS S3 Capacity of Group of Bo Feeding Me Header, in T per Houi * to B G ° .5 *3 fig Tons of Ste per hr per dm of Cro Section of M Header. Tons of Ste per hr requi by one Eng Tons of Ste per hr per dm of Engi Steam Pip » 2* u "> to Gi • O 60 Glasgow . 36,4 40,5 2,76 19 35,5 1,92 11 Chelsea . 62,0 53 35,5 5,35 12 C.L.R. . 10,9 30,4 1,5 8 20,3 2,48 11 Greenwich 44,4 30,4 6,12 26,2 30,4 9,7 14 Neasden . 27 25,4 5,4 12 requires respectively 755 and 762 kw hr per ton, or a difference of only 1 per cent. The chief remaining element to be considered relates to the relative cost of the steam piping in the two cases. We have seen that a length of some 45 meters is a fair average value. In Table XLVIII. are brought together data relative to the cross section of piping employed with boilers of various capacities and pressures. It is evident from the above table that practice as regards steam piping varies very widely. For a pressure of some 11 to 13 atmospheres, a flow of 5 tons of steam per hr per sq dm section, or a section of about 0,2 sq dm per ton of steam per hour, may be taken as good practice. It is undesirable to have too large a pipe, since not only is the cost greater, but also the radiating surface. The 6800 kw turbine with which we are dealing is fed from four boilers at a distance of 45 meters from the turbine, and we require STEAM BAISING PLANT 69 51 tons of steam per hour. There should be provided a steam pipe with 0,2 X 51 = 10,2 sq dm cross section. This has a diameter of 35,6 cm and a periphery of 112 cm. The radiating surface for a length of 45 meters is thus equal to 450 X 11,2 = 5100 sq dm. The loss from uncovered steam pipes amounts to some 0,17 watts per sq dm surface per degree cent, difference of temperature between the steam temperature inside the pipes and the temperature of the surround- ing atmosphere. In the case with which we are dealing the steam temperature is 250° C, or some 225° C higher than the tempera- ture of the air. There is thus a loss of about 225 x 0,17 = 38 watts per sq dm of pipe surface ; and hence a total loss of 0,038 x 5100 = 194 kw. This amount may be reduced to one quarter or less by suitably covering the pipes. Thus the loss becomes about 50 kw. As the total energy in the steam delivered from the boilers. when the turbo-generator is operating at its rated load is 37600 kw, the loss by waste from the piping is in this case a negligible amount. Even at one-tenth load it would only be a matter of from 1 to 2 per cent, for covered pipes, rising to some 5 per cent, for bare pipes. Hence our earlier estimate of 95 per cent, for " efficiency of steam piping " is shown to be very conservative for large plants. The interesting question arises whether the practice of covering pipes with insulating material is of material importance in so many cases as is generally assumed. It is in general the more important the smaller the capacity of the plant. We are not much concerned with the loss of pressure due to friction of the steam in flowing through the steam pipe, so long as it is of limited amount, since the energy of friction is heat energy and remains in the steam. Thus the loss in pressure tends to produce a rise in temperature. At a specific pressure of 14 kg and a superheat of 50° a drop of specific pressure of 0,1 kg may be taken for each 40 meters length of straight piping. Bends greatly increase this amount, and precise estimates are impracticable. With carefully designed piping with few bends, and these of large radius, the "equivalent" length should not more than double the actual length. Thus in the case in question the " equivalent " length may be taken as some 70 HEAVY ELECTRICAL ENGINEERING 90 meters, and the loss in specific pressure would amount to some 0,2 kg. In practice it is found that the quantity of steam that can be transmitted by a pipe of a given diameter does not vary much with quite considerable variations in pressure and superheat. The curves of Fig. 24 give values for the amount of steam which can be transmitted in tons per hour, at a specific pressure of 14 kg in pipes of various diameters. The curves are plotted on the basis of a drop in pressure of 0,1 kg per sq cm for a length of T 6 8 ID 12 k 16 18 20 22 24 26 28 30 32 34 36 38 W fo U ft In tern aJ Diameter of Steam Pipe in Cm Fig. 24. — Showing the Size of Steam Pipes required for different Weights of Steam. 40 meters. The upper curve gives the velocities corresponding respectively to pressures of 10,5 and 14 kg, for pipes of the diameters defined by the abscissae, and transmitting per hour the amounts of steam corresponding to the lower curve on the sheet. The steam at the lower pressure must of course have the higher velocity since the density, i.e., the weight per unit volume, is less. Now the fric- tion is a function both of the density and the velocity, and these so nearly offset one another as to render it needless to use much if any larger pipes for transmitting the same quantity of steam at lower pressures. STEAM HA1SING PLAN* 71 For pipes of a given diameter, the lower pressures would tend towards lower cost. Thus from every standpoint we see that with steam turbines we may employ lower pressures with equal operating costs, and with probably some slight saving in capital outlay. This is, of course, not the case when piston engines are employed, for then the steam consumption rapidly increases with decreasing working pressure. The rough values of the temperature of the flue gases, as set forth in the following table, are of interest : — TABLE XLIX. Rough Values of the Temperature of the Flue Oases iit their Passage from Grate to Chimney. Gases Leaving Temperature in Degs Cent. Grate Boiler Bconomiser . 1300 250 to 350 150 to 200 In the following table are set forth the rates of transference of heat under various conditions : — TABLE L. Heat Conduction Values. Conditions. Kate of Transference in Watts per Degree Centigrade per sq Decimeter of Heating Surface. Boiler tubes with feed water at 50 D C . Boiler tubes with feed water at 150° O . Superheater tubes .... 0,2 0,3 0,04 In the boiler which we have considered, energy is conveyed to the interior of the boiler at the rate of 9400 kw. Let us take the temperature of the furnace gases as they leave the grate at 1300°, and at 300° on leaving the boiler tubes. The mean temperature is thus 800° . Let us take the feed-water temperature at 50°, and — in the case with a pressure of 8 kg per sq cm — the steam temperature at 170°. Thus the mean temperature is 110°. This gives us a 72 HEAVY ELECTRICAL ENGINEERING mean difference of temperature between flue gases and boiler tube contents of some 700°, and the rate of transference of heat may be taken as 700 X 0,2 = 140 watts per sq dm of tube surface. For the case of steam at a pressure of 8 kg per sq cm, super- heated 80°, we have seen that the heat required to raise one ton of steam from feed-water at 50° is 762 kw hr. Now the heat required for saturated steam at the same pressure is 712 kw hr, so that 712 ~ X 100 = 93 per cent. of the total energy conveyed to the interior of the boiler is devoted to heating the feed-water and evaporating it into steam. This is 9400 x 0,93 = 8750 kw. Hence we require Yjk — = 62 500 sq dm of boiler tube heating surface. Now let us estimate the amount of superheater surface required. This must be sufficient to transfer heat at the rate of 650 kw. The mean temperature of the steam in the superheating tubes is 170 + ^ = 210°. Thus the difference of temperature between the mean temperature of the flue gases (800°) and the mean temperature of the contents of the superheater tubes is about 600°, and the transference of beat is at the rate of 600 X 0,04 = 24 watts per sq dm. We shall thus require — aj — = 27 000 sq dm of superheater tube surface. 1 SUMMAEY.. Boiler tube surface . . . = 62 500 sq dm. Superheater tube surface . . = 27 000 ,, Grate surface . = 1210 ,, 1 The large amount of surface required for superheaters has in some instances led to the use of corrugated tubes in order to reduce the size and cost of the apparatus. CHAPTEE IV PISTON ENGINES AND STEAM TDKBINES For electric generating stations, steam-turbine-driven generating sets are becoming more and more frequently employed, and there is every indication that the piston engine will gradually be superseded for large units. Although there are still a good many difficulties to be overcome before the steam turbine can be considered thoroughly satisfactory, the progress in its development has been and continues to be remarkably rapid. Steam Consumption. — Nevertheless there have not yet, except possibly at uncommercially low exhaust pressures, been obtained with steam turbines such good results, as regards low steam consumption, as have frequently been obtained with the best modern piston engines of certain types. Thus a careful analysis of a large number of results has shown that the curves of Pig. 25 may fairly be taken as representing the steam consumption of piston engines and steam turbines respectively, when operated under reference conditions which may be considered as normal and commercial. These reference conditions are : — Admission pressure = 13 kg per sq cm (absolute). Superheat = 50° (actual temperature of steam = 241°). Exhaust pressure = 0,15 kg per sq cm (absolute). Eepresenting by 100 the full load steam consumption under the above reference conditions, then the variation in the full load steam consumption with varying admission pressure, superheat and exhaust pressure, may be taken as shown in Fig. 26. Of course these rates of variation differ greatly with the type and size of piston engine and of turbine. Also, the rate of variation — say with varying exhaust pressure — varies with differences in the accom- panying superheat and admission pressure. But the extent of these variations has as yet been insufficiently investigated, and we cannot at present do better than abide by the curves of Fig." 26. Corresponding to Fig. 26 for full load, we have Fig. 27 for ^ load, and Fig. 28 for \ load. By means of the curves in Figs. 25 to 28 74 HEAVY ELECTRICAL ENGINEERING / y f / 3* CM Q to ^ CN O CO SI 5 1 I // / a. / /j ■ // / / / Ki <-> a- // J / / O ^ ^ a; 3 tv i S > Q 3 «l > M c\ s 5; sc tf c> 1J + •o c£ 5l U ^ ■U O * •O ■o tl «; jnoy qibmo/!)i jad swpjffo/ij/ M O o H M H H fH o o H O a c^ 9b l- Q,: Q 10 20 10 20 10 15 20 2b 25 25 Abscissae denote Absolute admission pressure in Kg per sqm Admission Pressure 13 Kg per Sq cm Exhaust Pressure 0.15 Kg per. Sq cm 116 108 100 92 84 76 s "^^ ^■^ ^^ ST v, ^ PE l. 116 «j 108 to 100 11 Tl Q? 1. l/i W m Q /b If 20 40 60 80 100 120 140 160 ISO ST 20 40 60 80 100 120 140 160 180 ST 20 40 60 80 100 120 140 160 180 Abscissae denote Superheat in degrees Cent Admission Pres sure B Kg per Sq cr Superheat 50" Cent 140 132 124 116 103 100 140 U.J la, JS IV ( 124 tit Q. 116 to 108 100 140 132 124 116 108 100 ST PE -"■ -"' \,, < ^" £'' OJ 02 0,3 0.4 Q5 0,6 0,7 0,8 0,9 1,0 ST 0.1 0,2 0.3 0.4 0,5 0,6 0,7 0,8 0,9 1,0 ST / / 0,1 02 OJ 0,4 0,5 0,6 0.7 0,8 OS 1,0 Abscissae denote Exhaust Pressure in Kg per Sq cm Fig,. (No 26— -2 Curves Showing the effect of Admission Pressure, Superheat, and Exhaust Pressure on the Full Load, A Steam Consumption. and I Load -In correcting for Pressure, Superheat, and Exhaust Pressure of Piston Engines (P. E.) use same curves for A and J Load as for Full Load. In correcting the Pressure for Steam Turbines (S. T.) use same curve for ] and A Load as for Full Load.) [Tlifitri'ji. 7.". PLATE III. C5 Pressure=8 Kg per Sq Cm. Exhaust Pressure 0,10 Kg perSq Cm. o 3 o o o -o Q ST. 1 p.e -^ J^vJ. - --T 4 - __ 3/4 Full S.T. P.E. * ~~~ ^>> '/z *k Full ST. ***<. ^ 3U Full ST. <;- -= — 1/4 'l2 5/4 Full Exhaust Pressure 0JD7 Kg per Stj Cm. P.E > ST. ^, „ ^_ ^ 1/4 3 U Full Pt ST. /4 3 h Full S.T. \. P.E^>. *5» S.T. P.E. -~ u 3 U Full ST. P.E \ -^t o_o v o"o"o" *III mui uiojj COttN tOOiN tOOl t- 8.1llt)S9JJ[ ^SlllilfXS o ca co m CO CO CO tM MjO (O to^o cqco o co co co V s 1 B9 H ^u^l /[ - ui = e SCOO t-^-o HCDift uoi;esuapuoo JO q.B8H fflOH 1^ CO OT m w co 'III ©W^I ^oaj ajiissgjj ^snuiixg; g HMO -* CO CM HMO •* co cq HMO ■** cocq ^■B THUQ^g p8^UJtl^'Gg b- t~t~ t-I».fc- l?-r-l;- joq.i38H urea^S 2 TJ ft & c ■ ■ Tfmo tH(M o ONW ^ o Tf CN I-< co m co O i^ >0 03 ■sg-M COO CO CO CD co CO O CO ■s Is II co ,M B O p. II s ©c° ooo OOO «3 + r^ CO O) O * MOH ITS COc3a W i CO t-»» i- co m t-d •* , 3 ^ = ooo COOH ooo CM Clt- ooo t-"^ CO (oooi- 00 T x 000U jnoH J9d *" t-b- in £-i£>-& COTli pa^Bdissia VB&H •oureu^a ssjfos c£c£c& 8?aSc£ pun &ujq.Tnx jo "31 O Ol CO CD CO 00 owo jfotiQioiya pauiqtuoo lO WED w CD £> ooo ooo ooo ooo >n aor- QOO i-l Oi~<# C3 -gw 3 "q5°. O 00 CO ait- co ei o H II w'l s!f tH rfTj Q,Sm tt t- 00 esi CO c-. O «_, CD O d c ft ^o o .2 +3 Selx o 13 crTr-ToT CO r-< r-l r-i o oo Ol ■* CO_ o*"oTt>^ "S 1 "" " rt co H O £ o * £cd a 03 -.ON « i-( (M 0_ co^r-ToT COHH i-T ©"co" 3i -d^ift o"oTi>T £ •(aitiiosqE) O O ift' oo m oom UIQ *>S »o O O I-H o m r-t o in i— i at aanssgjtt ^smjqxg; nOO* HO'd rH*0"0*~ •(jaao 'Ssa e o o o o m ^Beqjsdns »o 78 HEAVY ELECTRICAL ENGINEERING The total heat supplied is tabulated in column /, the first component in column h, and the rate of expenditure of useful elec- trical energy at rated load is equal to 1000 kw, that is 1000 kw hr per hour. Thus the third component can be obtained by simple subtraction, and is inserted in column k. Dividing by the weight of steam used per hour (column d), we obtain the heat of one ton of the mixture discharged from the A. Steam Heat at Admission . -3»- -»- B. Heat in the Exhaust. C. Heat available for Conversion \' i' E. Friction D. Electrical Output. Fig. 30. Diagrammatic Representation of the Transformation op the Heat of Steam into Electrical Energy. turbine. If now we note the steam heat of saturated steam at the' exhaust pressure (column n), the difference will give the amount of heat corresponding to the water condensed in the cylinder. This amount of heat, divided by the latent heat of steam at the exhaust pressure, gives the wetness factor of the exhaust mixture. Table LI. may now be represented diagrammatically as in Fig. 30. In this figure the square A is set off to scale to represent the steam heat in kw hr per ton of steam admitted to the cylinder, as recorded PISTON ENGINES AND STEAM TURBINES 79 in column e of the Table. To the same scale is set off the area B to represent the heat per ton of mixture discharged from the cylinder (column I). The difference between the areas A and B represents the energy set free by the expansion of the steam in the cylinder. This is shown in the diagram by the square C. This amount of energy is still further transformed into useful electrical work, and into wasted heat, as indicated by the squares D and E. The areas in Fig. 30 are scaled off to represent the case of a 1 1 > 1 1 1 | Speed qF Rotation 20000 rp.m 2,5 r 1 °enphe 1 1 ral Speed 2 1 1 15m per Set : //' $2,0 // m '/> t ■S 5 1,5 .c Sat ura tedbtei S s // ''/Super heated iFIKq.perSq. cm. 18 8 '•" — h ear Value / 0,5 er heated Stead ssureoFOAKn of \at rSq cm / 7/ 0,/ 0,2 0,3 0,4 0,5 Density oF Steam in Kg per cu m. Fig. 31. Showing how the Friction Losses due to the Eotation of a 22 kw de Laval Turbine Wheel vary with the Density of the Surrounding Steam. (Note. — The Friction of the Bearings has been deducted.) 1000 kw turbo generator working at rated load with steam at an admission pressure of 13 kg per sq cm, superheated 50° C, and expanded to an absolute pressure of 0,15 kg per sq cm. The steam heat at admission is 810 kw hr per ton. The heat of dis- charge is 630 kw hr per ton, so that 180 kw hr per ton of steam are available for conversion into work. But for the rated output of 1000 kw, 8,1 tons of steam are required per hour, so that one ton of steam only provides -^r- — 124 kw hr of useful electrical 8,1 energy. 80 HEAVY ELECTRICAL ENGINEERING Hence the friction losses per ton of steam amount to 180 - 124 = 56kwhr. It will be noticed that the area B in Fig. 30 is not, like the others, a complete square. It has been drawn as shown for the purpose of indicating the amount of heat set free by the condensa- tion of steam in the cylinder. If the area B is completed to form a perfect square, it represents the steam heat of saturated steam at the exhaust pressure. < The results arrived at in Table LI. show the great influence r~ 3,0 i «*>'' f ?,s $ f !" / f if/ 2,0 7 i u 7 & 1,5 < r , i , , ,J Density in Kg per cu.m. Fig. 35. Belltjzzo's Tests of Friction Losses oe Wheels Bevolving IN DBY Sl'EAM. Hence, so far as relates to obtaining low friction losses, the peripheral speed of the rotors of steam turbines should be low. But this is diametrically opposed to the conditions which should obtain in order that a maximum percentage of the kinetic energy of the steam may be transferred to the rotor in the form of mechanical e 2 84 HEAVY ELECTBICAL ENGINEERING energy. Thus, suppose a perfectly elastic body, 1 with a mass M, of 1 kg, to be travelling in a straight line through a frictionless medium (in a region where the acceleration due to gravity is equal to 9,8 metres per second per second) at a uniform velocity, V, of lasf6^-5+» -9?- V2-5 -140- Pig. 36. Tuebinb Wheels and Blades with which the Curves op Pig. 35 were obtained. 1000 metres per second. The kinetic energy of this body, i.e., \ energy possessed by it in virtue of its motion, is equal to \ M V 2 . X ~ x 1000 2 = 51 000 kilogrammeters. i 2 9,8 Suppose this body to collide with a far larger perfectly rigid b moving in the same direction at one-half the speed, i.e. at a sp of 500 meters per second, the relative speed of the two bodies be contact being 1000 — 500 = 500 meters per second. Its mo relatively to the far larger body will, in virtue of the collision reversed in direction. That is to say, the perfectly elastic bod one kilogram will, relatively to the far larger body, precisely ie\ 1 It is convenient to mentally picture this body as a sphere. PLATE IV. Fig. 37 Fig. 38. Fig. 39. Fig 40. o o tu to t. to tu «V. to 5» .5 «j t. to t. 0, • * a to to * to — ( 8 10 12 14 1 S 6 8 10 12 14 16 6 8 10 12 14 IG 6 8 10 12 14- 16 Abscissae denote Admission Pressure in Kilograms per Square Centimeter. Figs. 37—40. Showing the Speed of Steam emerging from a Correctly Proportioned and Frictionless Diverging Nozzle supplied at various Pressures and Temperatures. [Tofuerp. 85. PLATE III. C5 Pressure=8 Kg per Sq Cm. Exhaust Pressure 0,10 Kg perSq Cm. o 3 o o o -o Q ST. 1 p.e -^ J^vJ. - --T 4 - __ 3/4 Full S.T. P.E. * ~~~ ^>> '/z *k Full ST. ***<. ^ 3U Full ST. <;- -= — 1/4 'l2 5/4 Full Exhaust Pressure 0JD7 Kg per Stj Cm. P.E > ST. ^, „ ^_ ^ 1/4 3 U Full Pt ST. /4 3 h Full S.T. \. P.E^>. *5» S.T. P.E. -~ u 3 U Full ST. P.E \ -^t Steam Turbines operated at an Admission Pressure of 13 kg per so. cm, a Superheat of 50 c C and an Exhaust Pressure of 0.15 kg per SQ CM. (* 12 10 \. V 3 > X Cf^ ■ifift 8 ' 'st on Engines 6 100 % Thermo- iyn amic Efficiency 4 2 1000 2000 3000 4000 5000 Rated Output in Kilowatts Pig. 46. Representative Curve for the Steam Consumption at Half Load of Modern Generating Sets employing Piston Engines and Steam Turbines opkrated at an Admission Pressure of 13 kg per sq cm, a Superheat of 50° and an Exhaust Pressure of 0-15 kg per sq cm. [To face p. 87. PLATE vn. 0,8 0,1 9 J t°C- Fn<7' ies. hull Loi d r^ r£" qtne s. Half L ood / '$■ / t 0,4 E * „ -, c 9,3 e v. 02 0,1 1000 2000 3000 4-000 Rated Output in Kilowatts. 5000 60C0 Fig. 47. Curves showing the Thermodynamic Efficiency of Representative Piston Engines at Bated Load and Half Bated Load. ■■ l f 0,6 1 I Lose 0J -orb' ries- full 5^ -air Loa d 0,6 m T^CSii es-f s te- O.b j 0,4 j 0,4 0,i U.I . WOO 2000 5000 4000 Raced Output in Kilowatts 5000 6000 Fig. 48. Curves showing the Thermodynamic Efficiency of Representative Steam Turbines "at Bated Load and Half Bated Load. [ To face ji, 87. PISTON ENGINES AND STEAM TURBINES 87 obtained from which the curves in Fig. 49 have been plotted. Unfortunately, from Eotscher's data as published, the precise steam temperatures at admission, and the precise exhaust pressures corre- sponding to these curves, cannot he allocated with certainty, but the general order of these quantities during the tests appears to have been as stated on the curves. Eotscher states that his investigations will be described in complete detail in a forthcoming issue of the " Mitteilungen iiber Forschungsarbeiten." The conditions under which Eotscher carried out his investiga- tions were not such that he could obtain the steam consumptions at 20 250 Kyi 'SOt >r.p m. c, )QK 750 Kw in ^«— inn Or. i.rr, .In irn if)l snf erf) A WK n 750 Kyi •— « OKv 14-01 rat Kw 'nq nor rial 6 7 8 3 10 II 12 Admission Pressure-Kg per sg, cm.(abs.) 13 14 Pig. 49. Steam Consumption as Function op Admission Pkessure. The Admission Pressure = 200 to 250° C. Exhaust Pressure = 0,05 to 0,15 kg per sq cm. a given speed and various admission pressures for any one parti- cular load throughout the range. Thus, as will be seen from the curves in Fig. 49, the loads ranged from some 10 per cent, to 30 per cent, of rated load at the lower pressures, well up to full load at the higher pressures. This, however, in nowise invalidates the import- ant conclusion which the present author desires to draw from these tests, namely, that the decrease in steam consumption obtainable by the employment of high admission pressures is in the case of steam turbines (at any rate of the type and design in question) exceed- ingly slight. Thus, since the steam consumption at light loads is always greater than at rated load, it follows that had the rated load 88 HEAVY ELECTEICAL ENGINEERING been maintained down to the lower pressures, the curves of Fig. 49 would have much more nearly approached horizontal lines; in other words, the steam consumption would have been much more nearly independent of the admission pressure. Thus, were the steam consumption absolutely independent of the admission pressure, then the lower curve shows that at 3000 rpm the steam consump- tion at quarter load is only some 20 per cent, greater than at rated load. Now the steam consumption at quarter load is, as is well known, rarely so low as only 20 per cent, in excess of the steam consumption at rated load, and we may safely say that it is certainly no lower than 15 per cent, greater than the steam con- sumption at rated load. Taking this latter figure, the increased economy at 13 atmospheres as compared with that at 4 atmospheres is only a matter of some 5 per cent. At the speed of 1500 rpm these statements do not apply to as great an extent, but this turbine was designed for a rated speed of 3000 rpm and the conditions at 1500 rpm are abnormal, this speed having simply been employed for experimental purposes. Since, however, we have before us these tests for the two speeds, it would appear interesting to examine tbe effect of thus decreasing the speed to one-half. Let us, with this purpose in view, compare the steam consumptions at outputs of 500 and 750 kw respectively. For both of these loads the steam consumption at the lower speed works out at some 50 to 55 per cent, greater than at rated speed of 3000 rpm. This bears out the arguments already set forth to the effect that the steam turbine on the whole benefits considerably by design and operation at high rated speeds, but the case is not so serious for low speeds as these figures would indicate, for this particular turbine was designed for 3000 rpm. Turbines for the same rated output when designed expressly for the lower speed, namely, 1500 rpm, have much lower steam consumptions at this low speed than this turbine, which was only run at the low speed for experimental purposes and naturally was, under these conditions, distinctly handicapped. Figs. 50 to 55 relate to an investigation of the effect, at normal rated load, of varying admission pressures when constant steam temperature at admission and constant exhaust pressure of 0,15 kg per sq cm are maintained. The calculations have been made for a 4000 kw turbo generator of the Parsons type. The first five curves relate to a steam temperature of 250° C at admission. Let us follow through the calculations for an admission pressure of 18 kg per sq cm. PISTON ENGINES AND STEAM TURBINES 89 Prom Fig. 25 it is seen that, at rated load, an admission pressure of 13 kg, 50° C of superheat, and an exhaust pressure of 0,5 kg, the 60 E S E 5 jljMy/Jad 6y ui uo/jdainsuoy uie3l$ 6b * PM steam consumption of a 4000 kw set is 7 kg per kw hr. From Fig. 26 we find that the steam consumption at an admission pressure of 18 kg per sq cm is 0,985 as great, i.e., 7 X 0,985 — 0,69 kg per kw hr. 90 HEAVY ELECTRICAL ENGINEERING The saturation temperature for a pressure of 18 kg is 206° C. Therefore, to raise the steam to a temperature of 250° C, the superheat will be 44° C. From Fig. 26 we find that the steam consumption at 44° C superheat is 1,01 as great as that at 50° C superheat. Therefore the steam consumption at 18 kg admission pressure and 44° C superheat will be 0,69 X 1,01 = 0,70 kg. In like manner the steam consumption for various admission pressures has been estimated and the results are expressed in the curve of Fig. 50. For the same admission pressure of 18 kg let us proceed to estimate the amount of energy required per ton of steam. The feed-water is supplied at a temperature of 50° C. To raise one ton of water from 50° C to 206° C, the temperature of saturated steam at 18 kg pressure, we require 189 kw hr. This figure may be derived from Table I. on p. 4 of Chapter I. The total latent heat of evaporation at this pressure is 536 kw hr per ton (see Table III.), and to raise the temperature further from 206° to 250° C we require another 31 kw hr per ton, making a total of 756 kw hr per ton of steam. Calculations have been made for other admission pressures, and the results are given in the curve of Fig. 51. The boiler plant is assumed to have an efficiency of 70 per cent. ; therefore for every 756 kw hr given up to the steam we must supply fuel with a calorific capacity of ^ = 108 kw hr. From Fig. 50 the steam consumption per kw hr is 7 kg; there- fore for these 1080 kw hr of fuel supplied to the boiler ^=143 kw hr are delivered by the dynamo. Therefore the kw hr of fuel supplied to the boiler per kw hr of electrical energy is 1080 _._. . -j^g- = 7,55 kw hr. The fuel employed has a calorific capacity of 8,7 kw hr per kg. Therefore the amount of fuel consumed per kw hr is ^ = 0,865 kg. This fuel consumption has also been calculated for various admission pressures and the results have been plotted in Fig. 52. The energy required per kw hr of electrical energy is shown in PISTON ENGINES AND STEAM TURBINES 91 Fig. 53. As shown above, the fuel energy is 7,55 kw hr in this particular case, and as the boiler efficiency is 70 per cent., the steam energy is 0,7 X 7,55 = 5,3 kw hr. w - G .c 16 § c ^.14 b 12 5 Efficier, cv from St earn Ei 'Fic/e icy fi om Fuel 300 C. 250°C. 200° C. 200 C. 250°C. 200°C. 6 6 10 12 14 16 18 Admission Pressure in Kg per Scf Cm. Fig. 55. Showing the Thermal Efficiencies foe various Steam Temperatures as a Function of the Admission Pressure. Feed Water Temperature = 50° 0. Exhaust Pressure = 0,15 kg per sq cm. Boiler efficiency = 70 per cent. Calorific Value of Fuel = 8700 kw hr per ton. In Fig. 54 are shown the efficiencies. The thermal efficiency from steam at 18 kg admission pressure is — - = 19 per cent., and the thermal efficiency from fuel is 1 =-=p = 13,2 per cent. 1,00 Fig. 55 shows these thermal efficiencies, and also the thermal efficiences for steam temperatures of 200° and 300° C. CHAPTER V CONDENSING PLANT We have seen that for steam turbine installations, low steam consumption is only obtainable by means of a low exhaust pressure. While with piston engine plant an exhaust pressure of 0,20 kg per sq cm gives fair results, such low pressures as 0,15 to 0,10 kg per sq cm are absolutely necessary to obtain reasonably low steam con- sumptions with steam turbines, and installations are sometimes estimated on the basis of an exhaust pressure of 0,05 kg per sq cm. In order to obtain these low pressures circulating water of low temperature must be available, and in large quantities. The quantity required is so large that if any appreciable charge per 1000 gallons is made, it is usually cheaper to install cooling towers and employ the circulating water over and over again. By the time the necessary outlay for condensing plant of sufficiently large capacity and for cooling towers has been estimated, the advan- tages of steam turbines as regards savings effected through decreased floor space and in other directions will often be found to have been more than outweighed. Thus the subject of condenser calculations has now become one of much importance. We have seen that when heat is absorbed by water the temperature rises, and at some definite temperature, called the temperature of vaporisation, the water com- mences to evaporate. This temperature of vaporisation is a function of the absolute pressure, and has been given in Table III. on p. 8. It is again given for low pressures in the second column of Table LII. When all the water has been evaporated, any further addition of heat causes a renewed rise in temperature, as has been shown by the curves in Fig. 2 on p. 6. If we consider the reverse case, where heat is extracted from the steam, we find that the temperature of the steam falls until it reaches the temperature of vaporisation corresponding to the steam pressure. From this point any further abstraction of heat is accompanied by a condensation of the steam. The temperature remains constant until all the steam is condensed. Thus the temperature of vaporisation may equally correctly be termed the CONDENSING PLANT 93 " temperature of condensation." If still further heat is extracted from the water, the temperature once more begins to fall. The heat that is required to change water into steam at the temperature of vaporisation is called the latent heat, and in the reverse process, this amount of heat must be extracted from the steam before it can be completely condensed into water. Let us now consider how we are to extract the necessary amount of heat from the steam. If a body at a lower temperature than the TABLE LII. The Heat absorbed by one Ton of Circulating Water. to & a Kw hr absorbed by one Ton of Circulating Water when Heated from >o the following Temperatures ;o the Temperature of Vaporisation of the Steam. So * u CO & s ■3 5 a si a* m H 0°C. 5°C. 10° O 15° C. 20° C. 25° C. 30° C. 35° C. 40° C. 45° O. 50° O. 55° C. 60° C. 0,02 17 20 14 8 2 0,04 29 34 28 22 16 10 5 0,06 36 42 36 30 24 19 13 7 1 0,08 41 48 42 36 30 25 19 13 7 1 0,10 46 53 48 42 36 30 24 19 13 7 1 0,12 49 57 51 45 39 34 28 22 16 10 5 0,15 54 63 57 51 45 40 34 28 22 16 10 5 0,20 60 70 64 58 52 46 41 35 29 23 17 12 6 0,25 65 75 70 64 58 52 46 41 35 29 23 17 12 6 0,30 69 80 74 68 63 57 51 45 39 34 28 22 16 10 0,35 72 84 78 72 66 60 55 49 43 37 31 26 20 14 0,40 76 88 82 76 71 65 59 53 48 42 36 30 24 19 steam, is brought into proximity with the steam, the difference in temperature of the two bodies causes a flow of heat to the body of lower temperature. Water is at present considered the most suitable substance to use for the purpose of extracting heat from steam with a view to its con- densation. The capacity of water for absorbing heat is set forth in Table LII. In this Table, water is taken at various initial tempera- tures, 0°, 5°, etc., up to 60°. Calculations are then made of the heat necessary to raise its temperature to the temperatures indicated in the second column, which are the temperatures of vaporisation corresponding to the pressures given in the first column. We see, 94 HEAVY ELECTRICAL ENGINEERING for instance, that to raise the temperature of one ton of water from 0° to 17°, 20 kw hr of energy are necessary. We further see that if the initial temperature of the water had been 5°, only 14 kw hr would have been required to heat it to 17°, that is to say, one ton of water only absorbs 14 kw hr, when its temperature is raised from 5° to 17°. We can now estimate the amount of water required to condense one ton of saturated 1 steam. In the third column of Table LIII. are recorded the latent heats of steam for the pressures tabulated in Table LII. We see that when the absolute pressure is 0,02 kg per sq cm, the latent heat is 680 kw hr per ton, and that the temperature of vaporisation (or condensation) is 17°- Since one ton of water absorbs 20 kw hr when its temperature is raised from 0° to 17°, it follows that to condense one ton of steam we require — - =z 34 tons of water at 0°, if the temperature of the water is raised to 17°. The remaining portion of Table LIII. can be readily calculated in the same manner, and the results are shown graphically in Fig. 56, where the weight of water required to condense one ton of saturated steam is plotted against the initial temperature of the circulating water. It must be clearly understood that Table LIII. and Fig. 56 are based on the assumptions that the steam is saturated steam {i.e., that it is neither superheated nor wet), and that the temperature of the water is raised to the temperature of the steam {i.e., to the temperature of vaporisation corresponding to the pressure). Let us now deal with the modifications necessary to give Fig. 56 a more general application. (1) DlFFEBENCE OF TeMPEEATUBE BETWEEN THE StEAM AND THE Final Tempebatuee of the Circulating Watee. — As an example, let us consider one ton of saturated steam at a pressure of 0,15 kg per sq cm, and circulating water entering the condenser at an initial temperature of 35°, and emerging at a temperature 5° less than that of the steam, i.e., at a temperature of 49° instead of 54°, the temperature of vaporisation of steam at a pressure of 0,15 kg per sq cm. The heat absorbed by one ton of water is directly proportional to the rise of temperature (if we neglect -the slight variations in the specific heat of water, as these are of no importance to engineers). 1 When the term " saturated " steam is employed, it is to be understood that the steam is neither superheated nor wet. CONDENSING PLANT 95 But in Table LIII. and Fig. 56 the temperature rise of the water is assumed to be equal to the difference between the temperature of the steam and the initial temperature of the water. We are, how- ever, unable to avail ourselves of the whole of this difference in temperature. Hence we must make a corresponding allowance by assuming that the water is heated to the temperature of the steam from an initial temperature which exceeds the actual temperature by an amount equal to the final difference of temperature between the water and the steam. TABLE LIII. Tons of Circulating Water required to Condense one Ton of Saturated Steam when the Temperature of the Water is raised to the Temperature of the Steam. M c Tons of Circulating Water required to Condense one Ton of Steam when § s o the Circulating Water has the following Initial Temperatures. go og> Sot 8Q gj= ■a SJ CO ►3 0" C. 5°C. 10° C. 15" C 20° C. 25" C. 30° C. 35" C. 40° C. 45° C. 50° C. 55° C. 60° C. a H 0,02 17 680 34 52 85 300 0,04 29 672 20 24 30 42 61 150 0,06 36 667 16 19 22 28 35 51 95 580 0,08 41 665 14 16 19 22 27 35 51 95 580 0,10 46 663 12,5 14 16 18 22 28 35 51 95 570 0,12 49 660 11,5 13 15 17 19 24 30 41 66 140 0,15 54 657 10,5 12 13 15 17 19 23 30 41 60 140 0,20 60 654 9,5 10 11 12 14 16 19 23 28 36 55 113 0,25 65 650 8,7 9,3 10,0 11,0 12,5 14 16 19 22 28 38 54 113 0,30 69 647 8,1 8,8 9,5 10,0 11,5 13 14 16 19 23 29 40 66 0,35 72 645 7,7 8,3 9,0 9,5 10,5 12 13 15 17 20 25 32 46 0,40 76 642 6,6 7,8 8,5 8,0 10,0 11 12 13 15 18 21 28 36 Tims in our numerical example, the actual initial temperature of the water is 35°, but the final temperature of the water is 5°, less than the temperature of the steam, and in using Table LIII. and Fig. 56, we look for the weight of water corresponding to an initial temperature of 35° + 5° = 40°, and find that we require 41 tons of water per ton of steam. We may now formulate the following rule for the use of Fig. 56. If the temperature of the water does not rise to the temperature of the steam, the amount of the difference should be added to the initial temperature of the steam. An ordinate in Fig. 56 through 96 HEAVY ELECTRICAL ENGINEERING the temperature thus obtained, will, at its intersection with the appropriate curve, give the weight of water required. (2) Wet Steam. — If a mixture of steam and water is required to be transformed into water at the same temperature, the amount of Exhaust Press 0,02 ure in Kg per Sq, Cm 0,04 0,06 0.08 0,100,12 0,15 0,20 ' **> ~ (0 ,uu '_ w _ / o — 6 = c 1? q V - J A 2 z 'ons c Mil nil in i llll III! llll llll llll llll llll llll llll llll 0,25 0,30 0,35 0,40 0°C I0'°C 20°C 30°C *6°C 50'»C 60°C Initial Temperature of Circulating Water, Fig. 56. Curves Shoving the Quantity of Water required to Condense One Ton oj? Steam. (Note. — The final difference of temperature between the water and the steam may be allowed for by adding it to the initial temperature on the above scale.) circulating water required may be readily determined if the wetness factor is known. Let us suppose that we have water at a temperature of 35° and that we require to condense one ton of steam at a pressure of 0,15 kg per sq cm and with a wetness factor of 0,10., That is to say, the mixture arriving at the condenser is composed of 0,10 ton of water, and 0,90 ton of steam. The curves of Fig. 56 show that 30 tons of water are required to condense one ton of steam (provided the temperature of water rises CONDENSING PLANT 97 to the temperature of the steam), but we have seen that the mixture only contains 0,90 of a ton of steam, so that we shall only require 0,90 X 30 = 27 tons of water. Thus the rule for wet steam is as follows : From the wetness factor, find the weight of water present in the mixture, and by subtraction obtain the net weight of steam requiring to be con- densed. The curves of Fig. 56 may then be used in the ordinary manner. (3) Superheated Steam. — If the steam is saturated, we have to extract from it only the latent heat in order to obtain com- plete condensation, but if the steam is superheated, we require to extract an additional amount of heat ; as indicated in columns E, F and G of Table III on p. 8. The simplest method of performing the calculation is to find the weight of saturated steam (at the same pressure) which would involve the extraction of the same amount of heat. Thus, if we require to condense one ton of steam at a pressure of 0,15 kg per sq cm and superheated 50°, we require to extract 657 + 28 = 685 kw hr per ton. But saturated steam at this pressure would only require 657 kw hr per ton, so that one ton of this superheated steam is equivalent to „^= = 1,04 tons of saturated steam as regards the amount of heat requiring to be extracted to produce complete condensation. If now the temperature of the circulating water is 35°, and if it can be raised to the temperature of vaporisation, we shall require 30 tons of water per ton of saturated steam, and 1,04 X 30 = 31,2 tons of water per ton of superheated steam. General Problems. — Thus we see that all problems relating to the amount of water required to condense a given amount of steam can be solved from the elementary principle that Heat gained by water = heat lost by steam. As an example let us determine the weight of water required to condense 15 tons of steam under the following conditions : The water enters the condenser at a temperature of 23°, and is raised in the condenser' to a temperature of 37°. The steam, which has a wetness factor of 0,17, enters the condenser at a pressure of 0,12 kg per sq cm, and the temperature of the hot well is 46°- The steam heat of saturated steam at a pressure of 0,12 kg per sq cm is 717 kw hr per ton, and the heat of water at 46° is 53 kw hr per ton; so that every ton of saturated steam parts with H.E.E. H 98 HEAVY ELECTRICAL ENGINEERING 717 — 53 = 664 kw hr when it is condensed to water at 46°- The weight of the mixture is 15 tons, and the wetness factor is 0,17, so that the net weight of steam is (1 — 0,17) X 15 = 0,83 X 15 = 12,5 tons. Hence we require to extract 12,5 X 664 = 8300 kw hr from the steam. It only remains to rind the weight of water required to absorb 8,300 kw hr, while the temperature of the water is raised from 23° to 37°. The rise in temperature is 37 - 23 = 14°. When one ton of water is heated through 1° it absorbs 1,16 kw hr. Hence when one ton is heated through 14°, it must absorb 14 X 1,16 = 16,3 kw hr, and the weight of water required is 8300 e1 _, — = 510 tons. Types of Condenser. — Having obtained some idea of the func- tion of a condenser, let us now briefly consider the principal types that have been adopted for practical use. The four chief types are as follows : — (1) Jet Condenser. (2) Surface Condenser. (3) Ejector Condenser. (4) Evaporative Condenser. (1) Jet Condenser. — The first and most obvious method of con- densing steam is by means of the jet condenser, so called because the exhaust steam from the engine passes into a chamber, where it comes into contact with a jet of cold water, which is sprayed into the chamber.- The incoming steam mixes intimately with the jet of water, and an exchange of heat is rapidly effected, the steam condensing and the water rising in temperature. "We have seen that, in general, we require a large amount of water to condense a relatively small quantity of steam. This necessitates making ample provision for removing the great bulk of water from the condenser by means of large pumps which are generally called air pumps, from the circumstance that a portion of their duty consists in removing any air which has entered the condenser with the steam. The presence of air necessarily increases the pressure in the condenser, or, in other words, impairs the vacuum. It is of the utmost importance, therefore, to reduce the leakage of air as much as practicable. __(2) Surface Condenser. — The surface condenser was introduced in order to avoid the necessity for pumping out such large quantities of water from the condenser chamber. In this type of condenser CONDENSING PLANT 99 which appears to be superseding other types for plants working under normal conditions, the cooling water does not come into contact with the steam which it condenses. As generally arranged, the water circulates through a bank of brass tubes of some 15 milli- meters external diameter, situated in a cast iron chamber. The exhaust steam enters this chamber, and impinges on the brass tubes. The heat of the steam is transferred through the metal walls of the tubes to the water which is continually circulating through them. In a surface condenser, the temperature of the circulating water on emerging is somewhat less than the temperature of the condensed steam, so that more water is necessary than with a jet condenser. But this consideration is generally far outweighed by the circum- stance that the condensed steam does not mingle with the cooling water. From this it not only results that the capacity of the air pumps may be much less, but also that the condensed steam, which is comparatively pure, may at once be used again as feed water for the boilers. This is an advantage which, with piston engines, has the drawback that the condensation is contaminated with cylinder oil. But with steam turbines the surface condenser leads to almost ideal conditions in this respect. (3) Ejector Condenser. — Ejector condensers are only used in small plants. They are designed on the principle of impelling a spray of water past the mouth of the exhaust steam pipe. They possess the important advantage that no air pump is required, the only moving machinery being a centrifugal pump to deal with the circulating water. A good supply of water is essential for the successful working of an ejector condenser. (4) Evaporative Condenser. — Where the temperature of the cooling water available for condensers is high, or where the cost for large quantities is prohibitive, it may be of advantage to install evaporative condensers. In this type of condenser the exhaust steam enters a series of cast iron tubes, over which a continual supply of water is kept trickling. The heat given out by the steam during condensa- tion raises the temperature of the water, and evaporates a certain portion of it. The remainder of the water falls into a tank immediately beneath the tubes, and is in turn again pumped over the tubes. The amount of water evaporated may be some two-thirds of the weight of steam condensed. In order to obtain economically a maximum of tube surface, the cast iron tubes are sometimes corrugated. Excellent descriptions and detailed illustrations of the foregoing .h 2 100 HEAVY ELECTRICAL ENGINEERING types of condensers may be found in text-boots. From this point onwards we shall confine ourselves to considerations relating to surface condensers, since this is the type which is in by far the most extensive use at present. By means of Table LIII. and Pig. 56, we are able to calculate the amount of water required for maintaining a given exhaust pressure, provided we have the necessary data as to the range of temperature change of the circulating water. As a rule we can ascertain the initial temperature of the available circulating water, but we shall not know how closely the final temperature of the cir- culating water may be brought to that of the condensed steam, and we must have recourse to test results. An exhaustive series of tests has been carried out by Allen, 1 and the author has, from Allen's results, deduced the curves in Figs. 57 to 59. From Fig. 57 we see that when operating the condenser at the rate of 0,25 kg of steam per hour per sq dm of surface, Allen required 52 tons of water at an initial temperature of 20° to con- dense one ton of steam at a pressure of 0,08 kg per sq cm. If we refer back to Fig. 56, we see that 52 tons of water at 30° would have sufficed to condense one ton of steam at the same pressure, if the final temperature of the water had been the same as that of the steam. From this we conclude that in a condenser of the type tested by Allen, the final difference in temperature between the water and the steam was in this instance 30 — 20 = 10°. The dotted curves in Figs. 57 — 59 indicate the final difference of tempera- ture between the circulating water and the condensed steam. The values are obtained in the manner outlined above. Examining the corresponding curve in Fig. 58 corresponding to ' 0,38 kg of steam per sq dm per hour, we find that Allen required 57 tons of water to condense one ton of steam at a pressure of 0,08 kg per sq cm, and from Fig. 56 we calculate that the final difference of temperature is 11°. Again, from Fig. 59 it is seen that there were required 62 tons of water per ton of steam, and the final difference of temperature is 12°. The condenser used by Allen in these tests had a total tube surface of 2800 sq dm. In one series of tests the average weight of steam condensed per hour was 0,68 tons or 680 kg. This is approximately equal to 0,25 kg of steam condensed per sq deci- meter of tube surface per hour. Fig. 57 shows the result of these 1 Surface-condensing Plants, by R. "W. Allen, " Proc. Inst. Civil Engineers," vol. clxi., Feb., 1905. CONDENSING PLANT 101 tests, and Pigs. 58 and 59 correspond to tests at 0,38 and 0,50 kg of steam per sq dm per hour respectively. We thus see that the greater the rate of condensation of steam 60 5 60 -! 8? / / „ 1 / .1 ■^ 1 *fc ^•, A' / to /. / , =2. s — «•> -S3 r Hi t.- 1 — — -— _ t _e ■<• CO O C4 $ — " ~~" *j <5 =-. 1 CD o 2? CO 1 "f ,•/ '" / b / / !-&■ 3 3 ,-- / J t it ■ <*1 „_* •^ * 5 «*"- ■"~ ^ l << -=: CO 1 co QJ s ca >« - ^ Si • '/ / $ It / / / c» / L /. «1_ 1 .- ~f 1 <*■> ^.^ & if ^ "6 C 4 5 :> Q <: a a s -uJ3'b$Jiid Byui w W H A -A < W H H M .X w p o o o a b £ (= « g PhPM 5 W H H B O H rat jre \ of Wa \er | I 20° r- 15° i ■10' 'C 10 I40Q V \ . \ v \ %I200 \ \ -5 tiooo 1) \ v 5 800 °\ 0.600 <0 B too 200 D t 400 800 1200 1600 2000 2400 2800 3200 3G00 4000 4400 4800 Rated Output in Kilowatts. Fig. 62. Eelation of Bated Speeds and Outputs of Direct-connected Electric Generating Sets. This leads to no difficulties whatsoever ; on the contrary, the readi- ness with which electrical energy can be transformed from one of these forms into the other is one of the chief features which have contributed to the rapid developments in electrical engineering. One of the chief reasons for the superiority of continuous .current . for distribution relates to the superiority, as regards secondary voltage regulation, of motor generators as compared with stationary transformers. Other important features relate to the more effective 120 HEAVY ELECTRICAL ENGINEERING means for speed variation afforded by continuous current motors, as well as to their superiority in the matter of starting with heavy torque. New developments may, of course, at almost any time quite reverse this order of things ; nevertheless, developments of the last twenty years have very consistently tended toward these general conclusions with regard to the respective fields of usefulness of these types of electrical machinery. CHAPTEE VII THE DESIGN OF GENERATING STATIONS In the general design of stations containing generating apparatus attention should be directed to the attainment of the maximum simplicity consistent with economy. The underlying plan should be such as to permit of systematic extensions on the lines adopted for the first sections constructed. A modern building for a generating station, or for a sub-station, usually consists of a steel framed structure of sufficient strength to support the girder rails for the travelling crane. The walls are either filled in with brick, or they are of corrugated iron. In either case, in a well-designed building, in order to permit of systematic exten- sion, both the boiler house and the engine house should be provided with temporary end walls which may be of corrugated iron. The main building of an electric generating station comprises a boiler house, an engine room, and, in cases where the main switch- board is not located in the engine room, a separate switch room. Provision is also usually made for coal storage, the capacity of the store depending on the facility for obtaining coal. Where the prompt delivery of an ample supply can be relied upon, the need for providing great storage capacity is decreased. There will, in addition, be a number of minor buildings consisting of general stores, repair shops and offices. The location of these minor buildings should be such as not to interfere with any extension to the main buildings. Choice of Site. — For a power or lighting system the site should preferably be chosen at the centre of the area of supply. The selection of the site may, however, be influenced by several factors, among which are the facilities for the supply of coal and water, and considerations relating to the price of land and to the rates. It is desirable to choose a site near a railway, canal or navigable river, as this permits of coal delivery at a minimum cost. A situation adjacent to a river or canal is also convenient if the condensing water or the feed-water may be drawn therefrom. The facilities for condensing water supply may also have some bearing on the choice 122 HEAVY ELECTRICAL ENGINEERING of steam generating plant, the absence of a cheap and plentiful supply of water for condensing purposes constituting a factor in favour of using piston engines. This matter has been dealt with in Chapter IV. If the undertaking is in connection with a refuse destructor plant, the site should not be too far from the area from which the refuse is collected, since the cost of cartage is thereby reduced. On the other hand, a destructor plant constitutes a nuisance, and should be at a considerable distance from thickly settled districts. Since, however, it is now amply demonstrated that real economy is rarely, if ever, secured by the employment of refuse as a fuel, these considerations have but slight importance for electrical engineers. The rates and the price of land in a large town rarely vary greatly in those districts where an electric generating station is likely to be situated. In cases where land is expensive, it is desirable to employ a compact design for the station. High-speed generating sets offer, in this respect, considerable advantages over slow-speed sets. The saving in floor space effected by steam turbines is of importance, although, as we shall see, it has not so great an influence on the total space occupied by the whole of the plant and buildings as might at first sight be supposed. The shape of the site affects the design of the buildings for the main plant. Provided the site is of convenient rectangular shape and of ample dimensions, the design of the buildings generally follows certain standard lines. General Arrangement of Station. — With a view to obtaining a maximum of simplicity the plant should be so laid out as to provide the energy with a direct and short path through the station from the coal bunkers to the outgoing feeders. For this purpose the boiler house is arranged alongside the engine room, the coal is delivered to the boilers at the outer side of the boiler house, and the switchboard is arranged along the opposite side of the engine room. This is a simple arrangement which usually works out well. A diagrammatic outline of this arrangement employing a single boiler house and engine room is given in Fig. 63. The coal is delivered to the boiler house at the left-hand side by trucks coming from the point of delivery, whether a railway siding or waterway, and running alongside the boiler house. Where hand firing is employed, the coal is usually shot directly upon the boiler house floor. Where mechanical stoking is employed, the coal is delivered to hoppers in the roof of the boiler THE DESIGN OF GENEKATING STATIONS 123 house and is fed through chutes directly down upon the grates. The coal is usually fed into the hoppers by means of an endless conveyor running the whole length of the boiler house. The coal conveyor generally comprises an endless belt or chain, the former carrying the coal in a continuous stream and the latter carrying buckets containing the coal. In the latter type, the conveyor delivers the coal as it travels along above the hoppers by tripping the buckets at suitable points. The empty buckets pass along the bottom under the floor and may be employed for removing the ash. A station following these general lines is shown in Figs. 64 and 65. Tft \J/>">>>////////////////> \T7, Fig. 63. Section op a Typical Power Station, with Slow-speed Vertical Engines. In this case there is a double row of boilers and engines. The coal hoppers may be seen in the roof of the boiler house. Trucks running in the basement below the boiler house floor are employed for disposing of the ash and clinkers. The double row of boilers and engines make it necessary to employ excessive lengths of steam piping, and this would be reduced if two boiler houses, one along each side of the engine room, were employed, as could be done by duplicating Fig. 63. This arrangement is quite practicable, especially when the switchboard, as in Figs. 64 and 65, is arranged at one end of the engine room instead of along one side. The disadvantages of such an arrangement, however, outweigh this slight gain, since two buildings instead of one would be necessary for the boilers. Two coal conveyors would also be required and a larger boiler house staff. 124 HEAVY ELECTRICAL ENGINEERING o H ■1 H CO « o o o l-l H ■< H pq hi o M § & = ftflB Sin s "5 d 0, '5 H >5 3" o OO.S - — P.£ m « c go > £ c- "", & ■- »a a a> « Ed 3j ass '3.2 •3 + En is >> a o O Dimensions of Engine Room length x breadth x height (Meters). [J o o 1 & eg & 00 Area of Engine tioom, Sq Meters. = 1 ■ IS 5 SO0 H Total Room Space per K\v Sq Meters. V 8 8 (fi 850 6800 11,0 x 8,5 0.11 0,19 6 300 33,0 0,11 0,63 7100 783 ' 61,0 X 26,5 x 16,8 ! 0,48 1620 27 200 0,23 3,8 5 4 ,« 1500 6750 13,1 x 9,2 0,08 0,19 4 R. C.'s & (2400 | 390 57,0 0,02 0,14 9540 610 85,5 X 19,8 x 13.5 0,36 1700 23 000 0,18 2,44 1 ^ 750 7,6 x 9,5 3 Exciters 3 3 ^ 200 600 1 75 675 28,5 x 15,5 440 0,65 7 7 (« 1500 10 500 16,3 x 9,0 13,0 x 9,2 0,10 0,048 0,17 3 225 23,5 0,10 2,0 10 725 1054 89,6 x 25,5 x 11,0 0,46 2280 2080 2500 0.21 2.34 2,0 8 2 @ 4000 16 000 0,11 4 1300 33,3 0,026 0,26 17 300 794 91,5 X 22,8 x 17,0 0,38 35 400 0,12 4 @ 1600 12,4 x 9,2 2 (£ S = *| 1* m u J "3 'goo u '3 3 1 to as & e n H a fSaj Z; 5-1 Central London Kailway Horizontal Slow 8 8 800 1 6400 9,5 x 6,4 0,076 0,14 Continue 9 Dublin Tramways, Ringsend s ^ 6 6 (a 550 [ 3300 6,1 x 5,8 0,065 0,21 Continue 10 Glasgow Tramways •• 6 4 ta 2500 ! 11 200 2 @ 600 16,0 x 7,3 6 300 11 Kelham Island T. & P. Co. 4 3675 0,23 12 Mersey Tunnel Railway 3 3 @ 1250 3750 9,2 x 7,6 0,056 0,14 3 | 525 13 Leicester Electric Tramways 3 3 @ 500 1500 9,15 x 7,3 0,13 0.28 14 Stalybridge Electric Tramways Co. 6 6 (ft 500 3000 0,29 15 Interboro R. T. Co., U.S.A. 11 21 11 @ 5000 55 000 15,2 x 13,7 0,04 0,13 6 1 8000 16 Birmingham (Summer Lane) Vertical High 16 (* 1500 : 26 500 10,0 X 5,2 0,035 0,10 2 200 Speed Steam 2 @ 500 7,6 x 1,8 3 3500 0,2 23 Birmingham Tramways (Smethwick) •• 7 4 £' 500 ! 2900 3 ^! 300 7,0 x 4,0 7,0 x 2,6 0,061 0,15 2 R. C.'s&i ( 600, 24 Ilford. Electricity Works 5 1 2600 0,16 25 Greenock Electricitv Works 8 2000 0,24 26 Lowestoft Electricity Works 5 2 @ 550 1575 1 (« 250 1 (fli 150 | 1 i' 75 [ 2 (ry 100 1 1600 0,13 " 27 Poplar Electricity Works 6 5.5 X 1,8 0,054 0,18 2 ^ 200 6,6 x 1,8 2 j, 500 6,7 X 3,1 28 Middlesboro Corporation 5 1600 0,23 29 Burnley Corporation 7 1500 0,39 30 Eastbourne Corporation mj 5 2 ^ 400 j 1200 0,22 1 •/;< 200 1 tf 150 1 (ffi 50 31 Bournemouth Corporation 4 4 (£ij 292 | 1168 6,7 X 3,4 0,079 0,28 32 Christehureh Electricity Works ,, 3 3 op to is a . OK H = 05 -*j ^ c rt oGQ w o s its O 0> ~- i o » si es td t- g£ra (-. fe y o ■$£ O -i, [_ o o -" HK • fi U U 2 * ££ o o c '§p • <— * o 5 5 o H Dimensions of Boiler Room, length x breadth x height (Meters). Is ss at O < u o c fa a, 3 O u m ft © en i » &« 1 * 8« a $ j|M o H I 3 I 8 CD N "5 . Eg OS 2 • «s .Sou tp m 0«H , °t £ ; ~Z Q S3 11,3 ! 700 5,4 108 332 8,3 40,0 6640 62,0 590 0,09 5,5 7100 45,0 x 26,5 X 17,0 1190 0,50 20 000 0,17 2,8 1620 0,74! 11,3 470 9540 86,0 x 15,2 x 12,3 1300 0,36 16 000 0,14 1,7 1690 0,77 11,3 4,9 14,8 290 5,5 53,0 870 59,0 675 28,0 X 15,0 420 0,62 440 0.95 350 6300 615 0,10 10 725 89,6 X 19,0 X 9,0 1700 0,36 15 300 0,16 1,3 2280 0,75 11,3 2 = 5,4 4= 7,4 10 = 10,8 147 425 500 750 5,8 7,75 11,6 73,0 64,0 65,0 10 350 70,0 490 0,05 3,3 17 300 91,5 X 22,8 X 19,5 2080 0,24 40 500 0,12 2,35 2080 1,0 10,5 5,0 50 175 3,7 47,0 1750 35,0 375 0,21 7,5 3440 28,4 x 19,0 540 0,70 0,16 626 0,87 12,0 5,4 130 330 9900 61,0 870 0,11 6,7 9600 61,0 x 28,6 X 19,6 1750 0,50 34 000 0,18 3,6 1390 1,26 11,3 5,4 86 4,4 590 6,9 6400 69,0 X 17,0 x 13,5 1170 0,50 15 800 0,18 2,5 900 1,3 11,3 235 4700 550 0,12 3300 39,0 x 23,0 X 12,0 900 0,60 10 800 0,27 3,3 685 1,3 11,3 8,9 286 480 5,9 82,0 15 400 54,0 11 500 74,0 X 25,5 X 21,4 1900 40 600 0,17 3,5 1700 1,12 11,3 Total 35,6 37,0 1340 3675 685 6300 0,19 1,7 850 0,8 12,0 405 3650 250 0,07 4275 43,0 X 24,0 1050 0,24 0,2 660 1,6 11,3 160 1500 23,5 X 16,5 X 11,0 390 0,41 4300 0,26 2,9 416 0,9 12,7 710 3000 765 4780 0,25 1,6 873 0,9 15,8 555 9,25 60,0 40 000 3600 0,09 4,0 63 000 212,0 X 25,2 x 28,0 5350 0,66 150 000 0,09 2,4 1,02 7600 0,7 12,7 10,8 260 572 9,25 62,0 13 700 53,0 1030 0,075 26 700 84,0 X 27,0 X 12,0 2270 0,45 27 200 0,09 2560 0,9 1000 674 18 420 71,0 X 34,0 X 21,4 2400 0,28 51 400 0,13 2,8 2000 1,2 10,5 455 7,05 64,5 10 000 450 0,045 5700 50,5 X 34,0 x 12,8 1720 0,26 22 000 0,30 3,9 710 2,4 i 9,2 = Total 30,0 850 4880 590 3600 0,12 0,74 740 0,8 28,2 10,6 370 304 6,2 49,0 1820 1060 35,0 X 16,0 X 8,0 555 4440 0,52 4,2 525 1,1 14,8 4= 4,5 -A = 6,3 30,5 264 372 1800 j 52,5 224 0,125 7,4 4945 40,0 X 12,2 490 0,46 0,10 610 0,8 12,3 = Total 64,5 65,5 4225 3500 1030 9400 0,29 2,7 700 1,5 11,3 6,3 50,0 330 2640 53,0 215 0,08 4,3 3590 46,0 X 15,3 X 12,2 710 0,30 8640 0,2 2,4 635 1,12 11,3 3,8 23,0 240 5,2 46,0 1430 62,0 2600 430 3140 0,16 1,2 405 1,06 14,0 3,3 20,0 170 4,7 36,0 1010 50,5 2000 422 348 0,17 1,75 490 0,86 11,3 2,5 10,0 165 3,25 51,0 663 66,3 1575 284 22 0,16 1,45 224 1,27 12,7 2= 6,3 4= 2,7 23,2 248 4,4 57,0 1490 64,0 140 0,09 6,0 1600 22,0 X 24,5 X 9,5 540 0,26 5100 0,34 3,2 284 1,9 9,9 3,6 21,5 113 4,8 29,0 680 32,0 1600 433 2900 0,27 1,8 366 1,2 9,2 134 1500 463 3260 0,31 2,2 583 0,8 10,6 = Total 1290 2= 4,5 160 3,5 46,0 970 1200 28,0 X 12,8 X 9,2 358 3300 0,3 2,75 268 1,3 12,7 3,6 14,3 114 8,0 1168 20,0 X 15,3 X 9,7 305 0,37 2970 0,26 2,5 325 0,9 10,6 133 530 60 0,11 400 17,4 X 13,0 X 7,0 224 0,27 1570 0,56 3,9 165 1,35 9,5 57 200 4200 107 i 12,3 520 ' 7,6 610 483 7,7 63,0 38 600 63,5 3320 0,086 5,4 58 250 138,0 X 30,5 x 31,5 0,8 132 000 0,07 2,3 3150 1,38 12,7 8,9 125 530 10,9 49,0 7400 59,0 560 0,08 4,5 14 300 98,0 x 16,2 x 14,0 1590 0,35 22 400 0,11 1,6 905 1,76 14,0 8,9 90 384 4,3 11000 35,0 x 20,0 x 11,0 700 0,55 7700 0,06 0,7 680 1,03 12,3 407 5700 520 0,09 9650 92,0 x 15,25 x 16,5 1400 0,37 23 000 0,145 2,4 1020 1,4 14,0 13,4 53,5 575 7,5 78,0 2300 43,0 290 0,13 5,4 6000 33,0 X 21,3 X 19,2 700 0,42 13 500 0,12 2,25 585 1,2 11,6 6,7 53,5 410 5,2 79,0 3280 61,0 270 0,08 5,0 4300 44,0 X 17,8 X 9,2 780 0,35 7200 0,18 1,7 750 1,04 14,0 485 15 500 960 0,06 33 000 80,0 X 31,5 X 25,0 2500 0,38 62 500 0,08 1,9 1600 1 56 11,3 2 = 2,2 7,6 375 14,6 X 12,8 X 7,9 187 1480 0,5 3,95 135 1,4 1= 3,1 14,0 11,2 200 530 16 650 1500 | 14,0 8,9 53,5 9,25 57,0 3200 60,0 240 0,075 4,5 8450 21,4 X 24,4 X 14,6 520 0,46 7600 0,06 0,9 345 1,5 11,3 8,9 53,5 535 9,5 57,0 3200 60,0 240 0,075 4,5 8450 21,4 X 24,4 x 14,6 520 0,46 7600 0,06 0,9 345 1,5 14,0 750 690 9,3 74,0 6900 550 0,08 10 375 37,0 X 24,5 X 18,0 900 0,61 16 200 0,09 1,56 900 1,0 1 Boilers on two floorp. [To face p. 135. PLATE IX. TABLE LVI. Data of Boiler Rooms of Generating Stations. 1 2 3 4 5 c 7 8 9 10 n 12 13 14 16 Floor Area per Ton of Steam per Hr, c! Sq Meters. c V. O - 03 03 Name of Station. Type of Boilers. "o oj a g 55 bo M so &* t. 03 « & '3 « 1 a) wis s o SB CD c0 I®! -d -ft § o5 «! -a >> o £ •- 05 O 1° u ?3 » 48 North Wales P. & T. Co. (Snowden) " i 1 Boilers on two floor. . THE DESIGN OF GENEEATING STATIONS 135 area. It may be noted that the latter ratio increases as the rated speed of the generating plant in the engine room increases. Thus, for steam turbines, the boiler house occupies about 50 per cent, more space than is occupied by the engine room. The boiler house thus occupies some 60 per cent, of the total area. For piston engine stations the boiler house only occupies some eight-tenths as much space as is occupied by the engine room, or only some 45 per cent, of the total area. From these figures the preliminary dimensions for the boiler house may be determined for a given rated capacity of plant. Column 11 shows that the ratio of heating surface to grate surface averages about 50. From these data the following values may be deduced : — TABLE LVII. Average Values for Boiler House Design. Average Values. (1) Heating surface per ton of steam evaporated per hour (normal rated capacity) (2) Floor area per sq meter of heating surface . (3) Floor area per ton of steam evaporated per hour (normal rated capacity) 60 sq m 0,075 sq m 4,5 sq m Preliminary Calculations for Generating Station Design. — Before proceeding further with the general principles of design of the other parts of the station, it is proposed, as an example, to make some preliminary calculations for a particular case. For this purpose let us take a generating station for an annual output of 270 million kw hr at a 50 per cent, load factor. This is the case which has already been considered in Chapter II., where it was shown that it was necessary to install 8 generating sets, each of 6800 kw rated capacity, and that the average coal consumption would be 33 tons per hour or a total of 290 000 tons per year. Let us first consider the engine room. From Table LV. we see that the average engine room area required for steam turbine generating sets is 0,05 sq m per kw. Thus there are required 0,05 X 55 000 = 2750 sq m of engine room space. Before deciding on the proportions of the engine room, let us make a similar estimate for the boiler house. The proportions of both engine room and boiler house, if not 136 HEAVY ELECTRICAL ENGINEERING restricted by the shape of the site, will depend only on the grouping of the plant. For a single 6800 lrw generating set we found in Chapter III., p. 60, that 51 tons of steam per hr were required when operating at rated load. In Table LVII. of this chapter, 60 sq m was shown to be an average value for the boiler heating surface per ton of steam per hour. Hence for the 6800 kw set, 51 x 60 = 3060 sq in of boiler heating surface are required. Taking a large standard boiler of 750 sq m heating surface, it is seen that four boilers are required for each generating set. For the S600 4800 % 4000 3200 5- 2-;' : rt 3 1600 « 800 £T< m( an J f IE Y77 < 1M *m **J ■ Fig. 78. Fig. 77. Figs. 75 — 78. Alternative Arrangements of Boilers and Turbo-generating Sets the switchboard. The outline of the engine room and boiler house is indicated in Fig. 81. The next matter for consideration is that of the flues and the chimneys. The most symmetrical arrangement for the case under consideration is that indicated in Fig. 81. Let us consider more in detail the general proportioning of chimneys and the related question of economiser proportions and of suitable provisions for coal storage. THE DESIGN OF GENEBATING STATIONS 139 Eig. 79. Plan and Elevation or Power House proposed for supplying Electricity for Operating the Berlin Elevated Bailways. 140 HEAVY ELECTRICAL ENGINEERING For the present we have shown, in Fig. 81, one economiser in the flue leading to each chimney. Coal Storage. — It is desirable that provision should be made for o H ft W w o «1 ig ft 5 ° O Ph O O ft P o O ft o R ft o t-1 CO s storing a quantity of coal sufficient to last for a few weeks. This is drawn on in the event of the supply being cut off through interrup- tions of the railway or waterway services or from any other cause. THE DESIGN OF GENEBATING STATIONS 141 In Table LVIII. we have brought together data of the coal storage for the generating stations in Tables LIV. and LVI. The period for which the store suffices varies from one to three weeks. With a large station burning a large amount of coal per day, the space required for storing coal for a period of over a week becomes a serious consideration. In estimating the provision for storage the average coal consump- Q Q J WS it?- r£- * j $ ps g / $ol jjgp- •5 / (/ V / £ 2 // V ' 41 nWsp> CJ ' > / ZOMett rs 40 SO 120 160 200 240 280 320 360 400 440 480 Difference of Temperature in Degrees Cent. Eig. 82. Curves showing the Draught obtained from various Chimneys when the Temperature and the Height op the Shaft are Varied. forced draught systems, the general preference is still for natural draught in spite of the considerable cost of chimneys. With a view to the more effective removal of the gases, chimneys are often built much higher, and consequently on more expensive lines, than are required for the provision of the necessary draught. A height of 150 m is, however, rarely exceeded. In Table LIX. are given particulars of the chimneys of a number of electric generating stations. There is excellent agree- ment with respect to the weight of furnace gases carried away per hour per square decimeter of sectional area of chimney. The draught produced by a chimney, and the volume of gas flowing through it per hour per unit of sectional area, depend upon the difference in the absolute temperature between the gases inside the 144 HEAVY ELECTRICAL ENGINEERING X I ~- H tf i-l PA < H « Oh '09g J9d sja^j^; m si?£) jo pggdg ft OCOHODOIOJO -dj tJ<" CO~ co" CO~ * C- IM "sH ■* O CO HHCTCilHHH ° CJ ■s|£, "S 8*3 "WIS JO ma *>S •«<* £ 0O t> IN ■* 00 O O iH tH tH •yuqg J3d a O O O O © O O o o o o o o o O O O O lO o o O t- H O I> CO US CTOlOt-Olt-H tH r-( tH rH tH Weight of Gas in Tons per Hour for Ratio of 20:1. ■qj^is JO ma OS J9( * Hi HCOt-OJHOOCO i-f t-H tH tH rH O rH o" o" o o" © o" o" ■IjEqs .rad W IOI>!OOOHCO o >c oo cm co co cd co cm cm co i-i O jJ B S O Qj •anon d9d inntmxirjf l-s CO CO CN O CM CO C5 CO "CH CnT CO lO t-" CN -hh" tH i-H i-H rH 'JO^ou^ puoq ■^U90 J9d OS JOJ 1138.1 iod tt^ox W O O O O O O O O O O O O O O lO CO CD 1Q O CD O comoicotxMO CDlOOCDMHtM •yuqg Md saa|io(i jo iaqiun^[ e CD CO CM O IM 00 CD r-t r-i r-\ r-\ i-l •smaf'S a ! WIS J° *MV PH © © © © © © »o CO t- ^H ^ CO CO CM CO 00 CD CD -^ t- f CM rH rH rH rH H 00 t- t- C- lO TjH oo oo «o io cm o o •sw^H ni ijqSraH ft C0 -CM^^ C0 .(M' - O 00 t- iO CO 00 CM OS CO GO O *IT3U9|13J\[ o •sa,jw[g jo J9qumx ffl -# rH CO rH CM CM rH <1 Chelsea (Lots Rd.) Glasgow I.R.T., N.Y. Neasden Greenwich . C.L.R. . Brimsdown . THE DESIGN OF GENERATING STATIONS 145 chimney, and the air outside. For chimneys of from 20 to 120 m in height, the values are worked out in the curves of Fig. 82. For the plants studied in Table LIX. the precise conditions as regards temperatures have not been analysed. The temperature of the gases on entering the chimney has been assumed as 175° C in all these cases. At this temperature, a ton of the furnace gases TABLE LX. Relation between Weight and Volume of Air at different Temperatures. Temperature. Relative Volume. Weight Kg per CuM. Volume Cu M per Ton. Centigrade. Absolute. —10 263 0,96 1,36 735 273 1,0 1,3 770 10 283 1,04 1,25 800 20 293 1,07 1,2 825 30 303 1,11 1,17 855 40 313 1,15 1,13 885 50 323 1,18 1,1 910 60 333 1,22 1,07 940 80 353 1,29 1,01 990 100 303 1,37 0,95 1060 120 393 1,44 0,91 1110 ,140 413 1,51 0,86 1160 160 433 1,59 0,82 1230 180 453 1,66 0,78 1280 200 473 1,73 0,75 1330 250 523 1,92 0,61 1480 300 573 2,1 0,62 1620 350 623 2,28 0,57 1750 400 673 2,47 0,53 1900 450 723 2,65 0,49 2040 500 773 2,83 0,46 2180 occupies a volume of 1260 cu m, as against a volume of 850 cu m at 25° C, the ordinary temperature of the atmosphere. These values are taken from Table LX. Thus a cubic meter of furnace gas in the two cases weighs : At 25 degs. Cent. . . 1,18 kg. ,, 175 ,,,,.. U,7y ,, For every meter height of chimney, there is a difference of pressure of 1,18 - 0,79 = 0,39 kg per sq m, or 0,039 g per sq cm. H.E.E. L 146 HEAVY ELECTRICAL ENGINEERING A chimney with a height of 100 m thus produces a draught equal to 3,9 g per sq cm. Since 1 sq cm of water weighs one gram, this 100-meter chimney produces a draught equal to the pressure of a column of water of a height of 3,9 cm i.e., the draught in cm height of water column is equal to 3,9. For other temperatures of the furnace gases when entering the chimney, the suitable values of the density of these gases may be taken from Table LX. For coal of a calorific value of 8700 kw hr per ton, 20 tons of air should be supplied per ton of coal burned; i.e.,~l ton of air should QJTAA be supplied for every = 435 kw hr of calorific value of the coal burned. Allowing for loss in ashes and in radiation from furnace, we may say that the calorific value of one ton of furnace gas at 1300° is about 400 kw hr, or, say, about 0,31 kwhr per deg. Cent. Thus for a generating station with 10 per cent, overall efficiency, 1 ton of air should be supplied for every 43,5 kw hr output from the station. The theoretical quantity is only 12 tons of air per ton of coal, but in practice the weight of air is seldom reduced below 16 tons per ton of coal burned, when this eoal has a calorific value of 8700 kw hr per ton ; 20 tons of air per ton of coal burned is a good representative figure. It is desirable to proportion the chimney with sufficient draught to permit of operating the boilers for a short time at 50 per cent, or more above their rated capacity. For the 270 million kw hr station regarding which we have calculated the boiler plant, eight chimneys should be installed ; each serving four of the thirty-two boilers. Each of these boilers is rated at 9600 kw, or 4 x 9600 = 38 400 kw for the four boilers served by one chimney. At a 50 per cent. overload, we have 1,5 x 38 400 = 57 600 kw If we take a boiler efficiency of 70 per cent, at this overload, we must burn coal at the rate of 57 600 n „ A -0^- = 82 000 kw 82 000 _ . , , or „ = 9,4 tons per hr. THE DESIGN OP GENERATING STATIONS 147 Thus we should require 20 X 9,4 = 190 tons of air per hr. It is not desirable to estimate on transmitting more than 14 tons of furnace gases per sq m per hr, at the maximum overload. Hence we 190 require -yj = 13,6 sq m section per chimney, or a diameter of 4,2 m per chimney, or say 4,5 m. Estimating on a temperature of 175° for the gases entering the chimney, we have a volume of 1260 cu m per ton. The gas must be transmitted at the rate of 190 wttkr = 0,053 ton per sec, or OuUU 0,053 X 1260 = 67 cu m per sec. As the section is 13,6 sq m the velocity must be — — = 4,9 m per sec. Let the chimney have a height of 100 m. We have seen that the " draught " in a 100-m chimney amounts to 3,9 g per sq cm. The total pressure is thus lfrgjOO 000 X 3,9 = 53Q kgg Thus work is being done at the rate of 530 X 4,9 = 2600 kg m per sec. 1 kg m per sec = 9,81 w. Work is, consequently, being done at the rate of 9 i 8 L x_2600 1000 This is of some interest in getting an idea of the general order of magnitude of the power which would be required in driving fans where induced or forced draught systems are employed. A large multiplier should be employed in connection with the above figure, and this should vary with the varying conditions of each case. This 26 kw is almost entirely required to overcome the friction of the air through the grate and the fuel, then on amongst the boiler tubes, superheater tubes, and economise* tubes, and afterwards through the chimney. Forced draught systems have the disadvantage of increasing leakage of the air and gases. Induced draught systems avoid this objection, but have the disadvantage that the fan works in a medium of such high temperature and composition as to be subject to rapid deterioration. Economise™. — If, after passing through the boiler, the gases are l 2 148 HEAVY ELECTRICAL ENGINEERING carried through an economiser, the temperature of the gases will be lowered by an amount proportional to the extent of economiser tube surface installed. The gases may thereby be reduced to so low a temperature that it would not be practicable to obtain the necessary draught entirely by a chimney, and the chimney must be supplemented by an induced draught installation. When the temperature of the gases on emerging from the economiser to pass to the chimney is much less than 150° Cent, it is generally impracticable to obtain the required draught by the chimney alone. Thus there arise a number of conflicting considerations with regard to the extent of economiser surface which can be economically installed, and even whether it should not be altogether dispensed TABLE LXI. Data of Economisers Jn"o. Name. 03 U ^ c o - m O is O 03 CD 'H . O BOO* +5 » 18 255,0 0,71 1,0 1,41 2,0 2,8 24,0 0,53 0,74 1,06 1,50 2,1 18,0 a 20 314,0 0,64 0,93 1,31 1,85 2,6 23,0 0,48 0,70 0,99 1,38 1,94 17,0 tH 22 381,0 0,62 0,87 1,22 1,74 2,4 22,0 0,46 0,64 0,92 1,31 1,84 16,0 3 24 2 453,0 0,50 0,82 1,16 1,65 2,3 21,0 0,44 0,62 0,86 1,24 1,72 15,4 3,14 8,0 15,0 21,0 30,0 42,0 226 6,0 11,2 16,0 22,5 320 167 u 4 12,6 23,0 35,0 48 71 102 640 17,2 26,0 36,0 53,0 770 473 ft 6 28,3 40 61 86 125 175 1170 30 46 65 94 130 870 8 50,3 64 90 126 179 260 1810 48 67 94 134 135 1340 10 78,7 85 120 169 240 330 2530 63 90 126 175" 246 1370 **§ 12 113,2 108 150 210 300 420 3320 SO 112 15S 222 310 2460 «■§ 14 154,0 132 184 260 365 510 4200 100 137 195 270 380 3100 -M C 16 201,0 156 220 310 415 610 5130 116 165 230 310 450 3800 go 18 255,0 180 260 360 510 715 6100 135 190 270 380 530 4520 U 20 314,0 200 300 410 680 820 7170 150 220 310 435 610 5300 22 381,0 240 350 465 660 930 8250 175 245 350 500 700 6100 24 453,0 270 375 525 750 1050 9450 200 280 390 560 780 7000 only worked through for sections of 50, 100 and 150 sq mm. For the sake of comparison, the costs of transmission lines with alumi- nium conductors have been worked out for sections of 50, 100, 150 and 200 sq mm. The maximum permissible stress in an aluminium conductor may be taken as 4 kg per sq mm. This again is a very conserva- tive value, i.e., it is rather less than one-half of the elastic limit of hard-drawn aluminium, but it is consistent with the figure of 10 kg per sq mm for hard-drawn copper. The specific gravities of copper HIGH-TENSION POWEE TBANSMISSION LINES 163 and aluminium are 8,9 and 2,7 respectively. The conductivity of hard-drawn aluminium is 60 per cent, of that of hard-drawn copper. Table LXVI. gives the temperature rise of overhead conductors at various current densities. The expansion coefficients may be taken as 0,000017 for copper, and 0,000023 for aluminium, per degree Centigrade. The three conductors of each circuit are mounted on insulators fixed to the top of the tower, and, as the same voltage exists between any two of the three conductors, they are usually placed at equal distances apart at the vertices of an equilateral triangle so as to economise space and make the system symmetrical as regards self-induction and capacity. Let us consider the factors determining the distance apart. Distance between Conductors. — The chief factors which theoreti- cally govern the distance apart of the conductors are the voltage between the conductors and the diameter of the conductor. In practice, however (for pressures up to 20 000 volts), the conductors cannot be placed so near as these considerations would indicate, since arcs would often be started by pieces of wire, or stick, or by birds flying or falling against the wires. Above a pressure of 20 000 volts, the brush discharge loss necessitates a still greater distance between conductors, and above 40 000 volts the stress is so great at the surface of conductors of small diameter that the air resistance is broken down and a brush discharge takes place, no matter how great be the distance apart at which the conductors are placed ; for instance, the smallest wire that it is possible to use at 40 000 volts is one of about 25 sq mm section. The curve in Fig. 86, plotted from figures proposed by Esson, gives values which agree well with modern practice ; the numbered points on the curve refer to actual values for certain installations, full particulars of which are given in Table LXIX. on pp. 176 and 177 at the end of this section. Let us next consider the distance between the towers, i.e., the " span "of the suspended conductors. The Span. — The distance between the supporting towers is limited by the height of the towers, the maximum pull for which they are designed, and the regulations in force in the district traversed. Where the transmission line is not straight, the conductors make an angle at the tower, and in this case either the spans must be short in order to make this angle as oblique as possible, or special towers capable of withstanding the strong side-pull must be erected, m 2 164 HEAVY ELECTEIGAL ENGINEERING The longer the span the more costly the towers, and for any given section of conductor there is a most economical span. This may be taken as between 130 and 160 meters for the usual sections of conductor employed. 1 In the following investigations we shall take as a standard, for all cases, a span of 143 meters, that is 7 towers per km, with six conductors, i.e., two circuits per tower. Taking this value of the span and the above-mentioned sections 3,0 2,0 ", /0 , 9 ^3 11 14 S 1 '7 1,0 6 1 * 3' ^r ' k Fig. 86. 10 20 30 10 SO GO 70 SO 30 Kiloi/olts between Conductors. Distance between Conductors, in Meters, for different Working Voltages. of conductor, we must next determine the maximum sag which the conductor will have, and from this and the minimum height of conductor above ground we can determine the necessary height of tower. The case of a single series of towers supporting two transmission circuits has been taken, as a steel tower construction would be 1 For investigations concerning the "most economical spau," see T. L. Kolkin in Electrical Review, Dec. 28, 1906 ; and L. Kallir in Elektrotechnih und Maschinenbau, Oct. 21, 1906. From considerations of the cost of poles only, the former arrives at 100 — 130 meters, the latter at 130 — 160 meters. HIGH-TENSION POWEK TRANSMISSION LINES 165 rarely erected for a single transmission circuit for the reasons mentioned on p. 157. The formulae used in estimating the sag 5 1 s 11 •s ■5> .■ CO •:C 1-1 I- rH CO rH CO M IO u °co O N- -* m o io O cT of o -* m CO r-H cc © ©" >- CO CM r-i rH M -J- 1-1 m rH ■:> rH 3_5 9 s -g ® bo « c tn'g S a S & S^ 4-> o 0/ W s 1= o w ^ T3 CJ "rt c o ^ £ X co cd H a +2 q+^4- is ^- a E > E £P° S 5 o c^^O ft o SOn ^h a ==-= & « g.£ 5 « .3+icflO" 44 m cl> ° ft R ri . P. . r> s . o . • ^ ft • a> + a> c>o o SO n j- « * — S « £ s = 'So ftte 5 a tn 0§ft5°.S.S sft , o^ ©cmCm ; c w o o o h ^ ! 2 fc, w-pim di o o o o CO o O to Ol CS CO m ■* iO to to ,_, in 1*1 ,_, tP 2 CM* rH CO rt CO © CM CO -# to o CO CM ■* ■* CO •M OS ■_■ CO '-•1 ■* CO CO ci co CO m ■* -w ,_, r ,_, - rH" M T— 1 CM en o" ■* rH CM >-h 1-1 co o o o CM 1- ' ' CO rH o f CO CO m CO CO H -V CM ■X CO Tf o rH to 01 ' ' 1-1 rH •# rvi CO TO rH in ro OS OS o o 1-1 o ■* CI CM CM ©" ■^ CM ■* '.1 o CO 1.1 J 1-1 m rH to co CM r-" i- tO 'O CO CMtOtOO^COrHCM"^00 t- OS rH CO O O -^ xn o © sq cd ^ K rf co w m « ~ § S §3 _§ . ^ gcti qjqjqjc^qj .q^qjeflqi a e a sa ■2S to ^ £ s a a ■ s a ^s EP-- '« a p. "— t-i o.l o ■ o °> ^I'd »3 RS ^p; a^ *a x-^ as ' TJ ' * O g 5 ■& -S a a a a r3 S 3 .2 -^ ■3 s. a a .fc! p, ft S >, . 3 | go e -s ; S «h u&*- --' Hi ^ -^ iS -- J Z$& S ti- cs *^l 10 .5 (* C I 9 2 3 4 5 6 c 7 8 5 1 W II 12,0 Maximum Pull of Conductor in Tons Eig. 88. Weight of Steel Towers of various Overall Lengths and for various Loads. should be some 7 meters. Adding two meters for the embedded portion and one meter for the height above the lowest insulator, we arrive at a total length of 17 meters. Weight and Cost of Tower. 1 — The weight of the tower will depend on the length and on the maximum pull which it must withstand. The pull exerted by the conductors on either side of the tower under the worst conditions is the product of the maximum value of the tensile stress occurring in the conductor (10 kg per sq mm) and the 1 See also paper by D. E. Scholes on " Transmission Line Towers." Proceedings A. I. E. E., May, 1907. HIGH-TENSION POWER TRANSMISSION LINES 169 total cross sectional area of all conductors. Were all the con- ductors of one span to break, this pull would be exerted on one side of the tower only, and the structure should be designed to withstand this stress. The curves in Fig. 88 afford a basis for rough estimates of the weights of gteel towers. In the present developmental stage of power transmission practice, such data is far from standardised, and is liable to be greatly modified. Not only the length but the width of the tower will increase with the voltage, as the conductors have to be mounted farther apart. This, however, is taken into account in the curves in Fig. 88. The cost of towers may be estimated on the basis of £16 per ton. A suitable form of structure is that shown in Fig. 89, C and T>, which is the tower construction used on the Niagara- Toronto Line in Canada and on the Necaxa Line in Mexico. Concrete foundations will be necessary for the towers, and a figure covering the cost of the foundations must be included in estimates. The conductors must be supported on these towers, but well insulated from them by means of umbrella-shaped or petticoat insulators specially designed for high pressures, and rigidly fixed to the steel cross-arm and well away from the steel structure. Insulators. — The insulators used should be of porcelain, highly glazed to keep the interior perfectly dry. Insulators for high pressures are generally made in parts, cemented together with Portland cement or other suitable material. Glass has been used for insulators, one advantage being that any flaw is seen at once and elaborate testing is rendered less necessary. Porcelain is, how- ever, mechanically stronger and is more generally used. Insulators weigh from 5 to 15 kg, and cost from 5s. to 25s. each, including the insulator pin. The insulator pin should preferably be of galvanized iron, cemented into the insulator. In the construction under consideration there will be, normally, six insulators on each tower, i.e., 42 per km ; but in the case of copper conductors of 200 sq mm section, this would provide less than four insulators per ton of copper. In this case, therefore, we must take double the number of insulators, the weight of each conductor being supported by two instead of one insulator per tower (as illustrated in Fig. 89, A). The remaining items comprised in the cost of the line are the various pieces of auxiliary apparatus, such as lightning arresters, switches, etc., the cost of which may be taken as £30 to £45 per km. All the above costs are for the 170 HEAVY ELECTRICAL ENGINEERING A- One Single Circuit Line. Taylor's Fall Line. B-Two Single Circuit Lines. Lockport, Niagara and Ontario Line. C— One Duplicate Circuit Line. Niagara — Toronto Line. D— Two Duplicate Circuit Lines. Necaxa Line. Fig. 89. Classification of Overhead Transmission Lines. HIGH-TENSION POWEE TEANSMISSION LINES 171 prepared material only, delivered on site. There now only remains to consider the cost of erection. Erection. — The cost of erection may with sufficient accuracy for our present purposes be taken as proportional to the weight of material, and, as the cost pf the material in the case of such structures is nearly proportional to the weight, 10 per cent, of the total cost of material may be taken as being sufficient to cover i: §200 «J/00 si — (u 1 \\c 3 \\ 2\\ y ^M _ tb ©\ fa ' « v\\ ^^< C / -«o CO Q -». Jo iS 25 50 75 100 125 150 175 (Six Conductors) Cross Section per conductor. Sq mm e V. Hi 100^- 200 Fig. 90. Cost of Thkee-phase Duplicate Circuit Transmission Line (Copper Line). erection expenses. This of course is only very rough, but it is sufficiently accurate for the present investigation. Let us now proceed to estimate the total capital cost for duplicate circuit transmission lines at various voltages and having the copper sections given in Table LXV. Table LXVIII. (a) shows in detail the costs of lines for the various copper sections and the various voltages as found by employing the data and methods set forth in the preceding pages. The results are represented graphically in Fig. 90, which shows 172 HEAVY ELECTRICAL ENGINEERING the cost of a transmission line of any copper section between the limiting sections for various voltages. The cost is expressed in pounds sterling per ton of line copper, and as copper has been taken at £100 per ton, the scale on the right-hand side of the diagram gives the cost of the complete line minus the cost of the copper per ton of line copper, i.e., cost of tower, insulators and erection. Thus the total cost may readily be found for any given market price of copper, as for a given section of copper and a given voltage ; the combined costs of the other items may be taken as fairly constant. From these curves the ratio of Fin 25 SO ys too 125 iso /ys 200 (5/a Conductors) Cross Section per Conductor 90a. Cost of Three-phase Duplicate Circuit Transmission Line, with Aluminium Line Conductors. the total cost of line to the cost of copper can be taken, when hard- drawn copper is at £100 per ton. This figure is only 1,5 (for the larger sections of conductor), but for the smallest section rises to 2,6. Table LXVIII. (b) shows in detail the costs of aluminium lines where the price of aluminium wire has been taken at £200 per ton. The results are shown graphically in Fig. 90a. As in the case of Fig. 90, these curves can be used for any given market price of aluminium. HIGH-TENSION POWER TRANSMISSION LINES 173 . In Fig. 91 the total costs per km are plotted for various voltages, as a function of the section of conductor, and in this case, for the sake of comparison, the costs for the aluminium lines at 60 000 volts are also given. These curves show that under normal conditions, and with the above prices per ton of the two metals (i.e., copper £100, aluminium £200 per ton of hard-drawn wire), an aluminium line will cost £1500 £ £1000 £500 /S xA vy M Mi rfli r hjjS jggi y 6 50 100 150 ZOO (Six Conductors). Cross Section per Conductor: Sq mm Fig. 91. Cost op Three-phase Duplicate Circuit Transmission Lines. almost exactly as much as a copper line of equal conductivity. Thus from Fig. 91 a three-phase duplicate circuit 50 sq mm line at 60 000 volts would cost about £630 per km ; an aluminium line of equal conductivity, i.e., 82 sq mm, would cost about £640 per km. As another instance we may note that a copper line of 100 sq mm section would cost £980, and an aluminium line of 165 sq mm section would cost the same. The reason for this is that, (—) VO.61/ although the aluminium conductors weigh only 50 per cent, of the copper conductors, less than one-half the tensile stress can be 174 HEAVY ELECTEICAL ENGINEERING allowed in the wires, and consequently, on account of this and of the larger area offered to wind pressure, the sag and consequently the height of tower must, for a given span, be greater than that with a copper conductor. For comparisons at other than the above prices of the two metals, the curves of Figs. 90 and 90a must be used. 1 £ 1500 3 S;/fl00 o Is 00 1 , \ \ 1 \ ' \ G5i -Af2- % X '&. V %■■ 10 ZO 30 40 50 SO 70 Kiloi/olts between Conductors, 80 90 Fig. 92. Cost of Three-phase Duplicate Circuit Transmission Line ■with 0,3 per Cent. Loss per km eor various Voltages between Conductors. In order to show the significance of these results in relation to the power transmitting capacity of the line, let us estimate the cost of duplicate circuit transmission lines for transmitting various amounts of power at various voltages, and at a loss of 0,3 per cent, per km (or 0,1 per cent, per km per phase). Let us take the case of a duplicate circuit line capable of transmitting 32 000 kilowatts 1 See footnote on next page, and for a further discussion on the subject, see Metrical Beview, vol. 61, p. 872, November 22nd, 1907. HIGH-TENSION POWER TRANSMISSION LINES 175 (i.e., 16 000 kilowatts per circuit) at 30 000 volts between conductors, and with a 0,3 per cent, loss per kilometer at full load and unity power factor. Let us consider one of the two circuits : — v , 16 000 KQQ . Kw per phase — = — = 5334 o , n , , 30 000 Volts per phase ., = 17 320 I, ioa n , , 5 334 000 orio Current per phase ., QO = 308 amp. At a 0,3 per cent, loss per km we have : — Loss per km per phase = 5 334 000 X 003 or 16 000 000 x 0,001 = 16 000 watts. ^ • . i i 16 000 n1 „ n , Eesistance per km per phase = ,„„„ 2 = 0,170 ohm Eesistance of copper per centimeter cube (at 20° C.) = 0,000 0017 ohm a . ■ , , 0,000 0017 X 100 000 .*. Section per conductor = = 1,00 sq cm. From Fig. 91 the cost of a duplicate circuit line at 30 000 volts and 100 sq mm per conductor is found to be ^900 per km. 1 In a similar manner the costs for other voltages and other power capacities have been estimated, and the results are shown in Fig. 92. From these curves it is clearly seen that for transmitting even as much as 8000 kw over a duplicate circuit transmission line with a loss of 0,3 per cent, per km at full load and unity power factor, little advantage is gained by employing a transmission voltage of over 50 000 volts. For long distances, where the loss must be less than 0,3 per cent, per km, or for larger amounts of power transmitted, the economical voltage will be greater. It must be noted, also, that at high voltages and a given amount of power transmitted, the required section will fall below the 1 With hard-drawn copper wire at £100 per ton. If the current price of hard-drawn copper wire were £70 per ton, we should make use of the curves in Fig. 90. Thus, for 100 sq mm wire at 30 000 volts, the cost of the line, minus copper, per ton of contained copper is £75. We require 100 X 8, 9x10-3x6 = 5,3 tons of copper per km ; therefore the cost of the line per km, including copper, is (75 + 70) 5,3 = £770 per km. 176 HEAVY ELECTRICAL ENGINEERING X X CO J « * IS w V > -A 1 o C o IS co o O Creosoted Norway fir poles with oak cross-arms Steel lattice poles, 3 conductors per pole Steel lattice poles, 6 conductors per pole Steel poles, wooden cross-arms Wooden poles and cross-arms Cedar poles with fir cross-arms Steel Towers Galvanised steel towers Galvanised steel towers Steel towers Steel towers, 6 con- ductors per tower Cedar or Cyprus poles i "sja^apj 'sio^onpuoo uaaA^aq aoire^stQ in 0" O O" O" 0,6 (min) 0,S5 2,0 2,12 2,0 1,82 1,82 1,82 ■uiuibs 'jopnpuoo J9d uoi^09S l^ox -* O CO co in cm CM CO *# Tti co m ^ cm © in © Q T)< 10 h- CO -* "- 1 ■sioq.onpuoo jo laqnm^ CO O CO CO CO CO CO CO CO CO CM CO ■raui *jo^onpuoo jo jojounnci cT Oi CO CO in m *~ co" co" ir- O CM cq *, i-l oj H 'S^O^ Sui^.BJ9U99 13 500 1000 3500 m t~ 2300 4000 15 000 •puoaas -i?d sapA'o A'ouanbaiji in cm in -# O CM OOO m co m 10 (M CO CM «0 O ■urg; 'uoissilusu'b.tx jo sou^siq; m CM O OO co co m -* cm in CO CO co m m cm i— to CM r- rH i-H CM ■Aia UI UOISSiraSUEJJj I9A\0 co is, si 1& ,-= cct H ft CD B u So « u s| Paderno to Milan, Italy 'Clermond - Ferrand Line, France Toulon Line, France, (Societ6 Energie Electnque) Los Angeles to En- gel wood Gromo to Nembro, Lombardia Missouri Power Co., Montana Syracuse Line Ontario Power Co. Guanajuato Line, Mexico Niagara to Toronto Winnipeg Line, Manitoba Necaxa Power Co., Mexico Grand Rapids Mus- kegon Power, Co. •jequinti - CM CO "# m CO CO OS O i-l ©1 CO rH HIGH-TENSION POWEB TEANSMISSION LINES 177 a 1 pq ^ h-i ~ « -c < H "fe> s M 4 09 CJ s . ■g,co Is B a l'-i d Si O ii ^ O C rl ■1 CD . s 1 h- r-i © _ 1 g ^ ft •UOT^'BJSdO o o CO O CO JO q.U9UI90U8UilUO0 JO JB8Jt s - 1 J5» u a u ft ft CO o "8 (3 CO a CO "■a 3 at at ft s ft a ft -co ■§§ si Ph r3 o o |S T3 O o o IS Is W "en •sja^api 'punojf) in iftdaci CO "SJajaj\[ 'J9AVOX ^ jo o © CM co" o Cl CO CM CO o o *sq.|OA 2aryBiau9£) o CM CM o co CI o o CM o ■puooag aad sajoXQ Xouanbajj O CO o CO CM o CO CM CO CO o co ^ O Tf<- fc- CO -* CM O o o o - •AV2 lit uoissinisuuij, J8A\.0l (',, V V Curves plotted From Jona's Formula . R=antilog l0 (0, 434 fa * log r) where r-radius oF Copper Oore. R=r + depth oF insulation. - wSaFe stress in volts perm.m. w taken as 2000 i.e. a saFety Factor " S, paper having a normal dielec- - vc strength oF 10000 volts perm.m. -ti 1 i i i I 10 20 30 Working value of effective kilo volts between Cores, V. 40 Eig. 95. Insulation Thickness foe Homogeneous Cables from Jona's Formula. voltages and for various minimum radii of curvature. These curves have been plotted from the formula given by Jona. It will be noticed that for pressures of over 20 000 volts, and for cores of normal radii, the thickness of dielectric becomes too large where w is the maximum stress in volts per mm that the insulating material can safely withstand. At surface of insulation (dv\ _ 0,431 V \dp) R Eloo R minimum stress. B Ratio of maximum to minimum stress = — . r Note. — There is a certain value of r, which for a given R gives the smallest value of maximum stress w possible. This value of r = — = . e 2,71 HIGH-TENSION POWER TRANSMISSION LINES 183 to be practicable. It is possible, however, to reduce this depth of insulation by placing near the core a material of higher dielectric strength. This procedure is known as "grading" the insulation. Thus we can have several layers of different dielectrics, materials of higher dielectric strength being employed for the inner layers where the dielectric stress is greatest. By this means the overall diameter of the cable may be considerably reduced. When we vary in this way the nature of the dielectric, there is 32 / 1 / 28 f rfl 24 i/ fit vy '''' < i 5^ ie < 7 J # 4\ A ^ y^ With these values thesafety fac- tor will be 3 or more depending on the quality of dielectric used, ris the minimum radius of curv- ature when the conductor has not a circular section. jous 4 Horj o<# 10 20 30 Kilo volts between Cores 40 Fig. 96. Thickness of Insulation of Gkaded Cables foe Alternating Cueeent. another important point to be considered. This relates to the effect on the potential curve of the varying dielectric capacity. 1 Care must be taken that the " specific capacity " of the dielectric decreases in proportion to its distance from the core. This has the effect of decreasing the steepness of the potential curve near the core and increasing the steepness near the lead, thus putting a more uniform stress upon the dielectric. In this way the required thickness of dielectric is further decreased. By a combination of the above two principles, we may reduce See Q'Gorman, Journ. I. E. E.. vol. xxx. p. 60S. 184 HEAVY ELECTRICAL ENGINEERING the necessary thickness of material considerably below that which the curves in Fig. 95 would indicate to be necessary. Lastly, Jona and others have ascertained experimentally that for cables with very small cores at high voltages, the insulation required is, when correctly applied, very appreciably less than that calcu- lated, there being some other phenomena as yet unexplained. For the purposes of the following investigations, the radial thickness of the insulation will be taken from the curves in Fig. 96. A minimum radius of curvature of 3 mm will be taken for voltages over 5000, and a thin sheath of lead will, as proposed by O'Gorman and Jona, be placed round the stranded core so that it shall conform to this curvature. At 40 000 volts the diameter of core for low values of the kilowatts transmitted comes out less than this lowest value shown, and in these cases an aluminium or a tubular conductor of the minimum outside diameter might be used. For high voltages it might often be advisable to use an aluminium conductor, since the radial depth of the required insulation decreases rapidly with increasing radius of curvature of the core. Jona has shown that if a stranded core is not covered with a lead sheath, the stress is liable to be increased to 1,2 — 1,4 times the amount obtaining for a smooth core. To allow for tbe room taken by this lead sheath, which, however, may be very thin, and also for the fact that the core is composed of stranded wire, the real copper section is increased by one third, and this figure is called the apparent section. Since the cores are twisted, an addition of 3 per cent, is made on the length of cable in estimating the weight of copper per km. The space factor of the three-core cable is estimated thus : — Space factor - 3 X real cross section core Cross section up to the internal wall of the lead covering Suitable thicknesses of lead covering are given in the following table : — ■ TABLE LXXII. Showing Suitable Thicknesses of Lead for Three-core Cables. Diameter of Insulated Cable in Mm. Thickness of Lead Covering in Mm. 50 75 100 4,0 4,5 5,0 HIGH-TENSION POWEB TRANSMISSION LINES 185 Estimation of Cost of Three-core Cable. — The cost of the materials used in the manufacture of cables will be expressed in pounds sterling per ton. Let us first estimate the weight of material used. The section and length of the cable being known, we require only the specific gravities. The following values may be taken : — Weight of 1 cubic dm of copper . . . = 8,9 kg „ „ „ „ lead . = 11,4 kg „ „ „ „ jute . . . = 1,2 kg „ „ ,, „ impregnated paper . = 1,2 kg From these values the respective weights of the various materials used may be estimated. The prices per ton of material may be taken as follows : Copper per ton = £95 Lead „ „ = £20 Impregnated paper per ton . . . = £40 Eaw jute per ton = £30 In order to estimate the Total Works Cost of the finished cable, the cost of labour and other costs must be added. The following figures taken from O'Gorman's paper before the Institution of Electrical Engineers 1 give some idea of the proportions these costs bear to one another, but these figures will not be used in the present investigation : TOTAL WORKS COST. Proportioning of items (O'Gorman). (1) Copper. £ Cost of copper per ton 95 - Cost of wire drawing ..... 5 Cost of stranding 7 Shop costs and administration . . . .10 Total cost per ton . £117 (2) Lead. £ Cost of lead per ton 20 Cost of labour 3 Cost of administration, etc 7 Total cost per ton . £30 Journal, I. E. E., vol. xxx. p. 6-14. 186 HEAVY ELECTRICAL ENGINEERING (3) Impregnating Paper. £ Cost of impregnated paper per ton . . 40 Cost of labour ...... 10 Cost of administration, etc 20 Total cost per ton . ^70 (4) Jute. £ Cost of jute per ton ...... 30 Cost of labour, etc. ...... 3 Total cost per ton . £33 (5) Rubber. Cost ir. per ton (pure para rubber) . . £400 For our present purposes we shall employ the following values : — Cost of materials in the form in which they are delivered to the Cable Manufacturer. Hard drawn copper wire . . £100 per ton Impregnated paper ) Eubber /-taken together . £40 to £60 per ton. 1 Jute filling > Lead ...... £20 per ton Hard drawn aluminium wire . . £200 per ton Using these values, we obtain the cost of material per km of completed cable. ESTIMATION OF TOTAL WORKS COST. Having estimated the total cost of material for any proposed cable, we shall multiply this by a constant which we shall designate as the " Works Cost Constant," in order to obtain a rough figure for the Total Works Cost of the cable per km when turned over by the Manufacturing Department to the Sales Department. This constant will depend on the quality and quantity of labour, etc., required to manufacture the cable from the above material, and will also be affected by local conditions, cost of labour and power, composition of cable, etc. With increasing voltage, more care will have to be expended on the insulation, and as the material cost decreases with the voltage, except for extra high voltages, for 1 The cost of the insulation is taken at £40 per ton for a 10 000 volt cable and £60 per ton for a 50 000 volt cable, as, at the higher voltages, the insulation will be partly rubber and will have to be careiully graded, HIGH-TENSION POWER TRANSMISSION LINES 187 a given copper section, the value of the constant will increase with the voltage. For a given voltage, the labour expressed as a percentage of the total cost of material will decrease with increasing copper section, as the labour required will not increase to such a degree as the outlay for material increases. Taking these points into consideration, the curves in Fig. 97 have been deduced, showing the value of the " Works Cost Constant " for different copper sections and voltages, the curves being based on values worked out from actual cases. Table LXXIII. gives the costs of cables corresponding to the z,o 1,8 ip. *s^ ^ fa i,e ^,/z Q£ *<£/ &* ,** r^S. "3>?, 4i& * 'A 1,2 WO ZOO 300 Real Cross Section per Core. Stj.mm. Fig. 97. Works Cost Constant foe Three-core Cables, as Function op Copper Section and Voltage. various copper sections and voltages between cores set. forth in Table LXX. The various items have been estimated according to the method given in the preceding pages. The curves in Fig. 98 are plotted from these results and give the Total Works Cost of a cable of any given copper section, per core, at various voltages. The T.W.C. is expressed in pounds sterling per ton of contained copper. The results are obtained by taking the price of copper as being ,£100 per ton. The price of copper varies, however, within wide <* 1- © iO I-- 1-COcoo-* t-c»c© oo CO O CO *~ CO CO t-Oi °LOl I~ CD Co"cO '-' ■* CO GJ rH CO CO CM O CO lOOMmH ^ IN (M N I- H H -V* rH co CO CO CM **_ CJ hHHCTiO' ^,t— CM W to iO co_ CO 1 i> d O O >* Ol IO CO ON Ht >-i50_r>-i i-i 1 _ C 2' : »eMTt<'HH_0 CDC 0_ -t- rH CQ ^< ^ ci <°_±- -* u 00*| 00 r+^ r ^-rm co co cm ^o co co ^ . . , - jio r-r-^S COrJ "# r-tm r "•Eo c^crtqicrt «ll*gcftC|J ■~ O CJ 7. -. o CD ■v ■2 n :c ti ■+-> c5 o s a 5.2 *i3 a; rQ 5 o (H J > o t! 183| r ■'' Sta fo£ £ £ p w,HrH O u ooooot HOOOEhP 3 5. & oho 33 &3 o o o o fcHH H & HIGH-TENSION POWER TRANSMISSION LINES 169 limits. For a given section of copper and a given voltage, the size of cable, and all costs, with the exception of that of the copper, U.UU 1 1100 II \ 1000 10 \ \ $5 900 1 "8 800 5 9 \ "5 8(5 \ 1 \ \ 1 o 1 **■ 600 o &> o to is soo 7 *KJ \ v QJ O UJ -o <3 .'IB \ \ \ «£ V > ■a ■o K 400 O ^ -> 300 <5 K* 200 Jt£ 5?> too / 1000 900 800 h S v 700 eoo soo 100 zoo Real Copper Section per Core.- Sq. mm 300 ! 400 t. ■a. 300 K 200 100 Fig. 98. Cost of Three-phase Three-core High-tension Cables. remain constant (as the combined cost of lead, insulation and labour may be taken as fairly constant). From the ordinates on the right of Fig. 98 we can read off the 190 HEAVY ELECTRICAL ENGINEERING T.W.C. per ton of contained copper, minus the cost of the copper itself. Therefore, in order to estimate the cost of a cable, we have only to read off this cost from the curve and add to it the current price of hard drawn copper wire per ton. This gives us the T.W.C. of the cable per ton of contained copper. Multiplying this by the total weight of copper in the line, we obtain a rough estimate for £3000 i.£tooo ■c to to <*. o j^ <* ^ )V- 5"° 100 ZOO 300 Real Copper Section per Cor e-sq.mm. Fig. 99. Cost op Three-phase Three-core High-tension Cables. the T.W.C. of the complete cable as turned over by the Manufac- turing Department to the Sales Department. In Fig. 99 the T.W.C. of the cable per km, with copper at £100 per ton, is plotted for various voltages as a function of the section of conductor. As in the case of the overhead line, the significance of the results is again best shown by means of examples. Let us, as before, take the case of transmission lines of various capacities as regards the number of kilowatts of energy to be trans- mitted and at various voltages, and for a loss of 0,3 per cent, per km. In this case, however, let us take one cable, i.e., a single HIGH-TENSION POWEE TEANSMISSION LINES 191 three-phase circuit. The copper section necessary is calculated in the same way as before. From this the weight of copper per km is obtained and finally the cost per km at various voltages. The results are given in the curves of Fig. 100. From these curves we see that with copper at £100 per ton, and with a line loss of 0,1 per cent, per km per core, a pressure of about 15 000 volts corresponds to the cheapest cable for 1000 kw, but for transmitting large amounts of power, higher voltages correspond £ s-6000 6 Q 5000 \ < 1 \ to o \ CI ^3000 \ i Szooo V s N v ^ \ s*Cj 7 r>.- 2V - ^ & 1000 "$ %& (T"] "^ %■ - 10 20 Kilo volts between Cores. 30 H-0 Fig. 100. Cost op Three-phase Three-core Cables at different Voltages between Cores, with 0-3 per Cent. Loss per- km. to cheaper cables. The cheapest cable for a 16 000 kw transmission works out for a pressure of 28 000 volts. The increase in depth of insulation required for wire of small diameter causes the cost of the 8000 kw cable to be more than that of the 16 000 kw cable when a pressure of 40 000 volts is employed. The 8000 kw cable at this pressure would have been cheaper and smaller if the strands had been wound round a central core of jute, as the diameter over the thin lead sheath would have been greater. In Fig. 101 the most economical voltage is plotted as a function 192 HEAVY ELECTRICAL ENGINEERING of the kilowatt transmitted per cable. These curves have been deduced directly from the curves of Fig. 100. The curve of Fig. 102 gives the cost of cable per km per kw transmitted at the most economical voltage as a function of the kw transmitted per cable. Insulated Cables of other Metals than Copper. 1 Although copper has been, and is still, the recognised metal for the cores of electric power cables, the supply and the price of the 30000 20000 y w •w / / § / 10000 4000 20000 8000 12000 16000 Kw. Transmitted per Cable. Eig. 101. CURVES SHOWING MOST ECONOMICAL VOLTAGE FOE, KW TRANSMITTED PER GABLE AT 0,3 PER CENT. LOSS PER KM. metal are by no means steady, and there is always the possibility that another metal or alloy may become more suitable. Indeed, cables having aluminium as the conducting metal are already on the market. The curves given in Fig. 98, although intended in the first place for copper cables, can be used as a basis for estimating the cost of three-phase three-core cables with cores of any other metal. On the right-hand side of Fig. 98 we have as ordinates " the T.W.C. of cable per ton of contained copper minus the cost of the copper conductor itself," i.e., the T.W.C. of a complete cable (of such a length that it contains one ton of copper) exclusive of the cost of the conductor. 1 See also " Aluminium as a Substitute for Copper for Electrical Transmission Purposes," Electrical Review, vol. lxi. p. 796, November 15, 1907. HIGH-TENSION POWER TRANSMISSION LINES 193 Now, for a given section of conductor, a cable containing one ton of aluminium will be longer tban a cable containing one ton of copper, in the inverse ratio of the specific weights, i.e., in the ratio of 8,9 to 2,7, or in general in the ratio : — Specific weight of copper Specific weight of metal used For a given section of conductor, the cost of the insulation per unit £ IP °A i •3- OJ 0.2S 0-2 0,IS 0,1 005 \/ot OH.ll 'at /BOO OK [200 OK Vat iaoc OV. \ao WK W c it 21 10V. t 80 WK. vy a l .24C 00 V wc OO/I w. at2& 000 V. 4OQ0 8000 12000 Kilowatts Transmitted 16000 Fig. T02. Cost of Cable pee km pee kw Transmitted with Increasing k¥ (foe most Economical Voltage), with 0,3 pee Cent. Loss pee km. length will be independent of the metal used as conductor. There- fore, to find the " T.W.C. of cable per ton of aluminium, minus the cost of the aluminium conductor itself," we must multiply the 8,9 ordinate of the right-hand side of Pig. 98 by 2,7' We have now the means of readily estimating the cost of an aluminium cable of any section. h.b.e. o 194 HEAVY ELECTKICAL ENGINEEKING (A.) As an example let us estimate the cost of a three-phase, three-core aluminium cable of 82 sq mm per core for 10 000 volts working pressure. Weight of aluminium per km (allowing 3 per cent, for stranding) 82 X 2, 7 X 8 X 10~ 3 X 1, 03 = 0,685 tons. Cost of aluminium cores per km (aluminium wire at £200 per ton) — 200 X 0,685 = £137 From Fig. 98 we find that theT.W.C.of cable per ton of copper, minus cost of conductor, for 82 sq mm and 10 000 volts is equal to £180. Therefore T.W.C. of cable per ton of aluminium, minus cost of conductor, for 82 sq mm and 10 000 volts is equal to £180 x || = £593 or T.W.C. of cable per km minus cost of conductor = £593 X 0,685 = £406. Therefore Total Works Cost of cable per km = £406 + £137 = £543. (B.) For the sake of comparison let us work out the cost of a copper cable of equal conductivity and for the same working pressure. Section of copper = 82 X 0,61 = 50 sq mm Weight of copper per km = 50 X 8,9 X 3 X lO - " X 1,03 = 1,38 tons. Cost of copper per km (with copper at £100 per ton) 100 X 1,38 = £138. From Fig. 98. T.W.C. of cable per ton of copper, minus cost of conductor, for 50 sq mm and 10 000 volts = £240. Therefore T.W.C. of cable per km, minus cost of conductor = £240 X 1,38 = £331. Therefore Total Works Cost of cable = £138 + £331 = £469. 469 That is —77: = 0,865 times the cost of the aluminium cable. 543 (C.) Let us now estimate the price per ton of copper, in order that the copper cable should cost the same as the aluminium cable, when the price of aluminium is at £200 per ton. Cost of cable to be £543. But cost of insulation, etc. = £331 (see above). Therefore cost of cores will be £212. Weight of cores = 1,38 tons. 212 Therefore cost of copper per ton = — -— = £154. 1,08 HIGH-TENSION POWER TRANSMISSION LINES 195 (D.) Or we can estimate the price per ton of aluminium in order that the aluminium cable should cost the same as the copper cable, when copper is at £100. Thus the cost of cable = £469. But cost of insulation, etc. = £406. Therefore cost of cores = £63. Weight of cores = 0,685 tons. I.e., cost of aluminium per ton = _ „„„ = £92. r 0,685 The above results are summarised in tabular form in "Table LXXIIIa. TABLE LXXIIIa. Comparison of Costs of Copper and Aluminium Cables. B D c A 10 000 Volt Three-phase Cable. Cu. Al. Cu. Al. Section per core (sq mm) 50 82 50 82 Weight of metal per km (tons) .... 1,38 685 1,38 0,685 Cost of metal per ton (£) 100 92 154 200 Cost of metal per km (£) 138 63 212 137 Cost of insulation, manu- facture, etc., per km (£) . 331 406 331 406 Total cost per km (£) . 469 469 543 543 For very high voltages and small sections, the larger diameter of the aluminium core permits a smaller depth of insulation (see Figs. 95 and 96 on pp. 182 and 183 of this Chapter). Take for example the exceptional case of a 40 000 volt cable, 50 sq mm for copper, 82 sq mm for aluminium. The cost of complete cable works out at £1850 per km for the copper cable, and £1770 per km for the aluminium cable, i.e., the aluminium cable is a little cheaper. This is, however, a very exceptional case, and with the present prices of the metals and for normal cases, the aluminium cable will, for high-tension work, be more costly than the copper cable. Underground Construction. — The curves in Fig. 98 give the cost of cable as delivered by the Manufacturing Department to the Sales Department, and in order to compare the total outlay for an underground with that for an overhead system we must estimate the costs of the underground construction. The cost of the insulated cable corresponds to the cost of the o 2 196 HEAVY ELECTRICAL ENGINEERING wire and insulators of an overhead system, and the cost of the underground construction corresponds to the cost of the steel tower construction, including labour in all cases. As, however, the avail- able data for the cost of underground construction vary over such wide limits, it was decided not to include this item in the curves for the cost of cable. The form of underground construction in most general use is that in which the lead-covered cables are drawn into vitrified clay- tile ducts, embedded in concrete, and buried 0,6 to 1,2 meters under the surface. 1 The conduit can be of either single or multiple duct 79T? CD '/' // V // / / / / / ssggr^r? // / / / / / / / / / / ''/.'/" / / . / / / / / / / . / ' '/'//'-//.I'/ /, . A/ / / yz^Sprukd '/ s / / / / Concrete/ ' Eig. 103. Section through Undergbound Conduit. construction, the former being preferable. The holes should be square, not round, on account of the greater ease with which the cables may be drawn in in the former case. Four to six duct multiple duct conduit is customarily supplied in three-foot lengths, and two duct multiple and single duct in shorter lengths. It is preferable not to place more than one cable in a duct, but if the cables are small it may become necessary to do so in order to avoid waste of duct space. 1 For a full description of such a conduit line, see the paper on ' ' Under- ground Construction," by W. P. Hancock, read before the National Electric Light Association at Boston, May, 1904, and published in the Western Elec- trician, June, 1904. See also the paper presented to the St. Louis Congress by L. A. Ferguson, 1904 (Transactions, vol. ii.). Also a paper by W. D. Burford Electrical World, Feb. 10, 1906. HIGH-TENSION POWEE TEANSMISSION LINES 197 The internal diameter of standard ducts varies between 8 and 12 cm, and consequently if cables having the dimensions given in Table LXXIII. are used, each will be placed in a separate duct. Manholes should be at intervals, preferably not exceeding 150 meters, in order to give easy access to any part of the cable, and also to facilitate pulling in. When a large amount of power is to be transmitted, it is, in the case of an overhead system, sometimes thought advisable to construct a double tower line. In the same way, it is thought advisable to construct a double conduit line, the conduits being preferably laid in different streets. If too many cables are buried together, the temperature rise may be considerable, as the heat generated is not easily dissipated. The following is an example of a 15 duct conduit, given by Hancock in the paper to which reference has been made. It is reproduced to show the relative costs of the various items. The conduit was composed of 15 single clay ducts cemented together with mortar. These were embedded in concrete (5 parts mixture, 1 part cement, 2 parts crushed stone, 2 parts sand), the thickness of the concrete being 7,5 mm at the sides and top, and 10 mm at the bottom. The boards at the side and on top were of spruce. The depth from the surface of the road to the top of the conduit was one meter (see Fig. 103). Hancock's estimate was as follows : — Excavation and reinstalment 3,9 shillings per cubic meter. 2,5 cm spruce boards Concrete mixture . Clay ducts (delivered on site) . Eoad stone block paving on concrete base (pitch filling) 9,5 ,, ,, sq meter. Taking these values the cost per meter of conduit worked out as follows: — Excavation and reinstalment 1,1 ,, sq meter. 25,4 „ ,, cubic meter. 0,65 „ ,, duct meter. Spruce boards . 2,0 „ Concrete mixture 4,6 „ Clay ducts (delivered) . 9,8 „ Stone block paving . . y,y ,, Engineering expenses (labour, etc.) 10,5 „ 42 shillings i.e., £2100 per km (see table). 198 HEAVY ELECTRICAL ENGINEERING Table LXXIV. gives the total cost for conduit laying as given by various authorities. TABLE LXXIV. Estimates of Total Cost/ or Conduit Laying. +3 ■5 Component Costs. *- !~> 3 or c o CJ .5 tJD «l O °c p ^■S rf^W ~H » Q Authority and v. ~ o \A fe '£,_} i- d-i Particulars of Construction Reference. "S h ft ■!■«» c5 and Location. Qt o D o w ft Sot a o H -P O H 8" » c c S § g o s 55 £ £ £ £ £ Highfield, Journal 620 207 — — 3 Stoneware conduit laid I. E. E., p. 496, along country roads vol. 38 Andrews, Journal 220 220 1 Stoneware duct laid in 1. E. E., p. 529, concrete in country dis- vol. 38 tricts Watson, Journal 320 107 110 210 — 3 Duct conduit in country I. E. E., p. 529, district vol. 38 Burford, Elect. ) 810 202 165 265 390 4 Clay tile conduit em- World, Feb. 10,1 940 157 180 370 390 6 • bedded in concrete 1906 ) 1100 137 290 420 390 8 brick-paved road Springer, Elect. World, Feb. 10, • 1906 560 780 1120 140 130 280 — — — 4 6 4 Conduit under macadam road Conduit tinder asphalt 1440 240 — — . — . 9 road Ferguson, St. Louis Congress, - 1904 880 220 — 4 ) Clay conduit under stone- f block paved road ) Clay conduit under 1110 1080 185 270 — — — 6 4 1320 220 — — . 6 ] asphalt road Hancock, Western 2100 140 264 1320 516 15 Clay conduit under stone- Electrician, June, block paving 1904 As a basis for estimating the cost of any conduit line, the figures in Table LXXV. are of service. These figures are deduced from data given in the above-mentioned papers. To this must be added the cost of pulling in the cable, which may be taken as £20 to £50 per cable per km r depending on the size of cable, also the cost of the manholes, about six per km, and each costing from £15 to £35, depending on the size of the manhole. Section 4. — The Efficiency of the Transmission Line. On page 4 Kelvin's law was stated as follows: — "Maximum economy is obtained when the annual cost at the generating station, HIGH-TENSION POWER TRANSMISSION LINES 199 of the power wasted in transmission, is equal to the interest, depreciation and maintenance of the transmission line." To this, however, should be added, "when the cost of the trans- mission line may be expressed as a function of the copper section, without any constant figure." In the case of an underground conduit line there is a large figure for the cost of the underground conduit and trench. This figure remains practically constant for all sections of copper, and consequently a modification must be made in this case, the maxi- mum economy being obtained at a higher efficiency than that indicated by the precise wording above set forth. If the figure for interest, depreciation, and maintenance could be TABLE LXXV. Approximate total Cost of laying Single duct Clay Conduit in Pounds Sterling per Duct per Km. Number of Ducts. No Paving. Stone Block Paving with Pitch and Pebble Joints at 10s. per Sq Meter. Asphalt Paving at 17s. per Sq Meter. l 2 4 6 9 12 220 140 110 90 90 90 500 300 200 160 140 130 700 450 260 220 190 170 resolved into two components, a constant component and a vari- able component, then the efficiency for maximum economy would be that for which the variable component is equal to the value of the wasted energy (see Fig. 103a). To show the influence of the efficiency of the line on the cost of transmission, the following case has been considered. An annual transmission of 50 million kw hr over distances of 25, 50 and 100 km, under the following conditions : — Power factor 0,9. Cost of energy at generating station 0,5 pence per kw hr. Both overhead and underground lines are considered, a duplicate circuit transmission line being taken in all cases, i.e., a single tower line, carrying two three-phase circuits, or a single underground conduit containing two three-core cables. 200 HEAVY ELECTEICAL ENGINEEBING To show the method employed, let us work out two examples, one for an overhead line and one for an underground line. 3 I 4 d5 f X <, r _! *S 1 ■,* ^ rf? \y | e° c y i S' \ \ h. 1 [st- y* * s if / ' .•p & 10000 1 1 / ^ % 1 / ^ X \ ¥ Y 1/ fe K / a l Ni V V^-* i*r 5000 / / :§ £ — 1 1 '■£§, ^ \o o£j l nl [ nr+ h— / i 1 . Ji i i l Cot star t imp: w« t i I ' i t ■ ' 5 /O Z./ne ioss /"/? Percent. 100 85 Fk 95 90 Line Efficiency in Percent 103a. Determination of most Economical Line Efficiency fob Transmission of 50 Million icw he pee Tear over a Distance of 25 km. (Two Three-core Cables (20 000 Volts between Cores) laid in One Underground Conduit.) A. — Overhead Line. Take the ease of a 20 000 volt transmission over a distance of 50 km, and 50 million kw hr delivered annually. i.e., an average of 5700 kw delivered, or 2850 kw per circuit, or 950 kw per conductor, Power factor = 0,9. Therefore kva per conductor = 1055 kva. 2 Cable Underground Conduit Line. 2 Circuit Overhead Tower Line. Ordmates denote Cost in Pence per kv> hr at receiving End of Line c >> <5 en <*> vi Co / . / to /A Q $ to i ft / § \ to ( CD ^ Cr, oi Si f\ O} ]>/ I s Si VFZ. c i F *. V Co / Oi C2 1 L*=5 1 \^ *>. fe. % ^ Co en 55 Co / <*> , to / h o z V* to ir *» / ^ In ■fo (i to L fe $ 4? \ §, r "cn _C3 05 Vi CD / / o> / to V. o / L V * ^ ■fe o to \ A 5 a o CM 1 ft CO ru a 5 'in f\j a a. n> <3 » t ^ 0. ^ fc- -^ 5 to n> Co HIGH-TENSION POWER TRANSMISSION LINES 201 Volts per phase = 11 530 volt. Therefore amps per conductor = 91,5 amp. Take the case of an annual efficiency of 96 per cent. Then watts lost per conductor 40 000 watts. Total resistance per conductor = = 4,79 ohms, or 0,096 ohms per km. This corresponds (o a copper section of y^ = 182 sq mm. 1 This gives a weight of 1,68 tons of copper per km, or for 6 con- ductors and 50 km, 504 tons. With copper at £100 per ton : — Total cost of copper = £50 400. Prom Fig. 90 the ratio of total cost of line to the cost of copper at 20 000 volt, 182 sq mm section is 1,5. .-. total cost of line = £75 600. For an overhead line the interest, depreciation and maintenance may be taken at 16 per cent., i.e., £12 100. Cost of 50 million kw hr = £104 000. Cost of kw hr lost = £4500. Therefore total cost of the 50 million kw hr at the receiving end is £120 600, which is 0,58d. per unit. This value is plotted in Fig. 104. The other points on the curves of Fig. 104 have been calculated in a similar manner. B. — Underground Lines. ■As before, let us take the case of a 20 000 volt transmission over 50 km at 96 per cent, annual efficiency. Watts per core = 40 000 watts. Corresponding to 0,096 ohms per km as before. This corresponds to a copper section of ' ■ = 194 sq mm. The specific resistance is taken higher in the case of underground cables, as the average temperature will be higher than that of an overhead conductor. An aggregate weight of 540 tons of copper is obtained. With copper at £100 per ton, the total cost of copper is equal to £54 000. 1 If the " Load Factor" is assumed to be 0,5, then the maximum, current per core will be 183 amps, and the current density only 1 amp per sq mm; i.e , about one-half the maximum permissible, as given in Table LXXL, p. 180. 202 HEAVY ELECTRICAL ENGINEERING From Fig. 98 the ratio of total cost of the cables to the cost of the. copper, at 20 000 volt, 194 sq mm section, is 2,4. Total cost of cables = ,£129 500. From Table 97, the cost per duct km for underground conduit in a country district is £140. For 50 km of two-duct conduit, cost will be £14 000. Taking 6 manholes per km at £25 each, cost will be £7500. .g o .0) G 1 1 Oyer head Line. Underground Line. 100% 98 96 34 32 90 88 86 84 82 80 C 98 96 34 32 90 88 8S 84 82 80 C f ,i §S f CO CO CO CO O CO 0+3 50 -<* ' 1 OS I CO CO I I CO (M CO -* I 1 CM CO CO CM O O tff M ■3 W 1 CO 1 GO OS 1 j GO CO OS I | rH CO t> CO fi rH (M >-H rH t— ( r—< CM CO iQ a —^ 60 o5 -u 00000000 O OOOOO O O 1 00000000 O O HH O O O 10 O t i> 1 CO -* CO CO »o »o CO to CO i--- O CO iO CM CM CO rH CM iO CM CN -P Pn 1-1 co N "HMCOH r ~' CO CM t- O * * -2 d CO lO tN CO ■ vi ■■;■ 1 - CD CO CM HH CM "* CO CO -* fc rH CO • , '■ , - — , — ' ■ini[ ■+3 'imDJio jo O -* t- i« N ON IO CO OOO O CN O c CN CM CO CO U3 COlO CO CM CO CM CN CO <-* CO 1-1 CO & •sdiuy ia O O >o OOO JO IO OOO O O 10 Eh 'qugjjmQ 9017 -& »0 ■>* CO IO JO iO CO CO CO 10 -H CO IO l> * •Suppo^ JO qU9UI OS 1-1 CO »o QJ P 5" CO . QJ so CO e§3 rti w r-t QJ OJ -^ CO QJ s| ^ 03 p o3 cr pi S3 CD „ CO K- OJ fH P « P h =3 l.g'la^ S » a 8 as Ph g r^ DOSD SCO a k QJ § HIGH-TENSION CONTINUOUS CUEBENT SEEIES SYSTEM 205 situated on the edge of the area to be supplied. In the case of the alternating current system, this is by no means the most suitable location. The cables are assumed to be laid along country roads. Their locations are indicated in Fig. 106, the full lines represent- ing the continuous current cable routes, and the dotted lines the POWER STATION 7000 KW. Alternating Current Cables shown dotted lines. Continuous » " >• Full » SuhsiAtJgns thus • Eig. 106. Diagram of Typical Bulk Supply Area. alternating current cable routes. The sub-stations are indicated by the small black spots. The alternating current system is the three phase star system, with the neutral point of the system earthed. The voltage between cores is taken at 20 000 volts. The continuous current system, with 100 000 volts total pressure, is earthed at the middle point, conse- quently the insulation between core and lead sheath must be sufficient to withstand a working pressure of 50 000 volts. Let us first consider the transmission line, and let us begin with the cables employed for the alternating current system. From the 206 HEAVY ELECTEIOAL ENGINEERING generating station to sub-station 4 there are two three-core cables, section per core 48,5 sq mm ; from the generating station to sub- station 13, two similar cables, and from sub-station 13 to sub- station 12 one such cable, giving a total length of 84 km of this 48,5 sq mm three-core cable. The cost of these cables may be estimated as follows : — Section per core 48,5 sq mm. Tons of copper per core per km . . . 0,445 Tons of copper per km .... 1,335 Cost of copper at £100 per ton . . £133,5 From Fig. 98 ratio of cost of 20 000 volt lead-covered cable to cost of contained copper = 4,75 Therefore cost of cable = £634 per km. (Highfield gives £650 per km.) Cost of 84 km of this cable = £53 200. The cable connecting the other sub-stations has a section per core of 32,2 sq mm, and a total length of 106 km. Section per core 32,2 sq mm Tons of copper per km .... 0,885 Cost of copper per km .... £88,5 From Fig. 98 the ratio of the cost of 20 000 volt lead-covered cable to the cost of the contained copper = 5,8 Therefore cost of cable = £512 per km. (Highfield gives £560 per km.) Cost of 106 km of this cable = £54 400. We cannot make use of Fig. 98 to estimate the cost of the con- tinuous current cable, but we can estimate the cost ' in the same way as was done in Chapter VIII. In this case there is only one cable 135 km long, with a single core of 64,5 sq mm. This core will be stranded, and will thus have an apparent section of about 87 sq mm and a diameter of 10,5 mm. The first question to consider is the thickness of insulation necessary. So great a thickness as that indicated in Fig. 96 will not be required. For a sine wave alternating e.m.f. curve, the ratio of the maximum to the effective value of the e.m.f. is 1,41 : 1, and if the maximum voltage determines the thickness of insulation necessary, then for any given insulating material the dielectric strength for continuous current is 1,41 times that for alternating current, i.e., the ratio of the dielectric strength for continuous current to that for alternating current is 1,41 : 1. HIGH-TENSION CONTINUOUS CUEEENT SEEIES SYSTEM 207 It has been alleged, however, that the effect of the alternating stress is to still further lower the dielectric strength. Although very little is known concerning the matter, the advocates of the continuous current high-tension system have taken the ratio as 2 : 1. (See curves and figures in Highfield's paper.) On this basis, the insulation thickness for the 50 000 volt continuous current cable should be the same as that for a 25 000 volt alternating current cable. Eeferring to the curve of Fig. 96, p. 183, the required thickness is, on this latter basis, seen to be 14 mm. The cable exhibited by Highheld at the Institution of Electrical Engineers had an insula- tion thickness of 14 mm and was intended for a working pressure of 50 000 volts. We can now proceed to estimate the cost of this cable. Section of core 64,5 sq mm 0,59 tons £59 tons 1079 sq mm 1,2 1,3 tons £59 4 mm 6,1 tons per km Weight of copper per km Cost of copper per km . Section of insulation Specific gravity Weight of insulation per km Cost of insulation at £45 per ton Thickness of lead . Weight of lead Cost of lead per km at £20 per ton . £122 Total cost of material per km = £59 + £59 + £122 = £240. Taking the T.W.C. as 1,5 times the cost of material : — Cost of cable per km delivered by manufacturer is 1,5 X 240 = £360, which is the cost given by Highfield. Cost of 135 km of this cable = £48 700. The cost of the underground construction may be estimated from Table LXXV., given in Chapter VIII., as follows : — For the alternating current system : 40 km of two duct conduit 110 km of single duct conduit. For the continuous current system : 135 km of single duct conduit. Assuming a stone block paving for the road, or a macadam road costing about the same, the cost per duct-km for a single duct conduit is (from Table LXXV.) £500, and for a two duct conduit £300 per duct km. 208 HEAVY ELECTEICAL ENGINEEEING Consequently : For the alternating current system — £ Cost of 84 km of 48,5 mm section cable • = 53 200 Cost of 106 km of 32,2 mm section cable . = 54 400 Cost of 40 km two duct conduit at £600 per k m = 24 000 Cost of 110 km single duct conduit at £500 per km = 55 000 Drawing in 190 km of cable at £25 per cable per km = 4750 150 km of trench with six manholes per km at £20 each = 18 000 Total . . . £209 350 Highfield gives £199 000 as the total cost. For the continuous current system — £ Cost of 135 km of 64,5 mm section cable . . 48 700 Cost of 135 km of single duct conduit at £500 per km . . ' 67 500 Cost of pulling in 135 km of cable at £25 per cable per km 3370 Cost of 135 X 6 manholes at £20 each . . 16 200 Total . . £135 770 Highfield gives £124 300 as the total cost. The data on which Highfield based his generating station costs are set forth in Tables LXXVIL and LXXVIII. These data are open to the following criticisms : — I. Larger units should have been taken in the case of the alternating system and smaller units in the case of the continuous current system. The largest sets yet employed in continuous current series systems are the 600 kw sets installed in 1906 for the Moutiers-Lyon plant, and each of these sets is made up of two 300 kw generators. No other sets yet installed are of over 400 kw aggregate rated output. II. As a consequence of I., the cost for buildings should be less for the alternating, and more for the continuous current system, than the values given by Highfield. PLATE -XL ESTIMATES OF COSTS OF GENERATING STATIONS. TABLE LXXVII. TABLE LXXIX. Highfuld's Costs. limited Costs. Total Capacity. 2400 Kw. 14 000 Kw. Sr 500 Kw. 110 000 Kw. No. of units and size (normal rating) 6 400 kw 10 000 volts 7 2000 kw 12 000 volts 10 3750 kw 15 000 volts 22 5000 kw 20 000 volts Buildings, includ- ing' chimneys £12 130 £38 695 £87 320 £248 325 Generating plant £21 6110 £84 895 £200 765 £520 905 Switch gear . £21)8(1 £5760 £8700 £18 440 Boilers, auxiliaries and coal hand- ling pumps £19 380 £68 780 £164 445 £498 370 Total cost . £56 ISO £201 130 £473 230 £1 318 040 Cost per kw . £23,4 £14,4 £12,6 £12,0 % L Total Capacity. 2400 Kw. 14 000 Kw. 37 500 Kw. 110 000 Kw. No. of units and size (normal rating) 4 600 kw 10 0011 volts 4 3500 kw 12 000 volts 6 6 250 kw 15 000 volts 12 920o kw 20 001 1 volts Buildings, includ- ing chimneys £11 800 £37 600 £85 000 £240 000 Generating plant £20 500 £80 OHO £188 000 £490 000 Switch gear . £2700 £52511 £79110 £16 7(10 Boilers, auxiliaries and coal hand- ling pumps £18 400 £66 000 £157 000 £475 000 Total cost . £53 400 £188 850 £437.900 £1 221 700 Cost per kw . £22,2 £13,5 £11,7 £11,1 TABLE LXXVIII. Highfield 's Costs. Total Capacity. 2400 Kw. 14 000 Kw. 37 500 Kw. 110 000 Kw. No. of units and size (normal rating) 12 200 kw 60 amperes 3300 volts 11 1000 kw 250 amperes 4000 volts 20 1875 kw 417 amperes 4500 volts 44 2500 kw 1000 amperes 2500 volts Buildings, includ- ing chimneys £12 130 £50 245 £103 490 £288 750 Generating plant £27 7011 £149 320 £325 680 £915 780 Switch gear . £910 £1225 £1370 £2580 Boilers, auxiliaries and coal hand- ling pumps £19 380 £68 780 £164 445 £498 370 Total cost £60 120 £269 565 £594 985 £1 705 480 Cost per kw . £25,05 £19,25 £15,86 £15,5 TABLE LXXX. Revised Costs. Total Capacity. 2400 Kw. 14 000 Kw. 37 500 Kw. 110 000 Kw. No. of units and size (normal rating) 4 600 kw 180 amperes 3300 volts 24 585 kw 145 amperes 4000 volts 62 600 kw 135 amperes 4500 volts 184 600 kw 240 amperes 2500 volts Buildings, includ- ing chimneys £11 800 £66 000 £120 000 £360 OuO Generating plant £26 000 £168 000 £410 000 £1 200 000 Switch gear . £600 £2000 £3000 £5000 Boilers, auxiliaries and coal hand- ling pumps £20 000 £74 000 £180 000 £535 000 Total cost £58 400 £300 000 £713 000 £2 100 000 ' v Cost per kw . £24,4 £21,4 £19,0 £19,0 [To fan- p. 208. HIGH-TENSION CONTINUOUS CURRENT SERIES SYSTEM 200 III. For the same reason this will also he the case with the cost of generating plant. IV. This is also the case with the switch gear, the cost of which is very dependent upon the number of units into which the total plant must be subdivided. V. Boilers, auxiliary and coal handling plant should, even in Highfield's original plan, have been taken as of higher cost for the continuous current plant, since the larger number of smaller units entail greater steam consumption. Also the low efficiency of a constant current plant at light loads requires more lew hr to be sent out from the generating station for a given quantity delivered to the customers than with a constant pressure system. In this continuous current series system the load is varied by varying the voltage, whilst the current remains constant ; conse- quently the transmission system losses are also constant for all loads. Hence it is, that the efficiency of the transmission system is low at low loads and high at overloads. Figures revised to take these various considerations into account are set forth in Tables LXXIX. and LXXX. The cost of the sub-stations with a total capacity of 7000 kw was given by Highfield as £70 000 in each case. This figure is reasonable and may be taken uncorrected. Table LXXXI. gives the total costs as given by Highfield and Table LXXXII. gives the revised figures. From Table LXXXII. it is seen that, as regards capital costs, the continuous current system has, in this particular case, a small advantage over the alternating current system. If, however, the costs of the separate items are compared, it is seen that the cost of the generating station is very much less for the alternating current system, and that it is due only to the high costs of the transmission lines, particularly the alternating current line, that the total capital cost is lower for the continuous current system. Now, if the transmission were overhead (and this would enable us to use a much higher transmission voltage for the alternating current), the cost of the transmission line would be less than the cost of the sub-stations, i.e., less than M70 000 in each case, and although the continuous current line would again cost less than the alternating current line, the difference would not be by any means sufficient to offset the advantage on the alternating current scheme due to the lower cost of the generating station, which is £5Q 000 lower for the alternating current than for the continuous current scheme. H.E.E. p 210 HEAVY ELECTRICAL ENGINEERING With an overhead transmission, consequently, the total capital cost would, for the case considered by Highfield, be less for an alternating current transmission system. As regards operating costs, the continuous current series system is also at a great disadvantage, as pointed out by several engineers who participated in the discussion, since the line loss is just as great TABLE LXXXI. Highfield's Total Costs of Series System and of Alternating System. A. O. Per Kw. c. c. Per Kw. Power station of 7000 kw (A. C. includes step up transformer) Sub-stations of 7000 kw . Line of 7000 kw . Total . £119 000 £70 000 £199 000 £388 000 £17,0 £10,0 £28,4 £55,4 £140 000 £70 000 £124 220 £334 220 £20,0 £10,0 £17,7 £47,7 TABLE LXXXII. Revised Total Costs of Series System and of Alternating System. A. c. Per Kw. c. c. Per Kw. Power station of 7000 kw (A. C. includes step up transformer) Sub-stations of 7000 kw . Line of 7000 kw . Total . £105 000 £70 000 £209 350 £384 350 £15,0 £10,0 £30,0 £55,0 £161 000 £70 000 £135 770 £366 700 £23,0 £10,0 £19,5 £52,5 at light load as at heavy loads, and if the line is proportioned for, say, a loss equal to 10 per cent, of the energy delivered to the line from the generating station at the rated load, 20 per cent, of the energy delivered from the generating station will be wasted in line loss at half load, and 40 per cent, at quarter load. In the parallel system, on the contrary, the line loss with decreasing load is a decreasing percentage of the total energy HIGH-TENSION CONTINUOUS CURRENT SERIES SYSTEM 211 transmitted. Thus, if the full load line loss is 10 per cent., then the line loss at half load is only 5 per cent., and at quarter load 1\ per cent. If, for the two systems, the line loss is plotted as a p o S H O D o ft 4 Y 3\ 4 cA 4 / A $ \ vy \ \ \ ^ O a u. l> O to ft; .t c -4 to o a H ft ft g O [M ft M 2 w « £ w o CO « co pq O H OS « 03 ■6 t l * nj M • X " o Co V \ \ 21 ) 4 d i j So 100 Time in Seconds Fig. 113. Modified Speed-time Diagram. 1 Stop per km. Average Speed 36 km per hour. 80 * 60 ■, E4ft5 20 -- — \ ■\ 0,75 n \ iec' r c \5012 + 250 + 0,45 L where R = tractive resistance in kilograms per ton V = speed in kilometers per hour L = length of the train in meters. The curves of Fig. 118 have been plotted, by means of this formula, for train lengths of 30, 300 and 600 meters. The results obtained c 1 °Q » > t 10 s 40 80 120 160 Speed in Km per Hour. 200 Fig. 122. Tractive Resistance Cukves foe Different Weights of Trains. consideration, and, if used with judgment, sufficient accuracy may be obtained with these more convenient curves. Table LXXXVI. gives for a number of railways certain particulars of weight of train, length of train, etc., and shows that, with the exception of the abnormal experimental rolling stock at Zossen, the weight per meter of train length does not vary very considerably ; so that the curves in Pig. 122 would give very much the same results as the curves in Fig. 118, where the length, and not the total weight of the train, is the criterion taken. Goods trains of course form an exception to any such approximate conclusion. The curves for train resistance in tubes, given in Fig. 120, are only for speeds up to some 40 km per hour. For estimating the 230 HEAVY ELECTKICAL ENGINEERING train resistance at higher speeds, we must rely on a suitable formula, as no test results are available. Let us consider what form such a formula will have. There will be, as in the case of a train in the open, a constant figure relating chiefly to the mechanical resistance per ton, and a TABLE LXXXVI. Boiling Stock Data. Name of Eailway. o ft 4J » > »"S lis - ? 60 too« |Sp4 u a> . 02 a) o o Central London Ely. oont. curr. Metropolitan Ely. ,, „ Metropolitan District Ely. „ ,, Waterloo & City Ely. ,, ,, Great Northern & City Ely. „ ,, Zossen Car (Siemens & Halske) » (A. E.G.) Burgdorf Thun. (3-phase) 40 49 48 50 54 48 48 66 14 16 15 14,3 15,3 23 22 15 25 37 24 74 90 32 1,8 2,3 1,6 3,2 4,1 2,1 2,85 3,1 3,2 3,5 3,5 2,1 2,2 4,4 1,6 1,33 2,0 0,65 0,54 2,1 03 s o H Central London Ely. cont. curr. Metropolitan Ely. ,, ,, Metropolitan District Ely. „ ,, Waterloo & City Ely. „ ,, Great Northern & City Ely. „ „ City & South London Ely. ,, „ 48 56 48 54 •56 32 14 16 15 10,6 15,3 9,5 13,4 17,0 16,5 7,0 0,96 1,06 1.1 0,74 3,4 3,5 3,2 5,1 3,65 3,4 3,6 3,3 2,9 4,6 to '3 o - g o Central London Ely. (7 car train) Metropolitan Ely. (6 car train) Met. District Ely. (7 car train) Waterloo & City Ely. (4 car train) GreatNorthern&CityEly. (7 car train) City & South London Ely. (4 cars & loco) Manhatten Elevated Ely. (CC 6 car train) Mersey Ely. (CC motor car train) 324 322 328 208 422 128 286 292 100 98 105 50 108 43 86 92 112 144 139 59 168 33 107 120 1,12 1,47 1,32 1,18 1,55 0,77 1,25 1,30 3,24 3,3 3,1 4,2 3,9 3,0 3,3 3,18 2,9 2,24 2,36 3,5 2,5 3,9 2,7 2,42 figure (depending chiefly on the speed) for the air resistance per ton of train. The air resistance will increase at least as rapidly as with the square of the velocity, quite possibly as the cube, as the air being confined in front of and behind the train, and the clearance being only 15 to 30 cm between train and tube walls, there will be a ELECTRIC TRACTION CALCULATIONS 231 column of air sucked along with the train and a column of air pushed before it, the resistance offered being dependent on the length of the tube 'and the means of inlet and outlet of air. The author proposes the following formula as applicable to the ordinary designs of tube railways and trains : — I 2 W R = tractive resistance in kg per ton W = weight of train in tons V = speed in km per hour In Fig. 123 the tractive resistance at constant speed in kilograms R = 3 + 0,3 ^ S 20 J. f A Ib .5 y \< / u 5 10 •S3 «5 0j 4 ;9 Y * S £ 40 60 120 160 Speed in Km per Hour. 200 Fig. 123. Author's Curves for Tractive Resistance for a 200 Ton Train in Tube and in Open. per ton is plotted as a function of the speed in km per hour for a 200 ton train. The lower curve A gives the tractive resistance per ton when the train is travelling in the open (this curve is the same as C in Fig. 122). The upper curve B gives the probable tractive resistance if the train were in a tube, and is plotted from the formula proposed above. Although curves plotted to give the tractive resistance in kilograms per ton at various speeds are in the form generally most convenient to the engineer, sight should nevertheless not be lost of the fact 232 HEAVY ELECTRICAL ENGINEERING that the more instructive way of considering these questions is to employ the coefficient of friction. From Fig. 122 we see that a 200 ton train on a well built level psads afiR/asy § 3 ° jnoi/ J ad suiy ui c ,- Q paads a/npayos Sin ^ f i J if * i / ^ 3 <*. 9 to m jnoif jad wyi ui paads '-/tew jnoy jad'swy ui C2 «o c> paads ainpaqo's * i " .A ■JC 2: 6*- CsJ S / ~s -^ f Sis jnoij jad my ui paads XB W Hi p H g < « 8 o o 02 >- § w W H CQ ^ 3 to as I paads aBoja/iy ^ £ § jmifjad smj/ uj ^ paads a/npai/os "> "i ^ jy y j*, * * Csl CP LL. y 58 J — « ^ /Osso^ afipja/iy^ t, -jnoi/jadswyuii^ ^ ! paads s/npal/os "> **■ j S3 i3 fc *« ■* -ft 1 w 7 1 § IT) LL ■jnoy Jad uy ui paads 'xem S s o S> ■ jy § «o «o 5 . i "SjV S. V^ s — c\ c AN ) CM Q 00 ~r -o cT to ■* saasO'dojsjo uopejng CD C2 Co to ■^CQ \s \ v 2 D — iZ y i % CO -Si. soasos= doQSJO uoiqejng --cm ii n to §- £ o 0) ? tb Cj . s ■*> CO Cu *J Cu y> o ; ■5 to" co nj ■S Si *. t. - to \7 *.a 80 1 60 40 20 * 20 40 60 80 100 120 140 160 Fig. 139. Fig. 14-1. too r T< r 6,0 7,0 a.o 3,( T A bO p 2ft* 3r 60 1 o> A vy K J 40 V 20 /zo /oo 80 60 40 20 usM £/£ " 3 4 4,0)5, vW± M ,e r to' 1 8^ at WJJ! N ^ *\ \? ]2X \ sN ft' \ 00 \ \ *e-" x _^ *S i >y ' ^» % $ if ,?0 40 eo 80 /oo /. Cl'EYES SHOWIXU the Watt-houes PEB ToX Kilometer AT A = Distance between Stops = i Kilometer; B = ,, ,, = 2 ., C = ,, ,, „ = 1 Kilometer. Axles foe a 200-Tux Tiuix, also Ayeeaoe Lnpvt at Axles ix Kilowatts peii Tox. O far,' p. 23.-- ELECTRIC TRACTION CALCULATIONS 235 The dotted line curves in Fig. 132 show the speed attained at any time after starting and at any rate of acceleration, curves being put in for 50, 100, 150, and 200 km per hour. The dotted line curves in Fig. 133 show the distance travelled at any time after starting, and at any rate of acceleration, curves being put in for 100, 500, 1000, 1500, 2500 meters. These curves apply to 200 ton trains, since the frictional resist- ances are taken to correspond with curve C of Fig. 122, but the frictional resistance is, during acceleration, and especially for high Fig. 132. A cceleration, Tractive Force, i and Speed (in Km per Hour). 20 40 GO 80 WO 120 140 Time in Seconds Fig. I33./1 cceleration,Tractive Force, and Distance(in meters) 20 40 B0 80 100 120 140 Time in Seconds- Tractive Force with Various accelerating Rates For 200 Ton Train. Figs. 132—133. Tractive Force for Accelerating. accelerating rates, so small as compared with the inertia resistance, that the data in Figs. 132 and 133 may be used without much error for other train weights. "We now have sufficient data to make rough estimates of the energy consumed at the train axles in operating trains on a level track at given schedules. The results are set forth in the full line curves of Figs. 134 to 142. To explain the process let us take the case of a run of 1 km from start to stop, at a schedule speed of 20 km per hour and with a stop of 30 seconds duration. Let the accelerating and braking rates be 0,8 meters per second per second. 236 HEAVY ELECTRICAL ENGINEERING Collecting together the conditions we have, Distance between stops ... ... 1 kilometer Schedule speed 20 kilometers per hour Accelerating and braking rates ... 0,8 meters per sec per sec Duration of stop ... ... ... 30 seconds. Total time occupied by the journey (including 1 stop of 30 sees) 3600 ion = -j~r- = 180 sees. Time occupied by journey (excluding stop) = 180 — 30 = 150 sees. Average speed attained = zr^rpr x 20 = 24 km per hour. 15U Time of accelerating and retarding periods = 8,8 sees. Maximum speed attained = 8,8 x 0,8 = 7,05 meters per second = 7,05 x 3,6 = 25,4 km per hour Average speed during accelerating period = —^— — 13 km per hour Tractive force per ton for accelerating (from Pig. 132) = 83 kg. Distance covered during acceleration = (8,8) 2 X —■ = 31 meters Work performed during accelerating period = 83 X 31 = 2570 meter kilograms 2570 _ , , , = o«7~ = ^ watt-hours. Tractive force per ton at constant speed (from curve C, Fig. 122) = 1,7 kg. Distance covered at constant speed = 1000 — 62 = 938 meters. Work performed at constant speed = 938 * 1>7 = 4,3 watt-hours oo7 Total work performed during the whole journey — 7 4- 4,3 = 11,3 watt-hours. The groups of curves in Figs. 134 to 142 have been plotted from the results of similar calculations for the various conditions. From this chart we may obtain, for any given distance between stops, any given duration of stop, any given schedule speed and PLATE XIII. Rate of Acceleration and Retardation 0.4 Meters per sec per sec 0,8 Meter s per sec per sec 1.2 Meter s per sec per sec S * A , A / \ / \ / / \ \ / S , 100 20 20 40 60 SO 100 120 140 wm 20 10 60 80 100 120 140 r \ t \ 1 \ 20 40 60 80 100 120 140 CL V ^ 120 100 80 60 40 20 7T ■5 i a s I20C US it 2 I 2 § l =>. *h ■5-S i l 2 9 4 6 S u 10 u '0 :■ w E 120 100 80 40 20 20 40 CO 80 100 120 140 F 80 60 40 20 20 40 SO 80 100 120 140 $00 400 20 40 60 80 100 120 140 WOO 1600 1200 mo 400 20 40 60 80 100 120 148 20 40 60 80 100 BO 140 2 1 « 6 8 It 10 1. '0 / 40 1 1 20 40 60 80 100 120 140 20 40 60 80 100 120 140 20 40 60 80 100 120 140 y — e— 20 40 60 80 100 120 140 160 120 SO 40 — 20 40 60 80 100 120 140 Abscissae denote - Time in Seconds Fig. ] -18. Speed, Tractive Force, Power ajst> Energy at Axles for Average Speed of 51 w per Hour. Distance of 2 km a 200-Ton Train operated at between Stops. [To face ji. 237. ELECTRIC TRACTION CALCULATIONS 237 any given accelerating rate, the corresponding energy consump- tion at the axles in watt-hours per ton-kilometer and' the X =3 .1 X <3 5- ■s I I I V. 80 60 40 20 02 0.4 0.6 0.8 1.0 1.2 Rate of Acceleration in Meters per Sec. per Sec. B. 20 _ ^ ^- .. t^~ 0.2 0.4 0.6 0.8 1.0 1.2 Rate of Acceleration in Meters per Sec. per Sec. Fig. 144. Energy Expended at Axles and Maximum Instantaneous Power for different Rates of Acceleration. Average Speed = . 51 km per hour. length of run = 2 km. corresponding average rate of consumption of energy at the axles, in kilowatts. 238 HEAVY ELECTEICAL ENGINEEKING From calculations similar to the above, Pig. 143 has been prepared. This shows graphically the various steps in the calcula- tions for estimating the energy consumption at the axles. As in all the other figures the case of a 200-ton train is taken, and the calculations are made for the particular case of a 2 km run, with an average speed of 51 km per hour ; the energy consumption being shown for three different values of the rate of acceleration. The first important point to be noticed is that at a certain rate of acceleration the maximum instantaneous kw input to the axles is a minimum. 120 k 100 1,80 1 S 60 •*> to *0 Q) «>. m | 20 Rate of Acceleration in Meters per Sec per Sec. 0, * Meters per sec per sec 0,8 Meters per sec per sec 1,2 Metres per sec per sec \ \ \ \ \ \ \ V \^ V3 \ ^ - ^ £. \ \ fe v° \ \ c V3 o A f 3 \*" \\ i V 1 J XiO tk > v. \ \ \ 4$ ,\ \ \ \ ( 5 TO 75 80 65 70 75 80 65 70 75 80 Overall Efficiency of Equipment Fig. 145. Curves giving the Overall Efficiency op Equipment. From Pig. 144 (b) this rate of acceleration is seen to be about 0,6 m per sec per sec for the particular case considered. The energy consumption at the axles for the whole run (Fig. 143 (m — o) ), however, decreases with increasing rate of acceleration, as is seen from Fig. 144(a). Both these figures were plotted from the values shown in Fig. 143 and from values obtained by calculations similar to those used for Fig. 143. The next step is to estimate the energy input to the trolley, that is, the total energy supplied to the train, including the useful energy (that given up to the axles), the energy lost in the motors and gearing, and the energy lost in the controlling rheostats. PLATE XIV. Acceleration- OAMeters per Sec.perSec. Fi ? .146 80 1 % f> 9% 60 J I* j ^\ -B 40 -C 20 40 120 F 'S .I4S . 100 80 0,10 60 10! r A <# Jf 40 -B -C 20 40 80 120 Fig 152. 80 60 40 20 1( '10 ^L A «5 ^^ -B 40 80 120 Acceleration-0,8Meters per Sec per Sec. Fig . 147. 100 ao 60 40 20 \f r1i 3"|o A tjj> f / B C 40 80 120 160 200 Fi 9 I50. inn .o 010 HO 5»M *J «« P fin & %/ — > \ \ •* 1 /\ S V \- B So V ^ S \ V s. \ C 40 k 20 40 80 120 160 200 Fig 159. 40 80 120 Fig. 161 80 60 40 20 i i i V n p - •fo ' ■>J Tv °v -B \l P\ i \ — r c i 1 1 i 100 80 60 40 20 to 1 5 vl— «<■- ■o\ S *? ft) B \ ^ \ c \ 1 Acceleration=l,2 meters per sec per sec Fig. 157. Fig. 160. 40 80 120 160 200 120 100 80 60 40 20 £ — - .-" «»-* /i c r T •"* A ^ *^* X ■V. * f 1 \ V s v by s x *) "t» B V \ -^■i. L 40 80 120 160 200 240 280 Fig. 162 80 120 80 60 40 20 | rn" / 3 A ff ' 7 x^ V B \ N. C ' N 1 40 80 120 160 200 Fig .163 100 80 60 40 20 e -— - — — A .T0 n iflv I- \ V f ^ 1 s \ a \ -) B s \ ^r" C > 40 80 120 160 200 240 280 Abscissae Denote Watt Hours per Ton Kilometer. Eies 155—163 Corras showing the Atibage Input to the Teolley in Kilowatts pee Ton and also the Watt-hours Input to the Trolley pee T. e ' Kilometeb (from Figs. 146—154) foe a 200-Ton Teaix. A = Distance of 4 Kilometers between stops. B = .. 2 ^ „ C = ,, 1 Kilometer ,, ,, [To f ii re v. 23!i ELECTRIC TRACTION CALCULATIONS 239 The ratio, of the energy given up to the axles (Figs. 134 — 142) to this total energy supplied is the overall efficiency of the equipment. The efficiency of the motors at their average load (including gear- ing) can be taken as 85 per cent, for a continuous current motor equipment suitable for a 200 ton train. That this is a reasonable value is readily seen by referring to the efficiency curves of modern continuous current railway motors. The overall efficiency of the equipment, however, is considerably lower, on account of the energy lost in the rheostats during the acceleration period. The chief factors which determine the value of the rheostat loss are the length of the acceleration period and the maximum velocity required. The curves in Fig. 145 show the overall efficiency of equipment plotted as a function of the average speed. The values from which these curves were plotted are representative of present practice with continuous current equipments. They are necessarily only approximate. Curves are shown for various lengths of run and for various rates of acceleration. As would be expected, the efficiency is higher the longer the run (as the necessary maximum speed for any given average speed will be less). The efficiency is also higher, the lower the average speed required. Applying these efficiency curves to the curves of Figs. 134 — 142 (for input to the axles), the curves in Figs. 146 — 154 are obtained, which gives the input to the trolley. The overall efficiencies are shown plotted in fine lines across the input curves. The " energy input to the trolley " curves are again reproduced in Figs. 155 — 163, and the average kw input to the trolley is shown by the thick lines across these curves. The above curves are deduced from considerations of continuous current equipments, but the total energy consumption curves (Figs. 146 — 163) may be used for single phase equipments, as, although the average efficiency of the motors is less, this is largely or entirely offset by the fact that there is no rheostat loss, the loss in the transformers being comparatively small. The more exact and exceedingly laborious methods of calculating from the precise characteristic curves of the motor employed in each individual case are described in Chapter IV. of " Electric Eailway Engineering." CHAPTEK XI TRACTION MOTORS AND THE ELECTRIFICATION OF RAILWAYS A. Traction Motors. Introduction. — The train consumption in watt hours per ton km is, as stated at the conclusion of the preceding chapter, sufficiently independent of the particular system of electric traction adopted in various cases to justify the general employment of the values in Figs. 146 to 154, for 200-ton passenger trains, in all cases where the permanent way and rolling stock are of modern construction. From this point onwards, however, there must be taken into account in the calculations a number of conditions with respect to which the particular system employed exercises a considerable influence. No one who has followed electric traction developments during recent years can have failed to note the wide difference in the individual capacities of the motors which are becoming customary in the three leading systems. Instances of three phase railway motors with a rated capacity of 1500 hp each 1 are now available; whereas the rated capacity of the largest continuous current railway motors is not over 550 hp. As to single phase railway motors, it is becoming quite evident that 200 hp per motor is the highest rating which, in the present state of engineering knowledge, can be considered advisable. Indeed, Eeichel in March, 1907, 2 expressed the opinion that for single phase railway motors, " a one-hour capacity of 180 hp per single motor is, in general, to be regarded as the extreme limit, if no special means for artificial cooling by air circulation are provided." Eeichel further points out that "it is not a simple matter to suitably provide for the introduction of 1 See p. 277 of Electrical Engineering for February 20, 1908. 2 " Erne Stundenleistung von 180 P.S. fur den einzelnen Motor ist im allgemeinen als aussere Grenze anzusehen, wenn keine besondere kiinstliche Kuhlung mit Frischluft stattfindet. Die Zufiihrung der Luft ist bei Motor- ■wagen nicht leicht, und daher ist es besser, obne solehe auszukommen." " Zeitsehrift Vereines Deutscber Ingenieure," vol. 51, p. 1027. TRACTION MOTORS AND ELECTRIFICATION OF RAILWAYS 24l air into the motor in the case of motor carriages, and hence it is preferable to dispense with forced draft." The 550 hp continuous current motors of the New York Central locomotives are not of the enclosed type. Enclosed con- tinuous current railway motors of rated capacities of 400 lip each will, however, be no heavier than 200 hp single phase railway motors, assuming equal armature speeds at rated load in the two cases. In equipments for motor carriages, the upper limits should preferably be taken at 150 hp for single phase, 300 hp for continuous current, and 400 hp for three phase. For customary purposes the most suitable sizes for equipments for motor carriages will generally be found to be 150 hp, 200 hp and 250 hp in the three cases. In an article in the Railway Gazette for May 10th, 1907, the present author ha3 indicated the misleading nature of the data which has been put forward by the advocates of single phase railways. It may not be amiss to point out here a few instances. (1) On p. 270 of vol. 36 of the Journal of the Inst, of Elec. Engrs., Schoepf states that " the Westinghouse single phase motor of 150 hp capacity weighs 2,46 tons, and a similar continuous current motor of equal capacity weighs 2,52 tons, which proportion is practically the same throughout the range of Westinghouse traction motors." This works out at 16 kg per hp. In the Times Engineering Supplement for April 17th, Kelly quotes the weight of the 150 hp Westinghouse single phase motor as 2,72 tons, which is 18 kg per hp. Kelly on this occasion makes the following statement : " The most enthusiastic advocates of the single phase system have never claimed that the motor was as light in weight or as low in first cost as the present 600-volt continuous current motor." Kelly is now chief of the department conducted up to a couple of years ago by Schoepf, and yet we have Schoepf asserting that the single phase motor is lighter than the continuous current motor and Kelly asserting that it is considerably heavier. Both Schoepf and Kelly are advocates of the single phase system. On p. 683 of Electrische Bahnen und Betriebe for December 14th, 1906, the weight of a Westinghouse 100 hp single phase motor is given as 2,36 tons ; this is 23 kg per hp. Thus we have for Westinghouse motors of about the same rated capacity 16, 18 and 23 kg stated to be the weight per hp. (2) In a letter published in the Times Engineering Supplement h.e.e. R 242 HEAVY ELECTRICAL ENGINEERING for November 22nd, 1905, Eichberg states that " Excepting the power transformer, the weight of the alternating current equipment is practically the same as that of the continuous current for the same working conditions. But, owing to the use of a power trans- former, the total weight per car will be increased by about 2 per cent, for the normal city service." On p. 486 of the Railway Gazette for May 24th, 1907, Dalziel states that: "As regards weights, these are not of supreme importance in railway work, but taking the actual practical weights of single phase motors, as applied to vehicles, without any academic discussion as to whether forced ventilation has or has not been applied to continuous current motors, or could, or could not be, it may be stated at once that motor for motor, on present designs, the weights are about equal. The transformer makes the equipments, as a whole, heavier than continuous current, but as it confers the advantage of perfectly flexible and efficient speed control, besides reducing the pressures of all the working parts to a low value, reliable in working and safe to attend to and manipulate, it is worth its carriage." (3) Dawson has stated (p. 264 of Vol. XXXVI. of the Joum. Inst. Elec. Engrs.) that " the weight of a 150 hp continuous current motor, rated on the 1 hour 75° C basis, is 2,7 tons, and the weight of a 115 hp single phase motor rated exactly on the same basis is 2,4 tons. If we take the weights of two motor trucks, one set equipped with four 150 hp continuous current motors, the other with four 115 hp single phase motors— that is, simply the complete motor trucks — we find that the weight of the continuous current motor equipment would be nearly 26 tons as against 27 tons for the single phase equipment." Dawson passes over the fact, how- ever, that he is comparing an aggregate of 600 hp of continuous current motors with an aggregate of only 460 hp of single phase motors. Furthermore, the heaviest trucks employed under motor coaches equipped with continuous current motors do not exceed 5,5 tons each in weight, or 11 tons per pair of trucks, and even the 240 hp G E 69 motor weighs with gear and gear case only about 2,75 tons, or 11 tons for four motors. Thus a pair of trucks equipped with four G E 69 motors, i.e., with an aggregate of 960 hp of motors, will weigh only 22 tons. The 26 tons stated by Dawson to be the weight of two trucks carrying 600 hp of continuous current motors is altogether unreasonable. A pair of trucks carrying four 125 hp G E 66 motors, i.e., an aggregate of 500 hp of continuous current motors, weighs only 18,5 tons. If Dawson's TEACTION MOTORS AND ELECTRIFICATION OF RAILWAYS 243 figure of 27 tons is correct for the weight of a pair of trucks carrying an aggregate of only 460 hp of single phase motors, he has certainly not made a point for the single phase system. Ample material is available for concluding that the weight of an unventilated and correctly rated 150 hp 25 cycle single phase motor is, at the present stage of development, not less than some 26 kg per hp for an armature speed of 500 rpm at rated load. This is when rated on the basis that at the end of one hour during which it has been carrying its rated load, the thermometrically determined temperature rise of the hottest accessible interior part is 75° C. We have ample data for knowing that the weight of the corresponding unventilated continuous current motor designed in the light of modern practice, and for the same speed at its rated load, is some 13 kg per hp. In both these cases the weights are exclusive of gear and gear case. To allow for gear and gear case, some 15 per cent, may be added to the weight for continuous current and some 8 per cent, for single phase motors. The One Hour Rating. — The maximum output which a traction motor is called upon to develop is several times greater than its average output during the time in which it is in service ; but this maximum output is only required for a few seconds, and usually only at periodic intervals of a few minutes. The average output of the motor is too low a figure, however, to serve as a basis for the rating of traction motors, and also gives little idea of the maximum output required of the motor. The empirical basis of a one hour constant output sufficient to cause a maximum temperature rise of 75° C at the end of this hour has been widely accepted as the basis upon which to rate traction motors. The value of this one hour rating will be dependent on the following properties of the motor : — (1) The efficiency of the motor without gear ; (2) The weight of the motor without gear ; (3) The provisions for ventilation. Let us consider the influence of these three factors upon the rated output of the motor. (1) The Efficiency. — The energy, represented by the internal losses of the motor, is expended in heating the material of the motor. Neglecting the loss of heat by radiation and conduction to the circulating air, the rise in temperature is directly proportional to the value of the internal loss. (2) The Weight. — Under the conditions as above stated, the average temperature rise will, for a given value of the internal loss, r 2 244 HEAVY ELECTKICAL ENGINEERING be inversely proportional to the weight of the motor. A large motor will require more heat energy to raise it to a given temperature than will be required in the case of a small motor. The con- sequence of this as regards the ratio of the one hour rating to the service capacity is discussed in the section at the foot of this page, entitled " The Service Capacity." (3) The Ventilation. — Ventilation enables more energy to be expended in the motor without overheating it, since much of the heat will be conducted away by the circulating air. It is preferable to give the motors natural ventilation only, i.e., to limit the openings in the case to very small apertures. The armature core should, however, be provided with ducts, in order that there may be a circulation of air through all internal parts of the motor. Apexs tures in the casings of the motors are only allowed when there is no danger of mud or water entering the motor, and, in general, a totally enclosed motor is to be preferred. Single phase motors, however, and in a few cases continuous current motors, are, in the more recent designs, often provided with an artificial circulation of air by forced draught, the natural circulation due to the armature being reinforced by a draught of air through the motor from a fan equipment. The Service Capacity. — The one hour rating, although the only basis of rating which is sufficiently simple to permit of comprehen- sive comparisons, is nevertheless by no means a satisfactory criterion of the service capacity of a motor when installed on loco- motives or cars and running under actual service conditions. While service capacity depends but slightly on the weight, it is very dependent upon the ventilation facilities provided for carrying away the heat developed in the motor as a consequence of the iron and copper losses in it. Of two motors which rate equally on the one hour basis and are equally ventilated, the lighter will have the greater service capacity. For this reason the service capacity of motors of totally distinct type cannot be deduced from a comparison of their one hour ratings. The latter is only quantitatively useful in establishing comparisons between motors of the same type. Thus, if the single phase equipments would do as much per ton in service as continuous current equipments, the fact that they rate lower on the one hour basis would not even be worth mention. As a matter of fact, however, they are worse when compared rigorously on the basis of their actual service capacity than when compared on the basis of their one hour rating, inasmuch as in the TRACTION MOTORS AND ELECTRIFICATION OF RAILWAYS 245 hour's run the greater part of the heat is used in raising the temperature of the motor, so that the heavier the motor the higher it will rate, whilst in service the temperature becomes steady and all the heat has to be got rid of by ventilation. Since, however, a rigorous comparison on the basis of actual service capacities is so elaborate an undertaking as to preclude arriving at broad con- clusions, and since furthermore the single phase motor is favoured by basing the broad comparison on the one hour rating, the latter basis of rating is employed in the following investigation. A Comparison on the Basis of the One Hour Rating. The efficiencies at rated output do not vary greatly for the different types of motors, but this comparatively small difference has an appreciable effect on the weight. For every ton of material in a ventilated motor (i.e., in a motor which, while provided with a few small openings, does not have air forced through it) running at, say, 500 rpm, some 4700 watts must be expended in order to occasion, in one hour, a thermometrically determined temperature rise of 75° C above the temperature of the surrounding atmosphere. If the motor is provided with forced draught, some 6600 watts per ton must be expended. With these figures as a basis, let us see what hp output (one hour 75° C) can be obtained from a motor weighing 2,5 tons without gear, and to run at 500 rpm. The output will, of course, be different for the three types on account of the different efficiencies, and so we must deal with each type separately. (a) Continuous Current Motor of the Ventilated Type. — The weight of the motor without gear is 2,5 tons. The total internal loss at rated load will be 4700 X 2,5 = 11 250 watts. A modern continuous current motor of such a size will have an efficiency (without gear), at rated load, of about 93 per cent. Thus the loss of 11 750 watts is some 7,0 per cent, of the total input. Consequently the input in kw = 11750 X 100 1RQ1 Tcnoooo" = 168 kw - The output in kw to the gear will be 168 X 0,93 = 156 kw. Assuming a gear efficiency of 96 per cent., the output to the axle will be 150 kw. This is the rated output and, expressed in horse power, is equal to 200 hp. The weight is thus 12,5 kg per hp of rated output. We thus see that a 200 hp 500 rpm continuous current motor of the ventilated type will weigh about 2,5 tons.. In order to confirm this conclusion, let us compare these figures 246 HEAVY ELECTRICAL ENGINEERING with the ascertained data of two well-known motors, which are designated as G E 69 and G E 66 respectively. G E 69. Rated output (one hour 75° C) 240 hp. 179 kw. Efficiency at 240 hp 550 v. . 93,3 per cent, excluding gear. Gear loss . . .4,5 per cent, of input. "Efficiency at 240 hp (with gear) 88,8 per cent. 179 Input in kw = ■ (JOO = 201,5 kw. U,ooo Loss in motor (100—93,3) per cent. = 6,7 per cent, of input. = 13,5 kw. Weight without gear and case 2,51 tons. Watts per ton = n ... = 5380 watts. z,ol G E 66. Eated output . . .125 hp. 93,3 kw. Efficiency at 125 hp . 92,8 per cent, including gear. Gear loss . . . 3,5 per cent, of input. Efficiency at 125 hp (with gear) .... 89,3 per cent, of input. Input in kw = n ' = 104,5 kw. u,oyo Loss in motor 100 — 92,8 = 7,2 per cent, of input. = 7,53 kw. Weight without gear and case .... 1,8 tons. 7530 Watts per ton = —-5- = 4200 watts. 1,0 (b) Single Phase Motor of the Ventilated Type. — The weight of the motor without gear, is, as before, taken equal to 2,5 tons. Also, as this weight of material is to be raised to the same temperature as in the case of the continuous current motor, the internal loss must be the same, i.e., 4700 X 2,5 = 11 750 watts. The efficiency (with- out gear) of a modern single phase motor is not greater than 87 per cent., thus the loss of 11 750 watts is some 13 per cent, of the total input, or the input in kw = 11 750 X 100 nn K , 13 X 100 = 9 °' 5 kw " TRACTION MOTORS AND ELECTRIFICATION OP RAILWAYS 247 The output to the gear, in kw, will be 90,5 X 0,87 = 78,5 kw. Assuming a gear efficiency of 96 per cent., as before, the output to the axle will be 75,0 kw. This is the rated output, and, expressed in horse power, is equal to 100 hp. The weight is consequently 25 kg per hp of rated output. (c) Three Phase Motor of the Ventilated Type.— As before, the weight of the motor without gear is 2,5 tons. The internal loss, as before, is 4700 X 2,5 = 11 750 watts. The efficiency (without gear) of a modern three phase railway motor of this size may be taken at 94,3 per cent., thus the loss of 11 750 watts is some 5,7 per cent, of the total input, or the input in kw = 11 750 X 100 onfil ' 5,7 X 100 = 2 ° 6 kw - The output to the gear in kw will be equal to 206 X 0,943 = 194 kw. Again assuming a gear efficiency of 96 per- cent., the output to the axle will be 186 kw. This is the rated output, and, expressed in horse power, is equal to 250 hp, or a weight of 10 kg per hp of rated output. These results are brought together in Table LXXXVII. :— TABLE LXXXVII. Bated Output of Motors of different Types but of equal Weight and for equal Speed of 500 rpm ; Ventilated, but not with forced Draught. Type of Motor. Weight of Motor without Gear (Metric Tons). Assumed efficiency without Gear, at Rated Output. Assumed efficiency of Gear. Rated hp on 1 hr 75° C. Basis, Weight in kg, per hp of Rated Output. Cont. Curr. Single phase Three phase 2,5 2,5 2,5 93,0% 87,0% 94,3% 96% 96% 96% 200 100 250 12,5 25,0 10,0 Thus we find that for motors of equal weight, and for equal ventilating provisions, the continuous current motor will have double the output of- the single phase motor. Also, that the three phase motor will have one and a quarter times the output of the continuous current motor. Let us see whether these results are confirmed by the actual weights and outputs of existing motors. In Table LXXXVIII. the 248 HEAVY ELECTRICAL ENGINEERING rated hp, total weights and weights per hp are given for three of the largest and most modern single phase motors, for three modern continuous current motors, and for three three phase motors. The average values of the weight, in kg per hp, are some 17 kg for single phase, 11 kg for continuous current, and 10 kg for three phase. The nine examples in this table were selected, as representing the most modern practice, from the larger Table XC, which includes, besides many other examples of motors, columns setting forth the weight of complete electrical equipment. Our estimated figure for the three phase motor is in correspondence with the average value for existing motors, i.e., some 10 kg per hp. The estimated figure of 12,5 kg per hp for continuous current also corresponds well with the average for existing motors. The most modern continuous current motors are even lighter, occasionally having a weight per hp as low as 10 kg. The estimated figure of 25 kg per hp for single phase motors is much higher than the average of the three set forth in Table LXXXVIII., which is some 17 kg per hp. It must be remembered, however, that the above figure of 25 kg per hp refers to a motor provided only with natural ventilation, whereas the single phase motors taken as examples for Table LXXXVIII. are provided with forced draught. This, together with their higher armature speeds, accounts for the relatively low figure for the weight per hp. TABLE LXXXVIII. Data of Representative Railway Motors. O w -3 03 . £ 6 CD fcb System. Type of Motor. a) o 2." 'E g.S 'S3 o. Railway on which Motor is in use.i 03 03 600 O isS Single phase A.E.G. W.E. 51 115 25 2,4 20,8 London B. S. Coast By. Alternating Siemens Schuckert 175 700 25 2,77 15,8 Heysham-Morcambe M. Ey. Oerlikon 200 650 15 3,38 16,9 Seebach-Wettingen By. Continuous G.E. 68 175 2,15 12,3 Boston Elevated By. current G.E. 69c 232 470 — 2,5 10,8 New York Central By. G.E. 69b 240 530 — 2,51 10,4 Metropolitan District Ey. Three phase Siemens & Halske 250 900 50 3,2 12,8 Marienfeid-Zossen Ganz & Co. 300 730 25 2,7 9,0 Tender for Metropolitan Ganz & Co. 1500 225 15 13,1 8,7 Simplon and Valtellina 1 For references see Table XC. TEACTION MOTORS AND ELECTRIFICATION OF RAILWAYS 249 In the published descriptions of single phase motors, it is not always clearly stated in what way the motors are ventilated ; thus in one case the 175 hp Siemens Schuckert motor is described as having " artificial ventilation " (Kiinstliche Kuhlung), but whether or not an external blower is' provided is not stated. But in another instance (in the Seebach-Wettingen Locomotive) this same motor is cooled with a forced draught. 1 In some cases the information is more definite ; thus, referring to the New York, New Haven and Hartford locomotive equipped with four 250 hp Westinghouse single phase motors (see Table XC, No. 8), McHenry, the Vice-President of the N.Y.N.H. & H. Eailway, writes thus : — " The four main traction motors, the high potential transformers and the main circuit rheostats are cooled by air furnished at low pressure by means of two motor-driven centrifugal blowers, which draw air through openings in the cab. The low-pressure air has two paths. One path passes first through the transformer and then to the rheostat." The other path goes directly to the motors. It enters the armature near the shaft, passes around and between the armature laminations, flows outward through the ventilating ducts in the field cores, and reaches the outer air through perforated caps on the frame of the motor. Since a considerable volume of air is required for each motor, and since it is undesirable to cause the air to assume a high velocity, it has been necessary to provide a large flexible conduit between the air passages on the cab and those on the motors proper. The flexible conduit is made of heavy canvas tubing, which is reinforced with wire and given an accordion pleating. By the use of the air blast, the temperature of the motors under load has been so decreased that the continuous rating (200 hp) is nearly equal to the one hour rating (250 hp)." 2 If we assume that all three types of motor are ventilated with forced draught, then for the same temperature rise, we can expend about 6600 watts per ton instead of 4700 watts. The hp outputs on the 1 hour 75° C basis will now be somewhat different. They will be as follows : — (a) Continuous Current Motor with Forced Draught. — The total losses will be 6600 X 2,5 = 16 500 watts. Assuming the efficiency to be the same as before, i.e., 93 per cent., the total input will be 16 500 X 100 7 X 1000 = 236 kw. 1 Electrical Engineering, Vol. III., p. 679. 2 The Railway Gazette, August 30, 1907, p. 205. 250 HEAVY ELECTRICAL ENGINEERING The output to gear will be 236 X 0,93 = 219 kw. And assuming a gear efficiency of 96 per cent., the output to the axle, will be 210 kw, and the rated horse power output will be 280 hp, or a weight of 8,9 kg per hp output. (&) Single Phase Motor ivith Forced Draught — The total loss will, as in the case of the continuous current motor, amount to 6600 X 2,5 = 16 500 watts. Assuming the efficiency to be, as before, 87 per cent., then the total input will be 16 500 X 100 1(V7l 13 X 1000 = m kW> The output to the gear will be 127 X 0,87 = 110,5 kw. And assuming a gear efficiency of 96 per cent., the output to the axle will be 106 kw, or the rated horse power output will be equal to 142 hp, or a weight of 17,6 kg per hp of rated output. (c) Three Phase Motor with Forced Draught— The total loss is 6600 X 2,5 = 16 500 watts. Assuming the same efficiency as in the previous case, i.e., 94,3 per cent., the total input to the motor will be equal to 16 500 X 100 oon . 5,7 X 1000 = 29 ° kW - The output to the gear will be 290 X 0,943 = 274 kw. And assuming a gear efficiency of 96 per cent., the output to the axle will be 263 kw, and the rated horse-power output 350 hp, or a weight of 7,15 kg per hp. Collecting these results in tabular form we have the following : — TABLE LXXXIX. Rated Output of Motors of different Types, but of equal Weight, and for equal Spt [namely, 500 rpm) with forced Draught. Type of Motor. Weight of Motor without gear (Metric Tons). Assumed efficiency (without Gear) at Rated Output. Assumed efficiency of Gear. Rated hp on 1 hr 75° C. Basis. Weight in kg per hp of Ral ed Output. Continuous current Single phase Three phase 2,5 2,5 2,5 93,0% 87,0% 94,3% 96% 96% 96% 280 142 350 8,9 17,6 7,2 TRACTION MOTORS AND ELECTRIFICATION OF RAILWAYS 251 The figure given in the above table for the continuous current motor is distinctly lower than any of the figures given in Table LXXXVIIL, since these last do not refer to motors provided with forced draught. The figure for the single phase motor, on the other hand, compares very closely with those given in Table LXXXVIIL Thus we have, for a single phase motor, weighing 2,5 tons, and provided with forced draught, a rated output of 142 hp, or a weight of 17,6 kg per hp. The average value in Table LXXXVIIL was 17,0 kg per hp. Let us compare our estimated values of Tables LXXXVII. and LXXXIX. with those given in Table LXXXVIIL Take for example the continuous current motor designated as GE 69 B, and rated (on the 1 hour, 75° C basis) at 240 hp. This motor weighs only 2,51 tons without gear and gear case, or a weight of 10,5 kg per hp. The case of this motor has small openings for providing natural ventilation. The weight per hp decreases slightly with increasing output, and con- sequently our figure of 12,5 kg per hp, given in Table LXXXVII., compares very favourably. The efficiency (without gear) of this motor is 93,3 per cent, and the efficiency of the gear is 95,8 per cent. As an example of a single phase motor, let us take the Allgemeine Elektricitats Gesellschaft's W E 51 115 hp motor, which weighs 2,4 tons without gear and gear case, or 20,8 kg per hp. This motor is of the artificially ventilated type, and consequently we must compare the weight per hp with our figure of 17,6 from Table LXXXIX. The efficiency (without gear) of this motor at rated load is 86 per cent., and the efficiency of the gear is about 96,5 per cent. In Figs. 164 and 165 are drawn to the same scale (1 to 24,4) outline sketches of the G E 69 B and the WE 51. It is evident from the figures that the WE 51 is actually the larger motor, although it has only half the capacity. The Siemens- Schuckert series motor, which is rated at 175 hp, has a weight of only 2,77 tons without gear and gear case, or 15,8 kg per hp. This is, however, a larger motor, and runs at a 30 per cent, higher speed than the 2,5-ton motor of Table LXXXIX., which is rated at 142 hp with forced draught. The two motors, the G E 69 B continuous current motor and the Siemens- Schuckert 175 hp single phase commutator motor, are, so far as the author is aware, the lightest for. their (1 hour 75° C) output, of the respective types so far as relates 252 HEAVY ELECTRICAL ENGINEERING to authenticated weights. The three phase motor of the Ganz Co., rated at 300 hp, weighs 2,7 tons, or only 9 kg per hp. This (4 O H O hi M H a M o i m o fc> izi M H O o P4 CD w i 2 02 o W H W w 02 b O tic figure compares well with our estimated figure of 10 kg per hp for a 250 hp motor weighing 2,5 tons. TRACTION MOTORS AND ELECTRIFICATION OF RAILWAYS 253 In Table XC. will be found many other examples. The table also includes weights of equipments. In column E, the weight of w o H o I M < W ft 9 S3 o Hi H & o 60 motor (without gear) per hp per 500 rpm is given. In column S, the figure known as " Valatin's Weight Coefficient " x is given. The 1 See "Electric Railway Engineering," Parshall and Hobart, pp. 372—375. 254 HEAVY ELECTEICAL ENGINEEEING figures in these columns give a good idea of the relative utilisation of material in the motors. As regards the power consumption of any railway, the precise efficiency of the motors is not very important per se, as the losses in the motor itself are very small in comparison with the losses in transmission and control. Nevertheless, the internal losses determine the heating, and consequently, as has been shown, have a preponderating influence on the rated output and the service capacity of the motor. Thus the lower efficiency of the single phase motor as compared with that of the continuous current motor, though it has but little effect on the overall efficiency of the equipment, is the chief cause of the very much greater weight of the single phase motor for a given rated output. Since the efficiency of the three phase motor is some- what higher than that of the continuous current motor, the latter is somewhat heavier than the three phase motor for a given rated output. In further confirmation of the very low weights which are being obtained in three phase railway motors, it is of interest to quote from an abstract of a recent article by Valatin. The abstract was published on p. 277 of Electrical Engineering for February 20, 1908, and is to the effect that some of the Ganz Electric Co.'s recent three- phase locomotives are provided with three ranges of speeds, and that the 8-pole motor of a locomotive of this type, built for the Italian State Eailways, has a capacity, on the one hour rating, of 1500 lip, and a weight of 13,4 tons (metric), and at a speed of 220 rpm. While building new locomotives of the same type, the manufacturers have recently found it possible, through some changes in the design, to increase the rating of the motors by 20 per cent, to 1800 hp, while the external dimensions and the speed of the motor remain unaltered. Another 8-pole motor of similar construction, designed by the Ganz Electric Co., developing 1100 hp on the one hour rating at 3000 volts, 15 cycles, and 220 rpm., weighs 10 metric tons. Neither of these motors has forced draught. This last motor is suitable for a comparison with the single phase motor of the Pennsylvania locomotive, since neither the weights nor the speeds of the two motors differ materially. The capacity, on the one hour rating, of each motor of the Pennsylvania locomotive is stated to be 500 hp, the tractive force at rated load and normal speed is given at 6,7 metric tons, and the diameter of the drivers is 1830 mm. From these data the speed of the motor is seen to be 236 rpm. The PLATE XVI. TABLE XC. Data of Modern Trc ction Moto n and Equipments. ■ A B C D E F O H 1 J i K L M N 1 Q a IB |a|§ S 5 ti to tc e a a « o S H S i ;'c ^' = •a -9 M -5 M c .- M S-8 M :f £1 £, = X ° \ ■ ■2 at o ss ^— ^ ^-^. u s — ^ = r j '- v *t '~ S= '5 'O ^ £ ' — . | CS X c SC|S "q t. op ?l H~ &3 Bf * -i'X i) o d c [3 6 :£- 6 Z O 03 (.H v r~' — o Vi "* ■" ' a 3 > te * 5 i, id Instances of Railways "^ - Type. i£ V l o gf J3 " a. i "5 Qi o a-| e, •c* ft Authority and Reference. on which Motor is X OS u 5 X I~ o » O X, ft 1 S 3 si o x c o c a. If So fcfl "o > as m o o % o o o g S " 2 !jd in use. .._ 1 K 5 '5 o £ .5? ^ a. '5 is 11,0 44% s at a o 6 Z 32,4 G.E. A605 .... 75 26 700 1,73 23,1 1,91 25,4 2,74 36,6 0,83 200 4,30 4 0,062 Sprague, Proceed. A.I.E.E., Bloomington-Pontiac, July, 1907, p. 1186 Illinois; Blooming- ton-Peoria, Illinois. " Wesfcinghouse .... 75 15 700 1,70 22,6 1,88 25,1 3,05 40,6 1,13 15,1 60% — 4,65 — 4 31,6 0,063 Sprague, Proceed. A.I.E.E., July, 1907, p. 1186 Bergamo Brembana. 3 W.E. 51(A.E.G.) . 116 25 600 2,40 20,8 2,60 22,6 — — _ " 750 4,20 1,0 3*4 25 0,08 Dawson, Journal I.E.E., vol. 36, p. 264 ; Eichberg, E.T.Z., Aug. 1, 1907. Blankenese-Ohlsdorf ; London B. South Coast. 4 G.E. A603 .... 125 25 640 2,42 19,4 2,60 20,8 4,00 32,0 1,40 11,2 54% 225 4 24,8 0,08 Sprague, Proceed. A.I.E.E., July, 1907, p. 1147—1150; Sprague, Street Railway Journal, May 25, 1907 Washington- Balti- more ; Richmond Chesapeake. 5 Weatinghouse .... 150 25 — 2,52 16,8 2,72 18,1 3,83 25,5 1,11 7,4 41% — 3,90 1,04 — — — Kelly, Times Eruj. Supplement, Swedish Experimen- ttt April 17, 1907 tal Ry. js 6 Siemens-Schuckert . 175 25 700 2,765 15,8 3,00 17,1 5,50 31,4 2,50 14,3 83% 320 2,90 1,1 2 22,1 0,09 Richter.-E.r.Z., Aug. 22, 1907 ; Oranienburg, Prussia ; s- La Lvmure Electrique, Feb. 8, H e y s h a m - More- ® 1908 ; Daziel, Times Encj. cam be Midland Ry. 5c Supplement, April 17, 1907 a 7 Siemens-Schuckert B.M.E. 60 40 15 400 ~ 2,62 65,5 ~ 300 4 Electrotechnik v. Maschinen- bau, Nov. 11, 1907 Oranienburg (Prussian Experimental), Vienna, Baden. 8 Westinghouse E.M.Co. . 250 25 225 6,60 26,4 6,60 26,4 — — — — — 240 1,0 1,57 4 11,9 0,168 E.T.Z., Feb. 7, 1907 Samia Tunnel, Michi- 9 W.E. 31B. (A.E.G.) 40 40 800 1,385 34,6 1,00 40,0 1,85 46,2 0,25 6,25 15,5% 550 5 — 2 55 0,036 E.B. u. Betr., 295, 1905 gan. Borinage Ry. 10 Oerlikon (Interpole) 200 15 650 3,38 16,9 3,70 18,5 — — — — 250 3,1 — 2 22 0,091 E.B. u. Betr., p. 49, 1906 Seebach-Wettingen. 11 A.E.G. W.E 350 25 400 6,60 15,7 6,25 17,9 — — — — — — 4,15 — — 12,6 0,159 E.B. u. Betr., Feb. 4, 1907 Oranienburg. 12 13 14 15 Siemens-Schuckert . 175 25 700 2,765 15,8 3,00 17,1 7,5 42,9 4,5 25,7 150% 320 2 22,1 0,09 Wilson Lydall, p. 237, vol. II. Rotterdam-Hague. 10 G.E. 65 B 225 3,70 16,5 3,95 17,5 5,00 22,2 1,05 4,65 26,6% 625 4,26 4 Baltimore, Ohio 17 Westinghouse .... 160 — — 2,20 14,7 2,50 16,7 3,18 2\fi 0,68 4,52 27,2% 500 — 0,91 4 — — Kelly, Times Encj. Supplement, April, 1907 Carter. Journal I.E.E., vol. 36, Metropolitan Ry 18 G.E. us 175 2,15 12,3 2,42 13,8 _ — — — — _ — — — Boston Elevated Ry. p. 280 ; Engineering, vol. 77, p. 387 19 G.E. 09C 232 470 2,50 10,8 2,80 12,0 5,00 21,6 2 2 9,50 78,5% 650 1,88 0,91 2 KM 0,197 Sprague, Electrical Engineer- ing. Aug. 8, 1907 ; Sprague, New York Central. Street Railway Journal, Nov. 4, 1905 20 G.E mil 240 530 2,51 10,45 2,80 11,7 3,64 15,2 0,84 3,5 30% 500 3,2 0,91 2 11,1 0,18 Sprague, Electrical Engineer- ing, Aug. 8, 1907 ; Sprague, Proceedings A.I.E.E., Julv, Metropolitan District Ry. ; Interborougli j Rnpid Transit; *i 1907, p. 1147 Metropolitan Ry. ; c Bakerloo ; H a m p - E stead ; Piccadilly and 6 Brompton, &c. 21 Dick, Kerr & Co. . 100 — — 1,76 17,6 1,95 19,5 — — — — — — 2,8 — — — — — Liverpool Overhead. o 22 Siemens-Schuckert D J^ 60 800 ! 1,4 23,3 1 575 26,2 — — — — — 750 4,1 0,85 4 37,2 0,053 E.B. u. Betr., p. 87, 1904 Berlin Hoch u, Unter- ground. ■2 23 G.E. 55 160 — 2,3 14,4 2,5 15,6 — — — — — 650 3,0 1,03 4 — — Traction' and Transmission, Milan - Gallarette, c pp. 29—31, 1903 Chicago W. Side 6 Elect., &c. 24 130 545 2,3 17,5 2.46 18,9 3,6 27,7 1,14 8,8 46,5% 750 4,34 — 4 19,1 0,104 E.B. u. Betr. , p. 652, Dec. 4, 1906 E.B. u.Betr., p. 509, Sept. 24, 19*16 Vienna Stadtbahn. 25 Siemens-.Sehnekert 130 - 720 2,8 17,5 2,5 19,2 4,5 34,5 2,0 15,4 80% 1000 - - 2 25,2 0,078 Cologne- Bonn 26 Oerlikon T.M. 22 . 200 — 400 3,2 16,0 3,58 17,9 - - - - - 800 - - - 12,8 0,156 E.B. u. Betr., p. 621, Nov. 14, 1905 E.B. u. Betr., p. 384, July 14, 27 G.E. 84A 550 300 5,6 10,2 5,6 10,2 7,6 13,8 2,0 3,64 35,7% 600 1 1,35 4 6,1 0,328 New York Central 1906 Gearless Loco. 28 G.E. 76 . 165 — 530 2,08 12,6 2,34 14,2 600 3,5 0,965 — — — G.E. Bulletin Hammersmith & City 29 30 Ry. ; Metropolitan By. 31 Ganz Electric Co. . 250 15 300 3,8 15,2 3,8 15,2 5,3 21,2 1,5 6,0 28% 3000 1 1,17 4 9,1 0,219 Zeitschrift dm Vereins Deut- sche Ing., Feb. 21, 1903 Valtellina Motor Car. 32 Siemens and Halske 250 50 900 3,2 12,8 3,2 12,8 - 1150 1 1,25 4 23,0 0,087 — Marienfeld-Zossen. 38 Ganz Electric Co. . 300 25 730 2,9 9,7 3,1 10,35 4,4 14,7 1,3 4,35 42% 3000 3,2 0,915 2 + auxiliary 14,2 0,142 Tender for Metro- politan. 34 Ganz Electric Co., Sp. . 1500 15 225 13,2 8,8 13,2 8,8 16,5 11,0 3,3 2,2 20% 3000 1 1,50 1 + 4,0 0,505 E.B. u. Betr., So. 6, 1907 Valtellina Ry. <£ auxiliary ej 35 Ganz Electric Co., 8p. 600 15 225 8,2 13,6 8,2 13,6 — — — — — 3000 1 1,50 2 twin motors 6,1 0,325 E. B. u . Betr. , Nos. 1 and 2, 1905 Valtellina Ry. and — Simplon. 3(3 Ganz Electric Co., 12p. . 1200 15 150 11,1 9,3 11,1 9,3 14,4 12,0 3,3 2,75 23% 3000 1 1,50 — 2,8 0,72 E.B. v. Betr., No. 6, 1907 Valtellina Ry. « 37 Siemens-Schuckert . 260 45 900 3,75 14,4 4,1 15,7 10 000 2,13 — 38 A.E.G 250 50 1000 4,1 16,4 4,1 16,4 435 1 — 4 26,0 0,077 — Marienfeld-Zossen. r* 39 Brown Boveri .... 550 16 224 10,75 19,5 10,75 19,5 14 25,5 3,25 5,9 30% 3000 1 1,45 2 32,8 8,7 0,061 0,228 Broicn Boveri Bulletin, May, 1907, No. 145 L Revue lie VElectriciU, Nos. 2—10 " Simplon Tunnel. ] 40 Brown Boveri .... 60 40 600 — — 1,5 25 2,5 41,5 1,0 16,6 67% 750 3,0 1,02 4 Burgdorf-Thun. ['Jo face 2'- 254. TRACTION MOTOES AND ELECTRIFICATION OF RAILWAYS 255 chief data of the two motors are then as shown in the following Table :— Single Phase Motor. Three-Phase Motor. Rated capacity in hp Weight, in kg . Eevolutions per minute Weight in kg per hp 500 8800 236 17,6 1100 10 000 220 9,1 From this Table it appears that the weight, for equal speed, of the single phase motor is double that of the corresponding three phase motor; that is to say, the three-phase motor will develop more than double the power of the single phase motor at the same weight and number of revolutions per minute. Moreover, the single phase motor has forced draft while the three-phase motor depends solely on natural ventilation. B. Weight of Extra Equipment. There is much difficulty in obtaining reliable figures for the total weight of electrical equipment. Weights of " electrical equipment " are occasionally given in descriptions of railway rolling stock, but it is seldom definitely stated what is included in these weights. The figures given in column I of Table XC. represent the weight of equipment per motor, and this weight may fairly be taken as including the motor with gear and gear case, and the weight of the extra equipment per motor. The extra equipment should include controllers, switch gear, resistances, transformers, wiring and any auxiliary apparatus, including the current collecting apparatus. When making comparisons, the weight of the pneumatic and other braking equipment should be excluded from the above weight of " electrical equipment." It is impracticable to set up any general rule for calculating the weight of equipment for the various systems, and consequently it is proposed to make comparisons between the figures given in Table XC. These figures for the weights of electrical equipment have been collected from all available sources, and have been corrected and checked at every opportunity. We can only compare them with one another in a general way, however, since, as above stated, it is not always apparent just what is included in the term " electrical equipment." 256 HEAVY ELECTRICAL ENGINEERING The first two examples of Table XC. are those given by Sprague in his recent paper before the American Institute of Electrical Engineers. 1 The first is a four motor equipment, each motor (G E A 605) being rated at 75 hp 25 cycles 700 rpm. The total weight of equipment per hp works out at 36,6 kg, and the weight of extra equipment (i.e., excluding the geared motor) at 11 kg per hp. In column M, the weight of extra equipment per motor is expressed as a percentage of the weight of the geared motor. In this case the figure is 44 per cent. The weights given in this and the following case include only those items specified on p. 255. The second example is also a four motor equipment, the motor (in this case a Westinghouse motor) being rated at 75 hp, 15 cycles, 700 rpm. The total weight of equipment per hp works out at 40,6 kg, and the weight of extra equipment at 15,1 kg per hp. This higher weight is probably accounted for by the extra weight of the transformer for 15 cycles, as compared with that for 25 cycles in the first case. The motor itself is somewhat lighter in the second case, and the extra equipment per motor weighs 60 per cent, of the weight of the geared motor. There is, however, little difference between the total weight of equipment, whether a frequency of 15 cycles or 25 cycles is employed. As a further example let us take the two motor equipment of the Heysham-Morecambe line of the Midland Eailway. Each of the Siemens motors, of which four have been supplied to this road, has a rated output of 175 hp, and the total weight of equipment appears to be 2 31,4 kg per hp. 3 The weight of the extra equip- ment per motor is thus some 83 per cent, of the weight of the geared motor, or 14,3 kg per hp. Very full particulars have been published of the two motor equipment of the Eotterdam- Hague motor coach. As at Heysham, the motors are of the Siemens- Schuckert compensated series type, and are rated at 175 hp each. In this case the total weight of equipment works out at 42,9 kg per hp — much heavier than the corresponding figure given by Dalziel for the Heysham-Morecambe equipment. The weight of the extra equipment per motor is some 150 per cent, of the 1 A.I.E.E. Proceedings, July, 1907, p. 1188. 2 See Dalziel's letter in the Times Engineering Supplement for April 17 1907. 3 The Railway Gazette for June 19, 1908, has appeared since the above data was compiled and in an article describing the Heysham-Morecambe line, it is stated that the one-hour 75°C. rating specified for these Siemens motors is 180 hp. The weight of the motor, including gearing, is given as 3,12 tons. The total weight of electrical equipment of a motor car with 2,180 hp motors, is 14,4 tons, or 40 kg per hp, a figure 27 per cent, greater than that given by Dalziel in the Times Engineering Supplement for April 17, 1907. TRACTION MOTORS AND ELECTRIFICATION OF RAILWAYS 257 weight of the geared motor, or 25,7 kg per hp. The following is a list of the component items of the equipment on the Rotterdam- Hague motor coach : — Electrical Equipment of One Motor Coach. Metric Tons. One transformer • . . . 2,80 High voltage switch . 0,20 High voltage resistance . > . 0,20 High voltage fuse . . 0,01 High voltage cables . 0,20 Bow collector . 1,00 Two motors with gearing and suspension . 6,00 Low voltage cables . . 0,45 Contactors with case, etc. . 1,60 Equipment in driver's compartment . 0,30 Master controller . . 0,20 Motor driven fan . . 0,25 Motor driven compressor . 1,00 Miscellaneous parts . 0,75 Total electrical equipment . 15 tons (Or 7,5 tons per motor) The two bogies weigh . 10 tons The car body weighs . 22 tons Consequently the total weight of the motor coach without passengers is 47 tons Let us compare with the above, some of the figures for continuous current equipments. Take for example the Westinghouse four- motor equipment for the Metropolitan Eailway. Each motor is rated at 150 hp, and weighs 2,5 tons with gear. This is not a light motor for its output, but the weight of the extra electrical equipment is only 4,52 kg per hp as compared with 11, 15,1, and 14,3 kg per hp for the above mentioned single phase equipments. As another example let us take the two-motor equipment used on the Metro- politan District Eailway. Each motor, designated as G.E. 69 B is 1 This table is reproduced by permission from p. 237 of Vol. II. of Electrical Traction, by Messrs. Wilson and Lydall, published by Edward Arnold, London. H.E.E. S 258 HEAVY ELECTRICAL ENGINEERING (on the one hour 75° C basis) rated at 240 hp, 1 and weighs 2,8 kg per hp with gear. The total equipment weighs 7,3 tons, or 15,2 kg per hp ; under half the weight per hp for the single phase equipments, which were 36,6, 40,6, and 31,4 kg per hp respectively. The weight of the extra electrical equipment, i.e., the electrical equipment excluding the geared motor, is 3,5 kg per hp, or 30 per cent, of the weight of the geared motor. In Table XCI. are given particulars of a large number of con- tinuous current equipments as manufactured by the General Electric Co. of America and the Westingliouse Co. The data in this table fully confirms the figures which we have adduced above. The G.E. 69 is, in this table, given the nominal rating of 200 hp. As above stated, however, it rates at 340 hp on the one hour 75° C basis. TABLE XCI. Data of Weights of Standard Continuous Current Railway Motors and Equipments. (Tlie figures in the last column are the ratios of the weight of total electrical equipment to the total weight of motors, including gear and gear case.) Trade Name. S-t o © o a o o O d 25 "5 o o o a I a o O . ox is S a) a," c T„«3 .2 A bb X ft u ft d N B bb ft A © ft d PQ G.E. 800 G.E. 54 G.E. 60 Westingliouse 12 A "Westingliouse 69 G.E. 1000 G.E. 78 G.E. 58 25 J 25 | 25 | 25 -1 3J j 85 | 35 | 35 | 2 4 2 4 2 4 2 4 2 4 2 4 2 4 2 4 K10 K12 K10 K12 K10 K12 K10 K12 K10 K12 K10 K28 K10 K28 K10 K28 427 534 427 534 427 534 480 535 430 535 427 615 427 615 427 615 880 880 830 830 756 756 1000 1000 890 890 1000 1000 1160 1160 98C 980 2185 4050 2090 3855 1940 3550 2500 4650 2210 4150 2430 4615 2750 5255 2390 4535 43,5 40,5 42,0 38,5 35,5 34,7 50,0 46,5 37,0 35,0 34,7 33,0 39,3 37,5 34,1 32,4 1760 3520 1660 3320 1510 3020 2000 4000 1780 3560 2000 4000 2320 4640 1960 3920 35,2 85,2 33,2 33,2 30,2 30,2 40,0 40,0 30,0 30,0 28,4 28,4 33,2 33,2 28,0 28,0 1,24 1,15 1,26 1,16 1,28 1,18 1,25 1,16 1,24 1,17 1,21 1,16 1,18 1,13 1,22 1,16 1 On p. 1326 of the Proo. of the A.I.E.E., Sprague states that 418 G.E. 69 B motors are employed by the Interborough Rapid Transit Co. He states that they " are sometimes ' rated at 200 hp at 300 amp,' but actually test to 241 hp with 75° rise of temperature, according to the standard practice of the American Institute of Electrical Engineers. Several hundred more of these motors are in use on the London Underground Railways, and 268 motors of similar frame, known as the G.E. 69 C, built for 50 volts higher normal operation, nearly 100 less revolutions at the one-hour rating, but developing, notwithstanding, 232 hp with like rise of temperature, are in use on the New York Central Railroad," TRACTION MOTORS AND ELECTRIFICATION OP RAILWAYS 259 ■ji c o ■a 2 * to o to £P bo Trade Name. o p4 o o o O c o o . £- o 50- X^ \ - / A ■40- ' \ 1C- ^i \ p N •^ \ 30- *<;> \ V \-& f s v 10 N \ .5 ■WOO ■/C00 500 2(70 300 400 ,500 600 700 Amperes Input per Motor. 800 900 1000 Fig. 166. Starting Curves of Stemens-Schuckert 175 hp Compensated Series Motor. Including the average transformer efficiency of 96 per cent., the overall efficiency of the electrical equipment is 0,76 X 0,96 = 0,73, or 73 per cent. This figure should be compared with the values given in Figs. 146—154, facing p. 239 of Chap. X. TitAUTlUN MOTORS AND ELECTRIFICATION OF RAILWAYS 265 The following figures are of interest : — Average kw per motor during acceleration = 136 kw Maximum kw per motor during acceleration = 238 kw One hour rated kw per motor (175 hp) = 148 kw % 30 1 1 1 1 1 Siemens Schuckert :#0 /„/* s — 80 5^1 70 fs . — £> i / ~ >e h 60 S N. r ^ «* ^Z± s < ■%s S 50 \0 \ J* o 1,0 . -c -*j 0,3 S 40 ~~-~S J^ c 5 30 •z ^> a. Uj Povi e>S -s? >er ^4^ 0,7 20 ^ 10 w - \ R 0,6 k !h 0,5 \ \ v 0,4 \ 200 300 400 500 600 700 800 Amperes Input per Motor 300 1000 Pig. 167. Efficiency and Power Factor Curves of Siemens-Schuckert 175 hp Compensated Single Phase Motor. Time elapsing from start to start = 12-4 + 20 = 144 sec. Average kw per motor = 10 X .3600 6 X 144 41,7 kw. 266 HJiAVY .KUECTKICAL ENGINEERING 148 Eatio of rated load to average load — — - = 3,5. Thus we find that the average load during acceleration is within O en O CO O C3 CO C^ <* 8 c C3 CJ Q) CO C 13 6 r da .ion to^f er$ -ak ng f eta W p < O • ft g< y O E" 1 S e/ CD «? C. < ■$ Q ^ Q Q ^^» Q (i CI ^<» «) r, ■> ;£<»• *n Q to c CO (U ") 00 o - — o H n° f 0,9 nP e ■ Sec kin 1 ; F e tar' ati° CO Bra o| r* 3 / T> o t -1 < 3; OQ O «/ I, to 1 ■'£• -5 •* -ft. o" "1" -1- _l. ■ 1 V. i. "CI ■8 .5 els 'A ^ '£ l-l H P Ho S ^i *5 .0 ■5/ ■a i 1 .^ V ii to to 1 *0 O -J < i / /. / Wg to ■0 o / „ t & / ^ z 'J W / Diagram a provided hour over ^ ^ \V 1 V crX; S 0> S « a ?x . — - R W o ylS 1 * Pi ^\ HOT At '?? \VA w f 1 ! P ffl 4i* *t? fc* Asei y^. \^' fc« -S A Oil "^5^ ^ A Off/ ^ / 0// l| Hi <1 y 1S9 1— 1 ■5 u c c o J- J c *■ JB c J c c P'M£ >lf)f c ' Pi c c ^ isrf< 3 c c 1 c c t 1— I in steps to 320 volts. The motors are running at a comparatively high speed on these last steps, and the current can be increased without incurring commutation difficulties. Thus in the particular case considered in Fig. 170, the maximum current is 850 amp. The TRACTION MOTORS AND ELECTRIFICATION OP RAILWAYS 271 mean rate of acceleration in this case is of course much less than that obtained by the first method, and consequently the power will have to be supplied to the train for a longer time, in order to reach the necessary maximum speed. The speed-time curve and the energy input curves, under the above conditions, are given in Fig. 171. The average rate of acceleration (until the " motor curve " is reached) is 0,34 m psps, the maximum speed 71 km ph; and as the speed is higher, the retardation during coasting has been taken at 0,044 m psps. The braking retardation has been taken at 0,9 m psps, as in the previous case. The energy input to the motors, the internal loss in the motors, and the gear loss, are represented by the areas of the respective input curves as was explained for the first case. For this example the following figures only need be given : — Total energy consumed by the six motors is 12,5 kw hr, or 25 per cent, in excess of the consumption in the first case. The input to the motors is therefore 12,5 X 1000 Kn . , , — -j— — — = 50 w hr per ton km. 156 X 1,6 r Assuming, as before, an average transformer efficiency of 96 per cent., the energy consumption of the train is 52 w hr per ton km. The internal losses in the motors amount to 2,15 kw hr ; the average efficiency of the motors is therefore 82,8 per cent. The gear loss amounts to 0,75 kw ; the average overall efficiency is therefore 77 per cent., excluding the transformer. The energy delivered to the axles is 9,6 kw hr, or 38,5 w hr per ton km. Including the average transformer efficiency of 96 per cent., the overall efficiency of the equipment is 0,77 X 0,96 = 0,74, or 74 per cent., only 1 per cent, higher than the efficiency in the first case. The following figures are of interest, and should be compared with those on p. 265 : — Average kw per motor during acceleration = 116 kw Maximum kw per motor during acceleration = 232 kw One hour rated kw per motor (175 hp) = 148 kw Average kw per motor from start to start = 52 kw. 148 Eatio of rated load to average load = -^r = 2,85. During acceleration 2,15 kw hr are wasted in the motors. The time from start to start is 144 sec ; therefore the average watts per motor are 2,15 X 3600 X 1000 QO „ n , , Ui x 6 = 896 ° watts - 272 HEAVY ELECTRICAL ENGINEERING The weight of one motor without gear is 2,77 tons. Therefore average watts per ton = -^-~ — 3240 watts per ton. A, I I The average watts per ton, during acceleration only, are of course J3 13 § ■9 &> »? SO .4: >*> «3 s " ^ 5 £ ^ 5 — ■*>- ^ 5; ^ it "I •It $ ^ '■if ^ \\\ fe ~7s $ ^ ^ §s & -4- . ii -1- — S- ■*o -■s- ■Jjr- ^ |t ^ *s>JS ^ «Jv ■3 ivS AS I ^ ^ A\ s$ s$ f i 5 t a ^ 5 ^ ic> S> S q ^; c^ is ^ paqse/tf •jsmoj jo an/ej snosue]ue]?ui jo <=> £? § S 5 H H M M < o go B.fc * d M H O GO C_l o f a w H HOQ O Ml higher ; in the particular case considered, they amount to 2,15 X 3600 x 1000 _ OQn ,, , 64 X 6 X 2,77 = 728 ° WattS per t0n - The losses are shown separately in Fig. 172. Tn the first case considered, in which the rate of acceleration until reaching the "motor curve " portion of the accelerating period TKACTION MOTOBS AND ELECTRIFICATION OF EAILWAYS 273 was 0,50 m psps, we found that the total energy supplied to the axles of the train was 7,6 kw hr. Furthermore, on p. 267 we found that nearly all this energy was utilized in giving the, train the velocity of 400 24 Fig. 173. Speed Characteristic and Tractive Force Curves of 175 hp Compensated Siemens-Schuckert Single Phase Motor. 63,5 km per hr. In the second case we found that 9,6 kw hr had to be delivered to the axles, i.e., 26 per cent, more than in the first case. This shows the importance of a high rate of acceleration, as in both cases the schedule and average speeds were the same; the rates- of acceleration were 0,50 and 0,34 m psps respectively. H.JS.B. I '274 HEAVY ELECTRICAL ENGINEERING At the instant of cutting off the supply in the second case, the speed of the train is 71 km per hr. From this figure and the weight of the train, we can deduce the total energy input as in the previous case. ™ r , , v 1 56 X 1000 v / 71 X 1000 V The kmetic energy = \ X ^— X ( 3600 J = 3 100 000 kg m But 1 watt hour = 367 kg m. Therefore the kinetic energy of the train due to the translational motion is 8,45 kw hr. The second item, the kinetic energy of the rotating parts, can be taken, as before, as being some 8 per cent, of the first item. There- fore the total kinetic energy = 8,45 X 1,08 = 9,15 kw hr. The energy which must be supplied during the accelerating period (which is longer in this second case) to overcome the tractive resistance will bring this amount up to 9,6 kw hr : which last figure was the estimated value of the energy input to the axles from a consideration of the motor characteristic curves. Second Alternative Run. — Fig. 173 shows yet another cycle of starting operations. In this case the average starting current is 440 amp. Were this alternative chosen, the train would not reach a sufficiently high speed to be able to complete the run in 124 sec. This is shown clearly in Fig. 174 which is the speed-time diagram for the case considered. Braking is commenced at such an instant, that the train will stop 124 sec after starting. The average speed is only 35,5 km per hr, and so the distance covered will be only 1,22 km, instead of 1,6 km. The train cannot attain to a schedule speed of 40 km per hr under these conditions. This last case was given in order to emphasise the fact that the motors must be able to with- stand, during some stage of the accelerating period, a starting current considerably in excess of the normal current at rated load. Limitations of Single Phase Motors. — The single phase motor is very limited as regards the capacity for overload, and in order to clearly demonstrate this, the characteristic curves for the 175 hp compensated series motor discussed above are given in the following figures (Figs. 175 — 178) in a somewhat different form to that in which they were given in Fig. 166. In this case the speed, current, power factor and efficiency are plotted against the output in horse power as abscissae. From this series of curves it will be seen that the maximum output is sharply defined at each operating voltage, and, further, that the maximum output decreases rapidly with decreasing voltage. Thus in the case of this motor, [PLATE XVII. 5> u 5 k 9, 1400 1,0 1200 0,3 1000 0,8 800 0,7 600 400 200 40 80 120 160 200 HP delivered to Car Wheel Axle 240 Fi<*. 175. Pep.formance Curves of Sieme.s-s-Schuckert 17.3 hp Com- ° pensated Series Single Phase Motor at the Maximum Working Voltage of 320 Volts. <0 ■ " o r- ») e m ft; fc o i. 1400 Cr * » V M * ) 0,5 200 /SiTlfc?' egj- ,,' -•■' /0 20 30 40 50 H P delivered to Car Wheel Axle. 60 Fig. 178. Performance Compensated Series 150 Volts. Curves of Siemens-Schuckert 175 hp Single Phase Motor at a Pressure of [To face j). 275. TRACTION MOTOES AND ELECTRIFICATION OF RAILWAYS 275 rated at 175 hp, the maximum horse power at the normal voltage of 320 volts is about 230 hp, or only 26 per cent, more than the one-hour rated output. At 275 volts the maximum output is n,$ m? 7f «5 £i-~ Ret: r d3 i,0" of 5^i iifljj. =3 ■a. "5 !2~ ^N «§ -s- "^\ «7 % \ % *3 ^ >\ s ^\ \ :^ -*£ \ 1 o *% O H w a sa O M o £ CD 3 >-< H R « U P W M f-i Ph 3 M Q » R p, CO h y CO fe O ■3 « as °o o !a ■* •jnofj jsa my ui pasog to about 160 hp, and at 220 volts only 95 hp, while at 150 volts it is only some 36 hp. Of course, these low voltages are only used starting, but the torque, required to obtain the necessary high rate of acceleration, is also low. All single phase motors are limited in this way, but the continuous current motor has a T 2 276 HEAVY ELEOTBICAL ENGINEERING momentary capacity some three or four times its rated output, and is thus in this respect much superior to the single phase motor. Although these curves are for the compensated series commutator motor, it must be remembered that the compensated repulsion commutator motor is limited in the same respect. 1 Let us now examine the case of a single phase motor of the com- pensated repulsion type. The Energy Consumption of a Train Equipped ivith Eight " A. E. G. W inter -Eichherg " 115 hp Compensated Repulsion Motors. The Electrician, for June 14th, 1907, contains an article by Dawson, the consulting engineer for the L.B. & S.C. electrifica- tion undertaking. Figures are given for the energy consumption of a train consisting of two motor coaches each equipped with four motors (i.e., eight motors in all), and one trailer coach. There are two classes, and seating accommodation for 188 persons. The total weight of the train is given as 132 tons. The particular journey taken as an example is the run between Battersea Park and Peckham Eye, a distance of 6,3 km. There are four stops in this run (exclusive of start and stop at Battersea and Peckham Bye respectively). The run is made under the following conditions : — Schedule speed, 42 km ph ; Average speed, 48,5 km ph ; Duration of stop, 15 sec ; Bate of braking, 1,0 m psps. In order to simplify the calculations it is assumed that the entire run is over a level track. Pig. 179 shows the characteristic curves for the W.E. 51 115 hp single phase compensated repulsion motor, eight of which are to be used on the train under consideration. In order to attain to the required scheduled speed, it will be necessary to work the motors on the cycle shown in Fig. 179, i.e., with a starting current of 26 amp (the current in the motor is, of course, much greater ; the amperes here mentioned are those measured on the primary of the transformer). The gear ratio is taken as 3,3 and the diameter of the driving wheel as 1,06 m, which values are those of the actual gears and wheels of the L.B. & S.C. cars. The above cycle of operations 1 See also an articlo by the author in The Light Railway and Tramway Jvurnal, June 10th, 1904, pp. 447-451. TRACTION MOTOES AND ELECTRIFICATION OP RAILWAYS 277 will give the necessary draw-bar pull and speed at all points of the cycle, to correspond with the speed-time curve given in Fig. 180. A single run, representative of the complete 6,3 km run, is that between Denmark Hill and Peckham Eye. The speed-time and 85 80 75 80 70 %B0 ■ — n Q >s S XT ' / Max Volt s—i 9 Mm i Volt s— / 1 */t > \ K f V a c D 1600 1400 1200 1000 k^ 800 500 a 400 200 10 20 Amperes Input to Motor. 30 Fig. 179. Speed, Ampere, and Torque Curves of W.E. 51, 115 hp Single Phase Compensated Repulsion Motor. input curves of the run are shown in Pig. 180. Prom these curves the following data can be obtained : — (1) Maximum speed necessary in order to cover the 1,21 km distance between stops is 68,5 km ph ; (2) The average speed over this distance is 49 km ph ; and (3) The schedule speed with a 15 sec stop is about 42 km ph. These are practically the same as the corresponding figures for the whole run of 6,3 km, consequently the particular run under consideration is quite representative. 278 HEAVY ELECTRICAL ENGINEERING The input curve of Fig. 180 represents the power input from the eight motors to the axles of the train at any instant, and conse- quently from this curve we can obtain by integration the total energy (in this case about 8,2 kw hr) utilized by the train in "1 , «* "0 t^ jnoy jad SJ3J9W0//)/ ui p3aa$ § % to I 5=5 V i o-> pe.r se. ■4 n " B Uta. -dgiiBll < . -r *> &L eJ>- 1* « t> s. f> tu < * a s 3 i- on Q * to IN c> fc 5 1= o ft < ■? «■ c-> \ "* 1—1) "*> — < 2 ~C3 C3 0) Cm «o % >o H / E % K — qj en < ^ <=<: / «* < / ~k 4 \ VI °i <» S ^ j: -* * *■ 5 + 50,8 + 0,0278 L lb per ton where V is the speed in miles per hour and L is the length of the train in feet [ 5 : R = X ' 12 + 250 + 0,46 L kg Per t0n ' where V is the speed in kilometers per hour, and L is the length of the train in meters.] For the train under consideration, for which L = 520 ft. [160 meters], the formula reduces to s B = 2,5 + gg-s ib P er ton - 5 [or R = 1,12 + ^ kg per ton. J Inasmuch, however, as Mr. Aspinall's results were obtained by means of a dynamometer in the drawbar behind a locomotive, the formula does not include the head resistance, which is experienced 1 Proc. Institute of Civil Engineers, vol. cxlvii., p. 155. 2 In Mr. Carter's original report, the data are given in feet, miles, and pounds. The author has ventured to add the metric equivalents. U 2 292 HEAVY ELECTRICAL ENGINEERING by the locomotive itself, or in the case of an electric train, by the leading coach. In order to take some account of this, the variable term in the above formula has been increased by 5 per cent., leading to the working formula : — 5 R = 2,5 + £ lb per ton (1.) 0.4,1 5 £or R = 1,12 + ^ kg per ton J Inasmuch, again, as the electrical equipment, whilst doubtless adding somewhat to the air resistance, will not increase it in anything like the proportion of the added weight, the above formula has been applied .to the unequipped train of 250 tons only, whilst the extra resistance due to the electrical equipment has been taken at the uniform rate of 4 lb [or — say — 2 kg] per ton. Thus, if E be the equipment weight, the total train resistance at speed V is : — 250 R + 4 E lb (2.) [or 250 R + 2 E kg]. The mean speed of the train whilst actually running is assumed to be 0,75 of the free running speed on a level track. The scheduled speed, including service stops, is assumed to be 0,70 of the free running speed. The mean train resistance will be greater than that at the mean running speed, inasmuch as the portion depending on the speed varies as a power higher than the first. For instance, if a run be made for 1 mile [1,61 km] at a speed of 80 miles per hr [129 km per hr] and 1 mile at 48 miles per hr [77 km per hr] , the mean speed will be 0,75 X 80 = 60 miles per hr [97 km per hr] , whilst the mean train resistance will correspond to 65,3 miles per hr [105 km per hr]. Consequently, in obtain- ing the work clone against train resistance, the mean value has been taken as that at 0,8 of free running speed. The energy output of the motors, expended in work against train resistance, will be 2 w hr per train mile per pound of mean train resistance [2,73 w hr per train km per kg of train resistance]. In order to take account of the kinetic energy lost in braking at station and signal stops, slacks, etc., it is assumed, as sufficiently characteristic of this service, that the speed of the train is reduced from free running speed to a half of this, once in every 15 miles [24 km]. Assuming that the effect of rotary inertia is equivalent to an addition of 10 per cent, to the weight of the train, the effect of these slacks is to require an output from the motors of TRACTION MOTOES AND ELECTRIFICATION OF RAILWAYS 293 0,00155 M V 2 w hr per train mile — M being the total weight of the train in tons and V the free running speed in m ph, [or 0,000374 MY 2 w hr per train km where V is the free running speed in km ph]. Energy will also be used in shunting and in idle journeys. Additional energy will be required where the train resistance is increased by curves, crossings, bridges, tunnels, winds, etc. The general effect of grades is usually also to increase the energy con- sumption slightly. In order to take account of these factors the bare figures given by the above formulae have been increased by 15 per cent., making finally the mean output of the motors when in service : — 2,3 X mean train resistance + 0,00179 MV 2 w hr per train mile [or 3,1 X mean train resistance + 0,00043 MV 2 w hr per train km, when the train resistance is expressed in kg per ton and V in km per hr]. This quantity divided by the average efficiency of the equipment gives the energy input. The writer has found from experience that the above dynamical method of obtaining the energy consumption, if used with care, yields excellent results. In electrical apparatus where it is necessary to develop so much power in so confined a space as obtains in the case of train-driving motors, the heating of the vital parts of the motor will always be a limiting feature, since all available kinds of insulating material are more or less damaged or weakened by high temperature. It is necessary, therefore, to make the amount of energy to be dissipated the basis from which to derive the particulars of the train equipment. Thus, although no experience is available on the electrical operation of the class of traffic now under consideration, the investigation is made upon a basis derived entirely from experience in railway operation, and independent of the special features of the class of traffic. Eailway motors of large size, such as require bogies of, say, 8 ft. [2,4 m] wheel base, if completely enclosed and without artificial cooling arrangements, are capable of dissipating, under service con- ditions from 1000 to 1250 w per ton of motor with an ultimate tem- perature rise of approximately 70° C, as indicated by a thermometer placed in contact with the hottest accessible part. The above figures for the power that can be dissipated include iron and copper loss in the motor, with the commutator losses due to brush contact resistance 294 HEAVY ELECTRICAL ENGINEERING and friction. In order to allow for exceptionally great train resistance or weight, breakdown in train equipment, etc., it is advisable to base the calculations on the smaller of the above figures, viz., 1000 watts per ton of motor, where there are no artificial cooling arrangements, since 70° C rise by thermometer is as much as should be allowed in service. Where the motors are cooled by forced draught, however, possibly twice as great a dissipa- tion might be attained with suitable arrangements. 1 This assumes that the motors are on the trucks of the coaches, where they cannot well be given much attention. In a locomotive a somewhat greater draught might be used for cooling, as the motors can be kept under observation and deleterious matter more carefully strained from the air before forcing it into the motors. In the following it will be assumed that the motors are mounted on the trucks of the coaches, which is, in the matter of operation, preferable to the use of loco- motives, and is in any case sufficient for the purpose of the present general discussion. The following tables give the constants assumed in the calcula- tions. In these tables, column A gives average values found in practice employing the continuous current system with motors cooled by natural draught. Column B gives to each item the best values that can be expected with this system. Column C gives the best values that can be expected using the continuous current system with motors cooled by forced draught. Column D gives the best values to be expected using the single phase system with motors cooled by forced draught. In the continuous current system, the supply to the motors is not necessarily at the low pressures usual on urban systems, but to the degree of approximation possible here, the exact pressure of supply is not important. However, rather large figures have been allowed for cost and maintenance of line conductors, to provide for a considerable quantity of protecting boards. In the single phase system the constants have usually been chosen more favourable than could be attained at present, in order to make allowance for future improvements. Remarks on Table XC1I. — The difference between the first two items represents energy used in controlling the motors, in operating the air compressors, etc., and in the case of column D the loss in the main transformer. The difference between the second and third items represents energy lost in gears, which has throughout 1 The examples worked through in connection with the Siemens Schuckert 175 hp compensated series motor on pp. 261 to 274 indicate this to be the case. TRACTION MOTORS AND ELECTRIFICATION OF RAILWAYS 295 been taken as 4£ per cent, of the input. Motor-bearing friction, being a very small quantity, may be taken as included in this. If the motors were assumed gearless, however, the final results would not be greatly affected. The fourth item includes iron and copper losses in the motor, with commutator losses both of brush contact resistance and friction. In the class of service considered, the train operates for much of the time at free running speed where the brush friction will be large. The single phase motor will have an TABLE XCII Chnracteristics and Conditions of Garter's Four Alternative Projects. A B C D Average efficiency of complete equipment 84 85 85 78 Average efficiency of motor, including 87,5 88,0 88,0 82,5 gear Average efficiency of motor, excluding 92,0 92,5 92,5 87,0 gear Average loss in motors (per cent, of input) 8,0 7,5 7,5 13 Ratio of motor weight to equipment weight Watts dissipated per ton of motor 0,6 0,6 0,5 0,5 1000 1000 2000 2000 Watts dissipated per ton of equipment 600 600 1000 1000 Average efficiency of transmission (bus 78 80 80 89 bars to train) Power used in generating station in per 6 4 4 4 cent, of power generated Standby plant at peak of load in per 30 20 20 20 cent, of total Trains in service at peak of load in per 62,5 62,5 62,5 62,5 cent, of total Load factor (per cent, for 365 days per 35 45 45 45 annum) Train miles per annum per mile of single 10 400 10 400 10 400 10 400 track Train km per annum per km of single 10 400 10 400 10 400 10 400 track especially large brush friction on account of the large number of brushes which are required, whilst it will, in virtue of its characteristics, require to be run for much of the time at reduced voltage and correspondingly reduced efficiency. With equipment weight defined as above, the motor weight is usually about 60 per cent, of this in the continuous current system with natural draught. If with forced draught, it is possible to reduce the motor weight by a half, other apparatus being unchanged ; 296 HEAVY ELECTEICAL ENGINEERING this weight would become 43 per cent, of the equipment weight To assume it at 50 per cent, is probably somewhat favourable to forced draught. This figure is also fair to the single phase system in which the controlling gear includes heavy transformers. The efficiency of transmission, in the case of the continuous cur- rent system, is taken from experience, but it is estimated for the single phase system. The number of trains in service at the peak of load, and the load factor, have been estimated from main line time-tables, and are both probably a little high. The load factor may be denned as the ratio of the average load for the year to the average during the time of the maximum daily peaks. It is assumed that the full load capacity of the plant, exclusive of standby, is just sufficient to provide for the average load during the time of the maximum peaks — its overload capacity taking care of variations above the average. The last item gives the number of trains passing over each mile (kilometer) of track, being the average for the whole kingdom. It is obtained from the Board of Trade returns for 1905 by dividing the total train mileage (400 millions) [or a total train kilometerage of 645 million] by the total length of running track of 38 430 miles (62 000 km). It is used in estimating the expenses per train mile (train-kilometer) for upkeep, etc., of line conductors. TABLE XCIII. Capital Outlay with Garter's Four Alternative Projects. A T! D Cost generating station, £ per kw capacity 18 15 15 15,75 Cost sub-stations, £ per kw generating 10 7,5 7,5 2,5 station capacity Cost transmission lines, £ per generating 3 2,5 2,5 2 station capacity Cost train equipment, £ per ton weight 120 90 110 120 Allowance for contingencies 5 5 5 5 Cost line conductors, £ per mile of single 1200 1000 1000 1300 track Cost line conductors, £ per km of single 750 620 620 810 track Remarks on Table XCIII. — The cost of "the generating station includes site, buildings, docks, sidings, etc., as well as the actual plant. The minimum for the single phase system is taken at 15s. TRACTION MOTORS AND ELECTRIFICATION OF RAILWAYS 297 per kw more than for the continuous current system, inasmuch as single phase generators are about one-third more expensive than three-phase generators of equal full load and overload capacity. The cost of sub-stations also includes sites, buildings, and all necessary for completeness. The cost of transmission lines depends on the lay-out of the distribution system, as well as on the capacity, but being a comparatively small item, an average figure per kw lias been assumed. The figure has been taken 10s. per kw lower in the single phase system than in the continuous current system, although there would be more copper for a given pressure between conductors, since the lines would doubtless be carried on the gantries provided for supporting the overhead line conductor, so that a line of poles would be saved. The cost of train equipments is rather more when forced draught is employed than when the motors are naturally cooled, inasmuch as the total cost will not be diminished in the same proportion as the weight, whilst the arrangements for providing the forced draught will add to the cost. The single phase equipments will be more expensive than continuous current equipments, principally on account of the motors being more complicated in construction. The cost of line conductors in the case of the continuous current system includes a third rail, bonding of track rails, protecting devices to prevent accidental contact with the third rail, the equip- ment necessary for an average amount of special work, sectionalising and isolating switches, and other accessories. In the single phase system the cost includes the overhead conductor mounted on insulators and carried in general by gantries spanning the line, bonding of track rails, boosting transformers, special work at bridges, tunnels, turnouts, etc., with sectionalising switch cabins and other accessories. A cheaper form of construction might be adopted on a tramway or unimportant branch line, but the figure given is certainly as low as would be possible if the substantial construction characterising British railways were adopted. Remarks on Table XCIV. — The cost of power includes coal, water, oil, waste, etc., wages, office expenses, removal of ashes, and all expenses in connection with the repair and renewal of plant. Even in the largest and most modern generating stations, carrying a railway load, it is rare for this cost to be less than 0,275 pence per kw hr {i.e., per " unit ") of output, and the minimum figure of 0,225 pence is hardly likely to be reached unless coal can be obtained at 298 HEAVY ELECTRICAL ENGINEERING pit-bank prices and other circumstances are favourable. The sub- station expenses are derived from experience in the case of the continuous current system, and are estimated for the single phase system. The standing charges include rates, taxes, insurance and the like, on generating station and sub-stations. They are estimated at 3 per cent, of the first cost in the case of column A, and at 2J per cent, in the case of the other three columns, and are exj>ressed in the table in pence per kw hr generating station output. The Operating TABLE XCIV. with Carter's Four Alternative Projects. A B D Generating expenses, peace per kw hr 0,275 0,225 0,225 0,225 output Sub-station expenses, per kw hr output 0,025 0,02 0,02 0,006 from generating station Standing charges, generating station and 0,094 0,0428 0,0428 0,0348 sub-station Maintenance transmission lines per kw hr 0,006 0,0045 0,0045 0,0045 output from generating station Maintenance train equipments per mile 0,00125 0,0011 0,00125 0,002 perhp Maintenance train equipments per km 0,00078 0,00069 0,00078 0,00124 per hp Maintenance line conductors per train mile 0,55 0,46 0,46 0,75 Maintenance line conductors per train km 0,342 0,286 0,286 0,465 Drivers' wages per train mile 2,99 2,99 2,99 2,99 Drivers' wages per train km 1,86 1,86 1,86 1,86 Interest on capital, excluding line con- 3,75 3,75 3,75 3,75 ductors (in per cent.) Interest on capital, line conductors, per 1,04 0,86 0,86 1,12 train mile Interest on capital, line conductors, per 0,65 0,54 0,54 0,70 train km maintenance of transmission lines is a small matter, and the figures given are taken from urban practice. The maintenance of train equipments depends on the number of equipments per train, or on the horse power. The figures given are expressed in terms of the horse power required at free running speed on level track, and are approximately correct when the motors are large and mounted on the bogies of the coaches. The single phase system as compared with the continuous current system will have approximately twice as many motors for a given TRACTION MOTORS AND ELECTRIFICATION OF RAILWAYS 299 horse power, and the motors, being more complicated, will be more costly to maintain, so that the figures given are really much more favourable to the single phase system than to the continuous current system, and allow a great deal for future improvements in the former system. The maintenance of line conductors in the continuous current system is not a heavy item, as the third rail does not appear to wear appreciably with use. Including inspection, renewal of pro- tection boards, occasional replacement of broken insulators and bonds, with the bonding of renewed track rails and the extra material and labour involved when sleepers are renewed, the annual expense is estimated at £20 to £25 per mile of track [£12 to £16 per km of track], and the figure given is 2 per cent, of the first cost. In the single phase system the catenary and trolley wires will require occasional renewal, whilst the gantries will require periodical painting and overhauling. The expense involved, together with that of inspection, replacement of broken insulators, track bonds, etc., is estimated at £30 to £40 per mile [£20 to £24 per km] per annum, and the figure given in the table is 2J per cent, of the first cost (£32 10s. per mile per annum) [£20 per km per annum]. The figure given for wages of drivers and assistants is an average figure derived from steam operation. It is subject to the correction of those in a better position than the writer to estimate on the matter, but is inserted here provisionally for the sake of complete- ness. It is obtained as follows : The Board of Trade Eeturns give figures for wages in connection with the working of locomotive engines for a number of the chief railways of the country. In 1905 this expense amounted to 3,78 pence per train mile [2,35 pence per train km]. This, however, includes not only wages of drivers and firemen, but also of cleaners, coal handlers, etc. The propor- tion of the total which is paid to drivers and firemen is taken the same as quoted in the late Mr. Langdon's paper "On the super- session of the steam by the electric locomotive," 1 leading to the figure given. The interest on the extra capital needed for electrification is taken at the rate of 3| per cent, per annum, which appears to be approxi- mately the value of money invested in British railway securities. The results of the calculations as derived from the constants in 1 Journ. I.E.E., vol. xxx., p. 139. 300 HEAVY ELECTRICAL ENGINEERING the above tables are embodied in the curves of Figs. 181 to 188. In Figs. 181 a to 188 a, the curves of Figs. 181 to 188 have been replotted in metric measure. Figs. 181 and 182 show respectively the capital outlay and operating expense for the constants in the columns marked A in the tables, being segregated to show how the total is built up. Figs. 183 and 184 stand in the same relation to the columns marked B ; Figs. 185 and 186 to those marked C, and Figs. 187 and 188 to those marked D. The curves of capital outlay include only the items that can be expressed "per train," that is, they do not include line conductors where cost is naturally expressed " per mile " [kilometer], and is given in Table XCIII. In order to show exactly how the curves have been derived, a calculation for a particular point will here be given. The constants will be taken from column A, and the free running speed on level track will be assumed at 75 miles per hour. The mean train resistance, namely, that at 60 m ph (0,8 of 75 m ph) as given by formula 1, is 17,3 lb per ton, or 4330 lb for the 250 ton train. To this must be added 4 lb per ton of equip- ment weight. A simple equation' for the latter quantity is obtained by equating the loss in the motors expressed as 8 per cent, of the input (derived from formula 3 and the motor efficiency) to the loss expressed in watts as 600 times the equipment weight. This gives, in the present case, an equipment weight of 117,5 tons. The total mean train resistance is, therefore, 4330 + 470 = 4800 lb, and the output of the motors, given by formula 3, is 14 720 w hr per train mile. Dividing this by the equipment efficiency of 84 per cent., the input measured at the train is 17 530 w hr per train mile. Dividing again by the transmission efficiency (78 per cent.) the energy output of the generating station is 22 500 w hr per train mile. The scheduled speed being 0,7 of the free running speed, the average power output of the generating station is (0,7 X 75 x 22,5) 1180 kw per train in service. Taking account of the number of trains in service at times of maximum load, as compared with the total numher, the amount of standby plant, and the power used in the generating station itself, we obtain for the capacity of the ,. , . , 1180 X 0,625 T , ( . generating plant, -^ ■ — - - = 1121 kw per tram. The tram resistance at the free running speed of 75 ml ph, as given by formula 2, is 6470 lb. The power required for free running is therefore 6470 X 75 -=- 375 = 1294 hp. The average distance covered by each train in the course PLATE XVIII. ■5 =5. §" ^i Column A . Column B . Column A is based on the best values Column B is basedon the best values fo> Found /^practice employing the Continuous Current System with Motors cooled ■th Natural Draught each item that can be expected 'us m a the Continuous Current System with Motors cooled with Natural Draught. 90000 80000 70000 60000 £0000 40000 30000 20000 10000 181. \ II 'I / ! ' —A V // , / \b 40 50 60 70 SO 30 40 50 60 70 80 SO 90000 80000 70000 60000 50000 40000 30000 20000 10000 183. t c d // / A [> / p ^ F Column C. Column C is based on the best values for each item that can be expected using the Continuous Current System with Motors cooled with forced Draught Column D. is based on the best values Tor each item that can be expected using the Single Fhjse System with Motors cooled with Forced Draught 186. 80000 70000 60000 50000 40000 30000 20000 10000 // h | // Y), c ///. d w&^r e # Column 40 50 60 70 80 SO 40 50 60 70 60 SO 40 SO 60 70 80 SO 40 50 60 70 80 30 90000 80000 70000 60000 50000 40000 30000 20000 10000 187. n /A / f h // r / ' .#> d / <& e -S0& =ss* .5l 40 50 60 70 80 SO 6 ,5Hi 6 ^ io k: k »j H $ ■ 5 £S 40 50 60 70 80 30 Abscissas denote Free Running Speed in Miles per Hour. o> to ^0 6 c Figs. 181- 1SR Data of Capital Costs "and Operating Expenses corresponding to the Electric Railway Systems of Columns A, B, 18b. .LATA 01 KjAt g Am g 4 _ > [Jo face /i. 300. [PLATE XIX. Column A is based on the best values found in practice employing the continuous current system with motors cooled with natural draught Column A 90000 80000 70000 60000 50000 10000 30000 20000 10000 8 181 A b it c _y/ // 1 AA I . j w\ / / i y i ! // ' \/ • // ! /i * ' J/i ■^ 1 i "\ i Column B Column B is based on the best values for each item that can be expected using the continuous current system with motors cooled with natural draught Column C is based on the best values for each tern that can be expected using the continuous current system with motors cooled with forced 90000 BO 70 SO 90 100 110 120 ISO W 150 Column C Column is based on the best values for each item that can be expected using the Single Phast drauoMsvstem with motors cooled with forced draught 90000 Column D 90000 r SO 70 SO SO HO 120 130 m ISO 20 18 IG It 12 10 8 e 4 2 y z 60 70 SO SO 100 110 120 130 110 150 SO 70 80 90 100 110 120 130 140 150 20 IS 16 14 12 10 8 S 4 2 186A •-' r s / 9 /.* /. * J i^i Ctr St ^_ n BO 70 80 90 100 110 120 130 HO 150 GO 70 80 90 100 110 120 130 140 150 188 A IS 16 14 f 12 .10 9 h y ' !// 8 J b ^ H 1 'II ^~ n 2 a <0, "^ c; Tj "^ o c c Co K K si s to — § B &1 Co 53^ 2; V •5=35 V O^-g Abscissa? denote Free Running Speed in Kilometres per Hour Figs. 181A— 183a. Data of Capital Costs and Opebating Expenses cokkesponding to the Electric Railway Systems or Columns A, B, C, and D of TablesJ2, 93,^and 94. TRACTION MOTORS AND ELECTRIFICATION OF RAILWAYS 301 of a year is 0,7 x 75 x 0,35 X 0,625 X 24 x 365 = 100 500 miles. The capital costs per train are, therefore, as follows : — £ Generating station complete 1121 kw at £18 per kw . 20 180 Sub-stations complete 1121 kw at £10 per kw . .11 210 Transmission lines, 1121 kw at £3 per kw . . 3360 Train equipments, 117,5 tons at £120 per ton . . 14 100 Contingencies, 5 per cent, of the sum above . . 5440 Total capital outlay per train . . . £51 290 Capital outlay on line conductors per mile of single track (Table XCIII.) £1200 The operating expenses per train mile are as follows : — Pence Generating costs, 22,5 units at 0,275d. per unit . . 6,19 Sub-station expenses, 22,5 units at 0,025rf. per unit . 0,56 Standing charges, 22,5 units at 0,094d.. per unit . .2,12 Maintenance transmission lines, 22,5 units at 0,006d per unit 0,13 Maintenance train equipments 1294 hp at 0,00125rf. per hp ........ 1,62 Maintenance line conductors, £24 per 10 400 miles . 0,55 Wages of drivers and assistants 2,99 Interest at 8| per cent, on £51 290, 100 500 ml per annum 4,59 Interest at 3| per cent, on £1200, 10 400 ml per annum 1,04 Total operating expense per train mile 19,79 The chief object that Mr. Carter had in view in carrying out this investigation was to show how electrical operation compared with steam for main line service. Mr. Carter points out that the actual comparison must, however, be left to those in a position to form an estimate of the costs of steam operation for this class of service. The railway companies' returns give average figures including goods and passenger, local, main and branch line service, but do not separate the results and show what would be the cost for such trains and such service as are discussed in this thesis. Mr. Carter states that since he is not in a position to ascertain what these costs would be, he accordingly leaves the subject at this point. 302 HEAVY ELECTRICAL ENGINEERING Sprague, in a recent paper entitled " Some Facts and Problems bearing on Electric Trunk Line Operation," states, " The continuous current and the three phase motors each have a continuous, rate of energy input, while the single phase motor has an intermittent and variable rate. Moreover there is combined in the single phase motor two distinct functions, those of a motor and of a transformer, and the latter cannot be entirely eliminated. The result is a reduction in both normal and overload capacities. It is in this particular that the single phase motor, despite a great amount of experimental development, has remained defective ; and while not prohibitive to the extent of making it an unworkable machine, its defects are so inherent as to place it at a serious disadvan- tage in individual comparisons with other types of motors. To attain the pre-eminence hoped for, the external advantages in current supply must be very marked. In fact, rated in the same manner and under like physical conditions, it is only about half as good as the continuous current motor. Or to put it another way, the weight of the complete single phase electrical equipment on a car or locomotive, including transformers, motors and controlling apparatus, for continuous hard service, and with like physical limitations and ventilation, is about twice that required for continuous current apparatus. In addition to this there is, of course, a material increase in the mechanical equipment necessary to carry the electrical apparatus. The reason is simple — it is because of the heat generated on account of lower electrical efficiency, and of working the fields of the motors at a reduced magnetic flux." Sprague concludes his paper with the following statement : " No one can deny that if the single phase motor be developed to a high state of weight efficiency, unhandicapped by excessive weight of the collateral apparatus necessary on a car to utilize it, and if the capacity of conductors, especially steel conductors, for alternating currents can by any discovery be raised, the elimination of moving machinery in, and the simplification of sub-stations would open up a very extended and important field for the use of this type of apparatus. It seems to me that the present principal hope of usefulness of the single phase system is on roads of considerable extent which operate an irregular and sparse traffic, and where only a moderately expensive, or what may be called a second class overhead construc- tion which will keep down the ratio of line investment to that of the balance of equipment, is tolerable. As one departs from this TRACTION MOTORS AND ELECTRIFICATION OF RAILWAYS 303 condition, adopts more permanent construction, and faces the problems of denser traffics and higher capacities, the advantages of the single phase system will disappear, and the superiority of the con- tinuous current equipment, with such improvements as are in sight, will become manifest. But whatever may be the future of single phase operation under the conditions stated, any present claim for it as the preferable equipment for congested service demanding high schedules and great capacity is not worth a moment's thought, for in this field, at least, it cannot touch the continuous current system. I see no practical necessity to formulate conclusions by averaging conditions, and I cannot conceive the responsible officers of any TABLE XCV. Considerations affecting the Commercial Success of El-ctric Railtray Undertakings. iA P cQ Millions of Seat kin per +j Trains in Service per km of Doable Track at Schedule s o H . Annum per km of Double ~ Speeds stated at Top of each Column in -sg^i. Track with Seats per Train s km iter lir. •P°0 B stated at Top of each £ = .S '3 Column. >, % si i M 15 25 j 40 50 65 80 1,5 100 1,2 130 0,92 ISO 100 200 300 400 ! 500 1,0 8,0 4,8 3,0 2,4 1,84 0,75 0,342 34,2 68,4 102,7 136,8 171,0 1,5 6,0 3,2 2,0 1,6 1,23 1,0 0,80 0,615 0,50 0,228 22,8 45,6 j 6S,5 ; 91,2 114,0. 2,0 4,0 2,4 1,5 1,2 0,92 0,75 0,60 0,46 0,375 0,187 18,7 37,4 ' 56,1 ' 74,8 i 93,5 2,5 3,5 1,92 1,2 0,90 0,74 0,60 0,4S 0,37 0,30 0,137 13,7 27,4 41,1 54,8 '' 6S,5 3,0 3,0 1,(50 1,00 0,80 0,62 0,50 0,40 0,31 0,25 0,114 11,4 ■22,8 , 34,2 , 45,6 57,0 4,0 2,0 1,20 0.75 0,60 0,46 0,375 0,30 0,23 0,1S7 0,086 S,6 17,2 ! 25,8 34,4 43,0 5,0 1,75 0,96 0,60 0,48 0,37 0,30 0,24 0.1S5 0,15 0.06S M 13,6 ! 20,4 27,2 34,0 6.0 1,5 0,80 0,50 0,40 0,31 0,25 0,20 0,155 0,125 0,057 6,7 11,4 17,1 22,8 28.5 S,0 1,0 0,60 0,375 0,30 0,23 0,187 0,15 0,115 0,093 0,043 4,3 8,6 12,9 17,2 21,5 10,0 0,87 0,48 0,30 0,24 0,185 0,15 0,12 0,092 0,075 0,034 3,4 0,8 10,2 13,6 17,0 15,0 0,58 0,32 j 0,20 0,16 0,124 0,10 O,0S 0,062 0,05 0,023 2,3 4,6 6,9 9,2 11,5 trunk line road being guided in their determination of what seems best for their own requirements, by consideration of what some road thousands of miles removed in location and enormously re- moved in operating conditions may do." In selecting the lines along which to work in improving the net earning capacity of a railway, while we must make every effort to employ the most appropriate systems and equipments, we must not overlook the fact that there are other conditions essential to success which, although they are altogether independent of these engineer- ing considerations, must be taken carefully into account by the engineer. Heavy capital outlay has already been incurred by all 304 HEAVY ELECTRICAL ENGINEERING large railways, and provision for interest and depreciation on this outlay will constitute one of the largest items for which provision must be made from the earnings. It is important to make every effort to increase the millions of seat kilometers per annum per kilometer of route. This is a function of the headway between TABLE XCVI. Considerations affecting the Commercial Success of Electric Railway Undertakings. ei 1* c Gross Receipts in Pounds (for Average Fare in Operating Expenses in Pounds (corresponding CO u « S> P* CO (H Decimals of a Penny per Passenger kin stated at to Operating Expenses in Pence per ft-, * k 9 o 03 -> | o M 0,35 0,40 0,45 0,50 0,55 0,60 1,0 1,5 2,0 2 5 3,0 3,5 ( 0,2 13 10 000 21 700 24 400 27 100 20 800 32 500 ] 65 J 0,3 10,5 28 400 32 500 36 600 40 600 44 700 48 700 [ 2680 4060 5360 6700 8130 0400 1 0,4 26 3S000 43 400 48 800 54 200 59 600 65 000 1 l 0,2 20 29 200 33 300 37 500 41 600 45 800 50 000 100 J 0,3 30 43 750 50 000 56 250 62 500 68 800 75 000 I 4120 6250 8240 10 300 12 500 14 400 I 0,4 40 58 400 66 600 75 000 S3 200 91 600 100 000 1 / 0,2 26 3S000 43 400 48S00 54 200 59 600 65 000 130 J 0,3 39 56 800 65 000 73 200 81 200 89 400 07 500 I 5360 8120 10 720 13 400 16 250 18 800 1 0,4 52 76 000 86 800 07 600 108 400 119 200 130 000 J ( 0,2 32 46 700 53 400 60 000 66 600 73 400 80 000 I 6600 160 J- 0,3 48 70 000 SO 000 90 000 100 000 110 000 120 000 10 000 13 350 16 680 20 000 23 350 1 0,4 64 93 400 106 800 120 000 133 200 146 800 160 000 ) ( 0,2 40 5S400 66 600 75 000 83 200 91 600 100 000 \ 200 J 0,3 60 87 500 100 000 112 500 125 000 137 500 150 000 [ 8250 12 500 16 500 20 600 25 000 28 800 1 0,4 SO 116 S00 133 200 150 000 166 400 183 200 200 000 1 { 0,2 46 67 200 76S00 86 400 96 000 105 500 115 000 \ 230. 0,3 60 100 600 115 000 129 400 144 000 15S 000 172 500 - 9500 14 400 10 000 23 S00 28 800 33 200 l 0,4 92 134 400 153 600 172 800 192 000 211 000 230 000 1 / 0,2 62 76 000 S6S00 97 600 108 400 119 200 130 000 \ 260 J 0,3 78 113 600 130 000 146 400 162 400 178 800 195 000 L 10 720 16 250 21 440 26 800 32 500 37 600 ■ I 0.4 104 152 000 173 400 195 200 216 S00 238 400 260 000 f 1 0,2 58 S4 700 97 000 109 000 121 000 133 000 145 000 200. 0,3 sr 127 000 145 000 163 000 1S1 000 190 000 217 500 I 12 000 18 150 24 000 30 000 36 300 42 000 t 0,4 116 169 400 194 000 218 000 242 000 266 000 290 000 ) l 0,2 64 93 400 106 S00 120 000 133 200 146 800 160 000 l 320- 0,3 96 140 000 160 000 ISO 000 200 000 220 000 240 000 I 13 200 20 000 26 700 33 360 40 000 46 700 l 0,4 12S 186 800 213 600 240 000 266 400 293 600 320 000 ( 0,2 SO 116 S00 133 200 150 000 166 400 183 200 200 000 i 400 i 0,3 120 175 000 200 000 225 000 250 000 275 000 300 000 '. 16 500 25 000 33 000 41 600 50 000 58 400 I 0,4 160 233 600 266 400 300 000 333 S00 366 400 400 000 J 480 J 0,2 96 140 000 160 000 180 000 200 000 220 000 240 000 I 0,3 144 210 000 240 000 270 000 300 000 330 000 360 000 I 20 000 30 000 40 000 50 000 60 000 70 000 I 0,4 1112 280 000 320 000 360 000 400 000 440 000 480 000 f 0,2 112 163 500 187 000 2)0 000 233 500 256 500 280 000 | 560 i 0,3 168 245 000 280 000 315 000 350 000 385 000 420 000 \ 23 300 35 000 46 600 5S400 70 000 81 600 ( 0,4 254 327 000 374 000 420 000 467 000 513 000 560 000 J All values stated are "per annum per kilometer of double track." trains and the number of seats per train as shown in Table XC V. Hence we must provide long platforms at stations and trains designed for maximum seating capacity per meter length of train, and we must run with a minimum of headway between trains. Table XCV. also shows us that the millions of seat kilometers per TRACTION MOTORS AND ELECTRIFICATION OP RAILWAYS 305 annum per kilometer of route is independent of the schedule speed. High schedule speed will, however, be an inducement to traffic, and will improve the train load factor, that is to say, the average percent- age of the seats occupied during the entire year. The cost for power for obtaining moderately high schedule speeds is an insignificant item, and should not be a deterrent ; but beyond a certain point, the seats per meter of length of train will be seriously limited by high schedule speeds, and this will be a factor in determining the speed consistent with maximum earnings. The fares should be adjusted to the value at which, with the train load factor, resulting from them, the gross receipts per kilometer of route are a maximum. Some roads would be able to increase their earnings by lower fares in pence per kilometer, others by higher fares. The receipts corresponding to various schedules, train load factors and fares per passenger-kilometer are set forth in Table XCVL, in the last section of which are shown the running costs in pounds per kilometer of route, for various running costs ranging from 2,5d. to 5d. per hun- dred seat kilometers. In the examples worked out in this article the running costs were about 3d. per hundred seat kilometers. An enterprising management, with an appreciation of the engineering elements involved, and always on the alert to introduce incentives to traffic, and thus to improve the train load factors for a given fare per passenger-kilometer, can, in the case of any given road, often exert a more marked effect in improving the earning capacity than can be accomplished by engineers. H.li.E. APPENDIX ABBREVIATIONS AND EQUIVALENT VALUES FOR UNITS OF ENERGY, POWER AND PRESSURE TABLE XCVII. Energy Units, with Abbreviations ; and Corresponding Values cxpr in Joules. 1 Unit. Abbreviation. Value in Joules. 1 Kilowatt hour . 1 Kilogram calorie 1 Kilogram meter 1 Horse power hour . 1 British Thermal unit 1 Foot pound 1 kw hr 1 Ug cal 1 kg in 1 hp hr IBThU 1ft lb 3 600 000 4190 9,81 2 680 000 1055 1,356 TABLE XOVIII. Power Units, with Abbreviations; and Corresponding Values expressed in Watts. Unit. Abbreviation. Value in Watts. 1 Kilowatt .... 1 Kilogram calorie per second . 1 Kilogram meter per second . 1 British Thermal unit per second 1 Foot pound per second 1 Joule per second .... Ikw 1 kg cal ps 1 kg m ps lhp 1 B Th U ps 1 ft lb ps 1 joule ps 1000 4190 9,81 746 1055 1,356 1,000 The joule may be defined as 10' ergs, or as one watt second. X 2 308 APPENDIX TABLE XCIX. Equivalent Values for Energy expressed in different Units (English and Metric). 1 kw hr is equal to 1 kg cal 1 kg m 1 hp hr 1 BThU 1 ft lb 1 joule 1 0,00116 0,00000272 0,746 0,000203 0,000000377 0,000000278 Kg cal. Kg in. 860 367 000 1 427 0,00234 1 041 274 000 0,252 107,6 0,000324 0,13S2 0,00023S5 0,1020 Hp lir. 1,34 0,001559 0,00000365 1 0,000393 0,000000505 0,000000373 3411 3,97 0,00930 2545 1 0,0012S5 0.000948 Ft lb. 2 659 000 30S1 7,23 1 980 000 778 1 0,738 3,6 x 106 4190 9, SI 2,68 X 106 1055 1,356 1 TABLE C. Equivalent Values for Power expressed in different Units (English and Metric). 1 kw hr is equal to 1 kg cal ps 1 kg m ps llip 1 13 Th U ps 1 ft lb ps 1 joule ps Kw. 1 4,20 o.oonsi 0,746 1,055 0,001356 0,001 Kg cal ps. 0,238 1 0,00234 0,1781 0,262 0,000324 0,0002385 Kgmps. 102,0 427 1 76.0 107,6 0,1383 0,1020 Hp. 1,34 5,61 0,00315 1 ,415 0,001818 0,001342 B Th U ps. Ft 1bps. 0,947 3,97 0,00930 0,707 737 3088 1 778 0,001285 1 0,000948 0,738 Joule ps. 1000 4190 9,81 746 1055 1,356 1 TABLE CI. Pressures. 1 lb p sq in . 1 kg p sq mm 1 in of mercury 1 mm of mercury . Lb p sq in. 1 14,22 0,4912 0,0193 Kg p sq cm. 0,0703 1 0,0345 0,00136 Inches of Mercury. 2,030 28,96 1 0,03937 Mm of Mercury. 51,71 735,5 25,4 1 INDEX [By.E. S. W.] Note. — The figures throughout refer solely to the pages of the book, not to the numbers assigned to the different illustrations or tables. Aa.chen, Annual output and overall efficiency of generating station, Tables 29, 30 Absolute pressure, 2 Acceleration Graphical determination of value of mean acceleration from speed time curve, note, 223 High rate of, for service with frequent stops — CO o. single phase motors, 284 On the motor curve, 223 Schedule speed and, relation between, 234, Figs. 232, 233 Tractive force, speed and, relation between, 234 Accumulators, transmission loss in, 32 Adiabatic expansion, 17 Admission pressure, effect on steam consumption of steam turbines and piston engines, 73—75, 87, 88 Air Pumps, 98 Eesistance, relation between mechanical resistance and, 228 Allen, E. W., tests showing relation between temperature of condensing water and exhaust pressure, 100, Fig. 101 Allgemeine Elektricitats Gesellschaft Data of traction motors and equipments, Plate XVI. W. E. 51 motor, data, 248, Plate XVI. ; comparison with G. E. 69 B. motor, 251, Fig. 253; energy consumption calculations, 276—280 Zossen motor car, rolling stock data, Table 230 Alternating current, Suitability for main generating station, 118, 119 System of transmission. See High Tension Transmission Systems. Alternator windings, mechanical design, 109 Alternators, excitation power for, 155, Table 154 Aluminium Cables, 192 ; comparative costs of copper and, 194, 195 (for) Overhead transmission lines, 160; copper versus, 161—163, 171 — 174 ; data of lines in various countries, 177; dimensions, weights, and costs, 167 310 INDEX Analysis of losses in Generating station, 36 Supply system, 32 Andrews, estimate of total cost for conduit laying, 198 Animas Power Co., Colorado : overhead transmission line data, Table 177 Annual overall efficiency of 26 generating stations, 29 — 31, Fig. 28. See also Efficiency. Aspinall, formula for tractive resistance, 226, 291 Atmosphere, metric, unit of pressure designated as, note, 2 Auxiliary plant, 155 Advantage of steam-driven accessories, 156 Highfield's costs for 00 and AC systems, Plate XL ; criticisms of, 209 Average speed, 218 Axles, calculation of energy consumption at, 235 — 238, Plates XII. and XIII. Bakerloo Eailway, data of motors and equipments, Plate XVI. Baltimore, Ohio, data of traction motors and equipments, Plate XVI. Barrow, annual output and overall efficiency of generating station, Tables 29, 30 Bath Electric Tramways generating station Coal storage, Table 142 Engine room and boiler house data, Plates "VTII. and IX. Bearing friction losses, Lewicki's tests on 22 kw de Laval turbine, 82, Fig. 80 Behrend on Single phase system of electrification, 288 Thury 00 series system, 217 Belluzzo, wheel friction loss tests, 82 — 84 Berlin Electricity supply, Table 42 Street lighting, relation to private lighting, Table 41 Berlin Electricity Works Euel, cost and calorific value, 26, 27 Generating station, particulars of, Table 34 ; efficiency, 26 Berlin Elevated Railways, general arrangement of power house, Fig. 139 Birmingham Interior lighting data, Table 39 Sumner Lane generating station, Coal storage, Table 142 Engine room and boiler house data, Plates VIII. and IX. Tramways (Smethwick), engine room and boiler house data, Plates VIII. and IX. Board of Trade unit, 2 Boiler Efficiency of steam generating sets, 53 Pressures for steam turbines, 64 ; Botscher's steam consumption tests, 87 Booms, size of, 131 ; data of certain generating stations, 134, 135, Plate IX. INDEX 311 Boilers Cost : average per kw, Table 155 ; Highfield's costs for 00 and AC systems, Plate XL ; criticisms of, 209 Number and arrangement, 60, 61 Space occupied by, 58 Water-tube type for generating stations, 58 ; capacity of, 59 Boston Elevated Railway, data of motors and equipment, 248, Plate XVI. Boston (Mass., U.S.A.) Edison, particulars of generating station, Table 34 Bournemouth, interior lighting data, Table 39 Bournemouth. Corporation generating station Coal storage, Table 142 Engine room and boiler house data, Plates VIIL and IX. Bradford Generating stations, particulars of, Table 34 Growth of demand for electricity per inhabitant, Tables 44 and 45 Bremen electricity supply, Table 42 Breslau Electrical output and efficiency of generating stations from 1901 to 1905, Table 47 Electricity supply, Table 42 Bridlington Electricity Works, engine room and boiler house data, Plates VIII • and IX. Brighton, surface tramway load data, Table 41 Brighton Corporation (Southwick) generating station Coal storage, Table 142 Engine room and boiler house data, Plates VIIL and IX. Brimsdown generating station, particulars of chimney shafts, Table 144. Bristol tramways, arrangement of power station, Fig. 126 British thermal units, equivalent of 1 kw hr, note, 19 Brown Boveri, weights and other data of motors and equipments, 261, Plate XVI. Brushes, dynamo, coefficient of sliding friction, 234 Brussels Electric Tramways generating station Coal storage, Table 142 Engine room and boiler house data, Plates VIIL and IX. Budapest, annual output and overall efficiency of generating station, Tables 29, 30 Buenos Aires, annual output and overall efficiency of generating station, Tables 29, 30 Buildings and chimneys, average cost per kw, Table 155 ; Highfield's costs for CO and AC systems, Plate XL ; criticisms, 208 Burford's estimate of total cost for conduit laying, 198 Burgdorf-Thun Bailway Data of traction motors and equipments, Plate XVI. Boiling stock data, Table 230 Burnley Corporation generating station Annual output and overall efficiency, Tables 29, 30 Engine room and boiler house data, Plates VIIL and IX. Burton, surface tramway load data, Table 41 312 INDEX Cables Aluminium, 192 ; comparative costs of copper and, 194, 195 Comparative cost for rotary converters and motor generators, 114 Three-core lead covered, for underground transmission, Cost : estimation, 185 — 192 ; comparative, for AG and CO systems, 206 — 208 ; comparative, of copper and aluminium, 194, 195 Dimensions, weights, and costs, Table 188 Factor of safety for AC and CC systems, 215, 216 Insulation: cost, note, 186; thickness, 181 — 184; comparison for AC and CC, 206, 207 Lead covering, thickness, 184 Sections of core, 179, Table 180 Calculations, traction. See Electric Traction Calculations. Calorific values of fuels, 18 ; examples of amount of energy contained in one ton of coal of a calorific value of 8700 kw hr per ton, 19 — 21 Candle power hours per kw hr, 11 Capacity of single generating station, 50 Capital outlay and operating expenses of electric traction, 288 — 301 ; com- parison of CC and single phase systems, 290 — 300, Plates XVIII. and XIX. Cardiff Interior lighting data, Table 39 Surface tramway load data, Table 41 Carlisle, surface tramway load data, Table 41 Carter, F. W. Capital outlay and operating expenses of electric traction, 288 — 301, Plates XVIII. and XIX. Single phase v. CC systems of electrification, 287 Weights of motors and equipments, Plate XVI. Central Electric Supply Co.'s generating stations, Table 34 Coal storage, Table 142 Engine room and boiler house data, Plates VIII. and IX. Marylebone station, arrangement of, 128, Fig. 131 Central London Railway Electric power required, 42 Generating station, Annual output and overall efficiency,. Tables 29, 30 Chimney shafts, 144 Coal storage, Table 142 Economisers, 14S Engine room and boiler house data, Plates VIII. and IX. General arrangement of power station, 123, Figs. 124, 125 Leading particulars, Tables 50, 51 Steam piping data, 61, 68 Load factor, 60 Rolling stock data, Table 230 Tractive resistance, 225 — 227 Charing Cross and City Electric Supply Co., generating station— coal storage, Table 142 ; engine room and boiler house data, Plates VIII. and IX. INDEX 313 Charing Cross Co. (Bow), particulars of generating station, Table 34 Charlottenburg, 1904, particulars of generating station, Table 34 Chelsea Alpha Place generating station, engine room and boiler house data, Plates VIII. and IX. Lots Road power station. See Underground Electric Railways Co. Chicago (Fisk St.) Edison, particulars of generating stations, Table 34 Chimneys Average cost per kw, Table 155 ; Highfield's costs for CC and AC systems, Plate XI. ; criticisms, 208 Considerations relating to, 143 — 147 Christchurch Electricity "Works generating station Coal storage, Table 142 Engine room and boiler house data, Plates VIII. and IX. Circulating water Coal and, relation between cost of, 103 Temperature of condensed steam and, relation between, 94 ; Allen's tests, 100, Fig. 101 ; Weighton's tests, 102 City and South London Railway Generating station, particulars of, Table 34 Rolling stock data, Table 230 Tractive resistance, 225 — 227 Classification of overhead transmission lines, Fig. 170 Clermond-Perrand overhead transmission line data, Table 176 Clyde Valley Electric Power Co. (Yoker) generating station Coal storage, Table 142 Economisers, 148 Engine room and boiler house data, Plates VIII. and IX. Coal Calorific values, 18 ; examples of energy contained in one ton, of a calorific value of 8700 kw hr per ton, 19 — 21 Consumption of certain generating stations, 35, Tables 34, 36 ; of four stations of various capacities, bb delation between electrical energy and, 18 et seq. Conveyor, 123 Cost Per kw hr for various boiler efficiencies, 22, Table 24 Relation between cost of circulating water and, 103 Storage for generating stations, 140 — 143 Tons of steam raised per ton of coal for various boiler efficiencies, 22, Table 23 See also Euel. Coal handling plant Average cost per kw, Table 155 Highfield's costs for CC and AC systems, Plate XL ; criticisms, 209 Coefficient of friction, 232—234 Colgate to Oakland overhead transmission line data, Table 177 Cologne generating station, particulars, Table 34; annual output and overall efficiency, Tabhs 29, 30 314 INDEX Combustion, energy of, per ton, of various coals, 18 Compensated repulsion motor, energy consumption of train equipped with eight 115 hp, 276—280 Compensated series motor, energy consumption of train equipped with six 17-3 hp, 261—276 Complete unit system of grouping of steam turbine plant, 128 Condensation, temperature of, 93 Condensing plant, 92 et seq. Condenser : calculations, 92 — 98 ; types, 98 ; considerations relating to surface condensers for use with piston engines and steam turbines, 100 — 104 ; average cost per kw, Table 155 Condensing station, overall efficiency of, 25 — 32 Condensing water circuit, 151 Conductors for Overhead transmission, 160 — 168; distance between, factors governing, 163, Fig. 164; span, 163; data of lines in various countries, 176, 177 Underground transmission, 17S Conduit construction for underground transmission, 196 — 198 ; AC and CO systems, 207 Continuous current Generators. See Generators CC. Motor equipments, overall efficiency, 239, Fig. 238, Plate XIV. Series system of transmission. See High Tension Transmission System. Suitability of, for distribution purposes, 118 — 120 System of electric traction, estimate of cost for L. B. & S. 0. Ry., 280 — 282 See also Electrification of Railways. Convertible energy, 14, Table 15, Plate I. Cooling towers, 92 Copenhagen generating stations, particulars, Table 34 Copper cables. See Cables, Three-core Lead Covered. Copper for overhead transmission lines, 160 Aluminium versus, 161 — 163, 171 — 174 Data of lines in various countries, 176 Dimensions, weights, and costs of copper lines, 166 Cork surface tramway load data, Table 41 Corrugated tubes for reducing size and cost of superheaters, 72 Cost of Cables, estimation, 185 — 192; AC and CC, comparative cost, 206 — 208 Condensing plant, relative advantages of piston engines and steam turbines, 103 Conduit laying, 197, 198 ; AC and CC systems, 207 Duplicate circuit transmission lines, estimation, 171 — 175, Tables 166, 167 Generating stations and plant, 156, Table 155 ; AC and 00 systems, Highfield's data, Plate XI. ; criticisms of, 208, 209 Poles and towers for overhead transmission, 159, 160, 169, Tables 166, 167 Single phase and CO systems of electrification, comparison, 280 — 282 INDEX 315 County of London Co., particulars of generating stations, Table 34 Crefeld, annual output and overall efficiency of generating station, Tables 29, 30 Currents and current densities for underground cables, 180 Dalby, Prof., analysis of losses in steam generating plant, 37, 38 Dalziel on weights of single phase and CC motors, 242, 261 Darlington, interior lighting data, Table 39 Darmstadt, annual output and overall efficiency of generating station, Tables 29, 30 Darwen, surface tramway load data, Table 41 Dawson Energy consumption of A. E. G. "W. E. 51, 115 h.-p. motor, 276 Weights of single phase and CC motor equipments, 242, Plate XVI. Demand for electric power. See Electric Power. Derby, annual output and overall efficiency of generating station, Tables 29, 30 Design of steam-driven electric generating stations, 51 Dick Kerr & Co., data of motors and equipments, Plate XVI. Dielectric hysteresis loss, 212 — 215 Direct connected exciters versus separate exciter system, 154 Distributors, transmission loss in, 32 Drainage in exhaust pipes, 151 Dresden, 1904, Power and Light — particulars of generating stations, Table 34 Dublin United Tramways generating station, particulars, 50, 51 Annual output and overall efficiency, Tables 29, 30 Coal storage, Table 142 Engine room and boiler house data, Plates VIII. and IX. Dundee, annual output and overall efficiency of generating station, Tables 29, 30 Duplicate circuit steel tower transmission lines, cost of, 171 — 175, Tables 166, 167 Diisseldorf Electricity supply, Table 42 Street lighting, relation to private lighting, Table 41 East Ham, interior lighting data, Table 39 Eastbourne Corporation generating station Coal storage, Table 142 Engine room and boiler house data, Plates VIII. and IX. Economic steam pressures for piston engines and steam turbines, 64 ; Botecher's tests, 87 Economisers, 147 Average cost per kw, Table 155 Space occupied by, 148 Edinburgh, growth of demand for electricity per inhabitant, Tables 44 and 45 316 ■ INDEX Efficiency (of) Annual overall of 26 generating stations, 29 — 31, Fig. 28 Boilers, 62 Curves, 239, Fig. 238, Plate XIV. Motor, influence on rated output, 243 Overall (of) Equipment, 239, Fig. 238, Plait XIV. Generating stations, 18 el seq. ; calculation for a representative station in Great Britain, 25 ; circumstances affecting, 33 ; steam-driven electric station, 51 ; particulars of certaiu stations, 26, 29 — 31, 35 ; Figs. 28, 33 ; Tables 34, 36 Steam piping, 69 Thermodynamic, 14 Transmission line, 198 — 202 Eichberg on weight of AC and CC motor equipments, 242 Ejector condenser, 99 Elberfeld, 1904, particulars of generating stations, Table 31 Electra to San Erancisco overhead transmission line, data, Table 177 Electric Generating plant, 105 et seq. Alternative arrangement of, 137, Figs. 138 — 140 OC and AC, Highfield's costs for, Plate XL ; criticisms, 208, 209 ; respective fields of usefulness, 118 — 120 Insulation of high pressure machines, 106—109 Mechanical design of alternator windings, 109 Relative merits of generating sets of various types, 112 — 120 Size of unit, 105 Sub-stations: rotary converters versus motor generators, 114, 116; suitability of CC energy for, 119, 120 Power, demand for, 38 et seq. Continental generating stations, 45 — 48 Growth of, 43, Tables 44, 45 ; Hoppe's investigations, 48, 49 Interior lighting, 39, Table 43 Overhead and underground railways, 42, Table 43 Power, 42, Table 43 Batio of consumption for public arcs to that for private lighting, 41 Street lighting, 41, Table 43 Surface tramway load, 42, Tables 41, 43 Traction calculations, 218 et seq. Average and schedule speed, 218 Capital outlay and operating expenses, 288 et seq. ; comparison of CC and single phase systems, 294—300, Plates XVIII. and XIX. Energy consumption at axles, 235 — 238, Plates XII. and XIII. Input to trolley, 238, Plates XIV. and XV. Mean acceleration, method of determining value of, note, 223 Overall efficiency of equipment, 239, Fig. 238, Plate XIV. Speed time diagrams, 218; alternative speed time curves, 220 — 225 and Figs. INDEX 317 Electric traction calculations — continued. Stops, number and duration of for short and fast runs, 219, 220, 234 Tractive Eorce with, various accelerating rates, 234 Eesistance at constant speed, 224 Electrical Energy or " electricity," 1 ; relation between coal consumption and, 18 et seq. ; transformation of steam heat into, 76, Fig. 78 Equipment, Data of several motors, Plate XVI. Discussion and comparison of single phase and CO motors, 255 — 261 Overall efficiency, 239, Fig. 238, Plate XIV. Weights, comparative, of CO and AO equipments, 242 ; weight of extra equipment, 255 Electricity. See Energy, Electrical. Electricity versus steam for operation of railways, 285, 288, 289, 301 Electrification of railways, 240 et seq. Capital outlay and operating expenses, 288 — 301 ; comparison of CO and single phase sj'stems, 294 — 300 Considerations affecting commercial success, 303 — 305 Continuous current system, estimate of cost for L. B. & S. 0. Ey., 280 — 282 Single phase system, Cost of overhead construction, 284, 285 Delay in electrification owing to conflicting views regarding, 112, 283 Misleading data put forward by advocates, 241, 287 Points of inferiority, 287 Superiority of for long distance non-stop runs, 260, 283 Single phase versus CO system, 280 — 303 Capital outlay and operating expenses, 294 — 300 Costs of electrification of L. B. & S. 0. Ey., 280—282, 285 High acceleration, 284 Voltages, 285, 286 Three phase system, superiority for long distance non-stop runs, 260, 283 Train consumption, influence of system of electrification, 240 Energy Consumption calculations, 225 (at) Axles, 235—238, Plates XII. and XIII. Compensated repulsion motors, train equipped with 8 A. E. G. W. E. 51 motors, 276—280 Compensated series motors, train equipped with 6 Siemens-Schuckert • motors, comparison of three alternative runs, 261—275, Plate XVII. and Figs. Ten coach 250-ton train, 292, 293 (for) Interior lighting, 39, 40, Table 43 (for) Street lighting, 41, Table 43 Convertible, 14, Table 15, Plate I. Electrical or "electricity," 1 Eolation between coal consumption and, 18 et seq. Transformation of steam heat into, 76, Fig. 78 318 INDEX Energy — continued. Heat, 1 Energy of combustion of various coals, 18 Value of 1 kw hr, 12, 13 ; value of one ton of coal, 20 Input Curves for 132-ton train with eight 115 hp motors, 277, Fig. 278; for 156-ton train with six 175 hp motors, 263, Fig. 266 — alterna- tive diagram, 271, Fig. 270 (to) Trolley, 238, Plates XIV. and XV. Kinetic, of steam as a function of the speed, 84 — 86 ; calculations, 267 Mechanical or "work," 1; value of 1 kw hr, 7 ; value of one ton of coal, 19 Transformation or generation, 13; analysis of losses during, 36 — 38 Unit of, Abbreviations and equivalent values for [Appendix) Board of Trade unit, 2 Coal, examples of the amount of energy contained in one ton, of a, calorific value of 8700 kw. hr per ton, 19 — 21 Kilowatt hour, 1 ; Board of Trade unit, 2; equivalent in British thermal units, note, 19 ; examples of amount of energy represented by, 7, 11—13 Watt hour, 1 ; inconveniently small quantity in heavy electrical engineering, 2 Engine rooms, Data of 48 power stations, 131, 134, Plate VIII. Size of, 131 Space, 58 Esson, W. B., distance between overhead conductors, 163, Fig. 164 Evaporative condenser, 99 Examples of amount of energy Contained in one ton of coal of a calorific value of 8700 kw hr per ton, 19—21 Represented by 1 kw hr, 7, 11 — 13 Excitation power for alternators, 155, Table 154 Exciters, separate versus direct connected, 152, 154 Exhaust pressure, effect on economy of steam turbines and piston engines, 73—75 Expansion Bends, 151 Coefficients of copper and aluminium, 163 External latent heat, 5 Feeders, transmission loss in, 32 Eerguson, estimate of total cost of conduit laying, 198 Field, breakdowns on CC systems, 216 Flue gases, temperature of, 71 Forced draught systems, 147 Formula for tractive resistance, 291 ; Aspinall's, 226 ; alternative formula for high speeds, 231 INDEX 319 Frankfort, particulars of generating station, Table 34 Frequency for high tension power transmission lines, 159 ; data of lines in various countries, 176, 177 Friction Coefficient, 232—234 Losses, Bearing, Lewicki's tests on 22 kw de Laval turbine, 82, Fig. 80 Wheel, Belluzzo's tests, 82, 83, Figs. 83 84 ; Lewicki's tests on 22 kw de Laval turbine, 80—82, Figs. 79, 80; influence of on peripheral speed, 81 et seq. ; Ebtscher's tests on 2000 hp Biedler- Stumpf steam turbine, 82, Figs. 81, 82 Frome Electricity Works generating station Coal storage, Table 142 Engine room and boiler house data, Plates VIII. and IX. Fuels Calorific values of, 18 ; examples of energy contained in one ton of coal of a calorific value of 8700 kw hr per ton, 19 — 21 Choice of, 27, 28 Costs, 22 — 25 ; cost and calorific value of coal used in various generating stations, 26, 27 See also Coal. Ganz Electric Co., data of traction motors and equipments, 248, 252, Plate XVI. Gas engine Efficiency of, 14 Engine room data of certain generating stations employing, 134, Plate VIII. Gas engine-driven OC generators, high and low speed, 114, 115, ll7 Polyphase generators, relative merits, 112 — 115 General Electric Co. of America Motors and equipments, data, 248, 256, Plate XVI., Tables 258, 259 Comparison of 69 B motor with A. E. G. W. E. 51 motor, 251, Figs. 252 Weight and output data, 246 Generating sets. See Generating Stations. Generating stations Boilers, space occupied by, 58 Capacity, 50, 51 ; choice of generating sets for different capacities, 51 — 54 Condensing station, overall efficiency of, 25 — 32 Continental, growth of demand for electric power, 45—48 Costs, 156, Table loo ; Highfield's data for OC and AC systems, Plate XI. ; criticisms of, 208, 209 Design of, 121 et seq. Alternative arrangements of generating plant, 137, Figs. 138 — 140 Auxiliary plant, 155 Boiler house and engine room, size of, 131 Chimneys, considerations relating to, 143 — 147 Choice of site, 121 Coal storage, 140—143 320 INDEX Generating stations, design of — continued. " Complete unit " system of grouping of plant, 128 Economisers, 147 ; space occupied by, 148 Exciters, 152, 154, 155 General arrangement, 122 Preliminary calculations, 135 Eapid growth of demand for electrical power, design of station in view of, 43, 47 Steam-driven electric, 51 Steam piping, 149 — 153, and Figs. Steam turbine stations, 128 ; preliminary design for, 61, Fig. 62 270 million unit per annum station, preliminary calculations, 135, Fig. 141; alternative arrangements of generating plant, 137, Figs. 138 — 140 ; chimney calculations, 146 ; coal storage, 141, 143 ; economiser surface, 149; exciter plant, 154; steam piping, 151 Economic steam pressures, 64 Electric generating plant. See that title. Fuel, cost and calorific value of coal used, 26, 27 Generating sets Boilers and steam piping, efficiency of, 53 Choice of, for different capacities, 51 — 54 Eelative merits of different types, 112 — 120 Steam consumption, 51, 52 Steam-driven, efficiency of, 33 ; steam consumption and fuel costs, 22 — 25 Generation of energy in, 13 Leading particulars of certain well-known stations, 50, 51 Losses in, analysis, 36; analysis of losses in supply system, 32 Overall efficiency and relation between coal consumption and outgoing electrical energy, 18 et seq. Annual overall efficiency of 26 stations, 29 — 31, Fig. 28 Calculation for representative station in Great Britain, 25 Circumstances affecting, 33 Efficiencies of certain modern generating stations, 26 ; of four stations of various capacities, 54, 55 Particulars of generating stations given by Patchell, 33 — 36 ; Tables and Figs. Returns, insufficient data available, 31 Steam consumption of large electric, 57 Steam piping, length of, 61 "Transforming" station, preferable term, 18, 28 Generation or transformation of energy, 13, 18, 28 Generators Continuous current, Gas engines for, relative merits of high and low speed, 114, 115, 117 Steam engines for driving, 115 Voltage and speed, relation between, 116 Polyphase, Gas engine-driven, relative merits, 112 — 115 High and low speed, excitation power required for, 155, Table 154 INDEX 321 Generators, polyphase — continued. Speed, periodicity, and type of prime mover, relation between, 113, 115 Steam engines for driving, large slow speed, 113 Steam turbine-driven, relative merits of, 116, 117 Genoa, annual output and overall efficiency of generating station, Tables 29, 30 Glasgow Growth of demand for electricity per inhabitant, Tables 44, 45 Interior lighting, Table 39 Surface tramway load, Table 41 Glasgow tramways generating station Annual outputs and overall efficiencies, 26, Tables 29, 30 ; further data by Patchell, Table 34 Chimney shafts, 144, 145 Coal storage, Table 142 Engine room and boiler bouse data, Plates VIII. and IX. Fuel, cost and calorific value, 26, 27 Pinkston generating station, particulars, 50, 51 Steam piping, 68 Glass insulators for overhead transmission, 169 Grading the insulation for underground cables, 183 Grand Bapids Muskegon Power Co., overhead transmission line data, Table 176 Grate surface of boilers, 63 Gravity. See Specific Gravity. Great Eastern Eailway generating station, plan and arrangement, 131, Figs. 132, 133 Great Northern and City Eailway Generating station : coal storage, 142 ; engine room and boiler house data, Plates VIII. and IX. Boiling stock data, Table 230 Greenock Electricity Works generating station, engine room and boiler house data, Plates VIII. and IX. Greenwich generating station Chimney shafts, 144, 145 Steam piping, 68 Gromo to Nembro, Lombardia, overhead transmission line data, Table 176 Guanajuato, Mexico, overhead transmission line data, Table 176 Hackney Electricity "Works generating station Coalstorage, Table 142 Engine room and boiler house data, Plates VIII. and IX. Hamburg Electricity supply, Table 42 Generating station, particulars, Table 34 ; annual output and overall efficiency, Tables 29, 30 Street lighting, relation to private lighting, Table 41 Hammersmith and City Eailway, data of traction motors and equipments, Plate XVI. Hampstead Eailway, data of traction motors and equipments, Plate XVI. Hancock, conduit construction, 197; estimate of total cost of conduit laying, 198 H.B.B. Y 322 INDEX Harrogate, annual output and overall efficiency of generating station, Tables 29, 30 Heat Capacity of water for absorbing, 93 — 98 Conduction values, 71 Energy. See Energy, Heat. Latent, 5, 93 External and internal latent neat defined, 5 (of) Vaporisation of water, 3, 5 Specific, Definition, 4 (of) Superheated steam, 7 — 12 (of) Water at yarious temperatures, 4 Superheat. See Steam, Superheated. Temperature and, relation between, 3, 21 "Water, 3 Heating surface of boilers,, 62 Height of overhead conductor, 165, 168 Heysham-Morecambe line. See Midland Railway. High pressure machinery, development of, 105 ; insulation, 106 — 109 "High speed" engines for driving alternators, 115 High tension power transmission lines, 157 et seq. Cost, CO and AC systems, 205—212 Efficiency, 198—202 Frequency of alternating current, 159 Overhead transmission, 159 — 178 AC and CC systems, 209, 210 Aluminium and copper, 161 — 163, 171 — 174; dimensions, weights, and costs, Tables 166, 167 ; data of lines in various countries, 176, 177 Details of lines in various countries, 176, 177 Efficiency, calculations showing most economical, comparison with underground transmission, 200, Plate X. Line construction, 159 Conductors, 160 — 168 ; data of lines in various countries, 176, 177 Cost of erection, 171 Data of lines in various countries, 176, 177 Insulators, 169; data of lines in various countries, 176, 177 Weight and cost of tower, 168, Tables 166, 167 Total cost of duplicate circuit transmission lines, estimation of, 171—175, Tables 166, 167 Voltage of transmission, 158, 174, 175, 178; data of lines in various countries, 176, 177 Underground transmission, 178 — 198 Cables, Aluminium, estimation of cost, 192 ; comparative costs of copper and, 194, 195 Dimensions, weights, and costs of three-core lead covered, 185 — 1 92, Table 188 ; comparative costs for AC and CC systems, 205 — 207 INDEX 323 High, tension power transmission lines, underground cables— continued. Factor of safety, CO and AO systems, 215, 216 Insulated of otter metals than copper, 192 Conductor, 178 Conduit construction, 196 ; cost, 195, 198 ; Hancock's estimate, 197 ; comparison of CO and AC systems, 207 Continuous current and alternating current high tension systems, comparison, 203, 205—209 Efficiency, calculations showing most economical, comparison with overhead transmission, 201, Plate X. Insulation thickness, 181 — 184; comparison of CO and AO systems, 206,207 Voltage of transmission, 158, 186, 187, 190 — 192 High tension transmission system Alternating current three phase system, 157 Costs, comparison with 00 system, 206—210 Superiority of three phase and single phase systems for long distance non-stop runs, 260, 283 Comparison of AC and 00 systems, 203 — 216 Costs, 206—210 Dielectric strength of air (and certain insulating materials), 212 Safety factor, 215, 216 Continuous current series system, 203 et sea. Advantages of no dielectric hysteresis loss, 212 — 215 Behrend's views, 217 Breakdowns, causes of, 216 Costs, comparison with AO system, 206 — 210 Installations employing, Table 204 Safety factor, 215, 216 Losses in, analysis of, 32 Highfield, Conduit laying, estimate of total cost, 198 ; A0 and 00 systems, 208 High tension CC series system, 203 Costs, comparison with AO system, 206 — 210 Installations employing, Table 204 Hoppe on growth of demand for electric power, 48, 49 Huddersfield, interior lighting data, Table 39 Hull Annual output and overall efficiency of generating station, Tables 29, 30 Interior lighting data, Table 39 Humann, currents and current densities for underground cables, 180 Hydro electric installations, engine room data of power station employing water turbine, 134, Plate VIII. Ilfokd Electricity "Works, engine room and boiler house data, Plates Till. and IX. Interior lighting data, Table 39 Induced draught systems, 147 Y 2 324 INDEX Installations employing high tension CO series system, Table 204 Insulation Breakdowns, importance of regular tests, 108 (of) Cables, Cost, note, 186; AC and CO, 206, 207 Thickness, 181—184 ; AC and CO systems, 206, 207 (of) High pressure machines, 106—109 Tests. See Tests, Insulation. Insulators for overhead transmission, 169; data of lines in various countries, Tables 176, 177 Interborough Eapid Transit Co., N.T. Generating station Chimney shafts, 144, 145 Coal storage, Table 142 Engine room and boiler house data, Plates VIII. and IX. Traction motors, note, 258 ; data of motors and equipments, Plate XVI. Interior lighting Demand for electric power, 39, Table 43 (of) Various British towns, 39 Internal latent heat, 5 Jenkin on single phase system, 287 Jet condenser, 98 Jona on insulation thickness for homogeneous cables, 184, note, 181, Fig. 182 Joule {Appendix) Kallir, L., most economical span of suspended conductors, note, 164 Karlsruhe electricity supply, Table 42 Kelham Island T. and P. Co., generating station, engine room and boiler house data, Plates VIII. and IX. Kelly on weights of motors and equipments, 241, Plate XVI. Kelvin's law, 158,198 Kilowatt hour as unit of energy, 1, 2 Energy contained in one ton of coal of a calorific value of 8700 kw hr per ton, examples, 19 — 21 Equivalent in British thermal units, note, 19 Examples of amount represented by 1 kw hr, 7, 11 — -13 Kinetic energy calculations, 267 ; as function of speed, 84 — 86 Kolkin Steel and wooden pole lines for overhead transmission, 159 Suspended conductors, most economical span, note, 164 Konigsberg Annual output and overall efficiency of generating station, Tables 29, 30 Electricity supply, Table 42 Krizik motors and equipments, data, Plate XVI. Lamps Interior lighting, lamp consumption, 39, 40 INDEX 325 Lamps — continued. Number of incandescent lamps run by one kw hr, 11 for one year with one ton of coal, 19 Street lighting, lamp consumption, 41 Lancashire Electric Power Co. Generating station : engine room and boiler house data, 134, 135, Plates VIII. and IX. ; coal storage, Table 142 Overhead transmission line data, Table 176 Latent heat. See Heat, Latent. Lead covering for three- core cables, thicknesses, 184 Leading properties of steam, 7 — 11, Fig. 12 Leeds Generating stations, particulars, Table 34 ; annual output and overall efficiency, Tables 29, 30 Growth of demand for electricity per inhabitant, Tables 44 and 45 Interior lighting, Table 39 Surface tramway load, Table 41 Leek Electricity Works generating station, data of engine room, 134, Plate VIII. Leicester, interior lighting data, Table 39 Leicester Electric Tramways generating station Coal storage, Table 142 Engine room and boiler house data, Plates VIII. and IX. Leipzig, annual output and overall efficiency of generating station, Tables 29, 30 Length and weight of trains, relation between, 229, Table 230 Lewicki, Prof., friction losses, tests on 22 kw de Laval turbine, 80 — 82, Figs. 79, 80 Lighting Demand for electric power, 39 et seq. Interior lighting, 39, Table 43 Eatio of consumption for public arcs to that for private lighting, 41 Street lighting, 41, Table 43 Limitations of single phase motors, 274 — 276 Line loss, AC and CC systems, comparison between, 210, .211 Liverpool Growth of demand for electricity per inhabitant, Tables 44, 45 Interior lighting, Table 39 Surface tramway load, Table 41 Liverpool Overhead Railway, data of traction motors and equipments, Plate XVI. Liverpool-Southport Railway generating station Coal storage, Table 142 Economisers, 1, 48 Engine room and boiler house data, Plates VIII. and IX. Load factor Central London Railway daily load curve, 60 Definition, note, 25 Patchell's figures for certain generating stations, 35, Tables 34, 36 326 INDEX Lockport, Niagara, and Ontario line, tower construction for overhead transmission, Fig. 170 London, Brighton, and South Coast Bail way electrification A. E. G. W. E. 51 115 hp motor, 248 ; energy consumption calculations, 276—280 Costs, comparative, of single phase and CO systems, 280 — 282, 285 London County Council electricity supply, general arrangement of proposed generating station at Barking, Fig. 140. London Electric Supply Co., particulars of generating station, Table 34 London underground railways. See Underground Electric Eailways. Long Island City, Penn., U.S.A., generating station Coal storage, Table 142 Engine room and boiler house data, Plates VIII. and IX. Los Angeles to Engelwood overhead transmission line data, Table 176 Losses Priction. See Friction Losses. (in) Generating stations, analysis of, 36 Mechanical, effect of low exhaust pressure, 75 (from) Steam pipes, 69 (in) Supply system, analysis of, 32 Lots Boad Power Station. See Underground Electric Eailways. Lowestoft Electricity Works generating station, engine room and boiler house data, Plates VIII. and IX. Lusitania, speed of steam turbine, 105 Manchester Growth of demand for electricity per inhabitant, Tables 44, 45 Interior lighting data, Table 39 Surface tramway load data, Table 41 Manchester Corporation generating station, particulars, Table 34 Annual output and overall efficiency, Tablts 29, 30 Coal storage, Table 142 Engine room and boiler house data, Plates VIII. and IX. Manhattan Elevated Eailway, rolling stock data, Table 230 Marienfeld-Zossen Eailway, data of traction motors and equipments, 248, Plate XVI. Mauritania, speed of steam turbine, 105 McGregor, E., steam and exhaust pipes, note, 151 Mechanical Design of alternator windings, 109 Energy or " woik," 1 ; value of onekw hr, 7 ; value of one ton of coal, 19 Losses, effect of low exhaust pressure, 75 Eesistance, relation between air resistance and, 228 Tests of high speed machines, 109 — 112 Mersey Eailway, rolling stock data, Table 230 Mersey Tunnel Eailway generating station Coal storage, Table 142 Engine room and boiler house data, Plates VIII. and IX. INDEX 327 Metric atmosphere, note, 2 Metropolitan District Bailway Data of traction motors and equipments, 248, 257, Plate XVI. Boiling stock data, Table 230 See also Underground Electric Railways. Metropolitan Electric Supply Co. (Brimsdown) generating station, particulars, Table 34 Coal storage, Table 142 Engine room and boiler house data, Plates VIII. and IX. Metropolitan Bailway Neasden generating station, Capacity, 51 Chimney shafts, 144, 145 Coal storage, Table 142 Economisers, 148 Engine room and boiler house data, Plates VIII. and IX. Steam piping, 68 ; length, 61 Boiling stock data, Table 230 "Weight of electrical equipment and data of motor, 257, Plate XVI. Middlesbrough Corporation generating station, engine roo m and boiler house data, Plates VIII. and IX. Midland Bailway, Heysham-Morecambe line Siemens-Schuckert 175 hp motor, data, 248 ; energy consumption calcula- tions, 261—275, Plate XVII. and Figs. Weight of electrical equipment, 256 Missouri Power Co., Montana, overhead transmission line data, Table 176 Mollier, properties of steam, 7 — 11, Fig. 12 Motor generator versus rotary converters, 114 ; cost of high tension cables 114 Moutier-Lyon installation employing high tension CO series system, 204, 208 Munich, 1904, particulars of generating station, Table 34 Neasden generating station. See Metropolitan Bailway. Necaxa Power Co., Mexico, overhead transmission line data, Table 176 ; steel towers, 169, Fig. 170 New York Central Bailway, data of traction motors and equipments, 248, note, 258, Plate XVI. ; 550 hp CO locomotives, 241 New York, New Haven, and Hartford locomotive, ventilation data, 249 Newcastle Electric Power Co. (Carville) geneiating station, particulars, Table 34 Coal storage, Table 142 Engine room and boiler house data, 134, 135, Plates V11I. and IX. Newcastle-on-Tyne Growth of demand for electricity per inhabitant, Tables 44, 45 Interior lighting data, Table 39 Niagara Ealls to Buffalo overhead transmission line data, Table 177 328 INDEX Niagara, Lockport, and Ontario Power Oo.'s overhead transmission line, Table 177 Niagara-Toronto overhead transmission line, Table 176 ; steel towers for, 169, JFig. 170 North Wales P. and T. Co. (Snowden), data of engine rooms of generating stations, 134, Plate VIII. Nottingham surface tramway load, Table 41 Oberscbxesischee, Industrie Bezirk generating station, particulars, Table 34 Oerlikon Co., data of traction motors and equipments, 248, Plate XVI. O'Gorman, total works cost of three-core cables for underground transmission, 185 Oldham Interior lighting, Table 39 Surface tramway load, 'Table 41 One hour rating. See Eating of Traction Motors. Ontario to Buffalo overhead transmission line, Table 177 Operating expenses of electric traction, 288 — 301 ; comparison of 00 and single phase systems, 297—300, Plates XVIII. and XIX. Output Annual increase in, 44 Annual outputs and overall efficiencies, Patchell's figures for certain generating stations, 35, Tables 34, 36 Returns, insufficient data available, 32 (of) 26 generating stations, 29 — 31 Continuous current, single phase, and three phase motors, comparison on the one hour rating basis, 245 — 251 Slot insulation, advantages of reduction in thickness, 107 Speed and output of direct connected electric generating sets, relation between, 118, Fig. 119 Overall efficiency. See Efficiency. Overhead Bail ways, demand for electric power, 42, Table 43 Third rail versus, 284—288 Transmission. See High Tension Power Transmission Lines. Overload capacity, single phase versus CC motors, 274 — 276 PadeeNO to Milan overhead transmission line, Table 176 Parsons steam turbines. See Steam Turbines. Patchell, particulars of generating stations, 35, Tables 34 and 36, Fig. 33 Periodicities Low, desirable for gas engine-driven polyphase generators, 113, 115 Belation between type of prime mover, speed and, 113, 115 Peripheral speed, influence on wheel friction, 81 et sea. Piccadilly and Brompton Tube Bailway, data of traction motors and equipments, Plate XVI. Piping system, 149 — 153, and Figs. See also Steam Piping. Piston engines. See Steam Engines. INDEX 329 Plant Auxiliary, 155; advantages of steam-driven accessories, 156; Highfield's costs for CO and AO systems, Plate XL ; criticism of, 209 Coal handling : average cost per kw, Table 155 ; Highfield's costs for OC and AO systems, Plate XI. ; criticisms, 209 Condensing, 92 et seq. ; condenser calculations, 92 — 98 ; types, 98 ; con- siderations relating to surface condensers for use with piston engines and steam turbines, 100 — 104 ; average cost per kw, Table 155 Electric generating. See that title. Steam raising, 57 et seq. ; efficiency of, 33 ; relative costs for high and low pressures, 68 Steam turbine, complete unit system of grouping, 128 Polyphase generators. See Generators, Polyphase. Poplar Electricity Works generating station Coal storage, Table 142 Engine room and boiler house data, Plates VIII. and IX. Population, average rate of increase in nine provincial towns, Table 44 Porcelain insulators for overhead transmission, 169 Potteries district, surface tramway load, Table 4 1 Powell Duffryn Steam Coal Co., particulars of generating stations, Table 34 " Power," analysis of losses in steam generating plant, 37, 38 Power Station, Engine room and boiler house, 58 Highfield's costs for CC and AC systems, Table 210 Supply, demand for electric power, 42, Table 43 Unit, abbreviations and equivalent values for {Appendix) Pressure Absolute, 2 Admission, effect on steam consumption of steam turbines and piston engines, 73 — 75, 87, 88 Regulation, advantages of reduction in slot insulation thickness, 107 Unit of, 2; abbreviations and equivalent values for [Appendix). See also Voltage. Preston, interior lighting data, Table 39 Putnam. See Stillwell and Putnam. " Quick revolution," engines for driving alternators, 115 Quincy Point, Mass., U.S.A., generating station, engine room and boiler house data, 134, 135, Plates VIII. and IX. Rating of traction motors Capacity of single phase, CO, and three phase motors, 240 One hour rating, 243 ; service capacity ratio, 244 Rayner, dielectric strength of air, investigations, 212 Reciprocating engines and generators, average cost per kw, Table loo Reichel on rated capacity of single phase railway motors, 240 Resistance, tractive. See Tractive Resistance. Rheydt, annual output and overall efficiency of generating station, Tables 29, 30 330 INDEX Kichter, weights of motors and equipments, Plate XVI. Eiedler Stumpf 2000 hp steam turbine, wheel friction loss, 82, Figs. 81, 82 Rolling stock data for various railways, Table 230 Eotary converters Motor generators versus, 114 ; cost of high tension cables, 114 Eelative merits of, 114, 116 Eotherham surface tramway load, Table 41 Ebtscher Steam consumption tests at various speeds and steam pressures, 87 Wheel friction loss tests, 82, Figs. 81, 82 Eotterdam Electricity supply, Table 42 Street lighting, relation to private lighting, Table 41 Eotterdam-Hague Eailway, data of motors and equipments, 256, 257, Plate XVI. Safety factor for AC and CC systems, 215, 216 Sag of conductors for overhead transmission, 164, 165 Salford, growth of demand for electricity per inhabitant, Tables 44, 45 Salford Corporation generating station, particulars, Table 34 Annual output and efficiency, Tables 29, 30 Coal storage, Table 142 Engine room and boiler house data, Plates VIII. and IX. Saturated steam, 7, note, 94 ; specific volume and weight, Table 9 Schedule speed, 218 Schoepf, weights of single phase and CC motors, 241 Section of Conductors for overhead transmission, 160—162 ; data of lines in various countries, 176, 177 Cores in three-core cables for underground transmission, 179, Table 180 Seebach-Wettingen Eailway, data of Oerlikon motor and equipments, 248, 249, Plate XVI. Separate exciter versus direct connected exciter system, 154 Service capacit5 r of railway motors Estimation for single phase motors, 261 One hour rating, ratio of, 244 Shawinigan to Montreal overhead transmission line, Table 177 Sheffield Growth of demand for electricity per inhabitant, Tables 44, 45 Interior lighting, Table 39 Surface tramway load, Table 41 Sheffield Corporation tramways Fuel, cost and calorific value, 26, 27 Neepsend generating station, particulars, Table 34 ; coal storage, Table 142; engine room and boiler house data, Plates VIII. and IX. ; overall efficiency, 26, Tables 29, 30 Short circuit tests, 109, 110 Siemens and Halske Data of traction motors and equipments, 248, Plate XVI. Eolling'stock, data of Zossen motor car, Table 230 INDEX 331 Siemens-Schuckert motors and equipments, Plate XVI. 175 lip compensated series motor, 248, 249, 251, 256 ; energy consumption calculations, comparison of three alternative runs, 261 — 275, Plate XVII. and Figs. Simplon tunnel, data of traction motors and equipments, 261, Plate XVI. Simplon and Valtellina Bailway, data of railway motor, 248 Single phase system of electric traction. See Electrification of Eailways. Slot insulation of high pressure machines, 106 Advantages of reduction in thickness, 107 Importance of rigorous insulation tests, 106 — 109 Snoqualmie Palls to Seattle overhead transmission line, Table 177 Space factor, 134 Span of suspended conductors, 163, 164 ; data of lines in various countries, 176, 177 Sparking voltages, Thury's tests for CO and AC in air, 212, Fig. 213 Specific gravity (of) Copper and aluminium, 163 Definition, note, 7 Various materials, Table 11. Specific heat. See Heat, Specific. Speed Average and schedule, 218 Kinetic energy of steam as a function of, 84 — 86 Output and, of direct-connected electric generating sets, relation between, 118, Fig. 119 Periodicity, type of prime mover and, relation between, 113, 115 (of) Steam turbines for large units, 105 Stops, effect of number and duration on, 234 ; effect of duration for various average speeds, 21 9, 220 Tractive force, acceleration, and, relation between, 234 Voltage, relation of to, 116 Speed time diagrams, 218 Alternative speed time curves, 220 — 225 and Figs. Curve for 132-ton train with eight 115 hp motors, 277, Fig. 278 Curve for 156-ton train with six 175 hp motors, 263, Fig. 266 ; alternative diagrams, 271, 274, Figs. 270, 275 Graphical determination of value of mean acceleration, note, 223 Sprague on Continuous current and single phase motors, 302 Bated capacity of CC motors, note, 258 Weights of electrical equipment, 256, Plate XVI. Springer, estimate of total cost of conduit laying, 198 St. James and Pall Mall Co., particulars of generating station, Table 34 Stalybridge Electric Tramways Co. generating station, engine room and boiler house data, Plates VIII. and IX. Steam Circuit, 149 Condensation calculations, 92 — 98 ; types of condenser, 98 — 100 ; considera- tions relating to surface condensers, 100 — 104 332 INDEX Steam — continued. Consumption : of large electric generating stations, 57 ; of steam generating sets, 51, 52 ; of steam turbines and piston engines, 73 — 91 Convertible energy per ton, 14 — 17, Plate I. Electricity versus, for operation of railways, 285, 288, 289, 301 Energy absorbed in raising one ton from water at 50° C, 21 Energy required to evaporate one ton of water at 0° C. into steam, 21, 22, Tables 8, 10 Engines, Data of engine rooms of certain generating stations employing high and slow speed engines, 134, Plate VIII. Large slow speed for driving Continuous current generators, 115 Polyphase generators, relative merits of, 113 Low thermal efficiency, 37 Piston engines, Economic steam pressures, 64 High and low speed, relation between speeds and outputs, 118, Fig. 119 Steam turbines and, 73 et seq. Surface condensers for, 102 ; objection to use of, 99 ; costs, relative advantages of steam turbines and, 103 "Weights of steam turbines and high-speed steam engines, com- parison, 118 Transformation of energy in, 14 Heat and temperature, relation between, 3, 21 Kinetic energy of, as function of speed, 84 — 86 Leading properties, 7 — 11, Fig. 12 Pipes: importance of covering, 69; size required for different weights of steam, 70 Piping, 149 — 153, and Figs. Average cost per kw for steam piping and valves, Table 155 Data, 68—71 Length in generating stations, 61 Pressures, piston engines and steam turbines, 64 ; Eotscher's tests, 87 Eaising plant, 57 et seq. ; efficiency of, 33 ; relative costs for high and low pressures, 68 Saturated, 7, note, 94; specific volume and weight, Table 9 Superheated, Condensation calculations, 97 Economy of engines improved by use of, 64, 65 Specific heat of, 7 — 12 Specific volume and weight, Table 9 Temperature of circulating water and condensed steam, relation between, 94 Allen's tests, 100, Fig. 101 Weighton's tests, 102 Tons raised per ton of coal for various boiler efficiencies, 22, Table 23 Turbines, Average cost of turbo generators per kw, Table 155 INDEX 333 Steam turbines — continued. Boiler pressures, 64 ; Rotscher's steam consumption tests, 87 Curtis type, engine room data of certain generating stations employing) 134, Plate VIII. De Laval type, Rated speed and output, relation between, 118, Fig. 119 "Wheel friction losses, Lewicki's tests on 22 kw turbine, 80 — 82, Figs. 79, 80 Generating stations : arrangement of, 128 ; preliminary design for, 61, Fig. 62 Parsons, Engine room data of certain generating stations employing, 134, Plate VIII. Overall length and floor space, 137, Figs. 136, 137 Rated speed and output, relation between, 118, Fig. 1 19 Steam consumption investigations of 4000 kw turbo generator, 89—91 Weights of high speed steam engine sets and, comparison, 118 Piston engines and, 73 et seq. Riedler Stumpf 2000 hp, Rotscher's tests of wheel friction loss, 82, Figs. 81, 82 Speeds, 105; suitability for driving polyphase machines, 116, 117 Steam consumption investigation of 1000 kw generator, 75 — 79 Surface condenser for, 99, 102; costs, relative advantages of piston engines and, 103 Transformation of energy in, 14 Steel Conductors for overhead transmission lines, 160 Pole line for overhead transmission, 159, 160 Tower line for overhead transmission, 159 — 178 Conductors, 160—168 Efficiency, most economical, 200, Plate X. Erection, cost of, 171 Insulators, 169 Weight and cost of tower, 168, Tables 166, 167 Steinmetz on dielectric hysteresis, 21"4 Stillwell and Putnam on single phase motors, 260 ; continuous current systems versus, 283 Stockholm, electrical output and efficiency of generating stations from 1901 to 1905, Table 47 Stockton, interior lighting data, Table 39 Stodola, wheel friction and speed, 82 Stops, number and duration of, 234 ; duration for various average speeds, 219, 220 Stott, H. C, analysis of losses in steam generating plant, 37, 38 Strassburg, electrical output and efficiency of generating stations from 1901 to 1905, Table 47 Street lighting, demand for electric power, 41, Table 43 Stress permissible in conductors for overhead transmission, 161, 162 334 INDEX Stuttgart, electrical output and efficiency of generating stations from. 1901 to 1905, Table 47 Sub-station Equipment: CC generators preferable, 119, 120; rotary converters versus motor generators, 114, 116 Highfield's costs for CO and AO systems, 209, Table 210 Sunderland surface tramway load, Table 41 Superheat, effect on economy of steam turbines and piston engines, 73 — 75 See also Steam, Superheated. Superheated steam. See Steam, Superheated. Superheaters Average cost per kw, Table 155 Development of, 65, 67 Surface required for, 72 Superheating, difficulties attending, 65 Supply system, analysis of losses in, 32 Surface condenser, 98; considerations relating to use of with piston engines. and steam turbines, 100 — 104 Surface tramway load, demand for electric power, 42, Tables 41,43 Switchgear Average cost per kw, Table 155 Highfield's costs for AO and 00 systems, Plate XL ; criticisms, 209 Syracuse overhead transmission line, Table 176 Systematic procedure in the design of steam-driven electric generating stations, 51 Taylor's Fall line, tower construction for overhead transmission, Fig. 170 Teiehmiiller, currents and current densities for underground cables, 180 Telluride Power Co., Colorado, overhead transmission line, Table 177 Temperature Heat and, relation between, 3, 21 Rise (of) Copper and aluminium overhead conductors, 163, Table 162 Slot insulation, advantages of reduction in thickness, 107 (of) Vaporisation or condensation, 92, 93 Tests of high-speed machines Insulation, importance of, progress impeded owing to lack of investigation, 106—109, 111, 112 Mechanical, 109—112 Short circuit on alternator windings, 109, 110 Thermodynamic efficiency, 14 Third rail versus overhead construction, 284 — 288 Thornhill power station. See Yorkshire Power Co. Three-core lead covered cables. See Cables. Three phase AO system of transmission. See High Tension Transmission System, AC. Thury Continuous current series system. See High Tension Transmission System, CO. Tests of disruptive strength of air for CO and AC, 212, Table 213 INDEX 335 Toulon overhead transmission line data, Table 176 Traction motors and the electrification of railways, 240 et seq. Continuous current motors, G. B. 69 and G. E. 66, data of weight and output, 246 Bated output and comparison with single and three phase motors : ventilated, 245, 247, 248 ; with forced draught, 249—251 Weights of equipments, discussion and comparison, 257 — 261 Data of representative railway motors and equipments, 246, Table 248, Plate XVI. ; discussion and comparison, 256—261 Electrical equipment, weight of, 242 ; discussion and comparison, 255 — 261, Plate XVI. One hour rating, 243 ; comparison of three types on basis of, 215—251 Eated capacity of motors, comparison of three systems, 240 ; Valatin on, 254, 255 Rated outputs and weights, comparison of three systems : ventilated motors 245 — 248 ; forced draught ventilation, 249 — 251 Service capacity of motor, ratio to one hour rating, 244, 261 Single phase motors, Compensated repulsion motors, train consumption calculations, 276 — 280 Compensated series motors, train consumption calculations, 261 — 276 Limitations, 274—276 Eated output and comparison with three phase and OC motors : ventilated, 246—248; with forced draught, 250, 251 Service capacity, estimation of, 261 Ventilation, 249 Weights of equipments, discussion and comparison, 256 — 26), Plate XVI. Westinghouse 150 hp, weight of, comparison with similar CO motor, 241 Single phase versus three phase, Efficiency and weight, 241—243, 254, 255 Service capacity, ratio of one hour rating to, 244 Three phase motors, rated output and comparison with CO and single phase: ventilated, 247, 248; with forced draught, 250, 251 Trucks, weight of, 242 Ventilation, 244 Weight, 241—243 Tractive Force, acceleration and speed, relation between, 234 Resistance calculations, 224 — 235 Air and mechanical friction, relative values, 228 Formula for calculating, Aspinall's, 226, 291 ; alternative formula for high speeds, 231 Train consumption calculations, 235 — 239 Energy consumption, value of energy in one ton of coal, 20 System of electrification, influence of, 240 See also Electric Traction Calculations. Tramcar, energy consumption, 11, 19 336 INDEX Tramways, demand for electric power, 42, Table 43 Transformation of energy, 13 ; analysis of losses during, 36 — 38 Transformers, transmission loss in, 32 Transforming station. See Generating Station. Transmission Lines. See High. Tension Power Transmission Lines. Systems. See High Tension Transmission Systems. Voltage, 158, 174— 178, 190—192 Trolley, energy input to, 238, Plates XIV. and XV. Tube railways, tractive resistance on, 225, 226, Fig. 227 Turbines. See Steam Turbines. Tynemouth, interior lighting ,Table 39 Underground Electric Eailways Demand for electric power, 42, Table 43 Generating station (Lot's Road) Arrangement of power station, 128, Fig. 127 Capacity of power station, 51 Chimney shafts, 144, 145 Coal storage, Table 142 Engine room and boiler house data, Plates VIII. and IX. Steam piping, 61, 68 Motors, note, 258 Underground transmission. See High Tension Power Transmission Line. Unit (of) Abbreviations and equivalent values for units of energy, power and pressure (Appendix) Board of Trade, 2 British thermal, equivalent of 1 kw hr, note, 1 9 Energy. See Energy, Unit of. Pressure. See Pressure. Valatin Single phase and three phase locomotives, 254 Weight coefficient for various traction motors, Plate XVI. Valtellina Railway, data of traction motors and equipments, Plate XVI. Vaporisation, temperature of, 92, 93 Ventilation of railway motors Influence on rated output, 244 Single phase motors, 249 Vienna, particulars of generating stations, Table 34 ; annual output and overall efficiency, Tables 29, 30 Voltage Regulation, advantages of separate exciter system, 154 Single phase versus CO systems, 285, 286 Speed and, relation between, 116 Transmission, 158, 174—178, 190—192 Volume and weight, 2 ; specific of saturated and superheated steam, Table 9 Wallasey, interior lighting, Table 39 Walthamstow Corporation, engine room data of generating stations, Plate VLTI. INDEX 337 "Warrington surface tramway load, Table 41 Waste heat engines, 14 Water Energy required: to raise one ton of steam from water at 50° C, 21 ; to evaporate one ton at 0° 0. into steam, 21, 22, Tables 8, 10 Heat, 3 Capacity of water for absorbing, 93—98 Specific, at various temperatures, 4 Temperature, beat and water, relation between, 3, 21 Turbine, engine room data of power station employing, 134, Plate VIII. Weight and volume, 2 Water-tube boilers, 58, 59 Waterloo and City Eailway, rolling stock data, Table 230 Watson, estimate of total cost of conduit laying, 198 Watt hour, 1, 2 Weight and volume, 2 ; specific, of saturated and superheated steam, Table 9 Weight of "Electrical equipment, CC and AC, comparative weights, 242 Extra equipment, discussion and comparison, 255 — 261, Plate XVI. Indefiniteness of term " electrical equipment," 255 Motors, Influence on rated output, 243 Single phase and CC. motors, 241 — 243 Steel tower for overhead transmission, 168, Tables 166, 167 Trains : tractive resistance curves for different weights, 229 ; particulars for certain railways, Table 230 Weighton, B.. L., temperature of condensing water and exhaust pressure, tests showing relation between, 102 Weights, comparison between high-speed steam engine sets and steam turbine- driven sets, 118 West Ham interior lighting data, Table 39 West Ham Corporation generating station Coal storage, Table 142 Engine room and boiler house data, Plates VIII. and IX. Westinghouse Co., data of traction motors and weight of equipments, 256, 257 Plate XVI., Tables 258, 259; weight of 150 hp single phase motor, and Comparison with similar CC. motor, 241 Westminster, particulars of generating stations, Table 34 Wet steam, condensation calculations, 96 Wetness factor, 6, Table 16 ; of exhaust steam from 1000 kw turbo generator, 76, 78, Table 77 Wheel friction losses. See Friction Losses. Wilgus'on costs of overhead single phase construction, 285 Wimbledon Electricity Works generating station Coal storage, Table 142 Engine room and boiler house data, Plates VIII. and IX. Windings, alternator, mechanical design, 109 Winnipeg overhead transmission line, Manitoba, data, Table 176 • H.B.B. Z 338 INDEX Wolverhampton Corporation generating station, engine room and boiler house data, Plates VIII. and IX. Wooden pole line for overhead transmission, 159, 160 Work. See Energy, Mechanical. 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Drum Armatures and Commutators. (Theory and Practice.) A complete treatise on the theory and construction of drum- winding, and of commutators for closed-coil armatures, together with a full resume of some of the principal points involved in their design, and an exposition of armature reactions and sparking. Illustrated. 8vo., cloth, 295 pp Net, $3.00 WILKINSON, H. D. Submarine Cable-Laying, Repairing, and Testing. New Edition. Illustrated. 8vo., cloth In Press YOUNG, J. ELTON. Electrical Testing for Telegraph Engineers. Illustrated. 8vo., cloth, 264 pp Net, $4.00 ZEIDLER, J. and LUSTGARTEN, J. Electric Arc Lamps. Their principles, con- struction and working. 160 illustrations. 8vo., cloth, 200 pp. . . .Net, $2.00 3=page Catalog of Books on Electricity, classified by subjects, will be furnished gratis, postage prepaid, on application.