XI 



CONTENTS 



ABT. 



52. Prevention of sparking Practical considerations 175 



53. Mechanical details affecting commutation 178 



54. Heating of commutator Temperature rise 181 



CHAPTER IX 

 THE MAGNETIC CIRCUIT DESIGN OP FIELD MAGNETS EFFICIENCY 



55. The magnetic circuit of the dynamo 185 



56. Leakage factor in multipolar dynamos 186 



57. Calculation of total ampere-turns required on field magnets . . .187 



58. Arrangement and calculation of field windings 190 



59. Temperature rise of field coils 193 



60. Efficiency 195 



^CHAPTER X 

 DESIGN OF A CONTINUOUS CURRENT DYNAMO NUMERICAL EXAMPLE 



61. Introductory 199 



62. Design sheets for 75-kw. multipolar dynamo 200 



63. Numerical example Calculations 204 



64. Design of continuous current motors 235 



ALTERNATING-CURRENT GENERATORS 



CHAPTER XI 

 DESIGN OF ALTERNATORS FUNDAMENTAL CONSIDERATIONS 



65. Introductory 237 



66. Classification of synchronous generators 238 



67. Number of phases 239 



68. Number of poles Frequency 241 



69. Usual speeds of A.C. generators . . . 241 



70. E.m.f. developed in windings 242 



71. Star and mesh connections 2 



72. Power output of three-phase generators 247 



73. Usual voltages 24S 



74. Pole pitch and pole arc 2 



75. Specific loading 25 



76. Flux density in air gap 25 j| 



77. Length of air gap Inherent regulation 252 



CHAPTER XII 



ARMATURE WINDINGS LOSSES AND TEMPERATURE RISE 



78. Types of windings ^55 



79. Spread of winding 2 ^ 



80. Insulation of armature windings 258 



81. Current density in armature conductors 25i 



