v i CONTENTS 



PACE 



IR drop in armature Safe current capacity. 2. Field excitation 

 Self excited and separately excited machines Shunt, series, 

 compound windings Field rheostats Capacity of rheostat* 

 Tapering. 3. Commutation Causes of sparking Inductance of 

 armature coil Resistance commutation E.M.F. commutation 

 Commutating poles. 4. Armature reaction Division into cross and 

 demagnetizing m.m.f. Necessity of shifting the brushes Com- 

 pensating winding Commutating poles. 5. Characteristic curves 

 Their significance and value. 6. External characteristics of 

 the series, shunt, and compound generators Service to which 

 each is adapted. 7. Capacity of a dynamo-electric machine How 

 fixed by heating and by commutation Effect of ventilation on 

 capacity. 8. Operation of C.C. machines in series and parallel 

 connections. 



CHAPTER IV 



THE CONTINUOUS CURRENT MOTOR 1 : .< ) 



1. Reversibility of generator and motor. 2. Different t\ |> 

 motors and class of service to which each is adapted. 3. Calcula- 

 tion of the torque of a motor. 4. Current and torque curves for 

 different types of motors. 5. Speed and load curves Effect of 

 armature reaction on speed Effect of line voltage variation on speed. 

 6. Motor starting Rheostats No-voltage release Overload re- 

 lease. 7. Speed control of motors Multiple voltage control 

 Control by field weakening Series-parallel control of railway 

 motors. 8. Use of flywheel as load equalizer on compound motors. 



CHAPTER V 

 THE EFFICIENCY OF A DYNAMO ELECTRIC MACHINE 187 



1. Importance of high efficiency. 2. Losses occurring in a 

 machine Their variation with load Loss-load curves. 3. Cal- 

 culation of efficiency from loss curves. 4. Obtaining data for 

 determination of efficiency. / 



