354 



ELECTRICAL MACHINERY 



trolley and feeders and then through an autotransformer 

 on the car to the motor. Speed control is obtained by 

 varying the ratio of the transformer so no rheostat losses 

 occur at the motor; evidently the losses in such a dis- 

 tributing system will be much less than those of a c-c. 

 system. If the a-c. motor were as efficient and reliable as 

 the c-c. series motor probably all railway installations 

 would use alternating-current power. 



103. Principle of Operation. A continuous-current series 

 motor will run in the same direction which ever way it is 

 connected to the c-c. line provided the relative connection 



Transmission line 10 $ 



Step up 5$ 

 Transformer - 



Alternator 



Feeders 5 # 



Trolley 5 4 



10 ^Starting Resistance I t . 



/\MM/v--wrCX Car Motor 10$ 



Return Feeders 



FIG. 229. Possible Losses in the Various Parts of a c-c. Railway Dis- 

 tribution Syetem. 



of its armature and field is left undisturbed. Hence, it 

 follows that a c-c. series motor, connected to an a-c. line, 

 would exert a uni-directional torque, and would revolve 

 continuously in the same direction and not oscillate back 

 and forth as might be expected. 



Difficulties in Running a C-C. Motor on an A-C. Line. 

 Such an application of the c-c. motor is not feasible because 

 of the low torque which it would give, the heating of the 

 yoke and poles and the heavy sparking which would occur 

 at the brushes. The low torque would result from the 

 high impedance of the field winding, which would permit 

 but little current to flow through the motor; the heating 



