368 ELECTRICAL ENGINEERING 



Thus near synchronous speed the commutation of the repulsion 

 motor is better than that of the series motor. 



Since preventive leads are not used in the repulsion motor the 

 short-circuit current in it at start will be greater than in the series 

 motor and will weaken the main field and decrease the starting 

 torque. 



While running the short-circuit current is not so great, since it 

 cannot reach its maximum value on account of the self -inductance 

 of the coil. 



The repulsion motor cannot be operated more than 40 per cent 

 above synchronous speed on account of commutation troubles. 



A very large number of alternating-current commutator motors, 

 differing in certain details from the two described here, have been 

 designed and are in successful operation but the main principles 

 are the same. 



