ALTERNATING-CURRENT COMMUTATOR MOTORS 365 



circuited with its brushes in line with the field poles. Current is 

 induced in it as in the secondary of a transformer and is very 

 large but the torque exerted in both directions is the same and 

 thus the resultant torque is zero. In Fig. 346, with the brushes 



FIG. 345. 



FIG. 346. 



turned through 90 degrees there is no current induced in the 

 armature and therefore no torque. 



In order that the motor may exert torque the brushes must be 

 placed in some intermediate 

 position. The same result is compensating 



Winding 



accomplished by placing a sec- 

 ond winding at right angles to 

 the. main field winding. This 

 is shown as the compensating 

 coil C in Fig. 347 and is carried 

 in slots in the pole faces as in 

 the series motor. The brushes 

 are placed in line with this coil 

 and the armature receives its 

 current by induction from it. 

 Torque is produced which is 

 proportional to the product of 

 the armature current induced 



Pteld Winding 



FIG. 347. Repulsion motor. 



by the compensating coil and the flux produced by the main 

 field, but it is necessary to show that the current and flux are in 

 time phase with one another. 



If voltage is impressed on the motor at rest, current flows in 



