282 



ALTERNATING CURRENTS 



Fig. 172, the maximum value of the alternating flux traversing a 

 short-circuited coil is clearly reduced ; since now the portion of the 

 flux between the magnetic axis of the rotor and the brush position 

 does not become linked with the short-circuited coils, as it passes 

 into and out of the rotor core outside the arcs spanned by the two sets 

 of short-circuited brushes. 



167. Compensated Repulsion Motors 



The compensated repulsion motor was invented simultaneously 

 and independently by Latour in France and by Eichberg and Winter 



in Germany. In its simplest form it is 

 shown in Fig. 173. At first sight, it would 

 appear as if the motor differed but little from 

 the simple series-wound motor of Fig. 164. 

 In fact, the removal of the brushes BiB 2 

 would transform it into such a simple 

 series motor. But the presence of these 

 brushes considerably modifies the action of 

 the motor. One effect is to wipe out the 

 self-inductance of the field winding to a 

 very large extent, since the current flowing 

 between BiB 2 causes the armature winding 

 to act as the short-circuited secondary of a 

 transformer, of which the field winding is 

 the primary. The field winding, therefore, 

 simply acts as a transformer winding, and 

 it no longer (as in the series-wound motor) 

 supplies the entire magnetic field necessary 

 for the production of a torque. This latter 



field is mainly supplied by the armature current which traverses the 

 armature through the brushes B 3 B 4 . For this reason, the armature 

 current flowing between B 3 and B 4 is spoken of as the exciting current* 

 while that flowing between BI and B 2 is termed the short-circuit 

 current. The compensated repulsion motor is characterized by a 

 very high power factor for all speeds above synchronism, and by 

 the absence of sparking troubles. 



The double short-circuit arrangement of brushes devised by Latour 

 for the simple repulsion motor, and shown in Fig. 172, has also been 

 adapted by him to the compensated repulsion motor. The connections 

 are shown in Fig. 174. The short-circuit currents flow in the portions 

 of the winding spanned by the short-circuited brushes B]B 2 and B 3 B 4 



* By some writers it is termed the compensating current. 



FIG. 173. Diagram of Com- 

 pensated Repulsion Motor. 



