COMPENSATED SERIES MOTOR 



277 



as compared with tin- speed of synchronism. The normal full-load 

 speed is generally about double that of synchronism. 



It must be clearly understood, however, that the improvement in 

 I In- power t;irtor is due, not to any effect of increased relative speed 

 per se, but to a decrease in the reactance of the motor consequent on 



motor speed 

 increasing the ratio - 



speed of syncliromsm 



164. Compensated Series Motor 



Besides the methods already described for improving the power 

 factor, another method is frequently employed. This involves the use 

 of a supplementary field 

 win'liiiL,', known as a compen- "[", 

 sating winding. This winding 

 is displaced relatively to the 

 main field winding by half a 

 pole-pitch, so as to counteract 

 the magnetic effect of the 

 armature current, and practi- 

 cally suppress the self-induct- 

 ance of the armature. 



A series - wound motor 

 fitted with such a compen- 

 sating winding is known as 

 a compensated series - wound 

 motor. There are two methods 

 of connecting the compen- 

 sating winding. In one, shown in Fig. 168, it is included in the main 

 circuit. The compensating 

 winding CW supplies a num- 

 ber of ampere-turns roughly 

 equal to those on the armature. 

 In the second method, shown 

 in Fig. 169, the compen- 

 sating winding CW is short- 

 circuited on itself, and acts 

 as the secondary of a trans- 

 former, of which the primary 

 is represented by the arma- 

 tuit- winding. The armature 

 and compensating winding 

 constitute, in fact, an arrange- 

 ment corresponding to a 

 somewhat leaky short-circuited 



CW 



FIG. 168. Compensated Series Motor. 



FIG. 169. Compensated Series Motor. 



transformer, and the equivalent 



