304 



ALTERNATING CURRENTS 



direct-current motor. By using a transformer and by shifting 

 the brushes, considerable speed variation may be obtained. 



122. The Wagner Type B K, Unity Power-factor Motor. 

 The Wagner Electric Co. has placed on the market a single-phase 

 motor which has a leading power-factor up to about half load, 

 while for greater loads, the power-factor is almost unity. The 

 motor is a constant-speed motor, the regulation being from 1.5 

 to 4 per cent. There are two windings on the motor armature, 

 as is indicated by the slot section in Fig. 283 (6). The upper 

 winding is an ordinary drum winding connected to a commutator. 

 Beneath this is a squirrel-cage winding separated from the other 

 by a magnetic separator consisting of a steel wedge. 



Retaining Wedge 

 Commuted Winding (3) 

 .Magnetic Separator 

 Squirrel Cage (4) 



(&) One slot of rotor, showing con- 

 struction. 



1. Initial field magnet- 

 ization winding. 



2. Auxiliary winding 

 which controls power- 

 factor. 



(a) 

 FIG. 283. The Wagner Electric Co.'s unity power-factor, type BK motor. 



The diagram of connections is shown in Fig. 283 (a); 1 is the 

 main winding and 2 the compensating winding. When the 

 motor starts, the switch 9 is open and as the squirrel cage has 

 little effect at starting, due to the screening effect of the magnetic 

 wedges, the motor starts as a series motor. As it approaches 

 synchronism, the squirrel cage has more and more effect. As 

 synchronism is approached, switch 9 closes by centrifugal action 

 and throws in the compensating winding. The manufacturers 

 claim many advantages for this type of motor, such as high 

 power-factor, constant speed, light service required of the com- 

 mutator because of the assistance of the squirrel cage, suppres- 

 sion of short-circuit coil currents due to the proximity of the 

 squirrel cage, etc. 



