CALCULATION OF A SINGLE-PHASE CURRENT MOTOR. 



125. The effect of armature resistance consists in reducing the capac- 

 ity of the motor, and in shifting the maximum torque toward the 

 starting point. 



126. In designing the three-phase current motor, we had made the 

 condition that the motor should start with a torque equal to twice the 

 normal running torque. As all the starting devices that have been 

 tried for single-phase motors are not worth very much, such a con- 

 dition can, at present, not be fulfilled. We rate the motor, therefore, 



FIG. 36. 



according to its most favorable efficiency and power factor. For 135 

 kilowatts we have an efficiency of 94 per cent and a power factor of 

 82 per cent, corresponding to an apparent efficiency of 77 per cent. 

 The motor will safely yield 180 horse-power at 2250 volts. 



127. It is instructive to compare the current in the three phases 

 of the three-phase current motor reduced to the voltage of the 

 single-phase current motor with the current in the single- 

 phase motor. The three-phase motor took a magnetizing cur- 



69 



