Ans. It is sometimes employed for starting on single phase induction motors.
In this method, after bringing the motor up to speed, the winding is then short circuited upon itself, and the motor then operates on the induction principle.
Ques. What name is given to this type of motor?
Ans. It is called the repulsion induction motor.
Power Factor of Induction Motors.—In the case of a direct current motor, the energy supplied is found by multiplying the current strength by the voltage, but in all induction motors the effect of self-induction causes the current to lag behind the pressure, thereby increasing the amount of current taken by the motor. Accordingly, as the increased current is not utilized by the motor in developing power, the value obtained by multiplying the current by the voltage represents an apparent energy which is greater than the real energy supplied to the motor.
Fig. 1,913.—Fairbanks-Morse squirrel cage armature, showing ball bearings.
It is evident, that if it were possible to eliminate the lag entirely, the real and apparent watts would be equal, and the power factor would be unity.
The importance of power factor and its effect upon both alternator capacity and voltage regulation is deserving of the most careful consideration with all electrical apparatus, in which an inherent phase difference exists between the pressure and the current, as for instance in static transformers and induction motors.