The Repulsion-Induction Motor

Author: E.E. Kimberly

Fig. 21-12. Repulsion-Induction Characteristic

If the commutator of a repulsion motor be short-circuited, the rotor becomes merely a type of squirrel-cage rotor with a characteristic as shown by curve (b) of Fig. 21-11. The repulsion-induction motor starts by its repulsion characteristics; and then by the operation of a centrifugal switch the commutator is short-circuited at about the speed marked X, and the motor continues its acceleration on the ind action characteristic (b) which provides good speed regulation in the normal -load region of speed. See Fig. 21-12.

Fig. 21-13. Cut-Away Model of Repulsion-Induction Motor

Details of a repulsion-induction motor are shown in Fig. 21-13. These motors are usually designed for a starting torque of 4 to 6 times the full-load running torque. The starting-current inrush is from 2 to 4 times the full-load current. The starting current may be adjusted to a lower value by increasing the angle a of brush shift, but there will be a sacrifice in starting torque. Reversal is accomplished by shifting the brushes from one side of the neutral axis to the other, just as in the repulsion motor.

This type of motor costs more than a polyphase motor of comparable rating and is somewhat larger. It is well adapted to refrigerator compressors, milling machines, floor finishers, machine tools, hoists, etc.