Repulsion-Start Single-Phase Motor
The principle of operation of the repulsion-type single-phase motor is an interesting contrast with other motors.
In a repulsion-start single-phase motor, a drum-wound rotor is used, which is similar to a squirrel-cage rotor. The circuit is connected to a commutator with a pair of short-circuited brushes. These are set such that, the magnetic axis of the rotor winding is inclined to the magnetic axis of the stator winding. The current flowing in the rotor circuit reacts with the field, to produce a starting and an accelerating torque. At about 67% of the full load speed, the brushes are lifted, the commutator is short-circuited and the motor runs as a single-phase squirrel-cage motor.
The repulsion induction motor employs a repulsion winding on the rotor during the start and running. The repulsion induction motor has an inner squirrel-cage winding and an outer winding on the rotor, which acts as a repulsion winding. As the motor speeds up, the induced rotor current partially shifts, from the repulsion winding to the squirrel-cage winding and the motor runs partly as an induction motor.
Repulsion-start motors have a high-starting torque. Changing the position of the brushes can vary their speed.