Repulsion-Start Induction-Run Motor: Operating Principle and Characteristics

A repulsion-start induction-run motor consists of a stator carrying a single-phase exciting winding and a rotor which has a closed type armature winding with a commutator and brushes. The brushes on the commutator are short circuited. In the repulsion-start induction-run motor, the action of repulsion motor is combined with that of a 1-phase induction motor.

This motor is started as a repulsion motor with a corresponding high-starting torque. At some predetermined speed, a centrifugal switch short-circuits the commutator segments so that the motor operates as a 1-phase induction motor.

The centrifugal device is fitted on the rotor shaft of the motor. When the motor attains about 80% of its normal speed, the centrifugal device forces a short-circuiting ring to come in contact with the inner surface of the commutator which short-circuits all the commutator bars. Then, the rotor resembles the squirrel cage type rotor and the motor operates as a 1-phase induction motor.

At the same time of the short-circuiting of the commutator bars, the centrifugal device also raises the brushes from the commutator that reduces the wear of the brushes and commutator and makes the motor operation quiet.

Characteristics of Repulsion-Start Induction-Run Motor

A repulsion-start induction-run motor possess following characteristics −

• Repulsion-start induction-run motors have high starting torque about 2.5 to 4.5 times of the full-load torque.

• They have high starting current about 3.75 times of the full-load current.

• Repulsion-start induction-run motors pose a serious problem of maintenance of brushes, commutator and the centrifugal device.

Applications of Repulsion-Start Induction-Run Motor

These motor are rarely used nowadays. Due to the high starting torque, these motors are used to drive−

• Refrigerators
• Pumps
• Compressors, etc.