Question

With the help of diagram, explain the working principle of capacitor start motor.

Hint:

Capacitor start motors use a capacitor to create a phase shift that produces high starting torque.

Answer 1

Construction: A capacitor start motor is a type of single-phase induction motor having a capacitor connected in series with the starting winding (auxiliary winding) and the main winding connected directly to the supply.

Working Principle:
When the motor is started, the capacitor creates a phase difference between the currents in the main and starting windings.
This phase difference produces a rotating magnetic field which produces starting torque.
The motor starts and gains speed.
When the motor reaches about 70-80% of its full speed, the centrifugal switch disconnects the starting winding and capacitor from the circuit.
The motor then runs on the main winding alone. This design allows the motor to start under load with high starting torque.