Question

In case of permanent-split capacitor one-phase induction motor, the starting torque is:
1. 25% of the maximum torque
2. -25% of the maximum torque
3. 5% of the maximum torque
4. 0 Nm

Answer 1

Correct Answer - Option 1 : 25% of the maximum torque

Concept :

Single-phase induction motors are classified according to the auxiliary means used to start the motor. They are classified as follows:

1. Split-phase motor
2. Capacitor-start motor
3. Capacitor-start capacitor-run motor
4. Permanent-split capacitor (PSC) motor
5. Shaded-pole motor

Permanent-split Capacitor (PSC) motor:

These motors have a cage rotor, and its rotor consists of two windings namely, the main winding and the auxiliary winding. The single-phase induction motor has only one capacitor C which is connected in series with the starting winding. The capacitor C is permanently connected in series with the starting winding. The capacitor C is permanently connected in the circuit at starting and running conditions.

Advantages

A single-value capacitor motor has the following advantages:

• In this type of motor, no centrifugal switch is required.
• This motor has higher efficiency.
• It has higher power-factor because of a permanently-connected capacitor.
• It has higher pull-out torque.

Limitations of permanent-split capacitor motor:

• Electrolytic capacitors cannot be used for continuous running. Therefore, paper-spaced oil-filled type capacitors are to be used. Paper capacitors of the same rating are larger in size and more costly.
• A single-value capacitor has a low starting torque usually less than full-load torque.

Applications:

• These motors are used for fans and blowers in heaters.
• It is used in air conditioners.
• It is used to drive refrigerator compressors.
• It is also used to operate office machinery.