Which of following is the least efficient type of 1-phase induction motor?

Among the different types of single-phase induction motors, shaded-pole motors are the least efficient due to the following reasons:

• Low Starting Torque
• High Copper and Core Losses
• Low Efficiency (20-30%)
• Used mainly in small fans, exhausts, and appliances where efficiency is not critical.
   

Types of 1ϕ induction motor

Split-phase Induction Motor

• This motor consists of a main winding and auxiliary winding. The auxiliary winding is used to produce the starting torque, which makes the motor rotate.
• The starting current of the split-phase induction motor is very low. The torque developed by the split phase motor at starting is about 1.5 times the rated torque.
• When the motor reaches 75% of the rated speed, the centrifugal switch disconnects the auxiliary winding from the motor.
• The common applications of split phase induction motors are in fans, washing machines, blowers, mixer & grinders, machine tools, etc.

Capacitor Start/Run Induction Motor

• In this motor, a capacitor is connected to auxiliary winding that produces the required starting torque.
• The starting torque developed in the capacitor start induction motors is about 3 to 4.5 times the full load torque.
• When the motor reaches 75% of the rated speed, the centrifugal switch disconnects the capacitor from the motor.
• These motors are widely used for driving pumps, compressors, AC and refrigerator compressors, conveyors, and other mechanical loads of high inertia.

Permanent Capacitor Induction Motor

• In this motor, the capacitor is connected permanently to the circuit, the power factor is high.
• These motors have low starting torque, less than full load torque.
• These motors are widely used for fans and blowers, refrigerator compressors, and office machinery.

Shaded pole Induction Motor​

• Shaded-pole motors are used to drive devices that require low starting torque.
• These motors are very suitable for small devices like relays, fans of all kinds, etc., because of their low initial cost and easy starting.