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

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MPPGCL JE Electrical 19 March 2019 Shift 2 Official Paper
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  1. Capacitor-run type
  2. Split-phase type
  3. Capacitor-start type
  4. Shaded-pole type

Answer (Detailed Solution Below)

Option 4 : Shaded-pole type
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Detailed Solution

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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.

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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.

F2 U.B Madhu 31.12.19 D 1

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.

F1 Jai Prakash Anil 23.12.20 D1

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.

F1 Jai 5.2.21 Pallavi D12

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