Single Phase Induction Motor Interview Question Answer - 3

Important Questions of Single Phase Induction Motor

In this post, question answers of single phase induction motor is discussed which includes repulsion induction motor, DC Series Motor on AC Supply, Compensated Motor, Universal Motor, Single Phase Synchronous Motor, Principle of Reluctance Motor, Principle of Hysteresis Motor, Rotor of Hysteresis Motor, Advantages and Applications of Hysteresis Motor.

Repulsion Induction Motor

Which type of rotor construction does the repulsion induction motor consist of?

Repulsion induction motor – rotor

  • The rotor of the repulsion induction motor has squirrel cage winding and commutated winding. 
  • The squirrel cage winding is placed in the inner slots whereas the commutator winding is placed on the outer slot in the rotor.

State the application of the repulsion induction motor.

Application : Compressors, Petrol pumps, House hold refrigerators, Lift and hoists, Mixing machines, Machine tools

DC Series Motor Connected to AC Supply

What will happen if the DC series motor is connected to AC supply?

When the DC series motor is connected to AC supply

  • Alternating flux causes excessive eddy current losses in the yoke and field cores
  • Sparking at brushes
  • Low power factor due to high inductance of armature and field coils

Compensated Motor

What do you mean by conductivity compensating motor and inductively compensated motor?

Conductivity compensated motor

  • When the armature winding is connected is in series with compensating winding it is called as conductivity compensated motor.

Inductivity compensated motor

  • The armature winding is acts as primary winding of a transformer whereas the short circuit compensated winding acts as secondary winding. 
  • As there is no connection between armature winding and compensating winding, it is called as called as inductivity compensated motor.

Universal Motor

Which type of motor is operated on direct or single-phase ac supply?

Universal motor

Describe the different types of universal motor according to construction.

Types of universal motor

  • Non compensated (Low power rating)
  • Compensated (High power rating)

Which type of construction the universal motor consists of?

Non – compensated universal motor

  • Stator: Two salient poles
  • Rotor: Wound type armature (Similar to that in DC motor)

Speed of Universal Motor

How the no load speeds of the universal speed are controlled?

  • The no load speed of the universal speed is controlled by its own friction and windage load.

How the direction of the universal can be reversed?

Reverse rotation of the universal motor

  • The direction of the distributed field compensated type universal motor may be reversed by interchanging either the armature or field connection and shifting the direction of brush shift against the direction of the motor rotation. 
  • The direction of the concentrated type universal motor may be reversed by interchanging the either the armature or field connection.

Applications of Universal Motor

State the applications of the universal motor.

Application : Vacuum cleaners, Food Mixers, Sewing machines, Portable drill

Describe the different types of unexcited single phase synchronous motor.

Types of unexcited single phase synchronous motor

  • Hysteresis motor
  • Reluctance motor

Reluctance Motor

Describe the Principle of operation of reluctance motor.

Principle of reluctance motor

  • When a magnetic material is placed in the magnetic field, the force on the magnetic material such that reluctance of the magnetic path lies through the material will be minimum.

At which torque angle the reluctance torque becomes maximum in the reluctance motor?

  • The reluctance torque becomes maximum at torque angle 450 in the reluctance motor.

State the application of the reluctance motor.

Applications : Recording instruments, Signaling devices, Phonographs


Hysteresis Motor

Whether there is any eddy current loss in the hysteresis motor?

Eddy current loss in the Hysteresis Motor

  • The rotor of the hysteresis motor is made of smooth chrome steel.
  • It is impossible to set up eddy current in this type of rotor therefore there is no eddy current losses in the hysteresis motor.

What should be property of rotor material in the hysteresis motor?

Rotor material of Hysteresis Motor

  • The rotor of the hysteresis motor is made of smooth chrome steel.
  • It has high retentivity therefore it is impossible to change the magnetic polarity of the rotor once induced in it.

At what speed the rotor of the hysteresis motor rotates? Why?

Speed of Hysteresis Motor

  • The rotor of the hysteresis motor rotates at synchronous speed because the stator poles and rotor poles of opposite polarity locked each other.

On which factor the torque of the hysteresis motor depends?

  • The hysteresis torque in the hysteresis motor depends upon the area of rotor’s hysteresis loop.

Advantages of Hysteresis Motor

Describe the advantages of hysteresis motor.


  • Accelerates very quickly
  • Noiseless operation
  • No vibrations

State the application of the hysteresis motor.

Applications : Tape – decks, Turn – tables, Precision audio equipment, Timing devices, Electrical clocks 

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