When three phase supply given to the stator of a three phase induction motor, a rotating magnetic field is set up which rotates at synchronous speed.

principle of operation of three phase induction motor

  • The stationary rotor conductors cut the revolving magnetic field.
  • According to Faraday’s law of electromagnetic induction an emf is induced in the rotor conductors.
  • As rotor conductors are short circuited and current start flowing through the rotor conductor.
  • Due to flow of this current a magnetic field is set up in rotor conductor.
  • A resultant field is set up, which exerts force on the rotor conductors and rotor starts rotating.

Why the rotor does not rotates at Synchronous speed?

The rotor tries to attain the synchronous speed but rotor fails to do so.

  • If the rotor attains the synchronous speed then the relative speed between rotating magnetic field and rotor will be zero,.
  • If this cause no emf will be induced in the rotor conductors.
  • If there is no emf is induced in the rotor conductor, no current will flow through the rotor
  • No magnetic flux will set up in rotor.
  • Hence no torque is produced in rotor. That is why, an induction motor never runs at synchronous speed. It is always runs at a speed less than synchronous speed.
  • An induction motor is also called synchronous motor.
  • The principle of operation of this motor depends upon electromagnetic induction. Hence, the name induction motor.