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Terms and conditions

The maximum EMF is induced in the rotor of a 3-phase induction motor when it

  • The maximum EMF is induced in the rotor of a 3-phase induction motor when it is blocked.
  • The maximum EMF is induced in the rotor of a 3-phase induction motor at the start, when the rotor is blocked or during starting, as the relative speed between the rotor and the rotating magnetic field is maximum at this time.
  • At start the slip is equal to unity, i.e., s = 1 and the frequency of the induced EMF is the same as that of the supply frequency.
  • As the motor starts rotating, the relative speed between the rotor and the rotating magnetic field decreases and becomes equal to the slip speed of NS - N.
  • The magnitude of the induced EMF in the rotor depends on the rate of cutting flux, which is the relative speed NS - N.
  • Therefore, in the running condition, the magnitude of the induced EMF decreases as the speed of the rotor approaches the synchronous speed, and so does its frequency.