Electrical Machines
In a 3 - Φ IM in order to eliminate cogging the number of stator slots must be

  an integral multiple of number of rotor slots.
  equal to number of rotor slots.
  either (B) or (C).
  unequal to number of rotor slots and skewed in shape.

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Electrical Machines
In case of 3 - Φ IM, plugging means

  interchanging two supply phases for quick stopping.
  locking of rotor due to harmonics.
  starting the motor on load which is more than the rated load.
  pulling the motor directly on line without a rotor.

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