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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Electrical Machines
In a star - delta starting of an IM

  applied voltage per stator phase is 57.7 % of a line volt
  reduced voltage is applied to the stator.
  line voltage is 57.7 % of stator voltage.
  resistance is inserted in the rotor.

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