Electrical Machines
In dc machine armature windings are placed on rotor because of the necessity for

 commutation.
 generation of voltage.
 electromechanical energy conversion.
 development of torque.

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

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

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