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

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

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Electrical Machines
What is/are the necessary conditions for voltage build up in self excited generator?

 Field winding resistance should be less than critical resistance.
All of these
 Field winding should be properly connected to armature winding.
 Poles should contain residual flux.

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