Electrical Machines
A 3-φ alternator has negligible stator resistance. A short circuit test is conducted on this alternator. At a particular speed, a field current of If1 is required to drive the rated armature current. If the speed of the alternator is reduced to half, the field current required to maintain rated armature current

 Would be equal to If1.
 Woud be equal to 2If1.
  Cannot be predicted due to insufficient data.
 Would be equal to If1/2.

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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.
  pulling the motor directly on line without a rotor.
  locking of rotor due to harmonics.
  interchanging two supply phases for quick stopping.

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