Electrical Machines
The mmf produced by rotor currents of a 3 - Φ induction motor

  rotates at the speed of rotor in the air gap.
  rotates at synchronous speed with respect to rotor.
  rotates at slip speed with respect to stator mmf.
  is at standstill with respect to stator mmf.

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Electrical Machines
The damper windings also called the squirrel cage windings or damper grids

  consists of short-circuited copper bars embedded in the field pole faces.
  are provided in a synchronous motor to make it self starting.
  are provided on the stator for improving power factor.
  both (A) and (B).

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

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Electrical Machines
Where the shunt generators are widely used?

 Where the load is very high.
 Where often load fluctuation is occurred.
 Where voltage variation is needed over a wide load range.
  Where a constant voltage is required over a narrow load range.

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