Electrical Machines
The armature mmf of a DC machine has

  trapezoidal space distribution and is stationary in space.
  triangular space distribution and is stationary in space.
 stepped distribution and rotates at the speed of armature.
  triangular space distribution and rotates at the speed of armature.

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

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

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