Electrical Machines
In DC machine shape of armature MMF wave is?

 Triangular and directed towards main pole.
 Saddle shape.
 Peaky in nature.
 Triangular and directed towards brush axis.

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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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