Electrical Machines
With the increase in speed of a DC motor

 back emf falls and line current increases.
 both back emf as well as line current increase.
 back emf increases but line current falls.
 both back emf as well as line current fall.

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

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

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