Electrical Machines
DC generators are usually designed to develop armature voltages not exceeding 650 V because of the limitations imposed by

 starters
 commutator
 armature winding
 field winding

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

  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.
  pulling the motor directly on line without a rotor.

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