Electrical Machines
Current in a coil undergoing commutation is not able to get reversed completely by the end of commutation period. It is due to

None of these
  reactance voltage induced in the coil.
 armature emf.
  coil resistance.

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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.
  starting the motor on load which is more than the rated load.
  locking of rotor due to harmonics.

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Electrical Machines
Flashing of DC generator means

  increasing flux density by providing extra ampere-turns in field.
 neutralization of residual magnetism.
None of these
  creation of residual magnetism by a DC source.

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