Electrical Machines
In DC generators, the cause of rapid brush wear may be

 severe sparking.
 imperfect contact.
 rough commutator surface.
 any of above.

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Electrical Machines
In a 3 - Φ induction motor

  power factor at starting in the same as that while running.
  none of them.
  power factor at starting is low as compared to that while running.
  power factor at starting is high as compared to that while running.

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