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

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

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Electrical Machines
In an alternator, voltage drops occurs in

  armature resistance only.
  armature resistance, leakage reactance, armature reaction and earth connection.
  armature resistance and leakage reactance.
  armature resistance, leakage reactance and armature reaction.

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