Electrical Machines
What is the frequency of a alternator, if P = number of poles and N = revolution made per second?

 120N / P Hz.
 120 / PN Hz.
 120P / N Hz.
  PN / 2 Hz.

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Electrical Machines
Compensating windings are used in DC generators

  to neutralize the cross magnetizing effect of the armature reaction.
  mainly to reduce the eddy currents by providing local short circuit.
None of these
  to provide path for the circulation of cooling air.

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Electrical Machines
What is/are the necessary conditions for voltage build up in self excited generator?

 Poles should contain residual flux.
 Field winding resistance should be less than critical resistance.
All of these
 Field winding should be properly connected to armature winding.

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