Electrical Machines
Variation in speed by ward-Leonard control of DC motors occurs due to variation in

  Armature voltage.
  Field excitaion.
  Supply voltage.
  Armature current.

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

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

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