Electrical Machines
A DC series motor must started on no load because it would

  Run at dangerously high speed.
 Draw more current without producing sufficient torque.
 Not develop starting torque.
 Fail to start without load.

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Electrical Machines
In a DC machine the armature mmf is

  stationary with respect to field poles.
  stationary with respect to armature.
 rotating with respect to field poles.
  rotating with respect to field poles as well as armature.

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Electrical Machines
Compensating windings are used in DC generators

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

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

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

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