Electrical Machines
Flashing the field of DC generator means

  creating residual magnetism by a DC source.
  neutralising residual magnetism.
 increasing flux density by adding extra turns of winding.
  making the magnetic losses forces parallel.

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Electrical Machines
The introduction of interpoles in between the main poles improves the performance of a dc machine, because

 the flux waveform is improved with reduction in harmonics
 a counter-emf is induced in the coil undergoing commutation
 the inequality of air-gap flux on the top and bottom halves of the armature is removed
 the interpoles produce additional flux to augment the developed torque

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

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

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