Electrical Machines
Short circuiting is caused in the armature winding due to

  any of above.
  grounding of two or more turns of the same coil.
 failure of insulation between two commutator bars.
  failure of insulation between two turns of coil.

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Electrical Machines
For satisfactory parallel operation of two transformers which of the following conditions is most essential,

 MVA rating of all transformer inversely proportional to impedance.
  polarities of all transformers must be same.
 voltage ratio of all transformers must be same.
 percentage impedance of all transformers must be same.

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

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

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