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

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

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Electrical Machines
In a star - delta starting of an IM

  resistance is inserted in the rotor.
  line voltage is 57.7 % of stator voltage.
  reduced voltage is applied to the stator.
  applied voltage per stator phase is 57.7 % of a line volt

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