Electrical Machines
Sparkless commutation can be achieved by employing

  inter poles.
  any one or more of the above methods.
  high resistance carbon brushes.
 compensating winding.

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Electrical Machines
In a star - delta starting of an IM

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

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