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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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.
  line voltage is 57.7 % of stator voltage.
  reduced voltage is applied to the stator.

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