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
The damper windings also called the squirrel cage windings or damper grids

  are provided in a synchronous motor to make it self starting.
  are provided on the stator for improving power factor.
  consists of short-circuited copper bars embedded in the field pole faces.
  both (A) and (B).

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