Electrical Machines
In a 3 - Φ IM with line frequency f1 and winding factor kw1 and kw2 for stator and rotor respectively the ratio of per phase stator winding emf E1 to per phase rotor winding emf E2 at standstill is given by

  E1 / E2 = N1 / N2.
  E1 / E2 = N1kw1 / N2kw2.
  E1 / E2 = 1.
  E1 / E2 = f1kw1 / f2kw2.

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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
 the interpoles produce additional flux to augment the developed torque
 a counter-emf is induced in the coil undergoing commutation
 the flux waveform is improved with reduction in harmonics

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