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

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Electrical Machines
Consider the following statements about commutating poles which are fitted on most large dc Shunt motors: 1. The commutating poles are placed in the geometric neutral plane and their number is usually Equal to the number of main poles 2. The winding on the commutating poles is connected in series with the shunt-field winding on the main poles 3. The polarity of the commutating pole must be that of the next pole further ahead 4. The commutating poles neutralize the reactance voltage produced in the coil undergoing Commutation. Of these statements,

 1, 2 and 4 are correct
 2, 3 and 4 are correct
 1, 2 and 3 are correct
 1 and 4 are correct

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