Electrical Machines
The air gap between stator and the rotor of the 3 - φ induction motor is kept

  air gap does not matter.
  depends on the material of stator and the rotor.
  as small as possible.
  as wide as possible.

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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,

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

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