Electrical Machines
The interpoles in dc machines have a tapering shape in order to

 reduce the saturation in the interpole
 increase the acceleration of commutation
 economise on the material required for interpoles and their windings
 reduce the overall weight

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

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