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

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Electrical Machines
With the increase in speed of DC motor

 Back emf falls and line current increase.
 Both back emf as well as line current increase.
 Both back emf as well as line current fall.
  Back emf increase but line current falls.

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