Electrical Machines
Commutation in a DC machine may be explained as a process

 by virtue of which emf is induced in the armature conductors.
  by which electric current in a coil is reversed.
  in which magnetic field is set up.
 how alternate flux affects the main field flux.

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Electrical Machines
Consider the following statements: To control the speed of a dc shunt motor above the base speed over a reasonably wide range, the motor must 1. have compensating winding 2. have interpole winding 3. be started using a 3-point starter 4. be started using a 4-point starter Of these statements

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

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