Electrical Machines
To avoid formation of grooves in the commutator

  brush position has no effect on the commutator grooving.
None of these
 the brushes of same polarity should track each other.
  the brushes of opposite polarity should track each other.

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

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