Electrical Machines
To avoid formation of grooves in the commutator

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

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Electrical Machines
In a DC machine, for the same value of φ, Z and N; which one of the following statements is correct?

 Armature emf is less with wave winding than with lap winding.
 Armature emf depends on weather the machine is running as a motor or generator.
 Armature emf is same as long as the flux density in the air gap remains the same.
  Armature emf is more with wave winding than with lap winding.

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Electrical Machines
Torque angle of a synchorous machine operating from a constant voltage bus is usually defined as the space angle between

  Rotor mmf wave and stator mmf wave.
 Stator mmf wave and resultant mmf wave.
 Stator mmf wave and resultant flux density.
 Rotor mmf wave and resultant flux density wave.

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