Electrical Machines
To achieve spark less commutation brushes of DC generator are rocked ahead so as to bring them

None of these
 just ahead of magnetic neutral axis.
 in magnetic neutral axis.
 just behind the magnetic neutral axis.

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Electrical Machines
The armature mmf of a DC machine has

  trapezoidal space distribution and is stationary in space.
  triangular space distribution and is stationary in space.
  triangular space distribution and rotates at the speed of armature.
 stepped distribution and rotates at the speed of armature.

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Electrical Machines
The following statements relate to compensating winding (CW) and interpole winding (IW) of a dc machine : 1. CW neutralizes the armature reaction under a pole pitch 2. IW is connected in series with armature circuit 3. IW produces mmf in the commutating zone only 4. CWmmf is directed along the brush axis 5. Mmf produced by IW is equal to armature mmf From these, the correct statements are

 1, 3, 4, 5
 2, 3, 4, 5
 1, 2, 3, 4 and 5
 2, 3, 4

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