Electrical Machines
Satisfactory commutation of DC machine requires

 smooth, concentric commutator properly undercut.
 brushes should smoothly run in the holders.
All of these
 brushes should be of proper grade and size.

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Electrical Machines
For a single phase capacitor start induction motor which of the following is valid?

 Rotation can be changed by interchanging supply terminals.
 Direction of rotation cannot be changed.
  Rotation can be changed by reversing main winding terminals.
 None of these.

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Electrical Machines
What is/are the necessary conditions for voltage build up in self excited generator?

 Poles should contain residual flux.
All of these
 Field winding resistance should be less than critical resistance.
 Field winding should be properly connected to armature winding.

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