Electrical Machines
The oscillation in a synchronous motor can be damped out by

  oscillation cannot be damped.
  providing damper bars in the rotor pole faces.
  maintaining constant excitation.
  running the motor on leading power factors.

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Electrical Machines
In large sized DC machines the compensating windings are provided to

None of these
 compensate for the decrease in speed due to increase of load.
 reduce eddy current losses by providing local short circuits.
  neutralize voltage induced in coil due to fluctuation of l

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