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

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

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Electrical Machines
Consider the following statements : Interpoles in dc machines 1. reducearmature reaction effects in the interpolar region 2. have the same dimension as main polls 3. have their windings connected in series with the armature 4. have same number of turns as the armature 5. have the polarity same as that of the main pole ahead in a motor From these, the correct statements are

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

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