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Damper bars placed in the motor pole faces of any alternator help to reduce hunting
1. Above synchronous speed only
2. Below synchronous speed only
3. Above and below synchronous speed both
4. None of the above

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Correct Answer - Option 3 : Above and below synchronous speed both

Hunting:

Hunting is the phenomenon of the synchronous machines which oscillate at about their new equilibrium position i.e. the synchronous machines rotates at other than synchronous speed.

Damper windings are used to prevent the hunting of synchronous generators or to reduces oscillations of the rotor when the motor deviates from synchronism.

  1. When the rotor rotates at synchronous speed, there is no relative motion between armature flux and damper winding (since damper winding is placed on the rotor). Therefore, EMF induced in the damper bars is zero means current through the damper bars equal to zero and hence damper winding torque production is zero.
  2. When the rotor speed is more than synchronous speed, induction generator torque will be produced through damper bars in the opposite direction to synchronous machine torque such that the above synchronous speed becomes nearer to synchronous speed.
  3. When the rotor speed is less than synchronous speed, induction motor torque will be produced through damper bars in the same direction of synchronous machine torque such that below synchronous speed becomes nearer to synchronous speed.


Hence,

Damper bars helps to reduce hunting in above and below synchronous speed of rotor.

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