# In a synchronous motor, during hunting when the rotor speed exceeds the synchronous speed then damper bar develop

In a synchronous motor, during hunting when the rotor speed exceeds the synchronous speed then damper bar develop

### Right Answer is: Induction generator torque

#### SOLUTION

“Hunting is the phenomenon of the synchronous machines which oscillates at about its new equilibrium position” means the synchronous machines rotate at other than synchronous speed.

### Use of Damper winding to prevent hunting

• Hunting can be reduced by using damper winding.
• When hunting occurs, the difference in the speed of stator and rotor poles develops an induces emf in the damper winding, which acts in such a way to suppress the rotor oscillation.
• When the rotation at constant load is uniform, there is no relative motion between the rotor and stator forward rotating fields and hence no current is induced in these windings.
• 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. The relative motion of the rotor sets up eddy currents in these windings which flow such as to suppress the oscillations (as per Lenz’s Law).
• 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.
• The dampers should have low resistance . be more effective. However, this method cannot eliminate – completely.