Hunting in Synchronous Motor
The phenomenon is oscillation of the rotor about its equilibrium or steady state position in synchronous machines is called hunting in synchronous motor.
Hunting effect can be occur in synchronous motor. Because of hunting effect synchronous motor is not self starting.hunting means momentary fluctuations in rotor speed.
In synchronous machine magnetic locking is take place between rotor and stator its known as cogging.
A suddenly change in load causes sudden change in torque or load angle(A). Rotor is oscillation by angle(A) at steady States position because of moment of inertia. the stator magnetic field rotates fast and in very short duration. position of stator magnetic field is shown in fig.
Due to moment of inertia rotor is in previous position but its try to moves in clockwise direction due to attraction. After some time rotor try to rotate anticlockwise direction.This effect is continues ans stator will oscillates in clockwise and anticlockwise direction. This phenomena of rotor known as hunting. Its because of inertia of rotor. Because of hunting synchronous motor is not self starting.
The word hunting is used because rotor is hunt to its new position. And its also known as the phase swinging.
Effect of hunting:-
- Produced large variation in currents.
- Its produced mechanical stresses on rotor shaft.
- Its lead to loss of synchronism.
Causes of hunting :-
- When fault occur in system.
- Suddenly Change in load.
- Suddenly change in excitation.
Method to remedies for hunting:-
There are two methods are following below,
By using flywheel :-
The prime mover is fitted with a flywheel. It is increase the inertia and maintains the rotor speed at constant.
By using damper winding :-
Damper winding’s are placed in rotor pole faces. It is made from low resistance copper bars. Which are short circuited at both end but copper rings. Damper winding cuts the stator rotating flux. hence, emf is induced in it according to the lenz’s Law. This emf oppose the oscillation. So By damping winding we can damped the oscillation. The magnitude of damping torque is proportional to the slip speed.
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