SOLUTION

• A synchronous motor is very sensitive to fluctuation in the load. When the synchronous motor is under no load the stator and rotor poles axes almost coincide with each other.
• When the motor is loaded the rotor pole axis falls back with respect to the stator. On the other hand, if the rotor poles are suddenly decreased then the rotor poles pull upward or get advanced. Due to the inertia of the rotor, it can’t achieve its final position instantaneously. Therefore rotor will oscillate to its final new stable position. This oscillation of the rotor is known as hunting.

Causes of Hunting in Synchronous Machines

• A sudden change in load.
• The sudden change in field current.
• A load containing harmonic torque.
• Fault in the supply system.
• Periodic Variation of the load

 Effects of Hunting

• Hunting increases the chance of losing synchronism.
• Hunting causes variations in the supply voltage.
• Hunting increases the possibility of resonance.
• Due to hunting, huge mechanical stresses may be developed in the rotor shaft.
• Machine loss increases during hunting.
• The temperature of the machine rises during hunting.

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 induces emf in the damper winding, which acts in such a way to suppress the rotor oscillation.
• The induced emf generated develop induction torque in the synchronous motor.

Note: Mechanical losses such as friction loss does not cause hunting.

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