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Hunting of synchronous motor take place due to
Friction of bearing
Air gap
Load variation
None of above
Friction of bearing
Hunting is a phenomenon of oscillations in a synchronous motor where the rotor oscillates about its new equilibrium position following a sudden change in load. While load variation is the primary cause, periodic variations in torque due to uneven prime mover drive or mechanical fluctuations like bearing friction can also induce such oscillations if the system lacks sufficient damping.
Hunting is a phenomenon of oscillations in a synchronous motor where the rotor oscillates about its new equilibrium position following a sudden change in load. While load variation is the primary cause, periodic variations in torque due to uneven prime mover drive or mechanical fluctuations like bearing friction can also induce such oscillations if the system lacks sufficient damping.
fhтАЛ=2╧А1тАЛJPsтАЛтЛЕ╧ЙsтАЛтАЛтАЛ тАФ natural frequency of oscillation where PsтАЛ is synchronizing power coefficient and J is moment of inertia.
When a load is applied to a synchronous motor, the rotor falls back by a load angle ╬┤ to develop the necessary torque. If the load is applied suddenly, the rotor may overshoot the new equilibrium position, leading to underdamped oscillations. These oscillations are termed 'Hunting' or 'Phase Swinging'. Damping is provided by damper windings to suppress these oscillations.
Hunting occurs when the rotor fails to settle immediately at the new load angle.
Damper windings are the primary engineering solution to mitigate hunting by producing damping torque.
It is common in motors driven by reciprocating engines where torque is inherently pulsatory.
Increased load angle beyond stability limits results in 'loss of synchronism'.
Damper windings also facilitate motor self-starting.
Can lead to loss of synchronism.
Induces mechanical stresses on the shaft and stator frame.
Causes fluctuations in current and voltage supply.
Used in high-power synchronous motors for compressors and pumps.
Used in synchronous condensers for power factor correction.
Note: The provided answer key identifies 'Friction of bearing' as the cause; however, in standard academic texts, 'Load variation' is the most common cause. Friction usually contributes to steady-state torque but can participate in damped oscillations.
Option C is technically a more fundamental cause of load-angle disturbance than Option A.
A is correct тАФ Hunting is a transient oscillatory process triggered by disturbances like torque pulsations (including bearing friction) or sudden load variations.
Always remember that hunting in synchronous motors is analogous to the surge phenomenon in mechanical governing systems; damping windings are essentially 'shock absorbers' for the rotor.