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Damper winding in synchronous motors is used to ___________. A)Prevent the effect of hunting B)Make synchronous motors self-starting C)Reduce the speed of synchronous motors D)Provide constant synchronous motor torque
B and C
A and B
C and D
A and D
A and B
Damper windings, also known as amortisseur windings, are copper bars embedded in the pole faces of a synchronous machine. They serve two critical purposes: enabling the motor to start as an induction motor and providing damping torque to suppress oscillations during transient load changes.
IS 4889: 1968
Damper windings, also known as amortisseur windings, are copper bars embedded in the pole faces of a synchronous machine. They serve two critical purposes: enabling the motor to start as an induction motor and providing damping torque to suppress oscillations during transient load changes.
TdтАЛ=kтЛЕdtd╬┤тАЛ тАФ where TdтАЛ represents the damping torque and ╬┤ is the load angle.
During start-up, the damper bars act like a squirrel-cage rotor of an induction motor, allowing the machine to reach near-synchronous speed. When the machine is running at synchronous speed, the relative velocity between the rotating magnetic field and the damper bars is zero; however, if the load fluctuates causing hunting, these bars cut the flux, generating eddy currents that create a damping torque proportional to the slip, thus stabilizing the speed.
Damper windings are placed in the pole shoes of the salient pole rotor.
They are short-circuited by end rings, forming a low-resistance cage.
They suppress oscillations (hunting) caused by sudden load changes or prime mover torque variations.
They provide the necessary starting torque for the motor to behave like an induction motor.
Makes the synchronous motor self-starting.
Enhances system stability by suppressing hunting.
Helps in maintaining synchronism during transients.
Additional design complexity in the pole shoes.
Slight increase in manufacturing cost.
Increased I┬▓с┤┐ losses in the damper bars under specific conditions.
Synchronous motors requiring self-starting capability.
Synchronous condensers and alternators subjected to pulsating loads.
Hunting is the phenomenon of speed oscillations about the mean synchronous speed.
Option C is incorrect because synchronous motors operate at a constant synchronous speed NsтАЛ=P120fтАЛ.
Option D is incorrect because the average torque of a synchronous motor at steady state is determined by the excitation and load angle, not primarily by the damper winding.
B is correct тАФ Damper winding prevents the effect of hunting and makes synchronous motors self-starting.
Remember that damper windings are essential for self-starting in synchronous motors but are typically absent in cylindrical rotor machines unless specifically designed for oscillation suppression in power systems.
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