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Which of the following statements is/are NOT true for the damper windings in alternators? I)These are useful in preventing the hunting in alternators. II) Usually, damper windings are provided in smooth cylindrical type rotor alternators. III)Under normal working conditions, i.e., if machine is at synchronous speed, damper winding do not carry any currents. IV) Damper windings are also used to provide starting torque in alternators.
IV
I
III
II
II
Damper windings (amortisseur windings) are intentionally provided in salient-pole (projecting pole) rotor alternators to suppress hunting oscillations. They are not used in cylindrical rotor alternators because the solid iron rotor body of a cylindrical alternator already provides sufficient eddy current paths to serve the damping function, making dedicated damper windings redundant and mechanically difficult to install.
Damper windings (amortisseur windings) are intentionally provided in salient-pole (projecting pole) rotor alternators to suppress hunting oscillations. They are not used in cylindrical rotor alternators because the solid iron rotor body of a cylindrical alternator already provides sufficient eddy current paths to serve the damping function, making dedicated damper windings redundant and mechanically difficult to install.
TdтАЛтИЭdtd(╬Ф╧Й)тАЛ тАФ the damping torque is proportional to the rate of change of speed deviation.
When a disturbance occurs, the rotor speed fluctuates, causing the magnetic flux to sweep across the pole face. This induces eddy currents in the damper bars that generate a torque opposing the oscillation as per Lenz's law, effectively damping the mechanical vibrations.
Damper windings are copper/brass bars embedded in the pole shoes.
They suppress phase swings (hunting) during load transients.
They facilitate self-starting in synchronous motors.
Cylindrical rotors rely on natural eddy currents in the rotor forging for damping.
Suppression of hunting.
Provision of starting torque in synchronous motors.
Improvement of stability under unbalanced loading conditions.
Increases cost and constructional complexity.
Requires maintenance of additional winding slots.
Salient pole synchronous generators (Hydro-generators).
Synchronous motors (for starting).
Statement I is true: Damper windings damp out oscillations known as hunting.
Statement II is false: They are provided in salient pole machines, not cylindrical ones.
Statement III is true: At steady synchronous speed, there is no relative motion between flux and damper bars, hence zero current.
Statement IV is true: They provide asynchronous starting torque to reach near-synchronous speeds.
D is correct тАФ Damper windings are designed for salient-pole rotors, not smooth cylindrical rotors.
Remember that cylindrical rotors are preferred for high-speed turbo-alternators where physical integrity is paramount, making internal damper bars unnecessary.
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