What is damper winding?

The windings behave in the same fashion as the squirrel cage of an induction machine. When rotor speed differs from the stator-side electrical speed, currents are induced in the damper windings. These currents set up a torque that has the effect of pulling the rotor back toward synchronous speed. This is true whether the rotor is spinning above synchronous or below synchronous speed.

When the rotor is spinning at synchronous speed (i.e. zero slip), no currents are induced in the damper windings.

Damper windings are commonly found on large, low-speed, salient pole machines, where there is a tendency to have inadequately damped rotor oscillations without the amortisseurs.