Why is there a damper winding on the rotor of the synchronous motor?

General large and medium synchronous motor rotor, in addition to the excitation winding, but also equipped with damping winding. The damper winding is similar to the cage winding structure of the rotor of the cage type asynchronous motor. The whole damper winding consists of copper rods and short-circuit copper rings welded in the pole hole. The damping winding has two main functions:

(1) When the synchronous motor is started asynchronously, the asynchronous motor generates the asynchronous starting torque by using the induced current in the damper winding and the stator rotating magnetic field as the cage type asynchronous motor to start the synchronous motor. So that the damper winding is the starting winding.

(2) the relative movement between the rotor and the rotating magnetic field occurs when the synchronous motor is oscillating in the operation of the synchronous motor, and the induced current is generated in the damper winding, which interacts with the rotating magnetic field to produce a torque which prevents the rotor from rotating relative to the rotating magnetic field, Of the shock, which is the "damping" meaning.