Correct Answer - Option 2 : Salient pole rotor
Damper winding is used to suppress the vibrations in the rotor. As cylindrical rotor has no projections and there is a closed portion to contain field winding which is distributed. Therefore it acts as a smooth rotor. It does not require any damper winding as the smooth rotor it self acts as good damper. The salient pole rotor contain projected poles and the field winding is a concentrated winding on the pole core. The rotors are not mechanically stable and does not offer high operating speeds because of the projected nature. Any mechanical instability of the rotor i.e. vibration or hunting should be suppressed. This is achieved by providing damper bars in the poles/rotors.
