With respect to alternator rotor types, select the correct option

SOLUTION

Salient pole rotor:

• A salient pole rotor has a large diameter and short axial length, length to diameter is ratio is very small.
• 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.
• So that salient pole rotor type:- causes speed fluctuation and suitable for- low and medium-speed operation.

 

Cylindrical rotor:

• A non-salient pole type rotor has a small diameter and long axial length, length to diameter is ratio is very high.
• 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 and it does not require any damper winding as the smooth rotor it self acts as good damper. 
• So that cylindrical rotor type: causes no speed fluctuation and suitable for high-speed operation.

 

Note:

Salient pole rotor	Cylindrical rotor
Large diameter and short axial length	Small diameter and long axial length
Used for low-speed alternators	Used for high-speed turbo alternators
Has no projecting poles	Has no projecting poles
Needs damper windings	Do not need damper windings
Windage loss is more	Windage loss is less