In the salient pole of the phase synchronous machine, the rotor will have

• A. Larger diameter, larger axial length
• B. Smaller diameter, larger axial length
• C. Smaller diameter, smaller axial length
• D. Larger diameter, shorter axial length

Answer: (D)

The rotor of the synchronous machine carries a field winding that is supplied with d.c. through two slip rings by a separate d.c. source. Synchronous Rotor construction is of two types, namely :
Salient (or projections) pole type.
Cylindrical type (or non-salient pole type)
Salient-pole rotor:-
In this type, salient poles are mounted on a large circular steel frame which is fixed to the shaft of the alternator.
The rotors of salient-pole rotor machines have concentrated winding on the poles and a nonuniform air gap.
Salient pole generators have a large number of poles. sometimes as many as 50, and operate at lower speeds.
The synchronous generators in hydroelectric power stations are of the salient pole type and are driven by water turbines.
The rotors are shorter axial length but have a large diameter.