Salient pole alternator & Cylindrical pole alternator

Salient pole alternator

The salient poles are mounted on large circular steel frame which is fixed to the shaft of the alternator.
It is used for low speed alternator.
As the speed of the alternator is low, numbers of poles must be higher resulting diameter of the rotor must be large and short axial length.
The pole shoe covers 2/3 of the pole pitch.
The diesel turbine, hydraulic turbine and oil engine have salient pole construction.
The salient poles would cause excessive windage loss if it is driven at high speed & it would produce excessive noise.
The salient pole structure would not withstand excessive centrifugal forces at higher speed.
The damper winding is embedded in the pole faces of the salient poles in order to reduce hunting effect.

The field winding is embedded in the slots of the smooth cylindrical rotor.
The field coils are arranged such that central polar area has maximum flux density and gradually falls away on either side.
Noiseless operation particularly at high speed.
The flux distribution around the periphery is nearly sinusoidal waveform therefore better emf waveform is obtained than that of salient pole alternator.
The solid field poles themselves acts as damper therefore cylindrical alternator does not required damper winding.
The cylindrical rotor has small diameter and long axial length in order to avoid excessive velocity.
The cylindrical construction of the rotor gives better balance and noiseless operation.