Compare Salient Pole Alternator and 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.

Cylindrical rotor alternator 
  • 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. 
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