1. Alternator is a device that converts mechanical power into electrical power.
  2. The basic principle of operation of synchronous generator is electromagnetic induction.
  3. First law of electromagnetic induction  states that whenever a conductor cuts by the magnetic flux or field an emf is induced in the conductor.

Advantage of Stationary Armature

  1. It is easy to insulate stationary winding for high voltage.
  2. Only two slip rings are required for dc supply to the field winding on the rotor.
  3. Solid connections can be obtained on stationary armature.
  4. Due to simple and robust construction of the rotor, higher speed of rotating dc flux is possible.


  1. Stator of the alternator is made of cast iron (for small machine) and fabricated steel (for large machine).
  2. Stator Core is made of laminated silicon steel.
  3. Rotor is divided into two types:- (a) Salient Pole Type and (b) Non-salient Pole type
  4. Salient pole type rotor is used in slow and medium-speed alternators.
  5. Salient pole type rotors have large diameters and short axial length.
  6. Non-salient pole type rotor is used high speed alternators.
  7. Non-salient pole type rotors have small diameters and very long axial length.

Frequency of induced emf

  1. Frequency of the alternator is given by the relation, f = NP/120 Hz.
  2. The frequency of induced emf or current induced in the armature conductors of the alternator depends upon the number of poles and speed of the rotor.

Armature reaction in Alternator

  1. When load power factor is unity, the effect of armature reaction is to distort the main flux.
  2. When load power factor is zero lagging, the effect of armature reaction is to weaken (demagnetize) the main flux.
  3. When load power factor is zero leading, the effect of armature reaction is to strengthen the main flux.

Voltage Regulation

  1. The change in terminal voltage from no-load to full load divided by full load voltage.