- Alternator is a device that converts mechanical power into electrical power.
- The basic principle of operation of synchronous generator is electromagnetic induction.
- 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
- It is easy to insulate stationary winding for high voltage.
- Only two slip rings are required for dc supply to the field winding on the rotor.
- Solid connections can be obtained on stationary armature.
- Due to simple and robust construction of the rotor, higher speed of rotating dc flux is possible.
- Stator of the alternator is made of cast iron (for small machine) and fabricated steel (for large machine).
- Stator Core is made of laminated silicon steel.
- Rotor is divided into two types:- (a) Salient Pole Type and (b) Non-salient Pole type
- Salient pole type rotor is used in slow and medium-speed alternators.
- Salient pole type rotors have large diameters and short axial length.
- Non-salient pole type rotor is used high speed alternators.
- Non-salient pole type rotors have small diameters and very long axial length.
Frequency of induced emf
- Frequency of the alternator is given by the relation, f = NP/120 Hz.
- 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
- When load power factor is unity, the effect of armature reaction is to distort the main flux.
- When load power factor is zero lagging, the effect of armature reaction is to weaken (demagnetize) the main flux.
- When load power factor is zero leading, the effect of armature reaction is to strengthen the main flux.
- The change in terminal voltage from no-load to full load divided by full load voltage.