An alternator or AC generator produces AC supply. In other words, the generator or alternator converts mechanical energy into electrical energy. The rotor rotates at the synchronous speed. Therefore, we call AC generator as a synchronous generator. On the basis of design, the alternators are classified into two categories.
- Salient pole type
- Cylindrical rotor type.
The alternator work on the principle of Faraday’s law of electromagnetic induction. The rotor of alternator has field winding and it produces the magnetic flux. When we rotate the rotor by a turbine or a mechanical engine , then the rotating magnetic field produced in the air gap links to the armature coils.The linked flux to the stator or armature winding produces AC voltage.
The armature of alternator has coils placed 120 degree electrical apart. The magnitude of the AC voltage produced in the stator or armature of an alternator or synchronous generator depends on the magnetic flux, its frequency and number of turns in the stator winding.
Derivation of alternator or AC Generator EMF equation
Let us derive the emf equation of the alternator or ac generator or synchronous generator.
The speed of the rotor is ‘N’ RPM. The rotor completes ‘N’ revolution in 1 minute or 60 seconds. Therefore, rotor will complete 1 revolution in N/60 seconds.In one revolution, the total flux linked to the conductor is equal to φP.
According to Faraday’s law of electromagnetic induction,, the emf induced in the conductor is proportional to rate of change of flux.
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Please what is the defrent between the speed of the rotor (N) and frequency (F) and please how can we find the flux (Q)