Alternator

Representational Image
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Alternator is a machine which converts mechanical energy into electrical energy. Since the machine generates alternating current so it is called alternator. An alternator consists of a stator and a rotor. The stator provides the armature winding whereas the rotor provides the rotating magnetic field. According to their construction alternator is classified into two parts:-

1. Revolving armature type alternator
2. Revolving field type alternator

Revolving armature type alternator

Revolving armature type alternator

It has stationary field poles and revolving armature. It is usually of small kVA capacity and low voltage rating. It resembles a DC generator in general appearance except that it has slip rings instead of a commutator.

Revolving field type alternator

Revolving Field Type Alternator

It has a stationary armature or stator inside of which the field poles rotate. Most alternators are of the revolving field type in which the revolving field structure or rotor has slip rings and brushes to supply the excitation current from an outside D.C. source. Usually the field voltage is between 100 and 250 volts and the amount of power delivered to the field circuit is relatively small.

Working Principle

Synchronous Generator/Alternator

The alternator works on the principle of Faraday's Law of electromagnetic induction, i.e., when rotor is rotated by prime mover, the stator winding or conductors are cut by the magnetic flux  of the rotor magnetic poles. Hence an emf is induced in the stator conductors. The emf generated in the stator conductors is taken out from three leads connected to the stator winding as shown in figure.