What is an exciter and how does it work ?

 There are two types of exciters, static exciter, and rotary exciter. The purpose of the exciter is to supply the excitation dc voltage to the fixed poles of the generator. Rotary exciter is an additional small generator mounted on the shaft of the main generator. If it is a dc generator, it will supply dc to the rotary poles through slip ring and brushes (conventional alternator). if it is an ac exciter, the output of ac exciter is rectified by rotating diodes and supply dc to main fixed poles.ac exciter is the ac generator whose field winding are stationary and armature rotates. Initial voltage is built up by residual magnetism. It gives the starting torque to the generator.