An excitation system of an A.C. generator consists of a direct current generator and a voltage controlling unit known as the voltage regulator. An excitation system’s main function is to supply and control the direct current for the rotor pole windings. Voltage regulators are of several types and are used depending on the generator requirement. The level of excitation current and the resulting field pole strength produced is adjusted automatically using an AVR (automatic voltage regulator) attached to the system. https://www.brighthubengineering.com/commercial-electrical-applications/62223-wh...