On an AC alternator, a shunt or self excited excitation system operates by drawing power for the AVR straight from the main stator winding. While this technique of excitation is often used on many AC alternators, alternatives such as an auxiliary winding or PMG system give higher performance at a lower cost when compared to the cost of the entire unit.
Because the power for the AVR is drawn from the main alternator terminals in a normal shunt or self-excited AC alternator, when loads are applied to the AC Alternator, the terminal voltage drops and the power source of the AVR is lowered.
As a result, voltage responsiveness is slower, transient voltage dips are bigger, and the voltage may not return to its pre-set level.
As a result, voltage responsiveness is slower, transient voltage dips are bigger, and the voltage may not return to its pre-set level.
What makes it useful? How does it stack up against other methods?
When cost is the most important consideration, a shunt / self excited  permanent magnetic alternator is probably the best option; however, when performance is important, such as increased voltage stability and lower transient voltage dips, or when large disturbing loads are applied, an auxiliary winding or PMG system should be chosen.
