What is a Generator Automatic Voltage Regulator?
An automatic voltage regulator (AVR) is a solid state electronic device for automatically maintaining generator output terminal voltage at a set value. It will try and do this as the generator load or operating temperature changes. The AVR is part of the alternators excitation system.
A typical looking AVR - a Stamford SX460
Who provides the automatic voltage regulators?
Normally in a generating set, the alternator manufacturer will supply an automatic voltage regulator with their AC alternator. The biggest manufacturers of alternators for diesel generators are Stamford AVK, Mecc Alte, Leroy Somer and more recently WEG. The model supplied will depend on the alternator and any accessories fitted to it, which may need a different AVR. An example of such accessory would be a PMG or auxiliary winding.
How does an AVR work?
It controls output by sensing the voltage from the generator terminals and comparing it to a stable reference. The error signal is then used to adjust the field current by increasing or decreasing the current flow to an exciter stator, which in turn will lead to a lower or higher voltage at the main stator terminals.
Different AVR designs - what do they look like?
AVR's all look remarkable similar - they vary a bit in size and color, but seemingly all have similar features.