An automatic voltage regulator (AVR) is an electronic device that automatically maintains the generator's output terminal at a set value, and it does this through operating temperature changes and acting as the generator load.

The AVR also acts as part of the excitation system of the generator.

Generally, in a generator setup, the manufacturer for the alternator will supply the automatic voltage regulator and the AC alternator. The model provided is dependent on the alternator, plus any other accessories that will be fitted to it.

Where is the AVR located?

The automatic voltage regulator for the generator is usually located in either of the following three places; the generator’s main control box, under the alternator's rear cover, or in the alternator’s terminal box.

How does it work?

An automatic voltage regulator controls the output by sensing the voltage from the terminals and comparing them to achieve a stable reference. Usually, the error signal is used to adjust the field current. This is done by either increasing or decreasing the flow of current to the exciter stator. This will lead to either a lower or a higher voltage at the main stator terminals.

It also acts as the control switch for the output voltage of the connection to the load. In this way, the automatic voltage regulator is turned off in case of any sudden surge of the load, and it does not damage the generator.

The automatic voltage regulator for generator also plays a vital role in operating synchronous generator sets. This is a controller for the voltage output as it controls the excitation current it produces.

In this case, the voltage regulator then allows the control of the total generator set output.

What if the AVR fails?

If the AVR fails, then the generator will lose its excitation, and this loss will cause the voltage to fall suddenly and shut down with an under-voltage fault.

If, however, the generator doesn’t have under-voltage protection, then it may continue to run, although this may cause severe damage to it.

Why is the AVR Important?

Unregulated generators are generators that do not have an automatic voltage regulator, and they are usually unable to meet the requirements and power needs of the equipment.

This is because unregulated generators cannot control or regulate voltage, which means that the terminal voltage decreases as the load requirements increase.

When you do not control the voltage of the generator, then it will not be maintained at a constant fixed rate, and the overall performance of the generator will be negatively impacted by any equipment, machinery, or utilities that are being powered by it.

Having an automatic voltage regulator allows your generator to put out a lot more power and increases its longevity.