What is Automatic Voltage Regulator?

05/22/2025

An automatic voltage regulator is employed to regulate voltage, converting fluctuating voltages into a constant one. Voltage fluctuations mainly stem from variations in the load on the supply system. Such voltage variations can damage the equipment within the power system. These fluctuations can be mitigated by installing voltage - control equipment at various locations, such as near transformers, generators, and feeders. Multiple voltage regulators are often placed throughout the power system to manage voltage variations effectively.

In a DC supply system, for feeders of equal length, over - compound generators can be used to control voltage. However, for feeders of different lengths, feeder boosters are utilized to maintain a constant voltage at the end of each feeder. In an AC system, various methods, including booster transformers, induction regulators, and shunt condensers, can be employed to control voltage.

Working Principle of Voltage Regulator

It operates based on the principle of error detection. The output voltage of an AC generator is obtained via a potential transformer, then rectified, filtered, and compared with a reference voltage. The difference between the actual voltage and the reference voltage is called the error voltage. This error voltage is amplified by an amplifier and subsequently supplied to the main exciter or pilot exciter.

Consequently, the amplified error signals regulate the excitation of the main or pilot exciter through a buck or boost action (i.e., they manage voltage fluctuations). Controlling the exciter output in turn regulates the terminal voltage of the main alternator.

Application of the Automatic Voltage Regulator

The key functions of an Automatic Voltage Regulator (AVR) are as follows:
It regulates the system voltage and helps keep the machine's operation closer to steady - state stability.
It distributes the reactive load among parallel - operating alternators.
AVRs mitigate overvoltages that result from sudden load loss in the system.
Under fault conditions, it increases the system's excitation to ensure maximum synchronizing power when the fault is cleared.
When there is a sudden load change in the alternator, the excitation system needs to adjust to maintain the same voltage under the new load conditions. The AVR enables this adjustment. The AVR equipment acts on the exciter field, altering the exciter output voltage and field current. However, during severe voltage fluctuations, the AVR may not respond rapidly.

To achieve a quicker response, fast - acting voltage regulators based on the overshooting - the - mark principle are utilized. In this principle, when the load increases, the system's excitation also increases. But before the voltage rises to the level corresponding to the increased excitation, the regulator reduces the excitation to an appropriate value.