Automatic voltage regulators

The automatic voltage regulator is used to
regulate the voltage. It takes the fluctuate
voltage and changes them into a constant
 voltage. The fluctuation in the voltage mainly
occurs due to the variation in load on the
supply system. The variation in voltage
damages the equipment of the power system.
The variation in the voltage can be controlled
by installing the voltage control equipment at
several places likes near the transformers, 
generator, feeders, etc., The voltage regulator is provided in more than one point in the power system for controlling the voltage variations.

Working Principle of Voltage Regulator

It works on the principle of detection of errors. The output voltage of an AC generator obtained through a potential transformer and then it is rectified, filtered and compared with a reference. The difference between the actual voltage and the reference voltage is known as the error voltage. This error voltage is amplified by an amplifier and then supplied to the main exciter or pilot exciter.

Thus, the amplified error signals control the excitation of the main or pilot exciter through a buck or a boost action (i.e. controls the fluctuation of the voltage). Exciter output control leads to the controls of the main alternator terminal voltage.

Application of the Automatic Voltage Regulator

The main functions of an AVR are as follows:
 

It controls the voltage of the system and has the operation of the machine nearer to the steady state stability.

It divides the reactive load between the alternators operating in parallel.

The automatic voltage regulators reduce the overvoltages which occur because of the sudden loss of load on the system.

It increases the excitation of the system under fault conditions so that the maximum synchronising power exists at the time of clearance of the fault.