Application of the Automatic Voltage Regulator

The main functions of an AVR are as follows.

1. It controls the voltage of the system and has the operation of the machine nearer to the steady-state stability.
2. It divides the reactive load between the alternators operating in parallel.
3. The automatic voltage regulators reduce the overvoltages which occur because of the sudden loss of load on the system.
4. It increases the excitation of the system under fault conditions so that the maximum synchronizing power exists at the time of clearance of the fault.

When there is a sudden change in load in the alternator, there should be a change in the excitation system to provide the same voltage under the new load condition. This can be done with the help of the automatic voltage regulator. The automatic voltage regulator equipment operates in the exciter field and changes the exciter output voltage and the field current. During the violent fluctuation, the ARV does not give a quick response.

For getting a quick response, the quick-acting voltage regulators based on the overshooting the mark principle are used. In the overshoot mark principle, when the load increase the excitation of the system also increases. Before the voltage increase to the value corresponding to the increased excitation, the regulator reduces the excitation of the proper value.