Introduction to Voltage Control

Electrical energy from the generating station is delivered to the ultimate consumers through a network of transmission and distribution. For satisfactory operation of motors, lamps and other loads, it is desirable that consumers are supplied with substantially constant voltage. The principal cause of voltage variation at consumer’s premises is the change in load on the supply system. When the load on the system increases, the voltage at the consumer’s terminals falls due to the increased voltage drop in (i) alternator synchronous impedance (ii) transmission line (iii) transformer impedance (iv) feeders and (v) distributors. The reverse would happen should the load on the system decrease. These voltage variations are undesirable and must be kept within the prescribed limits.

         There are several methods of voltage control. In each method, the system voltage is changed in accordance with the load to obtain a fairly constant voltage at the consumer’s end of the system. The following are the methods of voltage control in an a.c. power system:

1. Excitation control                

2. Tap changing transformers

3. Auto-transformer tap changing      

4. Booster transformers

5. Induction regulators           

6. Synchronous condenser

 

Method (1) is used at the generating station only whereas methods (2) to (5) can be used for transmission as well as primary distribution systems. However, methods (6) is reserved for the voltage control of a transmission line.