When the load on the supply system changes, the voltage control at the consumer’s terminals also changes. The variations of voltage at the consumer’s terminals are undesirable and must be kept within prescribed limits for the following reasons
- In case of lighting load, the lamp characteristics are very sensitive to changes of voltage. For instance, if the supply voltage to an incandescent lamp decrease by 6 % of rated value, then illuminating power may decrease by 20 %. On the other hand, if the supply voltage is 6 % above the rated value, the life of the lamp may be reduced by 50 % due to rapid deterioration of the filament.
- In case of power load consisting of induction motors, the voltage variations may cause erratic operation. If the supply voltage is above the normal, the motor may operate with a saturated magnetic circuit, with consequent large magnetizing current, heating and low power factor. On the other hand, if the voltage is too low, it will reduce the starting torque of the motor considerably.
- Too wide variations of the cause excessive heating of distribution transformer. This may reduced their ratings to a considerable extent.
- It is clear from the above discussion that voltage variations in a power system must be kept to minimum level in order to deliver good service to the consumers. With the trend towards larger interconnected system, it has become necessary to employ appropriate methods of voltage control.
