Methods of voltage control in power system
Before learning the methods of voltage control in power system, we must first understand why do we need to control voltage. In power systems, voltage is supposed to be constant which is obviously not. So we have to control it in such a way that it remains constant. But why does the voltage need to be constant at all? Because, most of the devices, apparatus, electrical machines, consumer appliances etc. are all designed to work at a specified voltage. Wide variations of voltage may cause errors in operation, malfunctioning or performance deterioration. It is desirable that the consumers receive power at substantially constant voltage. In many countries, including India, the statutory limit of voltage variation is ±6% of the declared voltage at consumers' end.
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Therefore, it is important to apply certain techniques, certain methods to control the power system voltage to keep it constant. Following are the methods of voltage control in power system.

Methods of voltage control in power system
- Using excitation control or voltage regulators at generating stations
- By using tap changing transformers
- Using induction regulators
- By using shunt reactors
- By using shunt capacitors
- Using synchronous condensers
Excitation control or voltage regulators at generating stations
Induced emf (E) of a synchronous generator (alternator) depends on the excitation current (field current). The terminal voltage of an alternator can be given as V = E - IZ. As the load current, and hence the armature current, increases, voltage drop in the armature also increases. The field current must be increased to compensate this voltage drop, such that the terminal voltage is at the target value. For this purpose, alternators are provided with excitation control or automatic voltage regulator systems. There are two main types of automatic voltage regulators (AVR):- Tirril regulator
- Brown-Boveri regulator
Excitation control method is satisfactory only for short lines. For longer lines, the terminal voltage of alternator has to be varied widely for the voltage at far ends to remain constant. Obviously, this method is not feasible for longer lines.
By using tap changing transformers
The voltage control in transmission and distribution systems is usually obtained by using tap changing transformers. In this method, the voltage in the line is adjusted by changing the secondary EMF of the transformer by varying the number of secondary turns. Secondary voltage of a transformer is directly proportional to the number of secondary turns. Thus, the secondary voltage can be adjusted by changing the turns ratio of the transformer. Secondary number of turns can be varied with the help of tappings provided on the winding. Basically, there are two types of tap changing transformers.- off-load tap changing transformers
- on-load tap changing transformers