What Is VAR Control?

By Saifuddin Abdullah

AC motors employ reactive power to energize their circuits.
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VAR is an abbreviation of voltage-ampere reactive, a term that is used extensively in definition and measurement of reactive power within electrical circuits. Reactive power is the average of electrical power that is originated from active components like capacitors and inductors. This type of power is only observed in AC (alternating current) electrical circuits, and the unit of VAR is used to determine its levels. VAR control is used to manage the relationship of varying current and voltage that collectively originates from active electrical components.


When an electrical device is connected with an AC source, it generates its own reactive power through interferences of attached electrical components. This happens because of radiating fields generated from the coils and capacitors of these electrical devices. Furthermore, this power sustains itself within electrical circuits during the entire operation of these devices and is seen as an energizing influence for electrical circuits. This reactive power can be controlled and managed, and for this reason it is first calculated in the units of VAR.


VAR control is only required when both current and voltage are out of phase within an electrical circuit. More specifically, both current and voltage flow in the form of waves within AC circuits, and any incoherency between their flow results in the generation of reactive power. In this regard, VAR control becomes a significant factor for devices and components that require huge amounts of power to be energized. Remember that DC (direct current) circuits do not possess reactive powers, since their current and voltage do not flow in the form of waves.


VAR control is usually carried out by calculating the amount of reactive power present within a circuit. This calculation is done by finding the products of root mean square (RMS) of both current and voltage and multiplying them with the degrees of their mutual phase difference. In this relationship, both electrical current (in amperes) and voltage (in volts) are directly proportional to the amount of reactive power within a circuit. This means that varying current, voltage, or both can result in variations within reactive power levels.


Reactive power control is normally measured in those AC applications that consume lots of electricity. These include AC motors, transformers, electricity generators, power transmission lines and power generating grids. Some of these applications require reactive power to generate an electromagnetic field around their circuits, while others simply need it to initially energize their circuits. VAR calculating and controlling mechanisms are also employed in sophisticated low-voltage applications like microprocessor- and microcontroller-based circuits.