Volt-ampere reactive

In electric power transmission and distribution, volt-ampere reactive (var) is a unit by which reactive power is expressed in an AC electric power system. Reactive power exists in an AC circuit when the current and voltage are not in phase. The correct symbol is var and not Var, VAr, or VAR, but all three terms are widely used, and VAR is widely used throughout the power industry infrastructure. The term var was proposed by the Romanian electrical engineer Constantin Budeanu and introduced in 1930 by the IEC in , which has adopted it as the unit for reactive power.

Special instruments called varmeters are available to measure the reactive power in a circuit.

Vars may be considered as either the imaginary part of apparent power, or the power flowing into a reactive load, where voltage and current are specified in volts and amperes. The two definitions are equivalent.

The unit "var" does not follow the recommended practice of the International System of Units, because the quantity the unit var represents is power, and SI practice is not to include information about the type of power being measured in the unit name.

A sinusoidally alternating voltage applied to a purely resistive load results in an alternating current that is fully in phase with the voltage. However, in many applications it is common for there to be a reactive component to the system, that is, the system possesses capacitance, inductance, or both. These electrical properties cause the current to change phase with respect to the voltage: capacitance tending the current to lead the voltage in phase, and inductance to lag it.

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