Reactive volt-ampere (var)

The reactive volt-ampere, conventionally called the var and written with symbolvar, expresses reactive power. The official SI text notes the IEC's special name and states that its coherent unit is identical to the volt ampere. The name identifies the reactive quantity; it is not a different base-unit dimension.^[ref]

In sinusoidal steady operation with RMS magnitudes $V,I$ and relative phase $\phi$,Thus100V RMS,2A RMS and a lagging phase with $\sin \phi =0.6$ give120var. Under the same passive and phasor conventions, a leading phase of equal magnitude gives−120var. The signed value describes exchange phase rather than negative dissipated heating. The prefix relation is $1\mathrm{kvar}=1000\mathrm{var}$.

A reactive-power value is also not an amount of stored energy in joules. For an ideal inductor in sinusoidal steady operation,For an original200var example at50Hz, mean stored energy is $200/[2(2\pi 50)]\approx 0.3183\mathrm{J}$ and peak stored energy is twice that. The average absorbed active power is nevertheless zero in the ideal inductor. The primary circuit treatment derives this separation between energy storage and mean dissipation.^[ref]

In a sinusoidal100V example with $S=400+j300\mathrm{VA}$, the reactive component is300var, the active component400W and apparent power500VA. Adding400 and300 as ordinary scalar powers would not give the500VA magnitude. Complex electrical power retains the phase relation needed for this combination.