= Reactive volt-ampere
{title2=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.<The International System of Units (SI), ninth edition, SI Brochure>[NIST SP330 parallel text, §2.3.4, paragraph identifying the IEC var]{ref}
In sinusoidal steady operation with RMS magnitudes $V,I$ and relative phase $\varphi$,
$$
Q=VI\sin\varphi.
$$
Thus100V RMS,2A RMS and a lagging phase with $\sin\varphi=0.6$ 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,
$$
Q=\omega LI_{\rm rms}^2=2\omega\langle w\rangle.
$$
For an original200var example at50Hz, mean stored energy is $200/[2(2\pi50)]\approx0.3183\,\mathrm J$ 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.<AC Power Flow in Linear Networks by James L. Kirtley Jr.>[Energy and Power, equations52–55 and71]{ref}
In a sinusoidal100V example with $S=400+j300\,\mathrm{VA}$, the reactive component is300var, the active component400W and <apparent power>500VA. Adding400 and300 as ordinary scalar powers would not give the500VA magnitude. <Complex electrical power> retains the phase relation needed for this combination.
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