Reactive Power Converter

How to convert reactive power units

Enter a reactive power figure, pick the unit it is in, and pick the unit you want. VAR, kVAR and MVAR update together, which spans a capacitor bank in a factory and a compensation bank on a transmission line.

The volt-ampere reactive is the internal base and the ladder is exact powers of 1,000. Converting Q into P or S is trigonometry on the power triangle, not a unit conversion, so it stays out of this page.

• Work out the kVAR figure from the power triangle if you only have kW and power factor.
• Type it into the Value box, for example 42.13.
• Pick the From unit, for example Kilovolt-ampere reactive (kVAR).
• Pick the To unit, for example Volt-ampere reactive (VAR).
• Read the result and keep the sign convention (inductive positive, capacitive negative) in your own notes.

kW, kVA, and kVAR: three units, one triangle

AC power splits into three quantities that share a right triangle. Real power P, in kilowatts, is the part that does work. Apparent power S, in kilovolt-amperes, is the product of RMS voltage and RMS current and sets the size of the cable, the transformer, and the generator. Reactive power Q, in kilovolt-amperes reactive, is the leg that closes the triangle: S squared equals P squared plus Q squared, and power factor is P divided by S.

The three units exist so that the three quantities cannot be mixed up in a document. A watt, a volt-ampere, and a volt-ampere reactive all have the same dimensions, and a careless conversion between them will go through arithmetically while being physically wrong. That is why each has its own converter on this site: this page handles VAR, the Apparent Power Converter handles VA, and the Power Converter handles watts.

• P (kW): real power, the part billed as energy.
• S (kVA): apparent power, what the equipment must be rated for.
• Q (kVAR): reactive power, what capacitor banks are sized in.

Where kVAR figures actually come from

Almost nobody measures reactive power directly. It arrives either from a meter that reports it alongside kW, or from a calculation: Q equals P times the tangent of the phase angle, where the angle is the arccosine of the power factor. Sizing a correction bank is the difference of two such figures, Q equals P times (tan of the current angle minus tan of the target angle).

That calculation needs two inputs this page does not have, real power and power factor, so it is left to you. Once you have a number in kVAR, the converter does the part that is genuinely a unit problem: moving between the VAR a small filter is rated in, the kVAR a factory bank is specified in, and the MVAR a transmission operator dispatches.