Reactive Power & kVAR Calculator

Reactive power is the power that flows back and forth between the supply and inductive equipment such as motors, transformers and chokes to maintain their magnetic fields. It is measured in kVAR and does no useful work, but the current it adds still loads cables, switchgear and the network. The relationship with real power is kVA squared = kW squared + kVAR squared, so reactive power directly inflates the kVA your supply must deliver.

The correction required is Q = kW x (tan phi1 minus tan phi2), where phi1 and phi2 are the phase angles at your current and target power factors. This calculator does that for you: enter the load in kW, the power factor you have and the one you want. For example, a 50 kW load improving from 0.75 to 0.95 needs about 28 kVAR of capacitance, which cuts the apparent power from 66.7 kVA to 52.6 kVA.

Half-hourly metered sites have their reactive consumption recorded in kVArh alongside the kWh. Distribution network operators levy a reactive power charge, passed through on your bill, when the site's power factor falls below the threshold for the region, commonly around 0.95. The threshold and unit charge vary by network operator and contract, so read the reactive line on your own bill: if kVArh charges appear regularly, correction is usually worth pricing up.

No. Practical targets are 0.95 to 0.98. Chasing unity needs disproportionately large capacitor banks for diminishing benefit, and overshooting creates a leading power factor, which can cause voltage rise and instability, particularly at low load. Automatically switched capacitor banks that step in and out with the load hold the site near the target across the day far better than one large fixed bank sized for peak conditions.

From C = Q / (2 x pi x f x V squared), with the correction Q in volt-amps reactive, f the supply frequency and V the system voltage. On a 50 Hz, 400 V supply, 27.7 kVAR of correction works out at roughly 550 microfarads. In practice you specify commercial capacitor stages in kVAR rather than microfarads, but the microfarad figure is what links the electrical requirement to the physical components.

Only marginally. Correction reduces the current flowing through your cables and transformers, which trims resistive losses slightly, but the kWh your equipment consumes is essentially unchanged. The commercial benefits sit elsewhere: removing reactive power charges from half-hourly bills, freeing up agreed supply capacity in kVA, reducing voltage drop, and unloading switchgear and transformers. Treat it as a capacity and charges measure, not an energy efficiency measure.