Reactive Power & kVAR Calculator

Reactive power in kVAR is the energy that shuttles back and forth between the supply and the magnetising elements in motors, transformers and lighting ballasts. It does no useful work but it loads the network, which is why the DNO meters it and why most I&C supply contracts include a reactive demand charge above a 0.95 power factor threshold. Sizing reactive power accurately is the prerequisite for any conversation about power factor correction, capacitor bank investment or contract renegotiation.

For an industrial site with a meaningful inductive load (large motors, induction furnaces, welding plant, older fluorescent lighting), the kVAR number is what dimensions the correction. A 750 kW load at 0.80 power factor carries around 560 kVAR of reactive demand. Compensating to 0.96 requires about 350 kVAR of capacitance, which translates directly into a capacitor bank specification, a switchgear arrangement and a price. The calculation is what makes the supplier quotes comparable on like-for-like terms.

For a head of finance reviewing recurring non-commodity charges, the reactive power calculation also tells you which sites in a portfolio are worth investigating first. A multi-site estate will typically show one or two sites carrying most of the reactive demand spend, usually those with the oldest plant or the most variable load profile. Targeting those first concentrates capex where the payback is fastest, and it sets a precedent across the estate that the energy bill is line-by-line auditable rather than a single number to be argued about.