Installing power factor correction

Energy efficiency · Industrial practice · Updated 2026-06-01

Power factor correction adds capacitors (or active equipment) to a plant's electrical supply to offset the reactive power drawn by motors and transformers, bringing the power factor close to unity. It reduces the current the site draws for the same useful work, cutting losses, freeing supply capacity and avoiding utility reactive-power charges.

What it is

Inductive loads like motors and transformers draw reactive power that does no useful work but still flows as current through cables and transformers. Power factor is the ratio of useful to total power. Correction installs capacitor banks that supply the reactive power locally, so it no longer has to be drawn all the way from the supply, raising the power factor and lowering the current for the same load.

Why it is done

A low power factor means extra current flowing for no productive output, which heats cables and transformers, eats into available supply capacity and, in many tariffs, attracts a financial penalty. Correcting it cuts those resistive losses, releases capacity that would otherwise force a supply upgrade, and removes the reactive-power charge — usually at modest cost.

How it is done

The site load and its power factor are measured over a representative period, including how the reactive demand varies. A capacitor bank is sized to the reactive load, with switched or automatically stepped stages where the load changes, and located to correct as close to the inductive loads as practical. Harmonic conditions are checked, since capacitors can resonate with harmonics, and detuning reactors added if needed. The corrected power factor is then verified against the target.

1. Measure load & power factor
2. Size capacitor bank
3. Stage for varying load
4. Check harmonics
5. Add detuning if needed
6. Verify corrected factor

What to watch for

Fixed capacitors on a varying load can over-correct at light load, raising voltage and tripping protection — staged or automatic banks are needed where load swings. Installing capacitors in a harmonic-rich network without detuning reactors risks resonance that damages the capacitors and the supply.

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Power Factor · Specific Energy Consumption (SEC) · Demand Response

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