Move between power, current and power factor in a three-phase system. Enter the line current or the real power and get kW, kVA, kVAr and line current.
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Start free trialReal power in a balanced three-phase system is P = √3 × line voltage × line current × power factor. That single relationship links current and power.
Apparent power (kVA) is √3 × V × I; real power (kW) is that times the power factor. The difference is reactive power (kVAr), which does no useful work.
Knowing the current gives you the power; knowing the power gives you the current the supply and cable must carry. Both matter for sizing.
For a balanced load, real power P = √3 × V(line) × I(line) × power factor. With a 400 V supply drawing 20 A at 0.9 power factor, that’s about 12.5 kVA apparent and 11.2 kW real. Apparent power in kVA drops the power-factor term.
kVA (apparent power) is the total power the supply delivers; kW (real power) is the portion doing useful work. Their ratio is the power factor. Cables, switchgear and supply capacity are sized on kVA and current, while energy use and motor output relate to kW.
A standard Australian three-phase supply is 400 V line-to-line (between any two phases) and 230 V line-to-neutral (each phase to neutral). The √3 relationship connects the two: 400 ≈ √3 × 230.
A low power factor means more current is drawn for the same real power, increasing losses and the load on cables and supply — and it can attract network charges for larger installations. Correcting power factor reduces current and can free up capacity.
This calculator assumes a balanced three-phase load and is a general engineering aid, not a substitute for design to AS/NZS 3000. Real installations have imbalance and other factors. Electrical work must be designed and verified by a licensed electrician.
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