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Power and currentMetric units Unit converter

Active, reactive and apparent power from current

Power of a three-phase or single-phase load from the voltage, current and power factor — for example, from clamp meter and panel voltmeter readings.

Formula
3~: S = √3 · U · I1~: S = U · IP = S · cos φQ = S · sin φ = P · tg φ

The load is balanced, with sinusoidal current and voltage. For an unbalanced load, compute each phase and add them up. At the input of a variable frequency drive the current is distorted by harmonics: use the true power factor λ instead of cos φ, from the drive data or a power quality analyser.

Source: Circuit theory: power of a balanced three-phase circuit

Inputs

You can change a field's unit: the value is converted to the formula's units automatically.

m
U

Three-phase supply: line-to-line voltage, 380 V, 6 or 10 kV; single-phase: phase voltage, 220 V.

I
cos φ

Induction motors at rated load 0.80–0.90, lightly loaded 0.3–0.6; heaters 1.

Unit converter for this formulaVoltage · Current · Power · Apparent power · Reactive power
  • V1
  • kV0.001
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Result
P — Active power
Fill in all fields
  • S — Apparent power
    –
  • Q — Reactive power
    –
  • tg φ — Reactive power factor tan φ
    –

More in Power and current

Load and motor current from power

Operating current of a three-phase or single-phase load from its power; for a motor, from the shaft power and efficiency, with the starting current. Used to select the cable, circuit breaker and starter.

Results are engineering estimates from standard formulas; for design decisions check them against the codes, project documents and specialists' calculations. The formulas carried over from the original set are unchanged, and their errors are described in the notes.