三相電力計算機

How to use this calculator

1. Choose what you know: voltage & current or voltage & power (kW).
2. Enter the line-to-line voltage (e.g. 400 V) — the voltage measured between any two phases.
3. Enter the line current in amps, or the real power in kW.
4. Enter the power factor (0–1): about 0.9 for motors at full load, 1.0 for purely resistive loads.
5. Read the current, real power (kW), apparent power (kVA) and reactive power (kVAR).

Three-phase power formulas

For a balanced three-phase load using the line-to-line voltage V_L:

The same line-quantity formula works for both star (wye) and delta connections, because √3 already accounts for the phase-to-line relationship. Using phase quantities instead: P = 3 × V_phase × I_phase × PF.

Symbols and units

Quick reference: amps to kW at 400 V (three-phase)

How many kW a balanced three-phase load draws at 400 V:

For 415 V multiply by 1.04; for 380 V multiply by 0.95.

常見問題

What is the difference between kW and kVA?

kW is real power (the part that does useful work); kVA is apparent power (the total the supply must deliver). They are linked by the power factor: kW = kVA × PF, and are equal only when PF = 1.

How many kW is 100 A at 400 V three-phase?

At PF 1.0 it is √3 × 400 × 100 ÷ 1000 ≈ 69.3 kW; at PF 0.8 it is about 55.4 kW.

What power factor should I use?

About 0.85–0.9 for induction motors at full load, lower for lightly loaded motors, and 1.0 for purely resistive loads such as heaters.

Do I use line or phase voltage?

Use the line-to-line voltage (e.g. 400 V) with the √3 formulas above. The √3 factor already converts between phase and line values for a balanced load.