Three-Phase Power Calculator (kW/kVA)

Three-phase power packs three sine waves 120 degrees apart, delivering constant power to motors and transformers. Active power P = root3 x VL x IL x cos phi; apparent S = root3 x VL x IL; reactive Q = root3 x VL x IL x sin phi. Example: a 400 V motor drawing 22 A at PF 0.85 produces P = 1.732 x 400 x 22 x 0.85 = 12.96 kW, S = 15.24 kVA, Q = 8 kVAR - data that sizes the feeder, breaker, and correction caps at once. Transformer sizing follows directly: a 75 kVA transformer at 400 V carries 108 A per line, so a 100 A feeder is undersized - the power result feeds straight into equipment selection.

1. 1

   Enter line voltage

   E.g. 400 V line-to-line.

2. 2

   Enter line current

   Measured or nameplate amps.

3. 3

   Enter power factor

   cos phi of the load.

• Using 230 V (phase) instead of 400 V (line) and undershooting by root3

• Leaving efficiency out of motor current calculations

• Forgetting the 0.866 factor when converting between star and delta phase values