Three-Phase Power Calculator

Three-phase AC was pioneered independently by Nikola Tesla, Galileo Ferraris, and Mikhail Dolivo-Dobrovolsky in the late 1880s. Tesla patented his polyphase induction motor in 1888; Dolivo-Dobrovolsky, working for AEG in Germany, built the first practical three-phase system and, in 1891, demonstrated long-distance transmission from Lauffen to Frankfurt — 175 km over three-phase lines at 15 kV — cementing the technology's viability at scale.

The key insight is that three sinusoidal voltages offset by 120° sum to zero at every instant, so a balanced three-phase load consumes constant power rather than the pulsing 120 Hz power of a single-phase load. That constant-power property is what makes three-phase motors self-starting, smoother, and more efficient than single-phase equivalents — and why virtually every industrial motor above a few horsepower is three-phase.

Two winding topologies dominate: wye (star) connects one end of each winding to a common neutral, with phase voltage = V_LL / √3; delta connects the windings end-to-end in a triangle, with phase current = I_L / √3. The √3 factor is just the geometry of adding vectors 120° apart. Its practical gift to engineers: the total-power formula P = √3 × V_LL × I_L × PF works for both topologies, as long as you plug in line measurements.

Enter line-to-line voltage (e.g. 208V, 400V, 480V), line current from a motor nameplate or clamp meter, and the load's power factor. The calculator returns total three-phase real power (kW), apparent power (kVA), reactive power (kVAR), and per-phase real power. The visualization plots the three phase voltages offset by 120° so you can see why instantaneous total power is constant.

Balanced-load assumption applies — for grossly unbalanced systems (a large single-phase load on one leg), you need per-phase voltmeter and ammeter readings and should sum real power across phases individually. Everything runs client-side; no nameplate data leaves your browser.