kVA Calculator — Apparent Power, Real Power & Power Factor

公式

How this is calculated

In an alternating current (AC) system, three distinct power quantities describe how energy flows. Real power (P, kW) is the power actually converted to useful work — heat, light, motion. Apparent power (S, kVA) is the total power supplied by the generator or transformer, the product of RMS voltage and RMS current. Reactive power (Q, kVAR) is the power that oscillates between the source and inductive/capacitive loads (motors, transformers) without performing net work.

The three form a right triangle — the power triangle — where S² = P² + Q². The power factor (PF = cos φ) is the ratio P/S, ranging from 0 (purely reactive) to 1.0 (purely resistive, perfect efficiency). A low power factor means the supply must deliver more kVA to provide the same kW of useful work, increasing cable sizes, transformer ratings, and energy costs. Utilities often penalise industrial customers with PF below 0.85–0.95.

This calculator works for balanced single-phase or three-phase equivalent circuits. For three-phase systems, multiply the single-phase kVA by 3 (for three single-phase loads) or use √3 × V_line × I_line / 1000 as the apparent power — the per-phase power factor relationship remains the same.