apparentpower

Apparent power is a quantity used in alternating-current (AC) electrical systems to describe the total power flow in a circuit. It is the magnitude of the complex power S, which also comprises active power and reactive power. If V and I are the RMS (root-mean-square) quantities, the complex power is S = P + jQ, where P is the active power (watts) and Q is the reactive power (volt-amperes reactive). Apparent power is defined as |S| = V_rms I_rms. In a single-phase system, this reduces to S = V_rms I_rms. In a balanced three-phase system, the apparent power is S_total = √3 V_LL I_L, or equivalently S_total = 3 V_phase I_phase, with magnitudes.

Measuring units: apparent power is expressed in volt-amperes (VA). Real power is in watts (W), reactive power in volt-ampere reactive (VAR). The relationship |S|^2 = P^2 + Q^2 holds, and the power factor is cos(phi) = P/|S|, where phi is the phase angle between voltage and current. If phi is positive (inductive load), Q is positive; if negative (capacitive load), Q is negative.

Practical significance: apparent power sets the sizing requirements for equipment such as generators, transformers, and conductors, since these devices must be able to carry the combined effect of P and Q. It does not by itself represent energy actually transferred over time; energy delivered per unit time is the active power P, while Q relates to energy that alternates between the source and the reactive fields.