# Apparent power definition

1. What is the definition of apparent power?
2. How to calculate apparent power for three-phase circuit? Is it S = S1 + S2 + S3 or S = sqrt(P^2 + Q^2)

where

P is total active power P = P1 + P2 + P3

and

Q is total reactive power in system Q = Q1 + Q2 + Q3?

Apparent power is the vector sum of real power and reactive power. In effect it is V$_{RMS} \times I_{RMS}$ without any consideration of phase angle. Because real and reactive power are at right angles, the vector sum is: -
$\sqrt{Real^2 + Reactive^2}$