is an abbreviation for volt-amperes
, a measurement of the apparent power
in an alternating current
The apparent power S is the magnitude of the vector sum of the real power P and reactive power Q flowing through the system, i.e. S = (P2 + Q2)1/2. This is also expressed as the product of the RMS voltage V and RMS current I going into the system.
Most AC devices such as transformers and switchgear are rated in VA, as the real power used by the system may not be the same as the apparent power (due to any inductive and capacitive reactance in the system). For a more in-depth discussion on this see the discussion on power factor.