Contrary to popular believe, kW is not whats you get when you multiply Volts x Amps, kVA is!
kVA stands for kilovoltamperes as you probably suspected. For DC circuits and purely resistive circuits, Watts = VA.
The fun part comes in when you deal with AC circuits and power factor. The power factor directly relates VA to Watts; An 800 Watt circuit with a pf of 0.8 will be drawing 1000VA.
Watts = VA * PF
Watts = Amps^2 * Ohms
Watts = Volts^2 / Ohms
To try to explain PF gets a bit into calculus and geometry, but the simple explanation is that in circuits that contain capacitors and inductors, the peak current draw is NOT occuring the same time as the peak voltage. So, if the peak current of 20A occurs when the voltage is 96V and drops to 16A when the current is 120V (PF=0.8), you may be supplying 120x20=2400VA, but you're actually only supplying 1920 Watts. If this circuit was inductive, adding capacitors would help counteract the inductance and move the power factor closer to PF=1.0, which is more efficient.
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For most practical purposes, the VA and Watts are pretty close. But if you have to make any calculations for ampacity or OCP, it's important to know that the VA are going to be larger than the Watts and use PF in your calculations.
[This message has been edited by SteveFehr (edited 11-22-2006).]
