VA

VA stands for volt-ampere, the unit of apparent power in alternating current circuits. It is the product of voltage and current measured in RMS (root mean square) values, regardless of phase angle between them. In direct current, watts and volt-amperes are identical; in AC systems, they diverge because current and voltage may not peak at the same moment. The difference between apparent power (VA) and real power (watts) is crucial for sizing generators, transformers, and circuit protection.

Real power, measured in watts (W), is what actually does work: heating, lighting, mechanical rotation. Reactive power, measured in volt-amperes reactive (VAR), is the power that sloshes back and forth between the power supply and inductive or capacitive loads without performing useful work. Apparent power in VA is the vector sum of these two components. A load with a power factor of 1.0 draws equal watts and VA; a load with a power factor of 0.8 draws 0.8 watts for every volt-ampere of apparent power.

Industrial applications and sizing

Utilities and industrial facilities must account for VA when specifying electrical infrastructure. A transformer rated for 100 kVA can deliver 80 kW to a facility with a 0.8 power factor, but only 100 kW at unity power factor. Undersizing based on watts alone causes overheating and shortened equipment life. Motor loads, arc welders, and magnetic ballasts all create reactive demand that inflates VA requirements relative to actual work performed.

Power factor correction, usually through capacitor banks, reduces reactive power and improves the VA-to-watts ratio. Industrial customers are often charged for poor power factor through demand penalties or reactive power surcharges. Improving power factor from 0.7 to 0.95 can reduce VA demand by roughly 30 percent, lowering transformer losses and improving voltage stability across the site.

The term volt-ampere exists precisely because it is not a watt. Using VA signals to engineers and electricians that phase relationships matter and that real power consumption may differ significantly from the apparent load. This distinction is absent in DC systems and fundamental in any AC installation larger than a household circuit.