Apparent power (kVA)
The rated power (S = U·I) that sizes the transformer.
Definition
Apparent power, denoted S and expressed in volt-amperes (VA) or kilovolt-amperes (kVA), is the product of voltage and current: S = U × I for single-phase, S = U × I × √3 for three-phase. It is the reference quantity for sizing a transformer.
Unlike active power (in watts), apparent power accounts for the entire current the transformer must supply, including the reactive part. It therefore determines the conductor cross-section, the core size and the heating — in other words, the physical “build” of the unit.
A transformer is always specified in kVA, never in kW, because it must be able to supply loads of varying power factor.
The ABL tip
Size in kVA with a margin: a strongly inductive or harmonic-rich load stresses the transformer more than its active power alone. ABL Transfo calculates the apparent power actually required from your load schedule.
