What Is the Difference Between kVA and kW on a Transformer?
Quick answer — A transformer is rated in kVA (apparent power) — the product of voltage and current — because it supplies both real and reactive power. kW is real power (the work done), equal to kVA times the power factor. A transformer is not rated in kW because its current (and thus heating) is set by the apparent power, regardless of the load power factor.
What is the difference between kVA and kW?
kVA (apparent power)
It is V x I, the total power the transformer can deliver at the rated voltage and current, and what sets the conductor and core size and heating.
kW (real power)
It is the power actually used, equal to kVA x power factor. A low power factor load draws more current for the same real power, so it heats the transformer more.
Why it matters
Since the transformer heating is set by the current (apparent power), it is rated in kVA/kW... i.e. in kVA, not kW. Exceeding the kVA over-heats the unit regardless of the power factor.
References & standards
- IEC 60076-1
- IEEE C57.12.00
Related
Related manufacturers
Prolec GE (GE Vernova) · Prolec GE Waukesha · Hitachi Energy USA · Siemens Energy · Eaton · Virginia Transformer Corp
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Technical content is prepared from engineering references, standards frameworks, manufacturer documentation and industry sources. Contractual or compliance decisions should refer to current official standards. TransformerPath Technical Editorial.
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