KVA stands for kilo-volt-ampere, which basically is the unit of electric power. While calculating kVA of any piece of equipment the power factor is not taken into account. (i.e.) Power in kVA = Voltage x Current.

This means kVA is the unit of measurement for that equipment in which the output power is independent of power factor. For example Rating of Alternators, Transformers, and UPS etc. On the other hand, KW (KiloWatts) is also the unit of electric power for that equipment in which power factor plays a role. Normally machines that produce a mechanical output is rated in kilowatts. For example the rating of electric motors. Read More about power factor.

Power Transformer Transformers are an energy transfer device that transfers power from the primary side to the secondary side without altering the energy level (considering zero power loss). Iron loss and copper loss occurring in the transformer are also independent of the power factor. Moreover, the output power factor of the transformer purely depends on the connected load. The transformer does not alter the power factor of its output power. Transformers are rated in kVA because the losses occurring in the transformers are independent of power factor.

KVA is the unit of apparent power. It is a combination of real power and reactive power. Transformers are manufactured without considering the load being connected. So any kind of electrical load can be connected to it (either resistive, capacitive, inductive or combination loads). If the transformer is rated in KW, there may be confusions regarding the type of load being connected. This is why the transformer is rated in KVA. By doing so we can eliminate the confusions regarding the type of load being connected.