Below are the two reasons why are transformers rated in KVA and not in kW:
- Transformers are rated in KVA because the losses occurring in the transformers are independent of the power factor.
- The loads that will be connected to the transformer are never known to the manufacturer at the time of transformer design. Hence it cannot be rated in kW. The load kW depends on the power factor of the load.
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 confusion regarding the type of load being connected. This is why the transformer is rated in KVA. By doing so we can eliminate the confusion regarding the type of load being connected.