Why is transformer rated in kVA and not in kW?

The power rating of a transformer or any electric machines indicates the maximum value of voltage and current it can carry without over-heating.

Power = Voltage(V) × Current(A) × Power factor

As transformer is considered as a power source while the induction motor is considered as a load.
Manufacturers of Transformers cannot predict the power factor because power factor depends upon the load connected and load may be resistive, capacitive, and inductive.
Since transformer does not depend on power factor, therefore power factor is not considered while designing a transformer.

Power = Voltage(V) × Current(A)

Also, there are two major losses in transformer

1. Copper losses
2. Iron losses or Core losses

Copper losses depend on the current passing through transformer winding while iron losses or core losses depends on the voltage. Both losses are independent of power factor, so transformers are designed for rated voltage and rated current.

That’s why the transformer is rated in in kVA, not in kW.

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