Why transformer Ratings are in KVA?

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 All electrical devices are rated based on the maximum power it can consumes, generates or transfer. Transformers are rated in kVA or VA .

Transformers are an energy transfer device that transfers power from the primary side to the secondary side without changing frequency.

Why transformers are rated in kVA and why not it is rated in kW like heater, motor and other electrical equipments?

1- Copper loss in transformer depends on the current and the iron loss depends upon the voltage of the transformer. Total losses in a transformer depend upon volt-ampere (VA) only and not on the power factor of the load.This is the reason transformer is rated in KVA and not in KW

2- Transformers are manufactured without considering the load being connected. So any kind of electrical load can be connected it may be resistive, capacitive, inductive or combination loads. If the transformer is rated in KW, there may be confusions regarding the type of load being connected. That is why the transformer rating is given in kVA and not in kW.

3-The temperature rise of a transformer is directly proportional to the apparent power (kVA) which flows through it. This is also a principle factor behind that the rating of the transformer is given in kVA and not in kW.

In actual practice, Electrical devices which act as the load like Motors, always rated in kW and draw the current from the source according to their power factor while electrical devices which act as the source like alternator, transformer, always rated in kVA to make their operation independent of the load power factor.

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