A power transformer is usually rated in

The correct answer is: D. kVA

A power transformer is usually rated in kVA (kilovolt-amperes). This is because the transformer’s power rating is determined by its ability to transfer both real power (kW) and reactive power (kVAR). The kVA rating is the square root of the sum of the squares of the kW and kVAR ratings.

• kW is the real power, which is the power that is actually used to do work.
• kVAR is the reactive power, which is the power that is used to create a magnetic field.

The kVA rating is important because it determines the transformer’s size and cost. A transformer with a higher kVA rating can transfer more power, but it will also be larger and more expensive.

The other options are incorrect because they do not represent the power rating of a transformer.

• Option A, kW, is the real power rating.
• Option B, kVAR, is the reactive power rating.
• Option C, kWh, is the energy rating. Energy is the product of power and time.