What unit is commonly used to rate transformers?

Transformers are commonly rated in kilovolt-amperes (kVA) because this unit takes into account both the voltage and the current the transformer can handle without taking into consideration the power factor. The power factor, which represents the efficiency with which electrical power is converted into useful work, can vary depending on the nature of the load being supplied.

Using kVA as the rating provides a more straightforward representation of a transformer's ability to handle electrical loads. It allows for a better understanding of the transformer's capacity in a generalized way, regardless of whether the load is purely resistive or has reactive components (inductive or capacitive). Since transformers typically operate with alternating current (AC), using kVA simplifies the process by avoiding the complications that arise from power factor calculations in different applications.

In contrast, watts measure real power and can vary with the load's power factor, making them less suitable for transformer ratings. Volts represent electrical potential difference and are not a measure of capacity, while amperes indicate current flow, which does not fully account for the transformer's ability to transfer electrical energy effectively. Therefore, kVA is the most appropriate and commonly used unit for rating transformers.