How is a transformer rated for power output?

A transformer is rated for power output in kilovolts-amperes (KVA) because this unit reflects the apparent power in an electrical system. Unlike watts (W) or kilowatts (kW), which measure real power, KVA encompasses both the voltage and the current flowing through the transformer, without factoring in the power factor. This distinction is crucial because transformers are designed to handle a certain amount of voltage and current, regardless of whether that power is being converted into useful work or not.

KVA is essential for sizing transformers, as it indicates their capacity to handle loads and helps ensure that the transformer can deliver sufficient power under various operating conditions. By using KVA, electrical engineers can anticipate the transformer's performance in supplying power to different types of loads—resistive, inductive, or capacitive—which might not always operate at a unity power factor. This makes KVA a more comprehensive and practical rating for transformers than watts or kilowatts, which provide a narrower focus on usable power output based on specific conditions.