Which unit is used to express the apparent power of a transformer?

• A. kVA
• B. kW
• C. MW
• D. kVAR

Answer: (A)

Apparent power is the product of voltage and current, measured in volt-amperes (VA). This quantity represents how much power a transformer can handle regardless of the current’s phase angle, which is why transformers are rated by apparent power. The kilovolt-ampere (kVA) unit is used because it expresses this capacity without tying it to a specific power factor.

Real power, in watts (W) or kilowatts (kW), depends on the power factor and is the portion of the apparent power that does useful work. Reactive power, in VARs or kilovars (kVAR), accounts for energy stored in and released by the magnetic field but does not perform real work. Large ratings are sometimes given in MVA (megavolt-amperes), but the concept remains the same: apparent power is the V × I product, expressed in kVA for transformers.