kVA

Kilovolt-ampere (kVA) is the unit of apparent power in electrical systems. It represents the product of voltage and current without regard to the phase angle between them. Apparent power differs from real power, measured in kilowatts (kW), which represents the work actually performed, and from reactive power, measured in kilovolt-ampere reactive (kVAR), which relates to energy stored in electric and magnetic fields.

For calculations, apparent power S is given by S = V × I for a single-phase circuit, and S = √3 × VLL × IL for a balanced three-phase circuit, where VLL is the line-to-line voltage and IL is the line current. In kilovolt-amperes, S (kVA) = V × I / 1000 (single-phase) or S (kVA) = √3 × VLL × IL / 1000 (three-phase). Real power P (kW) and reactive power Q (kVAR) relate to S by P = S × pf and Q = S × sinφ, with pf (power factor) = cosφ. Equivalently, P = PkW = S × pf, and Q = √(S^2 − P^2).

kVA is commonly used to rate and specify electrical equipment such as transformers, generators, uninterruptible power supplies (UPS), and motors, reflecting the maximum load they can handle in apparent power terms. It is important to note that kVA does not measure energy consumption; energy is measured in kilowatt-hours (kWh) or similar.

Example: a 100 kVA transformer delivering a load at pf = 0.8 can supply about 80 kW of real power, with about 60 kVAR of reactive power (Q = √(100^2 − 80^2)). Understanding kVA helps in selecting equipment that matches the expected voltage, current, and power factor in a facility.