Apparent Power (kVA)
The total power in an AC circuit combining real (active) and reactive power, measured in kilovolt-amperes (kVA).
Apparent power is the product of RMS voltage and RMS current in an AC circuit, measured in kilovolt-amperes (kVA). It represents the total power that must be supplied from source to load, encompassing both useful work (real power in kW) and energy stored and returned by inductive or capacitive elements (reactive power in kVAR).
The relationship: S = sqrt(P^2 + Q^2). The ratio of real power to apparent power is the power factor (PF = P/S).
In transformer specifications, apparent power is the primary rating metric because transformers must handle both active and reactive current components. The kVA rating determines physical size, cooling requirements, and thermal design regardless of load power factor.
QDTB rates all transformers by kVA capacity for proper sizing across all load types. Refer to our transformer selection guide for detailed sizing guidance.
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Related Terms
Power Factor
The ratio of real power (kW) to apparent power (kVA) indicating how effectively electrical power is utilized.
kVA Rating
The apparent power rating of a transformer in kilovolt-amperes, determining load-carrying capacity.
Winding Resistance
The DC resistance of transformer windings, measured for loss calculation and connection quality verification.
More Terms Starting with “A”
Autotransformer
A transformer with a single winding acting as both primary and secondary, providing voltage conversion through electromagnetic induction and direct electrical connection.
Arc Furnace Transformer
A heavy-duty transformer designed to supply power to electric arc furnaces used in steelmaking and metal smelting.
ANSI C57
The American National Standards Institute standard series covering power transformer requirements for the North American market.
Amorphous Alloy Transformer
A distribution transformer using amorphous metal core material achieving 60-70% lower no-load losses than conventional silicon steel cores.
More in “Electrical Fundamentals”
Eddy Current
Circulating currents induced in conductive materials by changing magnetic fields, causing energy losses in transformers.
EMF (Electromotive Force)
The voltage generated by electromagnetic induction in a transformer winding, proportional to flux change and turns.
Excitation Current
Current drawn by transformer primary when energized with no load, consisting of magnetizing and core-loss components.
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