Perphase

Perphase, typically written as per-phase, is a term used in electrical engineering to describe quantities that are measured or specified for each individual phase of a polyphase system, most often a three-phase system. It distinguishes per-phase values from line or total values used to describe the system as a whole.

In practice, engineers refer to per-phase quantities such as per-phase voltage (Vph), per-phase current (Iph), and per-phase power (Pph). For a balanced three-phase load, the total power is Ptotal = 3 × Pph. Per-phase quantities are especially useful when analyzing unbalanced conditions, where each phase can have different voltages, currents, or impedances.

The relationship between per-phase quantities and line quantities depends on the system’s connection. In a star (wye) connection, the line voltage is related to the phase voltage by Vline = √3 × Vph, and the line current equals the phase current. In a delta connection, the line current is √3 times the phase current, while the line voltage equals the phase voltage. These relationships illustrate why per-phase analysis is relevant for design, fault analysis, and component sizing.

Perphase analysis is commonly used in electrical distribution, motor control, transformer design, and protective relaying to diagnose imbalances, optimize performance, and ensure safe operation. The term is a descriptive convention rather than a distinct physical concept, and it is widely encountered in technical documentation, calculations, and specifications.