threephase

Three-phase refers to a method of generating, transmitting, and distributing electrical power using three alternating currents, each separated in phase by 120 degrees. In a balanced three-phase system, the three sinusoidal voltages of equal amplitude create a rotating magnetic field that is smooth and continuous, which is advantageous for electric machines and power delivery.

Generators typically have three windings spaced 120 degrees apart on the stator. The system can be wired in either a wye (Y) configuration, which presents a neutral wire and line-to-neutral voltages, or a delta (Δ) configuration, which provides line-to-line voltages without a neutral. In a wye system, V_LL = √3 × V_Ph, where V_Ph is the phase (line-to-neutral) voltage.

Electrical power in a balanced three-phase circuit is P = √3 × V_LL × I_L × cos φ, or equivalently P = 3 × V_Ph × I_Ph × cos φ. Three-phase systems allow delivering more power with less conductor material compared to single-phase at the same voltage, and enable smooth torque in motors.

Three-phase power is standard for generation stations, long-distance transmission using high voltage lines, and distribution to factories and buildings. Large industrial motors, compressors, and processing equipment commonly run on three-phase power because of improved efficiency and performance.

Unbalanced loads or phase loss can create issues such as neutral currents in wye systems and degraded power quality. The development of three-phase systems in the late 19th century significantly influenced modern electric power distribution and is widely used worldwide.