Three-phase electric power

Three-phase electric power is delivered by three alternating voltages or currents of the same frequency, offset from one another by 120 electrical degrees. This arrangement provides nearly constant total power and supports efficient generation, transmission, and motor operation.

Three-phase system: An electrical system using three alternating quantities separated by 120 electrical degrees. The system’s phase relationships make total power nearly constant across each cycle.
Alternating current: Electric current that periodically reverses direction, usually varying approximately sinusoidally. Each phase is an alternating quantity with a shared frequency.
Three-phase induction motor: An alternating-current motor in which a three-phase stator field induces current in the rotor. Three-phase supply produces the rotating field that makes this motor self-starting.
Single-phase electric power: Electric power delivered by one alternating voltage or current waveform. Its instantaneous power fluctuates more than balanced three-phase power.
Nikola Tesla: An inventor and electrical engineer whose work advanced alternating-current power systems and induction motors. His patents and designs helped establish practical polyphase power.
Star connection: A three-phase wiring arrangement joining one end of each phase winding at a common neutral point. It provides phase-to-neutral voltage as well as phase-to-phase voltage.
Electrical phase: The relative position of a periodic electrical quantity within its cycle, expressed as an angle or time offset. The defining 120-degree displacement is a phase difference.
Synchronous generator: A rotating electrical machine that generates alternating voltage at a frequency synchronized with rotor speed. Utility generators commonly produce three-phase power directly.
Two-phase electric power: An alternating-current system with two voltages separated by 90 electrical degrees. It is a distinct polyphase arrangement, now largely displaced by three-phase systems.
War of the Currents: The late nineteenth-century commercial and technical contest between alternating-current and direct-current electrical systems. Three-phase AC became part of the infrastructure that helped AC prevail for power distribution.

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