Two phase
From Biocrawler, the free encyclopedia.
Two-phase electrical power was used in some early 20th century factories and the distribution systems that served them. It utilized two phases, 90° apart, and was usually supplied using four wires, two for each phase. Less frequently, three wires were used, with a common wire with a larger-diameter conductor.
Induction motors designed for two-phase operation use the same winding configuration as capacitor start single-phase motors.
Three-phase electric power provides smoother operation and requires smaller conductors for the same voltage and overall amount of power. It has all but replaced two-phase power.
Two-phase power can be derived from a three-phase source using two transformers in a Scott connection. One transformer primary is connected across two phases of the supply. The second transformer is connected to a center-tap of the first transformer, and is wound for 86.6% of the phase-to-phase voltage on the 3-phase system. The secondaries of the transformers will have two phases 90 degrees apart in time, and a balanced two-phas e load will be evenly balanced over the three supply phases.
Three-wire, 120/240 volt single phase power used in the USA is sometimes incorrectly called "two-phase". The proper term is 3-wire single phase.
