Editing Three-phase electric power (section)

== Alternatives to three-phase ==
; [[Split-phase electric power]]: Used when three-phase power is not available and allows double the normal utilization voltage to be supplied for high-power loads.
; [[Two-phase electric power]]: Uses two AC voltages, with a 90-electrical-degree phase shift between them. Two-phase circuits may be wired with two pairs of conductors, or two wires may be combined, requiring only three wires for the circuit. Currents in the common conductor add to 1.4 times (<math>\sqrt{2}</math> ) the current in the individual phases, so the common conductor must be larger. Two-phase and three-phase systems can be interconnected by a [[Scott-T transformer]], invented by [[Charles F. Scott (engineer)|Charles F. Scott]].<ref name="Brittain (2007)">{{cite journal |last=Brittain |first=J. E. |title=Electrical Engineering Hall of Fame: Charles F. Scott |journal=[[Proceedings of the IEEE]] |year=2007 |volume=95 |issue=4 |pages=836–839 |doi=10.1109/JPROC.2006.892488}}</ref> Very early AC machines, notably the first generators at [[Niagara Falls]], used a two-phase system, and some remnant two-phase distribution systems still exist, but three-phase systems have displaced the two-phase system for modern installations. 
; Monocyclic power: An asymmetrical modified two-phase power system used by [[General Electric]] around 1897, championed by [[Charles Proteus Steinmetz]] and [[Elihu Thomson]]. This system was devised to avoid patent infringement. In this system, a generator was wound with a full-voltage single-phase winding intended for lighting loads and with a small fraction (usually 1/4 of the line voltage) winding that produced a voltage in quadrature with the main windings. The intention was to use this "power wire" additional winding to provide starting torque for induction motors, with the main winding providing power for lighting loads. After the expiration of the Westinghouse patents on symmetrical two-phase and three-phase power distribution systems, the monocyclic system fell out of use; it was difficult to analyze and did not last long enough for satisfactory energy metering to be developed.
; High-phase-order systems: Have been built and tested for power transmission. Such transmission lines typically would use six or twelve phases. High-phase-order transmission lines allow transfer of slightly less than proportionately higher power through a given volume without the expense of a [[high-voltage direct current]] (HVDC) converter at each end of the line. However, they require correspondingly more pieces of equipment.
; DC: AC was historically used because it could be easily transformed to higher voltages for long distance transmission. However modern electronics can raise the voltage of DC with high efficiency, and DC lacks [[skin effect]] which permits transmission wires to be lighter and cheaper and so [[high-voltage direct current]] gives lower losses over long distances.