Editing Polyphase system (section)

==Motors==
[[File:3phase-rmf-noadd-60f-airopt.gif|thumbnail|right|Three-phase electric machine with rotating magnetic fields]]

Polyphase power is particularly useful in [[Alternating current|AC]] motors, such as the [[induction motor]], where it generates a [[rotating magnetic field]]. When a three-or-more-phase supply completes one full cycle, the magnetic field of a two-poles-per-phase motor has rotated through 360° in physical space; motors with more than two poles per phase require more power supply cycles to complete one physical revolution of the magnetic field and so these motors run more slowly. Induction motors using a rotating magnetic field were independently invented by [[Galileo Ferraris]] and [[Nikola Tesla]] and developed in a three-phase form by [[Mikhail Dolivo-Dobrovolsky]] in 1889.<ref>[https://books.google.com/books?id=thOPkFjrj5MC&q=tesla Ion Boldea, Syed Abu Nasar, The Induction Machine Handbook  - CRC Press, 2002, page 2]</ref> Previously all commercial motors were DC, with expensive [[commutator (electric)|commutators]], high-maintenance brushes and characteristics unsuitable for operation on an alternating current network. Polyphase motors are simple to construct, are self-starting and have little vibration compared with single-phase motors.