Editing Three-phase electric power (section)

== History ==
[[Polyphase power system]]s were independently invented by [[Galileo Ferraris]], [[Mikhail Dolivo-Dobrovolsky]], [[Jonas Wenström]], [[John Hopkinson]], [[William Stanley Jr.]], and [[Nikola Tesla]] in the late 1880s.<ref>{{cite web |title=AC Power History and Timeline |url=https://edisontechcenter.org/AC-PowerHistory.html |website=Edison Tech Center |access-date=January 24, 2022}}</ref>

[[File:Galileo Ferraris Alternating Current Motor.jpg|thumb| The [[Ferraris' motor|first AC motor]] developed by Italian physicist Galileo Ferraris. This was a two-phase motor and required four wires.]]
Three phase power evolved out of electric motor development. In 1885, Galileo Ferraris was doing research on [[rotating magnetic field]]s. Ferraris experimented with different types of asynchronous [[electric motor]]s. The research and his studies resulted in the development of an [[alternator]], which may be thought of as an alternating-current motor operating in reverse, so as to convert mechanical (rotating) power into electric power (as alternating current). On 11 March 1888, Ferraris published his research in a paper to the Royal Academy of Sciences in [[Turin]].<ref>{{Cite web |date=2022-06-14 |title=Milestones:Rotating Fields and Early Induction Motors, 1885-1888 |url=https://ethw.org/Milestones:Rotating_Fields_and_Early_Induction_Motors,_1885-1888 |access-date=2025-01-01 |website=ETHW |language=en}}</ref>

Two months later Nikola Tesla gained {{US patent|381968}} for a three-phase electric motor design, application filed October 12, 1887. Figure 13 of this patent shows that Tesla envisaged his three-phase motor being powered from the generator via six wires.

These alternators operated by creating systems of alternating currents displaced from one another in phase by definite amounts, and depended on rotating magnetic fields for their operation. The resulting source of polyphase power soon found widespread acceptance. The invention of the polyphase alternator is key in the history of electrification, as is the power transformer. These inventions enabled power to be transmitted by wires economically over considerable distances. Polyphase power enabled the use of water-power (via hydroelectric generating plants in large dams) in remote places, thereby allowing the mechanical energy of the falling water to be converted to electricity, which then could be fed to an electric motor at any location where mechanical work needed to be done. This versatility sparked the growth of power-transmission network grids on continents around the globe.

Mikhail Dolivo-Dobrovolsky developed a three-phase [[electrical generator]] and a three-phase electric motor in 1888 and studied [[star and delta connection]]s.<ref>{{Cite patent|number=US422746A|title=Dobrowolsky|gdate=1890-03-04|url=https://patents.google.com/patent/US422746}}</ref><ref>{{Cite web |title=US Patent: 422,746 - Electric induction apparatus or transformer |url=https://www.datamp.org/patents/displayPatent.php?pn=422746&id=73585 |access-date=2025-01-01 |website=www.datamp.org}}</ref><ref>{{Cite patent|number=US455683A|title=Dobeowolsky|gdate=1891-07-07|url=https://patents.google.com/patent/US455683}}</ref> His three-phase three-wire transmission system was displayed in 1891 in Germany at the [[International Electrotechnical Exhibition]], where Dolivo-Dobrovolsky used the system to transmit electric power at the distance of 176&nbsp;km (110 miles) with 75% [[Electrical efficiency|efficiency]]. In 1891 he also created a three-phase transformer and short-circuited ([[squirrel-cage rotor|squirrel-cage]]) [[induction motor]].<ref>{{Cite patent|number=US456804A|title=Dobrowolsky|gdate=1891-07-28|url=https://patents.google.com/patent/US456804}}</ref><ref>{{Cite web|url=http://www.mpoweruk.com/history.htm|title=Wayback Machine|website=www.mpoweruk.com}}</ref><ref>Gerhard Neidhöfer: ''Michael von Dolivo-Dobrowolsky und der Drehstrom. Geschichte der Elektrotechnik'' VDE-Buchreihe, Volume 9, VDE VERLAG, Berlin Offenbach, {{ISBN|978-3-8007-3115-2}}.''</ref> He designed the world's first three-phase [[hydroelectric power plant]] in 1891.<ref>{{Cite web |title=The Earliest Years of Three-Phase Power—1891–1893 [Scanning Our Past] |url=https://ieeexplore.ieee.org/document/8944322 |archive-url=http://web.archive.org/web/20241211105501/https://ieeexplore.ieee.org/document/8944322/ |archive-date=2024-12-11 |access-date=2025-01-01 |website=ieeexplore.ieee.org |language=en-US}}</ref> Inventor [[Jonas Wenström]] received in [[1890]] a Swedish patent on the same three-phase system.<ref>{{cite book|first=Lars|isbn=91-7536-330-5|last=Bergström och Nordlund|pages=283|publisher=Naturaläromedel|title=Ellära- Kretsteknik och fältteori|year=2002 }}<!-- auto-translated by Module:CS1 translator --></ref> The possibility of transferring electrical power from a waterfall at a distance was explored at the [[Grängesberg]] mine.  A {{val|45|ul=m}} fall at Hällsjön, Smedjebackens kommun, where a small iron work had been located, was selected. In 1893,  a three-phase {{val|9.5|ul=Kilovolt{{!}}kV}} system was used to transfer {{convert|400|hp|kW|link=in}} a distance of 15&nbsp;km (10 miles), becoming the first commercial application.<ref>{{cite book | last= Hjulström | first= Filip | title= Elektrifieringens utveckling i Sverige, en ekonomisk-geografisk översikt | year= 1940 | url= https://www.antikvariat.net/sv/rod151504-elektrifieringens-utveckling-i-sverige-en-ekonomisk-geografisk-oversikt-hjulstrom-filip | trans-quote= Excerpt taken from YMER 1941, häfte 2.Utgiven av Sällskapet för antropologi och geografi: Meddelande från Upsala univeristets geografiska institution, N:o 29, published by Esselte ab, Stockholm 1941 no. 135205 }}</ref>