Editing Transformer (section)

==History==

===Discovery of induction===
[[Image:Induction experiment.png|thumb|Faraday's experiment with induction between coils of wire<ref>{{cite book|url=https://archive.org/details/bub_gb_JzBAAAAAYAAJ| last=Poyser| first=Arthur William|year=1892|title=Magnetism and Electricity: A Manual for Students in Advanced Classes| location=London and New York|publisher= Longmans, Green, & Co.| page= [https://archive.org/details/bub_gb_JzBAAAAAYAAJ/page/n298 285], fig. 248}}</ref>]]

[[Electromagnetic induction]], the principle of the operation of the transformer, was discovered independently by [[Michael Faraday]] in 1831 and [[Joseph Henry]] in 1832.<ref>{{Cite web|url=http://web.hep.uiuc.edu/home/serrede/P435/Lecture_Notes/A_Brief_History_of_Electromagnetism.pdf|title=A Brief History of Electromagnetism}}</ref><ref>{{cite encyclopedia|encyclopedia=Smithsonian Institution Archives|title=Electromagnetism|url=http://siarchives.si.edu/history/exhibits/henry/electromagnetism}}</ref><ref name="MacPhersonRC">{{cite book|first=Ryan C.|last=MacPherson, Ph.D.|title=Joseph Henry: The Rise of an American scientist|url=http://www.ryancmacpherson.com/publications/3-book-reviews/49-joseph-henry-the-rise-of-an-american-scientist.html|access-date=2015-10-28|archive-url=https://web.archive.org/web/20151208121757/http://www.ryancmacpherson.com/publications/3-book-reviews/49-joseph-henry-the-rise-of-an-american-scientist.html|archive-date=2015-12-08|url-status=dead}}</ref><ref name="Guarnieri2013-56">{{harvnb|Guarnieri|2013|pp=56–59}}</ref> Only Faraday furthered his experiments to the point of working out the equation describing the relationship between EMF and magnetic flux now known as [[Faraday's law of induction]]:

:<math> |\mathcal{E}| = \left|{{\mathrm{d}\Phi_\text{B}} \over \mathrm{d}t}\right|,</math>

where <math>|\mathcal{E}|</math> is the magnitude of the EMF in volts and Φ<sub>B</sub> is the magnetic flux through the circuit in [[Weber (unit)|webers]].<ref name="Chow171">{{cite book|url=https://books.google.com/books?id=dpnpMhw1zo8C&pg=PA171|last= Chow|first= Tai L. |year=2006|title=Introduction to Electromagnetic Theory: A Modern Perspective| location=Sudbury, Mass.| publisher=Jones and Bartlett Publishers| page= 171| isbn=978-0-7637-3827-3}}</ref>

Faraday performed early experiments on induction between coils of wire, including winding a pair of coils around an iron ring, thus creating the first [[Toroid (geometry)|toroidal]] closed-core transformer.<ref name="Guarnieri2013-56"/><ref>{{cite journal|last=Faraday|first=Michael|year=1834|title=Experimental Researches on Electricity, 7th Series|author-link=Michael Faraday|journal=Philosophical Transactions of the Royal Society|volume=124|pages=77–122|doi=10.1098/rstl.1834.0008|s2cid=116224057|url=https://archive.org/details/philtrans08694360}}</ref> However he only applied individual pulses of current to his transformer, and never discovered the relation between the turns ratio and EMF in the windings.
[[Image:Induktionsapparat hg.jpg|thumb|left|Induction coil, 1900, Bremerhaven, Germany]]

===Induction coils===
{{main|Induction coil}}
[[Image:Faradays transformer.png|thumb|right|Faraday's ring transformer]]
The first type of transformer to see wide use was the [[induction coil]], invented by Irish-Catholic Rev. [[Nicholas Callan]] of [[Maynooth College]], Ireland in 1836.<ref name="Guarnieri2013-56"/> He was one of the first researchers to realize the more turns the secondary winding has in relation to the primary winding, the larger the induced secondary EMF will be. Induction coils evolved from scientists' and inventors' efforts to get higher voltages from batteries. Since batteries produce [[direct current|direct current (DC)]] rather than AC, induction coils relied upon vibrating [[electrical contact]]s that regularly interrupted the current in the primary to create the flux changes necessary for induction. Between the 1830s and the 1870s, efforts to build better induction coils, mostly by trial and error, slowly revealed the basic principles of transformers.

===First alternating current transformers===
By the 1870s, efficient [[Electric generator|generators]] producing [[alternating current|alternating current (AC)]] were available, and it was found AC could power an induction coil directly, without an [[interrupter]].

In 1876, Russian engineer [[Pavel Yablochkov]] invented a lighting system based on a set of induction coils where the primary windings were connected to a source of AC. The secondary windings could be connected to several [[Yablochkov candle|'electric candles']] (arc lamps) of his own design. The coils Yablochkov employed functioned essentially as transformers.<ref name=maglab>{{Cite web|url=https://nationalmaglab.org/education/magnet-academy/history-of-electricity-magnetism/museum/stanley-transformer|title=Stanley Transformer – 1886 - MagLab|access-date=2021-07-27|archive-date=2017-10-11|archive-url=https://web.archive.org/web/20171011232657/https://nationalmaglab.org/education/magnet-academy/history-of-electricity-magnetism/museum/stanley-transformer|url-status=dead}}</ref>

In 1878, the [[Ganz Works|Ganz factory]], Budapest, Hungary, began producing equipment for electric lighting and, by 1883, had installed over fifty systems in Austria-Hungary. Their AC systems used arc and incandescent lamps, generators, and other equipment.<ref name="Guarnieri2013-56"/><ref name=Hughes1993-95>{{harvnb|Hughes|1993|pp=95–96}}</ref>

In 1882, [[Lucien Gaulard]] and [[John Dixon Gibbs]] first exhibited a device with an initially widely criticized laminated plate open iron core called a 'secondary generator' in London, then sold the idea to the [[Westinghouse Electric Corporation|Westinghouse]] company in the United States in 1886.<ref name="allan">{{Cite journal | last = Allan | first=D.J.| title = Power Transformers – The Second Century | journal = Power Engineering Journal|date=Jan 1991|volume=5|issue=1|pages=5–14 | doi = 10.1049/pe:19910004| doi-broken-date=7 December 2024}}</ref> They also exhibited the invention in Turin, Italy in 1884, where it was highly successful and adopted for an electric lighting system.<ref name=Uppenborn1889>{{cite book|url=https://archive.org/details/historyoftransfo00upperich|last=Uppenborn|first=F. J.|title=History of the Transformer|publisher=E. & F. N. Spon|location=London|year=1889|pages=[https://archive.org/details/historyoftransfo00upperich/page/35 35]–41}}</ref> Their open-core device used a fixed 1:1 ratio to supply a series circuit for the utilization load (lamps). However, the voltage of their system was controlled by moving the iron core in or out.<ref>{{cite journal |last1=Halacsy |first1=Andrew |last2=Fuchs |first2=George |date=April 1961 |title= Transformer Invented 75 Years Ago|url=https://ieeexplore.ieee.org/document/4500994 |journal=  Transactions of the American Institute of Electrical Engineers. Part III: Power Apparatus and Systems|volume=80 |issue=3 |pages=121–125 |doi=10.1109/AIEEPAS.1961.4500994 |s2cid=51632693 |access-date=November 28, 2023 |archive-date=November 28, 2023 |archive-url=https://web.archive.org/web/20231128081004/https://ieeexplore.ieee.org/document/4500994 |url-status=bot: unknown |url-access=subscription }}</ref>

====Early series circuit transformer distribution====
Induction coils with open magnetic circuits are inefficient at transferring power to [[Electrical load|loads]]. Until about 1880, the paradigm for AC power transmission from a high voltage supply to a low voltage load was a series circuit. Open-core transformers with a ratio near 1:1 were connected with their primaries in series to allow use of a high voltage for transmission while presenting a low voltage to the lamps. The inherent flaw in this method was that turning off a single lamp (or other electric device) affected the voltage supplied to all others on the same circuit. Many adjustable transformer designs were introduced to compensate for this problematic characteristic of the series circuit, including those employing methods of adjusting the core or bypassing the magnetic flux around part of a coil.<ref name=Uppenborn1889/>
Efficient, practical transformer designs did not appear until the 1880s, but within a decade, the transformer would be instrumental in the [[war of the currents]], and in seeing AC distribution systems triumph over their DC counterparts, a position in which they have remained dominant ever since.<ref name="Coltman1988">{{harvnb|Coltman|1988|pp=86–95}}</ref>

[[Image:Trafo1885.jpg|thumb|right|Shell form transformer. Sketch used by Uppenborn to describe ZBD engineers' 1885 patents and earliest articles.<ref name=Uppenborn1889/>]]

[[Image:DBZ trafo.jpg|thumb|right|Core form, front; shell form, back. Earliest specimens of ZBD-designed high-efficiency constant-potential transformers manufactured at the Ganz factory in 1885.]]
[[Image:ZBD team.jpg|right|thumb|The ZBD team consisted of [[Károly Zipernowsky]], [[Ottó Bláthy]] and [[Miksa Déri]]]]
[[Image:StanleyTransformer.png|thumb|right|Stanley's 1886 design for adjustable gap open-core induction coils]]

===Closed-core transformers and parallel power distribution===
In the autumn of 1884, [[Károly Zipernowsky]], [[Ottó Bláthy]] and [[Miksa Déri]] (ZBD), three Hungarian engineers associated with the [[Ganz Works]], had determined that open-core devices were impracticable, as they were incapable of reliably regulating voltage.<ref name=Hughes1993-95/> The Ganz factory had also in the autumn of 1884 made delivery of the world's first five high-efficiency AC transformers, the first of these units having been shipped on September 16, 1884.<ref name="Halacsy1961">{{harvnb|Halacsy|Von Fuchs|1961|pp=121–125}}</ref> This first unit had been manufactured to the following specifications: 1,400 W, 40&nbsp;Hz, 120:72 V, 11.6:19.4 A, ratio 1.67:1, one-phase, shell form.<ref name="Halacsy1961"/> In their joint 1885 patent applications for novel transformers (later called ZBD transformers), they described two designs with closed magnetic circuits where copper windings were either wound around an iron wire ring core or surrounded by an iron wire core.<ref name=Uppenborn1889/> The two designs were the first application of the two basic transformer constructions in common use to this day, termed "core form" or "shell form" .<ref name="Lucas (2000)">{{cite web|last=Lucas|first=J.R.|title=Historical Development of the Transformer|url=http://www.elect.mrt.ac.lk/Transformer_history_2000.pdf|publisher=IEE Sri Lanka Centre|access-date=Mar 1, 2012}}</ref>

In both designs, the magnetic flux linking the primary and secondary windings traveled almost entirely within the confines of the iron core, with no intentional path through air (see [[#Toroidal cores|Toroidal cores]] below). The new transformers were 3.4 times more efficient than the open-core bipolar devices of Gaulard and Gibbs.<ref name=Jeszenszky>{{cite web|last=Jeszenszky|first=Sándor|title=Electrostatics and Electrodynamics at Pest University in the Mid-19th Century|url=http://ppp.unipv.it/Collana/Pages/Libri/Saggi/Volta%20and%20the%20History%20of%20Electricity/V%26H%20Sect2/V%26H%20175-182.pdf|publisher=[[University of Pavia]]|access-date=Mar 3, 2012|archive-date=June 27, 2022|archive-url=https://web.archive.org/web/20220627060208/http://ppp.unipv.it/Collana/Pages/Libri/Saggi/Volta%20and%20the%20History%20of%20Electricity/V%26H%20Sect2/V%26H%20175-182.pdf|url-status=bot: unknown}}</ref> The ZBD patents included two other major interrelated innovations: one concerning the use of parallel connected, instead of series connected, utilization loads, the other concerning the ability to have high turns ratio transformers such that the supply network voltage could be much higher (initially 1,400 to 2,000 V) than the voltage of utilization loads (100 V initially preferred).<ref name="Ideal (2008)">{{cite web|title=Hungarian Inventors and Their Inventions|url=http://www.institutoideal.org/conteudo_eng.php?&sys=biblioteca_eng&arquivo=1&artigo=94&ano=2008|publisher=Institute for Developing Alternative Energy in Latin America|access-date=Mar 3, 2012|url-status=dead|archive-url=https://web.archive.org/web/20120322223457/http://www.institutoideal.org/conteudo_eng.php?&sys=biblioteca_eng&arquivo=1&artigo=94&ano=2008|archive-date=2012-03-22}}</ref><ref name=BUTE-OMIKK-BlathyOtto>{{cite web|title=Bláthy, Ottó Titusz|url=http://www.omikk.bme.hu/archivum/angol/htm/blathy_o.htm|publisher=Budapest University of Technology and Economics, National Technical Information Centre and Library|access-date=Feb 29, 2012}}</ref> When employed in parallel connected electric distribution systems, closed-core transformers finally made it technically and economically feasible to provide electric power for lighting in homes, businesses and public spaces. Bláthy had suggested the use of closed cores, Zipernowsky had suggested the use of [[Shunt (electrical)|parallel shunt connections]], and Déri had performed the experiments;<ref name="Smil">{{cite book|url=https://archive.org/details/creatingtwentiet0000smil|url-access=registration|quote=ZBD transformer.|last=Smil|first=Vaclav|title=Creating the Twentieth Century: Technical Innovations of 1867–1914 and Their Lasting Impact|location=Oxford |publisher=Oxford University Press|year=2005|page=[https://archive.org/details/creatingtwentiet0000smil/page/71 71]|isbn=978-0-19-803774-3}}</ref> In early 1885, the three engineers also eliminated the problem of [[eddy current]] losses with the invention of the lamination of electromagnetic cores.<ref>{{cite book|author=Electrical Society of Cornell University|title=Proceedings of the Electrical Society of [[Cornell University]]|publisher=Andrus & Church|year=1896|page=39}}</ref>

Transformers today are designed on the principles discovered by the three engineers. They also popularized the word 'transformer' to describe a device for altering the EMF of an electric current<ref>{{cite web|url=http://www.kfki.hu/~aznagy/lecture/lecture.htm|last=Nagy|first=Árpád Zoltán|title=Lecture to Mark the 100th Anniversary of the Discovery of the Electron in 1897 (preliminary text)|location=Budapest|date=Oct 11, 1996|access-date=July 9, 2009|archive-date=November 25, 2012|archive-url=https://web.archive.org/web/20121125115109/http://www.kfki.hu/~aznagy/lecture/lecture.htm|url-status=dead}}</ref> although the term had already been in use by 1882.<ref>{{cite book|title = Oxford English Dictionary|url=https://archive.org/details/oxfordenglishdic0015unse|url-access = registration|edition=2nd|year=1989|publisher=Oxford University Press}}</ref><ref>{{cite book|url=https://archive.org/details/modernapplicati00hospgoog| last=Hospitalier|first=Édouard|year= 1882|title=The Modern Applications of Electricity|translator= Julius Maier|location=New York|publisher=D. Appleton & Co.|page=[https://archive.org/details/modernapplicati00hospgoog/page/n121 103]}}</ref> In 1886, the ZBD engineers designed, and the Ganz factory supplied electrical equipment for, the world's first [[power station]] that used AC generators to power a parallel connected common electrical network, the steam-powered Rome-Cerchi power plant.<ref>{{cite web|url=http://www.iec.ch/cgi-bin/tl_to_htm.pl?section=technology&item=144| title=Ottó Bláthy, Miksa Déri, Károly Zipernowsky| publisher=IEC Techline| access-date=Apr 16, 2010| url-status=dead| archive-url=https://web.archive.org/web/20101206042832/http://www.iec.ch/cgi-bin/tl_to_htm.pl?section=technology&item=144| archive-date=2010-12-06}}</ref>

===Westinghouse improvements===
[[File:Blachy transformatorowe.jpg|thumb|E-shaped plates for transformer cores developed by Westinghouse]]

Building on the advancement of AC technology in Europe,<ref>{{cite journal |last1=Brusso |first1=Barry|last2=Allerhand |first2=Adam |date=January 2021 |title=A Contrarian History of Early Electric Power Distribution|volume= |issue= |doi= 10.1109/MIAS.2020.3028630|url=https://ieeexplore.ieee.org/document/9292399 |journal=IEEE Industry Applications Magazine |page=12 |publisher=IEEE.org |s2cid=230605234 |access-date=January 1, 2023|archive-date=December 12, 2020 |archive-url=https://web.archive.org/web/20201212083429/https://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=9292399 |doi-access=free }}</ref> [[George Westinghouse]] founded the [[Westinghouse Electric Corporation|Westinghouse Electric]] in Pittsburgh, Pennsylvania, on January 8, 1886.<ref name="Tinicum Township">{{cite book|title=History of Tinicum Township (PA) 1643–1993|publisher=Tinicum Township Historical Society|year=1993|url=http://tthsdelco.org/wp-content/uploads/2014/02/History%20of%20Tinicum%20Twp.pdf|archive-url=https://web.archive.org/web/20150423202458/http://tthsdelco.org/wp-content/uploads/2014/02/History%20of%20Tinicum%20Twp.pdf|archive-date=April 23, 2015|url-status=live}}</ref> The new firm became active in developing alternating current (AC) electric infrastructure throughout the United States.  
The [[Edison Electric Light Company]] held an option on the US rights for the ZBD transformers, requiring Westinghouse to pursue alternative designs on the same principles. George Westinghouse had bought Gaulard and Gibbs' patents for $50,000 in February 1886.<ref>{{cite book|author=William R. Huber|title=George Westinghouse Powering the World|publisher=[[McFarland & Company]]|year=2022|page=84|isbn=9781476686929|url=https://books.google.com/books?id=UdBcEAAAQBAJ&dq=Westinghouse+purchased+the+patent+rights+to+the+Gaulard%E2%80%93Gibbs+system+in+February+of+that+year&pg=PA84}}</ref> He assigned to [[William Stanley, Jr.|William Stanley]] the task of redesign the Gaulard and Gibbs transformer for commercial use in United States.<ref name="Skrabec">{{cite book|last=Skrabec|first=Quentin R.|title=George Westinghouse: Gentle Genius|publisher=Algora Publishing|year=2007|page=102|isbn=978-0-87586-508-9|url=https://books.google.com/books?id=C3GYdiFM41oC&pg=PA102}}</ref> Stanley's first patented design was for induction coils with single cores of soft iron and adjustable gaps to regulate the EMF present in the secondary winding (see image). This design<ref name="Coltman2002">{{harvnb|Coltman|2002}}</ref> was first used commercially in the US in 1886<ref name="IEC History">{{cite book |author = International Electrotechnical Commission |author-link = International Electrotechnical Commission |title = Otto Blathy, Miksa Déri, Károly Zipernowsky |work = IEC History |url=http://www.iec.ch/cgi-bin/tl_to_htm.pl?section=technology&item=144 |access-date = May 17, 2007 |url-status = dead |archive-url=https://web.archive.org/web/20101206042832/http://www.iec.ch/cgi-bin/tl_to_htm.pl?section=technology&item=144 |archive-date = December 6, 2010 }}</ref> but Westinghouse was intent on improving the Stanley design to make it (unlike the ZBD type) easy and cheap to produce.<ref name="Coltman2002"/>

Westinghouse, Stanley and associates soon developed a core that was easier to manufacture, consisting of a stack of thin 'E‑shaped' iron plates insulated by thin sheets of paper or other insulating material. Pre-wound copper coils could then be slid into place, and straight iron plates laid in to create a closed magnetic circuit. Westinghouse obtained a patent for the new low-cost design in 1887.<ref name="Smil"/>

===Other early transformer designs===
In 1889, Russian-born engineer [[Mikhail Dolivo-Dobrovolsky]] developed the first [[Three-phase electric power|three-phase]] transformer at the [[Allgemeine Elektricitäts-Gesellschaft]] ('General Electricity Company') in Germany.<ref>{{cite book|last=Neidhöfer|first= Gerhard|others=In collaboration with VDE "History of Electrical Engineering" Committee|location= Berlin | isbn= 978-3-8007-3115-2|url=http://d-nb.info/990964361|title=Michael von Dolivo-Dobrowolsky and Three-Phase: The Beginnings of Modern e Technology and Power Supply |language=de|year=2008|publisher=VDE-Verl.|edition=2nd}}</ref>

In 1891, [[Nikola Tesla]] invented the [[Tesla coil]], an air-cored, dual-tuned resonant transformer for producing very [[high voltage]]s at high frequency.<ref name="PBS">{{cite web|last=Uth|first=Robert|title=Tesla Coil|date=Dec 12, 2000|work=Tesla: Master of Lightning|publisher=PBS.org|url=https://www.pbs.org/tesla/ins/lab_tescoil.html|access-date=May 20, 2008}}</ref>

[[Audio frequency]] transformers ("[[repeating coil]]s") were used by early experimenters in the development of the [[telephone]].<ref>{{Cite web |title=telephone {{!}} History, Definition, Invention, Uses, & Facts {{!}} Britannica |url=https://www.britannica.com/technology/telephone |access-date=2022-07-17 |website=www.britannica.com |language=en}}</ref>