Editing Rotating magnetic field

{{Short description|Resultant magnetic field}}[[Image:3phase-rmf-noadd-60f-airopt.gif|320px|thumb|'''Oscillating magnetic fields.''' Sine wave current in each of the three stationary coils produces three sinusoidally varying magnetic fields perpendicular to the rotation axis. The three magnetic fields add as vectors to produce a single rotating magnetic field.]][[Image:RMFpatent.PNG|320px|thumb|right|'''U.S. Patent 381968''': Mode and plan of operating electric motors by progressive shifting; Field Magnet; Armature; Electrical conversion; Economical; Transmission of energy; Simple construction; Easier construction; Rotating magnetic field principles.]]A '''rotating magnetic field (RMF)''' is the resultant [[magnetic field]] produced by a system of [[Electromagnetic coil|coils]] symmetrically placed and supplied with [[Polyphase system|polyphase currents]].<ref>{{Cite book|last=Graham|first=Frank Duncan|url=https://archive.org/details/audelsengineers01unkngoog|title=Audels Engineers and Mechanics Guide|publisher=THEO. AUDEL & CO.|year=1921|isbn=|location=New York|page=594}}</ref> A rotating magnetic field can be produced by a poly-phase (two or more phases) current or by a single phase current provided that, in the latter case, two field windings are supplied and are so designed that the two resulting magnetic fields generated thereby are out of phase.<ref name=":0">{{Cite journal|last=Bucher|first=Elmer E.|url=https://archive.org/details/WirelessAgeVols0607/page/n173/mode/2up|title=Practical wireless instruction|journal=The Wireless Age|date=January 1919|number=4|volume=6|pages=18–19}}</ref>

Rotating magnetic fields are often utilized for [[Electromechanics|electromechanical]] applications, such as [[induction motor]]s, [[electric generator]]s and [[induction regulator]]s.

==History==

In 1824, the French physicist [[François Arago]] formulated the existence of rotating magnetic fields using a rotating copper disk and a needle, termed “[[Arago's rotations]].” English experimenters [[Charles Babbage]] and [[John Herschel]] found they could induce rotation in Arago's copper disk by spinning a [[horseshoe magnet]] under it, with English scientist [[Michael Faraday]] later attributing the effect to [[electromagnetic induction]].<ref>{{Cite book|last=Carlson|first=W. Bernard|url=https://books.google.com/books?id=5I5c9j8BEn4C|title=Tesla: Inventor of the Electrical Age|publisher=Princeton University Press|year=2013|isbn=978-1400846559|location=|pages=52–54}}</ref> In 1879, English physicist [[Walter Baily's Motor|Walter Baily]] replaced the horseshoe magnets with four electromagnets and, by manually turning switches on and off, demonstrated a primitive induction motor.<ref>{{Cite book|last=Carlson|first=W. Bernard|url=https://books.google.com/books?id=5I5c9j8BEn4C|title=Tesla: Inventor of the Electrical Age|publisher=Princeton University Press|year=2013|isbn=978-1400846559|location=|page=55}}</ref><ref name="Babbage (1825)">{{cite journal|last=Babbage|first=C.|author2=Herschel, J. F. W.|date=Jan 1825|title=Account of the Repetition of M. Arago's Experiments on the Magnetism Manifested by Various Substances during the Act of Rotation|url=https://archive.org/stream/philtrans03806447/03806447#page/n0/mode/2up|journal=Philosophical Transactions of the Royal Society|volume=115|pages=467–496|bibcode=1825RSPT..115..467B|doi=10.1098/rstl.1825.0023|access-date=2 December 2012|doi-access=free}}</ref><ref name="Thompson (1895)">{{cite book|last=Thompson|first=Silvanus Phillips|url=https://archive.org/stream/polyphaseelectri00thomuoft#page/n5/mode/2up|title=Polyphase Electric Currents and Alternate-Current Motors|publisher=E. & F.N. Spon|year=1895|edition=1st|location=London|pages=261|author-link=Silvanus Phillips Thompson|access-date=2 December 2012}}</ref><ref name="Bailey (1879)">{{Cite journal|last=Baily|first=Walter|date=June 28, 1879|title=A Mode of producing Arago's Rotation|url=https://books.google.com/books?id=85AOAAAAIAAJ&pg=PA286|journal=Philosophical Magazine|publisher=Taylor & Francis|volume=3|issue=1|pages=115–120|bibcode=1879PPSL....3..115B|doi=10.1088/1478-7814/3/1/318}}</ref><ref name="Vuckovic (2006)">{{cite journal|last=Vučković|first=Vladan|date=November 2006|title=Interpretation of a Discovery|url=http://www.doiserbia.nb.rs/img/doi/1451-4869/2006/1451-48690603202V.pdf|journal=The Serbian Journal of Electrical Engineers|volume=3|issue=2|access-date=10 February 2013}}</ref>

The idea of a rotating magnetic field in an [[AC motor]] was explored by the Italian physicist and electrical engineer [[Galileo Ferraris]] and the Serbian-American inventor and electrical engineer [[Nikola Tesla]].<ref>{{Cite book|last=Hughes|first=Thomas Parke|url=https://archive.org/details/networksofpowere0000hugh|title=Networks of power: electrification in Western society, 1880-1930|publisher=Johns Hopkins University Press|year=1983|isbn=9780801828737|location=Baltimore|page=117}}</ref> Ferraris, who did research about the theory and design of alternating-current machinery, built a working model for a classroom demonstration in 1885, but did not describe it publicly until 1888.<ref>{{Cite encyclopedia|last=|first=|url=https://archive.org/details/encyclopediaamer0011unse_f6t5/page/124/mode/2up|title=Ferraris |encyclopedia=Encyclopedia Americana: Falstaff to Francke|publisher=Scholastic Library|year=2004|volume=11|edition=International|location=Danbury, Connecticut|page=124}}</ref> Tesla attempted several (unsuccessful) designs and working models through the early 1880s before building a working prototype in 1887<ref>{{Cite book|last=Carlson|first=W. Bernard|url=https://books.google.com/books?id=5I5c9j8BEn4C|title=Tesla: Inventor of the Electrical Age|publisher=Princeton University Press|year=2013|isbn=978-1400846559|location=|pages=63–68}}</ref><ref>[https://edisontechcenter.org/tesladebunked.html Debunking the Tesla Myth]</ref><ref>{{Cite book|last=O'Neill|first=John|title=Prodigal Genius: The Life of Nikola Tesla|pages=55–58}}</ref> According to Ferraris principle of rotating magnetic field, Friedrich August Haselwander developed the first AC 3 phase generator in 1887.<ref>{{cite book | chapter-url=https://ieeexplore.ieee.org/document/4401482 | doi=10.1109/AFRCON.2007.4401482 | chapter=Synchronous generator: Past, present and future | title=Africon 2007 | year=2007 | last1=Hooshyar | first1=H. | last2=Savaghebi | first2=M. | last3=Vahedi | first3=A. | pages=1–7 | isbn=978-1-4244-0986-0 | s2cid=28833835 }}</ref>  In 1888, Ferraris published his research in a paper to the ''Royal Academy of Sciences'' in [[Turin]] and Tesla obtained a United States patent ({{US patent|0381968}}) for his design. Based on the Haselwander generator, [[Mikhail Dolivo-Dobrovolsky]] developed a three-phase generator and motor for the world's first three-phase power plant built in 1891 in Frankfurt, Germany.<ref>[https://edisontechcenter.org/AC-PowerHistory.html AC Power History and Timeline]</ref>

==Description==
The rotating magnetic field is the key principle in the operation of [[Induction motor|induction machines]]. The induction motor consists of a [[stator]] and [[Rotor (electric)|rotor]]. In the stator a group of fixed windings are so arranged that a two phase current, for example, produces a magnetic field which rotates at an [[angular velocity]] determined by the [[frequency]] of the [[alternating current]]. The rotor or [[Armature (electrical)|armature]] consists of coils wound in slots, which are short circuited and in which the changing [[flux]] generated by the field poles induce a current. The flux generated by the armature current reacts upon the field poles and the armature is set in rotation in a definite direction.<ref name=":0" />
[[File:Rotating magnetic field.png|center|thumb|640x640px|'''Rotating fields.''' As the direction of the current through the windings changes, the polarity of the windings changes as well. Since there are two windings acting in conjunction with each other, the polarity of the main field will depend upon the polarity of each winding. The arrow or vector below each diagram indicates the direction of the magnetic field in each case.<ref>{{Cite book|last=United States|first=Bureau of Naval Personnel|url=https://archive.org/details/AdvWorkInAircraftElectricity|title=Advanced Work In Aircraft Electricity|publisher=U.S. Govt. Print. Off.|year=1945|isbn=|location=Washington|pages=149–150}}</ref>]]
A [[symmetric]] rotating magnetic field can be produced with as few as two polar wound [[Electromagnetic coil|coils]] driven at 90-degree [[Phase (waves)|phasing]]. However, three sets of coils are nearly always used, because it is compatible with a [[3 phase power|symmetric three-phase AC sine current system]]. The three coils are driven with each set 120 degrees [[in phase]] from the others. For the purpose of this example, the magnetic field is taken to be the [[linear function]] of the coil's current.

The result of adding three 120-degree phased [[sine wave]]s on the axis of the motor is a single rotating vector that always remains constant in magnitude.<ref name="rmf">[http://www.electricaleasy.com/2014/02/production-of-rotating-magnetic-field.html Production of rotating magnetic field], | electricaleasy.com</ref> The rotor has a constant magnetic field. The north pole of the rotor will move toward the south pole of the magnetic field of the stator, and vice versa. This [[magnetomechanical effects|magnetomechanical]] attraction creates a force that will drive the rotor to follow the rotating magnetic field in a [[Synchronization (alternating current)|synchronous]] manner.

[[File:Rotating-3-phase-magnetic-field.svg|alt=|thumb|640x640px|Rotating three-phase magnetic field, as indicated by the rotating black arrow|center]]
A [[permanent magnet]] in such a field will rotate so as to maintain its alignment with the external field. This effect was utilized in early alternating-current electric motors.  A rotating magnetic field can be constructed using two orthogonal coils with a 90-degree phase difference in their alternating currents. However, in practice, such a system would be supplied through a three-wire arrangement with unequal currents. This inequality would cause serious problems in the standardization of the conductor size. In order to overcome this, three-phase systems are used in which the three currents are equal in magnitude and have a 120-degree phase difference. Three similar coils having mutual geometrical angles of 120 degrees will create the rotating magnetic field in this case. The ability of the three-phase system to create the rotating field utilized in electric motors is one of the main reasons why three-phase systems dominate the world's electric power-supply systems.

Rotating magnetic fields are also used in induction motors. Because magnets degrade with time, induction motors use short-circuited rotors (instead of a magnet), which follow the rotating magnetic field of a multicoiled stator. In these motors, the short-circuited turns of the rotor develop [[eddy current]]s in the rotating field of the stator, which in turn move the rotor by [[Lorentz force]]. These types of motors are not usually synchronous, but instead necessarily involve a degree of 'slip' in order that the current may be produced due to the relative movement of the field and the rotor.

==See also==

* [[Dynamo theory]]
* [[Halbach array]], a magnetic field that rotates spatially
* [[Linear motor]]
* [[Magnetic stirrer]]
* [[Electromagnetic vortex intensifier with ferromagnetic particles]]
* [[Shaded-pole motor]]
* [[Squirrel-cage rotor]]
* [[Synchronous motor]]
* [[Tesla's Egg of Columbus]]
* [[Timeline of motor and engine technology]]
* [[War of the currents]]

==References==
{{Reflist|30em}}{{Source-attribution|{{cite book |title=The Wireless Age |year=1918 |publisher=New York, Marconi Pub. Corporation|ref=none}}}}

==Further reading==
*{{cite journal |author=C Mackechnie Jarvis |title=Nikola Tesla and the induction motor |journal=Phys Educ |volume=5 |issue=5 |pages=280–7 |year=1970 |doi=10.1088/0031-9120/5/5/306 |bibcode=1970PhyEd...5..280M |s2cid=250845406 }}
*{{cite journal |doi=10.1109/45.9969 |author=Owen, E.L. |title=The induction motor's historical past |journal=IEEE Potentials |volume=7 |issue=3 |pages=27–30 |date=October 1988 |s2cid=19271710 }}
*  Beckhard, Arthur J., "Electrical genius Nikola Tesla".  New York, Messner,  1959. LCCN 59007009 /L/AC/r85 (ed. 192 p.; 22&nbsp;cm.; biography with notes on the inventions of the rotating magnetic field motors for alternating current.)
*{{cite journal |author=Kline, R. |title=Science and Engineering Theory in the Invention and Development of the Induction Motor, 1880–1900 |journal=Technology and Culture |volume=28 |issue=2 |pages=283–313 |year=1987 |doi=10.2307/3105568 |jstor=3105568 }}
*{{cite journal |doi=10.1103/PhysRevE.66.061402 |pmid=12513280 |author=Cēbers, A. |title=Dynamics of an elongated magnetic droplet in a rotating field |journal=Phys. Rev. E  |volume=66 |issue=6 |pages=061402 |date=December 13, 2002 |bibcode=2002PhRvE..66f1402C }}
*{{cite journal |doi=10.1103/PhysRevE.69.021404 |pmid=14995441 |author1=Cēbers, A. |author2=I. Javaitis  |name-list-style=amp |title=Dynamics of a flexible magnetic chain in a rotating magnetic field |journal=Phys. Rev. E |volume=69 |issue=2 |pages=021404 |year=2004 |bibcode=2004PhRvE..69b1404C }}
*{{cite journal |doi=10.1103/PhysRevE.73.021505 |pmid=16605340 |author1=Cēbers, A. |author2=M. Ozols  |name-list-style=amp |title=Dynamics of an active magnetic particle in a rotating magnetic field |journal=Phys. Rev. E |volume=73 |issue=2 |pages=021505 |year=2006 |bibcode=2006PhRvE..73b1505C }}
*{{cite journal |doi=10.1109/TASC.2004.831024 |author=Tao Song|title=Rotating permanent magnetic fields exposure system for in vitro study |journal=IEEE Transactions on Applied Superconductivity |volume=14 |issue=2 |pages=1643–6 |date=June 2004 |display-authors=etal|bibcode=2004ITAS...14.1643S}}
* Labzovskii, L.N., A.O. Mitrushchenkov, and A.I. Frenkel, "[https://web.archive.org/web/20070416205911/http://pubweb.bnl.gov/users/frenkel/www/PHYS-LETT/labz-frenkel.pdf Parity Nonconserving Current in Conductors of Electricity]". 6 July 1987. (ed., Shows that the continuous current arises under the influence of the rotating magnetic field.)
* Naval Electrical Engineering Training Series, Module 05 - Introduction to Generators and Motors, Chapter 4 Alternating Current Motors, [http://www.tpub.com/content/neets/14177/css/14177_87.htm Rotating magnetic fields] (ed. different copy of the NEETS book is available, [https://web.archive.org/web/20120114171906/http://jricher.com/NEETS/ Add-free version])
* [https://web.archive.org/web/20060427025126/http://www.eng.ox.ac.uk/~epgmdm/A2/img89.htm Rotating Magnetic Field], eng.ox.ac.uk
* Tesla's Autobiography, III. My Later Endeavors; [http://www.teslaplay.com/autosection3.htm The Discovery of the Rotating Magnetic Field]
* [https://web.archive.org/web/20030503173932/http://web.mit.edu/Invent/iow/tesla.html Nikola Tesla and the electro-magnetic motor], Inventor of the Week Archive.
* [https://web.archive.org/web/20091027095516/http://www.geocities.com/SiliconValley/Lakes/3015/history004.html Galileo Ferraris: the rotating magnetic field]
* [http://www.lmphotonics.com/single_phase_m.htm Single Phase Induction Motors]
* H.Y. Guo, A.L. Hoffman, D. Lotz, S.J. Tobin, W.A. Reass, L.S. Schrank and G.A. Wurden, [http://wsx.lanl.gov/Publications/RSI-RMF-Tobin-paper.pdf The Rotating Magnetic Field Oscillator System for Current Drive in the Translation, Confinement and Sustainment Experiment], March 22, 2001.
*  Putko, V. F., and  V. S. Sobolev, [http://adsabs.harvard.edu/abs/1981gnpn.conf..113P Effect of a rotating magnetic field on the characteristics of a direct-current plasma generator].
*  '''Construction of a generalized mathematical model and fast calculations of plane-parallel rotating magnetic fields in process reactors with longitudinal currents of cylindrical inductors on a graphical calculator. https://www.researchgate.net/publication/385877325'''

== External links ==
* [http://www.sandroronca.it/elettrotecnica/asincrono/camporotante0.html Rotating magnetic field]: interactive lecture
* [https://www.youtube.com/watch?v=2M9CiAlBaSk Rotating field animation] (YouTube video)
* "''[http://www.tpub.com/neets/book5/18a.htm Rotating magnetic fields]''". Integrated Publishing.
* "''[https://web.archive.org/web/20050929102550/http://www.egr.msu.edu/~jurkovi4/Experiment4.pdf Induction Motor – Rotating Fields]''".

===Patents===
* {{US patent|0381968}}, Tesla, "Electromagnetic motor".
* {{US patent|3935503}}, Ress, "Particle accelerator".
{{Nikola Tesla}}

[[Category:Electromagnetic components]]