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| {{About||other kinds of motors|Motor (disambiguation)|a railroad engine|Electric locomotive}}
| | I'm Julia (22) from Sint-Michielsgestel, Netherlands. <br>I'm learning Swedish literature at a local university and I'm just about to graduate.<br>I have a part time job in a post office.<br><br>Feel free to visit my web site - [http://londonpassionescorts.net/plus/guestbook.php fifa 15 coin generator] |
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| [[File:Motors01CJC.jpg|thumb| Various electric motors, compared to 9 V battery.]]
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| [[File:MotorSymbol.png|100px|thumb|Electronic symbol for an electric motor]]
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| An '''electric motor''' is an [[electric machine]] that converts [[electromechanical|electrical energy into mechanical]] energy.
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| In normal motoring mode, most electric motors operate through the interaction between an electric motor's [[magnetic fields|magnetic field]] and [[electrical conductor|winding currents]] to generate force within the motor. In certain applications, such as in the transportation industry with [[traction motor]]s, electric motors can operate in both motoring and [[regenerative braking|generating or braking]] modes to also produce electrical energy from mechanical energy.
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| Found in applications as diverse as industrial fans, blowers and pumps, machine tools, household appliances, power tools, and disk drives, electric motors can be powered by [[direct current|direct current (DC)]] sources, such as from batteries, motor vehicles or rectifiers, or by [[Alternating current|alternating current (AC)]] sources, such as from the power grid, [[Inverter (electrical)|inverter]]s or generators. Small motors may be found in electric watches. General-purpose motors with highly standardized dimensions and characteristics provide convenient mechanical power for industrial use. The largest of electric motors are used for ship propulsion, pipeline compression and [[Pumped-storage hydroelectricity|pumped-storage]] applications with ratings reaching 100 megawatts. Electric motors may be classified by electric power source type, internal construction, application, type of motion output, and so on.
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| Devices such as magnetic solenoids and loudspeakers that convert electricity into motion but do not generate usable mechanical power are respectively referred to as actuators and transducers. Electric motors are used to produce linear force or torque (rotary).
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| [[File:Rotterdam Ahoy Europort 2011 (14).JPG|thumb|upright=1.35|Cutaway view through stator of induction motor.]]
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| ==History==
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| {{main|History of the electric motor}}
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| ===Early motors===
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| [[File:Faraday magnetic rotation.jpg|thumb|upright|200px|Faraday's electromagnetic experiment, 1821<ref name="Faraday (1822)">{{cite journal|last=Faraday|first=Michael|title=On Some New Electro-Magnetical Motion, and on the Theory of Magnetism|journal=Quarterly Journal of Science, Literature and the Arts|year=1822|volume=XII|pages=74–96 (§IX)|url=http://archive.org/details/quarterlyjournal12jour|accessdate=12 February 2013|publisher=Royal Institution of Great Britain}}</ref>]]
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| Perhaps the first electric motors were simple [[electrostatic motor|electrostatic]] devices created by the Scottish monk [[Andrew Gordon (Benedictine)|Andrew Gordon]] in the 1740s.<ref name="Gordon">Tom McInally, The Sixth Scottish University. The Scots Colleges Abroad: 1575 to 1799 (Brill, Leiden, 2012) p. 115</ref> The theoretical principle behind production of mechanical force by the interactions of an electric current and a magnetic field, [[Ampère's force law]], was discovered later by [[André-Marie Ampère]] in 1820.
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| The conversion of electrical energy into mechanical energy by [[electromagnetism|electromagnetic]] means was demonstrated by the British scientist [[Michael Faraday]] in 1821. A free-hanging wire was dipped into a pool of mercury, on which a [[permanent magnet|permanent magnet (PM)]] was placed. When a current was passed through the wire, the wire rotated around the magnet, showing that the current gave rise to a close circular magnetic field around the wire.<ref name="SparkMuseum (Motor)">{{cite conference|title=The Development of the Electric Motor,|url=http://www.sparkmuseum.com/MOTORS.HTM|publisher=SparkMuseum|accessdate=12 February 2013|booktitle=Early Electric Motors}}</ref> This motor is often demonstrated in physics experiments, brine substituting for toxic mercury. Though [[Barlow's wheel]] was an early refinement to this Faraday demonstration, these and similar [[homopolar motor]]s were to remain unsuited to practical application until late in the century.
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| [[File:Jedlik motor.jpg|thumb|200px|[[Ányos Jedlik|Jedlik]]'s "electromagnetic self-rotor", 1827 (Museum of Applied Arts, Budapest). The historic motor still works perfectly today.<ref name="TravelHungary (Dynamo)">{{cite web|title=The first dinamo?|url=http://www.traveltohungary.com/english/articles/article.php?id=136|publisher=travelhungary.com|accessdate=12 February 2013}}</ref>]]
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| In 1827, [[Hungary|Hungarian]] [[physicist]] [[Ányos Jedlik]] started experimenting with [[electromagnetic coil]]s. After Jedlik solved the technical problems of the continuous rotation with the invention of [[commutator (electric)|commutator]], he called his early devices as "electromagnetic self-rotors". Although they were used only for instructional purposes, in 1828 Jedlik demonstrated the first device to contain the three main components of practical DC motors: the [[stator]], [[rotor (electric)|rotor]] and commutator. The device employed no permanent magnets, as the magnetic fields of both the stationary and revolving components were produced solely by the currents flowing through their windings.<ref name="Guillemin (1891)">{{cite conference|last=Guillemin|first=Amédée|title=Electricity and Magnetism|year=1891|publisher=McMillan and Co.|coauthors='Le Magnétisme et l'Électricitée' trans., ed. & rev. from the French by Sylvanus P. Thompson|url=http://books.google.ca/books?id=QznSAAAAMAAJ&printsec=frontcover&source=gbs_ge_summary_r&cad=0#v=onepage&q&f=false}}</ref><ref name="Nature">{{cite journal|journal=[[Nature (journal)|Nature]]|title=Anianus Jedlik|first=Augustus|last=Heller|publisher=Norman Lockyer|date=April 1896|volume=53|issue=1379|page=516|bibcode = 1896Natur..53..516H |doi = 10.1038/053516a0 }}</ref><ref name="Blundel (2012)">{{cite book|last=Blundel|first=Stephen J.|title=Magnetism A Very Short Introduction.|year=2012|publisher=Oxford Univ Pr|isbn=978-0-19-960120-2|url=http://www.amazon.com/Magnetism-Introduction-Stephen-J-Blundell/dp/0199601208#reader_0199601208|page=36|publisher=Oxford University Press}}</ref><ref name="Thein (2009)">{{cite web|last=Thein|first=M.|title=Elektrische Maschinen in Kraftfahrzeugen |trans_title=Electric Machines in Motor Vehicles|language=German|url=http://www.fh-zwickau.de/mbk/kfz_ee/praesentationen/Elma-Gndl-Generator%20-%20Druckversion.pdf|accessdate=13 February 2013}}</ref><ref>{{cite book|url=http://www.uni-regensburg.de/Fakultaeten/phil_Fak_I/Philosophie/Wissenschaftsgeschichte/Termine/E-Maschinen-Lexikon/Chronologie.htm
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| |title=Elektrisiermaschinen im 18. und 19. Jahrhundert – Ein kleines Lexikon ''("Electrical machinery in the 18th and 19th centuries – a small thesaurus")''
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| |chapter=Elektrische Chronologie|date=March 31, 2004|accessdate=August 23, 2010|publisher=[[University of Regensburg]]|language=German}}</ref><ref>{{cite web|url=http://www.mpoweruk.com/history.htm|title=History of Batteries (inter alia)|accessdate=August 23, 2010
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| |date=June 9, 2010|publisher=Electropaedia}}</ref><ref name="Electropaedia (home)">{{cite web|title=Battery and Energy Technologies, Technology and Applications Timeline|url=http://www.mpoweruk.com/timeline.htm|accessdate=13 February 2013}}</ref>
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| ===Success with DC motors===
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| The first commutator DC electric motor capable of turning machinery was invented by the British scientist [[William Sturgeon]] in 1832.<ref>{{cite book|last=Gee|first=William|others=|title=Oxford Dictionary of National Biography|publisher=Oxford University Press|year=2004|chapter=Sturgeon, William (1783–1850)|doi=10.1093/ref:odnb/26748 }}</ref> Following Sturgeon's work, a commutator-type direct-current electric motor made with the intention of commercial use was built by the American inventor [[Thomas Davenport (inventor)|Thomas Davenport]], which he patented in 1837. The motors ran at up to 600 revolutions per minute, and powered machine tools and a printing press.<ref name="Garrison (1998)">{{cite book|last=Garrison|first=Ervan G.|title=A History of Engineering and Technology: Artful Methods|year=1998|url=http://books.google.ca/books/about/A_History_of_Engineering_and_Technology.html?id=5mvVElGudyYC&redir_esc=y|publisher=CRC Press|isbn=0-8493-9810-X|edition=2nd|accessdate=May 7, 2009</}}</ref> Due to the high cost of [[battery (electricity)|primary battery power]], the motors were commercially unsuccessful and Davenport went bankrupt. Several inventors followed Sturgeon in the development of DC motors but all encountered the same battery power cost issues. No electricity distribution had been developed at the time. Like Sturgeon's motor, there was no practical commercial market for these motors.<ref name="Nye (1990)">{{cite book |title= Electrifying America: Social Meanings of a New Technology|last=Nye |first=David E.|url=http://mitpress.mit.edu/books/electrifying-america |year=1990 |publisher= The MIT Press|isbn=978-0-262-64030-5|ref=harv}}</ref>
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| In 1855, Jedlik built a device using similar principles to those used in his electromagnetic self-rotors that was capable of useful work.<ref name="Guillemin (1891)"/><ref name="Electropaedia (home)" /> He built a model [[electric vehicle]] that same year.<ref name="Hungarianscience (Frankfurt)">{{cite web|title=Exhibition on the History of Hungarian Science|url=http://www.frankfurt.matav.hu/angol/magytud.htm|accessdate=13 February 2013}}</ref>
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| The first commercially successful DC motors followed the invention by [[Zénobe Gramme]] who had in 1871 developed the anchor ring dynamo which solved the double-T armature pulsating DC problem. In 1873, Gramme found that this dynamo could be used as a motor, which he demonstrated to great effect at exhibitions in Vienna and Philadelphia by connecting two such DC motors at a distance of up to 2 km away from each other, one as a generator.<ref name="gamme">{{cite conference|url=http://www.invent.org/hall_of_fame/270.html|title=Zénobe Théophile Gramme|accessdate=2012-09-19|booktitle=Invent Now, Inc. Hall of Fame profile.}}</ref> (See also [[:fr:Hippolyte Fontaine#1873 : l'expérience décisive|1873 : l'expérience décisive [Decisive Workaround] ]].)
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| In 1886, [[Frank Julian Sprague]] invented the first practical DC motor, a non-sparking motor that maintained relatively constant speed under variable loads. Other Sprague electric inventions about this time greatly improved grid electric distribution (prior work done while employed by [[Thomas Edison]]), allowed power from electric motors to be returned to the electric grid, provided for electric distribution to trolleys via overhead wires and the trolley pole, and provided controls systems for electric operations. This allowed Sprague to use electric motors to invent the first electric trolley system in 1887–88 in Richmond VA, the electric elevator and control system in 1892, and the electric subway with independently powered centrally controlled cars, which were first installed in 1892 in Chicago by the South Side Elevated Railway where it became popularly known as the "L". Sprague's motor and related inventions led to an explosion of interest and use in electric motors for industry, while almost simultaneously another great inventor was developing its primary competitor, which would become much more widespread.
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| The development of electric motors of acceptable efficiency was delayed for several decades by failure to recognize the extreme importance of a relatively small air gap between rotor and stator. Efficient designs have a comparatively small air gap.<ref name="Ganot (1881)">
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| {{cite book
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| |last=Ganot
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| |first=Adolphe
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| |title=Elementatry Treatise in Physics
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| |url=http://archive.org/details/elementarytreati00ganorich
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| |coauthors=Trans. and ed. from the French by E. Atkinson
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| |edition=14th
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| |pages=907–908, sec. 899<!-- Details inconsistent, there's no Fig. 888 {{Page needed|date=February 2013}} -->
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| |year=1881
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| |publisher=William Wood and Co.}}</ref>
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| {{efn|Ganot provides a superb illustration of one such early electric motor designed by Froment.<ref name="Ganot (1881)"/>}}
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| The St. Louis motor, long used in classrooms to illustrate motor principles, is extremely inefficient for the same reason, as well as appearing nothing like a modern motor.<ref>{{cite web|url=http://www.physics.umd.edu/lecdem/services/demos/demosk4/k4-21.gif |title=Photo of a traditional form of the St. Louis motor}}</ref>
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| Application of electric motors revolutionized industry. Industrial processes were no longer limited by power transmission using line shafts, belts, compressed air or hydraulic pressure. Instead every machine could be equipped with its own electric motor, providing easy control at the point of use, and improving power transmission efficiency. Electric motors applied in agriculture eliminated human and animal muscle power from such tasks as handling grain or pumping water. Household uses of electric motors reduced heavy labor in the home and made higher standards of convenience, comfort and safety possible. Today, electric motors stand for more than half of the electric energy consumption in the US.<ref>{{cite web|url=http://www1.eere.energy.gov/industry/bestpractices/pdfs/mc-0382.pdf|title=Buying an Energy-Efficient Electric Motor - Fact Sheet|publisher=USDoE}}</ref>
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| ===Emergence of AC motors===
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| In 1824, the French physicist [[François Arago]] formulated the existence of [[rotating magnetic field]]s, termed [[Arago's rotations]], which, by manually turning switches on and off, Walter Baily demonstrated in 1879 as in effect the first primitive [[induction motor]].<ref name="Babbage (1825)">{{cite journal|last=Babbage|first=C.|coauthors=Herschel, J. F. W.|title=Account of the Repetition of M. Arago's Experiments on the Magnetism Manifested by Various Substances during the Act of Rotation|journal=Philosophical Transactions of the Royal Society|volume=115|issue=0|pages=467–496|doi=10.1098/rstl.1825.0023|url=http://archive.org/stream/philtrans03806447/03806447#page/n0/mode/2up|accessdate=2 December 2012|date=Jan 1825}}</ref><ref name="Thompson (1895)">{{cite book|last=[[Silvanus Phillips Thompson|Thompson]]|first=Silvanus Phillips|title=Polyphase Electric Currents and Alternate-Current Motors|year=1895|publisher=E. & F.N. Spon|page=261|location=London|url=http://archive.org/stream/polyphaseelectri00thomuoft#page/n5/mode/2up|accessdate=2 December 2012|edition=1st}}</ref>
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| <ref name="Bailey (1879)">{{Cite journal|first=Walter|last=Baily|url=http://books.google.com/books?id=85AOAAAAIAAJ&pg=PA286&lpg=PA286|title= A Mode of Producing Arago's Rotation|date= June 28, 1879|journal=Philosophical magazine: A journal of theoretical, experimental and applied physics| publisher=Taylor & Francis}}</ref><ref name="Vuckovic">{{cite journal|last=Vučković|first=Vladan|journal=The Serbian Journal of Electrical Engineers|title=Interpretation of a Discovery|date=November 2006|volume=3|issue=2|url=http://www.doiserbia.nb.rs/img/doi/1451-4869/2006/1451-48690603202V.pdf|accessdate=10 February 2013}}</ref>
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| In the 1880s, many inventors were trying to develop workable AC motors<ref name="Jonnes (2004)"/> because AC's advantages in long distance high voltage transmission were counterbalanced by the inability to operate motors on AC. Practical rotating AC induction motors were independently invented by [[Galileo Ferraris]] and [[Nikola Tesla]], a working motor model having been demonstrated by the former in 1885 and by the latter in 1887. In 1888, the ''Royal Academy of Science of Turin'' published Ferraris's research detailing the foundations of motor operation while however concluding that "the apparatus based on that principle could not be of any commercial importance as motor."<ref name="Vuckovic"/><ref name="Ferraris (1888)">{{cite journal|last=Ferraris|first=G.|book=Atti della Reale Academia delle Science di Torino|journal=Atti della R. Academia delle Science di Torino|year=1888|volume=XXIII|pages=360–375}}</ref><ref name="TFI (now)">{{cite web|last=The Case Files: Nikola Tesla|title=Two-Phase Induction Motor|url=http://www.fi.edu/learn/case-files/tesla/motor.html|publisher=The Franklin Institute|accessdate=2 December 2012}}</ref><ref>{{cite web|title=Galileo Ferraris Physicist, Pioneer of Alternating Current Systems (1847–1897) Inventor of the Induction Motor "Father of three-phase current" - Electrotechnical Congress, Frankfurt 1891|url=http://edisontechcenter.org/GalileoFerraris.html|publisher=Edison Tech Center|accessdate=3 July 2012}}</ref><ref name="Smil (2005)">{{Cite book|first=Vaclav|last= Smil|title=Creating the Twentieth Century:Technical Innovations of 1867–1914 and Their Lasting Impact|url=http://books.google.com/books?id=ZANP8uYlu1cC&pg=PA76|year=2005|publisher=Oxford University Press|isbn=978-0-19-988341-7|page=76}}</ref><ref name="Froehlich (1998)">{{Cite book|first=Fritz E.|last= Froehlich|coauthors=Kent, Allen|title=The Froehlich/Kent Encyclopedia of Telecommunications: Volume 17 - Television Technology|url=http://books.google.com/books?id=8j5bJ5OkGpgC&pg=PA37|accessdate=10 October 2012|date=1 December 1998|publisher=CRC Press|isbn=978-0-8247-2915-8|pages=37–}}</ref><ref name="Drury">{{cite book|url=http://books.google.com/books?id=vDQHzeEmSfUC&pg=PR14&lpg=PR14&dq=tesla+Ferraris+induction&source=bl&ots=SLjNT7Ui97&sig=Mvp66d6LH3KWUxrjdVBvFpl-lbY&hl=en&sa=X&ei=eGx3UNCXKLCB0QHH1YFA&ved=0CEgQ6AEwBTgU#v=onepage&q=tesla%20Ferraris%20induction&f=false|first= Bill|last= Drury|title= Control Techniques Drives and Controls Handbook|page= page xiv|year=2001|publisher=Institution of Electrical Engineers|isbn=978-0-85296-793-5}}</ref><ref name="Langsdorf (1955)">{{cite book|last=Langsdork|first=Alexander Suss |last=Langsdorf|title= Theory of Alternating-Current Machinery|year=1955|edition=2nd|page=245|url=http://books.google.ca/books/about/Theory_of_Alternating_Current_Machinery.html?id=zKVd780XHGcC&redir_esc=y|publisher=Tata McGraw-Hill|isbn=0-07-099423-4}}</ref><ref name="EAE (1977)">{{cite book|title=The Encyclopedia Americana| volume= 19|year= 1977|page=518}}</ref><ref name="Ferraris (EBE)">{{cite web |url=http://www.britannica.com/EBchecked/topic/204963/Galileo-Ferraris |title=Galileo Ferraris|publisher=Encyclopædia Britannica}}</ref><ref name="Biography of Galileo Ferraris">{{cite web |url=http://profiles.incredible-people.com/galileo-ferraris/|title=Biography of Galileo Ferraris|publisher=Incredible People - Biographies of Famous People}}</ref><ref name="Neidhofer (2007)">{{cite journal|last=Neidhöfer|first=Gerhard|title=Early Three-Phase Power (History)|journal=IEEE Power and Energy Magazine|volume=5|issue=5|pages=88–100|doi=10.1109/MPE.2007.904752|url=http://ieeexplore.ieee.org/xpl/articleDetails.jsp?tp=&arnumber=4295047&contentType=Journals+%26+Magazines&queryText%3Dearly+three-phase+power+winner+in+the+development+of+polyphase}}</ref><ref name="Pansini (1989)">{{cite book |title= Basic of Electric Motors |last= Pansini |first= Anthony J. |year=1989 |publisher=Pennwell Publishing Company |isbn=0-13-060070-9 |page=45 |url=http://books.google.it/books?id=CxQdC6xPFSwC&pg=PA45&lpg=PA45&dq=GALILEO+FERRARIS+AC+MOTOR+INVENTION&source=web&ots=jjeS-hcv2T&sig=cYbNfNNeVwvMIhR-JCP8uReedRU&hl=it&sa=X&oi=book_result&resnum=1&ct=result#v=onepage&q&f=false}}</ref> In 1888, Tesla presented his paper '''''A New System for Alternating Current Motors and Transformers''''' to the ''[[American Institute of Electrical Engineers|AIEE]]'' that described three patented two-phase four-stator-pole motor types: one with a four-pole rotor forming a non-self-starting [[reluctance motor]], another with a wound rotor forming a self-starting [[induction motor]], and the third a true [[synchronous motor]] with separately excited DC supply to rotor winding. One of the patents Tesla filed in 1887, however, also described a shorted-winding-rotor induction motor. [[George Westinghouse]] promptly bought Tesla's patents, employed Tesla to develop them, and assigned [[Charles F. Scott (engineer)|C. F. Scott]] to help Tesla, Tesla leaving for other pursuits in 1889.<ref name="Vuckovic"/><ref name="Drury"/><ref name="Ferraris (EBE)">{{cite web |url=http://www.britannica.com/EBchecked/topic/204963/Galileo-Ferraris |title=Galileo Ferraris|publisher=Encyclopædia Britannica}}</ref><ref name="Biography of Galileo Ferraris"/><ref name="Neidhofer (2007)">{{cite journal|last=Neidhöfer|first=Gerhard|title=Early Three-Phase Power (History)|journal=IEEE Power and Energy Magazine|volume=5|issue=5|pages=88–100|doi=10.1109/MPE.2007.904752|url=http://ieeexplore.ieee.org/xpl/articleDetails.jsp?tp=&arnumber=4295047&contentType=Journals+%26+Magazines&queryText%3Dearly+three-phase+power+winner+in+the+development+of+polyphase}}</ref><ref name="Pansini (1989)">{{cite book |title= Basic of Electric Motors |last= Pansini |first= Anthony J. |year=1989 |publisher=Pennwell Publishing Company |isbn=0-13-060070-9 |page=45 |url=http://books.google.it/books?id=CxQdC6xPFSwC&pg=PA45&lpg=PA45&dq=GALILEO+FERRARIS+AC+MOTOR+INVENTION&source=web&ots=jjeS-hcv2T&sig=cYbNfNNeVwvMIhR-JCP8uReedRU&hl=it&sa=X&oi=book_result&resnum=1&ct=result#v=onepage&q&f=false}}</ref><ref name="Alger (1976)"/><ref name="Alger (1976)">{{cite journal|last=Alger|first=P.L.|coauthors=Arnold, R.E.|title=The History of Induction Motors in America|journal=Proceedings of the IEEE|year=1976|volume=64|issue=9|pages=1380–1383|doi=10.1109/PROC.1976.10329|accessdate=1 December 2012}}</ref><ref name="Klooster (2009)">{{cite book|last=Klooster|first=John W.|title=Icons of Invention the Makers of the Modern World from Gutenberg to Gates.|publisher=ABC-CLIO|location=Santa Barbara|isbn=978-0-313-34744-3|url=http://books.google.com/books?id=WKuG-VIwID8C&pg=PA305&lpg=PA305&dq=tesla+hired+by+westinghouse&source=bl&ots=KDI0aTz0EK&sig=oct2jnPyWkQ3qvUR-JmstK9F0FI&hl=en&sa=X&ei=jRwxUKK3LtS80QHjxoGYAg&sqi=2&ved=0CEEQ6AEwAw#v=onepage&q=tesla%20hired%20by%20westinghouse&f=false|date=30 July 2009 |page=305|accessdate=10 September 2012}}</ref><ref name="Klooster (2009)">
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| {{Cite book
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| |url=http://books.google.com/books?id=WKuG-VIwID8C&pg=PA305&lpg=PA305&dq=tesla+hired+by+westinghouse&source=bl&ots=KDI0aTz0EK&sig=oct2jnPyWkQ3qvUR-JmstK9F0FI&hl=en&sa=X&ei=jRwxUKK3LtS80QHjxoGYAg&sqi=2&ved=0CEEQ6AEwAw#v=onepage&q=tesla%20hired%20by%20westinghouse&f=false |first=John W.|last= Klooster|title=Icons of Invention: The Makers of the Modern World from Gutenberg to Gates| page=305 |publisher=ABC-CLIO, LLC |year=2009 |accessdate=10 September 2012|isbn=978-0-313-34746-7}}</ref><ref name="Day (1996)">{{cite book|last=Day|first=Lance |title=Biographical Dictionary of the History of Technology|year=1996|publisher=Routledge|location=London|isbn=0-203-02829-5|coauthors=McNeil, Ian; (Editors)|page=1204|accessdate=2 December 2012|url=http://books.google.ca/books?id=n--ivouMng8C&pg=PA1204&lpg=PA1204&dq=tesla+induction+motor+patent&source=bl&ots=CwZdCXFBMs&sig=yHtXcB6ukl3dO26c73h884URzsI&hl=en&sa=X&ei=1VpOUKCPAaLv0gGb14HwAw&redir_esc=y#v=onepage&q=tesla%20induction%20motor%20patent&f=false}}</ref><ref name="Froehlich (1992)">{{cite book|last=Froehlich|first=Fritz E. Editor-in-Chief|coauthors=Allen Kent Co-Editor|title=The Froehlich/Kent Encyclopedia of Telecommunications: Volume 17 - Television Technology to Wire Antennas|year=1992|publisher=Marcel Dekker, Inc.|location=New York|isbn=0-8247-2902-1|url=http://www.amazon.com/Froehlich-Kent-Encyclopedia-Telecommunications-Television/dp/0824729153#reader_0824729153|edition=First|accessdate=2 December 2012|page=36}}</ref>
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| <ref name="TEE (1888)">{{cite book|last=The Electrical Engineer|year=21 Sep. 1888|title=... a new application of the AC in the production of rotary motion was made known almost simultaneously by two experimenters, Nikola Tesla and Galileo Ferraris, and the subject has attracted general attention from the fact that no commutator or connection of any kind with the armature was required ... |publisher=Charles & Co.|volume=Volume II|location=London|page=239|url=http://books.google.ca/books?id=_KvmAAAAMAAJ&pg=PA239&lpg=PA239&dq=The+electrical+engineer+1888+by+two+experimenters,+Nikola+Tesla+and+Galileo+Ferraris&source=bl&ots=O9MmzKi-0t&sig=GQS21Uaduwa2VUfA55rO7bx7LgM&hl=en&sa=X&ei=fdG6UMrVNImBywHy44AI&ved=0CE0Q6AEwBg#v=onepage&q=The%20electrical%20engineer%201888%20by%20two%20experimenters%2C%20Nikola%20Tesla%20and%20Galileo%20Ferraris&f=false}}</ref><ref name=Sravastava>{{cite journal|title=Electromagnetic Rotation with an Alternating Current|first=Galileo|last=Ferraris|journal=Electrican|volume=36|year=1885|pages=360–375}}</ref><ref name="Tesla (1888)">{{cite journal|last=Tesla|first=Nikola|coauthors=AIEE Trans.|pages=308–324|title=A New System for Alternating Current Motors and Transformers|journal=AIEE|year=1888|volume=5|url=http://www.tfcbooks.com/tesla/1888-05-16.htm|accessdate=17 December 2012}}</ref><ref name="Harris (web)">{{Cite web|last=Harris|first=William|url=http://science.howstuffworks.com/nikola-tesla2.htm| title=How Did Nikola Tesla Change the Way We Use Energy?| page=3 |publisher=Howstuffworks.com |year=2008 |accessdate=10 September 2012}}</ref> The constant speed AC induction motor was found not to be suitable for street cars<ref name="Jonnes (2004)">{{Cite book|first=Jill|last=Jonnes|title=Empires of Light: Edison, Tesla, Westinghouse, and the Race to Electrify the World|publisher=Random House|year=2004|page=180|url=http://books.google.com/books?id=2_58p3Z69bIC&pg=PT162&lpg=PT162&dq=tesla+%22motors+were+in+the+air%22&source=bl&ots=6T_6E2qmuT&sig=8YDP2sdzVB13V-KtO0xxdm0_Ae4&hl=en&sa=X&ei=lflNUMLUH6Tw0gHLlYCIDA&ved=0CC0Q6AEwAA#v=onepage&q=tesla%20%22motors%20were%20in%20the%20air%22&f=false}}</ref> but Westinghouse engineers successfully adapted it to power a mining operation in Telluride, Colorado in 1891.<ref name="Maddox (2003)">{{Cite book|first=D. M.|last=Mattox|title=The Foundations of Vacuum Coating Technology|publisher=Random House|year=2003|isbn=0-8155-1495-6|page=39|url=http://books.google.com/books?id=31O4upzTHQwC&pg=PA39&dq=In+1891+Telluride+westinghouse+induction+motor&hl=en&sa=X&ei=Qc3PUP-ZA--n0AHah4HwBA&sqi=2&ved=0CFMQ6AEwBA#v=onepage&q=In%201891%20Telluride%20westinghouse%20induction%20motor&f=false}}</ref><ref name="Hughes (1993)">{{cite book|first=Thomas Parke|last=Hughes|title=Networks of Power: Electrification in Western society, 1880–1930|publisher=Johns Hopkins University Press|page=117|isbn=0-8018-2873-2|url=http://books.google.com/books?id=g07Q9M4agp4C&pg=PA117&dq=Galileo+Ferraris+and+rotating+magnetic+field&hl=en&sa=X&ei=NMp0T_bXL6Gc2AXt7e3ODg&ved=0CDAQ6AEwAA#v=onepage&q=Galileo%20Ferraris%20and%20rotating%20magnetic%20field&f=false}}</ref><ref>{{cite web|title=Timeline of Nikola Tesla|url=http://www.teslasociety.org/timeline.html|publisher=Tesla Society of USA and Canada|accessdate=5 July 2012}}</ref> Steadfast in his promotion of three-phase development, [[Mikhail Dolivo-Dobrovolsky]] invented the three-phase cage-rotor induction motor in 1889 and the three-limb [[transformer]] in 1890. This type of motor is now used for the vast majority of commercial applications.<ref>{{cite book|last=Hubbell|first=M.W.|year=2011|title=The Fundamentals of Nuclear Power Generation Questions & Answers.|publisher=Authorhouse|isbn=978-1-4634-2441-1|url=http://www.amazon.com/Fundamentals-Nuclear-Power-Generation-Questions/dp/1463424418|page=27}}</ref><ref name="IEEE German Ch. (2012)">{{cite journal|last=VDE Committee History of Electrical Engineering IEEE German Chapter|title=150th Birthday of Michael von Dolivo-Dobrowolsky Colloquium|volume=13|date=January 2012|url=http://www.vde.com/de/fg/ETG/Arbeitsgebiete/Geschichte/Aktuelles/Seiten/150JMDD.aspx|accessdate=10 February 2013}}</ref> However, he claimed that Tesla's motor was not practical because of two-phase pulsations, which prompted him to persist in his three-phase work.<ref name="Dolivo-Dobrowolsky (1891)">{{cite journal|last=Dolivo-Dobrowolsky|first=M.|journal=ETZ|year=1891|volume=12|pages=149, 161}}</ref> Although Westinghouse achieved its first practical induction motor in 1892 and developed a line of polyphase 60 hertz induction motors in 1893, these early Westinghouse motors were [[two-phase electric power|two-phase motors]] with wound rotors until [[Benjamin G. Lamme|B. G. Lamme]] developed a rotating bar winding rotor.<ref name="Alger (1976)"/> The [[General Electric Company]] began developing three-phase induction motors in 1891.<ref name="Alger (1976)"/> By 1896, General Electric and Westinghouse signed a cross-licensing agreement for the bar-winding-rotor design, later called the [[squirrel-cage rotor]].<ref name="Alger (1976)"/> Induction motor improvements flowing from these inventions and innovations were such that a 100 [[horsepower|horsepower (HP)]] induction motor currently has the same mounting dimensions as a 7.5 HP motor in 1897.<ref name="Alger (1976)"/>
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| ==Motor construction==
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| [[File:Stator and rotor by Zureks.JPG|thumb|right|Electric motor rotor (left) and stator (right)]]
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| ===Rotor===
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| {{main|Rotor (electric)}}
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| In an electric motor the moving part is the '''rotor''' which turns the shaft to deliver the mechanical power. The rotor usually has conductors laid into it which carry currents that interact with the magnetic field of the stator to generate the forces that turn the shaft. However, some rotors carry permanent magnets, and the stator holds the conductors.
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| ===Stator===
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| {{main|Stator}}
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| The stationary part is the '''stator''', usually has either windings or permanent magnets.
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| ===Air gap===
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| In between the rotor and stator is the air gap. The air gap has important effects, and is generally as small as possible, as a large gap has a strong negative effect on the performance of an electric motor.
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| ===Windings===
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| {{main|Windings}}
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| Windings are wires that are laid in coils, usually wrapped around a laminated soft iron [[magnetic core]] so as to form magnetic poles when energised with current.
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| Electric machines come in two basic magnet field pole configurations: ''salient-pole'' machine and ''nonsalient-pole'' machine. In the salient-pole machine the pole's magnetic field is produced by a winding wound around the pole below the pole face. In the ''nonsalient-pole'', or distributed field, or round-rotor, machine, the winding is distributed in pole face slots.<ref name="Mortensen (1949)">{{cite conference|booktitle=Standard Handbook for Electrical Engineers|edition=8th|year=1949|title=§7-1 'General Picture of a Synchronous Machine' in Sec. 7 - Alternating-Current Generators and Motors|first=S. H.|last=Mortensen|coauthors=Beckwith, S.|publisher=McGraw-Hill|editor-last=Knowlton|editor-first=A.E.|page=646-647, figs. 7-1 & 7-2}}</ref> A [[shaded-pole motor]] has a winding around part of the pole that delays the phase of the magnetic field for that pole.
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| Some motors have conductors which consist of thicker metal, such as bars or sheets of metal, usually [[copper]], although sometimes [[aluminum]] is used. These are usually powered by [[electromagnetic induction]].
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| ===Commutator===
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| {{main|Commutator (electric)}}
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| [[File:Tiny motor windings - commutator - brushes in Zip Zaps toy R-C car.jpg|thumb| Toy's small DC motor with commutator.]]
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| A '''commutator''' is a mechanism used to [[switch]] the input of certain AC and DC machines consisting of [[slip ring]] segments insulated from each other and from the electric motor's shaft. The motor's armature current is supplied through the stationary [[brush (electric)|brushes]] in contact with the revolving commutator, which causes required current reversal and applies power to the machine in an optimal manner as the [[Rotor (electric)|rotor]] rotates from pole to pole.<ref>Hameyer, §5.1, p. 62</ref><ref>Lynn, §83, p. 812</ref> In absence of such current reversal, the motor would brake to a stop. In light of significant advances in the past few decades due to improved technologies in electronic controller, sensorless control, induction motor, and permanent magnet motor fields, electromechanically commutated motors are increasingly being displaced by externally commutated induction and permanent magnet motors.
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| ==Motor supply and control==
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| ===Motor supply===
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| A '''DC motor''' is usually supplied through slip ring commutator as described above. '''AC motors' ''' commutation can be either slip ring commutator or externally commutated type, can be fixed-speed or variable-speed control type, and can be ''synchronous'' or ''asynchronous'' type. ''[[#Universal motors|Universal motors]]'' can run on either AC or DC.
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| ===Motor control===
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| Fixed-speed controlled AC motors are provided with direct-on-line or soft-start starters.
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| Variable speed controlled AC motors are provided with a range of different [[power inverter]], [[variable-frequency drive]] or electronic commutator technologies.
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| The term electronic commutator is usually associated with self-commutated [[brushless DC electric motor|brushless DC motor]] and [[switched reluctance motor]] applications.
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| ==Major categories==
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| Electric motors operate on three different physical principles: [[magnetism|magnetic]], [[electrostatic motor|electrostatic]] and [[piezoelectric motor|piezoelectric]]. By far the most common is magnetic.
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| In magnetic motors, magnetic fields are formed in both the rotor and the stator. The product between these two fields gives rise to a force, and thus a torque on the motor shaft. One, or both, of these fields must be made to change with the rotation of the motor. This is done by switching the poles on and off at the right time, or varying the strength of the pole.
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| The main types are DC motors and AC motors, the former increasingly being displaced by the latter.
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| AC electric motors are either asynchronous and synchronous.
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| Once started, a synchronous motor requires synchronism with the moving magnetic field's synchronous speed for all normal torque conditions.
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| In synchronous machines, the magnetic field must be provided by means other than induction such as from separately excited windings or permanent magnets.
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| It is usual to distinguish motors' rated output power about the unity horsepower threshold so that integral horsepower refers to motor(s) equal to or above, and [[fractional horsepower motors|fractional horsepower (FHP)]] refers to motor(s) below, the threshold.
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| {| style="margin: 1em auto 1em auto;"
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| |+ align="center" style="background:#f0f0f0;" !!colspan="5"|'''Major Categories'''<br />
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| |+ align="center" style="background:#f0f0f0;" !!colspan="5"|'''by'''
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| |+ align="center" style="background:#f0f0f0;" !!colspan="5"|'''Type of Motor Commutation'''<br /><ref name=USDOEVSPGuide>{{cite web|title=Variable Speed Pumping, A Guide to Successful Applications, Executive Summary|url=http://www1.eere.energy.gov/industry/bestpractices/pdfs/variable_speed_pumping.pdf|publisher=USDOE - Europump - Hydraulic Institute|accessdate=Feb 19, 2018|page=9, Fig. ES-7|date=May 2004}}</ref><ref name="Bose (2006)">{{cite conference|last=Bose|first=Bimal K.|booktitle=Power Electronics and Motor Drives : Advances and Trends|title=Chapters 6, 7 & 8|year=2006|publisher=Academic Press|isbn=978-0-12-088405-6|pages=see esp. 328, 397, 481}}</ref><ref name="King (UA)">{{cite conference|last=Knight|first=Andy|url=http://www.ece.ualberta.ca/~knight/electrical_machines/fundamentals/f_main.html|accessdate=20 February 2013|title=Electric Machines|publisher=U. of Alberta}}</ref><ref name="Hameyer *2001)">{{cite web|last=Hameyer|first=Kay|title=Electrical Machine I: Basics, Design, Function, Operation|url=http://materialy.itc.pw.edu.pl/zpnis/electric_machines_I/ForStudents/Script_EMIHanneberger.pdf|publisher=RWTH Aachen University Institute of Electrical Machines|accessdate=11 January 2013|year=2001}}</ref><ref name="Stolting (2008)">{{cite conference|first=Hans-Dieter|last =Stölting|editor-first=H. D.|editor-last=Stölting|editor2-first=E.|editor2-last=Kallenbach|editor3-last=Amrhein|editor3-first=W. (eds.)|title=§1.3.1.1 Motor Systematics in Chapter 1 - Introduction|booktitle=Handbook of Fractional-Horsepower Drives|year=2008|publisher=Springer|isbn=978-3-540-73128-3|url=http://books.google.ca/books?id=VCHumncaeAAC&pg=PA134&lpg=PA134&dq=fractional+horsepower+ac+motor+comparison&source=bl&ots=6uqhzdi1HV&sig=DtSYJ-53rU_IRny-yDui5bv1b8c&hl=en&sa=X&ei=EUgkUdveN8eRiAL1hICAAg&sqi=2&ved=0CH4Q6AEwCQ#v=onepage&q=shaded-pole&f=false|edition=Online|page=see esp. p. 5, Table 1.1}}</ref><ref name="Ionel (2010)">{{cite conference|booktitle=12th International Conference on Optimization of Electrical and Electronic Equipment (OPTIM)|title=High-Efficiency Variable-Speed Electric Motor Drive Technologies for Energy Savings in the US Residential Sector |last=Ionel|publisher=IEEE|first=D.M.|year=2010|doi=10.1109/OPTIM.2010.5510481|pages=1403–1414}}</ref>
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| |-
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| ! colspan="3" align="center" style="background:#f0f0f0;" |Self-Commutated
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| ! colspan="2" align="center" style="background:#f0f0f0;" |Externally Commutated
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| |-
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| ! colspan="2" align="center" style="background:#f0f0f0;" |Mechanical-<br />Commutator Motors
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| ! align="center" style="background:#f0f0f0;" |Electronic-<br />Commutator (EC)<br />Motors<ref name="Ionel (2010)"/>{{efn|The term 'electronic commutator motor' (ECM) is identified with the heating, ventilation and air-conditioning (HVAC) industry, the distinction between BLDC and BLAC being in this context seen as a function of degree of ECM drive complexity with BLDC drives typically being with simple single-phase [[scalar (mathematics)|scalar-controlled]] voltage-regulated trapezoidal current waveform output involving surface PM motor construction and BLAC drives tending towards more complex three-phase [[vector control (motor)|vector-controlled]] current-regulated sinusoidal waveform involving interior PM motor construction.<ref name="Ionel (2010)"/>}}
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| ! align="center" style="background:#f0f0f0;" |<br />Asynchronous<br />Machines
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| ! align="center" style="background:#f0f0f0;" |<br />Synchronous<br />Machines[[#CharacterizatioNote2|<sup>2</sup>]]
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| |-
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| ! align="center" style="background:#f0f0f0;" |AC<ref name="Alger (1949b)">{{cite conference|booktitle=Standard Handbook for Electrical Engineers|edition=8th|year=1949|title=§274-§287 'AC Commutator Motors' sub-section of Sec. 7 - Alternating-Current Generators and Motors|first=Philip L. et al.|last=Alger|publisher=McGraw-Hill|editor-last=Knowlton|editor-first=A.E.|pages=755–763}}</ref>{{efn|The universal and repulsion motors are part of a class of motors known as AC commutator motors, which also includes the following now largely obsolete motor types: Single-phase - straight and compensated series motors, railway motor; three-phase - various repulsion motor types, brush-shifting series motor, brush-shifting polyphase shunt or Schrage motor, Fynn-Weichsel motor.<ref name="Alger (1949b)"/>}} ||style="background:#f0f0f0;"|[[Brushed DC electric motor|DC]]||style="background:#f0f0f0;"|AC[[#CharacterizatioNote5|<sup>5</sup>]]<sup>, </sup>[[#CharacterizatioNote6|<sup>6</sup>]]||colspan="2" style="background:#f0f0f0;"|AC[[#CharacterizatioNote6|<sup>6</sup>]]
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| ! align="left" style="background: #ffdead;"|* [[Universal motor]]<br /> (AC commutator<br /> series motor<ref name="Stolting (2008)"/> or<br /> AC/DC motor<ref name="Hameyer *2001)"/>)[[#CharacterizatioNote1|<sup>1</sup>]]<br />* [[Repulsion motor]]|| align="left" style="background: #ffdead;"|Electrically<br />excited DC motor:<br />* Separately <br />excited<br />* Series<br />* Shunt<br />* Compound<br /><br />PM DC motor|| align="left" style="background: #ffdead;"|With PM rotor:<br />* [[Brushless DC motor|BLDC motor]]<br /><br />With<br />ferromagnetic<br />rotor:<br />* [[Switched reluctance motor|SRM]]<br />|| align="left" style="background: #ffdead;"|Three-phase motors:<br />* [[Induction motor|SCIM]][[#CharacterizatioNote3|<sup>3</sup>]]<sup>, </sup>[[#CharacterizatioNote8|<sup>8</SUP>]]<br />* [[Wound rotor motor|WRIM]][[#CharacterizatioNote4|<sup>4</sup>]]<sup>, </sup>[[#CharacterizatioNote7|<sup>7</sup>]]<Sup>, </sup>[[#CharacterizatioNote8|<sup>8</SUP>]] <br /><br />AC motors:[[#CharacterizatioNote10|<sup>10</SUP>]]<br />* Capacitor<br />* Resistance<br />* Split<br />* [[Shaded-pole motor|Shaded-pole]]|| align="left" style="background: #ffdead;"|Three-phase motors:<br />[[Synchronous motor|* WRSM]]<br />* [[Permanent magnet synchronous motor|PMSM]] or<br />[[brushless AC electric motor|BLAC motor]]<ref name="Ionel (2010)"/><br />- IPMSM<br/>- SPMSM<br />* Hybrid<br /><br />AC motors:[[#CharacterizatioNote10|<sup>10</SUP>]]<br />* Permanent-split<br /> capacitor<br />* Hysteresis<br />* [[Stepper motor|Stepper]]<br />* [[Reluctance motor|SyRM]]<br />* SyRM-PM hybrid
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| ! align="center" style="background:#f0f0f0;" |Simple electronics
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| ! align="center" style="background:#f0f0f0;" |Rectifier,<br />linear transistor(s)<br /> or DC chopper
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| ! align="center" style="background:#f0f0f0;" |More elaborate<br />electronics
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| ! colspan="2" align="center" style="background:#f0f0f0;" |Most elaborate<br />electronics ([[variable-frequency drive|VFD]]), when provided
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| |}
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| Notes:
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| # <span id="CharacterizatioNote1">Rotation is independent of the frequency of the AC voltage.</span>
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| # <span id="CharacterizatioNote2">Rotation is equal to synchronous speed (motor stator field speed).</span>
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| # <span id="CharacterizatioNote3">In SCIM fixed-speed operation rotation is equal to slip speed (synchronous speed less slip).</span>
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| # <span id="CharacterizatioNote4">In non-slip energy recovery systems WRIM is usually used for motor starting but can be used to vary load speed.</span>
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| # <span id="CharacterizatioNote5">Variable-speed operation.</span>
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| # <span id="CharacterizatioNote6">Whereas induction and synchronous motor drives are typically with either six-step or sinusoidal waveform output, BLDC motor drives are usually with trapezoidal current waveform; the behavior of both sinusoidal and trapezoidal PM machines is however identical in terms of their fundamental aspects.<ref name="Krishnan (2008)">{{cite book|last=Krishnan|first=R.|title=Permanent Magnet Synchronous and Brushless DC Motor Drives|year=2008|publisher=CRC|isbn=978-0-8247-5384-9|page=xvii|url=http://books.google.ca/books?id=U-RxikH3aXEC&pg=PA378&lpg=PA378&dq=Ionel,+D.M&source=bl&ots=3dMK2uR8Nx&sig=NN3mUqDsWms5wXNVMc7bQjjxFZE&hl=en&sa=X&ei=o2QyUdSJN-jXiAL7q4G4Cg&ved=0CDsQ6AEwAzgK#v=onepage&q&f=false}}</ref></span>
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| # <span id="CharacterizatioNote7">In variable-speed operation WRIM is used in slip energy recovery and double-fed induction machine applications.</span>
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| # <span id="CharacterizatioNote8">Cage winding refers to shorted-circuited squirrel-cage rotor, wound winding being connected externally through slip rings.</span>
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| # <span id="CharacterizatioNote8">Mostly single-phase with some three-phase.</span>
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| Abbreviations:
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| *BLAC - [[Brushless AC electric motor|Brushless AC]]
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| *BLDC - [[Brushless DC electric motor|Brushless DC]]
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| *BLDM - Brushless DC motor
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| *EC - Electronic commutator
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| *PM - [[Permanent magnet]]
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| *IPMSM - Interior permanent magnet synchronous motor
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| *PMSM - [[Permanent magnet synchronous motor]]
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| *SPMSM - Surface permanent magnet synchronous motor
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| *SCIM - [[Squirrel-cage rotor|Squirrel-cage]] [[induction motor]]
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| *SRM - [[Switched reluctance motor]]
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| *SyRM - [[Reluctance motor|Synchronous reluctance motor]]
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| *VFD - [[Variable-frequency drive]]
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| *WRIM - [[Wound rotor motor|Wound-rotor]] [[induction motor]]
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| *WRSM - [[Synchronous motor|Wound-rotor synchronous motor]]
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| ==Self-commutated motor==
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| ===Brushed DC motor===
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| {{main|DC motor}}
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| All self-commutated DC motors are by definition run on DC electric power. Most DC motors are small PM types. They contain a [[Brush (electric)|brushed]] internal mechanical commutation to reverse motor windings' current in synchronism with rotation.<ref name="Weiβmantel (2008)">{{cite conference|first=H|last =Weiβmantel|coauthors=Oesingmann, P.; Möckel, A.|editor-first=H. D.|editor-last=Stölting|editor2-first=E.|editor2-last=Kallenbach|editor3-last=Amrhein|editor3-first=W. (eds.)|title=§2.1 Motors with Commutator in Chapter 2 - Motors with Continuous Rotation|booktitle=Handbook of Fractional-Horsepower Drives|year=2008|publisher=Springer|isbn=978-3-540-73128-3|url=http://books.google.ca/books?id=VCHumncaeAAC&pg=PA134&lpg=PA134&dq=fractional+horsepower+ac+motor+comparison&source=bl&ots=6uqhzdi1HV&sig=DtSYJ-53rU_IRny-yDui5bv1b8c&hl=en&sa=X&ei=EUgkUdveN8eRiAL1hICAAg&sqi=2&ved=0CH4Q6AEwCQ#v=onepage&q=shaded-pole&f=false|edition=Online|pages=13–160}}</ref>
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| ====Electrically excited DC motor====
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| {{Main|Brushed DC electric motor}}
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| [[File:Electric motor cycle 2.png|thumb|right|200px|Workings of a brushed electric motor with a two-pole rotor and PM stator. ("N" and "S" designate polarities on the inside faces of the magnets; the outside faces have opposite polarities.)]]
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| A commutated DC motor has a set of rotating windings wound on an [[Armature (electrical engineering)|armature]] mounted on a rotating shaft. The shaft also carries the commutator, a long-lasting rotary electrical switch that periodically reverses the flow of current in the rotor windings as the shaft rotates. Thus, every brushed DC motor has AC flowing through its rotating windings. Current flows through one or more pairs of brushes that bear on the commutator; the brushes connect an external source of electric power to the rotating armature.
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| The rotating armature consists of one or more coils of wire wound around a laminated, [[soft magnetic material|magnetically "soft"]] ferromagnetic core. Current from the brushes flows through the commutator and one winding of the armature, making it a temporary magnet (an [[electromagnet]]). The magnets field produced by the armature interacts with a stationary magnetic field produced by either PMs or another winding a field coil, as part of the motor frame. The force between the two magnetic fields tends to rotate the motor shaft. The commutator switches power to the coils as the rotor turns, keeping the magnetic poles of the rotor from ever fully aligning with the magnetic poles of the stator field, so that the rotor never stops (like a compass needle does), but rather keeps rotating as long as power is applied.
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| Many of the limitations of the classic commutator DC motor are due to the need for brushes to press against the commutator. This creates friction. Sparks are created by the brushes making and breaking circuits through the rotor coils as the brushes cross the insulating gaps between commutator sections. Depending on the commutator design, this may include the brushes shorting together adjacent sections – and hence coil ends – momentarily while crossing the gaps. Furthermore, the [[inductance]] of the rotor coils causes the voltage across each to rise when its circuit is opened, increasing the sparking of the brushes. This sparking limits the maximum speed of the machine, as too-rapid sparking will overheat, erode, or even melt the commutator. The current density per unit area of the brushes, in combination with their [[resistivity]], limits the output of the motor. The making and breaking of electric contact also generates [[electrical noise]]; sparking generates [[Radio frequency interference|RFI]]. Brushes eventually wear out and require replacement, and the commutator itself is subject to wear and maintenance (on larger motors) or replacement (on small motors). The commutator assembly on a large motor is a costly element, requiring precision assembly of many parts. On small motors, the commutator is usually permanently integrated into the rotor, so replacing it usually requires replacing the whole rotor.
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| While most commutators are cylindrical, some are flat discs consisting of several segments (typically, at least three) mounted on an insulator.
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| Large brushes are desired for a larger brush contact area to maximize motor output, but small brushes are desired for low mass to maximize the speed at which the motor can run without the brushes excessively bouncing and sparking. (Small brushes are also desirable for lower cost.) Stiffer brush springs can also be used to make brushes of a given mass work at a higher speed, but at the cost of greater friction losses (lower efficiency) and accelerated brush and commutator wear. Therefore, DC motor brush design entails a trade-off between output power, speed, and efficiency/wear.
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| DC machines are defined as follows:<ref name="Dorf (1997)">{{cite conference|editor-last=Dorf|editor-first=Richard C. (editor-in-chief)|last=Liu|first=Chen-Ching et al.|booktitle=The Electrical Engineering Handbook|year=1997|title=§66.1 'Generators' in Chapter 66 - 'Electric Machines' of Section 6 - 'Energy'|publisher=CRC Press|isbn=0-8493-8574-1|url=http://books.google.ca/books?id=qP7HvuakLgEC&pg=PA1456&lpg=PA1456&dq=origin+of+electrical+term+armature&source=bl&ots=X0qY0ZGjJ1&sig=KSL5I8XwKUrXVAlQ6fsf8jxNhWI&hl=en&sa=X&ei=oBogUYiACsShiQLxi4Ew&ved=0CEwQ6AEwBQ#v=onepage&q=origin%20of%20electrical%20term%20armature&f=false|edition=3rd|page=1456}}</ref>
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| *Armature circuit - A winding where the load current is carried, such that can be either stationary or rotating part of motor or generator.
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| *Field circuit - A set of windings that produces a magnetic field so that the electromagnetic induction can take place in electric machines.
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| *Commutation: A mechanical technique in which rectification can be achieved, or from which DC can be derived, in DC machines.
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| [[File:Serie Shunt Coumpound.svg|thumb|300px|A: shunt B: series C: compound f = field coil]]
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| There are five types of brushed DC motor:
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| * DC shunt-wound motor
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| * DC series-wound motor
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| * DC compound motor (two configurations):
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| ** Cumulative compound
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| ** Differentially compounded
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| * PM DC motor (not shown)
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| * Separately excited (not shown).
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| ====Permanent magnet DC motor====
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| {{main|Permanent-magnet electric motor}}
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| A PM motor does not have a field winding on the stator frame, instead relying on PMs to provide the magnetic field against which the rotor field interacts to produce torque. Compensating windings in series with the armature may be used on large motors to improve commutation under load. Because this field is fixed, it cannot be adjusted for speed control. PM fields (stators) are convenient in miniature motors to eliminate the power consumption of the field winding. Most larger DC motors are of the "dynamo" type, which have stator windings. Historically, PMs could not be made to retain high flux if they were disassembled; field windings were more practical to obtain the needed amount of flux. However, large PMs are costly, as well as dangerous and difficult to assemble; this favors wound fields for large machines.
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| To minimize overall weight and size, miniature PM motors may use high energy magnets made with [[neodymium]] or other strategic elements; most such are neodymium-iron-boron alloy. With their higher flux density, electric machines with high-energy PMs are at least competitive with all optimally designed [[#Singly fed electric motor|singly fed]] synchronous and induction electric machines. Miniature motors resemble the structure in the illustration, except that they have at least three rotor poles (to ensure starting, regardless of rotor position) and their outer housing is a steel tube that magnetically links the exteriors of the curved field magnets.
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| ===Electronic commutator (EC) motor===
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| ====Brushless DC motor====
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| {{Main|Brushless DC electric motor}}
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| Some of the problems of the brushed DC motor are eliminated in the BLDC design. In this motor, the mechanical "rotating switch" or commutator is replaced by an external electronic switch synchronised to the rotor's position. BLDC motors are typically 85–90% efficient or more. Efficiency for a BLDC motor of up to 96.5% have been reported,<ref name="Nozawa (2009)">{{cite web|last=Nozawa| first=Tetsuo (2009)|title=Tokai University Unveils 100W DC Motor with 96% Efficiency|url=http://techon.nikkeibp.co.jp/english/NEWS_EN/20090403/168295/|publisher=Tech-On -- Nikkei Electronics}}</ref> whereas DC motors with brushgear are typically 75–80% efficient.
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| The BLDC motor's characteristic trapezoidal back-emf waveform is derived partly from stator the stator windings being evenly distributed, partly from the placement of the rotor's PMs. Also known as electronically commutated DC or inside out DC motors, the stator windings of trapezoidal BLDC motors can be with single-phase, two-phase or three-phase and use [[Hall effect sensor]]s mounted on their windings for rotor position sensing and crude, low cost [[closed-loop controller|closed-loop control]] of the electronic commutator.
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| BLDC motors are commonly used where precise speed control is necessary, as in computer disk drives or in video cassette recorders, the spindles within CD, CD-ROM (etc.) drives, and mechanisms within office products such as fans, laser printers and photocopiers. They have several advantages over conventional motors:
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| * Compared to AC fans using shaded-pole motors, they are very efficient, running much cooler than the equivalent AC motors. This cool operation leads to much-improved life of the fan's bearings.
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| * Without a commutator to wear out, the life of a BLDC motor can be significantly longer compared to a DC motor using brushes and a commutator. Commutation also tends to cause a great deal of electrical and RF noise; without a commutator or brushes, a BLDC motor may be used in electrically sensitive devices like audio equipment or computers.
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| * The same Hall effect sensors that provide the commutation can also provide a convenient [[tachometer]] signal for closed-loop control (servo-controlled) applications. In fans, the tachometer signal can be used to derive a "fan OK" signal as well as provide running speed feedback.
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| * The motor can be easily synchronized to an internal or external clock, leading to precise speed control.
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| * BLDC motors have no chance of sparking, unlike brushed motors, making them better suited to environments with volatile chemicals and fuels. Also, sparking generates ozone which can accumulate in poorly ventilated buildings risking harm to occupants' health.
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| * BLDC motors are usually used in small equipment such as computers and are generally used in fans to get rid of unwanted heat.
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| * They are also acoustically very quiet motors which is an advantage if being used in equipment that is affected by vibrations.
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| Modern BLDC motors range in power from a fraction of a watt to many kilowatts. Larger BLDC motors up to about 100 kW rating are used in electric vehicles. They also find significant use in high-performance electric model aircraft.
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| ====Switched reluctance motor====
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| [[File:Switched reluctance motor 6-4.svg|thumb|right|6/4 pole switched reluctance motor]]
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| {{Main|Switched reluctance motor}}
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| The SRM has no brushes or PMs, and the rotor has no electric currents.
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| Instead, torque comes from a slight misalignment of poles on the rotor with poles on the stator.
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| The rotor aligns itself with the magnetic field of the stator, while the stator field stator windings are sequentially energized to rotate the stator field.
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| The magnetic flux created by the field windings follows the path of least magnetic reluctance, meaning the flux will flow through poles of the rotor that are closest to the energized poles of the stator, thereby magnetizing those poles of the rotor and creating torque. As the rotor turns, different windings will be energized, keeping the rotor turning.
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| SRMs are now being used in some appliances.<ref name="Bush (2009)">{{cite web|last=Bush |first=Steve (2009)|title=Dyson vacuums 104,000 rpm brushless DC technology|url=http://www.electronicsweekly.com/Articles/13/08/2010/46377/dyson-vacuums-104000rpm-brushless-dc-technology.htm|publisher=Electronics Weekly Magazine}}</ref>
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| ===Universal AC-DC motor===
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| {{main|Universal motor}}
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| [[File:Universalmotor 3.JPG|thumb|Modern low-cost universal motor, from a vacuum cleaner. Field windings are dark copper-colored, toward the back, on both sides. The rotor's laminated core is gray metallic, with dark slots for winding the coils. The commutator (partly hidden) has become dark from use; it is toward the front. The large brown molded-plastic piece in the foreground supports the brush guides and brushes (both sides), as well as the front motor bearing.]]
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| A commutated electrically excited series or parallel wound motor is referred to as a universal motor because it can be designed to operate on both AC and DC power. A universal motor can operate well on AC because the current in both the field and the armature coils (and hence the resultant magnetic fields) will alternate (reverse polarity) in synchronism, and hence the resulting mechanical force will occur in a constant direction of rotation.
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| Operating at normal [[utility frequency|power line frequencies]], universal motors are often found in a range less than {{nowrap|1000 watts}}. Universal motors also formed the basis of the traditional railway traction motor in [[Railway electrification system#Low-frequency alternating current|electric railways]]. In this application, the use of AC to power a motor originally designed to run on DC would lead to efficiency losses due to [[eddy current]] heating of their magnetic components, particularly the motor field pole-pieces that, for DC, would have used solid (un-laminated) iron and they are now rarely used.
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| An advantage of the universal motor is that AC supplies may be used on motors which have some characteristics more common in DC motors, specifically high starting torque and very compact design if high running speeds are used. The negative aspect is the maintenance and short life problems caused by the commutator. Such motors are used in devices such as food mixers and power tools which are used only intermittently, and often have high starting-torque demands. Multiple taps on the field coil provide (imprecise) stepped speed control. Household blenders that advertise many speeds frequently combine a field coil with several taps and a diode that can be inserted in series with the motor (causing the motor to run on half-wave rectified AC). Universal motors also lend themselves to [[TRIAC#Application|electronic speed control]] and, as such, are an ideal choice for devices like domestic washing machines. The motor can be used to agitate the drum (both forwards and in reverse) by switching the field winding with respect to the armature.
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| Whereas SCIMs cannot turn a shaft faster than allowed by the power line frequency, universal motors can run at much higher speeds. This makes them useful for appliances such as blenders, vacuum cleaners, and hair dryers where high speed and light weight are desirable. They are also commonly used in portable power tools, such as drills, sanders, circular and jig saws, where the motor's characteristics work well. Many vacuum cleaner and weed trimmer motors exceed {{nowrap|10,000 rpm}}, while many similar miniature grinders exceed {{nowrap|30,000 rpm}}.
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| ==Externally commutated AC machine==
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| {{Main|AC motor}}
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| The design of AC induction and synchronous motors is optimized for operation on single-phase or polyphase sinusoidal or quasi-sinusoidal waveform power such as supplied for fixed-speed application from the AC power grid or for variable-speed application from VFD controllers. An AC motor has two parts: a stationary stator having coils supplied with AC to produce a rotating magnetic field, and a rotor attached to the output shaft that is given a torque by the rotating field.
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| ===Induction motor===
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| {{Main|Induction motor}}
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| ====Cage and wound rotor induction motor====
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| An induction motor is an asynchronous AC motor where power is transferred to the rotor by electromagnetic induction, much like transformer action. An induction motor resembles a rotating transformer, because the stator (stationary part) is essentially the primary side of the transformer and the rotor (rotating part) is the secondary side. Polyphase induction motors are widely used in industry.
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| Induction motors may be further divided into SCIMs and WRIMs. SCIMs have a heavy winding made up of solid bars, usually aluminum or copper, joined by rings at the ends of the rotor. When one considers only the bars and rings as a whole, they are much like an animal's rotating exercise cage, hence the name.
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| Currents induced into this winding provide the rotor magnetic field. The shape of the rotor bars determines the speed-torque characteristics. At low speeds, the current induced in the squirrel cage is nearly at line frequency and tends to be in the outer parts of the rotor cage. As the motor accelerates, the slip frequency becomes lower, and more current is in the interior of the winding. By shaping the bars to change the resistance of the winding portions in the interior and outer parts of the cage, effectively a variable resistance is inserted in the rotor circuit. However, the majority of such motors have uniform bars.
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| In a WRIM, the rotor winding is made of many turns of insulated wire and is connected to [[slip ring]]s on the motor shaft. An external resistor or other control devices can be connected in the rotor circuit. Resistors allow control of the motor speed, although significant power is dissipated in the external resistance. A converter can be fed from the rotor circuit and return the slip-frequency power that would otherwise be wasted back into the power system through an inverter or separate motor-generator.
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| The WRIM is used primarily to start a high inertia load or a load that requires a very high starting torque across the full speed range. By correctly selecting the resistors used in the secondary resistance or slip ring starter, the motor is able to produce maximum torque at a relatively low supply current from zero speed to full speed. This type of motor also offers controllable speed.
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| Motor speed can be changed because the torque curve of the motor is effectively modified by the amount of resistance connected to the rotor circuit. Increasing the value of resistance will move the speed of maximum torque down. If the resistance connected to the rotor is increased beyond the point where the maximum torque occurs at zero speed, the torque will be further reduced.
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| When used with a load that has a torque curve that increases with speed, the motor will operate at the speed where the torque developed by the motor is equal to the load torque. Reducing the load will cause the motor to speed up, and increasing the load will cause the motor to slow down until the load and motor torque are equal. Operated in this manner, the slip losses are dissipated in the secondary resistors and can be very significant. The speed regulation and net efficiency is also very poor.
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| ====Torque motor====
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| {{main|Torque motor}}
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| A torque motor is a specialized form of electric motor which can operate indefinitely while stalled, that is, with the rotor blocked from turning, without incurring damage. In this mode of operation, the motor will apply a steady torque to the load (hence the name).
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| A common application of a torque motor would be the supply- and take-up reel motors in a tape drive. In this application, driven from a low voltage, the characteristics of these motors allow a relatively constant light tension to be applied to the tape whether or not the capstan is feeding tape past the tape heads. Driven from a higher voltage, (and so delivering a higher torque), the torque motors can also achieve fast-forward and rewind operation without requiring any additional mechanics such as gears or clutches. In the computer gaming world, torque motors are used in force feedback steering wheels.
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| Another common application is the control of the throttle of an internal combustion engine in conjunction with an electronic governor. In this usage, the motor works against a return spring to move the throttle in accordance with the output of the governor. The latter monitors engine speed by counting electrical pulses from the ignition system or from a magnetic pickup and, depending on the speed, makes small adjustments to the amount of current applied to the motor. If the engine starts to slow down relative to the desired speed, the current will be increased, the motor will develop more torque, pulling against the return spring and opening the throttle. Should the engine run too fast, the governor will reduce the current being applied to the motor, causing the return spring to pull back and close the throttle.
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| ===Synchronous motor===
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| {{Main|Synchronous motor}}
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| A synchronous electric motor is an AC motor distinguished by a rotor spinning with coils passing magnets at the same rate as the AC and resulting magnetic field which drives it. Another way of saying this is that it has zero slip under usual operating conditions. Contrast this with an induction motor, which must slip to produce torque. One type of synchronous motor is like an induction motor except the rotor is excited by a DC field. Slip rings and brushes are used to conduct current to the rotor. The rotor poles connect to each other and move at the same speed hence the name synchronous motor. Another type, for low load torque, has flats ground onto a conventional squirrel-cage rotor to create discrete poles. Yet another, such as made by Hammond for its pre-World War II clocks, and in the older Hammond organs, has no rotor windings and discrete poles. It is not self-starting. The clock requires manual starting by a small knob on the back, while the older Hammond organs had an auxiliary starting motor connected by a spring-loaded manually operated switch.
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| Finally, hysteresis synchronous motors typically are (essentially) two-phase motors with a phase-shifting capacitor for one phase. They start like induction motors, but when slip rate decreases sufficiently, the rotor (a smooth cylinder) becomes temporarily magnetized. Its distributed poles make it act like a PMSM. The rotor material, like that of a common nail, will stay magnetized, but can also be demagnetized with little difficulty. Once running, the rotor poles stay in place; they do not drift.
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| Low-power synchronous timing motors (such as those for traditional electric clocks) may have multi-pole PM external cup rotors, and use shading coils to provide starting torque. ''Telechron'' clock motors have shaded poles for starting torque, and a two-spoke ring rotor that performs like a discrete two-pole rotor.
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| ===Doubly fed electric machine===
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| {{Main|Doubly fed electric machine}}
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| [[Doubly fed electric machine|Doubly fed electric motors]] have two independent multiphase winding sets, which contribute active (i.e., working) power to the energy conversion process, with at least one of the winding sets electronically controlled for variable speed operation. Two independent multiphase winding sets (i.e., dual armature) are the maximum provided in a single package without topology duplication. Doubly fed electric motors are machines with an effective constant torque speed range that is twice synchronous speed for a given frequency of excitation. This is twice the constant torque speed range as [[singly fed electric machine]]s, which have only one active winding set.
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| A doubly fed motor allows for a smaller electronic converter but the cost of the rotor winding and slip rings may offset the saving in the power electronics components. Difficulties with controlling speed near synchronous speed limit applications.<ref name="Lander (1993)">{{cite conference|last=Lander|first=Cyril W.|title=§9–8 'Slip Ring Induction Motor Control' in Chapter 9 - A.C. Machine Control|booktitle=Power electronics|year=1993|publisher=McGraw-Hill 480 pages|isbn=0-07-707714-8|edition=3rd}}</ref>
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| ==Special magnetic motors==
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| ===Rotary===
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| ====Hydraulic cylinder displacement====
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| Electric motors are replacing hydraulic cylinders in airplanes and military equipment.<ref name="Briere (1993)">{{cite conference|last=Briere|first=D.|coauthors=Traverse, P.|date=22–24 June 1993|url=http://personales.upv.es/juaruiga/teaching/TFC/Material/Trabajos/AIRBUS.PDF|pages=616–623|doi=10.1109/FTCS.1993.627364|title=Airbus A320/A330/A340 electrical flight controls - A family of fault-tolerant systems |booktitle=FTCS-23}}</ref><ref name="North (2000)">{{cite journal|last=North|first=David|date=Aug 28, 2000|title=Finding Common Ground in Envelope Protection Systems|journal=Aviation Week & Space Technology|pages=66–68|volume=153|issue=9|url=http://connection.ebscohost.com/c/articles/3624448/finding-common-ground-envelope-protection-systems}}</ref>
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| ====Ironless or coreless rotor motor====
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| [[File:Miniature Coreless DC Motor.jpg|thumb|A Miniature Coreless Motor]]
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| Nothing in the principle of any of the motors described above requires that the iron (steel) portions of the rotor actually rotate. If the soft magnetic material of the rotor is made in the form of a cylinder, then (except for the effect of hysteresis) torque is exerted only on the windings of the electromagnets. Taking advantage of this fact is the ''coreless or ironless DC motor'', a specialized form of a PM DC motor.<ref name="Weiβmantel (2008)"/> Optimized for rapid [[acceleration]], these motors have a rotor that is constructed without any iron core. The rotor can take the form of a winding-filled cylinder, or a self-supporting structure comprising only the magnet wire and the bonding material. The rotor can fit inside the stator magnets; a magnetically soft stationary cylinder inside the rotor provides a return path for the stator magnetic flux. A second arrangement has the rotor winding basket surrounding the stator magnets. In that design, the rotor fits inside a magnetically soft cylinder that can serve as the housing for the motor, and likewise provides a return path for the flux.
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| Because the rotor is much lighter in weight (mass) than a conventional rotor formed from copper windings on steel laminations, the rotor can accelerate much more rapidly, often achieving a mechanical [[time constant]] under one ms. This is especially true if the windings use aluminum rather than the heavier copper. But because there is no metal mass in the rotor to act as a heat sink, even small coreless motors must often be cooled by forced air. Overheating might be an issue for coreless DC motor designs.
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| Among these types are the disc-rotor types, described in more detail in the next section.
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| Vibrator motors for cellular phones are sometimes tiny cylindrical PM field types, but there are also disc-shaped types which have a thin multipolar disc field magnet, and an intentionally unbalanced molded-plastic rotor structure with two bonded coreless coils. Metal brushes and a flat commutator switch power to the rotor coils.
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| Related limited-travel actuators have no core and a bonded coil placed between the poles of high-flux thin PMs. These are the fast head positioners for rigid-disk ("hard disk") drives. Although the contemporary design differs considerably from that of loudspeakers, it is still loosely (and incorrectly) referred to as a "voice coil" structure, because some earlier rigid-disk-drive heads moved in straight lines, and had a drive structure much like that of a loudspeaker.
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| ====Pancake or axial rotor motor====
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| A rather unusual motor design, the printed armature or pancake motor has the windings shaped as a disc running between arrays of high-flux magnets. The magnets are arranged in a circle facing the rotor with space in between to form an axial air gap.<ref name="Krishnan (1987)">{{cite journal|last=Krishnan|first=R.|title=Selection Criteria for Servo Motor Drives|journal=IEEE Transactions on Industry Applications|date=March 1987|volume=IA-23|issue=2|pages=270–275|doi=10.1109/TIA.1987.4504902|url=http://ieeexplore.ieee.org/xpl/articleDetails.jsp?tp=&arnumber=4504902&contentType=Journals+%26+Magazines&sortType%3Ddesc_p_Publication_Year%26searchField%3DSearch_All%26queryText%3Dpancake+DC+motor|accessdate=26 February 2013}}</ref> This design is commonly known as the pancake motor because of its extremely flat profile, although the technology has had many brand names since its inception, such as ServoDisc.
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| The printed armature (originally formed on a printed circuit board) in a printed armature motor is made from punched copper sheets that are laminated together using advanced composites to form a thin rigid disc. The printed armature has a unique construction in the brushed motor world in that it does not have a separate ring commutator. The brushes run directly on the armature surface making the whole design very compact.
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| An alternative manufacturing method is to use wound copper wire laid flat with a central conventional commutator, in a flower and petal shape. The windings are typically stabilized by being impregnated with electrical epoxy potting systems. These are filled epoxies that have moderate mixed viscosity and a long gel time. They are highlighted by low shrinkage and low exotherm, and are typically UL 1446 recognized as a potting compound insulated with 180°C, Class H rating.
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| The unique advantage of ironless DC motors is that there is no [[Cogging torque|cogging]] (torque variations caused by changing attraction between the iron and the magnets). Parasitic eddy currents cannot form in the rotor as it is totally ironless, although iron rotors are laminated. This can greatly improve efficiency, but variable-speed controllers must use a higher switching rate (>40 kHz) or DC because of the decreased [[electromagnetic induction]].
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| These motors were originally invented to drive the capstan(s) of magnetic tape drives in the burgeoning computer industry, where minimal time to reach operating speed and minimal stopping distance were critical. Pancake motors are still widely used in high-performance servo-controlled systems, robotic systems, industrial automation and medical devices. Due to the variety of constructions now available, the technology is used in applications from high temperature military to low cost pump and basic servos.
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| ====Servo motor====
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| {{Main|Servo motor}}
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| A servomotor is a motor, very often sold as a complete module, which is used within a position-control or speed-control feedback control system mainly control valves, such as motor operated control valves. Servomotors are used in applications such as machine tools, pen plotters, and other process systems. Motors intended for use in a servomechanism must have well-documented characteristics for speed, torque, and power. The speed vs. torque curve is quite important and is high ratio for a servo motor. Dynamic response characteristics such as winding inductance and rotor inertia are also important; these factors limit the overall performance of the servomechanism loop. Large, powerful, but slow-responding servo loops may use conventional AC or DC motors and drive systems with position or speed feedback on the motor. As dynamic response requirements increase, more specialized motor designs such as coreless motors are used. AC motors' superior power density and acceleration characteristics compared to that of DC motors tends to favor PM synchronous, BLDC, induction, and SRM drive applications.<ref name="Krishnan (1987)"/>
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| A servo system differs from some stepper motor applications in that the position feedback is continuous while the motor is running; a stepper system relies on the motor not to "miss steps" for short term accuracy, although a stepper system may include a "home" switch or other element to provide long-term stability of control.<ref name="Patrick (1997)">{{cite conference|last=Patrick|first=Dale R.|coauthors=Fardo, Stephen W.|booktitle=Rotating Electrical Machines and Power Systems|edition=2nd|year=1997|publisher=Fairmont Press, Inc.|isbn=978-0-88173-239-9|title=Chapter 11}}</ref> For instance, when a typical dot matrix computer printer starts up, its controller makes the print head stepper motor drive to its left-hand limit, where a position sensor defines home position and stops stepping. As long as power is on, a bidirectional counter in the printer's microprocessor keeps track of print-head position.
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| ====Stepper motor====
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| {{Main|Stepper motor}}
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| [[File:Stepper motor.svg|thumb|A stepper motor with a soft iron rotor, with active windings shown. In 'A' the active windings tend to hold the rotor in position. In 'B' a different set of windings are carrying a current, which generates torque and rotation.]]
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| Stepper motors are a type of motor frequently used when precise rotations are required. In a stepper motor an internal rotor containing PMs or a magnetically soft rotor with salient poles is controlled by a set of external magnets that are switched electronically. A stepper motor may also be thought of as a cross between a DC electric motor and a rotary solenoid. As each coil is energized in turn, the rotor aligns itself with the magnetic field produced by the energized field winding. Unlike a synchronous motor, in its application, the stepper motor may not rotate continuously; instead, it "steps"—starts and then quickly stops again—from one position to the next as field windings are energized and de-energized in sequence. Depending on the sequence, the rotor may turn forwards or backwards, and it may change direction, stop, speed up or slow down arbitrarily at any time.
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| Simple stepper motor drivers entirely energize or entirely de-energize the field windings, leading the rotor to "cog" to a limited number of positions; more sophisticated drivers can proportionally control the power to the field windings, allowing the rotors to position between the cog points and thereby rotate extremely smoothly. This mode of operation is often called [[stepper motor#Microstepping|microstepping]]. Computer controlled stepper motors are one of the most versatile forms of positioning systems, particularly when part of a digital [[servomechanism|servo-controlled]] system.
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| Stepper motors can be rotated to a specific angle in discrete steps with ease, and hence stepper motors are used for read/write head positioning in computer floppy diskette drives. They were used for the same purpose in pre-gigabyte era computer disk drives, where the precision and speed they offered was adequate for the correct positioning of the read/write head of a hard disk drive. As drive density increased, the precision and speed limitations of stepper motors made them obsolete for hard drives—the precision limitation made them unusable, and the speed limitation made them uncompetitive—thus newer hard disk drives use voice coil-based head actuator systems. (The term "voice coil" in this connection is historic; it refers to the structure in a typical (cone type) loudspeaker. This structure was used for a while to position the heads. Modern drives have a pivoted coil mount; the coil swings back and forth, something like a blade of a rotating fan. Nevertheless, like a voice coil, modern actuator coil conductors (the magnet wire) move perpendicular to the magnetic lines of force.)
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| Stepper motors were and still are often used in computer printers, optical scanners, and digital photocopiers to move the optical scanning element, the print head carriage (of dot matrix and inkjet printers), and the platen or feed rollers. Likewise, many computer plotters (which since the early 1990s have been replaced with large-format inkjet and laser printers) used rotary stepper motors for pen and platen movement; the typical alternatives here were either linear stepper motors or servomotors with closed-loop analog control systems.
| |
| | |
| So-called quartz analog wristwatches contain the smallest commonplace stepping motors; they have one coil, draw very little power, and have a PM rotor. The same kind of motor drives battery-powered quartz clocks. Some of these watches, such as chronographs, contain more than one stepping motor.
| |
| | |
| Closely related in design to three-phase AC synchronous motors, stepper motors and SRMs are classified as variable reluctance motor type.<ref name="Bose, pp. 569-570">Bose, pp. 569–570, 891</ref> Stepper motors were and still are often used in computer printers, optical scanners, and [[Numerical control|computer numerical control (CNC)]] machines such as routers, plasma cutters and CNC lathes.
| |
| | |
| ===Linear motor===
| |
| {{Main|Linear motor}}
| |
| A linear motor is essentially any electric motor that has been "unrolled" so that, instead of producing a [[torque]] (rotation), it produces a straight-line force along its length.
| |
| | |
| Linear motors are most commonly [[linear induction motor|induction motors]] or stepper motors. Linear motors are commonly found in many roller-coasters where the rapid motion of the motorless railcar is controlled by the rail. They are also used in [[maglev train]]s, where the train "flies" over the ground. On a smaller scale, the 1978 era HP 7225A pen plotter used two linear stepper motors to move the pen along the X and Y axes.<ref>{{cite journal|last=Fenoglio|first=John A.|coauthors=Chin, Bessie W. C. ; Cobb, Terry R.|title=A High-Quality Digital X-Y Plotter Designed for Reliability, Flexibility and Low Cost|url=http://www.hpl.hp.com/hpjournal/pdfs/IssuePDFs/1979-02.pdf|journal=Hewlett-Packard Journal|date=February 1979|accessdate=9 February 2012}}</ref>
| |
| | |
| ==Comparison by major categories==
| |
| {| class="wikitable"
| |
| |+ Comparison of motor types
| |
| |-
| |
| ! Type
| |
| ! Advantages
| |
| ! Disadvantages
| |
| ! Typical application
| |
| ! Typical drive, output
| |
| |-
| |
| ! align="center" style="background:##ffdead;" colspan="5"|Self-commutated motors
| |
| |-
| |
| | [[Brushed DC electric motor|Brushed DC]]
| |
| | Simple speed control
| |
| | Maintenance (brushes)<br />Medium lifespan <br /> Costly commutator and brushes
| |
| | Steel mills <br /> Paper making machines <br /> Treadmill exercisers<br />Automotive accessories
| |
| | Rectifier, linear transistor(s) or DC chopper controller.<ref name="Stölting p. 9">Stölting, p. 9</ref>
| |
| |-
| |
| | [[Brushless DC electric motor|Brushless<br />DC motor<br />(BLDC)<br />or<br />(BLDM)]]
| |
| | Long lifespan<br />Low maintenance<br />High efficiency
| |
| | Higher initial cost<br />Requires EC controller with closed-loop control
| |
| | Rigid ("hard") disk drives<br />CD/DVD players<br />Electric vehicles <br /> RC Vehicles <br /> UAVs
| |
| | Synchronous; single-phase or three-phase with PM rotor and trapezoidal stator winding; VFD typically [[voltage source|VS]] [[Pulse-width modulation|PWM]] inverter type.<ref name="Krishnan (1987)"/><ref name="Stölting p. 9"/><ref name="Bose, pp. 480-481"/>
| |
| |-
| |
| | [[Switched reluctance motor|Switched<br />reluctance<br />motor<br />(SRM)]]
| |
| | Long lifespan<br />Low maintenance<br />High efficiency<br />No permanent magnets<br />Low cost<br />Simple construction
| |
| | Mechanical resonance<br />possible<br />High iron losses<br />Not possible:<br />* Open or vector control<br />* Parallel operation<br />Requires EC controller<ref name="Bose, pp. 569-570">Bose, pp. 569–570, 891</ref>
| |
| | Appliances<br />Electric Vehicles<br />Textile mills<br />Aircraft applications
| |
| | PWM and various other drive types, which tend to be used in very specialized / [[OEM]] applications.<ref name="Bose, pp. 569-570"/><ref name="Vukosavic (1991)">{{cite journal|last=Vukosavic|first=Slobodan|coauthors=Stefanovic, Victor R.|title=SRM Inverter Topologies: A Comparative Evaluation|journal=IEEE Trans. on Industry Applications|date=Nov–Dec 1991|volume=27|issue=6|pages=1034–1047|doi=10.1109/IAS.1990.152299}}</ref>
| |
| |-
| |
| | [[Universal motor]]
| |
| | High starting torque, compact, high speed.
| |
| | Maintenance (brushes)<br />Shorter lifespan <br />Usually acoustically noisy <br />Only small ratings are economical
| |
| | Handheld power tools, blenders, vacuum cleaners, insulation blowers
| |
| | Variable single phase AC, half-wave or full-wave phase-angle control with triac(s); closed-loop control optional.<ref name="Stölting p. 9"/>
| |
| |-
| |
| ! align="center" style="background:##ffdead;" colspan="5"|AC asynchronous motors
| |
| |-
| |
| | AC polyphase<br />squirrel-cage<br />or<br />wound-rotor<br />[[induction motor]]<br />(SCIM)<br />or<br />(WRIM)
| |
| | Self-starting<br />Low cost<br />Robust<br />Reliable<br />Ratings to 1+ MW<br />Standardized types.
| |
| | High starting current<br />Lower efficiency<br />due to need<br /> for magnetization.
| |
| | Fixed-speed, traditionally, SCIM the world's workhorse especially in low performance applications of all types<br />Variable-speed, traditionally, low-performance variable-torque pumps, fans, blowers and compressors. <br />Variable-speed, increasingly, other high-performance constant-torque and constant-power or dynamic loads.
| |
| | Fixed-speed, low performance applications of all types.<br />Variable-speed, traditionally, WRIM drives or fixed-speed V/Hz-controlled VSDs.<br />Variable-speed, increasingly, [[vector control (motor)|vector-controlled]] VSDs displacing DC, WRIM and single-phase AC induction motor drives.
| |
| |-
| |
| | AC SCIM<br />split-phase<br />capacitor-start
| |
| | High power<br />high starting torque
| |
| | Speed slightly below synchronous <br /> Starting switch or relay required
| |
| | Appliances<br />Stationary Power Tools
| |
| | rowspan="4" align="left"| Fixed or variable single-phase AC, variable speed being derived, typically, by full-wave phase-angle control with triac(s); closed-loop control optional.<ref name="Stölting p. 9">Stölting, p. 9</ref>
| |
| |-
| |
| | AC SCIM<br />split-phase<br />capacitor-run
| |
| | Moderate power<br />High starting torque<br /> No starting switch<br />Comparatively long life
| |
| | Speed slightly below synchronous<br />Slightly more costly
| |
| | Industrial blowers<br />Industrial machinery
| |
| |-
| |
| | AC SCIM<br />split-phase,<br />auxiliary<br />start winding
| |
| | Moderate power<br />Low starting torque
| |
| | Speed slightly below synchronous <br /> Starting switch or relay required
| |
| | Appliances<br />Stationary power tools
| |
| |-
| |
| | AC induction [[Shaded-pole motor|shaded-pole]]<br />motor
| |
| | Low cost<br />Long life<br />
| |
| | Speed slightly below synchronous <br />Low starting torque <br /> Small ratings <br /> low efficiency
| |
| | Fans, appliances, record players
| |
| |-
| |
| ! align="center" style="background:##ffdead;" colspan="5"|AC synchronous motors
| |
| |-
| |
| | [[Synchronous motor|Wound-rotor<br />synchronous<br />motor]]<br />(WRSM)
| |
| | Synchronous speed<br />Inherently<br />more efficient<br />induction motor,<br />low power factor
| |
| | More costly
| |
| | Industrial motors
| |
| | Fixed or variable speed, three-phase; VFD typically six-step [[current source|CS]] load-commutated inverter type or [[voltage source|VS]] PWM inverter type.<ref name="Stölting p. 9"/><ref name="Bose, pp. 480-481">Bose, pp. 480–481</ref>
| |
| |-
| |
| | [[AC motor#Hysteresis synchronous motor|Hysteresis<br />motor]]
| |
| | Accurate speed control<br />Low noise<br />No vibration<br />High starting<br /> torque
| |
| | Very low efficiency
| |
| | Clocks, timers, sound producing or recording equipment, hard drive, capstan drive
| |
| | Single-phase AC, two-phase capacitor-start, capacitor run motor<ref name="Roters (1947)">{{cite journal|last=Roters|first=Herbert C.|title=The hysteresis motor - Advances which permit economical fractional horsepower ratings|journal=Trans. AIEE|date=Jan 1947|volume=66|issue=1|pages=1419–1430|doi=10.1109/T-AIEE.1947.5059594}}</ref><ref name=Bakshi>{{cite conference|last=Bakshi|first=U. A.|booktitle=Electrical Machines - II|publisher=Technical Publications Pune|isbn=81-8431-189-3|edition=4th|year=2009|title=§9.3 'Hysteresis Motors' in Chapter 9 - Special Machines|coauthors=Bakshi, M. V.|url=http://books.google.ca/books?id=tG9LqKd2x2IC&pg=SA9-PA5&lpg=SA9-PA5&dq=hysteresis+motor+application&source=bl&ots=n8jJlfrSjI&sig=fonmxgJc-tckVlNYm9fE0df60eI&hl=en&sa=X&ei=EEApUb6gGYL5igKpl4DICA&sqi=2&ved=0CH4Q6AEwDg#v=onepage&q=hysteresis%20motor%20application&f=false}}</ref>
| |
| |-
| |
| | [[Reluctance motor|Synchronous<br />reluctance<br />motor<br />(SyRM)]]
| |
| | Equivalent to SCIM<br />except more robust, more efficient, runs cooler, smaller footprint<br />Competes with PM synchronous motor without demagnetization issues
| |
| | Requires a controller<br />Not widely available<br />High cost
| |
| | Appliances<br />Electric vehicles<br />Textile mills<br />Aircraft applications
| |
| | VFD can be standard [[Direct torque control|DTC]] type or [[voltage source|VS]] inverter PWM type.<ref name="Motoring Ahead 1/11">{{cite web|last=Lendenmann|first=Heinz et al.|title=Motoring Ahead|url=http://www.lead-central.com/AssetManager/02427e68-6f15-4f3a-9749-d37abf613741/Documents/APW2012/Low%20Voltage%20Drives%20Motors/ABB-136_WPO_Motoring%20ahead.pdf|accessdate=Apr 18, 2012}}</ref>
| |
| |-
| |
| ! align="center" style="background:##ffdead;" colspan="5"|Speciality motors
| |
| |-
| |
| | [[Electric motor#Pancake or axial rotor motor|Pancake<br />or axial<br />rotor<br />motors]]<ref name="Krishnan (1987)"/>
| |
| | Compact design<br />Simple speed control
| |
| | Medium cost<br />Medium lifespan
| |
| | Office Equip<br />Fans/Pumps, fast industrial and military servos
| |
| | Drives can typically be brushed or brushless DC type.<ref name="Krishnan (1987)"/>
| |
| |-
| |
| | [[Stepper motor|Stepper]]<br />motor
| |
| | Precision positioning<br />High holding torque
| |
| | Some can be costly<br />Require a controller
| |
| | Positioning in printers and floppy disc drives; industrial machine tools
| |
| | Not a VFD. Stepper position is determined by pulse counting.<ref>Stölting, p. 10</ref><ref>Bose, p. 389</ref>
| |
| |}
| |
| | |
| ==Electromagnetism==
| |
| {{expand section|date=March 2013}}
| |
| | |
| ===Force and torque===
| |
| The fundamental purpose of the vast majority of the world's electric motors is to electromagnetically induce relative movement in an air gap between a stator and rotor to produce useful torque or linear force.
| |
| | |
| According [[Lorentz force law#Force on a current-carrying wire|Lorentz force law]] the force of a winding conductor can be given simply by:
| |
| :<math>\mathbf{F} = I \boldsymbol{\ell} \times \mathbf{B} \,\!</math>
| |
| or more generally, to handle conductors with any geometry:
| |
| :<math>\mathbf{F} = \mathbf{J} \times \mathbf{B}</math>
| |
| The most general approaches to calculating the forces in motors use tensors.<ref name="Kirtley (2005)">{{cite conference|last=Kirtley|first=James L., Jr.|booktitle=6.6585 - Electric Machines|title=Class Notes 1: Electromagnetic Forces|publisher=MIT Dept of Electrical Engineering|accessdate=15 March 2013|url=http://web.mit.edu/course/6/6.685/www/chapter1.pdf|year=2005}}</ref>
| |
| | |
| ===Power===
| |
| Where [[rpm]] is shaft speed and T is [[torque]], a motor's mechanical power output P<sub>em</sub> is given by,<ref>{{cite web|url = http://zone.ni.com/devzone/cda/ph/p/id/46|title = DC Motor Calculations, part 1|date = 30 November 2011|publisher = National Instruments|accessdate = 7 December 2012}}</ref>
| |
| | |
| in British units with T expressed in foot-pounds,
| |
| :<math>P_{em} = \frac {rpm \times T}{5252}</math> (horsepower), and,
| |
| in [[International System of Units|SI units]] with shaft speed expressed in radians per second, and T expressed in newton-meters,
| |
| :<math>P_{em} = {speed \times T}</math> (watts).
| |
| | |
| For a linear motor, with force F and velocity v expressed in newtons and meters per second,
| |
| :<math>P_{em} = F\times{v}</math> (watts).
| |
| | |
| In an asynchronous or induction motor, the relationship between motor speed and air gap power is, neglecting [[skin effect]], given by the following:
| |
| :<math>P_{airgap}=\frac{R_r}{s} * I_r^{2}</math>, where
| |
| ::R<sub>r</sub> - rotor resistance
| |
| ::I<sub>r</sub><sup>2</sup> - square of current induced in the rotor
| |
| ::s - motor slip; ie, difference between synchronous speed and slip speed, which provides the relative movement needed for current induction in the rotor.
| |
| | |
| ===Back emf===
| |
| {{Main|Electromotive force}}
| |
| Since the armature windings of a direct-current motor are moving through a magnetic field, they have a voltage induced in them. This voltage tends to oppose the motor supply voltage and so is called "[[electromotive force|back electromotive force (emf)]]". The voltage is proportional to the running speed of the motor. The back emf of the motor, plus the voltage drop across the winding internal resistance and brushes, must equal the voltage at the brushes. This provides the fundamental mechanism of speed regulation in a DC motor. If the mechanical load increases, the motor slows down; a lower back emf results, and more current is drawn from the supply. This increased current provides the additional torque to balance the new load.<ref name="Dwight (1949)">{{cite conference|booktitle=Standard Handbook for Electrical Engineers|edition=8th|year=1949|title= §27 to §35A Electromagnetic Induction of EMF in Sec. 2 - Electric and Magnetic Circuits|first=Herbert B.|last=Dwight|coauthors=Fink, D. G.|publisher=McGraw-Hill|editor-last=Knowlton|editor-first=A.E.|pages=36–41}}</ref>
| |
| | |
| In AC machines, it is sometimes useful to consider a back emf source within the machine; this is of particular concern for close speed regulation of induction motors on VFDs, for example.<ref name="Dwight (1949)"/>
| |
| | |
| ===Losses===
| |
| Motor losses are mainly due to [[resistance heating|resistive losses]] in windings, core losses and mechanical losses in bearings, and aerodynamic losses, particularly where cooling fans are present, also occur.
| |
| | |
| Losses also occur in commutation, mechanical commutators spark, and electronic commutators and also dissipate heat.
| |
| | |
| ===Efficiency===
| |
| To calculate a motor's efficiency, the mechanical output power is divided by the electrical input power:
| |
| :<math>\eta = \frac{P_m}{P_e}</math>,
| |
| where <math>\eta</math> is [[energy conversion efficiency]], <math>P_e</math> is electrical input power, and <math>P_m</math> is mechanical output power:
| |
| | |
| :<math>P_e = I V</math>
| |
| | |
| :<math>P_m = T \omega</math>
| |
| where <math>V</math> is input voltage, <math>I</math> is input current, <math>T</math> is output torque, and <math>\omega</math> is output angular velocity. It is possible to derive analytically the point of maximum efficiency. It is typically at less than 1/2 the [[stall torque]].{{citation needed|date=September 2013}}
| |
| | |
| Various regulatory authorities in many countries have introduced and implemented legislation to encourage the manufacture and use of higher efficiency electric motors. There is existing and forthcoming legislation regarding the future mandatory use of premium-efficiency induction-type motors in defined equipment. ''For more information, see: [[Premium efficiency]] and [[Copper in energy efficient motors]].''
| |
| | |
| ===Goodness factor===
| |
| {{main|Goodness factor}}
| |
| Professor [[Eric Laithwaite]]<ref name=Laithwaite>{{cite journal|last=Laithwaite|first=E.R.|title=Linear electric machines - A personal view|journal=Proceedings of the IEEE|date=Feb 1975|volume=63|issue=2|pages=250–290|doi=10.1109/PROC.1975.9734|url=http://ieeexplore.ieee.org/xpl/articleDetails.jsp?tp=&arnumber=1451664&contentType=Journals+%26+Magazines&queryText%3DLinear+Electric+Machines-+A+Personal+View}}</ref> proposed a metric to determine the 'goodness' of an electric motor:<ref name="Patterson (2003)">{{cite conference|title=The "Goodness" of Small Contemporary Permanent Magnet Electric Machines|last=Patterson|first=D. J.|coauthors= Brice, C. W.;Dougal, R. A.; Kovuri, D.|url=http://vtb.engr.sc.edu/vtbwebsite/downloads/publications/IEMDCpaper.pdf|doi=10.1109/IEMDC.2003.1210392|booktile=Electric Machines and Drives Conference, 2003. IEMDC'03|publisher=IEEE|volume=vol. 2|pages=1195–1200|date=1–4 June 2003}}</ref>
| |
| <math>G = \frac {\omega} {resistance \times reluctance} = \frac {\omega \mu \sigma A_m A_e} {l_m l_e}</math>
| |
| | |
| Where:
| |
| :<math>G</math> is the goodness factor (factors above 1 are likely to be efficient)
| |
| :<math>A_m, A_e</math> are the cross sections of the magnetic and electric circuit
| |
| :<math>l_m, l_e</math> are the lengths of the magnetic and electric circuits
| |
| :<math>\mu</math> is the permeability of the core
| |
| :<math>\omega</math> is the angular frequency the motor is driven at
| |
| | |
| From this, he showed that the most efficient motors are likely to have relatively large magnetic poles. However, the equation only directly relates to non PM motors.
| |
| | |
| ==Performance parameters==
| |
| | |
| ===Torque capability of motor types===
| |
| {{context|section|date=March 2013}}
| |
| {{generalize|section|date=March 2013}}
| |
| {{POV-section|date=March 2013}}
| |
| When optimally designed within a given core saturation constraint and for a given active current (i.e., torque current), voltage, pole-pair number, excitation frequency (i.e., synchronous speed), and air-gap flux density, all categories of electric motors or generators will exhibit virtually the same maximum continuous shaft torque (i.e., operating torque) within a given air-gap area with winding slots and back-iron depth, which determines the physical size of electromagnetic core. Some applications require bursts of torque beyond the maximum operating torque, such as short bursts of torque to accelerate an electric vehicle from standstill. Always limited by [[Saturation (magnetic)|magnetic core saturation]] or safe [[operating temperature]] rise and voltage, the capacity for torque bursts beyond the maximum operating torque differs significantly between categories of electric motors or generators.
| |
| | |
| Capacity for bursts of torque should not be confused with field weakening capability. Field weakening allows an electric machine to operate beyond the designed frequency of excitation.
| |
| | |
| Electric machines without a transformer circuit topology, such as that of WRSMs or PMSMs, cannot realize bursts of torque higher than the maximum designed torque without saturating the magnetic core and rendering any increase in current as useless. Furthermore, the PM assembly of PMSMs can be irreparably damaged, if bursts of torque exceeding the maximum operating torque rating are attempted.
| |
| | |
| Electric machines with a transformer circuit topology, such as induction machines, induction doubly fed electric machines, and induction or synchronous wound-rotor doubly fed (WRDF) machines, exhibit very high bursts of torque because the emf-induced active current on either side of the transformer oppose each other and thus contribute nothing to the transformer coupled magnetic core flux density, which would otherwise lead to core saturation.
| |
| | |
| Electric machines that rely on induction or asynchronous principles short-circuit one port of the transformer circuit and as a result, the reactive impedance of the transformer circuit becomes dominant as slip increases, which limits the magnitude of active (i.e., real) current. Still, bursts of torque that are two to three times higher than the maximum design torque are realizable.
| |
| | |
| The [[Brushless wound-rotor doubly fed electric machine|brushless wound-rotor synchonous doubly fed (BWRSDF)]] machine is the only electric machine with a truly dual ported transformer circuit topology (i.e., both ports independently excited with no short-circuited port).<ref name="Klatt (2012)">{{cite journal|last=Klatt|first=Frederick W.|title=Sensorless Real Time Control (RTC): Brushless Wound-Rotor [Synchronous] Doubly-Fed Machine|journal=Sensorless Control for Electrical Drives -SLED 2012|date=Sept 2012|doi=10.1109/SLED.2012.6422811|publisher=IEEE}}</ref> The dual ported transformer circuit topology is known to be unstable and requires a multiphase slip-ring-brush assembly to propagate limited power to the rotor winding set. If a precision means were available to instantaneously control torque angle and slip for synchronous operation during motoring or generating while simultaneously providing brushless power to the rotor winding set, the active current of the BWRSDF machine would be independent of the reactive impedance of the transformer circuit and bursts of torque significantly higher than the maximum operating torque and far beyond the practical capability of any other type of electric machine would be realizable. Torque bursts greater than eight times operating torque have been calculated.
| |
| | |
| ===Continuous torque density===
| |
| The continuous torque density of conventional electric machines is determined by the size of the air-gap area and the back-iron depth, which are determined by the power rating of the armature winding set, the speed of the machine, and the achievable air-gap flux density before core saturation. Despite the high coercivity of neodymium or samarium-cobalt PMs, continuous torque density is virtually the same amongst electric machines with optimally designed armature winding sets. Continuous torque density relates to method of cooling and permissible period of operation before destruction by overheating of windings or PM damage.
| |
| | |
| ===Continuous power density===
| |
| The continuous power density is determined by the product of the continuous torque density and the constant torque speed range of the electric machine.
| |
| | |
| ==Standards==
| |
| The following are major design and manufacturing standards covering electric motors:
| |
| * [[International Electrotechnical Commission]]: IEC 60034 Rotating Electrical Machines
| |
| * [[National Electrical Manufacturers Association]]: [http://www.nema.org/Standards/Pages/Information-Guide-for-General-Purpose-Industrial-AC-Small-and-Medium-Squirrel-Cage-Induction-Motor-Standards.aspx MG-1 Motors and Generators]
| |
| * [[Underwriters Laboratories]]: UL 1004 - Standard for Electric Motors
| |
| | |
| ==Non-magnetic motors==
| |
| {{Main|Electrostatic motor|Piezoelectric motor|Electrically powered spacecraft propulsion}}
| |
| | |
| An electrostatic motor is based on the attraction and repulsion of electric charge. Usually, electrostatic motors are the dual of conventional coil-based motors. They typically require a high voltage power supply, although very small motors employ lower voltages. Conventional electric motors instead employ magnetic attraction and repulsion, and require high current at low voltages. In the 1750s, the first electrostatic motors were developed by Benjamin Franklin and Andrew Gordon. Today the electrostatic motor finds frequent use in micro-electro-mechanical systems ([[MEMS]]) where their drive voltages are below 100 volts, and where moving, charged plates are far easier to fabricate than coils and iron cores. Also, the molecular machinery which runs living cells is often based on linear and rotary electrostatic motors. {{Citation needed|date=March 2013}}
| |
| | |
| A piezoelectric motor or piezo motor is a type of electric motor based upon the change in shape of a [[piezoelectricity|piezoelectric material]] when an [[electric field]] is applied. Piezoelectric motors make use of the converse piezoelectric effect whereby the material produces acoustic or [[ultrasonic motor|ultrasonic]] vibrations in order to produce a linear or rotary motion. In one mechanism, the elongation in a single plane is used to make a series stretches and position holds, similar to the way a caterpillar moves. {{Citation needed|date=March 2013}}
| |
| | |
| An electrically powered spacecraft propulsion system uses electric motor technology to propel spacecraft in outer space, most systems being based on electrically powering propellant to high speed, with some systems being based on [[electrodynamic tether]]s principles of propulsion to the magnetosphere.<ref name="TethersUnlimited (web)">{{cite web|url=http://www.tethers.com/LaunchAssist.html|title=Tethers Unlimited}}</ref>{{citation needed|date=March 2013}}
| |
| | |
| ==Notes==
| |
| {{notelist}}
| |
| | |
| ==See also==
| |
| {{Portal|Electronics|Energy}}
| |
| * [[Electric generator]]
| |
| * [[Goodness factor]]
| |
| {{-}}
| |
| {{Electric motor}}
| |
| {{Alternative propulsion}}
| |
| | |
| ==References==
| |
| {{Reflist|2}}
| |
| | |
| ==Bibliography==
| |
| {{Refbegin}}
| |
| * [[Donald G. Fink|Fink, Donald G.]]; Beaty, H. Wayne, ''Standard Handbook for Electrical Engineers'', '14th ed., McGraw-Hill, 1999, ISBN 0-07-022005-0.
| |
| * Houston, Edwin J.; Kennelly, Arthur, [http://archive.org/details/recenttypesdyna00kenngoog ''Recent Types of Dynamo-Electric Machinery''], American Technical Book Company 1897, published by P.F. Collier and Sons New York, 1902
| |
| * {{cite book | last=Kuphaldt | first=Tony R. | authorlink= | coauthors= | editor= | others= | title=Lessons In Electric Circuits—Volume II | origdate= | origyear= | month= | url= | accessdate=2006-04-11 | edition= | date= | year=2000–2006 | publisher= | location= | language= | id= | pages= | chapter=Chapter 13 AC MOTORS | chapterurl=http://www.ibiblio.org/obp/electricCircuits/AC/AC_13.html }}
| |
| * Rosenblatt, Jack; Friedman, M. Harold, ''Direct and Alternating Current Machinery'', 2nd ed., McGraw-Hill, 1963
| |
| | |
| {{Refend}}
| |
| | |
| ==Further reading==
| |
| {{Refbegin}}
| |
| * {{cite book|last=Bedford|first=B.D.|title=Principles of Inverter Circuits|year=1964|publisher=Wiley|location=New York|isbn=0-471-06134-4|url=http://books.google.ca/books/about/Principles_of_inverter_circuits.html?id=iyZTAAAAMAAJ&redir_esc=y|coauthors= Hoft, R.G.}}
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| * {{cite book|last=Bose|first=Bimal K.|title=Power Electronics and Motor Drives : Advances and Trends|year=2006|publisher=Academic Press|isbn=978-0-12-088405-6|url=http://books.google.ca/books/about/Power_Electronics_And_Motor_Drives.html?id=ywiBVSnYm6IC&redir_esc=y}}
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| * {{cite book|last=Chiasson|first=John|title=Modeling and High-Performance Control of Electric Machines|year=2005|publisher=Wiley|isbn=0-471-68449-X|url=http://books.google.ca/books?id=cq6RPPsOyt8C&pg=PR14&lpg=PR14&dq=Modeling+and+high-performance+control+of+electric+machines&source=bl&ots=yBsEH7igCT&sig=DN136AEwyoU8ihl95hxPXco9fQ4&hl=en&sa=X&ei=DEUwUayWBaK9iwKS5oCgCw&ved=0CDUQ6AEwAQ|edition=Online}}
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| * {{cite book|last=Fitzgerald|first=A.E. |coauthors= Kingsley, Charles , Jr.; Umans, Stephen D.|title=Electric Machinery|year=2003|publisher=McGraw-Hill|isbn=978-0-07-366009-7|url=http://books.google.ca/books/about/Electric_Machinery.html?id=YBKk4kWSle0C&redir_esc=y|edition=6th|pages=688 pages}}
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| * {{cite book|last=Pelly|first=B.R.|title=Thyristor Phase-Controlled Converters and Cycloconverters : Operation, Control, and Performance|year=1971|publisher=Wiley-Interscience|isbn=978-0-471-67790-1|url=http://books.google.ca/books/about/Thyristor_phase_controlled_converters_an.html?id=l9YiAAAAMAAJ&redir_esc=y}}
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| * {{cite book|first=H. D.|last=Stölting|coauthors=Kallenbach, E.; Amrhein, W. (eds.)|title=Handbook of Fractional-Horsepower Drives|year=2008|publisher=Springer|isbn=978-3-540-73128-3|url=http://books.google.ca/books?id=VCHumncaeAAC&pg=PA134&lpg=PA134&dq=fractional+horsepower+ac+motor+comparison&source=bl&ots=6uqhzdi1HV&sig=DtSYJ-53rU_IRny-yDui5bv1b8c&hl=en&sa=X&ei=EUgkUdveN8eRiAL1hICAAg&sqi=2&ved=0CH4Q6AEwCQ#v=onepage&q=shaded-pole&f=false|edition=Online}}
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| {{Refend}}
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| | |
| ==External links==
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| {{Commons category|Electric motors}}
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| * [http://www.sparkmuseum.com/MOTORS.HTM SparkMuseum: Early Electric Motors]
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| * [http://www.eti.kit.edu/english/1376.php The Invention of the Electric Motor 1800 to 1893], hosted by Karlsrushe Institute of Technology's Martin Doppelbauer
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| * [http://www.phys.unsw.edu.au/~jw/HSCmotors.html Electric Motors and Generators], a U. of NSW Physclips multimedia resource
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| * [http://www.iea-4e.org/ IEA 4E - Efficient Electrical End-Use Equipment].
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| * [http://www.ipes.ethz.ch/ipes/2002Feldlinien/feld_dreh.html iPES Rotating Magnetic Field], animation
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| {{DEFAULTSORT:Electric Motor}}
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| [[Category:Electric motors| ]]
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| [[Category:Electrical engineering]]
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| [[Category:Electromagnetic components]]
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| [[Category:Energy conversion]]
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| [[Category:Nikola Tesla]]
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| [[Category:British inventions]]
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| [[Category:Magnetic propulsion devices]]
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