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| [[Image:Silniki by Zureks.jpg|thumb|upright=1.15|Three-phase totally enclosed fan-cooled (TEFC) induction motor, with and, at right, without end cover to show cooling fan. In TEFC motors, interior losses are dissipated indirectly through enclosure fins mostly by forced air convection.]]
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| An '''induction''' or '''asynchronous motor''' is an [[AC motor|AC electric motor]] in which the [[electric current]] in the [[rotor (electric)|rotor]] needed to produce torque is induced by [[electromagnetic induction]] from the magnetic field of the [[stator]] winding. An induction motor therefore does not require [[commutator (electric)|mechanical commutation]], separate-excitation or self-excitation for all or part of the energy transferred from stator to rotor, as in [[universal motor|universal]], [[DC motor|DC]] and large [[Synchronous motor|synchronous]] motors. An induction motor's rotor can be either [[wound rotor motor|wound type]] or [[squirrel-cage rotor|squirrel-cage type]].
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| [[Three-phase]] [[squirrel cage rotor|squirrel-cage]] induction motors are widely used in industrial drives because they are rugged, reliable and economical. Single-phase induction motors are used extensively for smaller loads, such as household appliances like fans. Although traditionally used in fixed-speed service, induction motors are increasingly being used with [[variable-frequency drive]]s (VFDs) in variable-speed service. VFDs offer especially important energy savings opportunities for existing and prospective induction motors in variable-torque [[centrifugal force|centrifugal]] fan, pump and [[Variable refrigerant flow|compressor]] load applications. Squirrel cage induction motors are very widely used in both fixed-speed and VFD applications.
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| [[File:Rotterdam Ahoy Europort 2011 (14).JPG|thumb|upright=1.15|Cutaway view through stator of TEFC induction motor. Note rotor air circulation vanes.]]
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| ==History==
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| [[Image:Tesla's induction motor.jpg|thumb|A model of Tesla's first induction motor, in Tesla Museum, Belgrade.]]
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| [[File:Squirrel cage.jpg|thumb|right|Early squirrel cage rotor]]
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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|pages=261|location=London|url=http://archive.org/stream/polyphaseelectri00thomuoft#page/n5/mode/2up|accessdate=2 December 2012|edition=1st}}</ref><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 (2006)">{{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> Practical alternating current induction motors seem to have been 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. Tesla applied for [[U.S. Patent Office|U.S. patents]] in October and November 1887 and was granted some of these patents in May 1888. In April 1888, the ''Royal Academy of Science of Turin'' published Ferraris's research on his AC polyphase motor detailing the foundations of motor operation.<ref name="Vuckovic (2006)"/><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> In May 1888 Tesla presented the technical paper ''A New System for Alternating Current Motors and Transformers'' to the ''[[American Institute of Electrical Engineers]]'' (AIEE)<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="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><ref name="TEE (1888)">{{cite book|last=The Electrical Engineer|year=21 Sep. 1888|title=. . . a new application of the alternating current 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> describing three 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. [[George Westinghouse]], who was developing an alternating current power system at that time, licensed Tesla’s patents in 1888 and purchased a US patent option on Ferraris' induction motor concept.<ref>[http://books.google.com/books?id=2_58p3Z69bIC&pg=PT163&lpg=PT163&dq=%22While+Westinghouse+continued+to+survey+the+general+status+of+AC+motors%22&source=bl&ots=6T_5GZlrtX&sig=UqZBWY0jxZSRmrcTGje8g2C6agI&hl=en#v=onepage&q=%22While%20Westinghouse%20continued%20to%20survey%20the%20general%20status%20of%20AC%20motors%22&f=false Jill Jonnes, Empires of Light: Edison, Tesla, Westinghouse, and the Race to Electrify the World, Edison Declares War]</ref> Tesla was also employed for one year as a consultant. Westinghouse employee [[Charles F. Scott (engineer)|C. F. Scott]] was assigned to assist Tesla and later took over development of the induction motor at Westinghouse.<ref name="Alger (1976)"/><ref>[http://books.google.com/books?id=ZOlQAAAAYAAJ&pg=PA340&dq=Charles+F.+Scott+tesla&hl=en&sa=X&ei=WV85UdDUNaiy0QHyiIHgAg&ved=0CDMQ6AEwATgK#v=onepage&q=Charles%20F.%20Scott%20tesla&f=false Electrical World, Volume 78, No 7. page 340]</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="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> Steadfast in his promotion of three-phase development, [[Mikhail Dolivo-Dobrovolsky]]'s invented the cage-rotor induction motor in 1889 and the three-limb transformer in 1890.<ref>{{cite book|last=Hubbell|first=M.W.|year=2011|title=The Fundamentals of Nuclear Power Generation Questions & Answers.|publisher=Authorhouse|isbn=978-1463424411|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]] (GE) 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)"/> GE's [[Steinmetz, Charles Proteus|Charles Proteus Steinmetz]] was the first to make use of the letter "j" (the square root of minus one) to designate the 90-degree [[rotation (mathematics)|rotation]] operator in electrical mathematical expressions and thereby be able to describe the induction motor in terms now commonly known as the [[Induction motor#Steinmetz equivalent circuit|Steinmetz equivalent circuit]].<ref name="Alger (1976)"/><ref name="Steinmetz (1897a)">{{cite journal|last=Steinmetz|first=Charles Porteus|title=The Alternating Current Induction Motor|journal=AIEE Trans|year=1897|volume=XIV|issue=1|pages=183–217|url=http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=5570186|accessdate=18 December 2012}}</ref><ref name="Banihaschemi (1973)">{{cite book|last=Banihaschemi|first=Abdolmajid|title=Determination of the Losses in Induction Machines Due to Harmonics|year=1973|publisher=University of New Brunswick|location=Fredericton, N.B.|pages=1, 5–8|url=http://dspace.hil.unb.ca:8080/bitstream/handle/1882/44564/Thesis%20E%2054.pdf?sequence=4}}</ref><ref name="Steinmetz (1897b)">{{cite book|last=Steinmetz|first=Charles Proteus|title=Theory and Calculation of Alternating Current Phenomena|year=1897|publisher=McGraw Publishing Company|coauthors=Berg, Ernst J.|url=http://openlibrary.org/books/OL7218906M/Theory_and_calculation_of_alternating_current_phenomena}}</ref> Induction motor improvements flowing from these inventions and innovations were such that a 100 [[horsepower]] induction motor currently has the same mounting dimensions as a 7.5 horsepower motor in 1897.<ref name="Alger (1976)"/>
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| ==Principle of operation==
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| [[Image:Rotatingfield.png|thumb|left|A three-phase power supply provides a rotating magnetic field in an induction motor.]]
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| In both induction and [[synchronous motor]]s, the AC power supplied to the motor's [[stator]] creates a [[rotating magnetic field|magnetic field]] that rotates in time with the AC oscillations. Whereas a synchronous motor's rotor turns at the same rate as the stator field, an induction motor's rotor rotates at a slower speed than the stator field. The induction motor stator's magnetic field is therefore changing or rotating relative to the rotor. This induces an opposing current in the induction motor's rotor, in effect the motor's secondary winding, when the latter is short-circuited or closed through an external impedance.<ref name="Knowlton (1949)">{{cite conference|booktitle=Standard Handbook for Electrical Engineers|edition=8th|year=1949|title= 'Induction Machines' 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=705}}</ref> The rotating [[magnetic flux]] induces currents in the windings of the rotor;<ref name=NSWHSCOnline>{{cite web|title=AC Motors|publisher=NSW HSC Online - Charles Sturt University|accessdate=2 December 2012|url=http://hsc.csu.edu.au/physics/core/motors/2698/Phy935net.htm }}</ref> in a manner similar to currents induced in a [[transformer]]'s secondary winding(s). The currents in the rotor windings in turn create magnetic fields in the rotor that react against the stator field. Due to [[Lenz's Law]], the direction of the magnetic field created will be such as to oppose the change in current through the rotor windings. The cause of induced current in the rotor windings is the rotating stator magnetic field, so to oppose the change in rotor-winding currents the rotor will start to rotate in the direction of the rotating stator magnetic field. The rotor accelerates until the magnitude of induced rotor current and torque balances the applied load. Since rotation at synchronous speed would result in no induced rotor current, an induction motor always operates slower than synchronous speed. The difference, or "slip," between actual and synchronous speed varies from about 0.5 to 5% for standard Design B torque curve induction motors.<ref name=NEMAMG1C>{{cite book |last=NEMA MG-1 2007 Condensed |title= Information Guide for General Purpose Industrial AC Small and Medium Squirrel-Cage Induction Motor Standards | year=2008 | url=http://www.nema.org/Standards/Pages/Information-Guide-for-General-Purpose-Industrial-AC-Small-and-Medium-Squirrel-Cage-Induction-Motor-Standards.aspx | accessdate=2 December 2012| publisher=[[NEMA]]| location=Rosslyn, Virginia US |page=29 (Table 11)}}</ref> The induction machine's essential character is that it is created solely by induction instead of being separately excited as in synchronous or DC machines or being self-magnetized as in permanent magnet motors.<ref name="Knowlton (1949)"/>
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| For rotor currents to be induced, the speed of the physical rotor must be lower than that of the stator's rotating magnetic field (<math>n_s</math>); otherwise the magnetic field would not be moving relative to the rotor conductors and no currents would be induced. As the speed of the rotor drops below synchronous speed, the rotation rate of the magnetic field in the rotor increases, inducing more current in the windings and creating more torque. The ratio between the rotation rate of the magnetic field induced in the rotor and the rotation rate of the stator's rotating field is called slip. Under load, the speed drops and the slip increases enough to create sufficient torque to turn the load. For this reason, induction motors are sometimes referred to as asynchronous motors.<ref>{{cite web|title=Induction (Asychronous) Motors|url=http://www.ece.msstate.edu/~donohoe/ece3183asynchronous_synchronous_machines.pdf|publisher=Mississippi State University Dept of Electrical and Computer Engineering, Course ECE 3183, 'Electrical Engineering Systems for non-ECE majors'|accessdate=2 December 2012}}</ref> An induction motor can be used as an [[induction generator]], or it can be unrolled to form a [[linear induction motor]] which can directly generate linear motion.
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| ===Synchronous speed===
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| An AC motor's synchronous speed, <math>n_s</math>, is the rotation rate of the stator's magnetic field, which is expressed in revolutions per minute as
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| :<math>n_s={120\times{f}\over{p}}</math> (RPM),
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| where <math>f</math> is the motor supply's frequency in Hertz and <math>p</math> is the number of magnetic poles.<ref name=MDEMRC>{{cite web|url=http://www.electricmotors.machinedesign.com/guiEdits/Content/bdeee11/bdeee11_7.aspx|title=Induction Motors|last=Electric Motors Reference Center by ''Machine Design'' magazine|title=Induction Motors|publisher=Penton Media, Inc.}}</ref><ref name=elec-toolbox>{{cite web|title=Motor Formulas|url=http://www.elec-toolbox.com/Formulas/Motor/mtrform.htm|publisher=elec-toolbox.com|accessdate=1 January 2013}}</ref> That is, for a six-pole three-phase motor with three pole-pairs set 120° apart, <math>p</math> equals 6 and <math>n_s</math> equals 1,000 RPM and 1,200 RPM respectively for 50 Hz and 60 Hz supply systems.
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| ===Slip===
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| [[File:Couple glissement MAs.svg|thumb|right|Typical torque curve as a function of slip, represented as 'g' here.]]
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| Slip, <math>s</math>, is defined as the difference between synchronous speed and operating speed, at the same frequency, expressed in rpm or in percent or ratio of synchronous speed. Thus
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| :<math>s = \frac{n_s-n_r}{n_s}\,</math>
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| where
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| <math>n_s</math> is stator electrical speed, <math>n_r</math> is rotor mechanical speed.<ref name=Sravastava>{{cite journal|title=Torque Slip Characteristics of Induction Motor|last=Srivastava|first=Avinash|coauthors=Kumar, Ravi|publisher=Malnad College Of Engineering|journal=Course notes}}</ref><ref name=NEMAASD>{{cite book |last=NEMA Standards Publication |title= Application Guide for AC Adjustable Speed Drive Systems | year=2007 | url=http://www.nema.org/stds/acadjustable.cfm | accessdate=2 December 2012| publisher=[[NEMA]]| location=Rosslyn, Virginia US |page=6}}</ref> Slip, which varies from zero at synchronous speed and 1 when the rotor is at rest, determines the motor's torque. Since the short-circuited rotor windings have small resistance, a small slip induces a large current in the rotor and produces large torque.<ref name="Herman">{{cite book
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| | last = Herman
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| | first = Stephen L.
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| | authorlink =
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| | coauthors =
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| | title = Alternating Current Fundamentals
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| | edition= 8th
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| | publisher = Cengage Learning
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| | year = 2011
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| | location = US
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| | pages = 529–536
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| | url = http://books.google.com/books?id=RRbIRBUQk-sC&pg=PA521&dq=squirrel+cage+motor+induction&hl=en&sa=X&ei=fwz7TqqmLY2OigKGuqCXDQ&ved=0CE0Q6AEwADgK#v=onepage&q=squirrel%20cage%20motor%20induction&f=false
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| | doi =
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| | id =
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| | isbn = 1-111-03913-5}}</ref> At full rated load, slip varies from more than 5% for small or special purpose motors to less than 1% for large motors.<ref name="Peltola (no year)">{{cite web|last=Peltola|first=Mauri|title=AC Induction Motor Slip|url=http://www.plantservices.com/articles/2002/48.html?page=1|publisher=Plantservices.com|accessdate=18 December 2012}}</ref> These speed variations can cause load-sharing problems when differently sized motors are mechanically connected.<ref name="Peltola (no year)"/> Various methods are available to reduce slip, VFDs often offering the best solution.<ref name="Peltola (no year)"/>
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| ===Torque===
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| {{see also|Fleming's left-hand rule for motors}}
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| ====Standard torque====
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| [[File:Torque electric motor AC.svg|thumb|Speed-torque curves for four induction motor types: A) Single-phase, B) Polyphase cage, C) Polyphase cage deep bar, D) Polyphase double cage]]
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| [[File:NEMA B Curve.jpg|thumb|right|Typical speed-torque curve for NEMA Design B Motor]]
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| The typical speed-torque relationship of a standard NEMA Design B polyphase induction motor is as shown in the curve at right. Suitable for most low performance loads such as centrifugal pumps and fans, Design B motors are constrained by the following typical torque ranges:<ref name=NEMAMG1C/>{{efn|NEMA MG-1 defines a) breakdown torque as the maximum torque developed by the motor with rated voltage applied at rated frequency without an abrupt drop in speed, b) locked-rotor torque as the minimum torque developed by the motor at rest with rated voltage applied at rated frequency, and c) pull-up torque as the minimum torque developed by the motor during the period of acceleration from rest to the speed at which breakdown torque occurs.}}
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| * Breakdown torque, 175-300 percent of rated torque
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| * Locked-rotor torque, 75-275 percent of rated torque
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| * Pull-up torque, 65-190 percent of rated torque.
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| Over a motor's normal load range, the torque's slope is approximately linear or proportional to slip because the value of rotor resistance divided by slip, <math>R_r^{'}/s</math>, dominates torque in linear manner.<ref name="Keljik">{{cite conference | last = Keljik| first = Jeffrey|chapter=12|title=Chapter 12 - The Three-Phase, Squirrel-Cage Induction Motor | authorlink = | coauthors = | booktitle = Electricity 4 : AC/DC Motors, Controls, and Maintenance| publisher = Delmar, Cengage Learning| year = 2009| edition = 9th| location = Clifton Park, NY| pages = 112–115| url = http://books.google.com/books?id=y69O8PnwLbYC&pg=PA105&dq=squirrel+cage+motor+induction&hl=en&sa=X&ei=rP_6TqbTA6aciQLswMDQDg&ved=0CE4Q6AEwAA#v=onepage&q=squirrel%20cage%20motor%20induction&f=false| doi = | id = | isbn = 1-4354-0031-3}}</ref> As load increases above rated load, stator and rotor leakage reactance factors gradually become more significant in relation to <math>R_r^{'}/s</math> such that torque gradually curves towards breakdown torque. As torque increases beyond breakdown torque the motor stalls. Although polyphase motors are inherently self-starting, their starting and pull-up torque design limits must be high enough to overcome actual load conditions. In two-pole single-phase motors, the torque goes to zero at 100% slip (zero speed), so these require alterations to the stator such as [[shaded-pole motor|shaded-poles]] to provide starting torque.
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| ====Starting====
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| {{main|Motor controller}}
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| There are five basic types of competing small induction motor: single-phase capacitor-start, capacitor-run, split-phase and shaded-pole types, and small polyphase induction motors.
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| A single-phase induction motor requires separate starting circuitry to provide a rotating field to the motor. The normal running windings within such a single-phase motor can cause the rotor to turn in either direction, so the starting circuit determines the operating direction.
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| In certain smaller single-phase motors, starting is done by means of a shaded pole with a copper wire turn around part of the pole. The current induced in this turn lags behind the supply current, creating a delayed magnetic field around the shaded part of the pole face. This imparts sufficient rotational field energy to start the motor. These motors are typically used in applications such as desk fans and record players, as the required starting torque is low, and the low efficiency is tolerable relative to the reduced cost of the motor and starting method compared to other AC motor designs.
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| Larger single phase motors have a second stator winding fed with out-of-phase current; such currents may be created by feeding the winding through a capacitor or having it receive different values of inductance and resistance from the main winding. In ''capacitor-start'' designs, the second winding is disconnected once the motor is up to speed, usually either by a centrifugal switch acting on weights on the motor shaft or a [[thermistor]] which heats up and increases its resistance, reducing the current through the second winding to an insignificant level. The ''capacitor-run'' designs keep the second winding on when running, improving torque.
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| Self-starting polyphase induction motors produce torque even at standstill. Available cage induction motor starting methods include direct-on-line starting, reduced-voltage reactor or auto-transformer starting, star-delta starting or, increasingly, new solid-state soft assemblies and, of course, VFDs.<ref name="Liang (2011)"/>
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| Polyphase motors have rotor bars shaped to give different speed-torque characteristics. The current distribution within the rotor bars varies depending on the frequency of the induced current. At standstill, the rotor current is the same frequency as the stator current, and tends to travel at the outermost parts of the cage rotor bars (by [[skin effect]]). The different bar shapes can give usefully different speed-torque characteristics as well as some control over the inrush current at startup.
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| In wound rotor motors, rotor circuit connection through slip rings to external resistances allows change of speed-torque characteristics for acceleration control and speed control purposes.
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| ====Speed control====
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| [[File:Variation-couple-uf.svg|thumb|right|Typical speed-torque curves for different motor input frequencies as for example used with [[variable-frequency drive]]s.]]
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| Before the development of semiconductor [[power electronics]], it was difficult to vary the frequency, and cage induction motors were mainly used in fixed speed applications. Applications such as electric overhead cranes used DC drives or wound rotor motors (WRIM) with [[slip ring motor|slip ring]]s for rotor circuit connection to variable external resistance allowing considerable range of speed control. However, resistor losses associated with low speed operation of WRIMs is a major cost disadvantage, especially for constant loads.<ref name="Jamil Asghar (2003)">{{cite journal|last=Jamil Asghar|first=M.S.|title=Speed control of wound rotor induction motors by AC regulator based optimum voltage control|journal=Power Electronics and Drive Systems, 2003. The Fifth International Conference on|year=2003|volume=2|pages=1037–1040|doi=10.1109/PEDS.2003.1283113|url=http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=1283113}}</ref> Large slip ring motor drives, termed slip energy recovery systems, some still in use, recover energy from the rotor circuit, rectify it, and return it to the power system using a VFD. In many industrial variable-speed applications, DC and WRIM drives are being displaced by VFD-fed cage induction motors. The most common efficient way to control asynchronous motor speed of many loads is with VFDs.
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| Example applications include [[Variable refrigerant flow]] compressors in high-efficiency [[air conditioner]]s.<ref name=thornton201212>
| |
| {{cite report |last=Thornton|first=Brian |title=Variable Refrigerant Flow Systems |date=December 2012 |url=http://www.gsa.gov/portal/mediaId/169771/fileName/GPG_VRF_Report_-_FINAL_DRAFT_4-16-13 |publisher=US Federal Government type=pdf |work=General Services Administration |accessdate=2013-11-22}}</ref>
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| | |
| Barriers to adoption of VFDs due to cost and reliability considerations have been reduced considerably over the past three decades such that it is estimated that drive technology is adopted in as many as 30-40% of all newly installed motors.<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%20-Voltage%20-Drives%20-Motors/ABB-136_WPO_Motoring%20-ahead.pdf|accessdate=Apr 18, 2012}}</ref>
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| | |
| ==Construction==
| |
| [[File:Vierpolig-3stränge.svg|thumb|right|Typical winding pattern for a three-phase (U, V, W), two-pole motor. Note the interleaving of the pole windings and the resulting [[Quadrupole magnet|quadrupole field]].]]
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| The stator of an induction motor consists of poles carrying supply current to induce a magnetic field that penetrates the rotor. To optimize the distribution of the magnetic field, the windings are distributed in slots around the stator, with the magnetic field having the same number of north and south poles. Induction motors are most commonly run on single-phase or three-phase power, but two-phase motors exist; in theory, induction motors can have any number of phases. Many single-phase motors having two windings can be viewed as two-phase motors, since a capacitor is used to generate a second power phase 90° from the single-phase supply and feeds it to the second motor winding. Single-phase motors require some mechanism to produce a rotating field on startup. Cage induction motor rotor's conductor bars are typically skewed to reduce noise.
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| | |
| ==Rotation reversal==
| |
| The method of changing the direction of rotation of an induction motor depends on whether it is a three-phase or single-phase machine. In the case of three phase, reversal is carried out by swapping connection of any two phase conductors. In the case of a single-phase motor it is usually achieved by changing the connection of a starting capacitor from one section of a motor winding to the other. In this latter case both motor windings are similar (e.g. in washing machines).
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| | |
| ==Power factor==
| |
| The [[power factor]] of induction motors varies with load, typically from around 0.85 or 0.90 at full load to as low as 0.35 at no-load,<ref name="Liang (2011)"/> due to stator and rotor leakage and magnetizing reactances.<ref name="Fink (1978)">{{cite book|title=Standard Handbook for Electrical Engineers|edition=11th|year=1978|first=D.G.|last=Fink|coauthors=Beaty, H.W.|publisher=McGraw-Hill|pages=20-28 thru 20-29}}</ref> Power factor can be improved by connecting capacitors either on an individual motor basis or, by preference, on a common bus covering several motors. For economic and other considerations power systems are rarely power factor corrected to unity power factor.<ref name="Jordan (1994)"/>
| |
| Power capacitor application with harmonic currents requires power system analysis to avoid harmonic resonance between capacitors and transformer and circuit reactances.<ref name="NEMA MG-1, p. 19">NEMA MG-1, p. 19</ref> Common bus power factor correction is recommended to minimize resonant risk and to simplify power system analysis.<ref name="NEMA MG-1, p. 19"/>
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| | |
| ==Efficiency==
| |
| (See also [[Variable-frequency drive#Energy savings|Energy savings]])
| |
| | |
| Full load motor efficiency varies from about 85 to 97%, related motor losses being broken down roughly as follows:<ref name="USDOE (2008)">{{cite web|last=U.S. DOE|title=Improving Motor and Drive System Performance: A Sourcebook for Industry|url=http://www1.eere.energy.gov/manufacturing/tech_deployment/pdfs/motor.pdf|accessdate=31 December 2012|year=2008|page=27}}</ref>
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| * Friction and [[windage]], 5% – 15%
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| * Iron or [[magnetic core#Core loss|core loss]]es, 15% – 25%
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| * Stator losses, 25% – 40%
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| * Rotor losses, 15% – 25%
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| * Stray load losses, 10% – 20%.
| |
| 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]].
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| | |
| ==Steinmetz equivalent circuit==
| |
| {{Technical|section|date=December 2012}}
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| (See also [[Transformer#Equivalent circuit|Equivalent circuit]], [[Blocked rotor test]], [[Open circuit test]])
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| | |
| Many useful motor relationships between time, current, voltage, speed, power factor and torque can be obtained from analysis of the Steinmetz [[equivalent circuit]] (also termed T-equivalent circuit or IEEE recommended equivalent circuit), a mathematical model used to describe how an induction motor's electrical input is transformed into useful mechanical energy output. The equivalent circuit is a single-phase representation of a multiphase induction motor that is valid in steady-state balanced-load conditions.
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| | |
| The Steinmetz equivalent circuit is expressed simply in terms of the following components:
| |
| * [[Stator]] [[Electrical resistance and conductance|resistance]] and [[leakage inductance|leakage reactance]] (<math>R_s</math>, <math>X_s</math>).
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| * [[rotor (electric)|Rotor]] resistance, leakage reactance, and slip (<math>R_r</math>, <math>X_r</math> or <math>R_r^'</math>, <math>X_r^'</math>, and <math>s</math>).
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| * [[magnetizing field|Magnetizing]] [[electrical reactance|reactance]] (<math>X_m</math>).
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| | |
| Paraphrasing from Alger in Knowlton, an induction motor is simply an electrical transformer the magnetic circuit of which is separated by an air gap between the stator winding and the moving rotor winding.<ref name="Knowlton (1949)"/> The equivalent circuit can accordingly be shown either with equivalent circuit components of respective windings separated by an ideal transformer or with rotor components referred to the stator side as shown in the following circuit and associated equation and parameter definition tables.<ref name="Liang (2011)">{{cite journal|last=Liang|first=Xiaodong|coauthors=Ilochonwu, Obinna|title=Induction Motor Starting in Practical Industrial Applications|journal=IEEE Transactions on Industry Applications|date=Jan 2011|volume=47|issue=1|pages=271–280|doi=10.1109/TIA.2010.2090848|url=http://ieeexplore.ieee.org/xpl/login.jsp?tp=&arnumber=5621895&url=http%3A%2F%2Fieeexplore.ieee.org%2Fiel5%2F28%2F4957013%2F05621895.pdf%3Farnumber%3D5621895|accessdate=4 December 2012}}</ref><ref name="Jordan (1994)">{{cite book|last=Jordan|first=Howard E.|title=Energy-Efficient Electric Motors and their Applications|url=http://books.google.co.uk/books?id=utWtW_9NMgcC&lpg=PA89&dq=induction%20motor%20power%20correction&pg=PA89#v=onepage&q=induction%20motor%20power%20correction&f=false|year=1994|publisher=Plenum Press|location=New York|isbn=0-306-44698-7|edition=2nd}}</ref><ref name="Hubert (2002)">{{cite book|last=Hubert|first=Charles I.|title=Electric Machines : Theory, Operation, Applications, Adjustment, and Control|year=2002|publisher=Prentice Hall|location=Upper Saddle River, N.J.|isbn=0130612103|pages=Chapter 4|url=http://www.ebay.com/ctg/electric-machines-theory-operating-applicatiaons-and-controls-charles-i-hubert-2001-paperback-/1929950|edition=2nd}}</ref><ref name="Beaty (2006)">{{cite conference|last=Beaty|first=H. Wayne (Ed.)|booktitle=Handbook of Electric Power Calculations|year=2006|publisher=McGraw-Hill|location=New York|title=Section 5 - Three-Phase Induction Motors by Hashem Oraee|url=http://magergy.com/documents/Ebooks/Handbook%20of%20Electric%20Power%20Calculations/62983_05.pdf|isbn=0-07-136298-3|edition=3rd}}</ref><ref name="Knight (2012)">{{cite web|last=Knight|first=Andy|title=Three-Phase Induction Machines|url=http://www.ece.ualberta.ca/~knight/electrical_machines/induction/basics/circuit.html|publisher=Hosted by University of Alberta|accessdate=21 December 2012}}</ref><ref name="IEEE112 (2004)">{{cite book|last=IEEE 112|title=IEEE Standard Test Procedure for Polyphase Induction Motors and Generators|year=2004|publisher=IEEE|location=New York, N.Y.|isbn=0-7381-3978-5}}</ref>
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| | |
| [[Image:IMEQCCT.jpg|thumb|center|550px|Steinmetz equivalent circuit]]
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| {{Collapse top|title=Table of Circuit Parameter Definitions}}
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| {| class="wikitable"
| |
| !
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| !
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| !Units
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| |-
| |
| |<math>f_s</math> ||[[stator]] synchronous frequency
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| |align="center"|Hz
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| |-
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| |<math>n_r </math>||[[rotor (electric)|rotor]] speed in [[revolutions per minute]]
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| |align="center"|rpm
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| |-
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| |<math>n_s </math>||[[synchronous speed]] in revolutions per minute
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| |align="center"|rpm
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| |-
| |
| |<math>I_s</math>||stator or primary [[alternating current|current]]
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| |align="center"|A
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| |-
| |
| |<math>I_r^'</math>||rotor or secondary current referred to stator side
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| |align="center"|A
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| |-
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| |<math>I_m</math>||magnetizing current
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| |align="center"|A
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| |-
| |
| |<math>j = \sqrt{-1}</math>||[[imaginary number]], or 90° [[rotation (mathematics)|rotation]], operator
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| |-
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| |<math>K_{TE}</math>|||<math>=X_m/(X_s+X_m)</math> [[Thévenin's theorem|Thévenin]] reactance factor
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| |-
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| |<math>m</math> ||number of motor phases
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| |-
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| |<math>p</math> ||number of motor poles
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| |-
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| |<math>P_{em}</math>||[[electromagnetic force|electromechanical power]]
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| |align="center"|W or hp
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| |-
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| |<math>P_{gap}</math>||air gap power
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| |align="center"|W
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| |-
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| |<math>P_r</math>||rotor [[copper loss]]es
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| |align="center"|W
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| |-
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| |<math>P_o</math>||input power
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| |align="center"|W
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| |-
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| |<math>P_h</math>||core loss
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| |align="center"|W
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| |-
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| |<math>P_f</math>||friction and windage loss
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| |align="center"|W
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| |-
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| |<math>P_{rl}</math>||running light watts input
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| |align="center"|W
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| |-
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| |<math>P_{sl}</math>|| stray-load loss
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| |align="center"|W
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| |-
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| |<math>R_s, X_s</math>||stator or primary resistance and [[leakage inductance|leakage reactance]]
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| |align="center"|Ω
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| |-
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| |<math>R_r^', X_r^'</math>||rotor or secondary resistance & leakage reactance referred to the stator side
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| |align="center"|Ω
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| |-
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| |<math>R_o, X_o</math>||resistance & leakage reactance at motor input
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| |align="center"|Ω
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| |-
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| |<math>R_{TE}, X_{TE}</math>||Thévenin equivalent resistance & leakage reactance combining <math>R_s, X_s</math> and <math>X_m</math>
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| |align="center"|Ω
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| |-
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| |<math>s </math>||slip
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| |-
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| |<math>T_{em}</math>||[[electromagnetic force|electromagnetic torque]]
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| |Nm or ft.-lb.
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| |-
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| |<math>T_{max}</math>||breakdown torque
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| |Nm or ft.-lb.
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| |-
| |
| |<math>V_s</math>||impressed stator phase [[voltage]]
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| |align="center"|V
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| |-
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| |<math>X_m</math>||[[magnetizing field|magnetizing]] [[electrical reactance|reactance]]
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| |align="center"|Ω
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| |-
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| |<math>X</math>||<math>X_s+X_r^{'}</math>
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| |align="center"|Ω
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| |-
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| |<math>Z_s</math>||stator or primary [[electrical impedance|impedance]]
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| |align="center"|Ω
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| |-
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| |<math>Z_r^{'}</math>||rotor or secondary impedance referred to the primary
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| |align="center"|Ω
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| |-
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| |<math>Z_o</math>||impedance at motor stator or primary input
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| |align="center"|Ω
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| |-
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| |<math>Z</math>||combined rotor or secondary and magnetizing impedance
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| |align="center"|Ω
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| |-
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| |<math>Z_{TE}</math>||Thévenin equivalent circuit impedance, <math>R_{TE}+X_{TE}</math>
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| |align="center"|Ω
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| |-
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| |<math>\omega_r </math>||rotor speed
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| |align="center"|[[radian per second|rad/s]]
| |
| |-
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| |<math>\omega_s </math>||synchronous speed
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| |align="center"|rad/s
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| |-
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| |<math>Y</math>||<math>=G-jB=\frac{1}{Z}=\frac{1}{R+jX}=\frac{R}{Z^2}-\frac{jX}{Z^2}</math>
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| |align="center"|mho
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| |-
| |
| |<math>\left\vert Z \right\vert</math>||<math>\sqrt{R^{2}+X^{2}}</math>
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| |align="center"|Ω
| |
| |}
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| {{Collapse bottom}}
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| The following rule-of-thumb approximations apply to the circuit:<ref name="IEEE112 (2004)"/><ref>Alger (1949), p. 711</ref><ref name="Özyurt (2005)">{{cite book|last=Özyurt|first=Ç.H.|title=Parameter and Speed Estimation of Induction Motors from Manufacturers Data and Measurements|year=2005|publisher=Middle East Technical University|url=https://etd.lib.metu.edu.tr/upload/12605774/index.pdf|pages=33–34}}</ref>
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| * Maximum current happens under locked rotor current (LRC) conditions and is somewhat less than <math>{V_s}/X</math>, with LRC typically ranging between 6 and 7 times rated current for standard Design B motors.<ref name=NEMAMG1C/>
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| * Breakdown torque <math>T_{max}</math> happens when <math>s\approx{R_r^'/X}</math> and <math>I_s\approx{0.7}LRC</math> such that <math>T_{max}\approx{K*V_s^2}/(2X)</math> and thus, with constant voltage input, a low-slip induction motor's percent-rated maximum torque is about half its percent-rated LRC.
| |
| * The relative stator to rotor leakage reactance of standard Design B cage induction motors is<ref name="Knight (nodate)">{{cite web|last=Knight|first=Andy|title=Determining Induction Machine Parameters|url=http://www.ece.ualberta.ca/~knight/electrical_machines/induction/parameters/params.html|publisher=Hosted by University of Alberta|accessdate=31 December 2012}}</ref>
| |
| :<math>\frac{X_s}{X_r^'}\approx\frac{0.4}{0.6}</math>.
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| * Neglecting stator resistance, an induction motor's torque curve reduces to the Kloss equation<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}}page=133</ref>
| |
| :<math>T_{em}\approx\frac{2T_{max}}{\frac{s}{s_{max}}+\frac{s_{max}}{s}}</math>, where <math>s_{max}</math> is slip at <math>T_{max}</math>.
| |
| | |
| {{Collapse top|title=Table of Basic Electrical Equations }}
| |
| :<math>\omega_r = \frac{2{\pi}n_s}{60} = \frac{4{\pi}f_s}{p}</math>
| |
| Motor input equivalent impedance
| |
| :<math>Z_m = R_s + jX_s + \frac{(\frac{R_s}{s} + jX_r^')(jX_m)}{\frac{R_r^'}{s} + j(X_r^' + X_m)}</math>
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| Stator current
| |
| :<math>I_s = V_s/Z_m = V_s/(R_s + jX_s + \frac{(\frac{R_s}{s} + jX_r^')(jX_m)}{\frac{R_r^'}{s} + j(X_r^' + X_m)})</math>
| |
| Rotor current referred to the stator side in terms of stator current
| |
| :<math>I_r^' = \frac{jX_m}{\frac{R_r^'}{s} + j(X_r^' + X_m)} I_s</math>
| |
| {{Collapse bottom}}
| |
| {{Collapse top|title=Table of Power Equations}}
| |
| From Steinmetz equivalent circuit, we have
| |
| :<math>\frac{R_r^{'}}{s}=\frac{R_r^{'}(1-s)}{s}+R_r^{'}</math>
| |
| That is, air gap power is equal to electromechanical power output plus rotor copper losses
| |
| | |
| :<math>P_{gap} = P_{em}+P_r</math>
| |
| | |
| :<math>P_r = 3R_r^{'}I_r^{'2}</math>
| |
| | |
| :<math>P_{gap} = \frac{3R_r^{'}I_r^{'2}}{s}</math>
| |
| | |
| :<math>P_{em} = \frac{3R_r^{'}I_r^{'2}(1-s)}{s}</math>
| |
| | |
| :<math>P_{em} = P_{gap}(1-s)</math>
| |
| Expressing electromechanical power output in terms of rotor speed
| |
| :<math>P_{em} = \frac{3R_r^{'}I_r^{'2}n_r}{sn_s}</math> (Watts)
| |
| | |
| :<math>P_{em} = \frac{3R_r^{'}I_r^{'2}n_r}{746sn_s}</math> (hp)
| |
| Expressing <math>T_{em}</math> in ft.-lb.:
| |
| :<math>P_{em} = \frac{T_{em}n_r}{5252}</math> (hp)
| |
| {{Collapse bottom}}
| |
| {{Collapse top|title=Table of Torque Equations }}
| |
| :<math>T_{em} = \frac{P_{em}}{\omega_r} = \frac{\frac{P_r}{s}}{\omega_r} = \frac{3I_r^{'2} R_r^{'}}{\omega_r s}</math> (Newton-meters)
| |
| In order to be able to express <math>T_{em}</math> directly in terms of <math>s</math>, IEEE recommends that <math>R_s, X_s</math> and <math>X_m</math> be converted to the [[Thévenin's theorem|Thévenin]] equivalent circuit
| |
| [[File:IMEQCCTTE.jpg|thumb|center|450px|IEEE recommended Thévenin equivalent circuit]]
| |
| | |
| where
| |
| | |
| :<math>V_{TE}=\frac{X_m}{\sqrt{R_s^2+(X_s+X_m)^2}}V_s</math>
| |
| | |
| :<math>Z_{TE}=R_{TE}+jX_{TE}=\frac{jX_m(R_s+jX_s)}{R_s+j(X_s+X_m)}</math>
| |
| | |
| Since <math>R_s^{2}\gg{(X_s+X_m)^2}</math> and <math>X_s\ll{X_m}</math>, and letting <math>K_{TE}=\frac{X_m}{X_s+X_m}</math>
| |
| | |
| :<math>V_{TE}\approx{Z_{TE}V_s}</math> and <math>Z_{TE}\approx{K_{TE}^2R_s+jX_s}</math><ref name="Özyurt (2005)"/>
| |
| | |
| :<math>T_{em}=\frac{3V_{TE}^{2}}{(R_{TE}+\frac{R_r^{'}}{s})^{2}+(R_{TE}+X_r^')^{2}}.\frac{R_r^'}{s}.\frac{1}{\omega_s} (N.m)</math><ref name="Özyurt (2005)"/>
| |
| | |
| For low values of slip:
| |
| :Since <math>R_{TE}+R_r^'\gg{R_{TE}+X_r^'}</math> and <math>R_r^'\gg{R_{TE}}</math>
| |
| :<math>T_{em}\approx\frac{1}{\omega_s}.\frac{3V_{TE}^{2}}{R_r^{'}}.s</math> (N.m)
| |
| For high values of slip
| |
| :Since <math>R_{TE}+R_r^'\ll{R_{TE}+X_r^'}</math>
| |
| :<math>T_{em}\approx\frac{1}{\omega_s}.\frac{3V_{TE}^{2}}{(X_s+X_r^{'})^2}.\frac{R_r^{'2}}{s}</math> (N.m)
| |
| For maximum or breakdown torque, which is independent of rotor resistance
| |
| :<math>T_{max}=\frac{1}{2\omega_{s}}.\frac{3V_{TE}^{2}}{R_{TE}+\sqrt{R_{TE}^{2}+(X_{TE}+X_r^{'})^{2}}}</math> (N.m)<ref name="Özyurt (2005)"/>
| |
| | |
| Corresponding slip at maximum or breakdown torque is
| |
| :<math>s=\frac{R_r^'}{\sqrt{R_{TE}^2+(X_{TE}+X_r^')^2}}</math><ref name="Özyurt (2005)"/>
| |
| | |
| In foot-pound units
| |
| :<math>T_{em} = \frac{21.21I_r^{'2} R_r^{'}}{n_r s}</math> (ft-lb)
| |
| | |
| :<math>T_{em} = \frac{7.04P_{gap}}{n_s}</math> (ft-lb)
| |
| | |
| {{Collapse bottom}}
| |
| | |
| ==Linear induction motor==
| |
| {{main|linear induction motor}}
| |
| Linear induction motors, that work on same general principles as rotary induction motors and are frequently three-phase, are designed to produce straight line motion. Uses include [[magnetic levitation]], linear propulsion, linear actuators, and liquid metal pumping.<ref name="BAS (1973)">{{cite book|url=http://books.google.co.uk/books?id=fgsAAAAAMBAJ&lpg=PA52&ots=NfAng_7A27&dq=einstein%20Linear%20induction%20motor&pg=PA52#v=onepage&q=einstein%20Linear%20induction%20motor&f=false |title=Bulletin of the Atomic Scientists |date=6 June 1973|accessdate=8 August 2012|publisher=Educational Foundation for Atomic Science}}</ref>
| |
| | |
| ==See also==
| |
| * [[Circle diagram]]
| |
| * [[Induction generator]]
| |
| * [[Premium efficiency]]
| |
| * [[Copper in energy efficient motors]]
| |
| * [[Induction motors modelling in ABC frame of reference]]
| |
| | |
| ==Notes==
| |
| {{notelist}}
| |
| | |
| ==References==
| |
| {{Reflist|2}}
| |
| | |
| ==Classical sources==
| |
| *{{cite book| url=http://books.google.com/books?id=r_dOAAAAMAAJ&printsec=frontcover&dq=induction+motor&source=bl&ots=g7Th09trR-&sig=onxjvgyC920oARs_LUDqnzV2kHg&hl=en&ei=1VS3TNTyNoKKlwfWwJ3MDA&sa=X&oi=book_result&ct=result&resnum=4&ved=0CDcQ6AEwAzgK#v=onepage&q&f=false| title=The Induction Motor| first=Benjamin Franklin |last=Bailey| publisher=McGraw-Hill| year= 1911}}
| |
| *{{cite book| url=http://archive.org/details/inductionmotorsh00behruoft| title=The Induction Motor: A Short Treatise on its Theory and Design, With Numerous Experimental Data and Diagrams| first=Bernhard Arthur|last= Behrend| publisher=McGraw Publishing Company / Electrical World and Engineer| year= 1901 }}
| |
| *{{cite book| url=http://books.google.com/books?id=hbM_AAAAYAAJ&printsec=frontcover&dq=induction+motor&source=bl&ots=_JgDsnjN2s&sig=LHXibhTQ9XXIOvzsWATRSHA-xkA&hl=en&ei=X1O3TOekFpCisAPomqGeCQ&sa=X&oi=book_result&ct=result&resnum=14&sqi=2&ved=0CFoQ6AEwDQ#v=onepage&q&f=false| title=The Induction Motor: Its Theory and Design, Set Forth By a Practical Method of Calculation| first=Henri |last=Boy de la Tour| others=Translated Cyprien Odilon Mailloux| publisher=McGraw Pub. Co.| year= 1906 }}
| |
| | |
| ==External links==
| |
| {{Commons category|Induction motors}}
| |
| * [http://aungwin.htut.googlepages.com/inductionmotor2.jpg An induction motor drawing]
| |
| * [http://www.sandroronca.it/elettrotecnica/asincrono/camporotante0.html Rotating magnetic fields]: interactive, {{it icon}}
| |
| * [http://magrf.grf.hr/~mtodorov/tesla/build_3ph_induction.html Construct your squirrel cage induction motor], using povray
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| * [http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/indmot.html Induction motor topics] from Hyperphysics website hosted by C.R. Nave, GSU Physics and Astronomy Dept.
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| * [http://www.ece.ualberta.ca/~knight/electrical_machines/induction/i_main.html Three-Phase Induction Machines] hosted by University of Alberta's Andy Knight
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| {{Electric motor}}
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| {{DEFAULTSORT:Induction Motor}}
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| [[Category:Energy conversion]]
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| [[Category:Electric motors]]
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| [[Category:Italian inventions]]
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| [[Category:AC motors]]
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| {{Link GA|fr}}
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