linear induction motor1

8/17/2019 Linear Induction Motor1

1/6

Linear induction motorFrom Wikipedia, the free encyclopedia

A transverse flux linear induction motor (here the primary is at top of picture) and has two sets of opposite poles side by

side. (Picture from ! Patent "#$%%&% by 'ric aithwaite)

A linear induction motor (*) is an A+ asynchronous linear motor that works by the sameeneral principles as other induction motorsbut is very typically desined to directly producemotion in a straiht line. +haracteristically, linear induction motors have a finite lenth primary orsecondary, which enerates end-effects, whereas a conventional induction motor is arraned inan endless loop.

espite their name, not all linear induction motors produce linear motion/ some linear inductionmotors are employed for eneratin rotations of lare diameters where the use of a continuousprimary would be very expensive. 0hey also, unlike their rotary counterparts, can ive a levitationeffect.

As with rotary motors, linear motors fre1uently run on a " phase power supply and can supportvery hih speeds. 2owever, there are end-effects which reduce the force, and it3s often not

possible to fit a earbox to trade off force and speed. inear induction motors are thus fre1uentlyless enery efficient than normal rotary motors for any iven re1uired force output.

*s are often used where contactless force is re1uired, where low maintenance is desirable, orwhere the duty cycle is low. 0heir practical uses include manetic levitation, linear propulsion,and linear actuators. 0hey have also been used for pumpin li1uid metals. 4&5

Contents

4hide5

• & 2istory

• $ +onstruction

• " Principles

• % Forces

o %.& 0hrust

o %.$ 'nd effect

o %." evitation

•

6 Performance

http://en.wikipedia.org/wiki/Linear_motorhttp://en.wikipedia.org/wiki/Linear_motorhttp://en.wikipedia.org/wiki/Induction_motorhttp://en.wikipedia.org/wiki/Magnetic_levitationhttp://en.wikipedia.org/wiki/Magnetic_levitationhttp://en.wikipedia.org/wiki/Linear_induction_motor#cite_note-1http://en.wikipedia.org/wiki/Linear_induction_motorhttp://en.wikipedia.org/wiki/Linear_induction_motorhttp://en.wikipedia.org/wiki/Linear_induction_motorhttp://en.wikipedia.org/wiki/Linear_induction_motor#Historyhttp://en.wikipedia.org/wiki/Linear_induction_motor#Constructionhttp://en.wikipedia.org/wiki/Linear_induction_motor#Principleshttp://en.wikipedia.org/wiki/Linear_induction_motor#Forceshttp://en.wikipedia.org/wiki/Linear_induction_motor#Thrusthttp://en.wikipedia.org/wiki/Linear_induction_motor#End_effecthttp://en.wikipedia.org/wiki/Linear_induction_motor#Levitationhttp://en.wikipedia.org/wiki/Linear_induction_motor#Performancehttp://en.wikipedia.org/wiki/Induction_motorhttp://en.wikipedia.org/wiki/Magnetic_levitationhttp://en.wikipedia.org/wiki/Linear_induction_motor#cite_note-1http://en.wikipedia.org/wiki/Linear_induction_motorhttp://en.wikipedia.org/wiki/Linear_induction_motor#Historyhttp://en.wikipedia.org/wiki/Linear_induction_motor#Constructionhttp://en.wikipedia.org/wiki/Linear_induction_motor#Principleshttp://en.wikipedia.org/wiki/Linear_induction_motor#Forceshttp://en.wikipedia.org/wiki/Linear_induction_motor#Thrusthttp://en.wikipedia.org/wiki/Linear_induction_motor#End_effecthttp://en.wikipedia.org/wiki/Linear_induction_motor#Levitationhttp://en.wikipedia.org/wiki/Linear_induction_motor#Performancehttp://en.wikipedia.org/wiki/Linear_motor


2/6

• 7 ses

• 8 !ee also

• # 9eferences

History 4edit5

0he history of linear electric motors can be traced back at least as far as the %:s, to the workof +harles Wheatstone at ;in3s +ollee in ondon,4$5 but Wheatstone3s model was too inefficientto be practical. A feasible linear induction motor is described in the ! patent 8#$"&$ ( &ermanenineer 2ermann ;emper built a workin model in &


3/6

0he manetic field of a linear motor sweepin to the left, past an aluminium block. +oloured by induced electric current.

n this desin of electric motor, the force is produced by a linearly movin manetic field actinon conductors in the field. Any conductor, be it a loop, a coil or simply a piece of plate metal, thatis placed in this field will have eddy currents induced in it thus creatin an opposin maneticfield, in accordance with en?3s law. 0he two opposin fields will repel each other, thus creatinmotion as the manetic field sweeps throuh the metal.

485

where, is supply fre1uency in 2?, p is the number of poles, and is the synchronousspeed of the manetic field in revolutions per second.

0he travellin field pattern has a velocity of@

485

is velocity of the linear travellin field in ms, t is the pole pitch.

For a slip of s, the speed of the secondary in a linear motor is iven by

485

Forces4edit5Thrust4edit5

0hrust enerated as a function of slip

0he drive enerated by linear induction motors is somewhat similar to conventionalinduction motors/ the drive forces show a rouhly similar characteristic shaperelative to slip, albeit modulated by end effects.4#5

End effect4edit5

nlike a circular induction motor, a linear induction motor shows 3end effects3. 0heseend effects include losses in performance and efficiency that are believed to becaused by manetic enery bein carried away and lost at the end of the primary bythe relative movement of the primary and secondary.

With a short secondary, the behaviour is almost identical to a rotary machine,provided it is at least two poles lon, but with a short primary reduction in thrustoccurs at low slip (below about :.") until it is eiht poles or loner.475

http://en.wikipedia.org/wiki/Magnetic_fieldhttp://en.wikipedia.org/wiki/Magnetic_fieldhttp://en.wikipedia.org/wiki/Magnetic_fieldhttp://en.wikipedia.org/wiki/Eddy_currenthttp://en.wikipedia.org/wiki/Electromagnetic_inductionhttp://en.wikipedia.org/wiki/Lenz's_lawhttp://en.wikipedia.org/wiki/Linear_induction_motor#cite_note-sunilsaharan-7http://en.wikipedia.org/wiki/Linear_induction_motor#cite_note-sunilsaharan-7http://en.wikipedia.org/wiki/Linear_induction_motor#cite_note-sunilsaharan-7http://en.wikipedia.org/w/index.php?title=Linear_induction_motor&action=edit&section=4http://en.wikipedia.org/w/index.php?title=Linear_induction_motor&action=edit&section=5http://en.wikipedia.org/w/index.php?title=Linear_induction_motor&action=edit&section=5http://en.wikipedia.org/wiki/Linear_induction_motor#cite_note-force-8http://en.wikipedia.org/w/index.php?title=Linear_induction_motor&action=edit&section=6http://en.wikipedia.org/wiki/Linear_induction_motor#cite_note-personalView-6http://en.wikipedia.org/wiki/Magnetic_fieldhttp://en.wikipedia.org/wiki/Eddy_currenthttp://en.wikipedia.org/wiki/Electromagnetic_inductionhttp://en.wikipedia.org/wiki/Lenz's_lawhttp://en.wikipedia.org/wiki/Linear_induction_motor#cite_note-sunilsaharan-7http://en.wikipedia.org/wiki/Linear_induction_motor#cite_note-sunilsaharan-7http://en.wikipedia.org/wiki/Linear_induction_motor#cite_note-sunilsaharan-7http://en.wikipedia.org/w/index.php?title=Linear_induction_motor&action=edit&section=4http://en.wikipedia.org/w/index.php?title=Linear_induction_motor&action=edit&section=5http://en.wikipedia.org/wiki/Linear_induction_motor#cite_note-force-8http://en.wikipedia.org/w/index.php?title=Linear_induction_motor&action=edit&section=6http://en.wikipedia.org/wiki/Linear_induction_motor#cite_note-personalView-6


4/6

2owever, because of end effect, linear motors cannot 3run liht3- normal inductionmotors are able to run the motor with a near synchronous field under low loadconditions. ue to end effect this creates much more sinificant losses with linearmotors.475

Levitation4edit5

evitation and thrust force curves of a linear motor

n addition, unlike a rotary motor, an electrodynamic levitation force is shown, this is

?ero at ?ero slip, and ives a rouhly constant amount of forceap as slip increasesin either direction. 0his occurs in sinle sided motors, and levitation will not usuallyoccur when an iron backin plate is used on the secondary, since this causes anattraction that overwhelms the liftin force. 4#5

Performance4edit5

inear induction motors are often less efficient than conventional rotary inductionmotors/ the end effects and the relatively lare air ap that is often present willtypically reduce the forces produced for the same electrical power. 2owever, linearinduction motors can avoid the need for earboxes and similar drivetrains, and thesehave their own losses/ and in any case power use is not always the most important

consideration. For example, in many cases linear induction motors have far fewermovin parts, and have very low maintenance.

Uses4edit5

*0B inear nduction *otor 0est Behicle in &


5/6

0he Cirminham nternational *alev shuttle

0he world3s first commercial automated malev system was a low-speed malevshuttle that ran from the airport terminal of Cirminham nternational Airport to thenearby Cirminham nternational railway station between &


6/6

inear induction motors are also used in looms, manetic levitation permit allowsbobbins to float between the fibers without direct contact.

linear induction motor1

Documents