Talk:Induction motor

Pole pairs

The relationship between pole pairs, frequency and speed is :- f = n*p not f = n*p/120 and also p is the number of pole pairs and not the number of poles.

I think you are using rpm and not revs/sec and you have used poles rather than pole pairs to get the 120. I think this could be a little confusing as the same variables (n and p) are used below.

Two-phase AC Induction Motors

The article only mentions single-phase and three-phase AC induction motors. There are also two-phase motors used in special applications (with the phases separated by a 90 degree phase angle). Is this worthy of inclusion? Maybe just mention that single and three phase are the most common? Tqcurtis (talk) 14:10, 8 January 2009 (UTC)

Speed Control

It seams like somebody keeps wanting to incorrectly change the voltage referred to in the Speed Control section to 33V and not 25V, so I think I had better explain.

If the signal is ON for a third of the time that it is off then there are 4 quarters (3 off, 1 on) therefore the average voltage over this period will be 25V (A quarter of 100V). how to work of celling fan motor ? — Preceding unsigned comment added by 2409:4053:78D:AB1C:B4B4:1D39:75E3:7631 (talk) 18:12, 28 February 2019 (UTC)

This is obviously causing some confusion, if somebody thinks that the maths is wrong can they please put their thinking on here BEFORE editing the page and making it incorrect. —Preceding unsigned comment added by 194.129.210.61 (talk) 09:28, 28 September 2007 (UTC)

think speed control of ac motors, think kirloskar mysore to match your requirements —Preceding unsigned comment added by 122.167.227.169 (talk) 09:39, 14 December 2007 (UTC)

If the speed is controlled by the frequency of the pulses, why are we discussing pulse width modulation? Changing the duty cycle does not change the frequency. Also, with all the discussion of the average voltage, it might be relevant to mention the RMS voltage. The 100V 50% duty cycle square wave is 70.7Vrms, and the 100V 25% duty cycle square wave is 50Vrms.70.230.188.90 (talk) 21:35, 26 September 2008 (UTC)

Spam

A link to electojects.com has been repeatedly added to Stepper motor, Electric motor and Brushless DC electric motor by Special:Contributions/217.53.109.235, Special:Contributions/82.201.156.201, Special:Contributions/217.53.107.168, Special:Contributions/217.53.16.164, and others.

The link in question is registered to Abdoh Ali Mohamed, Hay Swesri, Nasr City, Cairo, Egypt.[1]

I wonder if the four IP addresses listed above have any connection... Naw, couldn't be. [2][3][4][5] Egypt is a big country. Must be a coincidence.

I'm going to start patrolling wikipedia for any links to electojects.com or redirects to it and deleting them on sight. If they come back, I'll move to blacklist the address. Mdsummermsw (talk) 18:21, 28 December 2007 (UTC)

Syncronous motors WITH BRUSHES???

The article currently says 'The basic difference between an induction motor and a synchronous AC motor is that in the latter a current is supplied onto the rotor.' Really? Syncronous motors have brushes for rotor connection? The syncro motors I've disassembled look just like normal induction motors: brushless. The only difference is a magnetizable steel rotor rather than soft iron, so the rotating field becomes "frozen in" on the rotor, creating a permanent magnet. For this reason a syncro induction motor usually starts up with a random phase, since this "magnet" forms anew each time the rotor comes up to speed. --Wjbeaty (talk) 20:32, 28 February 2008 (UTC)

The magnet can be a permanent magnet (for smaller motors) or an electromagnet with brushes for larger motors. For a permanent magnet, the field doesn't get created each time. Shameer (talk) 06:06, 17 April 2008 (UTC)

you can also make a short circuit between the brushes and then have an induction motor. That was the subject of one practical work whan i was a student. we make it with some mosfet when the motor was rotating : that was fun

The difference between induction and synchronous motor come magnetic field created by the rotor : AC for induction DC for synchronous not from the presence of brushes. Yves-Laurent (talk) 19:33, 17 April 2008 (UTC)

some examples of slipring synchronous motors

http://ecatalog.weg.net/files/wegnet/WEG-synchronous-motors-50019091-brochure-english.pdf (page 6)

http://www.industry.usa.siemens.com/datapool/industry/industrysolutions/metals/siroll/en/Rolling-Mill-Main-Motors-en.pdf — Preceding unsigned comment added by 195.137.63.170 (talk) 08:54, 17 June 2014 (UTC)

Micro edit done.

I did a micro edit. Formulas => Formulae, since formulae is the plural of formula. —Preceding unsigned comment added by Lambda driver (talk • contribs) 10:02, 21 August 2008 (UTC)

Don't forget Galileo Ferraris!!

Galileo Ferraris discovered the Rotating Field Principle, and put the basis for the Theory of Induction Motors. I think that he needed to be mentioned in the "History" paragraph! -- An Italian Engineer -- —Preceding unsigned comment added by 81.112.253.226 (talk) 12:45, 26 November 2008 (UTC)

Ferraris?

Tesla designed the first motor in 1883. Ferraris probably just copied Tesla's work. There is nothing independent about something that is already designed and published in scientific papers. Tesla had many patents to his name. How many in Ferrari's name?

Typical Teslaphile. Accuse everyone for "stealing" Tesla's ideas when Tesla himself was jealous of other engineers and he probably stole others ideas for himslef. Tesla is an overrated patent theif and many of his so called "patents" were failed prototypes that no one uses. Tesla was joke

Comment to introduction

Not all inductions motors are squirrel cage motors (i.e. with short-circuit rotor). Often the rotor actually has a winding with brushes, which can be connected to external resistors to increase the slip to decrease the rotor speed (useful for start-up without frequency converter or for slight speed variations). Still these brushes are much more rugged than the DC motor commutator brushes. User:Nillerdk (talk) 11:27, 6 February 2009 (UTC)

Yes, not only is the second sentence of the introduction wrong, it also contradict the core of the article. I removed it. 128.178.26.187 (talk) 14:59, 29 July 2009 (UTC)

Good work

Just want to comment on the good work. The first few introductory paragraphs couldn't be better.Dave3457 (talk) 21:37, 23 June 2009 (UTC)

Suggested edit to Resistance starters

I don't know enough about the subject to be editing anything but the below paragraphs are poor.

xxxxxxxxx Original

Resistance starters

This method is used with slip ring motors where the rotor poles are connected to the slip rings. At start these are wired with a variable power resistors via brushes and at full speed switched to short circuit.

While start-up the resistors leads to lesser weakening of the field strength from the stator. As a result the inrush current is reduced. Another important advance is higher start-up torque. The resistors also generate a phase shift in the field and thus the resulting magnetic force onto the rotor has a favorable angle.

xxxxxxxxx My suggested edits in bold

Resistance starters

This method is used with slip ring motors where the rotor poles can be accessed byway of the slip rings. Using brushes, variable power resistors are connected in series with the poles. During start-up the resistance is large and then reduced to zero at full speed.

At start-up the resistance results in the stator's field strength being weakened less. As a result, the inrush current is reduced. Another important advantage is higher start-up torque. As well, the resistors generate a phase shift in the field resulting in the magnetic force acting on the rotor having a favorable angle.

xxxxxxxxxxx

I waited for a response and then went ahead and made the changes. The issues were grammer and not technical understanding.

induction motor

in 3 phase induction motor ,how many wire are used —Preceding unsigned comment added by 123.236.46.27 (talk) 08:02, 30 June 2009 (UTC)

Usually six, two wires per phase, thus you can decide if you connect them delta/star. On some small motors they may be just three wires accessible (hardwired to delta/star inside the motor). -- 92.203.32.193 (talk) 16:09, 2 August 2009 (UTC)

Is there ok with the wiring in the photo? Does the same color indicate both ends of the same phase winding or not? —Preceding unsigned comment added by 193.219.184.13 (talk) 12:20, 12 October 2010 (UTC)

No evidence that Tesla identified or applied the magnetic rotating field before 1888

Historical proves that Tesla "identified" (weird verb, usually exploited by someone who want to prove something without evidence. Usually inventors just publish, create, patent...)are non existent. The fact is that Tesla spent most of its energies by trying to create a mith of himself through letters or memorials. He was simply obsessed not to be recognised as the first having invented or applied or thought something......Tesla was aware that Ferraris had created induction motors in 1885,three years before him (1885 Ferraris's models still exist where are those created before 1888 by Tesla?), and just put about the history of the idea conceived in 1882. No priority on a discovery can be given to Tesla or to anyone else just refering to memorials based merely on owns testimonies without any rigorous evidence. —Preceding unsigned comment added by 193.136.94.218 (talk) 17:00, 8 September 2009 (UTC)

Definitely: The Tesla fan-boys should read "Nickola Tesla, His Work and Unfulfilled Promises" by Laurence A. Hawkins who was a contemporary of Tesla and was disgusted with Tesla's constant scrabbling for the limelight. (see https://archive.org/details/TeslaUnfulfilledPromisesHawkins) Gutta Percha (talk) 11:00, 27 September 2014 (UTC)

What? NO EVIDENCE

June 10th 1883 in France, Tesla demonstrated newly completed A.C. induction motor before Mr. Bauzin, former mayor of Strasbourg, and several potential investors. They watched the motor with interest, but it was apparent they did not understand the value of the invention. No evidence? Plenty of people saw it work, including people that helped him build the presentation in the city center. —Preceding unsigned comment added by Alser (talk • contribs) 03:13, 2 December 2010 (UTC)

So I could say that my grand-grand father "conceived" the theory of relativity in 1900 and explained it in front of the mayor of his village to see the face of Einstein substituted with that one of mine ancestor in every book around the world? History of science requires rigorous evidences and the 1883 presentation (presumed) has no historic consistency. Galileo Ferraris never wanted to patent any of his inventions yet he didn't "conceive" but built induction motors (models still exist) in 1885 and showed them working to everyone visiting his laboratory, this is the only consistent historical fact. Magnagr (talk) 10:58, 2 December 2010 (UTC)

Missing Equation for Induction Motor Speed?

The equation seems to be missing from the "AC Induction Motor" Section:
"

AC Induction Motor

where

n = Revolutions per minute (rpm)

f = AC power frequency (hertz)

[...]

"

Shouldn't there be an equation between the heading and "where"? —Preceding unsigned comment added by 72.236.152.194 (talk) 14:53, 19 May 2010 (UTC)

German article is better and more complete

There's a google translate here

I copied one across and some diagrams, but I don't have time right now for the remaining. We really should copy some of the remaining sections, the complex phasor stuff should come and probably a section or two as well.Rememberway (talk) 06:57, 24 November 2010 (UTC)

Interesting. The history is missing there, and only a German and Italian are mentioned, neither of whom made the breakthrough, nor the final modern version. Tesla's motor is analogous to Edison's light bulb, with all earlier inventions being failures which were never used. Or, analogous to Gramme's DC motor, which was the first success after fifty years of attempts following Faraday's initial discovery. Avoiding Tesla is like writing a history of incandescent bulbs, with no mention of Edison.

In addition, the Tesla-versus Dolivo-Dobrovolsky issue exposes some long-standing apparent dishonesty, with Dolivo-Dobrovolsky strangely insisting that Tesla's system was based on 2-phase only, yet this is simply wrong, Tesla's 1888 patents were for a "Polyphase system," even depicting a 3-phase motor in the patent drawings, and Tesla publicly chastises DD for wasting time in duplicating efforts, via not studying Tesla's published patents. Westinghouse, not Tesla, was apparently pushing the less-expensive 2-phase 4-wire version, in order to simply mount pairs of existing AC dynamos on a single shaft, with no need for complete redesign of enormous single-phase generators (as done in the 1893 Columbian Exposition, with 4-wire power grid driven by paired Westinghouse generators, offset 90deg on the drive shaft. AEG/Oerklion in Europe did build dedicated polyphase generators, after encountering Tesla's patents.) Prior to the controversy, CEL Brown of Oerklion conceived a full-scale 100KM test of AC transmission lines employing bare conductors, decided to also include a test of Tesla's new patents, and brought the project to DD (even later commented in the press that the new system being demonstrated was Tesla's invention.) Dolivo-Dobrovolsky was lying about it all? A patent-piracy attempt? No evidence of AC work prior to the Oerklion project (AEG was a DC company.) Did all AEG work in fact come from Tesla's published work, with no prior independent invention? These issues are obvious from the documents, but very OR, because they're not mentioned by any historian. Each nation's historians only promote a countryman as the "true" inventor. The above German version does the same, suffering from "light bulbs without Edison." But find CF Scott's articles in IEEE proceedings, re. early Westinghouse history. Arago's disk was first, then simultanously Tesla's KW-scale, rotor-windings motor (polyphase,) and Ferraris' incorrect analysis of 2-phase versions, then Dolivo-Dobrovolsky's 3-phase squirrel-cage, then Lamme/Shallenberger embedding the rotor's copper within the iron laminations. The modern induction motor is this latter version, not Tesla's and not Dolivo-Dobrovolsky's. (Ferraris would have been the clear winner here, but as exposed in court cases, he got his physics wrong, proving that high-wattage industrial versions were impossible. Tesla had no theory besides Poschl's reported disproof of brushless motors, instead simply building high-wattage industrial versions, probably via modification of the DC "Gramme Machine," as illustrated by all of Tesla's early torus-shaped prototypes.) 128.95.172.170 (talk) 04:23, 16 February 2024 (UTC)

Image

Perhaps that

File:Induction motor windings for electromagnet.png

the image to the right can be added to this article ?

91.182.255.53 (talk) 14:38, 2 February 2011 (UTC)

It doesn't really add much - certainly not compared to the animated image that's already there. I'm also wary of the */- markings, which (although justified to indicate winding polarity) could confuse some readers to think that it's a DC winding. Andy Dingley (talk) 15:00, 2 February 2011 (UTC)

I don't think the animated image isn't that good really (since it only shows a very weird motor with only 3 poles; normally there are much more; ie up to 36 for a 3 phase motor). For the windings, I would assume that they can be used for both types of current. That aside, indeed the image is only intented to show the construction of the windings, and hence it has more value in articles specifically about this topic

91.182.255.53 (talk) 15:29, 2 February 2011 (UTC)

Another image; see also the description of the image for more info

File:Induction motor (squirrel cage) workings.JPG

Workings of the induction motor

I'd hoped you weren't going to talk about that fourth image. Please, don't embarrass yourself. Andy Dingley (talk) 16:11, 2 February 2011 (UTC)

For the drawing of the four field coils, then it's definitely more relevant to this article than to the other two articles you tried to shoe-horn it into. However it still has problems.

The animation image is OK as a general overview, but yes, it doesn't show the field coils and their connection too clearly, and it's assumed to be a 3-phase drawing (nothing wrong with that though). If this article went into as much depth as the Australian source article did, it would certainly be justified. Mind you, it needs to not use the +/- markings you'd added to the original, just to give it that special KVDP je ne sais rien.

Most of all though, this image is just broken (discussed at the image). Note the lack of symmetry to how the coils are linked... It would have to be replaced by a correct image (come on, 5 minutes with a pencil, even assuming we don't already have something better at Commons). Andy Dingley (talk) 16:11, 2 February 2011 (UTC)

Practical induction motor

Independently from Tesla, and, probably, at the same time, Ferraris inventedand made a laboratory model of two-phase induction motor. He obtained the magnetic field by passing two phase-shifted alternate currents through two coilsphysically shifted for 90 degrees. The rotor consisted of a cylinder made of copper. Although knowing very well the electromagnetic theory, he made two mistakes in the analysis of the function of that motor: he neglected the leakage of the flux in the rotor, and he observed, nobody knows why, the efficiency at maximum power of the motor. Because of the first mistake he could not Tesla’s Polyphase System and Induction Motor understand why the motor does not have the highest torque at start, and because of the second mistake he came to the wrong conclusion that that motor can not have the efficiency higher than 0.5. That conclusion provoked the famous Ferraris’s statement, often mentioned when people talk about the need of caution when coming to theoretical conclusions without practical check, that a motor made in such a way, that means the induction motor created by polyphase alternate currents, can not be of use in industry to transform electric energy into mechanical work. What a mistake of a talented inventor and respected professor! Marcel Deprez, Bradly and of others who also described the devices in which the rotation of the rotor was achieved by polyphase currents, but they have mistake. Therefore is mentioned that Tesla invented the first practical induction motor!!! More [6]--Свифт (talk) 15:48, 25 April 2012 (UTC)

See section above on this very point. DieSwartzPunkt (talk) 18:18, 30 September 2012 (UTC)

'Eddy currents' vs 'currents'?

I don't really understand why the point about eddy currents being the particular type of currents that are set up in the rotor to make it move has been removed, and I notice that an anonymous user has the same opinion as myself on this.

It seems to me that the idea that it's specifically eddy currents involved that drag the rotor around is a simple way to describe what happens, and I'm certain that this cannot be considered to be an incorrect description, and there was a reference provided. What do others think?Embrittled (talk) 18:26, 28 September 2012 (UTC)

Maybe in an induction disk, but a squirrel-cage motor has an honest-to-Tesla winding made up of the heavy bars. If you've ever had the misfortune of having one of those bars break from the collector ring, you'll recall the terrible noise and vibration that result due to the non-uniform distribution of current in the remaining motor winding. If eddy currents in the rotor bars were sufficient, you wouldn't need to connect them all to the rings at the ends - shucks, you wouldn't need to make the rotor out of laminations at all. (There are hysteresis motors that have an unlaminated rotor, but they don't worry about eddy currents so much because they are synchronous motors). --Wtshymanski (talk) 21:19, 28 September 2012 (UTC)

In an induction motor, the laminations aren't in the conductors that carry the currents, they're only in the iron core.Embrittled (talk) 21:34, 28 September 2012 (UTC)

And it's still an eddy current even if it goes through the bars and the end plates and back again.Embrittled (talk) 21:34, 28 September 2012 (UTC)

Also linear induction motors routinely use simple conductive plates without laminations or bars at all. Are you saying that a linear induction motor isn't an induction motor? Because they definitely do use eddy currents.Embrittled (talk) 21:34, 28 September 2012 (UTC)

You have demonstrated your total lack of understanding of the fundamentals on so many occasions that I've lost count. I would trust a document published by a university (or almost anybody come to that) over you any day of the year. What do you think an 'eddy current' is if it is not a current induced by a varying magnetic field (i.e. an induced current)? But then inductance and induction has never been your strong suit as you demonstrated so ably with that debacle of a discussion over here. 86.166.70.84 (talk) 08:13, 29 September 2012 (UTC)

From the first technical dictionary I pulled off the shelf:

Eddy currents are electric currents that are induced in conductors when subject to a changing magnetic field either due to the relative motion between the field source and conductor or due to variations of the field itself with time.

The Wikipedia article Eddy current says something very similar.

That looks like a perfectly good definition. It would seem to cover the conductors in the rotor of an induction motor. I believe that the term 'eddy current(s)' are normally applied to a conductive plane as opposed to a linear conductor, but at the end of the day, an eddy current is just an induced current whatever the configuration of the conductor. In any case: who are we to argue with such an august institution as the Charles Sturt University of New South Wales? DieSwartzPunkt (talk) 14:01, 29 September 2012 (UTC)

Just adding 2 cents re: "who are we to argue". We are editors looking at many reference sources (hopefully peer reviewed books), not just one. There is allot on this[7], the question I see is, is it a notable part of operation or just wp:undue[8]?. The section should follow basic book references on electric motors.Fountains of Bryn Mawr (talk) 21:18, 29 September 2012 (UTC)

A transformer doesn't work by eddy currents, either. It needlessly confuses the reader by sticking in the word "eddy current" here. An induction motor would work pefectly well if it had filamentary current flow through bars of negligable cross section, immune to eddy currents; and if you break the bars of an induction motor, no current flows through the squirrel cage winding and it won't run. It's perfectly straighforward and there's no need to drag in "eddy" currents in this context. --Wtshymanski (talk) 03:18, 30 September 2012 (UTC)

So answer the question. What is an eddy current if it is not an induced current? 86.166.70.84 (talk) 09:52, 30 September 2012 (UTC)

It's not a "what" it's a "where". Look at where these currents are running within the rotor.

For one thing, an eddy current being an induced current does not mean that all induced currents are eddy currents.

Secondly, the currents that cause an induction motor to operate are not eddy currents.

There are indeed eddy currents within an induction motor rotor. They're not useful: they're an energy loss by Joule heating, just as they are in transformer cores. The cores of both are laminated to reduce such eddy currents.

Wtshymanski is quite right here. Stop calling these circulating currents in the squirrel cage "eddy currents", and certainly stop doing so until you have a RS that backs you up (and one that you understand too, so as to not mis-quote it). Andy Dingley (talk) 10:26, 30 September 2012 (UTC)

I don't think you quite understand, eddy currents are the source of all torques in induction motors; different directions and types and frequencies of eddy currents have different effects, and you control which eddy currents form where and when by slotting and shaping the rotor (using bars, different shaped bars and end plates etc), but that's specifically and only how they work.Embrittled (talk) 16:06, 30 September 2012 (UTC)

I think you are the one who has misinterpreted the citation in question.

Firstly: it is not a description of a 'high school experiment' as you claim but a statement of operation of what makes an induction motor work - and this from a university syllabus. It is reasonable to assume that this is what they are teaching their students.

Secondly: how has anyone misinterpreted, "An induction motor is so named because eddy currents are induced in the rotor coils by the rotating magnetic field of the stator. The eddy currents produce magnetic fields which interact with the rotating field of the stator to exert a torque on the rotor in the direction of rotation of the stator field."?

That is what it says and that is what has been inserted into the article. If anyone wishes to challenge it then a higher reference is required that specifically states that these induced currents that cause the motor to work are specifically not eddy currents. But since eddy currents are specifically induced currents, what else can they be? 86.166.70.84 (talk) 17:39, 30 September 2012 (UTC)

What is wrong with just describing these currents as induced currents? It is still factually accurate without unnecessarily adding redundant detail. The citation should remain as it does support the essential point. The currents may, or may not, technically be eddy currents in the sense that most people understand them but so what?

Having looked at several references on induction motors, not one specifically calls the rotor induced currents 'eddy currents' but merely induced currents. But by the inverse process, none of them specifically states that they are not eddy currents. So I am unable defeat the university syllabus page with evidence of incorrect information. DieSwartzPunkt (talk) 17:56, 30 September 2012 (UTC)

Eddy Current (Edit Point)

Not all induced currents are eddy currents. As a practical distinction, eddy currents are considered to follow small loops within materials. As these loops are small, and aren't physically extended (ie the current doesn't flow down one side of a "coil" and back along the other) then it's impractical to use them to generate a torque (as their spacing approaches zero, the couple they generate approximates zero). The currents in a squirrel cage are not termed "eddy currents" by any competent, reliable source. Andy Dingley (talk) 18:12, 30 September 2012 (UTC)

This is also my understanding. I was going to ask if you had a cite that they are specifically not eddy currents, but unless someone insists on editing the point back in, it is currently moot. DieSwartzPunkt (talk) 18:24, 30 September 2012 (UTC)

I would say that the fact that people here actually seem to think that they're not eddy currents is a strong reason for insisting it goes back in(!)Embrittled (talk) 00:38, 1 October 2012 (UTC)

Eddy currents form strongly when the metal conductor is bigger in the direction of the current than the skin depth.Embrittled (talk) 00:38, 1 October 2012 (UTC)

This is one reason why (there are others as well) why you don't often see small induction motors; at line frequency the currents just don't build up if the rotor size is too titchy (unless an inverter is used).Embrittled (talk) 00:38, 1 October 2012 (UTC)

If they didn't work by eddy currents, you could build an induction motor where the axial length of the rotor was smaller than the skin depth. Good luck with that!Embrittled (talk) 00:38, 1 October 2012 (UTC)

Does a wound rotor motor work by "eddy currents", too? How about a transformer? And if the currents don't travel around the winding, why does every squirrel-cage motor have all the rotor bars connected together at the ends? --Wtshymanski (talk) 02:28, 1 October 2012 (UTC)

Remember those old-time record players - they had shaded pole motors driving a little rubber wheel on the inside of the turntable, to give 33 or 45 or 78 RPM? These were the tiniest squirrel-cage motors, and I bet their rotors were comparable to a skin depth in length.

G. R. Slemon in Magnetoelectric Devices, Wiley 1966 pp. 373-374 doesn't describe the rotor currents as "eddy" currents. J. H. Kuhlmann Design of Electrical Apparatus Second Edition, Wiley 1940, mentions eddy currents in induction machines but only in the context of reducing stator losses by subdividing the stator wires. If the people instructing people on how to build these machines don't call them eddy currents, neither should this article. Besides, eddy currents are induced by flux changes *within* a conductor - in a squirrel-cage rotor, the flux is changing *between* the conductors in the rotor poles. (That's why the rotor is laminated - to reduce eddy currents in the rotor iron.)--Wtshymanski (talk) 02:54, 1 October 2012 (UTC)

Yes, and that the useful torque generated is miniscule, but then you don't need any torque for that application.Embrittled (talk) 17:22, 7 October 2012 (UTC)

So, according to you, eddy current braking is impossible?

No!

You've confusing and conflated skin effect with eddy currents, they are not the same thing. Skin effect is certainly caused by eddy currents, but not all eddy currents are skin effect.Embrittled (talk) 04:41, 1 October 2012 (UTC)

Another one: "AC Motors". Electrical Engineer's Reference Book (7th ed.). Newnes. 1954. p. 8-46. "induced" but not "eddy". Andy Dingley (talk) 09:18, 1 October 2012 (UTC)

They just don't mention it, either way.Embrittled (talk) 10:26, 1 October 2012 (UTC)

And your claim that eddy currents are: "As a practical distinction, eddy currents are considered to follow small loops within materials. As these loops are small, and aren't physically extended (ie the current doesn't flow down one side of a "coil" and back along the other) then it's impractical to use them to generate a torque (as their spacing approaches zero, the couple they generate approximates zero)."

Is completely false. In eddy current braking, the eddy currents are bigger than the poles of the magnets used, inches across, not in any way small, and they generate not 'approximately zero' forces, they generate very large forces indeed; comparable to the applied magnetic field. And the fact that there's also an iron core (not all induction motors have an iron core BTW) doesn't change that, this is exactly the same effect that is used in induction motors. This is simply how they work.Embrittled (talk) 10:26, 1 October 2012 (UTC)

You've confused force and torque (from a couple). Andy Dingley (talk) 11:50, 19 October 2012 (UTC)

No, I haven't at all. A circumferential force trivially generates a couple when there is an axle present; the force and the normal reactive force of the bearings form a couple.Embrittled (talk) 15:00, 23 October 2012 (UTC)

Look, an eddy current is just a closed loop of current within a solid conductor. It doesn't matter if there's gaps in the middle. If you take a sheet of metal and generate eddy currents in it, and machine a an arbitrary hole in the middle of the current, that's still an eddy current.Embrittled (talk) 10:31, 1 October 2012 (UTC)

No. An eddy current is current induced within a conductor by a change of flux *inside* a conductor. You can build a superconducting induction motor where the changing magnetic flux *cannot* penetrate the rotor bars, therefore the flux cannot generate *eddy* currents *within* the rotor bars, and it will work just fine (though you might not make any money selling them). Induction motors work by the *induced* currents flowing around the rotor winding, due to the change of flux in the area surrounded by the winding. Eddy currents in the rotor bars don't create any torque on the motor shaft. --Wtshymanski (talk) 13:22, 1 October 2012 (UTC)

Yes, changes of flux induce the currents, but the currents can be in the thickness of the conductor (as with skin depth) or in the plane of the conductor (as in eddy current braking, induction motors, and most notably linear induction motors). They're still just eddy currents.Embrittled (talk) 17:22, 7 October 2012 (UTC)

The big problem here is that we believe that we intuitively know what differentiates an 'eddy current' from any other induced current. But without adequate supporting references that would purely be a point of view, and we have already seen that point of view seems to vary somewhat. Continuing from above, I searched some more reference material including a few old books on electric machines that I inherited from my father. All are pretty well agreed on what induced currents are along with their properties. The problem is eddy currents. Most just state that eddy currents are induced currents without qualifying what it is about an eddy current than makes it different from a simple induced current (if there really is a difference), though the examples given are the usual eddy current brake etc. etc.

One of the older books did have this nugget, "If the conductor in which the current is induced is not a wire, then such currents are frequently referred to as eddy currents". This definition (if it could be considered a definition at all) is tainted by the use of the word 'frequently' suggesting that it may be a terminological convention rather than a hard fact. A page later the book went on to describe the familiar jumping ring demonstration using a closed 'loop of copper wire' in which 'eddy currents' cause the wire ring to jump upward when alternating current is applied to the coil underneath (thus breaching its own explanation). As the rotor bars in an induction motor are not really wires as such, then that piece of evidence suggests that 'eddy currents' would be a legitimate term to describe the induced currents (but not one that I personally would have used - at least until now!).

I did try googling Wtshymanski's 'definition' of an eddy current from above and many variations of it, but just came up with nothing more than the usual, 'eddy current is an induced current' theme. Perhaps he has some supporting evidence to support this definition that he may care to share?

But as I have already stated: unless someone is positively insisting that the word 'eddy' is reintroduced into the article to qualify the induced rotor currents, then this is all rather moot as this discussion is not serving to change the article only our collective understanding of eddy currents. That is not what talk pages are for. DieSwartzPunkt (talk) 15:21, 1 October 2012 (UTC)

It's not intuition or a point of view; it's as plain as the winding on a motor. If a conductor is small, the biggest loop that could be traced in it is also small, so the voltage and current induced are also small. If a conductor is large, a loop perpendicular to the magnetic flux encloses more flux, and so has a higher voltage which can drive more current around that loop. We use small wires wrapped aroung big (laminated) poles so that we maximize the induced current (that circulates around the pole and is propelled by the EMF induced by the changing flux penetrating the pole and passing through the area enclosed by the winding) while minimizing the induced current, eddy current, that stirs around inside the wire due to flux penetrating the wire. All the textbooks I've looked at are rather careful to distinguish paths "inside" the body of the conductor from paths *around* a region outside the conductor. --Wtshymanski (talk) 18:09, 1 October 2012 (UTC)

With all due respect. Without the requested reference, that happens to be your point of view. That it happens to accord with most other's points of view is supporting evidence but not conclusive proof.

However: yesterday something happened which turns this the other way. It's funny how these things seem to happen in pairs. We were investigating a failed induction motor (squirrel cage job for powering cooling fans on aircraft). Why the motor failed is immaterial, but I took one of our new graduate engineers along for some practical experience (as in: now he's got got the qualification we are teaching him to be an engineer!). During the discussions that ensued, he referred to the currents in the rotor bars as 'eddy currents'. Now I might not have noticed or said anything if it were not for this discussion. On questioning, he stated that he had been taught that eddy current is just another name for induced current. Well, to cut a long story short: graduates always come from university believing they know everything (an illusion that we always have to dispell), and this morning he brings me the student notes that he was given on induction motors. Sure enough the second paragraph of the notes in the introductory section reads:

"The rotor consists of coils of wire wound on a laminated iron core mounted on an axle. The rotor coils are not connected to the external power supply, and thus an induction motor has neither commutator nor brushes. An induction motor is able to create mechanical rotation because the rotating magnetic field from the stator induces eddy currents in the rotor coils. These eddy currents produce magnetic fields which interact with the rotating field of the stator to exert a torque on the rotor in the same direction." [My emphasis]

Curious! Our graduate has stated that nothing he has been taught separates an eddy current from an induced current and that as far as he was aware, they were alternate terms for each other. Is it possible that this is what they are actually teaching in the world's universities and colleges these days? I would be interested to know if Embrittled is a recent graduate of one of our schools of learning (my money is on the Charles Sturt University because that is where all this began). It might also explain why no one has yet come up with a reference diferentiating eddy currents from induced currents. DieSwartzPunkt (talk) 12:49, 2 October 2012 (UTC)

This story makes me sad. This is not how I was taught. It would seem to be useful to distinguish induced currents due to fields *inside* a conductor from the currents in a conductor induced by the fields *outside* the conductor - since they have radically different effects. The books on machine design talk about subdividing windings in the stator to *prevent* eddy current circulation (same for power transformers and IF transformers). My old Tipler physics text illustrates this, and so does the picture in our WP article on eddy currents. Perhaps we need to put a little more emphasis on *where* the magnetic field is that causes the eddy currents and *why* this is important, since we can't trust bored grad students giving Machines 101 lectures to not complexicate things for their students. --Wtshymanski (talk) 13:24, 2 October 2012 (UTC)

If the above is true, then it looks like it may have already started. Anything being taught today tends to become mainstream thinking in (probably) 10 years or so and (definitely) in 20. I presume that the nature of eddy current circulation in solid and sheet conductors in electrical machinery is still being taught (god help the future generation (no pun intended) if it isn't). Has new terminology been introduced or have they just obfuscated the existing terms? Unfortunately much teaching is often carried out by people who want to change the world or at least change the way we think (Environmentalism being the other natural home of such activists). Thank god, I no longer need to work and deal with these people.

Are you sure about your understanding of eddy currents? In the eddy current brake refered to above, the braking effect derives from the field from outside the conductor. Take that away and it doesn't work. In fact the EC brake doesn't need a sheet of conductor, a closed loop of wire will work as well and it is you that insists that that cannot carry an eddy current. AFAICT, it is the same effect in either the sheet or the wire. Same current from same source so why not give it the same name? 86.166.70.84 (talk) 15:03, 2 October 2012 (UTC)

An eddy current brake doesn't work like a squirrel cage in reverse. Andy Dingley (talk) 15:15, 2 October 2012 (UTC)

Induction generators would be hard to explain if only eddy currents existed. --Wtshymanski (talk) 15:48, 2 October 2012 (UTC)

But they do exist. Apparently they are called induced currents these days. 86.166.70.84 (talk) 16:08, 2 October 2012 (UTC)

It's easy because Eddy currents have induction, they generate magnetic fields. If you create them in a plate you can create them in the thickness (which is usually mostly just lossy, the magnetic field lines stick out the ends) or you can induce them in the plane, in which case the magnetic field sticks out the plane and you can use it for stuff. That's how induction motors work. That's how eddy current brakes work. That's how the maglev stuff works.Embrittled (talk) 17:22, 7 October 2012 (UTC)

That was not the point. 86.166.70.84 (talk) 16:08, 2 October 2012 (UTC)

Eddy current brakes, when you move the magnets past the conductor, are simply locked rotor induction motors. The torque/force curve is identical; they operate by exactly the same principles.Embrittled (talk) 17:22, 7 October 2012 (UTC)

FWIW somewhere or other in a book or a paper on the design of induction motors (that doubtless I won't be able to find) I read some largely throwaway thing where they mentioned that the induced currents in induction motors and eddy currents were of exactly the same type, but that as a terminology thing the term 'eddy current' was usually reserved for cases where they were predominately lossy.

However from Wikipedia's point of view that's problematic, because they're physically the same type of current so we should be linking to the relevant article, and pretty much all currents are lossy anyway.

There's also the issue that by not mentioning that it is eddy currents that drag the rotors around, it greatly complicates the explanation in this article of how these motors work.Embrittled (talk) 22:29, 16 October 2012 (UTC)

But the eddy currents in the conductors don't contribute to motor torque. Imagine a pole piece that 90 % iron and 10% copper in cross section, with uniform flux. 90% of the flux passes through the iron. The copper winding of the pole surrounds this flux and has a current induced in it. However, 10% of the flux passes through the *copper* itself. Since this, too, is changing, it necessarily induces current within the copper - this is eddy current, and because it just whirls around inside the bulk of the copper (eddies), it can't contribute to the current that is driven around the winding by the 90% of the flux that passes through *inside* the turn. As Andy Dingley said above, its *where* the flux is moving that makes the distinction between "induced current" (with no further qualification) and "induced *eddy* current". --Wtshymanski (talk) 02:30, 17 October 2012 (UTC)

The iron is a complete red herring and I don't know why you mentioned it, other than to obfuscate. As the poles rotate the lines of flux still have to cross the copper, and when doing so this generates the eddy currents that circulate around the poles as they move. The principle is exactly the same as this diagram, but played out on the circumference of the rotor:

Linear induction motors simply use sheet conductors, and they 100% simply use eddy currents, there are usually no bars or iron at all and there are no laminations to stop eddy currents forming; it works exactly the same as eddy current braking, but where the poles are being moved to cause motion of the rotor rather than simply stopping it. These are eddy currents in induction motors that cause the motion. It's just how they work.Embrittled (talk) 03:49, 17 October 2012 (UTC)

The iron is far from a red herring - maybe read up on salient poles. The purpose of the iron is to guide the magnetic flux, such that it passes entirely within a loop of copper. This places the maximum flux within the copper, for maximum useful induction. It also reduces the flux gradient across the copper winding (ie there is a sharp transition from the flux zone to the non-flux zone), to minimise lossy eddy currents induced within it. Andy Dingley (talk) 09:11, 17 October 2012 (UTC)

Oh sure iron does many useful things, and having it makes many induction motors a lot more efficient; but not all induction motors have or need iron.

What the iron doesn't do is change the nature of the currents that are doing the actual work.Embrittled (talk) 12:22, 17 October 2012 (UTC)

It may not change the "nature" of currents, but it certainly changes their magnitude. This is why it's used. What do you think it's for? Ballast? Andy Dingley (talk) 12:51, 17 October 2012 (UTC)

So far as I can tell from this thread, the main purpose of the iron is to use it to try to talk about something other than the induced currents and their properties, and avoid discussing which article in wikipedia covers these types of currents.Embrittled (talk) 15:32, 17 October 2012 (UTC)

Luckily motor builders don't read Wikipedia. Why a squirrel-cage winding, then? Why not maximize the eddy currents? Why not a solid cylinder of aluminum, then? (perhaps plated on an iron core.) I wonder if it would even turn. --Wtshymanski (talk) 19:46, 17 October 2012 (UTC)

Sure they turn. For example Tesla's Egg of Columbus is an induction motor, with no core in the rotor and huge air gaps and turns fine. How could you not know this? If you just use a solid conductive cylinder (which the very earliest induction motors did do) and you don't know what you're doing, then the reluctance of the flux loop can be very high and that weakens the field and eddy currents, and you tend to get low torque.

But research in the 40s showed that you can just use a cylindrical sheet of iron as a backing plate, and it can still be very efficient; like 85% or better; and some designs do away with the backing plate entirely, for example double sided axial flux induction motors don't need iron in the rotor at all. (Those particular motors the stators are expensive to manufacture, so they're not used very much, but they're very, very good, light, powerful and efficient.)

I must admit you're asking very odd questions, how is that you think you know this stuff when your education on this topic is so very thin and out of date? You're actually removing material from Wikipedia because "This is not how I was taught." Sorry, that's not how Wikipedia swings.Embrittled (talk) 00:05, 18 October 2012 (UTC)

Wtshymanski has never allowed citeable and reliable references to stand in the way of his personal and somewhat imperfect knowledge. You may have noticed that throughout this somewhat prolonged discussion, reliable references have been requested several times to support his view. So far, none have been provided beyond the assertion that he is right and every one else wrong. You may believe that that is 'not how Wikipedia swings', but Wtshymanski firmly believes that it should. DieSwartzPunkt (talk) 12:01, 18 October 2012 (UTC)

Just because you don't like Wtshymanski is no reason that he might not be right (in this case).

If I was to claim that induction motors only worked because they were pushed round by invisible elves on roundabouts, I hope it wouldn't take a ref from the IEE titled "Invisible Elf theory discredited in induction motors" before you knew I was wrong. Everyone agrees that induced currents are involved, necessary and useful, and that eddy currents are also unavoidably present. Embrittled's confusion that these are both, and always, the same thing is an addition to generally accepted principles and descriptions. As his own additional invention, it's hard to find a specific rebuttal of his particular confusion. Andy Dingley (talk) 12:53, 18 October 2012 (UTC)

I will agree with you that induced currents and eddy currents are not always the same thing. For example a transformer doesn't generate useful work due to eddy currents; and it certainly carries induced currents; the currents that flow in the secondary through the load are not eddy currents because the currents travel through multiple, separate components constructed with different materials.

However, conversely, eddy currents are always induced currents.

That eddy currents cause the motion in induction motors, you cannot find a rebuttal, because there is no rebuttal possible to this. In any reasonable definition of eddy currents, these are eddy currents that do the work.

I 100% guarantee you cannot explain any way in which these are not eddy currents, because they meet the definition of eddy currents.

It's a bit like claiming that brake pads cannot make a car go faster, but if you mount the brake pad on a shaft and spin the shaft you can (common name: 'a clutch'). And it's exactly the same with eddy current braking/induction motors. Eddy currents do useful work when you move the magnetic field, and that doesn't stop them being eddy currents.Embrittled (talk) 15:22, 18 October 2012 (UTC)

Liking or not liking anyone has nothing to do with it. And frankly, I am ambivalent on the point. Wtshymanski may be right. If he is right then it should be fairly easy for him to produce the requested references to back his claim up. But he has consistently failed to do so. What we are left with is the impeccably sourced reference that Embrittled cited that kicked this whole debacle off. That says Wtshymanski is wrong. Wtshymanski's personal knowledge does not trump a reliably sourced reference - even if he is correct. Wikipedia demands evidence. DieSwartzPunkt (talk) 11:38, 19 October 2012 (UTC)

"the impeccably sourced reference that Embrittled cited" I'm still waiting to see that. All I've seen was a bit of crappy writing from an overworked grad student, that looked like it was intended as a high school handout. Not a RS. Andy Dingley (talk) 11:48, 19 October 2012 (UTC)

The point is that the fundamental principle of induction motors is that they are pulled around by eddy currents in the rotor, and that needs to be pointed out in the introductory parts, because it makes it easier for the reader to understand. And we also need to point out that the terminology in this area usually refers to these driving eddy currents as 'induced currents' and as simply 'eddy currents' when they are losses in the iron or copper. But that's only terminology, they're still both eddy currents.

You're only going to find this point in relatively low level teaching type material, because everyone else is supposed to know this. In fact, clearly, not everyone knows that this is simply terminology.

For example, a secondary source that gets this right: [9] and is a good explanation of what's really going on.Embrittled (talk) 14:49, 19 October 2012 (UTC)

So if a standard handbook or textbook written for professional engineers distinguishes them, it's wrong, but if a dumbed-down explanation for kids mixes then up, it's right? Andy Dingley (talk) 14:55, 19 October 2012 (UTC)

An eddy current is any circulating current that stays within one piece of metal. Some eddy current flow directions do useful work, some don't. In this context the eddy currents that do some useful work in induction motors are, for convenience, referred to as 'induced currents' and those that do mostly useless work are referred to as 'eddy currents'. But either way they're both still only and always eddy currents, it's purely a terminology thing, so you know which current flow directions they're talking about.Embrittled (talk) 15:35, 19 October 2012 (UTC)

This is one of the demonstrations that we used to use for demonstrating the principle of the induction motor to students. We had a set up with three coils powered from the college electrical lab three phase supply surrounding a cylinder made from aluminium mounted on bearings (as I recall it was solid, but a hollow one would probably have worked just as well). On applying volts to the coils, the cylinder started to rotate up to just under synchronous speed. It did not accelerate particularly fast mainly because the coils drew a relatively small current. The demonstration also had a substitutable squirrel cage which accelerated faster, but this may have been as much due to the reduced mass as to the construction. There was also a magnetised cylinder but that is for another article. DieSwartzPunkt (talk) 12:01, 18 October 2012 (UTC)

There's a bit of trick there. Squirrel cages actually have higher resistance than sheet conductors of the same thickness. The real point of the squirrel cage in induction motors is to allow the iron to be used which closes the flux loop better. But if you're not using iron a sheet conductor of one skin depth is likely to perform better in most ways; it will give better torque for the same power. But changing the resistance changes the torque curve, a high impedance cage will be more 'draggy' and usually start much more quickly than a low impedance rotor, and be a better demo!Embrittled (talk) 15:22, 18 October 2012 (UTC)

Maximum torque is achieved in an induction motor when the resistance of the rotor (in whatever form it takes) is equal to its reactance. Probably a bit tricky for a solid rotor, but relatively easy for a squirrel cage or a wound rotor. DieSwartzPunkt (talk) 11:28, 19 October 2012 (UTC)

You can do this by having the right plate thickness if you use a cylindrical shell, or by raising the frequency and using skin depth to do much the same thing. Induction motors routinely use skin depth, that's why cages often have thick bars.Embrittled (talk) 14:49, 19 October 2012 (UTC)

Wrong Tesla patent is referenced

The reference for Tesla's first induction motor patent in this article is a 1996 book, "Lance Day, Biographical Dictionary of the History of Technology, page 1204" (ref 8), and it gives the first Tesla US induction motor patent as #381,968. This is the wrong patent, as I detail below. (Note my dispute has nothing to do with priority claims between Tesla and other inventors.) I claim the Tesla patent being identified as his first induction motor is simply the wrong Tesla patent. Tesla's first induction motor is actually to be found in his patent #382,279, which he filed six weeks after #381,968.

An examination of the referenced patent, #381,968, shows this motor to be a synchronous motor, specifically a variable reluctance synchronous motor. The patent figures clearly show an asymmetrical rotor, and the text describes the rotor as operating at exactly the same frequency as the rotating magnetic field, which is the key characteristic of a synchronous motor.

In Tesla patent #382,279, filed just six weeks later on Nov 30, 1887 (issued May 1, 1888), we see he has changed the rotor. Now the rotor has two single-turn shorted coils made of copper plates. The text makes clear that under load it runs slightly slower than the stator magnetic field. (In modern terminology it 'slips'.) And Tesla notes this motor has a "powerful tendency to rotation", which I think is his way of saying this motor has much more starting torque than his earlier synchronous motor. The motor of patent #382,279 is clearly an induction motor, so this article should reference this patent as the first Tesla induction motor.

The best reference I know for this is an essay on induction motors written by me, posted on my homepage [10], and I would like to change the Tesla patent reference to this essay. My credentials: 40 years as a motor control design engineer (retired), MIT graduate, 14 US patents several on induction motors, and since I retired and had an interest in motors I made a serious study of Tesla's early motor and generator patents. 24.61.212.124 (talk) 05:51, 4 October 2012 (UTC) Don Fulton, MIT 1964

Feel free to make changes. Wikipedia does have guidelines for citing yourself. In a nut shell from what I have seen the gist is "if you are an expert and have written well researched material on a subject then you should easily be able to cite the sources you used for your own material". The tricky bit is when you cite primary sources. Wikipedia does not encourage interpretation of primary source material unless you can cite where that interpretation has already been made in multiple peer-reviewed generally accepted secondary sources. A personal website also does not meet the WP:RS secondary source standard. Not that you have to master any of that to make a change or edit, if you want to make an edit that seems sensible, it will probably be right. Fountains of Bryn Mawr (talk) 14:19, 4 October 2012 (UTC)

Fiction in Wikipedia

I like Andy's suggestion that we allow "invisible elves" as an alternative explanation; after all, it can't be refuted by a reliable source. You'd also have a hard time finding a reference that says eddy currenrs aren't DC. I quoted a couple of books but who cares about that, they aren't on-line and so must be wrong. --Wtshymanski (talk) 17:11, 22 October 2012 (UTC)

They're related to the lift demons that keep aircraft flying. Andy Dingley (talk) 19:06, 22 October 2012 (UTC)

I suppose you think you have to resort to insults, since you have no valid arguments so far as I can tell. Physics textbooks are reliable sources and not fiction.Embrittled (talk) 21:25, 22 October 2012 (UTC)

The theory is spreading: [11] Andy Dingley (talk) 12:45, 23 October 2012 (UTC)

1. Please provide a clue as to what you are responding to.
2. As has been pointed out before to exhaustion, it is not up to anyone to refute an uncited claim. It is the person making it that has to prove it.
3. You are the one who started claiming that reliably sourced on-line references are wrong ([12] - check edit summary). 86.159.159.194 (talk) 12:58, 23 October 2012 (UTC)

Well, that isn't actually, technically, a reliable source in Wikipedia's definition, but it should at least have given them pause for thought; professors aren't usually flatly wrong about things like that. There's another example [13](about 31 minutes in and 47 minutes in) of this being taught as Eddy currents at MIT. Of course, that's not a reliable source(tm) either, but this is a reliable source: [14] and says the same things. Embrittled (talk) 15:34, 23 October 2012 (UTC)

Please note that User:Embrittled is currently using the following pages as his battleground:

Induction motor

Eddy current

Wikipedia talk:WikiProject Physics

--Guy Macon (talk) 09:43, 31 October 2012 (UTC)

Please note that Guy Macon is currently using those above pages to engage in multiple acts of hypocrisy revert warring, and major battlegrounding.Embrittled (talk) 20:46, 31 October 2012 (UTC)

Please stop attacking other editors. If you continue, you may be blocked from editing Wikipedia. --Guy Macon (talk) 03:00, 1 November 2012 (UTC)

Torque-speed curve, a short discussion on its derivation

Hopefully I come to the right place. I have a question concerning with the torque-speed curve.

I did quite a bit search on google and the model calculations I found based on equivalent circuit of a transformer are not good enough to me.

http://www.uotechnology.edu.iq/dep-eee/lectures/3rd/Electrical/Machines%202/IV_I.Machines.pdf

http://www.scribd.com/doc/18815834/188/Equivalent-Circuit-of-3-Phase-Induction-Motor-at-Any-Slip

http://www.scribd.com/doc/27304673/Torque-Slip-Characteristics

http://www.ece.ualberta.ca/~knight/electrical_machines/induction/basics/trq_speed.html

http://what-when-how.com/induction-motor/developed-torque-induction-motor/

Most calculations are based on the equivalent circuit, usually referred to as "transformer equivalent circuit". The key point of the derivation is that the part of the rotor which transforms electric energy into mechanic energy can be viewed as a resistance and its value is associated with the "slip" ($s$) by

$R_{r}={\frac {R_{2}}{s}}\,$

Using the circuit diagram on this wiki page, one can determine the power consumed by this resistance, it reads

$w=|{\frac {\varepsilon }{R_{s}+R_{r}+jX_{r}}}|^{2}R_{r}\,={\frac {\varepsilon ^{2}}{(R_{s}+{\frac {R_{2}}{s}})^{2}+X_{r}^{2}}}{\frac {R_{2}}{s}}\,$

Note that $X_{s}$ does not enter the expression since it does not affect the power consumed on $R_{r}$ once the input potential $\varepsilon$ is given. If one notices that the power is associated with torque $\tau$ and rotation speed of the rotor(not the "slip") $\omega$ (up to some constants) by the follows

$w=2\pi r\tau \omega ,$

If one assumes that $\omega$ is big enough therefore it can be treated as a constant,

$\tau ={\frac {1}{2\pi r\omega }}{\frac {\varepsilon ^{2}}{({\frac {R_{2}}{s}}+R_{r})^{2}+X_{r}^{2}}}{\frac {R_{2}}{s}}\,$

Above expression of the torque $\tau$ as a function of slip $s$ (and assuming everything else as constants) possesses exactly the feature shown in the plot on the page, and is reproduced from the above sources I have cited. A more realistic model may introduce more parameters but it will adopt essentially the same key features.

HOWEVER, look closely, the above model does not sound realistic to me at all. I will give two arguments below. First, let us for a moment consider that the the stator circuit and rotor circuit in general are physically separated (as in a transformer) and consequently they do have different currents, namely, $i_{1}$ and $i_{2}$. If one want to establish an equivalent circuit diagram as the one shown on the page, one has to take more care when calculating its effective resistance $R_{r}$ and reactance $X_{r}$. Considering two extreme cases. (1) When $s=0$, no induction will be present in the rotor circuit, therefore $i_{2}=0$ but in general $i_{1}\neq 0$. (2) When $s=1$, no work will be done, hence no energy transforms at all, this implies that the effective resistance is (almost) zero in the rotor circuit and the reactance is basically an inductance. In general one has $i_{1}\neq 0$ and $i_{2}\neq 0$. Note that these two cases are corresponding to end-points on the torque-speed curve. Now if one think the motor as a transformer, one should have

${\frac {i_{1}}{i_{2}}}\approx {\frac {N_{2}}{N_{1}}}=Const.\,$

where $N_{1},N_{2}$ are the corresponding turns. Obviously, here is not the case. The second argument is simple, the rotation speed $\omega$ in the above derivation is in fact associated with the "slip" by the following relation

$\omega =Const.\times (1-s)\,$

This is simply because the later is related to the difference of rotation speed between the stator and the rotor and the former is the rotation speed of the rotor. If one substitute this into the above expression, one no longer gets the "desired" torque-speed curve, so what now?

Following this line of thought, I actually tried to write down a proof by myself (a model of course, which reproduces the main feature of the observed torque-speed curve) and it turned out to be very different from the derivation shown above that I got from google.

I am not at all familiar with electronic circuit (except from those from college physics textbook), I am quite confused at this moment. If possible, could anyone please point out a source where one may find a well-established and well-recognized explanation, thanks in advance.

Gamebm (talk) 15:12, 8 November 2012 (UTC)

Non-notable history adds

I removed material on Philip Alger and Robert Park (dif) because they seem to be WP:UNDUE; they do not come up as notable inventors in any short history's on AC/induction motors[15][16][17][18] (Philip Alger only comes up as a historian). There needs to be some substantial secondary sourced material on this. Fountains of Bryn Mawr (talk) 15:13, 4 December 2012 (UTC)

Contributions stand on IEEE and other references and content provided.Cblambert (talk) 18:22, 4 December 2012 (UTC)

Philip L. Alger is the principal author (two other authors also being with GE) of the 'Induction Machines' section of 'Section 7 - Alternating-Current Generators and Motrors' of the 1949 (8th edition) Standard Handbook for Electrical Engineers (Archer E. Knowlton, Editor-in-Chief). Alger's author credits:

- Engineering General Apparatus Department, General Electric Company

- Fellow, American Institute of Electrical Engineers

- Member, American Society of Mechanical Engineers

- Member, American Society for Engineering Education

- Member, American Mathematical Society

- Fellow, American Society for Quality Control

- Member, The Institution of Electrical Engineers

- Member, Société Française des Electriciens

- Professional Engineer (New York State License

In that article, Alger-authored papers figure prominently:

- 1925, Development of Low Starting-current Induction Motors

- 1930, Induction Motor Performance Calculations

- 1939, with T.C. Johnson, Rating of General Purpose Induction Motors

- 1941, Transient Overspeeding of Induction Motors

- 1947, with H.R. West, The Air-gap Reactance of Polyphase Machines

You seem to be misunderstanding WP:V and WP:N. Verification does not come through how many papers you have seen somebody write (in fact that is WP:OR), its come through a consensus of reliable sources written ABOUT the person in question. Please supply some before you re-add this material. Fountains of Bryn Mawr (talk) 20:35, 4 December 2012 (UTC)

BTW re History of Woodworking refer to http://www.woodworkinghistory.com/appendix_21.htm

An account of the course of the development of the fractional horse-power motor is given by Philip Alger and Robert Arnold, in "The History of Induction Motors in America" Proceedings of the IEEE 64 1976, pages 1380-1383. (For another view of the fractional horsepower motor in America, click here for chapters 1 and 2 of George Schock's reminiscences of his pre-WWII time with the Baldor Motor corporation )

Alger and Arnold review the history of the induction motor from its invention by Nicola Tesla in 1888 through the various stages of its development: --the invention of the cast aluminum squirrel-cage winding,

--improvements in magnetic steel and insulation, and

--the progressive reduction of the dimensions for a given horsepower rating,

so that today a 100-hp motor has the same mounting dimensions as the 7.5-hp motor of 1897. Cblambert (talk) 22:35, 4 December 2012 (UTC)

I've just removed this yet again. If it's significant, it still needs to work harder at demonstrating its significance. It needs to do this by 3rd party statements saying "Alger was important for the development of the induction motor", not just citing Alger's own works and adding WP:OR to infer that this implies significance. Andy Dingley (talk) 00:15, 5 December 2012 (UTC)

I give up. If IEEE Global History Network and other references cited and if Park Transform's allowing an AC machine to behave like a DC machine is not history, the article in particular and Wikipedia in general has a big problem. I stand by the jist of my contribution a submitted earlier. So goodbye for now.Cblambert (talk) 01:00, 5 December 2012 (UTC)

Here is what Electrical Power Engineering Rensselaer Polytechnic Institute's Prof. M. Harry Hesse has to say in the 1st paragraph of the Introduction to Alger's 1970 book:

'From time to time there are cogent reminders that we are but dwarfs standing on the shoulder of giants. Philip Langdon Alger was one of those giants. In 1951 Dr. Alger published the book The Nature of Polyphase Induction Machines, John Wiley & Sons, and in 1965 The Nature of Induction Machines, Gordon and Beach Publishers. In 1970 he prepared the completely revised and updated second edition of the 1965 book. These books have become the classic standard reference works the world over and have earned him the name "Mr. Induction Motor."

. . .

'

And this is not history?!!!

You have got to be kidding.Cblambert (talk) 02:54, 5 December 2012 (UTC)

This is what IEEE Global History Network has to say, 'Philip Alger was most known for his work on induction motors and synchronous motors capable of direct, across-the-line starting, greatly simplifying motor controls. His 1928 AIEE paper, "The Calculation of Armature Reactance of Synchronous Machines," was long a classic in the annals of rotating electric machinery. Alger preciently imagined that for the expansion of electrification in industry, motors must be made smaller and lighter in weight. This task required a reexamination of many traditions in motor design engineering. He arduously promoted better engineering of motors and helped spur the adoption of new NEMA standards for motors in the 1940s. Motors built to those standards weighed less than a third as much as their predecessors and were quieter and more reliable.'Cblambert (talk) 03:07, 5 December 2012 (UTC)

Between 1928 to 2002, the IEEE Lamme Medal was award to 1 or 2 engineers on the basis of criteria consisting of ". . . leadership in the field, individual contribution versus group contribution, oriinality of contribution, breadth of work, inventive value and patents, publications, books and papers, achievements in other fields of activity or prominence in other fields, society activities and honors, length of time of dominance in field, quality of nomination.", medals being granted to Phil Alger in 1958, to Robert Park in 1972 and to Joachim Holtz in 2000. This is logical historical progressing from Alger's basic induction work, Park being able to exploit his 1925 paper because of interest in SCR-based VFDs, and Holtz ability to marry induction machines with fancy new VFDs.Cblambert (talk) 03:48, 5 December 2012 (UTC)

For the record, in the tribute at http://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=05876645 by IEEE Fellow R Krishman says:

“. . .P.L. Alger was known as "Mr. Induction Motor" for his seminal work on induction machines. In this era of variable speed motor drives, if anyone has to be named "Mr. Induction Motor Drive," the honor undoubedly goes only to Prof. Holtz for his everlasting this field. . . .” You heard it first here.Cblambert (talk) 18:11, 5 December 2012 (UTC)

In the 2000 "High Impact Papers in Power Engineering, 1900-1999" 2nd ranking paper

Park, Robert (1929). "Two Reaction Theory of Synchronous Machines". Trans. of the AIEE 48: 716–730

T. Heydt et al.’s has this to say :

“This paper present an extension of the work of Blondel, Dreyfus, Doherty, and Nickle. This paper presents seminal work on the development of Park's transformation: this transformation is widely applied in the analysis and study of both synchronous machines and asynchronous machines. The salient aspect of this work is a novel transformation the transforms linear differential equations with time varying coefficients with time ""invariant"" coefficients. The time varying coefficients arise due to inductances that vary with time and rotor position. The transformation converts the inductances to constant values. Park's transformation can be viewed as a transformation from stator variables to the rotor reference frame.”

Sounds 'way too deep' but another way of saying this is found in Krishman's tribute:

"The space phasor model enabled the understanding and reduction of the three-phase induction motor into an equivalent separated [sic] excited dc motor, which in turn led to decoupled torque and flux control (known as the vector control)."

And this is not worthy of Induction Motor article?!!!! Give up on the opportunity for induction motors to get rid of most of those pesky DC motors???!!!Cblambert (talk) 18:55, 5 December 2012 (UTC)Cblambert (talk) 06:11, 22 December 2012 (UTC)

Interesting précis of induction motor history can be found at http://classes.engineering.wustl.edu/2009/spring/ese435/docs/Induction_Motors.pdf.Cblambert (talk) 19:34, 26 December 2012 (UTC)

Equivalent circuit?

It is not apparent (by whats presented here) why this article even needs a section on Equivalent circuit. The old version was WP:JARGON that explained nothing to a general reader. The new version is worse. Probably should be deleted per WP:NOTTEXTBOOK, but since I know jack-shit about Equivalent circuits will leave for now so other editors can take a crack at making it encyclopedic. Fountains of Bryn Mawr (talk) 22:23, 7 December 2012 (UTC)

Wikipedia is a place to look up facts, an equivalent circuit is an appropriate fact for an electrical engineering article.Teapeat (talk) 03:35, 8 December 2012 (UTC)

The equivalent circuit is extremely notable. People that study induction motors in any depth in electrical engineering (and this clearly is an electrical engineering topic) are taught the equivalent circuit virtually 100% of the time. Not having it in the article would be completely unencyclopedic.Teapeat (talk) 03:35, 8 December 2012 (UTC)

Wikipedia does not just list "facts" (lists of facts are actually not considered encyclopedic per large sections of WP:NOT) This needs to be written for a general reader has no advanced education in the topic's field, or at least written to give them a clue as to why its there and what it has to do with induction motors. Also Formulae and the meaning of formulae should be explained in English (all per WP:TECHNICAL). Fountains of Bryn Mawr (talk) 23:02, 9 December 2012 (UTC)

I never said that there should be a list of facts, and this is not a list of facts. However, the wikipedia does contain facts. The equivalent circuit is for people that have to engage in electrical engineering with induction motors, electricians for example. I agree that it's not very useful for most people that simply want to know roughly how they work, but it's critical for people who want to know exactly how they can be used. For example if they were building an induction motor into an electric car, then this equivalent circuit is needed since it describes how the motor behaves when driven by a power supply, and it is also needed when including power phase correcting capacitors for calculating how big they need to be for any normal purpose.Teapeat (talk) 01:30, 10 December 2012 (UTC)

Note that Wikipedia is not an encyclopedia purely for a general reader, and if you think it is, I would invite you to read articles like: Topological ring.Teapeat (talk) 01:30, 10 December 2012 (UTC)

Dropping a block of nicely formatted algebra into an article without any explanation of *why* the maths is there, is not good for articles (in my much-humbled opinion). It's particularly bad in this case when the equivalent circuit has been simplified excessively without any notes on just how much of real motor behavior is being neglected. I've never met an electrician who was concerned about an equivalent circuit for an induction motor. This part needs more text and fewer equuations. Getting technical information out of Wikipedia is like getting meals at 7-11 - it's convenient, but unless you're really attentive to what you're doing, you're not going to get good nutrition out of the experience. The mathematics articles here are not very helpful - you can find recondite theorems of number theory explained in minute detail, but see what you get when you look at integral which goes off into inexplicable runes in the second sentence of the lead. --Wtshymanski (talk) 14:39, 10 December 2012 (UTC)

It is well to remember that until early December, the Equivalent circuit section read:

The equivalent circuit of an induction motor.

"The equivalent circuit of an induction motor has the equivalent resistance of the stator on the left, consisting of the copper and core resistance in series, as $R_{s}$. During operation, the stator induces reactance, represented by the inductor $X_{s}$. $X_{r}$ represents the effect of the rotor passing through the stator's magnetic field. The effective resistance of the rotor, $R_{r}$, is composed of the equivalent value of the machine's power and the ohmic resistance of the stator windings and squirrel cage."

That is, old Equivalent circuit section writeup was unmitigated rubbish! Current writeup is correct but considered too technical. It could be that the section should be simply eliminated.

Knowlton's Standard Handbook (1949, p. 711) for EEs provides insights:

"For design purposes and the calculation of performance characteristics^ from test data, the Steinmetz equivalent circuit theory of the induction motor is generally used. . . ."

^ For example, torque, current, P.F. and H.P. output.Cblambert (talk) 23:00, 17 December 2012 (UTC)

That's one strategy to make the Wikipedia more accessible on mobile devices; if we eliminated all the errors, we could probably fit the whole encyclopedia on a couple of 3 1/2 inch floppies. --Wtshymanski (talk) 01:49, 18 December 2012 (UTC)

See also http://de.wikipedia.org/wiki/Drehstrom-Asynchronmaschine, which has two interesting related sections:

• Idealized view / equivalent circuit
• Complex phasor model of the cage induction motors.

The latter section delves in even more complicated topics that this English Wikipedia article dealing with such issues as -- heaven forbid -- derivatives. Ugh!Cblambert (talk) 02:17, 18 December 2012 (UTC)

Note that there are two interrelated equivalent circuit issues:

• The Steinmetz equivalent circuit proper
• Routine Thévenin equivalent circuit analysis flowing from basic Steinmetz circuit, as for example, used for motor impedance $Z_{m}$ shown in Table of Basic Electrical Equations.

Re Thévenin equivalent issue, I noticed a breakdown torque discrepancy between Beaty version as shown currently in Table of Torque Equations

$T_{max}={\frac {1}{2\omega _{s}}}.{\frac {3V_{s}^{2}}{R_{s}^{2}+{\sqrt {R_{s}^{2}+(X_{s}+X_{r}^{'})^{2}}}}}$ (N.m)

and Knight version shown at link http://www.ece.ualberta.ca/~knight/electrical_machines/induction/basics/peak_trq.html

$T_{max}={\frac {1}{2\omega _{s}}}.{\frac {3V_{TH}^{2}}{R_{TH}^{2}+{\sqrt {R_{TH}^{2}+(X_{TH}+X_{r}^{'})^{2}}}}}$ (N.m)

where, in Knight version,

$V_{TH}={\frac {jX_{m}}{R_{s}+j(X_{s}+X_{m})}}V_{s}$

$Z_{TH}=R_{TH}+jX_{TH}={\frac {jX_{m}(R_{s}+jX_{s})}{R_{s}+j(X_{s}+X_{m})}}$

That is, Beaty version appears to assume $X_{m}$ is negligible whereas Knight version uses Thévenin equivalent where in the interest of accurately getting $T_{em}$ directly (without iteration using other equation) in terms of $s$,

$T_{em}={\frac {3V_{TH}^{2}}{(R_{TH}+{\frac {R_{2}^{'}}{s}})^{2}+(R_{TH}+X_{r})^{2}}}.{\frac {R_{r}}{s}}.{\frac {1}{\omega _{s}}}$

We may at some point need to accordingly correct this breakdown torque discrepancy.Cblambert (talk) 04:57, 22 December 2012 (UTC)

Cblambert (talk) 19:44, 25 December 2012 (UTC)

Equivalent circuit from Hungarian Induction Machine article that follows reflects nonsense?

More nonsense from equivalent circuit from following German Induction Motor article? (This is same equivalent circuit is as old equivalent circuit version for this article shown above in this section.

Cblambert (talk) 19:51, 28 December 2012 (UTC)

Well I, for one, am delighted with the content about the equivalent circuit, and am endebted to the authors for the name Steinmetz equivalent circuit. This is the sort of 'assumed knowledge' within the industry that is actually extremely difficult to find simply described, and even more difficult to find sources for. This whole section has saved me hours and hours of work today. And I find the algebra enlightening.--Robert EA Harvey (talk) 22:43, 16 April 2014 (UTC)

It is indeed good to get this sort of feedback on an article.Cblambert (talk) 05:22, 13 June 2014 (UTC)

Ferraris's research or Ferrari research or Ferraris' research?

My vote is for 'Ferraris research'. 'Ferraris's research' is likely not English. But not even 'Ferraris' research' is consistent. The research in question is presumably not all inclusive so that 'Ferraris research' leaves open the possibility that later research by Ferraris was published. Hence, 'Ferraris research' is correct.Cblambert (talk) 21:42, 5 January 2013 (UTC)

Ferraris's as per The Elements of Style (specifically this rule). a13ean (talk) 21:48, 5 January 2013 (UTC)

But there's not a hard and fast rule on wikipedia, see for example this discussion. a13ean (talk) 21:50, 5 January 2013 (UTC)

Reply is ok by me as far as possessive form of the two spelling options goes. Which leaves matter of whether two possessive options are not revelant. Is it 'Ferraris research' or not?Cblambert (talk) 22:01, 5 January 2013 (UTC)

The current phrasing "published Ferraris's research detailing the foundations of motor operation" is correct unless you need to make the possessive of the research somewhere else, then it's something like "Ferraris's research's lasting contribution to the field". a13ean (talk) 22:11, 5 January 2013 (UTC)

The plot thickens with heaven forbid two apostrophes in a row. I give up, but remain more comfortable with 'Ferraris research'. . . .Cblambert (talk) 22:36, 5 January 2013 (UTC)

How about Research by Ferraris eh?

Justification for history section claims about cleanup scattered and semi redundant claims, un-ref'ed claims, claims ref'ed to primary source)

A starting point for before-last History section maybe Fountain could provide justification for claims about 'cleanup scattered and semi redundant claims, un-ref'ed claims, claims ref'ed to primary source'. There should be a lot to chew on with these bald assertions. Refer also to History of the electric motor.Cblambert (talk) 05:23, 6 July 2013 (UTC)

Losing the Galileo Ferraris and Nikola Tesla pictures looks good, one of my two solutions. As to the other:

• In the "old version" claims per Galileo Ferraris and Nikola Tesla were scattered. The line "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." was moved to chronological order, paper was in April before Tesla's May demo, and end of sentence reads as a POV jab at Ferraris and does not have a valid reference.
• Semi redundant coverage of Tesla's paper, a little long, was truncated.
• "Tesla's U.S. Patent 382,279, filed in November 1887, however, described a shorted-winding-rotor induction motor." is a claim ref'ed to primary source.

Fountains of Bryn Mawr (talk) 22:02, 6 July 2013 (UTC)

The statement 'the apparatus based on that principle could not be of any commercial importance as motor.' comes from Vladan Vuckovic's paper, Interpretation of a Discovery which says in part

‘. . . Only in 1888, i.e. after the registration of Tesla's patents (a little before the mentioned Tesla's [sic] lecture), Ferraris presented to the public in Turin his way of production of rotating field and rotation induced by induction by means of immovable and contactless [author's emphasis] apparatus - by means of two-phase alternate currents. That was not a power system which would include the dynamo, the transmission and the motor, like Tesla's system, which was earmarked for replacing the entire existing electric power system with direct current, but it was an induction motor. On the contrary, Ferraris himself concluded in the same lecture that "the apparatus based on that principle could not be of any commercial importance as motor." This reference is definitely valid.

Motivation for highlighting Tesla's paper 'A New System of Alternate Current -- Motors and Transformer' by the following:

- Paper's multi-pronged coverage of alternate current power distribution involving motors and transformers,

- Paper's description is cited by 'Mr. Induction Motor' and historian, P.L. Alger, in his Proceedings of the IEEE 'The History of Induction Motors in America.' -- the paper is a seminal paper regarding AC motors of all types including induction motors. Tesla's genius comes through in the paper. But I agree that U.S. Patent 382,279 could also be included to advantage. Semi redundant is somehow less than satisfying justification.Cblambert (talk) 01:35, 7 July 2013 (UTC)

Content is not based what any particular source says, its based on what very reliable sources say and how they handle it. What Ferraris concluded about his induction motor or " Tesla's genius" is immaterial and a little WP:UNDUE in a short synopsis. Ferraris is simply considered the induction motors co-inventor per reliable sources such as The Induction Machine Handbook. Fountains of Bryn Mawr (talk) 21:37, 7 July 2013 (UTC)

Co-invention is not in question. You have to be kidding about genius being immaterial. I am not sure what your purpose in this is.96.52.198.210 (talk) 22:32, 7 July 2013 (UTC)

Although contentious conclusion about Ferraris is no longer in the text such a conclusion is of course an important potential part of the story.Cblambert (talk) 23:03, 7 July 2013 (UTC)

Winding in real motors

I'm trying to learn about induction motors.

the problem I'm having is that the windings in the models shown in websites, do not look like the ones in actual motors when I open them up.

I think it would help me if someone could tell me how an actual motor is wound and why

thanks

"Synchronous motor" example in introduction

What I'm concerned about is that the current version of the sentence in the introduction reads

"An induction motor...does not require mechanical commutation, separate-excitation or self-excitation...as in... synchronous motors."

This isn't true, is it? If I understand the terms right, not all synchronous motors use "mechanical commutation, separate excitation, or self excitation". Most of the small synchronous motors in consumer products, the ones readers are likely to have run into, are reluctance motors or hysteresis motors. For example, hysteresis motors have solid steel rotors in which a magnetic moment is induced by the rotating field. They are not induction motors, but they are not "mechanically commutated", "separately excited", or "self excited". So this is a false example. Readers who have any familiarity with small synchronous motors are going to be confused. I think the term synchronous motors should be removed from this sentence. --Chetvorno^TALK 09:47, 24 September 2013 (UTC)

Of course it's true, and it's the important advantage of induction motors. However this is Wikipedia, the encyclopedia that anyone can edit, so simple naive pattern-matching of the phrase "synchronous motor" is seen as over-riding any understanding of the technical sense of this sentence, i.e. that group of motors that don't use slip and induction to produce a field. The synchronous motors you describe are used domestically in microwave oven turntables and a shrinking number of clocks, little else. Those used in vacuum cleaners and food mixers are exactly the sort of brushed universal motors that this note is specifically addressing.

If you insist on changing this, then please at least do it in such a way as to make things clearer, not the usual half-understood wikibollocks that grabs onto "synchronous motor", misunderstands the point and then spends a page defining that these aren't unicorns whilst failing to explain the important comparison underlying all this, that which is already stated in the article as is. Andy Dingley (talk) 11:40, 24 September 2013 (UTC)

The sentence in question is contrasting induction motors, which do not require electrical connections to provide current to the rotor, with motors which do; there is nothing about slip. The sentence has two perfectly good examples already: universal and DC motors, which is enough to make the point. What I'm asking is why do synchronous motors have to be in there, when they are not a clean example? Some synchronous motors are separately-excited and some are non-excited. Why is it so important that they be in this sentence? If the desire is to compare synchronous with induction motors, this sentence is not getting to the heart of the matter; the presence or absence of slip. --Chetvorno^TALK 13:27, 24 September 2013 (UTC)

Consider the conservation of energy. If the rotor needs to be energised, that needs power to be transmitted to it. Either through brushgear, or through induction. If it's through induction (in the method used here) then it's necessary that the motor has slip and so isn't synchronous.

The sentence is making a valid comparison, highlighting the advantages of an induction motor (simpler excitation) but it does so using a term that is unclear (why "synchronous" implies "no induction" is far from obvious), a term that is imprecise (there are other types of synchronous motor too) and most of all, a term that highlights an aspect (synchronous rotation) that tends to imply that it's the rotation that's the significant aspect, not the excitation. I agree that the phrase here is unclear and that it needs to lose "synchronous motors". However, reading your first statement here, you seem to be suggesting that it's the idea of mechanical commutation that's the problem (agreed, the most obvious examples for synchronous motors aren't commutated) and that the phrase needs to be reworked to explain other types of synchronous motor, such as hysteresis motors. That change would be making this phrase utterly confusing to readers and completely disconnected to its purpose here in an introduction to induction motors. Once again, the wikigoggles effect - focus on one word at a time, focus on that word and an over-precise definition for it in a vain attempt to remove ambiguity, whilst at the same time completely ignoring editorial narrative for the overall article and the effect on the received learning of our readers. Andy Dingley (talk) 11:32, 25 September 2013 (UTC)

You misunderstood me. I'm only suggesting, as my original edit, repeatedly reverted by Cblambert shows, the removal of the term synchronous motors. I'm fine with the rest of the sentence. As a matter of fact, I'm the one who originally put it in the article. --Chetvorno^TALK 16:18, 25 September 2013 (UTC)

Unless anyone can make a convincing case that all synchronous motors are externally excited, I'm going to remove the term from the sentence in the introduction. I think the above discussion justifies this. Fair warning, Cblambert. --Chetvorno^TALK 04:27, 26 September 2013 (UTC)

I don't agree. There needs to be a way to word the first paragraph such that the complement of motors contrasted with asynchronous motors with other motors as not being asynchronous includes the synchronous subset as now described. That is important to drive home the idea that asynchronous motor excludes by definition synchronous motors.Cblambert (talk) 17:01, 2 October 2013 (UTC)

If you want to compare synchronous and asynchronous motors in the intro, instead of trying to force-fit synchronous motors into a comparison in which they don't belong, why not bring up the real difference, slip? Add something like: "Induction motors and synchronous motors are the most widely-used AC motors. The difference between the types is that while synchronous motors rotate exactly in step with the AC line frequency, induction motors require "slip"; the rotor must rotate slightly slower than the AC current alternations, to develop torque." --Chetvorno^TALK 23:32, 2 October 2013 (UTC)

By far the most important aspect of the induction motor is that economically, ruggedly, produces useful work in significant quantities. The induction motor does that without commutation or expensive separate or self excitation, or any other source of energy. Which is why such motors produced useful work in significant quantities are not typically universal, DC or synchronous. Hence the quite defendable sentence:

"An induction motor therefore does not require mechanical commutation, separate-excitation or self-excitation for all or part of the energy transferred from stator to rotor, as in universal, DC and large synchronous motors."

Slip is thus a distant secondary feature which does not warrant highlighting in the lead.Cblambert (talk) 05:54, 3 October 2013 (UTC)

Lead issues

It would be incredibly helpful if ya'll could re-write this lead. As it is, you pretty much have to already know what an induction motor is in order to understand it. Sometimes we forget that we're not writing these things for other experts, but for 6th graders and people who know zero engineering terminology.

Go 'head and nerd yourselves into oblivion in the body of the article, but please, for the sake of humanity.... re-write the lead as if you're explaining it to someone who's never heard of an induction motor. Seriously. Just try.

THANK. YOU.--Atlantictire (talk) 02:47, 19 June 2014 (UTC)

This should be made more clear !

"Synchronous speed An AC motor's synchronous speed, n_s, is the rotation rate of the stator's magnetic field,

n_s={2f\over{p}}, where f is the motor supply's frequency, where p is the number of magnetic poles and where n_s and f have identical units.[26][27] That is, for a four-pole three-phase motor with two pole-pairs set 180° apart, p equals 4, thus n_s = {2f\over{4}} which equals 25 Hz (1,500 RPM) and 30 Hz (1,800 RPM) respectively for 50 Hz and 60 Hz supply systems."

Although I am an electrical engineer, it is many decades since I last thought about induction motors. Hence I read this with the fresh eyes of the uninitiated:- "That is, for a four-pole three-phase motor with two pole-pairs set 180° apart". Apart from 'that is' instead of 'for example', I have this to say: As I understand it, the windings on the stator of a 3-phase motor will typically be of the distributed type, making it difficult to identify individual poles, but nevertheless the winding will produce a rotating field similar to that produced by a salient-pole type having 3 pole faces for a '2-pole' machine, and 6 for a '4-pole' machine. Thus 'poles' is being used in a particular and potentially confusing way, by analogy with the construction of a single-phase motor. The simplest type of three-phase stator (a 2-pole stator) actually has 3 magnetic pole faces. Moreover, in a 3-phase stator the physical pole faces are at 120 degree intervals around the stator in the first case (2-pole), and 60 degree intervals in the second (4-pole). so 'set 180° apart' also has a specialised jargon meaning which very few readers will understand. Only a motor specialist will understand that 'two pole-pairs set 180° apart' actually refers to a physical arrangement which can be more clearly described as 'two pole-triplets each occupying 180 degrees of the stator'. Or, alternatively '3 pole-pairs R-R', Y-Y', B-B', set at 60 degree intervals'. Would someone like to sort this out ? — Preceding unsigned comment added by 82.37.54.83 (talk) 07:02, 13 April 2016 (UTC)

I also don't like this...

"An induction motor therefore does not require mechanical commutation, separate-excitation or self-excitation for all or part of the energy transferred from stator to rotor, as in universal, DC and large synchronous motors." I suggest this as a replacement:- "An induction motor can therefore be made without electrical connections to the rotor as are found in universal, DC and synchronous motors."

I particularly dislike "for all or part of the energy transferred from stator to rotor" does this refer to electrical power converted to mechanical power (in which case it would be inappropriate for a dc machine), or to electrical power supplied by a separate source such as an exciter (in which case the power is not transferred from the stator). — Preceding unsigned comment added by 82.37.54.83 (talk) 07:34, 13 April 2016 (UTC)

Huh?

"Paraphrasing from Alger in Knowlton..."

This phrase makes no sense in this context, nor can Google shed any light on it. Can the author link it to an explanation (or just delete it)? Mark.velocino (talk) 16:18, 31 July 2016 (UTC)

It was added here, and is referenced.GliderMaven (talk) 20:04, 31 July 2016 (UTC)

Advanced Induction Motor?

I've seen multiple references recently to something called an Advanced Induction Motor, a few web searches suggest this is not just marketing language, but a change in technology for building induction motors suitable for low-speed operation, and useful in marine propulsion systems. https://www.researchgate.net/publication/3973201_The_Advanced_Induction_Motor It would be great if technology received more coverage in Wikipedia. Burt Harris (talk) 20:04, 11 December 2016 (UTC)

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Pole pair explanation

I believe the most relevant and misunderstood thing about 3 phase pole motors isn’t addressed. People see 3 main wound coils and don’t understand how and 3 legs feeding but don’t understand how you get 2 poles. They don’t understand only 2 coils have magnetic energy while the third coil is feed by equal energized legs equaling out or having little potential. The graphic showing 4 magnetic fields 90 degrees out equally confuses and misleads people as is 120 degrees. I look at other google recommendations for motor poles and most seem to not explain or just copy off wiki and copy the same mistakes Ox1111 (talk) 18:09, 20 December 2017 (UTC)

Otto Blathy invented the induction-based transformer but not the induction motor

According to, for example, Ottó Bláthy:

Kálmán Kandó, started work at the electrical section of the Ganz Works in 1894, understood that Nicola Tesla's induction engine could be used for railway traction. He and Bláthy began to investigate the problems of three-phase electric system including the traction. Bláthy developed the one-phase generator and transformer into a three-phase one and it was he, in fact, who actually improved the phase-converter electric locomotive devised in 1923.

According to, for another example, Biography of Otto Titusz Blathy}:

Blathy’s interest was also aroused by the three-phase system. (The system was discovered by the British engineer Hopkinson in 1880, when he realized that three alternating currents in phase shift with each other can be transmitted easier than normal alternating current.) Otto Titusz Blathy developed the up to now one-phase generator and transformer into a three-phase one.

The lesson here is that in principle the induction motor and the transformer are very similar and Steinmetz's equivalent circuit for the induction motor is essentially the same except for the motor slip having to be accounted for.

Bottom line, Induction motor#History's 2nd sentence that follows below here is definitely in error:

The first commutator-free single-phase AC induction motor was invented by Hungarian engineer Ottó Bláthy; he used the single-phase motor to propel his invention, the electricity meter.

His genius stems from inventing a single-phase generator and a single-phase transformer that were successfully used to work as a three-phase electric system. But he did not invent the induction motor. Cblambert (talk) 03:12, 30 January 2022 (UTC)

Link 37 dead

The 37th link is dead, requires replacement or addition source to provide further explanation 2607:FEA8:7A64:300:282A:3BF9:220E:432F (talk) 18:26, 25 March 2023 (UTC)