Talk:Three-phase electric power

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While this article talks about star arrangements for electrical machinery, it does not discuss Delta arrangements, which do not require a neutal connection, because there isn't one available. Also, the function of Earthing is not discussed. - kiwiinapanic 11:28 Feb 9, 2003 (UTC)

I believe Europe now uses 230 VAC supply (the average of UK's 240 VAC and continent's 220 VAC). - anon 24-May-2003

sort of the official standard is now 230V BUT it has such a wide tollerance band that both 220 and 240 are well within spec

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This page is still riddled with errors. UninvitedCompany 12:32, 6 Oct 2003 (UTC)

Contents 1 "two-phase" power in U.S./Canada is not quite right 2 phase sequence 3 splitting 4 more two phase 5 Rotary converter 6 Modern technology overloading neutrals 7 Regional bias? 8 Confusing phrases 9 Never heard of that one 10 constant power 11 Phase converters 12 Single Phase to Three Phase 13 Color Codes 14 A Laymen's Introduction Perhaps? 15 Phase Converters...comments needed on Solid State Digital Phase Converters

[edit] "two-phase" power in U.S./Canada is not quite right

"Two-phase" power in U.S./Canada is not quite right. Electrical grounding/earthing is "center tap", meaning that each small group of homes has a 240V transformer, with ground/earth tied to the middle. This makes the two opposite 120V sides exactly 180° apart, making them in-phase, and therefore considered single phase by most electrical engineers. Many appliances, including the central (forced-air) heating unit in my apartment, can operate anywhere from 208V to 240V, but the BTU/kW power and heating capacity ratings change correspondingly. Only resistive loads ignore phase like this though, whereas inductive loads like AC motors must have the phase[s] they were designed for. Larger commercial buildings almost always have three-phase, and sometimes do use true 208V two-phase for certain things, such as ballast for fluorescent lights. –radiojon 05:41, 2004 Feb 16 (UTC)

Connecting a ballast between A and C of a three-phase system does not make it a "two phase" load, it's a single-phase load connected line-to-line. And just to further confuse the issue, you can run a three-phase motor on single-phase power, though it will need help to get started and you usually don't plan to do this delibrately. --Wtshymanski 23:10, 16 Dec 2004 (UTC)

You're right. While there was at one time a fair amount of two-phase power in the U.S. (four wire service; two pairs 90 degrees out of phase), this hasn't been the case for decades. The two-phase systems had the advantage that the windings are the same for a capacitor-start single phase motor and a two-phase motor; that is, they are 90 degrees apart. Three phase service can be derived from two phase and vice versa using transformers.

The article is a mess right now because, as with the other electrical topics, there is so much difference in practices around the world that it is hard to make an integrated article, particularly since there aren't any contributors who have more than passing familiarity with practices outside their own country. UninvitedCompany 20:00, 17 Feb 2004 (UTC)

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Three phase systems have a very nice property, that if they are loaded by a linear load, the amount of power transferred is constant, it does not have a 50 or 60Hz ripple. This means that three-phase motors and generators do not have the vibrations associated with one or two phase motors.

I believe this is the reason for the popularity of the three phase system, as it allows enormous amounts of power to be generated using relatively light machines. If there were a ripple in the power, the machines would need to be very heavy to not be blown to bits by the it.

Would this be interesting information to put on this page?

Evert van de Waal

This is now worked out in some detail in the three phase article. --Wtshymanski 04:16, 31 Dec 2004 (UTC)

And, as as layman, someone explained 3-phase to me and commented that different houses in a street (or streets in a town) would be on different phases, whilst at the generating station 3-phase generation was most efficient. I found that very significant way to appreciating how I'd never known about it before - yet it was a ubiquitous feature. Would someone with a good understanding like to insert a short explanation of that feature. 134.244.154.182

Practices vary, and I'm speaking from a North American viewpoint, but often a branch feeder from a substation will be three phases but individual homes are only single-phase loads. I suppose you could dedicate a street per phase, but I'd expect to see that only in rural areas - in more densely populated places I've seen a three-phase feeder down the street and houses connected A,B,C...on either side. --Wtshymanski 23:10, 16 Dec 2004 (UTC)

[edit] phase sequence

from one of the images on your page Triplex outlet. The top 3 are used to run a phase sequence indicator comprised of 3 neon night lights. The bottom three run the desired triplex load. May i ask how exactly can neon lights indicate phase seqence? Plugwash 21:44, 26 Sep 2004 (UTC)

Beats me. You can interconnect lamps, capacitors and inductors to build a phase secquence indicator but that's not what the photo shows. I've never heard of or seen anyone attempt to supply a three-phase load with three regular duplex plugs - three-phase gear always has ONE plug with all phases in it. The photo is misleading because it shows a practice that is at the very best dubious and is almost certainly against any electrical code!

The most important thing about three-phase power is not the colo(u)r of the wires - this needs reorganization. All the stuff about testing is a bit too much "how-to manual", I think, for an encyclopedia...the article on heart I'm sure doesn't tell you how to start cutting for a transplant.

An article on the differences between UK and North American terms for electrical terms might make a good short Wiki project.

And on another matter: Anyone feeling up to explaining phasors and symmetrical components? Or higher phase order systems? --Wtshymanski 23:10, 16 Dec 2004 (UTC)

The more I look at the "triplexing" part of the article, the less I like it. I've never heard of such a scheme being used (three separate receptacles being used to power a single three-phase load - too error-prone to ever exist outside, perhaps, a laboratory situation). I'd like to remove that illustration as soon as I can get some proper images of real three-phase outlets. --Wtshymanski 04:16, 31 Dec 2004 (UTC)

there's a couple of images over at Industrial & multiphase power plugs & sockets e.g. the one to the right of this comment. or I intend to upload a 3P+N+E image soon.--Ali@gwc.org.uk 08:27, 31 Dec 2004 (UTC)

I can see how such an outlet arrangement could be usefull for lighting and i can see uses in a laboratoty situation but not for general perpose equipment supplies.

It is gone now. There is copy of the same in the Industrial & multiphase power plugs & sockets article, don't need two. Meggar 2005 June 29 03:00 (UTC)

[edit] splitting

This article is rather large anyway and it has almost noting on the mathematics of 3 phase.

I suggest a 3 way split three-phase: about the basic mathematics behind 3 phase three-phase electric power: about how and where 3 phase is used (ie most of what is here now) three-phase testing: basically what is now the testing section. This may be better located in a wikibook than here though i have little idea of the structure of wikibooks myself. Plugwash

ok no objections im going ahead Plugwash 21:36, 18 Dec 2004 (UTC)

ok well i've done it there is probablly still some content here that belongs on three-phase and there is a fair bit of three-phase that still needs writing. I've moved the color code information into a table beside the TOC expanded the intro section and altered the image so it fits beside the intro section. Plugwash 10:05, 20 Dec 2004 (UTC)

A good start but the article still rambles. "What's a neutral?" the reader will ask, or "Why are domestic loads single phase?" We need some a couple of simple diagrams to show the three voltage waveforms, and what we mean by "wye" and "delta" and "split phase". Something to work on during the holidays, I expect. --Wtshymanski 17:48, 20 Dec 2004 (UTC)

[edit] more two phase

"Two phase Like three phase, gives constant power transfer to a linear load." From my calcs this is not the case - can anyone confirm? --Ali@gwc.org.uk 23:48, 9 Jan 2005 (UTC)

Quick and dirty - call the phases sin(theta) and cos(theta), sin^2(theta)+cos^2(theta) = 1 for all theta, and power flow is proportional to the square of the voltage. So, two phases, 90 degrees apart in time, will also have a constant power transfer. --Wtshymanski 02:54, 10 Jan 2005 (UTC)

[edit] Rotary converter

The Wiki article rotary converter describes a completely different machine than the rotary phase converter used to make a 3-phase supply from single-phase power. This link is a little misleading. --Wtshymanski 01:52, 2 Jun 2005 (UTC)

It is written principally from the point-of-view of a traction engineer trying to convert three-phase AC power to direct current. But the rotary converter concept is fully-general; if you reversed the machine, it would create three-phase AC from DC. A similarly-constructed machine can convert single-phase AC to three-phase or vide-versa.

But you know what to do: be bold!! Please feel free to expand the rotary converter article as you see fit.

Atlant 11:50, 2 Jun 2005 (UTC)3fff

[edit] Modern technology overloading neutrals

Plugwash asks:

I've heared that this kind of thing is more of a problem in the usa due to lack of power factor correction cuircuitry. is this true?

I'm no expert but there's no doubt that modern switching power supplies seriously undermine the existing assumptions about how much current neutrals end up carrying in three-phase systems. As you doubtless realize, in the past, with passive loads (incandescent lighting, motor loads, and the like), the neutral only carried imbalance current and never more than the load of a single phase. The situation gets a bit worse with funny loads like fluorescent lamps and high-intensity discharge lamps. But now, with crappy switch-mode power supplies drawing huge current pulses but only at the peak of the sine wave (when the other phases are near zero volts), it's possible for the neutral to carry almost 3X the RMS current load of any phase wire!

One change that has definitely been made is that I think it has now become far less common to see "half neutrals" and such. Another change is that you guys over in the EU are starting to mandate power-factor correction on a lot more power supplies (although I don't think we're seeing as much of this in the US yet, but I'm sure it'll come along eventually).

I'm sure others know much more about this than I do.

Atlant 23:38, 3 Jun 2005 (UTC)

afaict half neutrals aren't allowed here in the uk anymore (i think they used to be but i'm not sure when they were phased out). I also belive that modern switched mode power supplies over here have correction cuircuitry to deal with this peak issue. However before we can add this to the article we need more solid information/sources. Can anyone here provide them? Plugwash 01:36, 4 Jun 2005 (UTC)

[edit] Regional bias?

Where the stepdown is 3 phase, the output of this transformer is ususally star connected with the standard mains voltage (120 V (in north america) or 230 V (in Europe)) being the phase-neutral voltage.

Someone embedded the following question in an HTML comment:

this comment shows rather a lot of national bias mentioning only north america and europe how best to deal with it?

-- Beland 01:57, 19 Jun 2005 (UTC)

Link to a list of systems, or place the list somewhere in this article. Crowding functional explanations with complete lists of examples isn't helpful. --Ikar.us 20:04:52, 2005-07-22 (UTC)

[edit] Confusing phrases

the output of this transformer is ususally star connected with the standard mains voltage

Can someone explain "star connected" with a sentence or two or a link to an appropriate article?

Another system commonly seen in the USA is to have a delta connected secondry with a centre tap on one of the windings supplying the ground and neutral.

Ditto for "delta connected secondry with a centre tap".

This allows for 240V three phase as well as 3 different single phase voltages (120V between two of the phases and the neutral, 208V between the third phase (known as a wild leg) and neutral and 240V between any two phases to be made availible from the same supply.

It's not clear why the third phase is 208V off from the neutral, or where the second 240V figure comes from, exactly. -- Beland 02:04, 19 Jun 2005 (UTC)

lemme think about this i think some diagrams may be needed of what star and delta are. it may be better to put them on the 3 phase page though as this one is already rather big. Plugwash 02:35, 19 Jun 2005 (UTC)

Hm, right now, there are no articles like Delta connection, Star connection... I only found Y-delta transform. As delta and star connections are a crucial part in phase systems, I would say there should be seperate articles for both. --Abdull 09:34, 22 July 2005 (UTC)

[edit] Never heard of that one

Three phase systems may or may not have a neutral wire. A neutral wire allows the three phase system to use a higher voltage while still supporting lower voltage single phase appliances. (from the introduction).

How does a neutral wire allow to use higher voltages on the phases? Thanks, --Abdull 08:51, 22 July 2005 (UTC)

If it is necessary to provide a specific one-phase voltage, then it is necessary to have this as the delta voltage, if there is no neutral wire. If the neutral wire is present, the voltage level can be chosen higher, so that the required voltage appears between phase and neutral. For example, in Austria existed 220/127V systems together with 380/220V, the latter need a neutral to supply 220V.

However, allowing a higher voltage is not the basic purpose of the neutral and may be confusing. --Ikar.us 10:47:58, 2005-07-22 (UTC)

thank you very much for that piece of information. Actually, what do you mean with the slash in 220/127V, or 380/220V? Thanks, --Abdull 11:45, 22 July 2005 (UTC)

The first number ist the delta voltage, i.e. the voltage between two phases. The second number is the star voltage, i.e. the voltage between each phase and the neutral (the first devided by sqrt(3)). --Ikar.us 11:59:48, 2005-07-22 (UTC)

so what is the main reason for chosing a 4 wire system with neutral and loads connected star over a 3 wire system with no neutral and the loads connected delta? higher voltage is the main one i can think of Plugwash 13:18, 22 July 2005 (UTC)

In a 4 wire system, you can connect incandescent lamps single-phase to neutral, and motor loads as three phases - for example, 120 V lamps and 208V motors for A/C ( in North America) or 240 V lamps and 415 V motors ( 240 volt countries). The advantage is that you don't need two systems at different voltages for lighting and power loads. I remember being troubled by the single-line diagrams for station service power of the Owen Falls Dam generating station extension till I realized...no lighting transformers! Lighting loads and motor loads all came from the same motor control center. In Canada, if you have a 600 V 4 wire 3 phase system, you can buy HID ballasts rated 347 V and they have a warranty, whereas 600 V ballasts aren't warranted by the manufacturers. --Wtshymanski 15:57, 22 July 2005 (UTC)

[adding my already written answer before reading Wtshmyanski's one]

One simple advantage: A one-phase circuit needs just one fuse in the phase. If it is delta-connected, it needs two fuses. In the case of real fuses (instead of circuit breakers), it is problematic that they aen't coupled.

Concerning power capacity, a 3-phase device can consume three times the power of a one-phase device, with same voltage and ampere rated components and lines. In delta-always-settings, the factor is only sqrt(3). So the same voltage level can accomodate a wider range of application needs.

Note that the four wire system doesn't mean that really all four wires have to be present (which would somewhat countervail the capacity gain). If the device consumes equal currents in all 3 phases, the neutral wire doesn't have to be present at all. The phase components can be star connected with open star point. If the currents aren't equal and the neutral wire is present, the sum of the 4 currents never exceeds 3 times the maximum current in one. This allows thrifty dimensioning of the lines.

--Ikar.us 16:19:29, 2005-07-22 (UTC)

[edit] constant power

I thought about the following statement from the article: Three phase has properties that make it very desirable in distribution. Firstly all three wires carry the same current. Secondly power transfer into a linear balanced load is constant.

the power transfer statement was some sort of odd to me, until i came up with the following:

We have three phases

Imagine a powerline system with star connection. We have a (nearly) evenly distributed resistance on all three phases, that is:

R₁ = R₂ = R₃ = R

Imagine a big city with thousands of households all having random electrical machines at random phases in use, so in general you can think of three resistances of nearly the same size with negligible aberration among them.

Now, if we want to take a look at the time behavior of electrical power within the three phase system, we would say:

With the help from trigonometric identities (that is power-reduction formulas), we will have:

480° equals 120°.

Next, we can use Angle sum and difference identities:

Sorting it all, we will have:

Actually, and , so we end up with:

Although we started to look at the behavior of the electrical power over the time, we finally ended up to find out that in a three phase system, power is time-invariant, constant - which is good for a power plant (isn't it?).

I hope I didn't make a mistake. In my eyes, the article is missing some formulas, and if someone wants to give the above calculation a final touch, go ahead, it'll be great to put it in the article. --Abdull 14:25, 23 July 2005 (UTC)

That means time-invariant within one period? Perhaps this should be stated more clearly, also in the already existing sentence. Readers could wonder how three-phase power can influence how loads are switched on and off. --Ikar.us 08:59:27, 2005-08-02 (UTC)

Hi Ikarus - once again, take a look at the last expression:

the t in p(t) can be 5 seconds, 12 seconds... any point of time. It turns out there is no "t" in the expression on the right side, therefore p(t) is constant at any point of time. It is time-invariant within one period, so to speak. --Abdull 12:10, 2 August 2005 (UTC)

It is time invariant provided the load stays the same. obviously if devices are turned on and off that will affect the power flow but there is no constant oscillation like there is with single phase transmission. Plugwash 01:24, 1 April 2006 (UTC)

[edit] Phase converters

I started a Rotary phase converter article that discusses rotary phase converters in general. I changed te link in the phase convertser section of this article to opint to that new page. The previously referenced page discusses rotary converters in general and made little relation to phase conversion (making of third phase). I hope that this change is acceptable and would like to ask for contribution to the Rotary phase converter article.

Thanks! Ichudov 19:41, 12 January 2006 (UTC)

User:65.184.166.57 added something about energy storage being required for phase converter operation. I think the revision by User:Atlant improved what the previous editor was apparently trying to say, but I don't think the original addition is correct. I think that energy storage is needed to produce a phase shift and is unrelated to the discontinuous vs. continuous power flow. --C J Cowie 15:15, 18 January 2006 (UTC)

I think that energy storage is needed to produce a phase shift and is unrelated to the discontinuous vs. continuous power flow.

Well, both, actually, they're sort of two sides of the same coin. If you think about a hypothetical single- to three-phase converter without any energy storage (imagine just three voltage converters that could instantaneously convert X volts in to Y volts out), then during the zero-crossings of the single-phase input waveform, the voltage converters would have no input voltage to convert to the three phase outputs! So a converter must store energy to continue outputing voltage during the zero crossings of the input waveform.

Another way to look at this is to say that the input single-phase waveform is time-shifted (~phase-shifted) to form the three output phases. But the time shifting process is just another cloak for energy storage.

Atlant 17:40, 18 January 2006 (UTC)

[edit] Single Phase to Three Phase

I want to convert single phase to in 'three phase', any one have solution about this matter?

I think the article discusses this (otherwise, one of our articles does; Google with "three phase site:en.wikipedia.org". But the usual solution today is an electronic converter. In t he old days, a motor-generator set or rotary converter was used.

Just curious: what application are you supporting that needs three-phase power? Usually, the serious applications are too big to conveniently power from a single-phase supply.

Atlant 12:55, 11 February 2006 (UTC)

The rotary phase converter article describes a relatively inexpensive "do-it-yourself" method. This method is often used by metal working hobbyists and others who buy used machine tools with three-phase motors. To operate a single three-phase motor you might consider using a Variable Frequency Drive. Newer small models accept either single-phase or three-phase input power and produce three-phase output power with provisions to change the frequency to adjust the speed of a three-phase motor. Some models even have a voltage multiplier circuit to accept 120 volt single-phase input power and operate a 240 volt, three-phase motor. Some older models that might be found on eBay will accept single-phase input power and operate reliably with a load current that is about half the normal rating. If you download the instruction manual before buying, you can determine the capability in advance. --C J Cowie 15:12, 11 February 2006 (UTC)

[edit] Color Codes

Are the color codes for North America correct? I thought L1=Black, L2=Red, and L3=Blue The page is currently showing L1=Red, L2=Black, and L3=Blue.

That's how they were, but 70.65.132.11 changed them (see here). Any reference(s) for the correct colours? --Evan C (Talk) 01:03, 1 April 2006 (UTC)

[edit] A Laymen's Introduction Perhaps?

First I want to say that this article was obviously written and contributed to by people who really know what they’re talking about. The depth of the technical detail is impressive.

However, coming in as a layman rather than an electrical engineer, electrician or mathematician, I was lost almost from the beginning, looking for a simple explanation of what three-phase as compared to a ‘normal’ electrical supply was. I have seen this issue before in Wikipedia articles—experts provide great in-depth detail without realizing that the average user may be looking for a concise, high-level explanation of the subject that can be quickly read and understood to a limited degree (drive-by users I call them). I doubt most people have more than a minimal understanding of AC power generation and transmission to begin with, so by immediately jumping into pretty technical details, a majority of readers may be left behind without gleaning even a basic understanding of the subject. For this article, I think it would be great to have a short introduction that in simple language explains, for example, why a three-phase supply is better suited to motors for industrial duty, while most household appliance motors can get by with single-phase that's usually supplied. peterr 02:55, 15 October 2006 (UTC)

It's in there, but maybe it should be moved to the top. The whole point of having a 3-phase system is to run AC induction motors. Or stated more clearly: the whole point of the Tesla Polyphase System installed by Westinghouse Corp is to operate Tesla's polyphase AC motors. These are brushless motors which require two or more AC circuits with differing phase to create a rotating magnetic field that drags a copper/iron cylinder into rotation. No other reasons for having multiple AC phases make much sense, since other types of loads don't require 3-phase, and smoother DC rectification is a historically later benefit (Rectifiers didn't even exist in 1896 when Westinghouse Corp first started installing the Tesla Polyphase System.) --Wjbeaty 02:24, 21 October 2006 (UTC)

I realize it’s all in there and well-explained, and the introductory sentence does mention AC induction motors. But the very next sentence is “Three-phase systems have at least three conductors carrying voltage waveforms that are 2π/3 radians (120°,1/3 of a cycle) offset in time. In this article angles will be measured in radians except where otherwise stated”. This reads like a textbook, and in my opinion could scare away a reader with no concept of waveforms that measure 2π/3 radians, or those not prepared to use units other that radians for angle measurements (when specifically told to do so).

The article titled “Three-phase” has as its introductory sentence the second sentence of this article. The other article too jumps straight into technical concepts and mathematics, rather than providing a quick overview of AC power, or at least a link to a layman’s article on the subject. (BTW I think these two articles should be combined—there is redundancy, and I’m not convinced of the usefulness of the shorter one that provides strictly a definition without touching upon application. For example if I wanted to find out what a bolt was, I would be pleased to have the same article that describes it as cylindrical and threaded go on to explain its primary use as a fastener.)

A waterfall that from the top down moves from high-level, easy to comprehend concepts for the layman, down to hard-core technical details for the initiated, is the structure I’m advocating. There may exist already guidelines on this, and certainly there are a multitude of other articles that would benefit from friendly introductions to their complex topics. I’m not picking on this article in particular; rather, because of its quality and wealth of information, I think it makes a good example of what a great Wikipedia article could be. Writers on technical topics should consider the possibility that much of their audience is being directed to their articles from mainstream searches, not from footnoted references in scholarly publications. Wikipedia should be not only accurate and comprehensive, but accessible to users of all educational backgrounds and fields of expertise. Introducing an article by supplying a useful, high-level definition in a non-intimidating manner may interest and encourage a user to read on to the nitty-gritty if he chooses. If he is satisfied with only the high-level definition, then the article has still served its purpose. Nothing is gained by anyone when a reader is scared away by immediate immersion into complex or esoteric discussion, and I don’t think it is in the spirit of Wikipedia to be, or appear to be, elitist.

From laymen looking for one-minute definitions to professionals seeking in-depth answers, people of all backgrounds should find Wikipedia the best all-around encyclopedic resource on the Web. Contributors of the highest caliber, however, must assume that many readers of their articles may be completely new to the topics. Detailed, technical information drawn from accumulation of knowledge and wealth of experience is of course invaluable to other professionals and students, those readers of the ability to comprehend such. However, there is should exist the responsibility to provide for the most casual of information seekers as well, those who enter having no knowledge of the topic whatsoever. These users deserve the best the contributor can provide in the manner of a concise, easily-understood definition or overview of the topic, and the contributor may take as much pride in creating this as in the sharing the detailed information that follows. It may well be that a great majority of readers require that high-level explanation, and the ability of an expert to distill the complexity of their topic into this concise, layman-friendly introduction speaks to his professionalism and generosity.

To conclude this overlong “comment”, although an introduction of sorts may be in there somewhere, it’s not what I envision for the layman who just wants to know if his toaster runs on three-phase current.

BTW from what else I’ve read regarding the adoption of three-phase AC generation and transmission, it was due to more than just its ability to start Tesla’s AC motor turning, but I get the feeling you don’t believe the other arguments for the system. I’d be interested in what makes your opinion on this so strong. I’m a layman myself, but this fascinates me, so I’ll try to keep up with whatever you want to tell me. And thanks in advance!

peterr 02:44, 23 October 2006 (UTC)

[edit] Phase Converters...comments needed on Solid State Digital Phase Converters

In doing some research on phase converters, it can all be rather confusing when trying to choose which are better than others, particularly looking at 10HP models, and intrigued of the new phase converter on the market by Phase Perfect which introduces a Solid State Digital True 3 phase converter. Intended to be a 3rd choice as opposed to rotary and static. Wondering if anyone has comments on this new device, seems to be revolutionary to Phase Converters? —The preceding unsigned comment was added by Mag43 (talk • contribs) 00:59, 5 December 2006 (UTC).