Talk:Three-phase electric power

From Academic Kids

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

"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)

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.

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)

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)

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)

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)

Regional bias?

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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)

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)