Talk:Alternating current

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[edit] Mathematics of AC Voltages

Why is this discussion done in terms of voltage? I realize that ac voltage often accompanies ac current, but seeing as how this is an article about ac current it seems better to just stick to ac current. The math won't be any different, so I just don't see the reason to switch to voltage for calculations.

[edit] Does anybody really know what times sign it is?

Just wondering if anyone else finds it confusing that the multiplication sign is an 'X', the symbol for cross product. I realize that this or a dot are often used, but with the inclusion of the sine function in the equation already it may be misleading. --Bmalicoat 23:47, 26 October 2005 (UTC)

The problem, of course, is that the "x" is the Wiki-generated symbol from the "times" markup (shown below). As long as that's the case, I think it should stand as currently written. You could, of course, start lobbying the Wiki software guys for a change (that would affect every usage of "times").

:<math>v(t)=A \times\sin(\omega t),</math>

Atlant 12:07, 27 October 2005 (UTC)

Ahh, I didn't realize that, thanks.

Bmalicoat 03:12, 28 October 2005 (UTC)

[edit] "Primitive" induction coils?

The wording "His design was a primitive precursor of the modern transformer, called an induction coil" is not very NPOV.

I'd like to see some pictures of AC in action words can't describe it well enough. --Cyberman 02:30, 10 Feb 2005 (UTC)

I think this page is nice. Congratulations to those who've been working on it. I nominated it for featured articles. A picture would be nice, though. Power cables, transformers or something. Washington Irving | Talk 23:21, 25 Mar 2004 (UTC)

I could write a part about transforming DC->AC through a solenoid- condensator circuit and a triode. Anyone think this is useful and/or fitting here?
- Xorx77 17:09, 28 Mar 2004 (UTC)

That would be good, but perhaps it would be more appropriate in the HVDC article under "Rectifying and Inverting". You could add a link from this article to that one. -- Heron 17:16, 28 Mar 2004 (UTC)

I changed the usual Teslaphile stuff to give due credit to some of the other critical workers in the field. Look guys, I know you venerate the guy, but the reality is that his contribution to the field, although undoubtedly important, was just one aspect of many advances in electrical engineering at the time. In particular, describing him as the father or inventor of AC makes a good book blurb but is totally unsupportable. Among the critical parts of the infrastructure he didn't invent were: transformers, the AC distribution system, AC generators, or meters. His major practical contribution was AC motors - and the first one he ever built that actually worked, was under contract to Westinghouse. Securiger 13:18, 21 Jun 2004 (UTC)

I updated the sections on power and 3 phase systems, which are hopefully a bit clearer now. Also the section on earths and neutrals which had become a little muddled. The earth is not the same as a neutral. A neutral is used to form a complete circuit in a healthy system, an earth is used to provide a specified path for current during a fault.

[edit] Perfect sine wave?

Did the guy who wrote this ever actually stick the probes of an oscilloscope into the wall outlet?

[edit] Focus

The article currently has a lot of stuff that is covered in other articles; three phase, grounding, etc. I think the discussion here could be compacted since details are only a mouse-click away. I also cleared up some leading spaces in the talk page - not everyone is signing contributions - use the button for signatures in the editor or else manually put --~~~~ at the end of your comments. --Wtshymanski 17:26, 1 Jun 2005 (UTC)

[edit] Notation

"(In this section overline will be used to indicate phasor or complex quantities and letters with no annotation will be considered the magnitude of those quantities.)"

Is this a standard notation? - Omegatron 23:16, August 14, 2005 (UTC)

It wasn't standard when I was studying or practising electrical engineering (although that may just indicate how old I am!). A one-side-head horizontal arrow over a symbol was sometimes used to indicate a vector quantity, but most texts used boldface symbols for that. I always used a simple overline in the statistics sense - a mean or average (rms of course). Magnitude was denoted with matrix notation e.g. |z|. Plain symbols were used only for DC. Of course we used e for electromotive force and i for current, which drove the mathematicians nuts because they had totally different meanings for them. To top it off, because i was already in use, we used j for what mathematicians call i. I'm certain we can never find a notation that satisfies everyone, so we have to clearly specify the one that we use, then keep it consistent across related articles. Boldface and || have the advantage that they can be expressed directly within WP - no CSS or PNG required. JohnSankey 17:54, 5 October 2005 (UTC)

[edit] Merging everything AC into one article

I consider the concepts of electrical current/voltage, resistance/reactance and power to be sufficiently different that they should not be merged, otherwise the combined article will become too long and very difficult to organize clearly. I note that there is inadequate discussion in these articles of non-sinusoidal waveforms, particularly of the substantial 3rd and 5th harmonics generated by the non-linearity of standard power transformers - that would make a combined article even longer. Then there are the square and 2-step waveforms of DC-AC power converters. I recommend keeping these three separate but consistent, with appropriate cross links. As a retired electrical engineer, I could try to start this process, but would do so only when agreement is reached on separation. JohnSankey 15:31, 5 October 2005 (UTC)

So much for an offer :-( JohnSankey 22:59, 5 October 2005 (UTC)

Can we remove some of the merge templates then?--John 23:45, 16 October 2005 (UTC)

[edit] Nomenclature

Just to note that "mains power" is a British term. I have never heard it used in North America. JohnSankey 22:59, 5 October 2005 (UTC)

It's used at least occasionally in North America. Especially as compared to (say) "battery power".

Atlant 01:03, 10 October 2005 (UTC)

[edit] Real Power / Apparent Power

Why do these articles simply redirect to this article, when this article makes no mention of them?

[edit] Problematic entry from the ground-up

I am sorry if I sound negative, but this article/entry (Alternating current) is un-organized, and even though it's extraordinarely short for such an important and vast subject, it feels too long to read.

The consequences of the bad architecture of the entry, is that even contributors have trouble striking the right balance when trying to add relevant information. For example, Nikola Tesla is under-represented, even though he has almost single-handidly produced virtually all the elements of the puzzle necessary for the AC power system (I won't spend time documenting this point, if anyone thinks it's open to dispute, I'm willing). I don't blame it on anyone's agenda, but simply, on the fact that the article is discouraging of contribution. I have tried, anonymously, to correct few of the more evident errors, and am preparing to beef up the body on Steinmetz and Tesla. Still, every time I think of this wikipedia entry, I feel pain in my stomach, so I keep putting off the big work for another day. Old-fool 17:56, 21 October 2005 (UTC)

One way to handle this dilemma is to create an entirely new version of the article. You can initially create it in something like "Alternating Current/new_version", tweak it until it's as you want it, and then open it up for review and collaborative editing. When the article is "fully baked" we can replace the existing article with the new article.

There is definitely a life-cycle to many Wiki articles:

They're initially created terse
Over time, they "accrete" aditional information, often in a somewhat-jumbled way
At some point, somebody takes the initiative and resturctures the whole thing to make all the accreted info flow as a coherent narrative.

That somebody sounds like you! Time for you to be bold!

Atlant 12:17, 27 October 2005 (UTC)

[edit] Power equation problem

I don't know what you mean by power lost = I^2 * R. This is supposed to be the equation for power transmitted, and since V=I*R, power = V*I also. Therefore, I don't see why the power equation explains why current affects power lost and not voltage. Can someone clarify this please?

It depends on which R you are referring to. Power lost is I^2 * R(of the conductor). Power delivered is I^2 * R(of the load). pstudier 03:55, 3 November 2005 (UTC)

I do see a problem with formulas however. P=I^2R and P=IV of course, but coupled with introduction of "This implies that in the same wire, if the current is doubled, the power loss will be four times greater", to some readers this might suggest that if the voltage is doubled, the power loss will NOT be four times greater, which is certainly not the case because P=V^2/R too. Something should be done about this, but I am not sure what. Nikola 09:33, 4 November 2005 (UTC)

You have to be careful, when you are using P=V^2/R, to specify what V you are referring to. Your statement above suggests that you are talking about the voltage drop across the wire. Doubling this would indeed cause a quadrupling of the power loss. However, the V usually referred to in this context is the transmission voltage. Doubling this causes a quartering, not a quadrupling, of the power loss. I'm reluctant to explain this in the article because it would just add confusion where there is presently simplicity. However, I'm open to ideas. --Heron 17:09, 5 November 2005 (UTC)

[edit] What is AC and DC and what do they do?

I would suggest that you read Wikipedia articles on alternating current and direct current. Nikola 22:54, 28 November 2005 (UTC)

[edit] Needs a complete rewrite

This is a shockingly sparse and badly organised article considering the importance of AC power in the world.

[edit] Volt-amp

Volt-amp redirects to this article, but I don't see any mention of it here. In particular, I'd like to know how volt-amps are related to watts. (I thought were the same, but then why is a UPS I'm looking at rated at "500VA" but "300W"?) - dcljr (talk) 04:50, 16 January 2006 (UTC)

i've just changed the redirect to point to AC power. enjoy ;) Plugwash 04:51, 16 January 2006 (UTC)

[edit] other parts of the world?

Quote:""It is generally accepted that Nikola Tesla chose 60 hertz as the lowest frequency that would not cause street lighting to flicker visibly. The origin of the 50 hertz frequency used in other parts of the world is open to debate but seems likely to be a rounding off of 60 Hz to the 1-2-5-10 structure, called a set of preferred numbers, popular with metric standards.""

What other parts of the world? I assume other than the U.S.A. If you take a look at the frequencies used you will notice that 50 hertz is the most commonly used frequecy , with a few (but major) exceptions (mainly North America). It's a minor issue of how you put it , since I don't think all users of wikipedia regard this from the point of view of an american as we can't be all americans :))

To a degree a reasonable point, but modern electrical systems was first developed in the US and then introduced in Europe, so I think the writer is unwittingly formulating it from a historical point of view. More importantly, Wiki shouldn't claim "general acceptance" (opinion) unless it really is so. As best as I can tell from some surfing and reading, the details of the 50-vs-60 HZ developments in the US vs Germany is to a large degree veiled in the mists of history around the previous turn of the century. And the "adapt to metric" theory for 50 Hz appears to be more of a postrationalization (as is the similar claim that 60 Hz makes it easy to have a synchronized clock showing the correct time, which is contradicted by the fact that the patent for such a clock post-dates the 60 Hz decision by decades). What is known is that 50 Hz was decided on by AEG in Germany, which drove the development of electrical power in Europe, and 60 Hz was decided on by Tesla and the Westinghouse team (Stillwell, Shallenberger, Schmid, and Scott). As far as I can tell, that is what is *known*, the rest is theory. I'll update accordingly.--Psm 20:23, 1 August 2006 (UTC)

[edit] History of 60 Hz vs 50 Hz

See my comment above. I'm deleting the following passage and replacing it. Included here in case someone wants to rollback or merge. --Psm 20:27, 1 August 2006 (UTC)

It is generally accepted that [[Nikola Tesla]] chose 60 [[hertz]] as the lowest frequency that would not cause street lighting to flicker visibly. The origin of the 50 hertz frequency used in other parts of the world is open to debate but seems likely to be a rounding off of 60 Hz to the 1-2-5-10 structure, called a set of [[preferred number]]s, popular with metric standards.

60Hz may also have been chosen as it would make for more convinent gearing ratios in electric clocks. A synchronus motor runing on 60Hz rotates at 3600rpm (or a submultiple therof) 3600 rpm through a 60:1 gear ratio is 60rpm (i.e. 1 rev/sec) with succesive 60:1 gear ratios giving 1 rev/min (for the second hand) and 1 rev/hour (for the minute hand) 87.113.7.148 17:48, 12 August 2006 (UTC)

That is just an issue of selecting the right gear ratios. For 50Hz a motor rotating at 3000 rpm through a 50:1 gear ratio is also 60rpm... -- RTC 21:08, 19 August 2006 (UTC)

[edit] first sentences are totally wrong...

An alternating current (AC) is an electrical current where the magnitude and direction of the current varies cyclically, as opposed to direct current, where the direction of the current stays constant. seems wrong.

The only difference between AC and DC is that AC alternate between positive and negative values as DC always stay positive...You can have a perfect sine wave which stay on positive values as a DC current. So the form of the wave as nothing to do with DC or AC. You can also have pulsed waves that can be AC. Magnitude have nothing to do here...

I think the author of the statement "You can have a perfect sine wave which stay (sic) on positive values..." wasn't thinking clearly. What must have been meant is that one can have a current that is a perfect sine wave (which, by definition, has positive and negative values) superimposed on a direct (constant) current. A time varying current that is always positive or always negative is not, strictly speaking, DC. It is easy to show that such a time varying current is composed of a direct (constant) current plus one or more alternating currents. For example, the current defined by the following:

$i(t) = 1 + sin(2 \pi 60 t)\,$

does not change direction but does vary in magnitude. Is it a DC or an AC? The answer is that it is the sum of both. Alfred Centauri 14:24, 9 March 2006 (UTC)

When you are mixing two currents it's sure you can't tell at this moment whether its DC or AC because its both but usually the DC will be use to transport AC and then be divided again by a coil and/or capacitors. The result will be a positive sine-wave and a alternating sine-wave.

I'm not sure that we've got to the bottom of this definition yet. There doesn't seem to be a consensus of the meaning of "AC". Here are some examples of the various meanings:

Chambers Dictionary of Science & Technology says that (i) it alternates in direction, (ii) it has a constant period of alternation and (iii) the normal waveform is a sinusoid.
McGraw Hill Illustrated Dictionary of Electronics gives alternation of polarity as the only criterion, but implies with the use of the word "frequency" that the period should be constant. It does not mention a sinusoid.
Horowitz & Hill's The Art of Electronics doesn't attempt a definition, but says that DC signals don't change in time and AC signals do.

I think we should say "AC is any current that repeatedly reverses direction so that its long-term average is zero. Unless the shape of the waveform is specified, it is usually assumed to be a sine wave." --Heron 09:59, 23 March 2006 (UTC)

[edit] Can someone more in the history section?

I forgot most of what i know of AC's history, but im pretty sure Edison hated it... I don't really remember, so I came here. I am dissappointed to find that this info isn't here, so I'll have to look elsewhere for now! Maybe I'll do some research and write it myself if I have time.

What you're looking for is probably under War of Currents, but there may be room for some more info in this article. --Heron 13:56, 29 July 2006 (UTC)

[edit] Missing sections

I think this article needs a section on how the alternating current is generated and one on how direct current can be transformed into alternating current. —The preceding unsigned comment was added by 193.226.140.133 (talk • contribs) .

This sounds like the perfect opportunity for you to be bold and improve the article!

Atlant 12:51, 4 August 2006 (UTC)

[edit] How is it delivered?

I wanted to know exactly what happens with the three holes in an outlet. Since voltage is a difference, and a circuit must be closed to receive it, does only one of the leads vary, or both, in opposite phases from each other? If the latter, does that mean connecting the same terminal from two different outlets produces no current? If the former, does that mean one of the terminals has no power? Does the ground terminal connect directly to the ground or a building's structure, as opposed to running through a power cable?Badmuthahubbard 20:33, 19 August 2006 (UTC)

The neutral/cold wire is grounded and the live/hot wire varies. You could say that the neutral wire 'has no power', in the sense that if you touch it you probably won't get a serious shock; but when you complete the circuit by plugging in a load, it carries just as much power as the live wire. The ground wire goes to a local ground in the building. It is there for safety, and normally carries no power. --Heron 20:48, 19 August 2006 (UTC)

P.S. There is a huge amount of detail at Domestic AC power plugs and sockets, and probably other places too. --Heron 20:50, 19 August 2006 (UTC)

[edit] twin lead

You have twisted pair but what about the twin lead we used to use for TV antennas? Some people used forms of twin lead for ham radio. Knob and tube and romex could be concidered twin lead as well. --Gbleem 13:54, 2 September 2006 (UTC)

I'm not following what does twin lead have to do with Alternating current. The twisted pair was shown to be a technique for reducing radiation loss, a by-product of alternating current. --Asbl 21:59, 2 September 2006 (UTC)

[edit] Who originated AC theory?

The article makes no mention of who first developed (or experimented with) the theory of alternating current...

[edit] positive and negitive

does alternating current have positive and negitive like direct current?--Falcon866 02:35, 5 January 2007 (UTC)

No. Every part of an AC circuit alternates continually between negative and positive. If you look at the symbol for an AC generator on a circuit diagram, you will see that it does not have + and - markings like a DC generator. In simple cases, the two wires coming from an AC generator are interchangeable. There are complex cases where they're not, but I won't go into that here. --Heron 21:02, 5 January 2007 (UTC)

So if both wires carrying AC are equivalent, what's the difference current and neutral blades on a polarized plug? —The preceding unsigned comment was added by 192.18.43.225 (talk) 21:48, 25 January 2007 (UTC).

The "hot" wire is connected to the smaller side of the polarized (American) plug. It carries a signal which oscillates between positive and negative with an RMS amplitude of about 120 volts. The larger plug is connected to the "neutral" wire which runs back to the electric companies generator where it is grounded. -AndrewBuck 22:55, 27 March 2007 (UTC)

[edit] Requested picture

The article on DC has an image showing the DC "symbol" that is used on electronics and such. I would assume there is a corresponding symbol for AC. I think it would be a good addition for the article to contrast it with DC. -AndrewBuck 22:49, 27 March 2007 (UTC)

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