Talk:Corona discharge

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This page springs from me working on the HVDC page when I came across some physics I didn't understand and now do (I think)! :).

It's currently overobsessed with mechanism, and would benefit from people working on the history applications, etc. This is because of my natural inclination, which I have to fight, :). I won't be happy with this page till it has more historical / apps stuff, but if you're waiting for me to do a competant job on that part, don't hold your breath! - Kaet 17:48, 14 Sep 2003 (UTC)

Contents

[edit] Subject Reference

[edit] Response

[edit] Some questions

I'd like to have a clearer description of the differences between arcs, sparks, and corona discharges. In air, do they have different colors? I remember playing with a Van de Graaff generator, I would sometimes see a purplish, wide, "fuzzy" discharge, and sometimes a thin white or yellow discharge. Is one a corona and the other an arc?

Also, what is the relationship to a plasma arc loudspeaker, is that really an arc, or a corona discharge? - Omegatron 13:53, May 10, 2005 (UTC)

See also Talk:Spark_gap#Clarify the difference - Omegatron 18:09, Jun 4, 2005 (UTC)
Yes, Omegatron, the purplish fuzzy discharge is a corona or brush discharge, and the white or yellow momentary discharge is a spark. - Omegatron 18:38, August 7, 2005 (UTC)
Yes, the simple difference is that with a corona discharge, the electrons get forced off the metal into the air, but have no place to go -- there's not a closed circuit. With an arc, there is a closed circuit from one conductor through the air to another conductor. 68.81.105.126 02:45, 26 November 2006 (UTC)

[edit] potential again

Once again, I don't understand potential without the "difference" at the end. You said "by using the ions generated to pass the charge to a lower potential (which may be earth)." Couldn't that also say "by using the ions generated to pass the charge to a lower potential (such as the Earth or infinity)."? Because a potential measured by itself is defined as the potential difference between that point and infinity, according to my discussions elsewhere. - Omegatron 02:33, August 5, 2005 (UTC)

I edited this page because it said both electrodes were at a high potential. THat was not correct. Only one electrode is at a high potential and the discharge current flows from this high potential back to the refefence point (which in the case of your lab VGG ,say, would be ground. Which is why I suppose all VGGs and HV systems should be grounded - to have a known reference). I used the word potential instead of potential difference to imply a high potential with repect to the reference electrode (normally ground or the earth. I dont think any current would want to go off to infinity ( what is the potential there?). Hope this clarifies my actions. Pls ask again if neededLight current 16:15, 5 August 2005 (UTC)
I think the current does go off to infinity in some situations. I think we both suffer from an incomplete understanding of potential.  :-) Imagine that the only thing in the universe is air and a small metal sphere. If that sphere has a charge, then it also has an electric field. If that electric field is strong enough, the air will breakdown and a corona will form around the sphere, regardless of the presence or lack of another electrode. Does this sound correct? - Omegatron 16:23, August 5, 2005 (UTC)
Hmmm... but this confuses me. It seems to say that potential is a relative measurement just like potential difference. I was under the impression that charge was an absolute quantity, potential was an absolute quantity depending on charge, geometry, and so on, and potential difference (voltage) is a relative quantity, depending on only where you decide to make 0 volts. - Omegatron 16:27, August 5, 2005 (UTC)
I seem to remember that the potential of any point in space is the work done in bringing a unit charge from infinity upto that point. (this assumes that the potential at infinity is zero i think). This is why an isolated conducting sphere in an empty universe can still have a capacitance. Does this help at all??Light current 00:58, 6 August 2005 (UTC)
Just thought:. if the potential at infinity is zero, then an isolated sphere at a high voltatge would indeed start to corona. The only problem is: how do you charge the sphere in the first place if it is completely isolated:-)? Potential, in the end has, to be relative (ie potential difference). Otherwise, how can it be measured?. Potential in the physics terminology is an absolute quantitiy based on the assumption that the absolute potential at infinity is zero. No one has yet been there to measure it !!!Light current 01:07, 6 August 2005 (UTC)
You put charge on it. Charge isn't relative. You mean if the only thing that existed in the universe was the ball? So how did the ball get there? It's just an imaginary problem so imagine that you are putting charge on it.
Potential, from what I have read, has no meaning by itself, it is only meaningful to talk of a potential difference. I think the important point here is that corona is dependent on electric field strength (~=potential gradient), anyway, not potential.  :-) We can continue the potential discussion on Talk:potential, though. - Omegatron 01:46, August 6, 2005 (UTC)

[edit] Equations

I started to make a Peek's law article, but I see that Peek's empirical measurements have been superseded by slightly better equations. High Voltage Engineering by E Kuffel, W S Zaengl, J Kuffel says Zaengl et al did it, so I will do some more research for those equations. Anyway, maybe we should just list the equations in this article instead?

This article is getting pretty big already, though. - Omegatron 17:25, August 7, 2005 (UTC)

Hah. I didn't even notice that Zaengl wrote that book, too. Self-citing? - Omegatron 17:26, August 7, 2005 (UTC)
Light current, can you find the name of the paper (reference #36) they were referencing? I think it's on page 366, which is restricted on google print. - Omegatron 17:29, August 7, 2005 (UTC)

Just entering equation 5.111 for cylindrical geometry:

\left ({E_c \over \delta} \right ) - 2 \left ({E_c \over \delta} \right ) E_0 \ln \left [ {1 \over E_0} \left ( {E_c \over \delta } \right )^2 \right ] - E_0^2 = { K / C \over \delta r}

[edit] Work on updating Peeks Law

THe paper referenced by Zaengl as Ref 36 is:

WS.Zaengl and N.U Nyffenegger. Proc. 3rd Int. Conf on gas Discharges, 1974,p303

Hehe. I thought "how did he type the pound symbol accidentally?" Oh, when I press shift+3 I get #, which is also a "pound symbol", American style, I guess. - Omegatron 00:14, August 10, 2005 (UTC)

[edit] New edition of Peek's book

I found an ISBN, but it actually refers to this edition, printed in 2002:

What's the difference? —Phil | Talk 16:13, 8 November 2005 (UTC)

None - it's an unabridged reprint of a classic work. Bert 15:00, 4 April 2006 (UTC)

[edit] Pictures of corona discharge

The DayCor camera was developed by EPRI and OFIL to capture corona and arcing. Since corona is a glimmering periodic phenomena is has to be captured with a video camera. The specialty camera belongs to the bispectral imagers, which means that is uses 2 optical channels: a visible channel and a solar blind UVc channel (240-280nm). The images are simultaneously taken and are overlaid to produce output that shows the corona source (the UV source) in its original (the visible picture) set. Pictures and video clips can be downloaded and watched from http://www.seeing-corona.com magazine and from the http://www.daycor/corona.html.

[edit] Laymans terms.

After reading half of this article, I have coem to the decision that someone needs to make this article more comprehensible to the common person... If someone could do this, I think it would be greatly appreciated by many people.

Omega Archdoom 06:55, 5 November 2006 (UTC)


[edit] Cool Corona Discharge Pictures

I have some (IMHO) extremely cool pictures of corona discharge from a home-built ozone machine here: http://erikmartin.com/sci/ozone/ozone.html They are marked as public domain on the web page. If anyone thinks that any of them might be appropriate in the article, please feel free to use them. 68.81.105.126 02:45, 26 November 2006 (UTC)