Paschen's law - spark gap distance at high pressures

[honeybadger]

Hi,
I "need" to know breakdown voltage of air at 8 bar pressure. I spent 2 hour of googling and found nothing. I just need a simple graph of "air breakdown voltage VS air pressure".

There is a lot of these charts: https://en.wikipedia.org/wiki/Paschen's_law#/media/File:Paschen_curves.svg  I don't understand them... vertical scale is in "V" , not "V/m".

And then there is the Paschen's law... can anybody understand that? Where can I find all these constants?

[mikerj]

Check the horizontal scale pd i.e. pressure multiplied by electrode separation.

[honeybadger]

mikerj: thanks, it makes sense now.

So if "pd = pressure x electrode gap" remains constant -> this means breakdown voltage must remain constant. Twice the pressure -> 1/2 electrode gap = same breakdown voltage.

Is it really this simple?

If at 1 bar (absolute) I need 3kV per mm -> at 10 bar (absolute) I would need 3kV per 0.1mm, which is 30kV/mm. Am I correct?

[floobydust]

I thought Paschen's law is more about the non-linearities on the low end (low pressures, very small µm gaps) but larger gaps/higher pressures behave more linearly.

8 bar is around 116 PSI or close to automotive compression stroke pressure. You can see this on sparkplug testers that take shop compressed air and apply that to a chamber with a sparkplug mounted in it. 1mm spark gap is around 30kV, although turbulence, electrode geometry, ozone, polarity matter.

[Le_Bassiste]

fyi,
http://home.earthlink.net/~jimlux/hv/hvmain.htm
especially,
http://home.earthlink.net/~jimlux/hv/paschen.htm

[Plasmateur]

Is this for AC or DC? For much higher frequencies, Pachen's curve will be modified.

Check out page 23 of the PDF here: https://apps.dtic.mil/dtic/tr/fulltext/u2/1018515.pdf