# [TCML] JAVATC - Question

Dex Dexter dexterlabs at dcemail.com
Wed Mar 18 12:03:04 MST 2009

```The important reason I think may be that the gap spacing for the same
breakdown voltage decreases.The arc is shorter.
Shorter the arc column-> smaller the voltage drop (and conductive loss).
There could be other things at work here why it works better too.
But I have no knowledge about them and just speculate.

Dex

--- bartb at classictesla.com wrote:

From: bartb <bartb at classictesla.com>
To: Tesla Coil Mailing List <tesla at pupman.com>
Cc:
Subject: Re: [TCML] JAVATC - Question
Date: Mon, 16 Mar 2009 18:37:03 -0700

Hi Jim,

Yes, a hyperbaric gap would have greater pressure and this will change
breakdown to some degree. As I understand the gap in question, it's not
hyperbaric. If it were a hyperbaric gap, then you would certainly want
to have the air flowing or at least the chamber pressurized equivalently
(assuming we knew a decent ball park pressure for a typical hyperbaric gap).

One of the main points that Paschen showed was a curve identifying
breakdown voltage with gap distance or pressure. It's a curve because of
the molecular density of air and the probability of electrons getting
from point A to B. The curve shows that as the pressure is decreased,
breakdown voltage will drop (340V) and then will increase as pressure
continues to drop (one of the strange phenomenons of the density of
molecules in a low pressure environment. So what happens when we
increase pressure? Well, breakdown voltage increases (unless were below
that area of the curve described above).

In general, as the pressure is increased, the breakdown voltage should
increase and mainly due to the product of d x p (distance and pressure).
So if we double p, we should halve d for the same arc voltage. This is
one of my main points about hyperbaric gaps I've tried to mention in the
past regarding "cause of performance". Say we double the pressure and
leave the gap distance unchanged. Did we just double our arc voltage?
Yes we did. Is this being accounted for? I doubt it. I think were
currently just applying a mechanical air force into the gap and
observing the "performance". I'm not sure what the actual pressure
differential is, but I have a hunch that the performance increase is due
to the pressure causing the arc voltage to climb and thus the energy
release to be greater (and thus, a hyperbaric gap at 0.2" cannot be
compared to a blown gap at 0.2" with all else the same). If the pressure
was known, then we could increase the blown gap distance equivalently,
at which point, both gaps may perform similarly.

With the physics, it may be wise to identify and adjust the breakdown
voltage of hyperbaric gaps under pressure on the workbench before
running the TC (at least with an NST).

Take care,
Bart

Jim Mora wrote:
> Hi,
> It seems to me that hyperbaric, curved gaps have some complicated
> aerodynamic physics....
>
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