Re: Static Gap question.

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: Ed Phillips <evp-at-pacbell-dot-net> 

Tesla list wrote:
 >
 > Original poster: Bart Anderson <classi6-at-classictesla-dot-com>
 >
 > Hi Luke,
 >
 > Tesla list wrote:
 >
 > >Original poster: "Luke" <Bluu-at-cox-dot-net>
 > >I have looked around at the types of static gaps and have a couple
 > >thoughts of my own.
 > >But let me see if I get this right.
 > >
 > >Assumptions.
 > >The versions using the copper pipes in parallel to on another work well
 > >because they allow lots of surface area for the gap to cool thus quenching
 > >it rapidly?
 >
 > The pipe is a good for heat dissipation with air-flow and it's easy to get
 > and use at the local hardware store (the latter probably being the #1
 > reason). I can't comment on the quenching (I feel quenching is more
 > assumption than measurement. Not the actual quenching, but the cause).
 >
 > >Question 1.
 > >If the gap is cooled off sufficiently and the gap is quenched well say by
 > >large amounts of air is there any other benefit to using a larger surface
 > >area for the spark gap?
 >
 > The benefit is more control over the arc voltage (is it stable or does it
 > fluctuate). Both the radius of curvature and temperature stability are two
 > key ingredients for control. Surface imperfections should also be kept at a
 > minimum. Note that with pipes, there is always one point on the pipe where
 > the arc occurs, and often it can be at the far ends where the edge is. I
 > like to round my ends down to prevent this.
 >
 > >And question 2.
 > >The JavaTC program estimation of the arc distance in relation to potential
 > >is based on the surfaces of the spark gap being curved like as in large
 > >dia. balls or pipes in parallel. This assumes the distance between
 > >electrodes is not greater than the diameter of the electrodes.
 > >
 > >Would the same approximate distances be obtained for said voltage if flat
 > >electrodes were used parallel to one another? Say like two 1" dia. discs
 > >separated by *". Would that have a breakdown voltage close to the
 > >breakdown voltage of two 1" dia. copper pipes in parallel to one another?
 >
 > Actually, North in his chapter 7 paper describes how if the radius of
 > curvature is large and the separation is much smaller, the electrodes
 > appear as planar (like your two discs proposed). He also used an analogy of
 > a person standing on the earth where the radius of curvature appears flat,
 > and does give a good idea of how this occurs. But note, as you get into
 > your spaceship and travel at say 2 or 3 times the distance of the earths
 > radius, the curvature becomes very apparent.
 >
 > I think the breakdown can be set up so that a ball electrode or disc
 > electrodes have very near the same arc voltage (mathematically), but with
 > the disc comes the edges, so there is an area for probable arcing. I think
 > realistically, imperfections with surface features and the parallel setup
 > would probably tend to move the arc voltage value from the best guess, but
 > I don't know how much.
 >
 > Take care,
 > Bart

	I'm not experienced in this area but did built one "parallel pipe" gap
which worked quite well.  Used 3/4" couplings for copper pipe and
rounded the ends a bit by chucking the pieces in the lathe and using a
fine file until things "looked right".  I was surprised that when the
pipe was reasonably parallel there didn't seem to be any particular
tendency to spark at the ends only.  My gap has 7 pipes, with spacing
which will just "note break down" with the 12 kV NST connected open
circuit.  I found that by mounting the gap so the axis of the pipes was
vertical I had enough convection cooling to permit 30 second runs at
around 600 watts input to the transformer.  When I originally ran the
thing I had problems with fairly hard black "stuff" building up on both
sides of each gap.  Once I cleaned the pipes the first time this effect
almost disappeared.

Ed