Re: Static Gap question.

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

Original poster: "J. B. Weazle McCreath" <weazle-at-hurontel.on.ca> 


At 08:03 AM 11/02/04 -0700, you 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 one another work well
 >because they allow lots of surface area for the gap to cool, thus
 >quenching it rapidly?
 >
 >Gaps like the hyperbaric do not use the large surface area, but the good
 >quenching is assisted by the high volume of air?
 >
 >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?
 >
 >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
 >diameter 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 ½”.  Would that have a breakdown voltage close to the break-
 >down voltage of two 1” dia. copper pipes in parallel to one another?
 >
 >Thanx
 >
 >Luke Galyan
 >

Hello Luke, Coilers,

Your assumptions are pretty much correct.  The larger surface area of the
parallel tube type gaps means that the heat generated by the spark is not
localised as it would be between two balls for example.  Also, having a
larger amount of metal means that there is more thermal mass to absorb
any generated heat.  That mass does not neccesarily have to be the active
portion of the electrode as I'll explain later.  However, heat is not the
only factor which effects quenching.  The spark generates ions as well as
heat, and if they are allowed to accumulate in the immediate vicinity of
the spark, the quenching ability of the gap is reduced.

Answer 1:

I think that it would depend a great deal on the power level you run at.
Obviously a gap on a coil powered by a 12/30 NST won't have to deal with
the same amount of heat as one say, powered by a MOT or PDT powered coil.
Even with lots of air flow an electrode that is too small will, over time,
heat up and begin to effect the quenching.

In my own hyperbaric gap, the electrodes are made from 1/2 inch copper
pipe sections about four inches long.  Even though the active area of
the gap is the circumference of the pipe sections at their ends, the
thermal mass is conciderable due to their length.  This, and the high
volume of air flowing through them, assures they remain cool.

Answer 2:

I would think that the breakdown voltage for a set of paralleled disk
electrodes would be less than that of a pair of balls or similar curved
type electrodes, assuming the same spacing.  The field would tend to be
more concentrated between the paralleled disks, and hence the breakdown
would occur at a lower voltage.  Perhaps Terry's E-Tesla program could
be used to graphically show this effect?

It will be interesting to read the comments from other list members.

73, Weazle, VE3EAR/VE3WZL

Details of my "Hyperbaric Gap" and Tesla coil are at:
http://www.hurontel.on.ca/~weazle