Re: Irregular static gap breakdown voltage

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

Original poster: "Dr. Duncan Cadd by way of Terry Fritz <twftesla-at-uswest-dot-net>" <dunckx-at-freeuk-dot-com>

Date: 31 December 2000 19:57
Subject: Re: Irregular static gap breakdown voltage


Hi Richie, Gary et al!

Happy New Year to all :-)

>Original poster: "R.E.Burnett by way of Terry Fritz
<twftesla-at-uswest-dot-net>" <R.E.Burnett-at-newcastle.ac.uk>
>
>
>Hi Gary,
>


<snip>

>A couple of years ago I did some breakdown distribution
experiments with
>various combinations of static gaps to find out how
consistent the firing
>voltage was.  I tested various widths of single gap and
various numbers of
>multiple series gaps,  but unfortunately did not experiment
with airflow
>or vacuums at the time :-(


I have taken to running mine with a pair of "resonant
chokes".  If I use 1,65nF (2x 3,3nF in the "balanced"
configuration) with my 500VA 10kV nst I reckon on the gap
being able to let go at 9500V 450VA (allowing the rest to
get lost in the filter) and accordingly guesstimate the
break rate at about 450 / [0,5 x 1,65E-9 x (9500^2)] =
approx 6000bps.  I then calculate that at this frequency it
needs 0,42H to resonate with 1,65nF and so made two chokes
with sliding iron wire (1mm thin fence wire annealed in a
fire) cores which are in series between caps and nst/filter
output, one in each 5kV ac line to preserve the balanced
circuit, each of which chokes will cover 0,21H with a bit to
spare each side.  Nothing drastic seems to happen as I slide
the cores in and out, so the resonance is low Q whatever
else it may be, but it seems to be quite happy - though you
can get massive sparks around 3-4cm long from the resonant
chokes ;-)  They appear pretty feeble and I assume there is
a large out-of-phase component.

The filter takes care that this doesn't get as far as the
safety gap, never mind the nst!

I have no idea if this helps make the firing of the gap
regular, but you'd think so if there's some resonance going
on.  Any Microsim experts tried this in a simulation ?

Oh yes, I like high break rates of 6000 or so - though I may
go back to 1000 for some experiments!  The sparks are a lot
shorter, but very highly branched and "tree-like" - nice
dendritic fractals they are.  And instead of the
chainsaw-like buzz, this thing **hisses** venomously.  If
ever I get my hands on a tranny of 2kVA or thereabouts I
shall be sorely tempted to up the breakrate to over 10k,
maybe even 20k :-)

I suppose if I made up a ferrite ring current transformer
with around 100 turns on it (ah - got one!) and stuck a low
pass filter on the output side, I could slip this over the
wire between choke and cap with a decent insulating tube
between them and take the output to a frequency meter or
scope.  Not too happy about bringing my electronics that
near the 500VA coil though.  I've done similar stuff on the
15W induction coil powered TC and had excellent results but
that of course is a whole different ball game.

Dunckx