From: Paul
Date: Sun, 12 May 2002 16:21:07 +0100
Subject: Re: [TSSP] Topload breakout potentials
I've completed the run on Marc's coil, and the waveforms are in
http://www.abelian.demon.co.uk/tssp/tmp/mm3p.wave.gif
which reach 900kV at the top, giving 28kV/cm toroid surface gradient.
That's 2 out of 3 coils that appear to be tuned low for the best use
of the toroid.
Terry wrote:
> When big streamers are present, the streamers add capacitance to
> the top load decreasing the resonant frequency. So to get the
> maximum power to the streamer loaded coil, we start off with the
> primary tuned about 5-8% on the low side.
I've heard this many times, and now it begins to make sense.
The low-side primary tuning limits the peak topvolts so that the
undersized topload only just breaks out. It also stores a reservoir
of energy in the primary which cannot reach the secondary because the
sec Fres is too high. The few streamers which form are able to grow
until after perhaps a few cycles (or a few beats?) the streamers are
contributing enough extra C to drop the sec Fres to a point where it
can take the remaining energy from the primary. Very neat - and all
done without a computer!
Marc's total Ces is around 47pF, and (Terry wrote):
> 1pF per foot of streamer length
To drop the sec Fres by 6% we need 53pF Ces, so we'd expect to see
a single streamer circa 6 foot to bring this off.
Marc wrote:
> gets multiple 80 - 90"ers
Is there really more than one streamer, or is this persistance of
vision? Do we need to argue about the 3pF/metre streamer cap? It
ought to depend on the thickness of the streamer, which in turn will
likely depend on streamer current and therefore operating frequency.
In the case of John's coil, Ces = 20.3pF and John's detuning was
about 14%, needing an extra Ces of around 6pF. That's one 6' streamer,
or a couple at 2 or 3 feet.
Bart's coil stands out from the other two for its inexplicable
breakout.
Bart wrote:
> typical mode of operation is to turn up the voltage to about 180V
> input (a habit) on a 14.4kv 10kva pig
I'm probably demonstrating my ignorance of the primary charging
circuits, but doesn't that make for something like
180/110 * 14.4 * sqrt(2) = circa 33kV. Where does the 15.3 kV come
from? Obviously I don't understand how the primary charge is set up.
I guess the ballasting and gap settings modify my naive picture.
I've got Bart's coil down at 15.3kV across 61nF into a secondary Cee
of 45pF, so we'd expect a (tuned) peak topvolts of
15.3 kV * sqrt( 61nF/45pF) = 560 kV.
The model reports 460kV and the primary tuning for 13 turns just
seems a couple of percent on the *high* side. Maybe I haven't got
the model tuned quite the same as the real coil? If the real coil
was in tune, the 560 kV would give 14.5kV/cm on the toroid - an
improvement but still well short of the 26kV/cm we expect. Why are
we 50% out? Either
a) We don't have a good representation of Bart's setup.
b) The model is predicting the wrong topvolts.
c) Tcap is predicting the wrong topload surface V/cm/V.
d) The 26kV/cm threshold isn't right.
Concerning producing a coil-independent table of topload surface
gradients, Marc's toroid give the variations
Free space: 0.028 V/cm/V
In room: 0.033 V/cm/V
In situ: 0.031 V/cm/V
so the details of the room and coil have quite a significant effect.
That does rather increase the size of the task of tabulating these
values! Our only hope is that variables can be separated without
loosing too much accuracy. In other words, we make a table of
free space gradients, and a separate table of 'in-situ' adjustment
factors to allow for the coil size, and a further table of adjustment
factors to account for wall and roof proximity.
John wrote:
> I have a 6" x 24" smooth toroid, but it may be too large?
I shall run it through the software.
--
Paul Nicholson,
--
Maintainer Paul Nicholson, paul@abelian.demon.co.uk.