Hello Jim,
Although very costly in the UK, I was considering a 350mm diam cast acrylic 1 metre long tube (that's how it comes) with 5mm wall thickness to go over my 300mm (12") diam secondary, it would cover about the first two thirds of the tube, a good few inches higher than the previous strikes. Your comment on a dissipative tube caught my eye for that particular reason but I don't understand the concept of loading or that my idea would work, any explanation and/or prediction would be much appreciated.I'm contemplating your other suggestions (which are totally novel to me) with interest.
Regards,Phillip.
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On Wednesday, 4 July 2018 21:26:39 BST, jimlux <jimlux@xxxxxxxxxxxxx> wrote:
On 7/4/18 11:40 AM, David Rieben wrote:
> Hi Phil,
>
> My deepest condolences for your loss. I know it's JUST a secondary coil,
> but as a fellow coiler, I most assuredly feel your pain. On the bright
> side, at least you did manage to capture some truly spectacular footage
> of this secondary coil mishap. I have had this happen on rare occasion
> with the operation of my big coil, though fortunately, none of my
> mishaps turned out quite that severe! Only once did I actually have to
> repair some damage to the side of my coil and was able to get it back
> into full functioning mode via the repair. Since I must operate mine
> outside, I did have one occasion where the wind actully "blew" one of
> the streamers back into the side of my secondary coil, too. Lesson
> learned - although refraining from outdoor operation during rainfall is
> an obvious good rule, non-starters in windy conditions are also well
> advised.
>
> I suppose this is a risk, that although may be small with a well-tuned
> and efficiently operating coil, is never completely absent. :^/
>
I wonder if we could figure out a way to segment a large coil
vertically, so if a segment gets damaged, you can just rewind that
segment. Just off the top of my head, I'm thinking about something like
segments with a hundred turns or so. Could we come up with a way of
making the connections in a "good" way. I'm almost thinking about how
you using field grading rings on a Van de Graaff. You don't want a
complete shorted turn, but you could terminate the winding in some sort
of flat terminal on the "mating face" of a segment. You'd stack the
segments, and then put some compression on it (threaded fiberglass rod?)
The other idea that comes to mind is if there is some way to "spread"
the energy of the secondary strike.. Say your secondary were coated with
a resistive (but still conductive) coating. Would that spread the
current density enough to prevent burning through the insulation? Or a
dissipative tube covering the secondary - not enough to "load" the
secondary, but enough to "take the hit".
OR, what about a second helix, space wound, that extends the length of
the secondary, with some suitable resistive conductor, so the voltage
profile matches that of the secondary (so no protective helix to
secondary arcs), but so it doesn't enter into the resonant circuit. The
protective helix would be mostly capacitively coupled to the secondary,
establishing the voltage.
What about something like a helix wound with wire, but with small gaps
along the length.. the gaps don't break down normally, but if a streamer
strikes, the gaps break down and provide a conductive (but lossy) path
to the base.
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