Re: stepped leaders (was Safety FAQ...)
>>From leyh-at-ix-dot-netcom-dot-comTue Aug 20 22:10:15 1996
>Date: Tue, 20 Aug 1996 00:44:44 +0000
>From: "G.E. Leyh" <leyh-at-ix-dot-netcom-dot-com>
>Subject: Re: stepped leaders (was Safety FAQ...)
>Robert Stephens wrote:
>> I don't believe that phenomenon occuring on the enormous scale of stepped
>> leaders in natural lightning are necessarily useful in the explanation of
>> phenomena observed in Tesla coil discharges.
> The smallest stepped leaders in naturally occuring ligthning are at a minimum,
>> at least an order of magnitude larger in scale than the biggest Tesla coil sparks
>> yet produced. The features of a Tesla coil streamer advancing upon itself in
>> small steps is absolutely microscopic compared to the stepped leader lightning
>> example referred to here by Greg. Sorry folks, I don't buy a small scale stepped
>> leader connection here for Tesla coils as based on the natural lightning example.
>The stepped leaders in a lightning strike will of course be much larger than the
>stepped leaders generated by a tesla coil, since the voltages involved in lightning
>production are much higher. Total cloud-to-ground voltages range from tens to hundreds
>of megavolts, which would yield leaders on the order of tens to hundreds of meters.
>My coil generates about 550kV, which should produce leaders of only a couple of feet.
>Perhaps some empirical data can solve this matter. Anyone out there have a streak
>camera, or a 'Boys Camera', as they used to call it?
Malcolm was kind enough to recently send me a copy of your paper
describing your big coil as published in the TCBA newsletter. First
off, nicely done! That project was an enormous undertaking, and will
be useful as a reference to anyone such as myself with an interest in
building a large Tesla coil system.
I can't seem to locate where I misplaced your paper to in order to
refresh myself, but I'm mentally recalling the dimensions and method
of construction of the toploading toroid as being very close, in fact just
slightly smaller to the one I put on my largest coil to date. Mine
was 15"X67", made from a custom manufactured single 33 foot length of
aluminum flex duct, compressed as far as it would go to incresase the
wall strength. The fact that yours was made from individual discrete
tubes, arranged to simulate a solid electrostatic surface by phantom
effect confuses the calculation for breakaway potential to me as I am not
personally familiar with that aspect of skeletal frame corona holdoff
My point is, did you actually measure the terminal voltage achieved,
or are you relying on a calculation by whatever CAD program you use.
The charts supplied in your paper appeared to be CAD program generated
rather than the output of a plotter hooked to a measuring voltmeter.
My gut feeling tells me that the holdoff potential of your toroid,
even being a skeletal design, ought to be significantly higher than 550 kilovolts!
I am aware of the difficulties involved in measuring such voltages
with any degree of assurance, and am presently attempting to build a
capacitive divider probe which will be capable of direct connection
to the TC toroid and operate up to 1 megavolt for use in my lab.
For now my guestimates of breakaway voltage from large holdoff terminals are
based on measuring the length of the very first streamer to be caught
breaking away from the toroid as seen stepping through a videotaped
record of the test. On my largest system to date with the aforementioned toroid,
the system went from no corona whatsoever to a 12 foot streamer in the first
ionization of virgin air. At 20,000 volts per inch (which is a low
number, 35KV per inch is probably more realistic), that represents
2.88 Megavolts. From 12 feet the streamer was then able to build, reaching a
maximum recorded length of 18 feet at one point during the test of