Experimental Results of Austin Show

           Experimental Results of Austin Show
           Thu, 03 Apr 1997 09:48:14 -0800
           Greg Leyh <lod-at-pacbell-dot-net>
           Tesla List <tesla-at-pupman-dot-com>

Hi All,

I took the 'long way' back from Austin, and I am just now sifting
thru the _404 messages_ from Tesla list and HV list!!!

First off, I would like to thank several people on this list who
came to the show early and lent a hand setting things up (and 
putting out fires):

Kurt Donavan, who finished the HV and control wiring for the 
100 kVA capacitor charging power supply.

Rob (From Man or Astro-Man), who worked many long hours setting up
the feeder from the generator, the earth ground connections, and 
constructing the strike towers, amongst many other things.

Vince (the guy with the dreadlocks) - who helped me with the 
gapmotor alignment, and the construction of the strike towers.

Bert Pool, 'Wild Bill', and 'Mild Bill', who came to the rescue 
when our cheesy wood pallette 'insulating support structure' for
the 75 kilojoule cap bank caught on fire.  Bert & Co built 
another structure using materials from around the speedway, 
a clever mixture of masonite, wood, lexan, and _asphalt shingles_
of all things, which turn out to be a pretty good insulator!!

Several major modifications were made to the coil for this show,
as a result of some PSPICE sims, and some spark gap msmts taken
last fall.  The changes were significant, but seemed to fall 
within the realm of conventional coil wisdom.

1)  Cpri was decreased from 0.495uF to 0.180uF, nominal.

2)  Lpri was increased from 12.3uH to 35uH, with the Litz tuner 
    in the center position.

3)  Coupling was raised from 0.12 to 0.155.

4)  The maximum break rate was increased from 280PPS to 370PPS.

5)  Vpri _was_ to be increased by root 3, from 27kV to 46.5kV, by
    changing the configuration of the HVDC PS xfmrs from delta-delta
    to delta-star.

All of the mods were carried out except for #5, as I did not want 
to risk burning something out before the show.  Unfortunately, 
there was no opportunity to test these mods in SF -- in fact,
some of these mods were performed at the show site.

In initial tests the day before the show (05:30, 27 Mar) the coil 
ran better than anticipated, considering the low Vpri and low Cpri.
I was concerned that the output voltage might not be sufficient to
break out from the toroid.
Even though the primary energy was only 36% of normal, streamers of 
over 20' were produced, with frequent ground strikes.  The faster 
gap speed probably made up for the energy deficit, in some part.
At full gap speed (about 360PPS on the tach) the current draw on
the 480V mains was 32A, or approx. 26.5kW.

Another new addition for this run was the secondary booster, which
backs up the secondary with a 75kJ, 25kV capacitor bank.  When the
streamer completes a path to ground the cap bank disruptively
discharges thru the arc and the secondary, producing a flash that
lasted on the retina about two minutes.  (Goggles were worn from
that point onward).  A set of 3 strike towers were arranged around
the coil, at a radius of about 20 feet.  Each tower consisted of
a 16 foot 2x4, with 32 4' fluorescent tubes dense-packed along its
length (A 'local' donated 400 fluorescent tubes to us).  The bottom 
end of the tube stack was wound with wire and metal tape, and then
connected to the business end of the cap bank.  The ground return
for the cap bank ran directly to the base of the coil.

The charging PS was an 1980's vintage 100kVA 3-phase full-wave doubler
arrangement, designed and built by Livermore Nat'l Labs.  We had
rescued it from the scrapyard, and vowed to get it back 'on-line'.
It worked beautifully, and could fully charge the 75kJ cap bank in 
about 3 seconds!  We really should have brought the other 225kJ of 
capacitors from home, even though they weigh 130lbs each.

Unfortunately, no specific electrode geometry or material (such as
graphite points) was applied to the tips of the towers, and no ball
lightning precursors were observed by us, except the old 'floating
after-image on the retina' type of ball lightning.  After a couple
dozen booster hits, the fluorescent tubes started failing.

Experiments at full power (delta-star config) after the show had to
be cancelled, as the owner of the speedway had his fill of the lot
of us, and had asked the sheriff to clear and secure the area shortly
after the show had finished.