RE: Strike rails/safety gaps IMPORTANT

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

Original poster: "Aron Koscho by way of Terry Fritz <twftesla-at-qwest-dot-net>" <kc5uto-at-wt-dot-net>

Hi All,

I have made many, many coils with no protection what so ever and had no
problems. BUT at the 2000 Texas telsathon I did have an interesting kickback
experience. Justin and I had been running our new 12" coil for some time
with arcs in the 10' range at about 10kva. We had the whole nine yards with
us, power controller, pig, srsg, etc. The controller consisted of two 60a
240v contactors and an single 30a 520v variac as well as some other extras.
It can be seen here: www.hvguy-dot-com.

 The first contactor was closed using a front panel key switch; the second
would close only when the green "start" button was pushed. Dave Wightman,
who has a incredibly over driven 8" that arcs 11' had also brought along his
coil. It has no incorporated safety features. To save time and space in
Phils barn we decided to hook his coil to our control equipment and pig. The
first time we ran it Justin was at the controls and I was watching from such
and angle that I could see the back of the controller. I noticed a small
rf-looking arc inside but didn't think much of it as there was a lot of
light flickering around and I wasn't sure it was an arc. A few runs later
with me at the controls the key switch arced rather violently about 1.5" to
the side of the variac. The contactor opened immediately do to the lost of
instrumentation power. The key switch had caught on fire! It preceded to
melt off of the front panel and extinguished it's self. The key switch was
quickly replaced with a clip cord and our 12" coil was reconnected, there
where no other problems. This sort of thing seems to happen fairly often. We
have never experienced it with our coils but no many who have. Seems like
there are plenty of arguments both ways...

-Aron

kc5uto
www.hvguy-dot-com

-----Original Message-----
From: Tesla list [mailto:tesla-at-pupman-dot-com]
Sent: Thursday, July 11, 2002 10:17 PM
To: tesla-at-pupman-dot-com
Subject: Strike rails/safety gaps IMPORTANT


Original poster: "Mr Gregory Peters by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <s371034-at-student.uq.edu.au>

Hello all,


I am SICK SICK SICK and tired of people saying "well, I don't use
safety gaps and strike rails and have had no problems". You are playing
Russian Roulette here. These devices don't only protect your equipment,
they protect YOU!! Don't forget that a nice 200kV streamer makes a very
nice conductive path for the output of your pole pig, or even the 240v
mains! You DON'T want it getting into your control/power circuitry. The
little effort in making a simple safety gap and strike rail are well
worth the bother. These devices don't HAVE to look good. Fencing wire
will do. I have included part of an old post from Richard Quick (A very
successful old school coiler) below. I urge you all to read it:

"Well I have seen a coiler or two who did not use contactors to
remotely switch their 60 cycle mains. I have operated coils at
1.5 kVA without contactors. But let me tell you about the one
time I had an incident that "resolved itself" inside the power
cabinet. The experience changed my mind.

Everything happened too fast to really give a "blow by blow"
description, but basically what started it was the secondary
discharge struck a primary that was not equipped with an RF
grounded strike shield. The secondary discharge shorted the
primary turns, and the main tank circuit ran away. By "run
away" I mean that the oscillator shifted to a much higher
frequency due to the arc shorted primary. The primary/secondary
field flux collapsed when the tune was lost. All of the input
energy, the field flux energy, and the energy already in the
secondary, appeared to feed back into the tank circuit; in any
case it looked like discharger had become a vacuum cleaner and it
sucked in the five foot streamers. All of the conductors in the
tank circuit sprouted six inch long sparks and corona at the same
time the safety gap and capacitor terminals went to flames.

What happened next I do not rightly know, but just when my finger
hit the switch to shut the runaway oscillator down, there was a
tremendous explosion inside the power cabinet. It was so bright
that I had spots in my eyes even though I did not directly see
the flash. The smell of ozone and electrical burn were strong in
the cabinet when I opened the back to peer inside. At first I
could not see anything wrong. But given the intensity of the
flash, I was determined to disassemble everything if required.

A careful examination of every inch of the wiring revealed a
small hole in the insulation on the bottom side of a 60 cycle
main. The hole was located about 1/2 inch from the first line
filter, closest to the coil. Apparently kickback had made it
inside of the cabinet and the impedance of the filter was
sufficient that the kickback blew out the insulation and left the
conductor entirely. The line filter, having been bypassed, was
undamaged! Looking around some more I found fine arc tracks
scored into the surface of the polyurethane coated plywood mount
board. The arc had left the wire and traveled nearly four inches
across a surface of poly-coated plywood while spreading into a
"fan" of fine arcs that struck all along the main ground strap.
The delicate fan-like spark pattern was nearly the size of a
man's hand!

As it turns out nothing in the cabinet was damaged. I tried to
power up later, but a neon in my bank had gone south. I assume
that the neon broke down internally, and the kickback had jumped
to the 60 cycle primary.

After all that I completely re-thought, re-designed, then re-
wired everything. BTW, I just happened to be standing on an
insulated platform, which I rarely do when I am at the controls.
Had I not, I firmly believe I would have been jolted to my
backside.

Richard Quick



Greg Peters
Department of Earth Sciences,
University of Queensland, Australia
Phone: 0402 841 677
http://www.geocities-dot-com/gregjpeters