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Re: [TCML] Pig safety gaps - was Winding the primary
Hi Gary,
Yes, you may be correct about it striking the primary
as well. I just happened to actually see the streamer
attach to the lower end of the secondary and to the
best of my memory, that was about the time that the
output quickly went to zero. It has been about 3 1/2
years ago (Jan, '05 I believe). It was after the arres-
ter died that I resurrected the idea of using a stationary
safety gap again and tried the horn gap this time and
even had a fan aimed across it for forced air extinguish-
ment if it power arced. This didn't work out so well
either though because when the safety gap did fire, the
air currents would actually try to "suck" the plasma
flames back into the fan but not extinguish it! I gave up
on this idea once and for all after this and found another
distribution arrester on ebay (this one rated at 36 kV-
yea, I know maybe a bit steep for a 14.4 kV pig) but
haven't had any more problems since. I think even a
36 kV rating would still protect the pig though as it's
biL rating is 110 kV.
David Rieben
----- Original Message -----
From: "Lau, Gary" <Gary.Lau@xxxxxx>
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
Sent: Wednesday, July 09, 2008 9:24 AM
Subject: [TCML] Pig safety gaps - was Winding the primary
Hi David,
Correct - I no longer use a strike ring.
I'm curious how a streamer striking your secondary could have caused
primary-side damage. I would guess that it must have also struck the
primary, causing the arrestor to avalanche, and with the current of the
charged cap (or maybe just the pig secondary) behind it, smoked the
arrestor.
That's an interesting report that normal safety gaps don't extinguish with a
pig driving it! I'm surprised that this hasn't come up before. Sounds like
the standard practice of using drawer knob electrodes (?) doesn't cut it in
your application! Have you tried a horn gap? Sorry, but I have no
experience at that power level.
Regards, Gary Lau
MA, USA
-----Original Message-----
From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
Behalf Of David Rieben
Sent: Wednesday, July 09, 2008 9:44 AM
To: Tesla Coil Mailing List
Subject: Re: [TCML] RE: Winding the primary
Hi Gary,
Nice and aesthetically pleasing coil. I assume that you're
NOT using a strike ring with your newer 2-layer primary?
IIRC, you were one the main proponents of the idea that
a strike ring was not really necessary. The physics would
seem to back up your thoughts on this issue but I think
many coilers just don't like the idea of the output sparks
power arcing directly to the primary coil. In my personal
experience, I once fired my coil outdoors on a windy day
and the wind blew one of the power arcs back into the
lower end of the SECONDARY coil, in spite of a well
placed and RF grounded strike ring. Good thing I had
a decent safety gap (actually an 18 kV rated distribution
arrester) in place across the output of my pole pig trans-
former as the arrester failed as a dead short! At first I
feared that my pig or my primary capacitor had bit the
dust but isolation showed the arrester to be the culprit.
Glad the arrester sacrificed itself over the transformer
or the capacitor as it was much cheaper to replace.
BTW, I use sufficinetly rated arresters in place of a
physical safety gap because when running coils in the
multi-kVA power range, I've always had trouble with
resultant arc not extinguishing once the safety gap fired.
David
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