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Re: [TCML] surge arrestor for pole pig



Hi Aaron,

No, I can't be sure of the internal construction of either but from the ones
that I have autopsied, they all seem to have those same line of cylinders, of
SiC, I presume. One of the older porcelain jacketed ones had what
appeared to be a little spark gap in between each of those cylinders.
The 18 kV one that failed as a dead short also had those cylinder
looking thingies seriesed inside (not sure what their composition was
but they appeared to be pretty much the same SiC-like material)? but
no spark gaps. This one WAS one of the newer style butyl rubber type,
too. I've always thought that they were all MOV based and the electrical
characteristics of the cylindracal blocks allowed for MOV type clipping
action. I really don't KNOW this, though. Maybe someone can chime in
who actually does know ;^)

On my first big pole pig driven coil, I originally had a 12 kV rated one
on a 14.4 kV pig. When I would turn the variac up past about 80% on
the dial, the output would start "clipping" but would stop once the voltage
was decreased back below the "cutoff" voltage. The arrestor never was
damaged in this fashion, though. I finally replaced with a higher voltage
unit because of this was annoying.

David

----- Original Message ----- From: "J. Aaron Holmes" <jaholmes@xxxxxxxxxxxxxxxxxx>
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
Sent: Wednesday, September 17, 2008 4:38 PM
Subject: Re: [TCML] surge arrestor for pole pig


Hi David: Figured you'd chime in on this one ;-) Are you sure about the construction? I'm pretty sure the new rubberized arresters are wayyyyyy different inside than the old percelain ones, being MOV-based rather than silicon carbide-based. SiC is far more linear than MOV technology, so I'd expect more dissapation and less effective clipping of high-frequency transients than with modern MOV arresters. These arresters that Jim is asking about are dated 1971 (!), so I'm going to go out on a limb and say that they're SiC and not MOV. I'd wait for something modern, m'self.

Cheers,
Aaron, N7OE

--- On Wed, 9/17/08, David Rieben <drieben@xxxxxxxxxxx> wrote:

From: David Rieben <drieben@xxxxxxxxxxx>
Subject: Re: [TCML] surge arrestor for pole pig
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
Date: Wednesday, September 17, 2008, 1:46 PM
Hi Jim,

I originally had a single 18 kV rated arrestor on my big
coil.
On one occasion, I was firing the coil outdoors on a windy
day
and the wind actually "blew" some of the
streamers/sparks
back into the lower third of the secondary coil and into
the primary
circuit. The output almost immediately died and further
inves-
tigation revealed that the arrestor had failed as a short
circuit.
However, nothing else in the system died so I guess the
arrestor
did its job by sacrificing itself to protect the
transformer and the
capacitor. I eventually replaced the 18 kV arrestor with a
36
kV arrestor, which would be in the same
"ballpark" rating as
your proposed (2) seriesed 15 kV arrestors since my
transformer
is also rated at 14,400 volts on the high voltage side. I
haven't had
anymore problems since I added the 36 kV arrestor but then
again, I have also since tried to avoid firing the coil
during
excessively windy conditions, too. BTW, my arrestor is one
of the more modern butyl rubber exterior types instead of
the
porcelain exterior type. It's much lighter and less
fragile, too.
The exterior is the only difference though and the older
por-
celain style ones will work just as well.

David


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