Re: [TCML] surge arrestor for pole pig

["David Rieben" <drieben@xxxxxxxxxxx>]

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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