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Re: [TCML] surge arrestor for pole pig
I've got a few of each kind, but haven't busted open any of the newer ones, so I'm not sure what the MOV ones look like inside. The SiC elements in the older porcelain-housed ones were black and rough like grinding wheel material.
Here's a doc from Cooper that tries to illustrate the differences in response and leakage current, etc., of modern MOV (1990's) versus SiC arresters:
http://www.cooperpower.com/library/TheLine/pdf/may06/MOVVogelArticleLine.pdf
This doc, of course, is basically an advertisement, so bear that in mind. I found a seemingly more impartial paper describing the differences a couple of years ago, and wish I'd saved it. There appear to be some IEEE publications on this subject too, but they have you jump through all kinds of hoops to get that stuff.
Anyway, I see those rubber-housed MOV elbow arresters go by on eBay all the time. Just seems like, if you can get the modern stuff for the same $$ (maybe less, because the porcelain ones are going to be heavier and more expensive to ship), then it's probably goodness.
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, 5:40 PM
> 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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> > Tesla@xxxxxxxxxxxxxx
> > http://www.pupman.com/mailman/listinfo/tesla
> >
>
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