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Re: Lightning Arrestors (was Geek Pig)



Original poster: "Bert Hickman by way of Terry Fritz <twftesla-at-uswest-dot-net>" <bert.hickman-at-aquila-dot-net>

Chris,

I've take a few pictures of the 9 kV Pyrex Arrestor. These include a
shot of the whole arrestor (about 15" long), a close-up of the chain of
spark gaps, and a close-up of the silicon carbide MOV. Arrestors made
from a combination of Silicon Carbide and spark gaps were commonly used
from between 1930 and 1970. They have more recently been supplanted by
Zinc Oxide MOV type. The pictures can be seen at:

http://www.aquila-dot-net/bert.hickman/photos/arrestor1.jpg
http://www.aquila-dot-net/bert.hickman/photos/arrestorgaps.jpg 
http://www.aquila-dot-net/bert.hickman/photos/arrestorMOV.jpg  

-- Bert --
-- 
Bert Hickman
Stoneridge Engineering
Email:    bert.hickman-at-aquila-dot-net
Web Site: http://www.teslamania-dot-com

Tesla list wrote:
> 
> Original poster: "Christopher Boden by way of Terry Fritz
<twftesla-at-uswest-dot-net>" <chrisboden-at-hotmail-dot-com>
> 
> Interspersed.....
> 
> >Original poster: "Bert Hickman by way of Terry Fritz <twftesla-at-uswest-dot-net>"
> ><bert.hickman-at-aquila-dot-net>
> >
> >Chris,
> >
> >Turns out they ARE a bit more complicated than that - remember that
> >arrestors are designed to provide a safe path to ground for HV
> >transients, but should open back up once the surge has gone. They must
> >be able to rapidly recover and hold off normal line voltage. Ideally,
> >they should pull little or no current at normal line voltage.
> 
> Thus a spark gap would be the perfect, cheap, simple solution. That's why it
> made sense.
> 
> >
> >To meet these requirements, most arresters are actually a combination of
> >spark gaps and MOV's, with the MOV element actually made of silicon
> >carbide. I happen to have a clear glass 9 kV (Pyrex) arrestor that I use
> >for demos - it has a MOV that's about  9" long by 3" in diameter, in
> >series with eight spark gaps (each about 1/16"). Will be interesting to
> >see what you find inside yours... :^)
> >
> >-- Bert --
> 
> It's killing me........I'm half temped to accidently "drop" it to open it up
> :) I have a pair of the little ones, so I can open one, but they're REALLY
> proud of their sealing mechanisms. The big ones have what looks to have once
> been a liquid (like tar), and poured in around the base. The insulator
> actually sets inside a 4" deep aluminum base, and is held in with this black
> nastiness. It works like glass, very brittle, powdery when it shatters, has
> a grainy, flaky property (like creosote, flint, or mica) and smells terrible
> when filed. What IS it? and how do I get rid of it? I want to open this
> without destroying the insulator....and cutting the case does not look like
> fun as I don't know what's on the other side.
> 
> I hate a puzzle in progress. :)
> 
> Thank's for the info, I could use any MOV inside, but it still doesn't make
> any sense to me why they would go to the trouble (and expense) of building
> anything more than a simple spark gap in a sealed container (these don't
> appear to be vented in any way).
> 
> Can the gaps be used as a static gap? What are they made of?
> 
> Constantly learning......constantly changing opinion :)
> 
> Christopher A. Boden Geek#1
> President / C.E.O. / Alpha Geek
> The Geek Group
> www.thegeekgroup-dot-org
> Because the Geek shall inherit the Earth!
> 
> _________________________________________________________________
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