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Re: Large Transformer Question (fwd)





---------- Forwarded message ----------
Date: Fri, 13 Feb 1998 08:09:37 -0800
From: Joshua Resnick <seraphim-at-WPI.EDU>
To: Tesla List <tesla-at-pupman-dot-com>
Subject: Re: Large Transformer Question (fwd)

>

Fr. Tom,

>
>
> I am confused. How can 'only one layer of foil' have 'two continuous
> strips interleaved with polyethelene.
>
> I am wondering if maybe your cap isn't really a cap after all.
> Do an ohmmeter check and see if you have continuity. If you do,
> then you don't have a cap, but a dead short with some poly for
> good looks :(
>
> What thickness of poly are you using?  It is also possible that you
> had
> a poly breakdown and therefore a foil short.
>
> NEVER NEVER NEVER fire your poly caps "dry". Surface conduction
> can cause a 15KV spark to snake along several inches of surface
> even though it might only be capable of 'jumping' a fraction of
> an inch. You NEED the oil!!!
>
> Hope this helps.
> Fr. Tom McGahee

Believe me it is a capacitor, a very big capacitor. I know that I need
the oil but I figured that I should at least test the system briefly to
make sure I wasn't wasting my time and money potting the cap.  My
makeshift gap for the cap test was only 3 mm larger than the dielectric
thickness so I was sure that no severe breakdown would occur. I also did
not feel that powering up slowly with a variac would cause any sudden ,
violent startup conditions. I learned alot from this test including the
method in which I should bus the cap. in order to distribute current
more evenly.

Thank you for clarifying the grounding situation with the xfmrs, that
cleared alot up.
Sincerely,
Joshua Resnick
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