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Re: Fr. Tom Paper Poly & oil
---------- Forwarded message ----------
Date: Wed, 1 Oct 1997 15:22:50 -0400
From: Thomas McGahee <tom_mcgahee-at-sigmais-dot-com>
To: Tesla List <tesla-at-pupman-dot-com>
Subject: Re: Fr. Tom Paper Poly & oil
----------
> From: Tesla List <tesla-at-pupman-dot-com>
> To: tesla-at-pupman-dot-com
> Subject: Re: Fr. Tom Paper Poly & oil
> Date: Wednesday, October 01, 1997 12:13 PM
>
>
>
> ---------- Forwarded message ----------
> Date: Wed, 1 Oct 1997 19:39:01 +1200
> From: Malcolm Watts <MALCOLM-at-directorate.wnp.ac.nz>
> To: tesla-at-pupman-dot-com
> Subject: Re: Fr. Tom Paper Poly & oil
>
> Hi Larry,
>
> > From: Larry Robertson <LWRobertson-at-classic.msn-dot-com>
> > To: Tesla Builders <tesla-at-pupman-dot-com>
> > Subject: Re: Fr. Tom Paper Poly & oil
> >
> > Hi ...
> >
> > My first cap looked like two very wide plates of your flat cap
> > rolled up -i.e. each of the two plates extended from a different
> > end of the roll.
> >
> > It's failure was exactly like yours - the place it broke through
> > was between an edge where another plate extended beyond.
>
> The edge of a conductor is generally (without going into all the
ins
> and outs) a highly favoured corona launching pad, plate below it or
> no plate below it.
>
> Malcolm
Larry, thanks for the response. I think that corona at the ends is
more of a problem than most people realize.
Malcolm,
I agree with what you said about corona finding ANY edge to be a good
launching pad.
However, what I was pointing out in the original post was that there
was direct visual evidence to show that corona activity is greatly
*enhanced* when the plate below extends past the plate above. One
might think that if 1" of extra poly is adequate around the sides,
then 2" would be adequate around the ends, since both amount to a
plate-to-plate distance of 2". But what I am actually seeing tells me
that the tendency for the corona to reach out in a particular
direction is ENHANCED by the presence of the other plate under the
poly, so we need to allow even greater insulation distance here.
In all the posts regarding cap construction that I have read (and I
have read all the Tesla List posts in the archives) I do not recall
having ever seen this *explicitly* mentioned, though there were some
hints here and there. What it means is that instead of suggesting an
end insulation distance of 2X the side distance, we should be
recommending an end distance of perhaps 3X the side distance. We all
want to build really rugged HV caps that can take a massive beating
for AGES. Here is one simple suggestion that can save us all a lot of
re-building later.
Hope this helps.
Fr. Tom McGahee