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Re: [TCML] Primary Support Materials


I think the concern with PVC on the primary is possibly when you get a
streamer hit to the primary, it can quickly carbonize it.  At least thats
why i prefer HDPE, it seems much more resilient to this.  If your strike
rail is supported by PVC, it can likely carbonize near the support points,
which makes the problem much worse as there is substantial E-field on the
strike ring, so any carbon-needles on the supports will promote flashovers
to the secondary (this has been my experience).  Of course, i had the same
problem with dirt build up on my HDPE supports, but it was fixed with a
thorough cleaning.


On Tue, Aug 24, 2010 at 1:23 PM, Gary Lau <glau1024@xxxxxxxxx> wrote:

> It's not clear that folks are in agreement on whether PVC is prone to
> surface tracking.  Here's my thoughts.
> If PVC were inherently prone to surface tracking, we'd all be in trouble,
> as
> pretty much all of our secondaries are wound on it, right?  Surely a
> secondary coil has a far higher voltage gradient than a primary support.
> I think Ralph's account of a PVC antenna support succumbing to carbon
> tracking is not surprising, given that it occurred when it was covered with
> dew.
> FWIW, I had carbon tracking on some (dry) Lexan primary supports - I had
> too
> many unused primary turns adjacent to a grounded strike ring.  Anything
> will
> surface track, then carbon track, if it's carbon-based.
> That said, it's hard not to notice the discoloration of white PVC near a
> spark gap.  If that brown stuff is more conductive than PVC (don't know),
> perhaps there is a higher risk of surface tracking on PVC near the gap,
> although I've never heard this reported.  But secondary coils are
> sufficiently shielded or distant to not be affected.  I'm guessing the same
> is true for primary supports as well.
> Regards, Gary Lau
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