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Re: Radical Flat Cap design
Where is a good source of electrical grade Kraft paper
that is buyable?
Barry
----------
|From: "tesla-at-poodle.pupman-dot-com"-at-PMDF-at-PAXMB1
|To: Benson Barry; "Tesla-list-subscribers-at-poodle.pupman-dot-com"-at-PMDF-at-PAXMB1
|Subject: Re: Radical Flat Cap design
|Date: Tuesday, October 22, 1996 3:15AM
|
|<<File Attachment: 00000000.TXT>>
|From jim.fosse-at-bdt-dot-comMon Oct 21 22:04:30 1996
|Date: Tue, 22 Oct 1996 02:22:11 GMT
|From: Jim Fosse <jim.fosse-at-bdt-dot-com>
|To: tesla-at-pupman-dot-com
|Subject: Re: Radical Flat Cap design
|
|
|>Date: Sun, 20 Oct 1996 13:13:51 -0400
|>From: DavidF4797-at-aol-dot-com
|>To: tesla-at-poodle.pupman-dot-com
|>Subject: Radical Flat Cap design
|>
|Dave,
| Good post .... but,
|>It has been recommended that "multiple" layers of dielectric be used in
order
|>to minimize the chance of breakdown due to flaws in the dielectric.
While
|>philosophically correct, this practice usually causes problem when
|>implemented.
|[snip]
|>
|>First, polyethylene sheets trap air bubbles between them, the more layers,
|>the more air is trapped. A 120 mil dielectric of twenty layers will trap
ten
|>times the air of a 120 mil dielectric composed of two layers. There is
|>therefore a trade off between reducing the likelihood of failure due to
flaws
|>by using multiple layers -and- using the minimum number of layers to
reduce
|>the total quantity of trapped air pockets (which can also cause failure
due
|>to heating effects).
|There is also a trade off involving the imperfections in the sheets of
|polyethylene. While the 0.030" and 0.060" thick sheets purchased from
|a plastic supplier are of much better quality than the film procured
|at the local hardware store, they still have flaws in them. I have
|blown holes in 3 of my 4 caps that I have built: a single layer 0.060"
|cap and both triple 0.030". I've not blown a hole in my remaining
|dual 0.060" cap.
|> I propose that two or three layers of thicker
|>dielectric -two 60 mill sheets, for example- is sufficient to reduce the
|>potential flaw line-up problem significantly while at the same time
*greatly*
|>reducing the amount of trapped air.
|>
|All of them were vacuum outgassed with an industrial vacuum pump to
|below 10^-2 torr and then filled with new transformer oil.
|
|[nip]
|>I propose that this problem may be solved by interleaving thin absorbent
|>paper sheets between each layer of dielectric to improve the wicking
action
|>of the oil and more completely and quickly displace the air pockets while
at
|>the same time having a negligible impact on the dielectric strength and
|>dielectric constant of the assembly. I implemented this approach on the
|>first -and only- rebuild of the cap. The result was a spectacular
success.
|> *All* off-gassing stopped within 12 hours and *all* air pockets were gone
by
|>24 hours.
|I've been working on this method for rolled caps. The kraft paper
|allows me to roll the multiple thin layers of polyethylene without
|them skewing.
|
| Regards,
|
| jim
|