Proposed capacitor design -Reply

To: tesla-at-pupman-dot-com
Subject: Proposed capacitor design -Reply
From: ROBERT CRESSLER <59CREROB-at-menasha-dot-com> (by way of Terry Fritz <terryf-at-verinet-dot-com>)
Date: Mon, 05 Oct 1998 18:06:59 -0600
Approved: terryf-at-verinet-dot-com

    gary,
           re:your comment on the large variation on PS dissipation factor
.05 to .0004 is probably because of the various grades.. eg gen
purpose,impact modifed,copolymer,ect.
robert

>>> <tesla-at-pupman-dot-com> 10/04/98 05:37pm >>>
Original Poster: Gary Lau  04-Oct-1998 1245
<lau-at-hdecad.ENET.dec-dot-com> 

>Original Poster: Aric <acr-at-infinet-dot-com> 
>
>I am seeking opinion and sage advice regarding design and construction

>of a cap. 
>
>I plan to make a stack cap from 9" X 13" impact-resistant styrene 
>cutoffs I can get at a very low price. The material is 20 mil thick. 
>For use with a 15kV, 60ma NST, I expect that six 0.06 uF caps made 
>with this material, potted in oil, and wired in series would suffice. 
>
>Is this too conservative? Not conservative enough? 
>
>If the stacks are under oil (I have Suniso refrigeration oil and Diala 
>AX on hand), is a 2" guard region between the edge of foils and 
>dielectric really necessary? Going to a 1" guard region will reduce 
>>the number of dielectric layers from 50 (for 2" guard region) to 29 
>layers. I plan to round the corners of the foils. 
>

Polystryene has about 2/3 the dielectric puncture voltage rating as
polyethylene, so the total dielectric thickness may just be marginal.
It's hard to say, the tables give a range of values for each material.
The two inch margin is way too conservative, considering that you're
building six units in series.  I'd suggest going to three units in
series, doubling up on dielectric thickness, and 1.5" margins.

The dielectric dissipation factor for PS isn't clear.  For LDPE, it's
.08E-3 -at-1MHz.  For PS, the table I have gives a range of .05-.4E-3, not
sure why the variation.

>I have samples of the styrene under the Suniso, castor, and mineral 
>oils. I haven't seen any damage thus far (2 days at room temp). 
>>Various reference differ as to compatibility of styrene with mineral 
>oil. Should I not use mineral oil with styrene? 

If it seems stable, go with it.

>Also, what enclosures would be suitable for such a cap. I'd prefer to 
>not use Rubbermaid containers. Would a particle board/MDF box, 
>painted with polyester resin be resistant to mineral oil? 
<snip>

I've not had experience with flat plate caps, but for rolled poly caps,
I've not had any problems using cemented PVC pipe enclosures,  it
seems
perfectly oil-tight.

Gary Lau
Waltham, MA USA