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Re: LDPE Pulse Capacitor
Pete wrote:
<<snip>>
>For these reasons I have opted for a flat horizontally stacked cap. I
>plan to use 10mil LDPE for which I have finally managed to find a
>supplier. The design philosophy is to make a block 10" x 10" using 30
>plates giving +/- 0.135uF. To get the correct voltage rating (40kV for
a
>12Kv 60mA NST) and +/- 0.016uF total capacitance I intend to series 8
>blocks. Each block will have 1/4" PVC backing plates for support. The
>blocks will be placed in a PVC container and filled with mineral oil
and
>left standing for two weeks. During this time and to remove trapped air
>bubbles I intend to apply 220 VAC for a few hours a day for the two
week
>period. By the way the plates will be heavy duty aluminium kitchen foil
>from the local food store.
>South African cost of LDPE is equivalant to $1-30 per meter (1.5meters
>wide). Al foil is equivalant to $1 per box (5 meters x 0.45 meters)
>
>Comments on the proposed design will be most welcome
>
>Pete
>South Africa
>
>
Pete, based on my own flat-plate HDPE/Al capacitor I suggest that
you consider a MUCH larger area because lots of dielectric
(the expensive stuff ) will be wasted around the edges, I'd suggest
25mm (1 inch) top & bottom and MORE than twice that at the ends.
For 10" x 10" dielectric you'd get a useable 8" x 6" 'capacitor'
area, less than half usefull.
If you use 12" x 24" you'd get 10" x 20" useable, 70% useful etc.
Bye ... Sulaiman
P.S. the 'ends' should be more than twice the top & bottom because
the end plates 'pull' the field along the dielectric.
BTW I've seen published figures of 500 - 700 V/mm for creepage
compared to 35 - 50 kV/mm dielectric strength for PE, I guess
that's similar for most dielectrics.
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