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mixed dielectric cap


From: 	teslaman-at-juno-dot-com[SMTP:teslaman-at-juno-dot-com]
Sent: 	Wednesday, September 24, 1997 9:30 PM
To: 	tesla-at-pupman-dot-com
Subject: 	Re: mixed dielectric cap


On Wed, 24 Sep 1997 18:06:45 -0500 Tesla List <tesla-at-pupman-dot-com> writes:
>
>From: 	Gwyn Zucca[SMTP:gwyn-at-tcbod.demon.co.uk]
>Sent: 	Wednesday, September 24, 1997 12:29 PM
>To: 	tesla-at-pupman-dot-com
>Subject: 	mixed dielectric cap
>
>Hello all,
>
>I am considering building a couple of high power discharge capacitors, 
>
>to a design that I have done some previous experiments with. The 
>design 
>uses 1mm (40 mil) polypropylene sheet as the dielectric with grease 
>proof cooking paper between the foil and the poly as a wicking agent.
>This mixed dielectric construction is of similar form to that of 
>professional build, but the grease proof paper is a substitute for 
>high 
>density capacitor paper. The experimental caps thus far have been of 
>the 
>flat plate type, and of a sealed, oil immersed form. The proposed new 
>ones will be 65nF in capacitance, 40Kvdc working, to be used in series 
>
>in a symmetrical equi-drive type tank circuit. This covers the basic 
>detail. 
>
>What I would like to know is, has any one else constructed caps of a 
>mixed dielectric type, and what experiences have they had. I think 
>that 
>home made mixed types offer the advantage of better oil penetration 
>and 
>so help expel trapped air, in which corona tends to form. I also agree
>with the view voiced by others on the list that certain oils can 
>enhance
>dielectric properties.
>
>any comments welcome ( useful ones anyway!!! )
>
>See ya...
>
>Gwyn
>
>
>Gwyn,

  It's a small world.  I am on vacation this week and my project is the
same as yours.  I am experimenting with 4 mil building supply type
polyethylene with masking paper soaked in mineral oil.  This paper can be
found at building centers also.  It's approx 3 mil thick and comes in
different size rolls.  I am using 12" x 60 yards cut into sections and
immersed in oil before assembly with the poly and foil.   I believe the
paper will more or less assume the dielectric constant of the oil and be
helpful keeping an oil supply between poly sections.  This is just what
the big boys do in there pulse caps.    referring to Aerovox technical
data/design literature I have.

 I agree on the entrapped air as it must be removed.  Watching a test
capacitor under oil as voltage was brought up to corona onset, revealed
the ominous blue glow in areas of small air bubbles and eventual rupture
in that same area.   The oil I plan on using will be transformer grade
mineral oil as it is on hand.  Hopefully we will both have success with
our venture.  More input from others out there on this subject  would be
appreciated.

 Kevin E.
>