 Self rolled RF pulse caps
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Kolas
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Fri Apr 18 2008, 06:36AM
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Registered Member #102
Joined: Thu Feb 09 2006, 08:15PM
Location: Raleigh, NC
Posts: 169
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Hi guys. I know this topic has been beaten somewhat beaten to death but I have to bring it up again.
I was looking at the best materials for dielectric in a 60hz TC tank cap. It's well known that oil + paper is one of the better dielectrics for RF caps. But they supposedly "leak" so much at 60hz that the dielectric dissipates too much heat. So I'm wondering: would a "sandwich" of polypropylene and paper soaked and heated in oil suffice?
I looked up a little about PP when impregnated in oil. I found when the PP is completely saturated it gains about 25% voltage break down, But it swells. Since mineral oil has a higher dielectric constant then PP, would it be safe to bet that the dielectric constant of PP would rise too?
Speaking of dielectric constants... I know it will depend a lot on the mineral oil used, but how much higher will paper's K go when soaked in oil? Paper is around 3, and most transformer oil is around 4.5... Has anyone nailed down how much higher the paper's K will get?
I must stress the type of operation this capacitor is going to see. The (relatively) slow charge time of the cap from 60Hz causes a completely different type of stress then the rapid oscillation of the ring down (~80 - 85kHz). So getting the least amount of dielectric stress is very important to me. I want any large tank caps i construct to last at least 20 - 30 hours of operation.
any thoughts would be great, and thanks for your time
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