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Re: Glass cap with polyethylene
From: Alfred A. Skrocki[SMTP:alfred.skrocki-at-cybernetworking-dot-com]
Sent: Sunday, September 14, 1997 2:00 PM
To: Tesla List
Subject: Re: Glass cap with polyethylene
On Sunday, September 14, 1997 6:09 PM Thomas McGahee
[SMTP:tom_mcgahee-at-sigmais-dot-com] wrote;
> Alfred,
> Perhaps the reason why oil and poly work so well together is that
> they have almost the same dielectric constant. This being the case,
> the electrostatic fields in this type of capacitor would actually be
> quite uniform in practice.
>
> So maybe what Dr. Resonance meant to say was that using two
> dielectrics which have very different electrostatic properties can
> sometimes lead to local corona and hence breakdown. Then again, maybe
> that's NOT what he meant.
>
> I wonder if using oil with a higher dielectric constant (such as the
> 4 rating in Ralph Down's SUNISON compressor oil capacitor) might
> exhibit the effect Dr. Resonance mentions.
I have used SUNISON compressor oil in polyethylene caps with no
problem what so ever, again if the polyethylene is thick enough to
tolerate the applied voltage, adding a second dielectric is not
going to induce breakdown.
> Glass has a dielectric constant between 4 and 7, depending on the
> type of glass. The really bad thing about the glass is its
> dissipation factor, which causes it to get VERY hot in TC use. The
> use of poly with glass does not address this dissipation problem, so
> the main problem would remain, and if anything, the poly would then
> REDUCE the effective dielectric constant. So poly and glass do not
> really seem to have any advantage when used together.
This is exactly what I said in an earlier post, namely if the weakest
dielectric is thick enough to tolerate the applied voltage breakdown
can not occur regardless of what other dielectrics are added BUT if
you add a high power factor dielectric you will induce dielectric
heating losses.
Sincerely
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Alfred A. Skrocki
Alfred.Skrocki-at-CyberNetworking-dot-com
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