Re: Paper/Oil Capacitors

["Duke, Ronn (CCI-San Diego CCC)" <Ron.Duke-at-cox-dot-com> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

Snip--
The Kraft paper used in these caps is made from high-grade wood pulp that's
been specially processed to have few conducting particles or pinholes, low
porosity, and uniform density. Because it readily absorbs atmospheric water,
it should be carefully dried before use (capacitor makers typically used
vacuum drying ovens). One pound of capacitor paper can easily contain a
couple of teaspoons of water at equilibrium prior to drying!
Typical paper thickness is 0.3 - 0.5 mils (0.00030 - 0.0005 inches).
Multiple layers are always used to prevent single-point defects from causing
failures and to increase operating voltage. For utility PFC use, voltage
stress was limited to about 300 volts/mil on the paper dielectric, and no
more than 1000 volts/mil in a controlled DC environment (Brotherton).
Longland indicates that the dielectric constant of mineral oil-impregnated
capacitor paper ranges from about 3.0 (low-density) to 4.3 (high-density).
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I thought it would be a good idea to make a rolled poly cap with
paper-poly-paper layers. I figure this would help keep the heat and corona
away from the poly that would prompt premature failure, and also improve the
voltage rating and dielectric properties.

Comments?

Ronn	
Dukester-at-home-dot-com