Re: Partial Discharges.....A good reason for cap failure?

• To: tesla-at-pupman-dot-com
• Subject: Re: Partial Discharges.....A good reason for cap failure?
• From: "Barton B. Anderson" <mopar-at-uswest-dot-net> (by way of Terry Fritz <twf-at-verinet-dot-com>)
• Date: Tue, 02 Mar 1999 17:00:48 -0700
• Approved: twf-at-verinet-dot-com

Hi Reinhard,


> Original Poster: "Reinhard Walter Buchner" <rw.buchner-at-verbund-dot-net>
>
> <snip>
>
> Any kind of disturbance (i.e. non uniformity) in the E-Field (sharp
> metal edges for example) will also increase the production of
> partial discharges (->corona formation). Important to know is that
> this phenomenon does NOT lead to instant failure, but rather, it
> accumulates over time and then leads to failure. I believe this to
> be one of the major reasons why commercial pulse caps are built
> with a very low volt per mil rating (lots of series caps). And now it
> should make sense why coilers like Bert Hickman (72-96 mils)
> or Ed Sonderman (90 mils) suggest such "gigantic" mil numbers
> for homebrew caps.  Oil DOES NOT prevent the formation of
> corona!! Of course a pulse cap always has a limited lifetime,
> simply because it is a highly stressed component.
>
> Coiler thoughts.............FWIW.
>
> Reinhard

Very good description of cap failure over time. This is interesting and
does sound like a valid reason why caps fail over time. Even professional
caps have discharge life expectancies. We should learn from the
manufacturers here that reducing the voltage across the cap (series
arrangements) promotes the best chance of longevity, especially since if
we will never be able to match a cap manufacturers processes, cleanliness,
and experience. However, we can series up what we have and increase the
life.

Bart

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