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

Hi Reinhard and all

My first effort at a classic rolled cap was 60 mil of polyethylene,
connections on the ends of the plates, in mineral oil. With 60 ma
15 kV it lasted about 3 hours total before punching through at a
plate edge. Worked really well though. Smelled very bad when
opened up.

Second try was 90 mil polypropylene in 3 x 30 mil with edge
connections, vacuum pumped, and a lot of care taken with
cleanliness and edge smoothing. It lasted many hours at 120 ma,
15 kV but the oil slowly darkened, and I finally put it to work as a 60
Hz resonator with the NST's when I got commercial caps.

It's quite evident that a single cap is not going to last forever
in Tesla use - several in series will likely last much longer.


> 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.