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Re: Blown Rolled "Hull" Capacitor Discussion

Hi all,
        I was interested to read this(after some recent indifferent
results with motor oil.....

> A possible reason for the very different performance of the same design:
> MINERAL OIL!! If I have understood correctly people used this and blew
> their caps.. What if the different brands of "mineral oil" are very
> different what comes to impurities, water content etc.. It might very well
> be that as long as it's not lethal (harmfull to people) the manufacturers
> don't mind about additional water etc. in the mixture.. At least in
> xformer oils the voltage rating goes rapidly down as water content gets 
> higher - or are there other (conductive?) impurities left to the "mineral 
> oil" as it is manufactured? 

I have just scored 20 litres of good quality transformer oil from a 
local power company. Not only did they give it to me ("paperwork's
worth more the the oil") but ran it through their test tank while I
was watching. I'm not sure whether they were using AC or DC in the
tank (and interestingly enough, the guy who did the testing didn't
know either - duh? :( , but the best holdup measured was 39kV across
a 3mm gap with 15mm balls. It looks just the goods - great insulation
and reasonably runny to boot. Amazing what can happen when you ask.

Malcolm