-----Original Message-----
From: Rich Measures <measures@vc.net>
To: Steve Thompson <amps@txrx.demon.co.uk>;
amps@contesting.com <amps@contesting.com>
To: <amps@contesting.com>
Date: 18 June 1999 09:22
Subject: Re: [AMPS] hipot testing
>>Is it an open transformer, Steve?
>
>
>It's probably what you mean by open. It's not encased in a
>sealed box of any sort but it has a very generous dip
>coating of varnish. It's from a good maker (Parmeko) so I
>expect it was vacuum impregnated too.
? If the slightly-leaky transformer were mine, to drive
out moisture,
I would bake it in a 180 deg. F oven for a few days, and
re-measure the
leakage. If the leakage decreased, I would hot-pot the
transformer with
fiberglass laminating resin. (info on my Web site)
>
- good luck, Steve
Rich...
I doubt if that's the sort of leakage problem it has,
although I'll give it a try. It was used in PSU which
another member of the contest group built and a flashover
happened and the mains fuse blew. Inside I found that there
was no ht current limiting and one leg of the bridge had
gone short. In the course of trying to get things working
again I found that there is a leakage path from the
secondary to the core which goes conductive at about 600V. I
tried it with the ground connection lifted off the core and
it worked ok. I spoke to a transformer winder who said there
would be a carbon tracking path which would never go away.
Yesterday I got hipot working and measured the primary
insulation to core, which prompted my question about leakage
levels. I'd love to get it going again as the secondary
resistance is only 18 ohms and the power just keeps coming.
It made me appreciate the advice from John, GW4FRX, about
being paranoid over protecting one's prize transformer at
all costs.
Steve
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