Re: pole pig ideas

To: tesla-at-pupman-dot-com
Subject: Re: pole pig ideas
From: Jim Lux <jimlux-at-jpl.nasa.gov> (by way of Terry Fritz <twf-at-verinet-dot-com>)
Date: Tue, 02 Feb 1999 11:59:15 -0700
Approved: twf-at-verinet-dot-com

Tesla List wrote:
> 
> Original Poster: "Mad Coiler" <tesla_coiler-at-hotmail-dot-com>
> 
> Hello Tesla Listers,
> 
> In the past month or two I have asked some questions about my design for
> my first pole-pig powered coil. I thank everyone who sent me comments.
> One of the re-occuring comments was that a 40kV cap was insufficient for
> a 19,920V pole pig. If I wanted to use this 40kV cap without a major
> change, would it be possible to apply 120VAC to the LV windings of the
> pig instead of 240VAC? If this works it should reduce the output to
> 10kV. But assuming the 10kVA rating is because of the wire size(?) it
> should still only be able to pass 42A, so the max power would be cut in
> half to 5kVA??? If this is the case, does anyone now if a pole pig can
> be overpower (I assume it can), and if so how much and for how long? I
> would think it could be run at 200% for runs of <1min, with cool down
> time inbetween. Is this correct?

You could easily overload that transformer by a factor of 2 or 3 without
problems. Your runs can be substantially longer than 1 minute too. The
best way to deal with this is to measure the dc resistance of the
winding, which will vary with temperature in a highly predictable way.
(You could also put a temperature probe in the winding, but that might
have insulation issues).

In any case, utility transformers are designed for rugged duty. If you
want to be sophisticated, measure the thermal time constant (or call the
manufacturer), then figure out how much overload for how long you can
take without exceeding the temp limit for the windings. 
> 
> Tristan Stewart, KC2EBM
> 
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-- 
Jim Lux                               Jet Propulsion Laboratory
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