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Re: [TCML] Pole transformer repair

David et al...

Indeed you can overvolyage and destroy a transformer.  How you ask?
Here is the explanation, and also ecplains why delta three phase systems
ARE so dangerous...


Best Regards
Dave “Sparky” Sharpe

On Fri, Jan 4, 2019 at 9:02 AM David Rieben <drieben@xxxxxxx> wrote:

> Tyler,
> Wow! Although $700 may be a decent deal for a 25 kVA pig these days, it
> ain’t cheap at all, at least not to me! Especially when it dies on you so
> soon after the purchase! Can you provide any details on the capacitor that
> you were using (uFd, kV rating) and whether you were placing the capacitor
> in parallel with the Jacobs ladder rails or in series between the
> transformer bushings and the Jacobs ladder rails?
> Like I said, I have let the magic smoke out of a couple of smaller
> transformers in the past by simply seriesing the hv output of the pole
> pig’s bushings through a capacitor. I found that if the capacitance was in
> the correct range, it would form a near resonance with the transformer’s hv
> output and allow the power arc to drawn out to several feet before
> breaking, as opposed to mostly 12” to 18”, at best, before breaking without
> the capacitor. I should mention that my ballast allows about 100 amps to be
> drawn when shorted across a 240 volt AC source and when I applied the line
> voltage to my transformer, it would draw upwards of around 80 to 90 amps
> (w/out the capacitor). Also, with the correct sized capacitor, the power
> arc is much louder and the current draw INCREASES (and can momentarily peg
> out my 150 amp ammeter, through my same ballast!) with increased arc
> length, as opposed to DECREASING current draw with arc length increase
> without the capacitor!
> Your experience, as well as my past experiences with a smaller (5 kVA)
> pole pig and a 3 kVA PT, is starting to make me reconsider this practice
> (google “arczilla”) with my own 25 kVA, 14.4 kV transformer! Maybe the
> ferro-resonance that Jan mentioned is what’s happening here and may not be
> healthy practice for any pole transformer?
> David
> Sent from my iPhone
> > On Jan 3, 2019, at 2:29 PM, Terry Oxandale <toxandale@xxxxxxxxxxxxx>
> wrote:
> >
> > I know we would see static charges develop during oil filtering/filling,
> but these were very short-lived changes, but still enough to get your
> attention.
> >    On Thursday, January 3, 2019, 1:07:31 PM CST, Teslalabor <
> teslalabor@xxxxxxxxxxx> wrote:
> >
> > How should this be possible? If there is any tiny charge, it surely is
> > not dangerous?
> >
> >
> >> Be sure to ground all terminals for a few minutes before disassembling.
> Some of these can hold a charge for a long time.
> >>
> >> Sent from my iPhone
> >>
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Dave Sharpe, TCBOR/HEAS
Chesterfield, VA USA

Sharpe's Axiom of Murphy's Law
"Physics trumps opinion!"
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