Re: [TCML] Pigs killed in the line of [Tesla coil] duty

[Garry Freemyer <garryfre@xxxxxxxxxxx>]

It's been long enough that I first thought you were talking about farm animals. I suppose for those who don't know the term pole pig at all, they might be rather shocked. Pun not intended, but I refuse no laugher.



----- Original Message ----
From: DC Cox <resonance@xxxxxxxxxxxx>
To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
Sent: Wednesday, September 10, 2008 2:58:42 PM
Subject: Re: [TCML] Pigs killed in the line of [Tesla coil] duty

I also killed a 14.4 kV pole xmfr before applying my filter design.

Dr. Resonance

On Wed, Sep 10, 2008 at 11:06 AM, Bert Hickman <bert.hickman@xxxxxxxxxx>wrote:

> Hi Aaron and all,
>
> You can add two more to the group of destroyed pigs: Greg Leyh and Charles
> Brush have also destroyed pigs (many years ago). Greg's was destroyed as it
> sat idle on the ground and one ear was accidentally struck by friendly fire
> from an errant TC streamer. Charles destroyed his while driving his Tesla
> Coil.
>
> While considerably more robust than most other HV transformers,
> distribution transformers are still vulnerable to high dv/dt transients. The
> insulation systems within the HV winding can be degraded and, eventually,
> destroyed through partial discharges (PD) and flash-overs when subjected to
> repetitive high voltage transients. The distributed winding inductances and
> capacitances form a complex network of coupled LC elements. When shock
> excited by an external voltage transient, these elements resonate, resulting
> in a nonlinear voltage distribution across the HV winding that can overly
> stress some portions of the winding insulation system (usually the outermost
> sections).
>
> Under sufficiently high dv/dt conditions, the overstressed portions of the
> winding and inter-layer insulation develop corona and PD. These lead to
> cumulative insulation damage, carbon tracking, and eventual insulation
> failure. The higher the dv/dt and pulse repetition rate, the faster the
> damage progresses.
>
> As Aaron found, the problem usually develops between the inter-winding
> insulation layers closest to a HV input/output. This is a recognized
> long-term reliability problem within utility power and distribution
> transformers, where failures are often induced through switching transients
> (especially with vacuum and SF6 interrupters), or by nearby lightning
> strikes. Remember: Tesla coilers apply very fast dv/dt transients EVERY TIME
> the main spark gap fires, and transformer damage may only be a matter of
> time.
>
> The preventative measure is similar to that used for NST's - reduce the
> maximum dv/dt seen by the HV winding. You can use either a higher power
> version of a Terry filter, or perhaps a simple series filter choke(s) as
> recommended by Dr. Resonance. Even if the MOV's are not used in the Terry
> filter, the RC filtering section is still recommended.
>
> YMMV - many coilers have successfully run pig-powered systems without
> protective measures for years. However, internal partial discharge damage
> can silently progress with virtually no outward symptoms, until the
> transformer catastrophically fails. Preventative insurance is relatively
> cheap.
>
> The first case that Aaron mentions appears to be classical dv/dt PD and
> tracking failure. The second failure is a bit more difficult to explain -
> perhaps a flashover that was mostly confined to the oil which then (mostly)
> healed itself after power was removed(?) - just like the explanation Aaron
> provided. Unfortunately, unlike some capacitors, self-healing transformers
> are pretty scarce... :^)
>
> Bert
> --
> ***************************************************
> We specialize in UNIQUE items! Coins shrunk by huge
> magnetic fields, Lichtenberg Figures (our "Captured
> Lightning") and out of print technical Books. Visit
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>
>
> J. Aaron Holmes wrote:
>
>> As long as we're keeping track of these incidents for posterity, I'll
>> add a couple more.
>>
>> Case 1)
>>
>> Friend and fellow Seattle coiler Matt Stiger toasted a 14.7kV 25kVA
>> unit a couple of years ago.  Granted, this was done whilst feeding
>> 240V to the 120V windings (which had been placed in parallel within
>> the can, as would be done for 120V-only service, or else 208Y
>> three-phase service) in an effort to increase the output voltage,
>> which appeared to work fine.  Pig had operated without incident under
>> these conditions for some time, but it seemed to me a matter of
>> when--not if--the pig would be ruined.
>>
>> Sure enough, the pig did give up the ghost one day while driving
>> Matt's monster coil.  Coil suddenly stopped performing.  Further
>> testing isolated the pig as the cause of the problem.  Small arcs
>> could be drawn off the pig, but running it open-circuit caused it to
>> arc internally.  The windings were later dissected and it was
>> discovered that multiple layers of paper on the HV side had burned
>> through near the end of the windings.  It was hard to tell exactly
>> where the first fault had occurred and what the sequence of
>> destruction might have been.
>>
>> Fortunately, Matt has other pigs and PTs, so this wasn't a terrible
>> loss, and it *was* an interesting experiment, if mainly serving to
>> illustrate what can happen if you overvolts transformers like this!
>> But ruining pole pigs is no good for many reasons, not the least of
>> which is that you must then figure out how to "throw it away".  I've
>> dissected and removed the windings from several pole pigs in an
>> effort to re-purpose the cores, and it is very un-fun.
>>
>> Case 2)
>>
>> Nick Berndsen, a former regular on the web site All Things Tesla
>> (RIP), bought a 10kVA 14.4kV pole pig.  Shortly thereafter, while
>> running his coil, the pig pooped out.  IIRC, like Matt's, it would
>> arc internally when run into an open circuit.
>>
>> Curiously for Nick, the pig seemed to rise from the grave a year
>> later; running into an open circuit no longer caused it to arc
>> internally.  Indeed, it appeard to have healed itself!  I offered
>> Nick my only theory, which was that the original fault had mainly
>> displaced/vaporized oil, making further arcing much easier.  After
>> sitting unused for a year, however, oil seeped back into the void
>> created by the initial fault and reinsulated things.  Any other
>> ideas?
>>
>> I guess #2 doesn't really count, since the pig came back to life.
>> Self-ressurrection is definitely a unique property of a pole pig, if
>> indeed that is what happened here :-)
>>
>> Cheers, Aaron, N7OE
>>
>> --- On Tue, 9/9/08, David Rieben <drieben@xxxxxxxxxxx> wrote:
>>
>> From: David Rieben <drieben@xxxxxxxxxxx> Subject: Re: [TCML] pole
>>> pig protection To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx> Date:
>>> Tuesday, September 9, 2008, 7:34 PM Hi,
>>>
>>> Yep, I concur here as well. As far as power transformers go, they
>>> don't come much tougher and more robust than a pole distribution
>>> transformer. Consider this- the high voltage primary (secondary for
>>>  coiling purposes) winding of a standard 14,400 volt pole
>>> transformer is designed to take a 50 micro-second pulsed voltage
>>> peak of 110 kV and survive! That's called the (B)asic (I)mpulse
>>> (L)evel rating. Of course, they do get a little bit of extra help
>>> for lightning impulse protection when they're sitting up on a pole
>>> in the form of distribution arresters. Still, it would take some
>>> real effort to kill a pig in Tesla coil duty and I've only heard of
>>> one confirmed in- cident of someone killing a pig in a Tesla
>>> circuit!
>>>
>>> David
>>>
>>>
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>
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