RE: PDT (Pig) failure modes

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Malcolm Watts by way of Terry Fritz <twftesla-at-qwest-dot-net>" <m.j.watts-at-massey.ac.nz>

Hi Dave,

On 23 Sep 2002, at 22:29, Tesla list wrote:

> Original poster: "Dave Hartwick by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <ddhartwick-at-earthlink-dot-net>
> 
> Malcom,
> I did not hear that telltale humming from this PDT. The IZ is 2.7%, if that
> is significant.
> 
> My variac certainly complained, but not a peep from the xfmr.
> Dave

That suggests to me that there is indeed a shorted winding, probably 
primary. Sounds like the variac is working into something approaching 
a short circuit. I'll sit back and wait for the failure analysis.

Thanks,
Malcolm

 
> 
> 
> 
> Original poster: "Malcolm Watts by way of Terry Fritz <twftesla-at-qwest-dot-net>"
> <m.j.watts-at-massey.ac.nz>
> 
> Hi Dave,
> 
> On 23 Sep 2002, at 7:16, Tesla list wrote:
> 
> > Original poster: "Dave Hartwick by way of Terry Fritz
> <twftesla-at-qwest-dot-net>" <ddhartwick-at-earthlink-dot-net>
> >
> > Malcom,
> > With a turn-to-turn short condition, would you not expect some output,
> > whether the short exist
> > in the HV or LV windings? This is not to put into doubt your experience
> with
> > xfmr failure modes.
> > Dave
> 
> It very much depends on the transformer and how good the coupling is
> between the windings. The least tightly coupled transformers exhibit
> a notable drop in the Q of their windings and a nmoderate to severe
> inductance drop in the shorted winding. Tightly coupled transformers
> act as though there is a short across all windings. There may be a
> modicum of output but it won't be much and the shorted winding will
> cause it to emit a loud hum as the winding attempts to jump out of
> the core. It will in all probability blow fuses readily. If your
> transformer hums like crazy as you apply power, the latter case
> probably applies. All serious power transformers should fall into the
> second category as coupling relates closely to regulation under load.
> 
> Regards,
> Malcolm
> 
>