Re: Bad Pig?

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "J. Aaron Holmes" <jaholmes@xxxxxxxxxxxxxxxxxx>

Curt, where are you located?

Definitely pop the top and tell us what you see.  Most
newer pigs seem to be wound in two identical
'sections' on the outside legs of a single large 'C'
core (one big donut of laminations).  If that is the
case with yours, then removal of the defective half of
the transformer may simply be a matter of a few hours
of persistent hacksawing, leaving you with a
120V-to-~9000V pig.  I dissected an RTE 15kVA unit of
this kind once.  Each section of windings contained
one half of each LV winding (half on the inside, half
on the outside) with one of the HV windings sandwiched
in between.  Cutting one of the HV windings off would,
in that case, pretty much force you to sacrifice one
of the LV windings also (hence 120V).  But you'd still
have a lot of transformer left, and might even be able
to overvolt it a bit.  If it's an older unit, it might
be two 'C' cores side-by-side with all the windings
around the middle.  Older Westinghouse and Kuhlman
units seem to be of this kind.  I never looked too
closely to see how they were wired.  In this case,
there may only be one big HV winding, which would make
isolation of the faulted section a bit more of a pain,
perhaps even impossible if it was on the inner turns.

I hacksawed all the windings off a dead 15kVA pig
once.  There was nothing particularly hard about it,
but it did take close to three hours.  I just had the
TV on and tried to keep a good rythm with my
subconscious :)  The HV windings and paper insulation
tended to go pretty quickly.  The LV windings are
think stuff and are a real pain.  In your case, it
might pay to unwind as much as you can before sawing
begins.  Others may have strategies to share, too.

If your transformer is of the single "C" core type,
then the two sections of the HV winding should be
conspicuously connected in series with a small wire
that you can tap to measure the DC resistance of each
half in turn.  This should permit you to quickly
establish which half (if not both) is the bad one.
These interconnections are generally on the bottom of
the transformer, however, so pulling the thing from
the can is probably a must.

aaron

--- Tesla list <tesla@xxxxxxxxxx> wrote:

>  > Original poster: "Gerry  Reynolds"
>  > <gerryreynolds@xxxxxxxxxxxxx>
>  >
>  > Hi Curt,
>  >
>  > At least this clears up conflicting info.  You
> might
>  > want to pop off
>  > the top and take a visual look.  Maybe (if you're
>  > lucky) the short is
>  > in the interconnect between the transformer and
> the
>  > bushings.  It
>  > might also be a good exercise to try to localize
> the
>  > short to one of
>  > the three coils (primary, HV1, HV2).  A DC
> current
>  > source like a
>  > current limited DC power supply can be used with
> a
>  > DVM to follow the
>  > current path.  Dump the oil into another
> container
>  > and pull the
>  > transformer from its case if you need to get
> better
>  > access.  Learn
>  > what you can before you pull it however.  If you
> can
>  > fix it, you may
>  > want to put new mineral oil back into the case to
>  > minimize contamination.
>  >
>  > Gerry R