Re: NST outer layers, was Re: chokes

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

Original poster: "Jon Tebbs by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jgtebbs-at-eos-dot-net>

Hi Ed, Malcolm,

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

> Hi Ed, Terry,
>                Whether the transformer is producing the voltage or 
> there is a transient fed in at the secondary terminals, the top layer 
> of the winding is surely the most likely place where an internal arc 
> would start. ?
> 
> Regards,
> malcolm


Tesla list wrote:
> 
> Original poster: "Ed Phillips by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<evp-at-pacbell-dot-net>
> 
> Tesla list wrote:
> >
> > Original poster: "Jon Tebbs by way of Terry Fritz <twftesla-at-qwest-dot-net>"
> <jgtebbs-at-eos-dot-net>
> >
> > Hi Ed, List,
> >
> > I can provide first hand confirmation from two depotted NSTs that died
> > from excessive static gap width in the early 1990's. The voltage
> > distribution certainly seems to be concentrated in the outer layers. In
> > both of these cases the burned spot on the secondaries was about one
> > third in from the outside layer, on the side and had arced to the core.
> >
> > Anyone else have a similar observation?
> > --
> > Jon G. Tebbs
> > <jgtebbs-at-eos-dot-net>
> >
snip
> 
>         Very interesting.  Did you by any chance take a picture?  Did the
> carbon track go along all of the inner layers to make its way to the
> core?
> 
> Ed

No, I did not photograph these secondaries at the time. I can describe
what I found. The inter layer insulation had a burned spot about 1/4" in
diameter located on the side of the winding. This was about 1/3 of the
distance in from the outer layer towards the core. I do not recall
seeing any additional damage to the inter layer insulation below that
point inline to the core. The carbon track apparently was through the tar.

Both NSTs, one 12/30 and one 9/30 showed the same. Both had an open in
the winding at that point. Both were stripped of the outer layers,
reassembled, repotted and returned to service complete with lopsided
voltages. That was about ten years ago and I have not used them since. A
more thorough failure analysis certainly would be interesting.
-- 
Jon G. Tebbs
<jgtebbs-at-eos-dot-net>