Re: NST secondary ?

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

Original poster: "Nebojsa Kovacevic by way of Terry Fritz <twftesla-at-qwest-dot-net>" <morfeus-at-EUnet.yu>

Hello Steve/All!

Yes, the NST`s are central tapped....but. A while back I was having some
difficulties with two NST`s
(15kV/30mA). I had to rewind both of them after they burned out. I have
also found that they are
central tapped, and because of that I couldn`t insulate them no longer,
after I have rewind them. I was
always having arcs between the last turns of the secondary and the body of
the transformer. Finally, I
decided to disconnect the secondary from the case, and got more voltage and
no arcs between the
secondary and the body of the transformer. Now I don`t use absolutly no
insulation(oil, plastic,
tar...), and wasn`t having any problems what so ever with my transformer.
The other one is done exactly
the same way, with the same results. It only looks funny to actually see
the secondary windings
inside...

Regards,
Nele

Tesla list wrote:

> Original poster: "Loudner, Godfrey by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <gloudner-at-SINTE.EDU>
>
> Hi Steve
>
> The essential feature is that the secondary system is center tapped to the
> iron core of the transformer. This is done to reduce the insulation
> requirements at the bottom of the secondary windings. Then the iron core is
> connected to the case. By grounding the case, the voltage stress is reduced
> from the top to the bottom of the secondary windings. Even if the case is
> not grounded, the core spreads the voltage stress over a large area, thereby
> helping to reduce the voltage stress to the top of the secondary windings.
> Because the bottom of the secondary coils are connected to the core by leads
> going right through the bobbins, it would be too difficult to lift the
> center tap from the core. The ground from the core to the case could be
> lifted, but there would be no advantage. You want to be able to ground the
> core. The transformer can be depotted from the case, but you still want to
> ground the core. Running a depotted NST under oil is a good procedure. There
> is the advantage of increased insulation and heat sinking. When a NST is put
> into tesla service, it can output much more power than its normal rating.
> The extra heat sinking will be appreciated.
>
> Godfrey Loudner
>
> > -----Original Message-----
> > From: Tesla list [SMTP:tesla-at-pupman-dot-com]
> > Sent: Saturday, February 09, 2002 10:40 AM
> > To:   tesla-at-pupman-dot-com
> > Subject:      NST secondary ?
> >
> > Original poster: "Steve Mach by way of Terry Fritz <twftesla-at-qwest-dot-net>"
> > <gossamer-at-cox-dot-net>
> >
> > Hello All,I discovered at work today (slow day) some really clean NST's
> > Also discovered that sec's are center tapped !
> > I never knew this.
> > Has anyone un-potted and lifted the ct from the case?
> > Will winding insulation hold up if run under oil?
> >
> > JOULES RULES       SM
> >
> >
> >