RE: Wiring two 15KV 240V/50Hz Transformers in Series for use with 110V (fwd)

["Tesla list" <tesla@xxxxxxxxxx>]

---------- Forwarded message ----------
Date: Fri, 15 Jun 2007 23:01:40 -0400
From: "Lau, Gary" <Gary.Lau@xxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Subject: RE: Wiring two 15KV 240V/50Hz Transformers in Series for use with 110V
    (fwd)

There's a good reason NST's are built with secondary mid-point grounded.
Assuming a 15kV secondary voltage - If it was built with no mid-point
ground, both ends of the secondary coil would need to be insulated from
the core to withstand at least 15kV (should the other end be grounded).
But if they ground the midpoint, the secondary may be wound as two 7.5kV
coils, with the inner-most winding directly connected to the core,
significantly reducing the insulation requirement.  Much cheaper to do
it this way, and safer too, as the terminal-to-ground voltage is 7.5kV
max.

Yes I'd go the new-NST route.  It would be a huge bother to have to find
a 240V appliance outlet in the house, and also a bother to lug around a
120/240 step-up xfmr.

Regards, Gary Lau
MA, USA


> Date: Sat, 16 Jun 2007 08:48:23 +0800
> From: westland <westland@xxxxxx>
> To: Tesla list <tesla@xxxxxxxxxx>
> Subject: Re: Wiring two 15KV 240V/50Hz Transformers in Series for use
with 110V
>     (fwd)
> 
> Gary:
> 
> Thanks so much for the insight.  I would never have known this.  Is
> there a particular reason for having a tap in the middle of the
secondary?
> 
> I suppose I could grab 230v off of the mains, but my setup is less
than
> 1KVA, so I probably will just buy a step up transformer here (they are
> much cheaper here) and put it in with the transformers.  Or maybe just
> buy some new transformers when I'm in the US
> 
> Thanks again
> 
> Chris
> 
> Tesla list wrote:
> > ---------- Forwarded message ----------
> > Date: Fri, 15 Jun 2007 09:42:34 -0400
> > From: "Lau, Gary" <Gary.Lau@xxxxxx>
> > To: Tesla list <tesla@xxxxxxxxxx>
> > Subject: RE: Wiring two 15KV 240V/50Hz Transformers in Series for
use with
> 110V
> >     (fwd)
> >
> > Hi Chris:
> >
> > Sorry, but you can't do what you propose.  15kV NST's are made with
the
> > secondary midpoint connected to the case.  If you connect the
> > secondaries in series, the two cases will have 15kV between them.
The
> > primary-to-case insulation is not designed to sustain that and will
> > fail.
> >
> > Most US households have 240V available in the breaker box to power
> > electric stoves, dryers, and other large appliances.  You'll have to
use
> > the NST's at their rated input voltage.  If you're in an apartment
that
> > doesn't have 240V available, your only alternative is to get a
120/240
> > step-up xfmr.
> >
> > Regards, Gary Lau
> > MA, USA
> >
> >
> >
> >> Date: Fri, 15 Jun 2007 14:10:05 +0800
> >> From: westland <westland@xxxxxx>
> >> To: Tesla list <tesla@xxxxxxxxxx>
> >> Subject: Wiring two 15KV 240V/50Hz Transformers in Series for use
with
> >>
> > 110V
> >
> >> I have an interesting variant on one of the questions that just
came
> >>
> > up
> >
> >> about series wiring of transformers.  I'll be moving to Chicago in
two
> >> months, and from 220V to 110V mains.  I currently have two 15KV
> >> 240V/50Hz/0.03A Transformers wired in parallel (for .060A) that
power
> >>
> > my
> >
> >> TC.  I'm wondering if there is any problem switching leads around
for
> >> 110V/60Hz ... running the secondary in series, and the primaries in
> >> parallel.  I figure since its a 50Hz transformer, it's already
about
> >>
> > 20%
> >
> >> overengineered, and the secondaries takes 15KV at .03A, so I should
> >>
> > end
> >
> >> up with output of 15KV at .03A (rather than the 0.03A I get in Hong
> >>
> > Kong).
> >
> >> I'm looking for a sanity check on my logic, just to make sure that
I
> >> don't bring them to the States only to burn them up.  Clearly, I
can
> >> keep the current arrangement, and just precede them with a 110 to
220V
> >> stepup transformer.
> >>
> >> Chris Westland
> >>
> >> --
> >>
> >> ___________________________________________________
> >>
> >> J. Christopher Westland, PhD CPA
> >> Professor, ISMT, University of Science & Technology, HK Clearwater
> >>
> > Bay,Kowloon,
> >
> >> Hong Kong
> >> Tel: 852 2358 7643
> >> Fax: 852 2358 2421
> >> Mob: 852 9528 1745
> >> URL: ihome.ust.hk/~westland
> >> Mobile e-mail: chris.westland@xxxxxxxxxxxx
> >>
> >>
> >>
> >
> >
> >
> >
> 
> 
> --
> ____________________________________________________
> 
> J. Christopher Westland, PhD CPA
> Professor, ISMT, University of Science & Technology, HK Clearwater
Bay,Kowloon,
> Hong Kong
> Tel: 852 2358 7643
> Fax: 852 2358 2421
> Mob: 852 9528 1745
> URL: ihome.ust.hk/~westland
> Mobile e-mail: chris.westland@xxxxxxxxxxxx
> 
> 
>