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



---------- Forwarded message ----------
Date: Sat, 16 Jun 2007 15:29:39 -0700
From: Barton B. Anderson <bartb@xxxxxxxxxxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Subject: Re: Wiring two 15KV 240V/50Hz Transformers in Series for use with 110V
    (fwd)

Hi Marko,

What you suggest is true. "If" you depot both NST"s and removed the core 
connection where each secondary winding connects to the core (and then 
connect the windings), you could do as suggested. But, the NST's are not 
robustly designed. Your then pushing the limits of the insulation and 
the depotting process is a real task not be done by those with little 
patience or scared of smells (the faint of heart souls out there). I've 
mentioned the same in the past, but I don't know of anyone who has 
actually gone to this extreme. So, I'm not sure how the NST's would 
handle double the voltage rating at one of the windings. It would be 
interesting to find out some day (even if the NST died immediately <grin>).

If it handled the voltage ok, it would lend itself to grounding one of 
the hv terminals to RF ground (i.e., connected to the inside turn of the 
primary). This would yield a non-floating NST in reference to the 
secondary (as can be done with pole pig).

Take care,
Bart

Tesla list wrote:

>---------- Forwarded message ----------
>Date: Sat, 16 Jun 2007 11:22:29 -0400
>From: Marko Ruban <Marko@xxxxxxxx>
>To: Tesla list <tesla@xxxxxxxxxx>
>Subject: Re: Wiring two 15KV 240V/50Hz Transformers in Series for use with 110V
>    (fwd)
>
>What if you disconnect the middle tap in both NSTs, and then connect one
>output terminal of each to both cases, thus making a new "middle tap". 
>Just a thought.  I'm sure you'd need to select the right terminals, to
>keep the secondary windings in the same direction, otherwise they will
>cancel the potential.  Of course the old middle taps might arc to the
>casing if left uninsulated.
>
>
>Tesla list wrote:
>
>---------- Forwarded message ----------
>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
>
>
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>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
>    
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>110V
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>I have an interesting variant on one of the questions that just came
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>up
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>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
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>my
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>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
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>20%
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>overengineered, and the secondaries takes 15KV at .03A, so I should
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>end
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>up with output of 15KV at .03A (rather than the 0.03A I get in Hong
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>Kong).
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>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
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>Bay,Kowloon,
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>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
>
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