re: NST modeling paper correction

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

Original poster: "Peter Lawrence by way of Terry Fritz <twftesla-at-uswest-dot-net>" <Peter.Lawrence-at-Sun-dot-com>

Tero,
     my understanding (quite possibly mistaken) is that a "current
limited" transformer (Neon Sign Transformer being an example) does not 
have a constant mutual inductance between primary and secondary as that must 
vary as magnetic flux does or does not go through the shunts (shunts are 
what differentiates a current limited transformer from the more common type).
Since K is a function of mutual inductance, it too cannot be a constant.

A typical current vs voltage graph of a current limited transformer shows
almost a straight line from rated-volts-at-zero-amps to 
zero-volts-at-rated-amps. Am I wrong in assuming that this can only be
the case if the "K" and/or mutual inductance of the transformer is different
at these end points and all the points in between.

As near as I can tell, neither Tero's , nor Terry Fritz' microsim, model
try to account for the variable mutual inductance of an NST. If I'm wrong
here please point it out, I've tried reading Tero's web page, but cannot
see anywhere where there might be a variable mutual inductance.

I am curious because I'm trying to wind my own current-limited transformer
on a core with shunts that I bought at a second-hand electronics parts
store, and I'm still working out the math for how many primary and secondary
turns I need and what sizes of wire to use.

So far I have checked my 6-20, and 7.5-30 NSTs, and neither one comes even
close to the calculations in the power-transformer web page:
        http://members.tripod-dot-com/~schematics/xform/xformer1.htm
I'm planning on extrapolating from my NSTs rather than using the info in
the power-transformer web page. My TCs are all static-gap, so a current
limited transformer is the only way to go (I've already tried using MOTs,
and in my experience they put out way too much current for a static gap).


-Peter Lawrence, San Jose CA.




> Dear List,
> 
> I have written a white paper about NST modeling and in particular how to
> find the linear transformer model parameters. The formulas I derived are
> pretty interesting and worth checking out.
> 
> In short, the L1, L2 and k values of the transformer can easily and
> accurately be calculated using only a ordinary multimeter (no
> oscilloscope needed).
> 
> The paper is here: http://tesla.tr-labs-dot-com/nstmodel/
> 
> I will be adding more material to the site in the future.
> 
> Comments are welcome.
> 
> 
> Regards,
> 
> Tero Ranta