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RE: Protection networks (was RE: LOW VOLUME)

Hi Finn:

A transmission line is just one thing that is an example of a distributed
parameter model, it is not the opposite of a lumped parameter model.

We usually model our secondary coil as a single inductor in parallel with a
single capacitor, and this is called a lumped parameter model.  While the
top load is truly a lumped capacitor, the C-self of the secondary coil is
really a distributed capacitance.  A more accurate model for it would be to
divide the secondary inductance into say 100 series connected and mutually
coupled inductors of 1/100th the total inductance.  Since each small
inductor couples to all of the others but at differing values of k, it would
be a major chore to work that all out.  At the junction of each two
inductors would be a capacitor to ground with a value of 1/100th (I think)
of C-self.  This would be an approximation to a distributed parameter model.
It turns out that (thanks to Terry's research) both lumped and distributed
parameter models work in terms of accurately modeling Tesla coil behavior.
Since lumped models are so much easier to use, this is what we do.

What I was getting at in the context of NSTs is, while each side of an NST
may have say 100 pF of capacitance to the grounded core (this is just a
guess), it is not the same as having a 100pF cap from the HV bushing to the
case.  An external bypass cap in an R-C network would shunt most of the RF
to ground before it ever got into the NST case.  If you had just a small
external inductor or resistor and only the distributed self-capacitance of
the NST secondary, each NST turn would only have a tiny fraction of a pF to
ground.  With such a tiny capacitance, the attenuation would be neglegable
and the outer NST turns would see the full RF voltage.

Regards, Gary Lau
Waltham, MA USA

		-----Original Message-----
		From:	Tesla List [mailto:tesla-at-pupman-dot-com]
		Sent:	Thursday, December 09, 1999 10:30 PM
		To:	tesla-at-pupman-dot-com
		Subject:	Re: Protection networks  (was RE: LOW
VOLUME)

		Original Poster: Finn Hammer <f-hammer-at-post5.tele.dk> 



		Tesla List wrote:
		> 
		> Original Poster: "Lau, Gary" <Gary.Lau-at-compaq-dot-com>
		Snipped..
		> 
		> The analysis of the L-only circuit was simplified,
ignoring the capacitance
		> from the NST secondary winding to ground.  This
capacitance does not count
		> towards making it an L-C network however, as it is a
distributed
		> capacitance, not a lump at the terminal, 
		                     ^^^^
		               Small clue here :-)

		I have always wondered, what is _exactly_ meant by the term
"lumped" as
		opposed to for example transmissionline, when a tesla coil
system model
		is being discussed.
		Transmission line vs. lumped parameter model seems to be the
phrases
		used.

		This is mumbo jumbo to me, part because I am a Dane, (not
that we are
		dimm, just less proficient in command of the english
language), part
		because I have no formal electronic background.

		What is a lumped parameter?

		Cheers, Finn Hammer