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Re: [TCML] SSTC Coupling

Hi Greg,
Warrington's and Blackburn's formulas are useful for estimating the steady-state resistance of low-frequency, point-to-point power line arcs. For these, the path is heavily ionized all along the path, current is the same throughout the entire length of a single arc channel, and space charges play virtually no role. These formulas may have limited usefulness for high-current toroid-to-ground arcs where peak currents may reach 10's or 100's of amps.
The branching leader structure of Tesla coil air discharges is quite different. Because these discharges are branched, you get current splitting amongst branches. The lower current branches also become progressively narrower, cooler, and more resistive as you move outward from root of the discharge. This process continues as you continue towards along progressively finer branches. Eventually the very character of the discharges change from arc-like to lower temperature streamer and corona-like discharges at the tips. Because the fractal-like structure of the TC discharges is considerably different than a single channel arc, a more accurate approach might be a distributed RC model with progressively higher resistance along subsequent branches.
It's also not clear that the measured terminal characteristics of a CW SSTC discharge can be directly ported to higher (peak) power discharges from a SGTC or DRSTTC. 

Bert
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Greg Morris wrote:

Have you guys ever heard of the Warrington formula? Rw = k/I^n * L, where n
and k are empirical constants, approximately 1.4 and 28688.5 resp. (for use
with meters, not feet).

Anyhow, I revised my circuit, and this is the result:
http://picasaweb.google.com/GBMorris/Tesla#5397805754928737186 It seems
correct to my knowledge, but the results are a bit disappointing. If
Tilbury's circuits are all wrong, where did he get them from and why did he
use them?

Cheers,
Greg



2009/10/27 Steve Ward <steve.ward@xxxxxxxxx>


Dex, do you have a better 'Rspark'???

Terry Fritz tried to characterize the corona impedance on a CW - SSTC at
one
point, but i dont recall if he determined it to be different than the 220k
that he characterized for disruptive sparks.  Recently ive worked on
non-linear spark models that give much better results in my DRSSTC
simulations... i may open a discussion on this once i get a better feel for
what im doing and get more measurements on a real system for direct
comparison.  But really, there seems to be good evidence that would suggest
the impedance of a spark will change with the voltage, generally the
impedance will go down as the voltage applied to it goes up.

I think Greg is probably more interested in gaining insight to the behavior
of these systems, whether or not the figures are absolutely correct.  You
can still learn from simulation and variation of parameters even if your
parameters are "wrong".

Steve

On Tue, Oct 27, 2009 at 2:08 PM, Dex Dexter <dexterlabs@xxxxxxxxxxx>
wrote:


Why do you think  Rspark = 220 kOhm is a realistic figure for SSTC ?

Dex


--- gbmorris@xxxxxxxxx wrote:

From: Greg Morris <gbmorris@xxxxxxxxx>
To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
Subject: Re: [TCML] SSTC Coupling
Date: Mon, 26 Oct 2009 19:43:43 -0300

So in other words my C_TERM should be shorted, and C_TERM_TO_GND should
have
the value of the current C_TERM?

Thanks,
Greg

2009/10/26 Antonio Carlos M. de Queiroz <acmdq@xxxxxxxxxx>


Greg Morris wrote:


My circuit
model can be found here,
http://picasaweb.google.com/GBMorris/Tesla#5396152968071832514 , and

has

been largely borrowed from Figure 8-1 of Tilbury's book on Tesla Coil
Design.



The terminal capacitance should be in parallel with the secondary
capacitance, not in series, with the load connected to both.

Antonio Carlos M. de Queiroz


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--
Greg Weyrich Morris
VP External - Engineering Undergraduate Society
B.Sc. Electrical Engineering (Final Year)
University of New Brunswick
G.B.Morris@xxxxxx
www.unb.ca/robotics



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