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Re: Measuring Streamer characteristics



Original poster: Terry Fritz <teslalist-at-twfpowerelectronics-dot-com>

I think what we really need is "new independent" data...  The 220k + 1 
pF/foot thing is "six years" old now!!!  It is just a first stab at a very 
averaged out streamer impedance that was nice to help computer models 
work...  In those days, computer modeling of Tesla coil operation was 
considered as a joke :o))))  Now, we can't live without 
it!!  Hehehe!!  That one we did win ;-))

But there are others now that have some very nice equipment to work with 
that can make "brand new" data!!!

Cheers,

         Terry


At 10:12 AM 10/4/2004, you wrote:
>Steve Connor wrote:
> > So I don't see how a model that says
> > "X ohms per foot" can be correct.
>
>I agree - we'd expect the effective load resistance to
>fall as the streamers grow.
>
>Here's a different standard to use for load impedance.
>
>This is based on the idea that a properly working
>coil (whatever its dimensions) should be loaded down to
>some low value of Q factor by the streamer load.
>
>If we specify a desired loaded Q factor, we can give
>the load resistance in terms of the characteristic
>impedance of the resonator, ie
>
>   Rl = load resistance = Ql * Zo
>
>where Ql is the loaded Q, and Zo = sqrt( L/C), with L and
>C being the equivalent reactances for the resonator.
>
>If Ql falls down to as low as around 6 as a result of
>streamer growth, the loading is such that the remaining
>stored energy of the resonator is dumped into the load
>in only around one more cycle.  Therefore we might conclude
>that 6 is about the lowest it will ever go.
>
>Thus it would make sense to test TC models with a load
>resistance of 6 * Zo to exercise the case of maximum
>streamer loading.  (Whether that degree of loading is
>actually achieved in the real coil depends of course on
>lots of factors such as toroid size, bang energy, BPS, ...)
>
>So much for the resistance, what about a parallel
>capacitance to represent the charge stored in the streamers?
>
>Perhaps the simplest way to estimate a load capacitance
>is to assume that the streamers reduce the resonant
>frequency by some percentage.   A nominal value for
>heavy loading might be, say, 10% reduction of frequency
>which would be achieved by around 25% increase in the
>total effective capacitance.
>
>As a worked example, my CW coil has L = 84mH and C = 55pF
>so Zo = sqrt(84e-3/55e-12) = 40k ohms.  A heavy streamer
>loading would therefore load the thing to around 6 * 40k,
>or 240k ohms.   The parallel load capacitance would be
>around 0.25 * 55pF = 14pF.
>
>Using this rule of thumb is sure to give you a reasonably
>realistic load model appropriate to the size of the system.
>
>If we apply this recipe to one of Terry's coils [tfltr45],
>we have L=70mH, C=40pF, so Zo=42k. Then the load model is
>252k || 10pF.
>
>A figure of 1pF per foot of streamer is a reasonable order
>of magnitude for an estimate of charge storage.  Terry might
>expect a couple of 5 foot streamers.

The 220K seems pretty stable, but the 1 or 2 or 3... pF per foot has always 
been pretty unstable...

Cheers,

         Terry


>--
>Paul Nicholson
>--