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Hi Steve,
Sounds very interesting. What is the title and author for the thesis?
If the TRIGGER energy was 1 kJ(!), the energy of the main pulse must
have been really huge. Many years ago I measured the effective
resistance of the trigatron spark gap I previously used to use in my
coin shrinker. At a peak current of 10 kA, gap resistance was about 20
milliohms. At 80 kA, gap resistance dropped down to about 2.5 milliohms.
There are several gap loss studies for Tesla Coils in the TCML archives.
A fairly good one can be found in the TCML Archives - see thread "Vortex
gap loss measurements" initiated by Gary Lau. In 2000, Gary took
detailed measurements of his vortex spark gap and I did a subsequent
analysis based on the data. He compared his vortex gap to a vacuum gap.
The calculated gap resistances for Gary's gaps were between 430-520
milliohms.
There are other interesting comments in this thread that you may also
find useful.
In 2007 Greg Leyh measured the spark gap resistance of a rotary gap in
his model 120L50K Tesla coil. At 4200 peak amps, he measured a total gap
resistance of 650 milliohms. Although not stated, I am guessing that the
rotary probably had 4 gaps in series, so each gap had about 163
milliohms. For comparison, a 4500 volt silicon switch measured only 5
milliohms at 4350 peak amps (since Vsat is much lower than the hundreds
of volts typically seen per spark gap. See
https://www.pupman.com/listarchives/2007/Dec/msg00196.html
An earlier discussion from 1999 shows results from wireless pioneers
Slaby and Zenneck over 100 years ago on HV spark gap-switched RLC
circuits. Gap resistance ranged between 0.01 to 7.0 ohms depending on
gap spacing and tank capacitance.
I was reading a thesis that studied spark gap losses recently. Although the test apparatus (electrode material, diameter, and gap spacing) does not match exactly what you would find in a typical tesla coil, I found the results very interesting. The closest to the tesla coil scenario was the following from the paper.
1. Electrode material: copper-tungsten
2. Electrode diameter: 2.5 cm
3. Gap spacing: 1.4 cm
4. Trigger voltage: ~30K volts
5. Trigger energy: ~1K joule
6. Air at 1 atmosphere
The test results at these conditions measured an energy loss of about 7%. If I extrapolate these results to my 4800 watt coil, I am losing about 336 watts in the rotary spark gap. This is less than I imagined since I have always been lead to believe that the spark gap was very lossy.
Does anyone else have any other data which shows the loss caused by a spark gap?
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