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Steve Conner DRSSTC Model question

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LAN_403

HV Enthusiast

Thu Jun 01 2006, 02:10PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

Hey Steve,

I was playing around with your PSPICE models last night to try verifying your spark loading model, and was wondering what is StrLn units? From backwards calculation, it appears to be meters, but just wanted to double check.

Thanks
Dan

Steve Conner

Thu Jun 01 2006, 03:03PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Yup, it's meters. I never did figure out which model was more suited, mine or Terry's 220k+1pF/ft, so if you have anything to add, I'd be glad to hear it

HV Enthusiast

Thu Jun 01 2006, 06:00PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

Attached are some simulations and simulated data i took regarding this DRSSTC III system i am currently testing. Per the model, the arc lengths seem to be out of whack quite a bit, so voltage is too high on V6 i think. Perhaps, in practice, the geometry of the toroid will limit the maximum voltage rise.

Any suggestions???

Attached Data (PDF)

1. Frequency Response PSPICE Circuit
2. Steve Conner PSPICE Circuit
3. Primary Natural Frequency Plots (Cpri = 0.0825uF)
4. Primary Natural Frequency Plots (Cpri = 0.11uF)
5. Secondary Natural Frequency Plots
6. Primary Current Tuning Plots (Cpri = 0.0825uF)
7. FFT of Primary Current Tuning Plots (Cpri = 0.0825uF)
8. Primary Current Tuning Plots (Cpri = 0.11uF)
9. FFT of Primary Current Tuning Plots (Cpri = 0.11uF)
10. Spark Length Prediction (0.0825uF, 9uH)
11. Spark Length Prediction (0.0825uF, 12uH)
12. Spark Length Prediction (0.11uF, 9uH)
13. Spark Length Prediction (0.11uF, 12uH)
14. Spark Length Prediction Pri Capacitor size vs. Pri Tuning (EXCEL)
] 1149184855_15_FT10609_simulated_data_package4.pdf[ /file]

Terry Fritz

Fri Jun 02 2006, 05:16AM

Registered Member #393 Joined: Tue Apr 18 2006, 12:30AM
Location:
Posts: 297

Hi,

Way COOL!! about Dan's new coils!!!! How does he get those "blowing up" pictures "timed" just right?? I use video cameras to catch such events (it works good!!), but Dan seems to have the "nice" camera ready to go at just the right split second!! Sound triggered shutter????

I have been working on streamer (leaders really) load models a lot the last two days (OK, "ALL" I have been doing

). For ScanTesla's new dynamic streamer load modeling. Many of the details are here:

But the streamer load is:

""""""""""""""
LengthTemp = 2.8 * sqrt(0.5 * VCsec_max * VCsec_max * (C2 + C3) * BPS); //Secondary energy length factor.

BreakoutLength = 2.8 * sqrt(0.5 * BreakoutVoltage * BreakoutVoltage * C2 * BPS); //Secondary breakout length.

if (LengthTemp < BreakoutLength) {C3 = 0.06666667 * LengthTemp * 1.0e-12;} //Streamer capacitive load.
else {C3 = (0.15 * LengthTemp - 0.08333333 * BreakoutLength ) * 1.0e-12;}
""""""""""""""

Now that is a mess... But basically, small streamers near the terminal have very little added capacitance. The secondary terminal voltage, and its trying to breakout, - dominate the "load". Once the secondary voltage breaks out, the capacitance is a nice linear line as a function of streamer length dictated by Freau's formula with a modified constant. The coil's terminal geometry dictates where the inflection or transition point is as "breakout voltage". It finally DOES predict bigger top loads are better

)))

BreakoutLength is due to the fact that you really can't break a 1 inch streamer from a 30 inch sphere

) If you breakout, you have a "minimum" length...

The program's number are pretty close now, but could use some adjusting or at least verification... E-Tesla 6.20 http://hot-streamer.com/TeslaCoils/Programs/E-Tesla620.zip
can do that in like weeks of modeling on a 3GHz computer!! I will get that going now

But it is really "odd" now... There are so many "rules and constraints" that the models seem pretty "obvious"... There are just not a lot of "options" in streamer modeling now...

Streamer ground strikes are super odd!!! It takes "massive" currents to drain the system to match measured scope readings!! ScanTesla cannot handle the currents unless ulta small time steps are used... I am faking it by draing the system directly at the matrix level... The streamer model "fails" for ground strikes... There is "another" capacitance... But its displacment current might explain racing arcs

The future will tell all....

I think Dan, posted enough info on his new coil now... I will see if I can figure anything out...

My SISG coil with its very low primary loss gets rid of most of the "noise"!!! I can "see" things now

)) Wonderful things

Cheers,

Terry

Steve Conner

Fri Jun 02 2006, 09:19AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

OMG, Terry is hacking the system at the matrix level. Any minute now he's going to jump out of my TV and offer me red and blue pills. :P

Dan, I guess the problem is that my model doesn't limit the secondary voltage. It has no conception of breakout from the toroid or flashovers down the secondary. So you can generate impossibly long arcs from a small coil (of course my model has no idea what physical size the coil is, so that's not surprising)

I did experiment with zener diodes of 100kV or 500kV or whatever hooked between the "topload" and "ground" to model this, but they made the simulations take far longer or fail to converge at all, so I gave up. Basically, you just have to ignore any configuration that would give output voltage considerably higher tha the breakdown voltage of the bare toroid.

HV Enthusiast

Fri Jun 02 2006, 11:34AM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

Thanks guys. I might try incorporating your (Terry) new streamer model in PSPICE to see what comes up.

Thanks again, and we'll keep you posted on any new developments!!

Terry Fritz

Fri Jun 02 2006, 11:09PM

Registered Member #393 Joined: Tue Apr 18 2006, 12:30AM
Location:
Posts: 297

Hi,

Steve said,

I did experiment with zener diodes of 100kV or 500kV or whatever hooked between the "topload" and "ground" to model this, but they made the simulations take far longer or fail to converge at all, so I gave up.

I have some streamer hit pics for the SISG here:

Only "6 inch hits at 108kV". But the terminal (31.1pF) is discharged in 20nS!! That works out to a streamer resistance of 129 ohms and a streamer peak current of "752 amps!!!" And that is just a 6 inch arc!

It is sort of interesting that the ring after the hit's frequency is 1 / (2 x pi x SQRT(Cs x Lp). But that is probably just chance in this case rather than any great truth...

The SISG fires consitantly enough that the scope's dealy function is easily able to catch hits.

But the streamer hit times are just too short for MicroSim to deal with it well. There are model setups in the program "somewhere" that might be fiddled with to help.

Dan said,

Thanks guys. I might try incorporating your (Terry) new streamer model in PSPICE to see what comes up.

That sounds like it would make my brain hurt!

If you know the arc length, put in 1.5pF/foot + 220k and be done with it. The "dynamic" stuff really does not vary the models that much. It is good for ScanTesla "trying things" since it detects configurations that are not real good and hurt the streamer length. But for a MicroSim model, I don't think you would gain anything.

There is a minimum breakout voltage and a minimum streamer length after breakout. But the streamers in the MicroSim world are basically established and the arc channel is solid, so it does not change during a streamer. You should just be able to set it and forget it.

Cheers,

Terry

Steve Conner

Sat Jun 03 2006, 12:18PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Hi Terry, all,

In streamer modelling, I always assumed arcs to ground to be more or less short circuits that discharge the topload instantly. So that agrees with what you measured. I discovered that it is possible to get ground arcs that stay dim and purple, when the coil is striking out just about as far as it can reach, and these don't discharge the topload instantly.

I think what is happening is this: When a streamer strikes ground, the current flow through it will increase because it now has a conductive path to ground as well as a capacitive one. This will make the streamer get hotter and lower its resistance, which increases the current even more. This process usually "runs away" and ends up with the streamer "transitioning" in a matter of nanoseconds, to a bright white arc that looks like a short circuit. However, it doesn't always run away. If the streamer is just about as long as the coil can produce (so its resistance is pretty high) and especially if it's a high frequency coil (so the capacitive currents are bigger compared to the conductive ones) it just might not happen.

As to the ringing after the strike that Terry saw: The quick discharge of the topload is a step function that could kick the system back into oscillation at any of its resonant modes.

HV Enthusiast

Sat Jun 03 2006, 12:49PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

Terry, All,

Did you actually measure the peak current (i.e. 752A) in the output arc ground strikes or was this simulated value? In practice, i have never measured anything above 10A peak current (for my medium size DRSSTCs) with high current ground arcs.

Terry Fritz

Sat Jun 03 2006, 05:25PM

Registered Member #393 Joined: Tue Apr 18 2006, 12:30AM
Location:
Posts: 297

Hi,

Did you actually measure the peak current (i.e. 752A) in the output arc ground strikes or was this simulated value? In practice, i have never measured anything above 10A peak current (for my medium size DRSSTCs) with high current ground arcs.

It might be the frequency reponse or rise time of the current monitor. I will look into that... Maybe the oscillation is messing with the monitor. The top terminal voltage was measured with planewave antenna good to 100MHz. Maybe a much better 100's of MHz CT is needed or a sheilded air core current transformer. My Pearson #101 100:1 CT is rated at 100nS rise time and 4MHz... The #110 is 20nS and 20MHz. Probably needs a 50ohm cable termination too at those speeds.

I used 108kV, 31.1pF, and 20nS for the RC time constant.

5RC = 20nS So R = 128.6 ohms.

If the terminal voltage is 108kV then the peak current is 108000 / 128.6 = 840 amps. (I had 97kV in my head yeasterday, but it is 108kV).

I discovered that it is possible to get ground arcs that stay dim and purple, when the coil is striking out just about as far as it can reach, and these don't discharge the topload instantly.

You can see the first low current light contacts in the scope pics in:

These are the leaders "tickling around" at the ground terminal. If you play it just right, those will be the only light arcing and you can avoid the "big one". Your other comments about this sound fine to me.

As to the ringing after the strike that Terry saw: The quick discharge of the topload is a step function that could kick the system back into oscillation at any of its resonant modes.

It could also be ground noise on the scope leads and such. Pumping 840 amps into the ground in 20nS might causee measurement errors

Not sure... - Apparently not... Further testing seems to confirm tha the scope reading are good and pure.

Cheers,

Terry

Hi Again,

To follow up. Dan said:

Did you actually measure the peak current (i.e. 752A) in the output arc ground strikes or was this simulated value? In practice, i have never measured anything above 10A peak current (for my medium size DRSSTCs) with high current ground arcs.

I tested my Pearson #110 (10:1 20nS rise time 20MHz) and #101 (100:1 100nS rise time 4MHz) side by side on the wire from the grounded strike point to see how they compare. The coax cables from them were both terminated into 50 ohms at the scope inputs. Everything is as before.

The Yellow trace is the 4MHz #101 and the Blue trace is the 20MHz #110.

So the 4MHz current monitor is pretty usless and the 20MHz one is probably loosing a bunch of the spike...

So if one want's to measure streamer strike currents really accurately, you probably need 100MHz if not 1GHz

0f current probe bandwidth. And it needs to probably do 1000 amps for just "little" arcs. I don't know what kind of current monitor Dan was using, but maybe this is what caused to apparently very low readings?

Cheers,

Terry

Hi Yet Again,

I looked into using a Rogowski coil. But if v(t) = -m/RC i(t), the numbers just work out into impossible elements at say 20nS rise time and 1000 amps... They just don't do 50,000 A/uS stuff

So going to try a mutual inductance loop... Very insensitive, but it might pick this monster signal up with some accuracy

Cheers,

Terry

Hi Again Again

The inductance loop works!! I just made about a 5 inch loop of wire terminated to a 50 ohm low inductance resistor. The 50 ohm coax was terminated to 50 ohms at the scope too.

The loop (purple) is about 6 inches away from the ground wire for the strike target (yellow). It just inductively couples to whatever high current high speed signals happen to be around.

I found one!

It is still real "ringy". I may have run out of bandwidth on the scope now too. The loop could be much smaller since the signal almost pegs the scope!! The resistor could have been a much smaller 1 Watt surface mount too but I don't have one handy. The current is not to any scale. But the signal is somwwhat cleaner although far from "really" clean...

Basically, the discharge is very fast. 20nS or less. And the current is "high" probably like 1000 amps.

So I would say that Dan's reading of 10 amps is "low"

It would take a small very well terminated for 1GHz loop and a 1GHz scope to really see it well I think. It is possible to "calibrate" such a thing too...

If one "touches" such a spark, it is odd to think about what say 100MW in 20nS might be doing to the atoms in ones body

And this is just a "tiny" 6 inch spark...

Cheers,

Terry

Me again,

Here is a real interesting post on streamer arc to ground currents and times:

Here is a note on the "new" ScanTesla7.61 and how it does streamer loading:

Cheers,

Terry

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