Re: THOR: First observations on streamer formation (try II)

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: Bert Hickman <bert.hickman-at-aquila-dot-net> 

Hi Marco,

Excellent - another tool is available for probing the mysteries of streamers!

Although it's not very surprising that you would see streamer growth during 
a single bang, especially if the initial corona breakout voltage is 
significantly below Vmax of your system, it is interesting that you saw 
forked and multiple streamers on a single bang. These are likely the 
effects of injected space charge from previous streamer(s) influencing the 
preferred direction taken during propagation of a new streamer.

Because there's significant charge transferred during each "step" of 
streamer growth, it should be possible to indirectly measure this via 
resonator base current. Following are a dozen good references covering 
various aspects of corona and streamer formation, modeling, and 
theory/measurement. Paper #7 below discusses an alternative approach of 
measuring streamer current using a low voltage electrode that may have 
potential applicability, and paper #10 covers charge expenditure versus 
streamer length. Several discuss streamer development/growth under 
oscillatory voltages (typically switching impulses in power transmission).

1. Corona Inception Under Steady and D=dV/dt (since corona is a precursor 
to streamer formation):
Abdel-Salam, M.; Allen, N.L., "Inception of corona and rate of rise of 
voltage in diverging electric fields",  Science, Measurement and 
Technology, IEE Proceedings A , Volume: 137 Issue: 4 , July 1990

2. A good discussion of initial corona formation and reverse discharges 
from local space charge region for oscillatory (33 kHz) discharges:
Harid, N.; Waters, R.T., "Statistical study of impulse corona inception 
parameters on line conductors", Science, Measurement and Technology, IEE 
Proceedings A , Volume: 138 Issue: 3 , May 1991

3. A good discussion of the effects of space charge and corona for 
conductors energized by AC. Not clear how much applies when the frequency 
is increased:
Rickard, D.A.; Dupuy, J.; Waters, R.T., "Verification of an alternating 
current corona model for use as a current transmission line design aid", 
Science, Measurement and Technology, IEE Proceedings A , Volume: 138 Issue: 
5 , Sept. 1991

4. Modeling of long sparks using equivalent RLC networks:
Fofana, I.; Beroual, A., "A model for long air gap discharge using an 
equivalent electrical network", Dielectrics and Electrical Insulation, IEEE 
Transactions on [see also Electrical Insulation, IEEE Transactions on], 
Volume: 3 Issue: 2 , April 1996

5. Good discussions of streamer growth and why streamers branch or have 
multiple segments:
A. Watson, D.B.; Ma, L., "Investigation of impulse spark trajectory in air 
between hemispherically-ended rod and plane electrode", Science, 
Measurement and Technology, IEE Proceedings- , Volume: 143 Issue: 2 , March 
1996

B. Watson, D.B.; Ma, L., "The impulse breakdown trajectory in air between 
rod and plane electrodes", Dielectrics and Electrical Insulation, IEEE 
Transactions on [see also Electrical Insulation, IEEE Transactions on] , 
Volume: 4 Issue: 1 , Feb. 1997

6. Good discussion of corona and the influence of space charge under double 
exponential and oscillatory impulses (at 33 and 125 kHz):
Rickard, D.A.; Harid, N.; Waters, R.T., "Modelling of corona at a 
high-voltage conductor under double exponential and oscillatory impulses", 
Science, Measurement and Technology, IEE Proceedings- , Volume: 143 Issue: 
5 , Sept. 1996

7. Measuring streamer currents in a novel fashion:
Lan Gao; Cooray, V.; Thottappillil, R.; Scuka, V., "Study of 
cathode-directed positive streamers in air by streamer current and 
luminosity measurements", Electrical Insulation and Dielectric Phenomena, 
1997. IEEE 1997 Annual Report., Conference on , Volume: 2 , 1997

8. Model for entire discharge for long air gap RF discharges under impulse 
and oscillatory excitation - extends modeling work from paper #4 above:
I Fofana and A Béroual, "A predictive model of the positive discharge in 
long air gaps under pure and oscillating impulse shapes", J. Phys. D: Appl. 
Phys. 30 No 11 (7 June 1997) 1653-1667

9. Discussion of the mechanisms involved in reigniting the arc channel in 
long air gaps (useful for understanding bang-to-bang leader/streamer growth):
N L Aleksandrov and E M Bazelyan, "The mechanism of re-breakdown within a 
post-arc channel in long non-uniform air gaps", J. Phys. D: Appl. Phys. 31 
No 11 (7 June 1998) 1343-1351

10. Useful discussion on Charge Consumption for long sparks (up to 20 
meters) - potentially important for understanding the magnitude of charge 
transfer between topload and streamers versus streamer length:
T Reess, J Paillol, A Gibert and P Domens, "A study of the mean charge 
consumption of long sparks in air as a function of the gap length and the 
impulse shape", J. Phys. D: Appl. Phys. 31 No 14 (21 July 1998) 1712-1722

11. Interesting paper showing modeling and behavior of moderate and long 
gaps under impulse and oscillatory excitation:
P Ortega, P Domens and A Gibert, "Predictive modelling of positive leader 
propagation under standard and oscillatory impulse shapes",
J. Phys. D: Appl. Phys. 27 No 6 (14 June 1994) 1233-1241

12. A good paper that discusses space charge and streamer branching, and 
why positive streamers and Lichtenberg Figures show branching angle of 
about 39 degrees. Also includes ANSYS modeling:
Mose Akyuz, Anders Larsson, Vernon Cooray, Gustav Stransberg, "3D 
Simulations of Streamer Branching in Air", 
http://www.hvi.uu.se/IFH/students/mose/mose_artiklar/Sreamer%20Branching.pdf

Please keep us posted of your findings!

-- Bert --
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Tesla list wrote:

>Original poster: Marco.Denicolai-at-tellabs-dot-com
>The first email was incomplete, sorry. Let's try again :)
>Hello all,
>I spent the last months designing, building and debugging a new
>controller board to allow my bigger TC (named THOR, see
>www.iki.fi/dncmrc) to perform a perdetermined number of bangs. Thor is a
>disruptive TC: a SMPS charges the primary capacitor, synchronizing the
>charge with the RSG electrode position and reaching a predefined
>voltage. The new board allows to do this a predefined number of times,
>as it can count the number of electrode presentations.
>80% of the effort had to be put into a mixture of shielding, grounding,
>filtering and optoisolation. Without this the board was prone to
>misfunctioning due to the powerful transient generated by the bangs. I
>was able yesterday for the first time to get rid of the noise and see
>the new board work as it was supposed to.
>The meaning of the setup was to investigate how bang size, bang
>repetition rate and number of bangs influenced the growth of the
>streamers. This is a question often asked in the list posts and the
>answers are usually different, based on observation, speculation or
>"measurements". For instance, I recall someone answering that he gets
>full length streamers even with a single bang (!). Then there are the
>explanations about ionized channel formation and its lifetime, etc.
>Yesterday, as I wrote above, I was able to play with the setup for the
>first time. I haven't got yet measurements and data but I still wanted
>to share with you what I have seen.
>I changed the number of consecutive bangs. With a single bang I got
>about 15 cm long streamers. Increasing the number of bangs I got
>increased length. At about 13-14 bangs I reached the full streamer
>length, that is a grounded stick at about 3 meters from the toroid.
>Nothing new here: this is what I expected to see. The surprising thing
>was the behaviour with a SINGLE bang. I could see the formation of:
>- a single streamer OR
>- a biforked streamer OR
>- at least two streamers from two different toroid locations
>  >>This means that a single bang is capable of producing a number of
>streamers, not just one<<
>Next I'll have to decide what to measure and how. First ideas:
>- current throught the grounded stick (with a Rogoski coil) when there
>is no hit. Could it register the smaller streamers?
>- current at the secondary bottom
>- readings with Terry's old Voltage-current antenna
>- run of statistical measurements bang_amount vs. streamer_length vs.
>bang_voltage
>Here your input and help is more than welcome. Also if you know/find
>interesting references on high frequency streamer formation, dielectric
>strength, etc. please, let me know.
>Regards
>
>.