From: Bert Hickman
Date: Thu, 11 Mar 2004 11:37:49 -0600
Subject: Re: [TSSP] THOR: First observations on streamer formation (try II)
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. Let me know if you have any difficulty obtaining any of them. 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 -- -- -------------------------------------------------------------------- We specialize in UNIQUE items! Coins shrunk by Ultrastrong Fields, Lichtenberg Figures (electrical discharges in acrylic), & Scarce OOP Technical Books. Stoneridge Engineering -- http://www.teslamania.com -------------------------------------------------------------------- Marco.Denicolai@tellabs.com wrote: > 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 > > > ----------------------------------------- > ============================================================ > The information contained in this message may be privileged > and confidential and protected from disclosure. If the > reader of this message is not the intended recipient, or an > employee or agent responsible for delivering this message to > the intended recipient, you are hereby notified that any > reproduction, dissemination or distribution of this > communication is strictly prohibited. If you have received > this communication in error, please notify us immediately by > replying to the message and deleting it from your computer. > > Thank you. > Tellabs > ============================================================ > > . >
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