Re: negative streamer propagation?

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

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

Tesla list wrote:
>Original poster: "J. Casey Crager" <jccrager-at-bu.edu>
>Are there any quantitative explanations based on theory why you need 
>higher voltages for negative streamer propagation?
>
>Thanks,
>Casey

Hi Casey,

Most literature tends to focus on positive leader propagation since this 
polarity is the most troublesome for air insulated high voltage systems due 
to the lower breakdown voltage. There is a wealth of experimental data for 
both positive and negative rod-plane gaps, and a number of detailed 
computer models for positive leader propagation. Positive leader 
propagation is considerably simpler to model, since streamer and leader 
propagation head only toward the cathode.

In negative leader propagation, streamers and leaders may propagate in BOTH 
directions from partially ionized regions inside the gap (called space or 
plasma stems) which behave as "fictitious electrodes" floating within the 
gap. Much of the work in negative leader propagation has been driven (at a 
macro level) by lightning research and modeling. Because of the added 
complexities, models for negative leader propagation are scarce, tending to 
be macro models for lightning propagation. Most papers simply refer to the 
leader process, assuming that the reader understands that they mean 
positive, cathode-directed streamers and leaders.

Since you have an "edu" email address, you probably have easy access to the 
scientific literature. Following are a few references that that discuss 
leader propagation theory, negative leader propagation, and the differences:

"An experimental study of negative discharge in a 1.3 m point-plane air
gap: the function of the space stem in the propagation mechanism", T Reess, 
P Ortega, A Gibert, P Domens and P Pignolet, J. Phys. D: Appl. Phys. 28 
(1995) 2306-2313

"Performance of a 16.7 m air rod-plane gap under a negative switching 
impulse", P Ortega, P Domens, A Gibert, B Hutzler, and G Riquel, J. Phys. 
D: Appl. Phys. 27 No 11 (14 November 1994) pp 2379-2387

"Self-similar properties of minimum sparkover voltage in air for both 
polarities in rod-plane (0.1-30 m) gaps", M M Kekez, J. Phys. D: Appl. 
Phys. 18 No 9 (14 September 1985) pp 1813-1823

"The Lightning Flash", Vernon Cooray (editor), IEE Power and Energy Series, 
ISBN 0852967802 - see section 3.15.2 General charateristics of impulse 
breakdown in rod-plane gaps, pp 114-123.

"Spark Discharge", E. M. Bazalyan, Yu. P. Raizer, CRC Press, 1997, ISBN 
0849328683 - See Chapter 6 (The Leader Process) for quantitative discussion 
of positive leader mechanism, and section 6.11.1 (A Negative Leader), pages 
353 - 256 for qualitative discussion of why long gap breakdown threshold 
for negative discharges is significantly higher than for positive discharges.

Good luck and happy hunting! And if you find some better papers on 
this  subject, please let me know.

-- Bert --
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