Lightning Explained, Part 2


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It is not unreasonable to assume that charge transfer systems or dissipation devices produce the same effect as sharp rods. Since both would produce charges via the same mechanism: streamers. And since increasing the number of sharp conductive points does not proportionally increase the charge produced, as the points interact. Any shielding effect produced by these point discharge based devices is the same shielding effect that causes conventional lightning rods to occasionally fail and should thus occur just as frequently. Any protective effect will be sporadic and extremely limited in range and may only be significant on very tall towers in excess of 100m, where upward lightning is a real possibility.

The ugly

The basic premise behind the Early Streamer Emission (ESE) lightning rods is that by producing streamers earlier than would have naturally occurred, this will result in an upward connecting leader earlier. Since the leader will have this additional time to propagate it will cover greater distances and provide a larger zone of protection.

Despite having the support of The French Standard NF C17-102, the very concept simply doesn't make sense.

Assuming it is possible to create the upward connecting leader early, the possibility of any gained advantage would only be true if the upward leader always moved at a constant speed. But in reality the speed of the upward leader is dictated by its proximity to the descending leader. If you launch the leader early, this necessarily means that the descending leader was farther away. Therefore the upward leader will simply move more slowly, if at all, and so it is far from clear that any advantage can be gained.

More critical analysis reveals that the attempt to produce the upward leader early may actually impede the ability to intercept a strike.

Despite the lack of any technical basis for ESE technology they continue to find customers. In part because the overall system installation, including all connections and conductors, is cheaper than the practices recommended by code and furthermore, those same code recommendations are known to occasionally fail.

It is expected that an ESE will function very much like a sharp-tipped rod installed in the same location and collect some percentage of strikes. This is consistent with all the reported failures as well as all the reported successes.

-- continued in Part 3

References

1. NFPA International, Standards Council Decision (Long Form): D301-26

2. F.A.M. Rizk, "Modeling of Lightning Exposure of Buildings and Massive Structures" IEEE Trans. On Power Delivery, Vol. 24, No.4, pp. 1987-1998 October 2009

3. M.A. Uman and V.A. Rakov, "A Critical review of Nonconventional Approaches to Lightning Protection" American Meteorology Society, December, 2002

4. C.B. Moore, W. Rison, J. Mathis and G. Aulich, "Lightning rod improvement studies", Journal of Applied Meteorology, Vol.39, pp.593-609, 2000

5. F.A.M. Rizk, "Modeling of Lightning Exposure of Sharp and Blunt Rods" IEEE Trans. On Power Delivery, Vol. 25, No.4, pp 3122 -3132, October, 2010

6. D. Mackerras, M. Darveniza, A.C. Liew, " Review of claimed enhanced lightning protection of buildings by early streamer emission air terminals", IEE Proc.-Sci Meas. Technol., Vol. 144, No. 1. January 1997

7. I.D. Chalmers FIEE, J.C. Evans and W.H. Siew MIEE, IEE Proc.-Sci Technol, Vol. 146, No. 2, March, 1999

8. N. Knudsen, F. Iliceto, "Flashover tests on large air gaps with dc voltages and with switching surges superimposed on dc voltage", IEEE Trans., Vol. PAS-89, No.5/6, pp. 781-788, May/June 1970

9. F.A.M. Rizk, "Rocket-Triggered Lightning: Modeling of Trigger-Wire Corona Effects" International Conference on Lightning Protection, ICLP, Cagliari, Italy, September 2010

10. F.A.M. Rizk, "Modeling of lightning Incidence to tall structures.", IEEE Trans., Vol. PWRD-9, pp. 162-171, Jan. 1994

11. US PATENT 1,266,175

12. F.A.M. Rizk, "Analysis of Space charge Generating Devices for Lightning Protection: Performance in Slow Varying Fields", IEEE Trans. On Power Delivery, Vol. 25, No. 3, pp. 1996-2006, July 2010

13. F.A.M. Rizk, "Exposure of overhead conductors to direct lightning strikes: Modeling of positive streamer Inhibition", IEEE Trans. on Power Delivery, Vol. 26, No. 2, pp. 1156 - 1165, April 2011




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