ornitz@kodak.UUCP (barry ornitz) (07/14/88)
In article <432@ns.ns.com> logajan@ns.ns.com (John Logajan x3118) writes: >In article <1314@kodak.UUCP>, ornitz@kodak.UUCP (barry ornitz) writes: >> shown that the sharp point is not optimum but instead an elliptical point >> should be used. >> The article also debunks a number of myths about the "cone of protection" >> and also about the neutralization of space charges > >I'm interested in this for reasons unrelated to the current discussion. >Do you remember what was the basis for these statements? >..... >Anyhow, I would guess for a lightning rod you would want as steep a gradient >as you could get. ... > >I don't know about the cone, but there must be some shape of protection around >the rod, i.e. some area where it is easier to go to the rod than to some other >structure. John, you really need to read the whole article since it is far, far too long to fully discuss here. The full reference is: Moore, C. B.: Improved Configurations of Lightning Rods and Air Terminals, "Journal of the Franklin Institute," Vol. 315, No. 1, January 1983, pp 61-85, Pergamon Press, Oxford. My memory was mistaken on Moore's address. He is with the Langmuir Laboratory of the New Mexico Institute of Mining and Technology. You have actually hit on the problem. The high gradient at the point causes breakdown of the air near the tip. The ion flow from the tip absorbs any increase in field strength above the ionization level. The point thus protects itself from further increases in field strength. The author of the article beleives the "cone of protection" exists, but it has a much smaller half-angle (probably around 22 degrees) than most people think. Some suggestions about the optimum rod are presented in the article that are quite useful. I would suggest that you find this article. I can photocopy it for you if your local library cannot find it (please send me a SASE). This article has both theory and experimental data sprinkled with some history. Even if Franklin got the sign wrong, most of his other work was right! :-) Barry WA4VZQ ----------------- | ___ ________ | | | / / | | Dr. Barry L. Ornitz UUCP:...!rochester!kodak!ornitz | | / / | | Eastman Kodak Company | |< < K O D A K| | Eastman Chemicals Division Research Laboratories | | \ \ | | P. O. Box 1972 | |__\ \________| | Kingsport, TN 37662 615/229-4904 | | -----------------