Lightning Explained, Part 1
The scientific views expressed in this article are those of Dr. Farouk A.M. Rizk as explained by Amir Rizk. Dr. Farouk Rizk is the former VP (Research Laboratories), Hydro Quebec, and former Scientific Director at IREQ. Amir Rizk (B.Sc., phys, MBA) is VP of Lightning Electrotechnologies Inc and a student of Dr. Rizk. Any technical matters dealing with lightning protection adhered to previously published, peer reviewed material.
It is interesting to note that although lightning is perhaps the most complex electrical phenomenon that we face, the methods and tools commonly used in lightning protection are amongst the simplest and least scientific. Furthermore since the physics of the matter is so complex, it can be very difficult to distinguish between real science and the kind of baseless pseudo science that plagues the lightning protection industry.
In this three-part series I hope to provide a simplified yet modern account of what a lightning strike is, to provide an overview assessment of existing lightning protection practices and to introduce some new technologies based in the latest peer reviewed science.
What is a lightning strike?
First we need to familiarize ourselves with some basic facts and definitions.
A positive high voltage electric discharge from a positively charged electrode is a situation where the electric field at the surface of the electrode becomes so intense that it starts to rip electrons away from neutral air molecules and leaves behind positively charged ions referred to as positive "space charge". Conversely, a negative electric discharge injects electrons into the air, which quickly attach to air molecules and form negative space charge. So in either case, it is a flow of electrons through the air, which produces space charge.
If enough charge is induced onto a grounded object, the resulting electric field around such a grounded object will appear very much like the electric field had it been isolated and maintained at high voltage. In such cases grounded objects will produce electric discharges that are virtually identical to the discharges produced by electrodes at high voltage.
In the earlier stages, these air-ionizing discharges are commonly referred to as "streamers". Streamers are the bluish/white filament-like structures most commonly associated with HV electric discharges. They produce a distinctive audible noise, are fairly cool in temperature and produce current pulses in the micro- to milliamp range and require intense electric fields within which to propagate. Given the right conditions, streamers grow in groups or bunches, and a "leader" will develop at the base of a volume of streamers. Leaders are hot, highly conductive and can travel great distances in relatively low electric fields. Leaders move 10 to 100 times more slowly than streamers.
The stepped leader
For reasons that are beyond the scope of this article, during thunderstorms and as a result of certain types of cloud formations, massive localized volumes of charge develop in the clouds. These localized volumes of charge give rise to a high voltage electric discharge phenomenon known as stepped leaders.
-- continued on page 2
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