Learn the basic skills of lightning protection

 Keywords: lightning protection, lightning protection for buildings
1995 The book "Basics of Modern Lightning Protection Technology", published by Tsinghua University Press in 1995, played a role in the popularization of lightning protection technology, but some plausible expositions have misled some lightning protection workers. Recently read the article "Physical Concepts of Lightning Protection Technology in the 21st Century" [2]. This article distorts the progress of high-voltage engineering and its basic content. Its potential discussion can be found in the book "Basics of Modern Lightning Protection Technology". Neither these books nor the author's recently published papers point out that the basis of modern lightning protection technology is high-voltage engineering, which includes: electric field, gas discharge, plasma physics, insulation materials, ground-to-earth electricity (grounding engineering) ), Wave electromagnetics and electrical overvoltages and their protection, etc., and talk about Maxwell's electromagnetic theory, criticizing the existing lightning protection theory is outdated, it should be modified according to its physical concept [2]. The author believes that the basic content and methods of high-voltage engineering should be specified. This article discusses the basic points of studying high-voltage engineering, and presumably writes criticisms of erroneous statements, or may or may not welcome discussion.
I. Experimental viewpoint
High voltage engineering is an experimental science, and every part of it is based on experiments. Professor Yang Jinji of Tsinghua University is one of the predecessors of high voltage engineering in China. His book Gas Discharge [3] is one of the basic theories of lightning protection. Its rich content shows that the gas discharge phenomenon is very complicated, and the discharge phenomenon under high and low voltage, high frequency and low frequency, pulse and DC voltage are all different. One cannot use the relationship between voltage and discharge distance at low voltage to linearly infer the breakdown distance at high voltage. Creep phenomenon occurs on the surface of insulators under high voltage. The scientific name is "flashover". The air is highly ionized under high voltage and there is abnormal discharge. We cannot routinely estimate the electrical performance of insulators, electrical components, and equipment at low voltages. These must be known through high voltage tests.
A certain charge (negative charge in most cases) separated from the thundercloud forms a pilot stream that extends to the ground. It meets the oncoming stream stream generated on the ground protrusion, and they form a main discharge. The plasma in the main discharge channel changes from low temperature to high temperature, and the equivalent resistance of the channel decreases rapidly. During the lightning discharge, the vertical voltage drop in the lightning channel decreased rapidly from 100V / cm to 5.5V / cm. It is a process that changes rapidly from corona discharge, glow discharge to arc discharge, and its process time is in the order of microseconds. According to the results of lightning observations and theoretical calculations, the consensus of lightning protection scholars is that lightning is not a voltage source, but a current source, and more strictly it is a current wave.
Many people who are familiar with ordinary electricians cannot understand this discharge process correctly, they often confuse it with the conductive process in the conductor. The electron movement in the conductor is an electronic relay movement, while the electron movement in the lightning channel is mainly the electron penetration movement. In the main discharge channel, the pilot stream and the oncoming stream pass through, and the positive and negative ions fuse to form a plasma channel. The pulse wave of the lightning current is formed by the ion current in the lightning channel, and the afterglow current after the pulse wave is the electrically conductive current from the thunderstorm cloud.
Someone compared the discharge process of a lightning strike suppressor to a neon transformer discharge, saying that "the high internal resistance of the neon transformer can reduce the discharge current, and the same can be done by connecting a high impedance in the pilot discharge channel to limit the lightning current." This argument denies that the main discharge is the nature of an arc discharge and does not recognize that a main discharge has occurred. The current record of the lightning strike suppressor shows that the discharge current is above 50A whether it is upward or downward. According to the discharge classification chart in Figure 1, they are all in the process of arc discharge.

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Feb.17 , 2020