Two objects side by side, one is an insulator; One is the conductor. They are vulnerable to lightning strikes under thunderclouds; However, the former is less struck by lightning, which is the manifestation of the selective law of lightning strike. The concept of insulation lightning protection is to block lightning with insulating materials, which is a series circuit concept (whether from the sky or underground). The law of lightning strike selectivity ≠ Insulation lightning protection cannot be confused. In the absence of parallel wires, when lightning strikes, corona phenomenon will inevitably occur on series insulators (at this time, insulation performance has begun to lose), and then surface discharge of insulating materials or electrical breakdown of insulators will occur. We say that high-voltage discharge cannot be blocked by insulating materials, which has a lot of experimental data; These experimental data are necessary for lightning protection design and calculation of lightning protection electrical strength. The paper [1] conducted a parallel simulation of human lightning strike experiment, which is an experiment of lightning strike selectivity law and cannot be used as a reason for insulation lightning protection.
Some people say that some ancient buildings have not been struck by lightning for the time being, and they (according to their own knowledge) are only considered as not struck by lightning; Even if buildings are struck by lightning, they still insist on insulation and lightning protection, such as the wooden tower in Yingxian County, Shanxi Province. There is an ancient pagoda (brick tower) in Dingxing, Hebei Province, which was struck by lightning and was in danger of collapse. Beijing ancient architecture department sent experts to reinforce the tower with epoxy resin, completely renovated the tower and installed lightning protection devices. The palaces of the Ming Tombs, the Forbidden City and other ancient buildings in Beijing have also been struck by lightning many times in history, all of which are recorded in detail.
In July of the third year of Hongzhi in Ming Dynasty (AD 1500), Renzi was struck by lightning and caught fire at the meridian gate of the Forbidden City.
In April of the twentieth year of Jiajing, Xinyou (154 1) was struck by lightning, and a fire broke out in the ancestral temple.
In April of the thirty-sixth year of Jiajing, Shen Bing (1557) was struck by lightning, and the three main halls, the Wumen Gate, the Second Gate of Wu Wen and the Fengtian Gate were all burned down.
On June 22nd, Wanli (1594), Xihuamen was struck by lightning and caught fire.
In the 16th year of Chongzhen (1643), on June 23rd, Fengxian Temple was struck by lightning and caught fire.
In the Qing Dynasty, Tiren Pavilion was struck by lightning in Guihai (1783) in the forty-eighth year of Qianlong, and so on.
After liberation, the people's government attached great importance to the protection of ancient buildings. Lightning rods have been installed in the main buildings of the Forbidden City for protection, and all palaces with lightning protection devices have been safely protected. From 65438 to 0985, under the guidance of Mr. Wang, he conducted more than ten years of investigation and research, lightning simulation experiment research, lightning protection design, engineering construction and detection with experts from the ancient architecture department of the Palace Museum. In the process of making the lightning protection plan for the Forbidden City, the palaces without lightning protection at that time were repeatedly struck by lightning. We realize that lightning protection must be fully implemented, but this is unrealistic. So far, we have only written a summary report on external lightning protection. Wang Lao, Yu Zhuoyun and Bai co-authored The History and Experience of Lightning Protection in the Palace Museum [6]. Because the lightning electromagnetic pulse protection of the Forbidden City was done by a technical department of the Ministry of Public Security, we failed to make a comprehensive summary of the lightning protection of the Palace Museum. The above facts show that the lightning protection research of ancient buildings is a meticulous and arduous work, which needs in-depth investigation and verification. Do as much as you know. You can't judge the lightning protection of ancient buildings after reading a few books. The "Leigong column" in ancient buildings is the column in the middle of the gables on both sides. The corner of an ancient building has the most lightning strike rate, and the top pillar under it is also the most vulnerable to lightning strike damage. Historically, the Lei Gong column was often burned by lightning. The statement that "Leigong column is equivalent to the grounding device of lightning rod today" is wrong [4] and does not conform to the facts.
For the lightning protection of ancient buildings, it is necessary to conduct a comprehensive investigation and study on the local geographical environment, such as local lightning activities, the structure and use of buildings, and the conductivity of underground soil. This is how we do lightning protection for the Palace Museum. We have no right to express our opinions without investigating the general environment and actual situation of Tiantong Temple in Ningbo, Zhejiang. According to the author's discussion in [1], the discharge of charged aerosol to hillside forest may be a mechanism of regional lightning protection [7], but this does not mean that "insulation lightning protection" is feasible.
Thirdly, the fuzziness of the concept of insulation lightning protection and the harmfulness of its propaganda.
The concept of insulation and lightning protection is very vague, and it is easy to associate with the insulation of commercial power. During the period of 1956, there were many lightning casualties in Shanghai (including urban areas, Songjiang and Kunshan) (7 1 person died and 99 people were injured), which caused people to panic and be superstitious. A primary school teacher in a certain place publicized lightning protection knowledge, saying that "insulation can prevent lightning". Farmers only know that wood does not conduct electricity. As a result, when it thundered, some people sat on the table, some climbed in the straw pile, and some people were caught off guard and stood on it with their feet turned over. Some propaganda talks over my head, saying that when it thunders, you can't hit the wall, column or foot, which makes everyone feel insecure. The author of the paper [1] thinks that insulating umbrellas and insulating clothes can protect against lightning, which is wrong. Because people hiding in brick and wood buildings can't avoid the danger of lightning strike, wearing insulating umbrellas and clothes in the wilderness can't guarantee that they won't be struck by lightning. People wearing insulating boots can avoid the harm of stepping voltage more than barefoot people, because the underground soil forms a bypass, and the voltage that people bear is not the whole voltage of lightning strike.
The concept of building lightning protection is clear and definite, and its principle is to attract lightning and isolate indoor personnel and electrical equipment. Independent lightning rods were widely used in early lightning protection design, and the isolation distance from buildings was 3 m, while lightning protection belts and lightning protection nets were mostly used in modern buildings. It is suggested to change the isolation distance between the independent lightning rod and the building to 5m, taking into account the influence of lightning electromagnetic induction on indoor electrical equipment. Lightning protection measures for intelligent buildings include faraday cage, grounding grid and shielded wire. With the advent of the telecommunications era, lightning protection technology has made great progress. The lightning protection project of modern system can ensure the safe operation of the electrical system (including power, telecommunications and automatic control) in the building without cutting off the power supply. However, some people ignore these advances and strangely ask us to return to the era of "insulation and lightning protection" [4]!
Four, the principle of modern lightning protection is guidance and isolation.
Generally speaking, lightning protection and water control are the same, and it is necessary to combine unblocking, that is, guidance and isolation in technical language. Now entering the information age, almost all buildings are inseparable from power supply and communication lines. The channels through which lightning invades buildings are not only direct lightning, but also antennas, power lines, communication lines, metal pipes, etc., so lightning protection should be carried out systematically. Atmospheric physicists tell us that mature lightning can't be stopped and destroyed, and lightning will always hit somewhere on the ground to release energy. Lightning pilot streamer is not affected by ground objects at high altitude. When it extends to a distance of 50- 150m from the ground object, it will be affected by the ground electric field distribution. The guiding streamer will develop in the direction of maximum electric field intensity. The principle of lightning rod and lightning belt is that they have the largest electric field intensity, which is the application of electric field theory. The electric field intensity in the middle of the flat roof is two or three orders of magnitude smaller than that at the eaves (or parapets) of the roof, so we suggest installing lightning protection belts at the eaves of the flat roof or lightning rods at the four corners of the roof. This is the application of cybernetics and electric field theory in lightning protection. The distribution map of lightning-prone parts of buildings suggested by us is also the application of electric field theory. [4] What is said (the dispute between "field" and "road") is groundless, that is, "plasma lightning protection" must also give a foothold (a device that safely leads lightning current into the ground), otherwise it will never succeed.
Paper [4] questioned the problem of lightning protection and grounding, saying that it is particularly difficult to obtain low grounding resistance. I think he exaggerated the problem. Now people have made it clear that * * * ground is the most reasonable choice for lightning protection engineering, and natural grounding body and grounding pipeline can be fully utilized to reduce grounding resistance. Therefore, it is not difficult to realize low grounding resistance in urban lightning protection engineering; It is indeed difficult to obtain low-value grounding resistance in mountainous areas and pebble areas, but the problem can be solved by expanding grounding network, using resistance reducer and laying underground subway pipes in and out. But the method of "insulation and lightning protection" suggested by the author in [4] must not be used. As the atmospheric physicist Mr. Guo Changming pointed out [8], if the protected system does not produce an upward pilot, it is necessary to make the electric field of each part of the system lower than a certain value when the lightning pilot approaches. If this is not impossible, it is difficult to do it in practice. So far, there has been no real success.
Verb (abbreviation of verb) conclusion
1. Most of the ancient buildings in China are wood structures and brick-wood structures. According to records, these buildings have been struck by lightning many times in history, and the buildings of the Forbidden City in Beijing have also been struck by lightning many times. The legend that ancient buildings have "insulation and lightning protection" performance is a myth.
2. Mature lightning cannot be stopped or eliminated by insulation.
3. The principle of modern lightning protection is to guide lightning current to people and the earth to ensure the isolation safety of people and electrical equipment.
refer to
[1] Jiang, is it the same thing that corona and lightning strike occur on insulation? Lightning Protection World, No.6, 2004, 6L-62;
[2] Ming Jiang Zagreb is the voltage borne by objects (including lightning rods and lightning eliminators, etc.). ) Under lightning strike 107- 108V? Lightning Protection World, No.6, 2004, 63 pages;
Ma Hongda, Discussion on Insulation Lightning Protection, Lightning Protection World, No.2, 2004, pp.57-58;
[4] Yu Hao, lightning rod or plasma lightning protection technology? —— Reflections on the prevention of direct lightning in the information society, Lightning Protection and Standardization, No.3, 2004, p.10/-107;
[5] Fang, is insulation lightning protection feasible? Lightning Protection World, No.6, 2004, pp.57-60;
[6] Wang, Yu Jiyun, Bai, Summary of the lightning protection history and experience of the Palace Museum, Summary of the Papers of the Third Academic Seminar of China Palace Museum, China Palace Museum, 10, 2000, 65 pages;
[7] Ma Hongda, New Concept of Lightning Protection for Mountain Power Grid-Regional Lightning Protection, No.7, 1995, 43-46.
[8] Guo Changming, My Opinion on the Debate of Lightning Protection Technology, Lightning Protection in China, 2003, ll- 12, 33-36.