The author has designed and installed many lightning protection devices, and there is no record of lightning strike so far. This is not how high his lightning protection design level is, but mainly shows that the probability of lightning strike is inherently low, and not being struck by lightning for one year, several years or longer can not fully explain the problem. From June 5th, 2006 to October, 2006, we installed an automatic weather station made in Wuxi in Xiangtan Waterworks. The automatic weather station consists of a vertical 10 meter boom, a lightning rod device and a data collector. At the end of that year, there was a "thundering winter", and some computers and televisions in the water plant where the automatic station was located were damaged by thunder (according to the water plant, this is a minefield, and power outages and trips caused by lightning strike occur almost every year), but the automatic weather station is running well. Does this mean that the lightning protection design of automatic station is perfect? No, because the power supply of the automatic station is a DC system converted from solar energy, the lightning waves propagating in the power grid cannot invade the automatic station; If lightning falls directly on the automatic station system, the result will be unpredictable. In fact, some automatic stations connected to the rural power grid are more vulnerable to lightning strikes. This leads to a topic: how to analyze the "road" and "field" of lightning accidents? For example, the computer network in my community was paralyzed after a thunder. After investigation, the switch in the family area was damaged. The cause analysis of switch damage is more inclined to thunder wave invading the switch through network lines. In this regard, the author puts forward a rhetorical question: the network line is connected with the main switch of the business platform, and the channel between the computer room network and telecommunications is optical cable. Why is the main switch not damaged? In addition, only a few home computer network cards in the family area are broken. Why? In other words, the lightning strike of switches and network cards is not necessarily the lightning carried by network cables, but the power cables. The cause of lightning strike can be said to be both complicated and uncomplicated, which is nothing more than the direct invasion of lightning current or the influence of magnetic field change caused by lightning current change and electric field change caused by lightning radiation field. Of course, analyzing and understanding these reasons requires some physical knowledge and knowledge of circuits and components. Once, the wind recorder at our station stopped working because of lightning strike. According to the test, lightning only damages the power fuse and the internal power transformer, which shows that the DC blocking function of the transformer prevents the lightning current from invading. Unfortunately, we are too limited to the thinking cycle of "direct lightning can't be prevented, induction lightning can't be prevented, lightning protection can only reduce lightning damage but can't eliminate it, and lightning protection can't achieve 100%", and we have moved out specious theoretical basis such as ball lightning and shielding failure. One day in July 2002, a local high-voltage line was struck by lightning on a 380-volt power supply line, which triggered a fire in the distribution rooms of two villages. Some technicians think that the side impact damaged the insulation rope. The author consulted the relevant data and interpreted it as "reverse flashover"-flashover to the insulation string along the high potential of the tower. One month in 2006, a bank residential building in Ningxiang County was struck by lightning. The building is located within the protection range of lightning rods on both sides and also has its own lightning protection zone. Witnesses said that lightning directly hit the window railing and the window frame was burned red. Another time, there was an electric spark (no accident) at the grounding point of the duty room of the observation station of our bureau (two grounded flat steel bars were not connected). At the same time, some people saw the lightning rod on the roof being struck by lightning, but no abnormality (flash mark) was found in the appearance of the lightning rod after being struck by lightning. These are not completely ignorant, but more misunderstandings, as well as optical illusions and errors of the naked eye. Let's take "mobile phone lightning" as an example. I have always advocated that I don't agree with the saying that mobile phones attract thunder, and I don't agree that you can use your mobile phone safely in thunderstorm weather. Imagine that the mobile phone is originally receiving radio waves, and the signal is originally the conversion of current. The frequency range and electromagnetic field of lightning strike are very wide. Won't the mobile phone receive the lightning signal? I foolishly believe that some experts only pay attention to professional vision and analyze problems in their familiar fields. In this respect, the author respects Professor Yu Hao very much, respects science, dares to correct his views and explore deeper things.

2 On the topic of grounding resistance

In 1993, the author first designed a lightning arrester for a factory substation at the request of a customer. I was really at a loss. The most popular arrester in the market is semiconductor arrester, but I chose conductor arrester. Why? First, semiconductor lightning arresters have requirements for grounding resistance, while conductor lightning arresters have no strict requirements for grounding resistance; Second, if the lightning eliminator does not have the propaganda function for "leaflets", then the conductor needle has the lowest function of lightning rod. Therefore, I think grounding resistance is not the only or main index, but it is necessary. Take lightning protection of automatic weather station as an example. At present, a large number of electronic devices meet the requirements of grounding resistance, but lightning damage cannot be avoided. Like the automatic station we installed in the water plant, the downlead leads to the grounding body near the wind pole, so the downlead is parallel to the data line in the hollow metal wind pole and close to the equipment cabinet installed on the wind pole. Considering the shielding effect of the metal hollow pole and the cabinet, even if the electric field effect caused by the leakage of the down conductor can be ignored, the resulting magnetic field effect still exists. For the down conductor, when the instantaneous current passes, the inductance of the down conductor itself is quite high, even at any height, the grounding resistance is 0. When measuring the resistance of a short conductor of 0.5m, the author found that the DC resistance is only a few tenths of an ohm, while the transient resistance exceeds 1000 ohm. According to this, it can be estimated that the potential of the down conductor with a height above 0.5m from the ground is above1.000×1.003v when carrying lightning current (lightning current is generally above 20kA). At that time, the downlead was considered redundant and harmful. In the later installation of automatic station, the metal wind pole itself was mainly used as the down conductor, and it was considered that the cylindrical metal pole was superior to the single down conductor with much smaller cross-sectional area in the uniformity and inductance of lightning current distribution.

Small grounding resistance is more to make the grounding point close to the zero potential of the earth and speed up the safe leakage, but I think it is of little significance in the case of strong lightning current. At present, equipotential measures are well implemented, and there are few reports of counterattack accidents. Because of the lightning accident, the research on lightning current distribution may not be enough, and the equipotential bonding line is not completely free of current. In some cases, equipotential bonding lines may become a coupling bridge between some equipment or components. The relationship between grounding resistance and grounding arrangement is a continuous and in-depth topic, that is, the position and distance between the ground and underground grounding points, the area of grounding grid, the direction of grounding wire and the position of bus are all worthy of study. Grounding is inseparable from the influence of electric field and magnetic field, and only the resistance in the constant current source circuit is considered.

In our daily inspection, judging whether the lightning protection device is qualified or not does not depend entirely on the size of grounding resistance. As a lightning protection system, the size of grounding resistance is only one aspect. In reality, the building quality supervision station regards lightning protection as a part of electricity, and the qualification only depends on the resistance of a certain point of the grounding body, which greatly dilutes the requirements of lightning protection. Although the grounding test of lightning protection center pays attention to the grounding resistance and electrical connection of the whole steel bar structure and down conductor of the building, due to the lack of test specifications, the electromagnetic environment and lightning stroke risk cannot be evaluated according to the grounding resistance, and the grounding resistance value is used as the judgment standard.

3 How to treat lightning protection

According to the author's understanding, lightning protection is not a development problem, but a necessary problem. There is no doubt that lightning disaster is a natural disaster, and it is the unshirkable responsibility of human society to eliminate and reduce lightning disaster. To eliminate lightning disasters, human beings need to understand and practice. At present, more and more people are involved in lightning protection activities, which in itself is worth celebrating. It is also because of lightning protection practice that the author gradually understands electricity, electric field, circuit and circuit components. Even on the surface, it makes us from ignorance to a little sober. For example, current is the change of charge; Resistance is the collision and friction of electrons in the movement of conductors, semiconductors and insulators. Therefore, it is necessary to understand the distribution and motion of space field charges. Do a good job of lightning protection is not to copy the norms, but to scientifically use the internal spirit in the norms. For example, the clause of "independent lightning rod should keep a certain distance from the related protected objects" defined in GB50057 can not only be applied to the first type of buildings, but should consider the field effect and its consequences after lightning strike of lightning rod; What is the essence of equipotential measures? What problem has been solved? GB50057 stipulates to prevent the invasion of direct lightning and lightning waves, but lightning arresters are rarely designed in electrical design, and equipotential measures or grounding resistance are generally mentioned in words. The lightning protection of buildings seems to be only the location of lightning protection belt or lightning rod. Chatting with individual electrical engineers and asking why, more answers are that the parameters of lightning arrester are uncertain and the selection is difficult; When it comes to lightning protection effect, there is almost no definite answer. For many years, lightning disaster has been regarded as an irresistible natural disaster. The first article in the explanation of GB50057 points out: "The lightning protection safety of lightning protection devices designed according to this specification is not 100%". With the deepening of lightning protection practice, I think these references must be revised. All lightning protection devices that have been designed and tested must ensure that the lightning damage is controlled in a small range, otherwise "pseudo-lightning protection" will be popular. The author found that poor lightning protection design is the main cause of major lightning accidents. Poor lightning protection design not only does not protect against lightning, but attracts lightning, which is really "inviting wolves into the room".

Today's lightning protection challenges the traditional three areas of lightning protection-electricity, telecommunications and architecture, and different technical factions begin to argue. What impressed me the most was the debate about lightning eliminators in the 1990s, and there was no conclusion about right and wrong. The general view is that with the increase of high-rise buildings in cities, the probability of lightning strikes also increases. However, the author holds a different view, because lightning strikes mostly occur in urban-rural transition areas, and lightning strikes are mainly aimed at high-voltage lines, and the places that hurt people are mostly low-lying open spaces. The carriers of lightning induced waves are mainly power lines and communication lines coupled with them. So, do urban cement buildings have a certain shielding effect? Therefore, the view of "insulation lightning protection" has its reasonable side, and it is unscientific to completely deny it. According to "the principle of striking distance and electric field distortion" and the theory of lightning leader, it is not impossible for the leader to change the original direction if the accumulation of charges or the movement of charges on the ground are blocked by insulation. The author's feeling is that after generally denying the function of lightning arrester, "rolling ball method" and "equipotential" seem to be the only rules of lightning protection technology. Unfortunately, there are also reports that fully protected liquefied gas metal tanks have been struck by lightning. How to integrate today's lightning protection technology really requires predecessors and elites in the field of lightning protection to abandon their personal opinions and explore good lightning protection laws. Lightning protection must be orderly, and the legal management of lightning protection is the necessity of social development. "Research on the Development Strategy of Meteorological Undertaking in China" has gathered the wisdom of 39 academicians and more than 300 professors and experts, in which lightning protection is defined as the track of meteorological business, and lightning research, lightning forecast and early warning and lightning protection technical services are carried out in an all-round way, which is essentially intensive lightning protection and has certainly promoted lightning protection. Whenever mankind approaches the mysteries of nature, it is inevitable to pay a lot of hardships and property, so we don't have to sigh for it. "There is no doubt about mountains and rivers, and there is another village." Fortunately, the meteorological department shoulders this responsibility and is also promoting the development of lightning protection. At an administrative licensing work coordination meeting, the author once mentioned two points on the ownership of lightning protection management: First, why is lightning strike inevitable for lightning protection projects designed according to specifications? Second, why should the state put the management function of lightning protection in the meteorological department? The former question is true, and the latter question is "legal". I'm afraid this is not entirely a matter of departmental interests. In the practice of lightning protection detection in which the author participated, although the detection means are still relatively backward, it is actually found that the down lead of lightning protection devices in many buildings (structures) is dummy, and the grounding wire in the computer room is disorderly.