1 When the local protrusions are hit by lightning strikes, the strong lightning voltage will penetrate the adjacent soil. With the development of modern society, the scale of the building is expanding, and the use of various electrical equipment is increasing, especially the computer network. With the popularization of information technology, buildings are increasingly using a variety of informational electrical equipment. Every year, the incident of destroying electrical equipment in buildings due to lightning strikes occurs frequently, and the losses caused are enormous. Therefore, the lightning protection design of buildings is particularly important. Abrasive And Whitening Filller
Abrasive and whitening filler contains superfine aluminum dioxide powder and superfine zirconium silicate powder. Both are stable fillers which is suitable to mix with epoxy base product to achieve excellent hardness and abrasion resistance. The products are extremely white type, fantastic for decoration effect.
Direct lightning strikes and inductive lightning are two forms of lightning that invade electrical equipment in buildings. Direct lightning is a lightning strike current that lightning strikes directly on the line and enters the ground through electrical equipment. Inductive lightning is a lightning strike caused by a strong electromagnetic field change caused by lightning current and an overvoltage induced by a conductor. According to the national standard "Code for lightning protection design of buildings" GB50057-94 (2000 edition), the lightning protection zone of buildings is divided into LPZ0A, LPZ0B, LPZ1, LPZn+1 and other zones (the specific meaning of each zone is not repeated here). Dividing the space to be protected into different lightning protection zones is to specify the severity of the lightning electromagnetic pulse and the position of the equipotential bonding point in different parts of the space, thereby determining which surge protector is used in the electronic equipment in the area. Where and how to achieve equipotential bonding with a common grounding body.
The protection area of ​​the building direct lightning strike is LPZOA area, and its protection design is well known to electrical designers. According to the national standard "Building Lightning Protection Design Code" GB50057-94 (2000 version), it is designed by lightning protection net (belt), lightning rod Or a combination of the lightning receptors, the steel mesh of the column foundation and the steel roof truss, the roof steel bar and the like constitute a whole, the lightning protection net acts as the grounding body through the steel bars of all the column foundations, and the powerful lightning current is put into the earth. The protected area of ​​the building inductive lightning is LPZ0B, LPZ1, LPZn+1 area, that is, it is impossible to directly suffer from the lightning strike area; the inductive lightning is generated by the lightning pulse electromagnetic induction or electrostatic induction, and the probability of forming the induced lightning voltage is very high. Electrical equipment in buildings, especially low-voltage electronic equipment, poses a huge threat, so the focus of lightning protection on building internal equipment is to prevent inductive lightning intrusion. There are three main ways of lightning overvoltage and overcurrent generated by inductive lightning: (1) Intrusion by power supply line; after high-voltage power line is struck by direct lightning strike, it is coupled to each low voltage 0.38KV/0.22KV line through transformer to be transmitted to the building. Low-voltage electrical equipment inside the object; in addition, the low-voltage line may also be hit by lightning or induced over-voltage. According to the test, the lightning overvoltage induced on the low-voltage line can reach 10KV on average, which can completely damage various electrical equipment, especially electronic information equipment.
(2) Intrusion by information lines such as computer communication in buildings; it can be divided into three cases:
1 When the local surface protrusion is hit by direct lightning strike, the strong lightning voltage will penetrate the adjacent soil, and the lightning current directly invades the cable sheath, and then penetrates the outer skin to make the high voltage invade the line.
2 When the thundercloud discharges to the ground, an overvoltage of several thousand volts is induced on the line, and the electrical equipment connected to the line is damaged, and the communication line is invaded through the device connection. This kind of intrusion spreads along the communication line, involving a wide range and a large range of harm.
3 If a multi-core cable is used to connect wires of different sources or multiple cables are laid in parallel, when a wire is struck by lightning, an overvoltage is induced in the adjacent wire to damage the low-voltage electronic equipment.
(3) The ground potential counter-attack voltage is invaded by the grounding body; the strong lightning current during lightning strikes is discharged into the earth through the down-conductor line and the grounding body, and the potential distribution of the radiation type near the grounding body, if other grounding bodies connected to the electronic device are close to each other That is, high-voltage ground potential counterattack is generated, and the intrusion voltage can be up to tens of thousands of volts. The lightning protection of buildings against direct lightning strikes introduces a powerful lightning current into the ground through the down conductor, which generates strong electromagnetic field changes in the nearby space, and induces lightning overvoltage on adjacent wires (including power lines and signal lines). Therefore, the building lightning protection system can not only protect the computer, but may introduce lightning. Integrated circuit chips of computer network systems and other devices have weak voltage resistance, usually below 100 volts. Therefore, it is necessary to establish a multi-level computer lightning protection system and layer-by-layer protection to ensure the safety of computers, especially computer network systems.
It can be seen that the design of anti-inductive lightning protection for various electrical equipment in buildings is an indispensable part; the rationality of design is crucial for the safe use and operation of electrical equipment.
At present, in the protection of inductive lightning, the use of surge protectors has become more and more frequent; it can respond to overcurrents in various lines, overcurrents, and overcurrents in venting lines, thereby achieving protection of electrical equipment. purpose.
According to the national standard "Building Lightning Protection Design Code" GB50057-94 (2000 Edition) Article 6.4.4: Surge protectors must be able to withstand the expected lightning current through them, and should meet the following two additional requirements: The maximum clamping force during the surge has the ability to extinguish the power frequency freewheeling generated after the lightning current passes. That is, the maximum clamping voltage of the surge protector plus the induced voltage at both ends should be consistent with the basic insulation level of the system and the maximum surge voltage allowed by the equipment.
Now, we select the maximum discharge current of the surge protector according to the lightning strike current values ​​of various lightning protection buildings specified in Appendix 6 of the National Standard Lightning Protection Design Code GB50057-94 (2000 Edition).
First, a type of lightning protection building
1. According to the national standard "Building Lightning Protection Design Code" GB50057-94 (2000 Edition) Appendix VI, the first lightning strike current amplitude is 200KA, the wave head is 10us; the second lightning strike current amplitude is 50KA, the wave head is 0.25μs; Figure 1, 50% of all lightning current i is calculated according to the grounding device flowing into the lightning protection device of the building, and the other 50% is allocated to the cable meter according to 1/3; the first lightning strike: the lightning current of the first power supply cable in the total distribution room The shunt value is 200*50%/3/3=11.11KA; the subsequent lightning strike; the lightning current shunt value of each power supply cable in the total distribution room is 50*50%/3/3=2.78KA; if the incoming cable has been carried out Shielding treatment, the shunt current of each power supply cable will be reduced to 30%, that is, 11.11KA*30%=3.3KA and 2.78KA*30%=0.8KA, while the surge protector bears 10/ The lightning energy of 350 μs is equivalent to 5-8 times of the lightning energy of 8/20 μs, so the maximum discharge current that can withstand the 8/20 μs waveform surge protector is 11.11*8=88.9KA; The maximum discharge current of the surge protector SPD is 100KA. For the HY company, for example, the HY38P-100J type is selected. According to the national standard "Building Lightning Protection Design Code" GB50057-94 (2000 Edition) Article 6.4.7, this level of surge protector should be installed in the main distribution room, that is, at the junction of LPZ0A, LPZ0B and LPZ1 Installed at the office.
2. According to the national standard "Building Lightning Protection Design Code" GB50057-94 (2000 Edition), 6.4.8, Article 6.4.9, install surge protection at the junction of LPZ1 and LPZ2 at the distribution box. The rated discharge current should not be less than 5KA (8/20 μs). Therefore, the maximum discharge current of the surge protector SPD should be 40KA, and the rated discharge current is 10KA. For the HY company, for example, the HY38P-40 type is selected. .
Second and second class lightning protection buildings
1. According to the national standard "Building Lightning Protection Design Code" GB50057-94 (2000 edition) Appendix VI, the first lightning strike current amplitude is 150KA, the wave head is 10μs; the second lightning strike current amplitude is 37.5 KA, the wave head is 0.25μs; According to Figure 1, 50% of all lightning currents i are calculated according to the grounding device flowing into the lightning protection device of the building, and 50% is allocated to the cable meter by 1/3; the first lightning strike: lightning current of each power supply cable in the total distribution room The shunt value is 150*50%/3/3=8.33KA; subsequent lightning strikes: the shunt current of each power supply cable in the main distribution room is 37.5*50%/3/3=2.08KA; if the incoming cable is already For shielding treatment, the shunt current of each power supply cable will be reduced to 30%, namely 8.33KA*30%=2.5KA and 2.08KA*30%=0.6KA, while the surge protector is subjected to 10 The lightning energy of /350 μs is equivalent to 5-8 times of the lightning energy of 8/20 μs, so the maximum discharge current that can withstand the 8/20 μs waveform surge protector is 8.33*8=66.6KA; The maximum discharge current of the surge protector SPD should be 65KA. For the HY company, for example, the HY38P-80 type is used. According to the national standard "Building Lightning Protection Design Code" GB50057-94 (2000 version) Article 6.4.7, this level of surge protector should be installed in the main distribution room, that is, at the junction of LPZ0A, LPZ0B and LPZ1 area Installed at the office.
2. According to the national standard "Building Lightning Protection Design Code" GB50057-94 (2000 Edition), 6.4.8, Article 6.4.9, install surge protection at the junction of LPZ1 and LPZ2 at the distribution box. The rated discharge current should not be less than 5KA (8/20 μs). Therefore, the maximum discharge current of the surge protector SPD should be 40KA, and the rated discharge current is 10KA. For the HY company, for example, the HY38P-40 type is selected. .
Three or three types of lightning protection buildings According to the national standard "Building Lightning Protection Design Code" GB50057-94 (2000 Edition) Appendix VI, the first lightning strike current amplitude is 100KA, the wave head is 10us; the second lightning strike current amplitude is 25KA, the wave head is 0.25μs; Figure 1, 50% of all lightning current i is calculated according to the grounding device flowing into the lightning protection device of the building, and the other 50% is allocated to the cable meter by 1/3; the first lightning strike: lightning current of each power supply cable in the total distribution room The shunt value is 100*50%/3/3=5.55KA; the subsequent lightning strike: the lightning current shunt value of each power supply cable in the total distribution room is 25*50%/3/3=1.39KA; if the incoming cable is already shielded Processing, the shunt current of each power supply cable will be reduced to 30%, namely 5.55KA*30%=1.7KA and 1.39KA*30%=0.4KA, while the surge protector is subjected to 10/350 The lightning energy of μs is equivalent to 5-8 times of the lightning energy of 8/20 μs, so the maximum discharge current that can withstand the 8/20 μs waveform surge protector is 5.55*8=44.4KA; The maximum discharge current of the surge protector SPD is 40KA. For the HY product, for example, the HY38P-40 type is selected. According to the national standard "Building Lightning Protection Design Code" GB5 Section 0.4.7 of 0057-94 (2000 edition) stipulates that this level of surge protector should be installed at the main distribution room, that is, at the junction of LPZ0A, LPZ0B and LPZ1.
2. According to the national standard "Building Lightning Protection Design Code" GB50057-94 (2000 Edition), 6.4.8, Article 6.4.9, install surge protection at the junction of LPZ1 and LPZ2 at the distribution box. The rated discharge current should not be less than 5KA (8/20 μs). Therefore, the maximum discharge current of the surge protector SPD should be 40KA, and the rated discharge current is 10KA. For the HY company, for example, the HY38P-40 type is selected. . In the power supply line, the specific installation of the surge protector is based on the more commonly used TN-S system, TN-CS system, and TT system, as shown below:
1) TN-S system overvoltage protection mode 2) TN-CS system overvoltage protection mode 3) TT system overvoltage protection mode
In summary, it can be seen that in the lightning protection design, the general lightning protection principle is to adopt three levels of protection:
1. Extending most of the lightning current directly into the underground foundation grounding device to vent;
2. Blocking overvoltages introduced along power lines or data and signal lines;
3. Limit the surge overvoltage amplitude (overvoltage protection) on the protected device. These three lines of defense are indispensable and cooperate with each other. At present, the usual practice is the following three points:
1) Establish a joint common grounding system to form an equipotential lightning protection system to build the foundation reinforcement of the building (including pile foundation, cap, floor, ground beam, etc.), beam and column reinforcement, metal frame, lightning protection down conductor, etc. Connected to form a well-closed Faraday cage grounding, connecting the grounding of all parts of the building (including AC work ground, safety protection ground, DC working ground, lightning protection grounding) and the building Faraday cage to avoid the grounding wires. There is a potential difference between them to eliminate induced overvoltage generation.
2) Power system lightning protection The building is a power supply unit. Surge protectors should be installed step by step in all parts of the power supply line (the lightning protection area junction) to eliminate lightning overvoltage.
3) Equipotential bonding system national standard "Building Lightning Protection Design Code" GB50057-94 (partial revision clause) clearly stipulates that equipotential bonding must be carried out at the junction of lightning protection areas; especially the weak motor room such as computer room in the building The possibility of direct lightning strike is relatively small, so in addition to the use of surge protectors for inductive lightning protection, the equipotential bonding method should also be used for lightning protection, which will not be described in this paper.
As electrical designers are very clear, the lightning protection design of buildings is a simple and cumbersome content, but it is of vital importance to the safe use of buildings and the normal operation of electrical equipment, so it is still waiting for you. Electrical designers should make further research and discussion; at the same time, they must be designed in strict accordance with national norms. This article only makes a little shallow discussion on this design, so the shortcomings in the text, I hope that the peers have educated us.
Http://news.chinawj.com.cn Editor: (Hardware Business Network Information Center) http://news.chinawj.com.cn
microfine aluminum dioxide powder,zirconium silicate powder,super white abrasive filler,microfine zirconium silicate
Shanghai Na Long Tech Co., Ltd , https://www.na-long.com