On the 23rd, a primary school was struck by lightning in Kaixian County, Chongqing. The newspaper said that the lightning rod was not installed, which meant that the responsibility was investigated afterwards. Do all houses have to be equipped with lightning rods?
I seem to have read an article that an incorrect lightning rod can lead to lightning!
What are the conditions for the country to install lightning rods?
Lightning counterattack usually refers to the metal body directly hit by lightning (including lightning receptor, grounding down lead and grounding body). At the moment of lightning contact, there is a high voltage between the lightning receptor and the earth, and the phenomenon that this voltage discharges other metal objects connected with the earth (also called flashover) is called counterattack. In addition, when lightning strikes a tree, the high pressure on the tree will react with nearby houses and metal objects. In order to eliminate the counterattack phenomenon, two measures are usually taken: one is to make equipotential connection, and connect two metal conductors with metal conductors to make them equal in potential when encountering lightning; Second, keep a certain distance.
Comprehensive lightning protection and counter-attack measures
Modern lightning protection includes external lightning protection (direct lightning protection of buildings or facilities) and internal lightning protection (lightning electromagnetic pulse protection). External lightning protection system is mainly to protect buildings from fire accidents and personal safety accidents caused by direct lightning strike, while internal lightning protection system is to prevent lightning wave intrusion, lightning induced overvoltage and system operation overvoltage from invading equipment, which cannot be guaranteed by external lightning protection system.
Lightning protection is a very complicated problem. It is impossible to completely eliminate the influence of lightning overvoltage and induced overvoltage only by one or two advanced lightning protection equipment and measures. According to the invasion route of lightning damage, we must eliminate all kinds of factors that may cause lightning strike and take comprehensive prevention and control-lightning protection, voltage sharing, shielding, grounding and shunt (protection) to minimize lightning damage.
1，flash
Lightning arrester is what we often call lightning rod, lightning belt, lightning wire or lightning protection network. Lightning receiving means that the lightning discharge in a certain range cannot be selected arbitrarily, and the lightning energy can only be discharged to the earth according to the designated channel of the lightning protection system designed by people in advance.
2. Balance pressure
When the lightning protection device receives lightning, the down conductor will immediately generate high potential, which will cause side flashover to the conductors around the lightning protection system that are still at ground potential, and make their potential rise, thus causing harm to personnel and equipment. In order to reduce the risk of flashover, the simplest method is to use the equalizing ring to connect the conductor at ground potential to the grounding device. If the distance between indoor metal facilities, electrical devices and electronic equipment and the conductor of the lightning protection system, especially the lightning arrester, cannot meet the specified safety requirements, thick wires should be used for equipotential connection with the lightning protection system. In this way, when lightning passes, all indoor facilities immediately form an "equipotential island" to ensure that there is no harmful potential difference between conductive parts and no lateral flashover discharge. Perfect equipotential bonding can also prevent the lightning current from entering the ground and causing the counterattack caused by the rise of ground potential.
In order to completely eliminate the destructive potential difference caused by lightning, it is especially necessary to implement equipotential bonding. Power line, signal line, metal tube, etc. Equipotential connection should be made through overvoltage protector, and the interface of each inner protection zone should be partially equipotential connected accordingly, and finally connected to the equipotential connection bus.
3. Protective
Shielding is to surround the protected object with conductors such as metal mesh, foil, shell or tube, so that all the channels invaded by lightning electromagnetic pulse waves are cut off. All shields, shells, etc. Need grounding.
Shielding is the most effective method to prevent the influence of lightning electromagnetic pulse radiation on electronic equipment.
4. Grounding
Grounding means that the lightning current that has entered the lightning protection system can flow into the earth smoothly, and the lightning energy cannot be concentrated in a certain part of the lightning protection system to cause damage to the protected object. Good grounding can effectively release lightning energy, reduce the voltage on the down conductor and avoid counterattack.
In the past, some specifications required electronic equipment to be grounded separately in order to prevent stray current or transient current in the power grid from interfering with the normal work of the equipment. Before 1990' s, the communication and navigation equipment in the army was mainly electronic tube devices, which used analog communication. Analog communication is particularly sensitive to interference. In order to prevent interference, the power supply and communication grounding are separated. At present, the field of lightning protection engineering does not advocate separate grounding. In IEC standards and ITU related standards, individual grounding is not recommended. American standard IEEE STD1100-1992 pointedly points out that it is not recommended to use any so-called separated, independent, computer-based, electronic or other incorrect earth grounding body as the connection point of equipment grounding conductor. Lightning protection grounding is the most basic link in the lightning protection system, and it is also the most basic safety requirement in the lightning protection installation acceptance specification. If the grounding is not good, the lightning protection effect of all lightning protection measures can not be exerted.
5, shunt (protection)
This is the focus of the rapid development of modern lightning protection technology, and it is also the key measure to protect all kinds of electronic equipment or electrical systems.
The so-called shunt means that a suitable lightning arrester SPD is connected in parallel between all conductors (including power lines, data lines, telephone lines, antenna feeders and other signal lines) coming from outside and lightning protection grounding devices or grounding wires. When the overvoltage wave caused by direct lightning or lightning strike on the line enters the room or equipment along these wires, the resistance of the arrester suddenly drops to a low value, approaching the short circuit state, and the lightning current flows into the ground. After shunt, a small part of lightning current will still enter the equipment along the wire, which is very dangerous for some microelectronic devices that are not resistant to high voltage. Therefore, for this kind of device, before the conductor enters the casing, multi-stage shunt should be carried out (that is, no less than three levels of lightning protection).
Now the research and development of lightning arrester has gone beyond the scope of shunt. Some lightning arresters can be directly connected in series on the signal line or antenna feeder, which can let useful signals pass smoothly and block lightning overvoltage waves.
When shunt lightning protection measures are adopted, special attention should be paid to the selection of lightning arrester performance parameters, because the installation of additional facilities will affect the performance of the system more or less. For example, the access of signal arrester should not affect the transmission rate of the system; The loss of feeder arrester in passband should be as small as possible; If it is used for directional equipment, it will not lead to positioning error.
Step 6 avoid
When choosing the location of infrastructure construction, we should avoid places where there are many minefields or lightning strikes, so as not to increase the cost and expenditure of lightning protection projects in the future.
When lightning strikes, turn off the equipment and unplug the power supply.
Lightning protection design scheme of network room 2007-05-0 17: 07 At present, with the rapid development of computer and network communication technology, the requirements of computer network system for lightning protection are getting higher and higher. Due to ineffective protective measures or cognitive deviation, the due protective effect is often not achieved, and the computer room is frequently struck by lightning. Especially in thunderstorm season, some electronic and electrical equipment of computer network system are disturbed by lightning, and some are burned by lightning, resulting in direct economic losses. We should pay enough attention to the lightning protection of computer network system, make good preparations, rectify lightning protection facilities and take overall protective measures to better maintain the safe operation of computer room.
Second, the solution
1. 1 building direct lightning protection
According to the national standard GB 50057-94 "Code for Lightning Protection Design of Buildings", the buildings where the computer rooms of important computer network systems are located are Class II or Class III lightning protection buildings, and generally lightning protection facilities are built as required, such as lightning protection network (belt) at the top of buildings, lightning rods or hybrid lightning arresters. These lightning arresters introduce powerful lightning current into the earth through the main reinforcement of the column foundation of the building, forming better lightning protection facilities for the building. The computer system is located in the building and protected by the lightning protection system of the building, so the possibility of direct lightning hitting the computer network system is very small, and there is usually no need to install equipment to protect the direct lightning.
1.2 induction lightning protection of computer network system
Induction lightning is generated by electrostatic induction or electromagnetic induction, and the probability of forming induction lightning voltage is very high, which poses a great threat to low-voltage electronic equipment in buildings. The lightning protection work of computer network system focuses on preventing induction lightning from invading. There are three main ways for lightning overvoltage and overcurrent to invade the computer system:
(1) is invaded by AC power supply line.
The power supply of the computer system is input indoors by outdoor overhead power lines, which may suffer from direct lightning and induced lightning; Direct lightning strikes the high-voltage power line directly, which is coupled to the 380V low-voltage side through the transformer and invades the computer power supply equipment; In addition, low-voltage lines may also suffer from direct lightning or induced lightning overvoltage. The lightning overvoltage on the 220V power line can reach 10000V on average, which can cause a devastating blow to the computer network system.
(2) Intrusion through computer communication lines
Computer communication line intrusion can be divided into three situations.
Case 1: When the ground protrusion is hit by direct lightning, the strong lightning voltage will penetrate the adjacent soil, and the lightning current will directly invade the cable sheath, and then penetrate the sheath, so that the high voltage will invade the line.
Case 2: When Lei Yun discharges to the ground, it induces thousands of volts overvoltage on the line, which damages the electrical equipment connected to the line and invades the communication line through the equipment connection. This kind of invasion spreads along communication lines, involving a wide range and causing great harm.
Case 3: If multi-core cables are used to connect wires from different sources or multiple cables are laid in parallel, when one wire is struck by lightning, overvoltage will be induced in adjacent wires, which will damage low-voltage electronic equipment.
(3) The back voltage of ground potential intrudes through the grounding body.
When struck by lightning, strong lightning current leaks into the earth through the down conductor and grounding body, and there is radial potential distribution near the grounding body. If other grounding bodies connected with electronic equipment are close, it will produce high-voltage ground potential counterattack, and the intrusion voltage can reach tens of thousands of volts. Lightning protection of buildings against direct lightning introduces strong lightning current into the ground through down lead, which produces strong electromagnetic field changes in the nearby space and induces lightning overvoltage on adjacent wires (including power lines and signal lines). Therefore, the lightning protection system of buildings can not protect the computer system, but may introduce lightning current. The integrated circuit chips of computer network systems and other equipment have weak withstand voltage, which is usually below100V. Therefore, a multi-level computer lightning protection system must be established to ensure the safety of computer network systems.
Step 2: Solution
The influence of (1) on lightning magnetic field is mainly that when direct lightning strikes the computer room building, the distribution of lightning current in the building directly affects the computer network system equipment, especially the computers and network communication terminal equipment sensitive to electromagnetic interference. Reasonable selection of the location of the computer room and reasonable arrangement of equipment in the computer room can effectively reduce lightning damage.
(2) Installing SPD at the interface between power supply system and computer network terminal equipment, shielding and grounding the cables entering and leaving the computer room to realize equipotential connection can effectively reduce the harm of lightning overvoltage to computer network system equipment.
(3) Using common grounding in the computer room can effectively solve the influence of rising ground potential, and qualified grounding grid is the key to effective lightning protection. The combined grounding grid of computer room usually consists of the foundation (including piles), ring grounding device and working (power transformer) grounding grid of computer room building. For the lightning protection of sensitive data communication equipment, the quality of grounding system is directly related to the effect and quality of lightning protection. If the grounding grid does not meet the requirements, the conditions of the grounding grid should be improved, the area of the grounding grid should be appropriately expanded, the structure of the grounding grid should be improved, so that the lightning current can be discharged as soon as possible, and the holding time of high overvoltage caused by the lightning current should be shortened to meet the lightning protection requirements.
Third, examples.
1. Basic information
The computer room of a company is located on the third floor of the building where the company is located. Buildings have external lightning protection facilities, such as lightning rods and lightning belts. The power supply system of the computer network system is powered by the mains three-phase low-voltage power supply, the power consumption of the computer room is directly supplied to the building distribution box by the distribution cabinet in the distribution room, and the UPS power supply equipment is supplied to the computer room distribution box by the building distribution box; UTP twisted pair is used for computer network communication lines entering and leaving the computer room, voice cable is used for special communication lines, and coaxial cable with BNC interface is used for satellite feeder. The grounding of the computer room adopts the building grounding grid.
2. Scheme design
The building where the computer room is located already has external lightning protection facilities such as lightning rod and lightning belt, so there is no need for external lightning protection supplementary design. The lightning electromagnetic pulse protection of computer network system is designed according to Class A requirements, and the power supply system is protected by Class 3~4 surge protector (SPD). The network communication system adopts fine protection, and properly installs signal interface surge protector (SPD) for cables and wires entering and leaving the protection zone. The computer room shall be grounded in common, a qualified grounding system shall be established, and the pipes, wires and troughs entering and leaving the interface of the protected area shall be connected with equal potential. Effectively reduce the lightning overvoltage to the level that the equipment can bear. The design contents mainly include:
(1) Design of transient overvoltage protection for equipment in computer room;
(2) Design of equipotential connection in computer room;
(3) Design of grounding grid.
3. Transient overvoltage protection of power supply equipment in computer room
As an area that needs protection, the computer network room can be divided into several protected areas from the outside to the inside from the perspective of EMC (electromagnetic compatibility). Outside the building is a minefield. The equipment in this area is the most fragile and dangerous. It is an exposed area, not a zone 0. The location from the building to the computer room is a non-exposed area, which can be divided into 1 area and 2 area. The deeper inside, the lower the risk. Power line is one of the main ways of lightning overvoltage intrusion. From the low-voltage output end of the transformer in the main distribution room to the equipment end of the computer room, classified protection must be implemented to reduce the lightning overvoltage to the level that the equipment can bear.
3. 1 Configuration of power arrester
(1) A 1 three-phase box arrester is set at the power output end of the main low-voltage distribution room as primary lightning protection. The nominal discharge current is 50 ~ 100 Ka to prevent direct lightning.
(2) In the building floor where the network equipment is located, a box-type lightning arrester is configured at the power inlet of the main distribution box as secondary lightning protection. Three-phase box arrester is equipped with a nominal discharge current of 40kA to prevent induced lightning strike or operating overvoltage.
(3) A power arrester is set at the power inlet of the distribution box in the network computer room as the third-level lightning protection. Equipped with single-phase box arrester, the nominal discharge current is 20kA to prevent induced lightning strike or operating overvoltage.
(4) Modular lightning arresters are used as the fourth-level lightning protection for important network cabinets or equipment terminals. The nominal discharge current is 5kA to prevent induced lightning strike or operating overvoltage.
3.2 Configuration of data (signal) communication interface lightning arrester
According to the specific situation of communication equipment, the lightning protection of data (voice) or video signal lines imported from outdoor is mainly considered. Lightning arresters are mainly connected in series at the equipment interfaces at both ends of the line.
(1) Single-port RJ45 signal arrester is installed at the input port of the server 100M to protect the server.
(2) The 24-port network switch is connected in series with the 24-port RJ45 signal arrester to avoid damage to the equipment caused by lightning induction or electromagnetic field interference.
(3) Install single-port RJ 1 1 port signal arrester on the DDN dedicated line receiving equipment to protect the equipment on the DDN dedicated line.
(4) Install the coaxial port feeder arrester at the front end of the satellite receiving equipment to protect the receiving equipment.
4. Equipotential bonding design
Make a grounding bus in the machine room, and share a grounding device for AC working grounding, safety protection grounding, DC working grounding and lightning protection grounding. The grounding bus of the machine room should be installed in the hidden place under the anti-static floor as far as possible. All communication cables and cables entering the building are shielded by metal pipes, and all metal pipes (including water pipes, gas pipes and various shielded pipes) are grounded nearby before entering the building. The purpose of using common grounding grid is to eliminate the potential difference between local networks and ensure that the equipment is not damaged by lightning strike back.
5. Production design of grounding grid
Grounding is one of the most important links in lightning protection technology. Whether it is direct lightning or induced lightning, lightning current is eventually introduced into the earth. Therefore, for sensitive data (signal) communication equipment, lightning protection cannot be reliable without a reasonable and good grounding system. Therefore, the grounding grid of buildings with grounding resistance >:1Ω needs to be rectified according to the specification requirements to improve the reliability of the grounding system of the computer room. According to the specific situation, different forms of grounding grids (including horizontal grounding bodies and vertical grounding bodies) are set up along the computer room building to expand the effective area of grounding grids and improve the structure of grounding grids.
The basic requirements are as follows:
(1) Make a grounding grid around the building, and complete the most effective grounding device with less materials and lower installation cost;
(1) grounding resistance requires r <1ω;
(2) The grounding body should be set about 3~5m away from the main building where the computer room is located;
(3) The buried depth of horizontal grounding body and vertical grounding body should be about 0.8m, the length of vertical grounding body is 2.5m, and a vertical grounding body should be set every 3~5m;
(4) The vertical grounding body adopts 50×50×5mm hot-dip galvanized angle steel, and the horizontal grounding body adopts 50×5mm hot-dip galvanized flat steel;
(5) When the grounding grid is welded, the welding area should be 6 times or more of the contact point, and the solder joints should be treated with anti-corrosion and anti-rust;
(6) All local nets should be welded with multiple building column steel bars at 0.6~0.8m underground, and be treated with anti-corrosion and anti-rust;
(7) When the soil conductivity is poor, the grounding resistance should be ≤1Ω by laying resistance reducer;
(8) Backfill soil must be new clay with good conductivity;
(9) Multi-point welding with building foundation network, and grounding test points are reserved.
The above is the traditional low-cost practical grounding method. According to the actual situation, the grounding grid material can also choose new technology grounding devices, such as maintenance-free electrolytic ion grounding system, low resistance grounding module, long-term copper-clad steel grounding rod and so on.
Four. Concluding remarks
The computer network system requires high protection against lightning overvoltage. The lightning protection design of computer network system should be comprehensively considered according to the geographical environment where the computer room is located. After reasonable lightning risk analysis, the main lightning power source invading the equipment in the computer room is protected as a whole, and according to some mature lightning protection technical experience, economic and effective protection measures are taken to ensure the safe and stable operation of the computer network system equipment.
I hope it helps you.