Thunder and lightning disaster is a serious natural disaster that humans cannot resist at present. Lightning causes casualties and equipment damage frequently. With the continuous development of modern communication technology, precision electronic equipment is widely used in computer communication network systems in various industries. Due to the extremely low ability of precision electronic equipment to resist overvoltage, overcurrent and electromagnetic pulses, an unguarded system will suffer Lightning strikes, the equipment will suffer severe damage. With the acceleration of my country’s informatization construction process, the investment in information systems has increased, and computer network information systems are playing an increasingly important role. The threats and harms caused by lightning disasters are also increasing, and more and more every year. Computer and network communication facilities are damaged due to lightning strikes, which leads to interruption of information transmission, information damage and even accidents that threaten personal safety.
2. Several ways of
thunder and lightning infringing on network equipment There are two ways for thunder and lightning to infringe on computer network: direct lightning infringement and induced lightning infringement. The lightning overcurrent that directly hits the building or equipment connection line where the equipment is located and enters the ground through the network equipment is called direct lightning; the lightning strike formed by the overvoltage and overcurrent induced by the strong electromagnetic field generated by the lightning current through the conductor is called Induction mine. Direct lightning strikes a building, which will generate a strong lightning current. If the voltage distribution is uneven, it will generate a local high potential, which will form a high potential counterattack to the surrounding electronic equipment, destroy the building, damage the equipment, and even cause casualties. Inductive lightning is generally generated by electromagnetic induction, and invades the computer network system through the power line and signal feeder induced lightning voltage, which causes large-scale damage to the network system equipment. Therefore, lightning intrusion into the computer network system mainly has the following three ways:
(1) Direct lightning strikes through the air-termination device of the building to discharge the lightning current, resulting in a ground potential of tens of thousands of volts, invading the network equipment through the equipment grounding wire Form a ground potential counterattack.
(2) When the lightning current enters the ground along the down conductor of the building, a strong magnetic field is generated around the down conductor, which induces an overvoltage on the metal pipe (line) around the down conductor, and the electricity through the network system Or the signal line invades the network system.
(3) The lightning voltage and overcurrent loaded by direct lightning or induced lightning outside the building such as power lines or communication lines entering and exiting the building will enter along the line and infringe on the network equipment.
It can be seen that lightning invades computer network systems mainly through power supply lines, communication lines and grounding systems. Therefore, the lightning protection of the network system is mainly aimed at the above three possible lightning protections, by adding lightning protection facilities at all levels, as far as possible to prevent and reduce the damage caused by the lightning disaster to the computer network system.
Third, lightning protection measures
3.1 lightning protection
for direct lightning strike protection, diversion measures can be taken, the use of lightning rods, lightning belt, lightning network lightning current into the earth along the deflectors to prevent direct lightning hit the building or On the device.
Air-termination tapes, air-termination nets or air-termination rods should be used as air-termination devices on the roof of buildings. The air-termination net (belt) should be laid along the corners, ridges, eaves and corners of the roof that are vulnerable to lightning strikes, and should form a grid that should not be larger than 10m×10m or 12m×8m on the entire roof. The lightning net (belt) and the lead-down connecting line are made of Φ12 galvanized round steel and -40×4mm galvanized flat steel. There should be no less than two down conductors, and they should be arranged evenly or symmetrically along the building’s circumference, and their spacing should not be greater than 18m. For newly-built buildings, the grounding wire of the lightning net (belt) should use the diagonal steel bars in the structural column. If the diameter of the steel bars in the column is not less than Φ16, use two diagonal steel bars in the column as the down conductor; if the diameter of the steel bars in the column is less than Φ16, use four diagonal steel bars in the column as the down conductor.
Power system protection 3.2
power of the computer network system is not independent of the power supply system, still enter the room by the power lines, power lines theoretically may suffer direct lightning and lightning. If a direct lightning strikes a high-voltage line, it is coupled to the low-voltage end through a transformer, and the computer network system is invaded through the computer power supply equipment; the low-voltage line may also be struck by a direct lightning or induced overvoltage. No matter what kind of situation the lightning causes the overvoltage of the power line, it will cause devastating damage to the computer network system equipment.
Because lightning produces strong over-voltage and over-current, it is impossible to complete current discharge and voltage limitation at one time, so the power system must adopt multi-level lightning protection, at least two levels of lightning protection before and after current discharge and voltage limitation must be adopted. . According to my country’s current computer information system lightning protection technical requirements, the power supply system should adopt multi-level lightning protection, that is, install a first-level lightning protection device when entering the LPZ0B zone and entering the LPZ1 zone, and install the first lightning protection device in front of the switching power supply rectifier equipment. Second-level lightning protection device, install the third-level lightning protection device on the UPS power input and DC output terminals, and set the power supply precision protection. Through the use of multi-level power supply lightning protection measures, the lightning overcurrent is completely discharged and the overvoltage is limited, so as to prevent as much as possible the lightning from entering the computer network system through the power line and damaging the system equipment.
(1) Choose PB25-385/B+C/4 power three-phase surge protector at the main power distribution cabinet where the power line enters from the LPZ0B zone into the LPZ1 zone. The test category is Type I test (limp=25kA, ln=25KA, Up=1.8KV, Uc=385V). The front end is connected in series with a 63A power circuit breaker, the length of the PE wire of the surge protector should not be greater than 0.5m, and the 16mm2BVR copper core wire is used for the nearest grounding.
(2) Choose PC40-385/4 power three-phase surge protector at the power distribution cabinet, and the test category is Type II test (ln=20KA, Up=1.7KV, Uc=385V). The front end is connected in series with a 32A power circuit breaker, and the length of the PE wire of the surge protector should not be greater than 0.5m, and the 10mm2BVR copper core wire is used for the nearest grounding.
(3) PD20-275/4 power three-phase surge protector is selected at the equipment distribution cabinet and UPS power inlet end of the equipment room, and the test category is Type II test (ln=10KA, Up=1.2KV, Uc=275V ). The front end is connected in series with a 32A power circuit breaker, the length of the PE wire of the surge protector should not be greater than 0.5m, and the 6mm2BVR copper core wire is used for nearby grounding.
(4) PDU1-J1G08/16 type power distribution unit surge protector is used at the equipment power supply in the computer room, and the test category is Type II test (ln=5KA, Up=1.2KV, Uc=275V). The length of the PE wire of the surge protector should not be greater than 0.5m, and the 6mm2BVR copper core wire should be grounded nearby.
3.3 protection signaling systems
information network within a modern building is no longer islands of information, it must be an open network interconnection, to meet the needs of people exchange information. The connection of physical media is required between buildings and between buildings and external networks. There are many ways of communication between the internal network and the external network. Some are interconnected by ordinary telephone twisted pair as the communication medium, such as PSTN. (Dial-up access), ISDN technology, DDN technology, ADSL technology, etc.; some use Category 5 unshielded twisted pair, optical fiber as the medium to achieve communication connection.
In the above-mentioned communication methods, in addition to the optical fiber medium (the metal inside the optical fiber should also be equipotentially connected at the entrance), other mediums may be subjected to direct lightning or induced lightning to infringe the network system connected at both ends.
First, exposed communication cables will be directly attacked by lightning; cables laid in parallel, when a cable is struck by lightning, overvoltage will be induced in the adjacent cables.
Secondly, even if it is a communication cable buried in the ground, when the ground is struck by a direct lightning or the lightning is discharged through the ground, the strong lightning voltage will penetrate the soil, causing the lightning current to invade the cable and enter the network. At present, my country is vigorously promoting broadband network technology. According to recent statistics, the most widely used broadband Internet access method in my country is ADSL, accounting for 89.3% of all users. The medium used by ADSL technology is ordinary telephone lines. Lightning strikes often cause accidents that damage the communication equipment at both ends. If any lightning protection measures are not taken for the network connected to this, once lightning strikes, the system will suffer huge losses.
In order to avoid the possibility of lightning damage caused by communication cables, the usual technology is to connect the signal lightning arrester (signal SPD) before the cable is connected to the network communication equipment, that is, a transient overvoltage protector is connected in series in the link. It can protect electronic equipment from conducting surge overvoltage caused by lightning strikes and other interference, block the intrusion of overvoltage and lightning waves, and reduce the impact of lightning on system equipment as much as possible. Since the signal arrester is connected in series in the communication line, the signal arrester must meet the requirements of network performance indicators such as signal transmission bandwidth in addition to the lightning protection performance characteristics. Therefore, when selecting related products, full consideration should be given to lightning protection performance indicators and network performance indicators such as network bandwidth, transmission loss, and interface type.
SNH-RJ45/16 network signal surge protector can be used for signal line lightning protection, and the test category is Type II test (ln=3KA, Up≤25V, Uc=6V). The length of the PE wire of the surge protector should not be greater than 0.5m, and the 6mm2BVR copper core wire should be grounded nearby.
3.4 and equal potential shield room
in the engine room are set around a pressure ring, as the ground lines of the lightning discharge and convergence device, and reliably connected to the ground means. The material of the equalizing ring is 30*3 copper bar. Equipotential connection of all metal objects in the computer room, such as equipment shells, metal wire ducts, PE rows of power distribution cabinets, etc., can reduce the impact of external induced lightning and lightning electromagnetic pulses on each device in the computer room when lightning occurs to a certain extent. damage.
3.5 grounding system
building should be combined common grounding system, grounding lightning protection, low voltage distribution system (protection) ground, grounding, the grounding shield, an equipotential grounding system common grounding. The grounding of the building generally uses the reinforced concrete foundation as the ground network. The reinforced concrete foundation of the building is buried deep, and the grounding resistance of the building can basically meet the requirements, so the main steel bar of the building can be used as the lightning protection grounding system. Its power frequency grounding resistance should not be greater than 1 ohm. If the soil resistivity is high and the grounding resistance is difficult to meet the requirements, you can reduce the resistance by adding artificial grounding bodies and using resistance-reducing materials.
Set the total equipotential terminal at the entrance of the building and connect it with the grounding device. Connect the grounding of all metal pipes and cables that enter the building, such as the grounding of the antenna feeder, the grounding of the fiber optic cable reinforcement core, and the grounding of the shielded pipe of the power supply line.
The material selection of the grounding device, the metal grounding body should be made of hot-dip galvanized material. Since the original hot-dip galvanized layer has been destroyed at each welding point, anti-corrosion treatment must be done. The length of the vertical grounding body is 1.5-2.5m, and the interval of the vertical grounding body is 1.5-2 times of its own length. The upper end of the grounding body is not less than 0.7m from the ground, and it should be under the frozen soil layer. The vertical grounding body can be made of ∟50*50*5mm angle steel or grounding copper rods, and the horizontal grounding body and grounding lead-in can be made of -40*4mm flat steel and grounding modules, and materials such as resistance reducing agents can be added to reduce the grounding resistance.
3.6 Other protective measures
to avoid risks due to the lightning protection system design legacy technology network engineering staff uneven, some designers not only a lack of knowledge of mine safety, mine safety and the lack of awareness often leads to network cabling system in the design Leaving a hidden danger of lightning protection. Therefore, for outdoor network wiring, optical fiber communication media should be used as much as possible, and cables should be buried in the ground. In addition, the information center is the core of the network system, and the important communication equipment of the network is set here, so the selection of the computer room also involves lightning protection safety. From the perspective of lightning protection, the computer room should avoid choosing the top or side of the building. The corner position should be set on the second or third floor for multi-story or high-rise buildings to reduce the impact of direct lightning on the network equipment when the building is struck by lightning.