of lightning is one of the ten most serious natural disaster, “the United Nations International Decade,” published. The latest statistics show that the losses caused by lightning have risen to the third place among natural disasters. For the top 1,000 companies in the United States, each company loses an average of US$200,000 per year due to lightning strikes. In my country, nearly 10,000 people are injured or killed by lightning strikes each year, and the property losses caused by lightning strikes are estimated to be around 5-10 billion yuan.
The advancement of science and technology has promoted the wide application of various electronic equipment in highway engineering. Many points, comprehensiveness, and long routes are the characteristics of highway electromechanical systems, which include large-scale monitoring, sensors, communication and other weak equipment, as well as strong electricity. equipment. Usually, field equipment has prominent equipment in various road sections and open areas. Usually, power lines have to pass through complex geological layers and over mountains and ridges. Due to these characteristics of electromechanical systems, they are extremely vulnerable to lightning damage, especially induced lightning strikes and counterattacks. Thunder damage. Seriously affect the normal operation of electromechanical facilities. In order to avoid potential safety hazards caused by lightning, it is very important to build a good lightning protection system.
Second, according to a comprehensive lightning protection design of highway
highway in the design of integrated mine mainly uses the following criteria for the reference design.
1. GB50057-2010 “Code for Lightning Protection Design of Buildings”
2. GB50343-2012 “Technical Specifications for Lightning Protection of Building Electronic Information Systems”
3. IEC61024 “Lightning Protection of Buildings”
4. I EC61312 “Lightning Electromagnetic Pulse Protection”
5 、GB50174-2008 “Code for Design of Electronic Computer Room”
3. Protective measures for direct lightning strikes of expressway buildings
1. The monitoring center building is generally set at the entrance and exit of the expressway or the center of the control and management area. Because the surrounding terrain is relatively empty, the floors are generally above six floors, the height is more than 20m, and various communication antennas are installed on the roof, and some are also equipped with iron towers. These are important targets for direct lightning strikes. Because there are a large number of real-time electronic and microelectronic equipment in the building, it is also the command height center of the entire airport. According to the provisions of GB50057-2010 “Building Lightning Protection Design Code”, it can be classified as a second-class lightning protection building. The lightning rod is designed according to the rolling ball method (the radius of the rolling ball method is 45m). For the design method, please refer to the requirements in Appendix IV of the “Code for Design of Lightning Protection for Buildings” to determine the number, layout, and height of the lightning rods. The wind resistance strength of the lightning rods against the local 30-year maximum wind should be considered during the design, and a certain margin should be left.
2. In order to reduce the maintenance of lightning rods and prevent acid rain from corroding the lightning rods, stainless steel lightning rods should be installed on the roof of the monitoring center building. The height and quantity of the lightning rods are calculated according to the rolling ball method. The protection range can cover the entire center building’s sky and various types. Antenna, so that it can effectively prevent direct lightning strikes to protect the roof of the building and the safety of various communication antennas.
3. Install a set of stainless steel lightning rods on the top of the pan/tilt pole where surveillance cameras are installed along the highway, the top of the pan/tilt pole of the toll station square, and the top of the LED sign to protect pan/tilt cameras and other equipment from direct lightning hazards.
4. Install a set of iron tower copper needle-point lightning rods on the steel roof of the expressway toll station and the top of the large outdoor electronic display symmetrically to protect the steel roof of the toll station and the electronic display frame structure from direct lightning damage.
5. It is better to use the steel structure column as the drain line for the down conductor of the lightning rod. If the conditions are not allowed, you can also use the copper stranded wire of 35mm2 or more to pass through the galvanized steel pipe for shielding, and make insulation treatment, and take the shortest distance directly from the tip of the lightning rod. The path enters the ground, in order to reduce the lightning electromagnetic pulse radiation during the discharge and damage the microelectronic equipment and the outdoor large-scale electronic display coding control system.
4. Protective measures for lightning electromagnetic pulse (LEMP)
The induced electromotive force generated by the lightning electromagnetic pulse (LEMP) is superimposed on the line signal through the intrusion channel to generate an instantaneous high voltage, which destroys all kinds of electrical equipment and microelectronic chips. Therefore, in the implementation of lightning protection projects, induced lightning strikes must be the key point. Effective defense. When designing comprehensive lightning protection, key protection should be carried out from the above channels, and at the same time, equipotential connection and common grounding system should be done.
4.1 Power system lightning protection measures
in accordance with China’s current computer information system lightning protection technical requirements, power should take a multi-stage lightning protection system, namely in the area of home LPZ0B enter LPZ1 area at the installation of a lightning protection devices, as well as switch Install a second-level lightning protection device before the power supply, install a third-level lightning protection device at the UPS power input and DC output terminals, and set up precision protection for the power supply. 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 electronic system through the power line and damaging the system equipment.
⑴Opley PB25-385/B+C/4 (limp=25kA, ln=25KA, Up=1.8KV, Uc) is used at the power distribution cabinet of the monitoring center building from the LPZ0B area to the home to enter the LPZ1 area. =385V) Power three-phase surge protector, the test category is Type I test. As the first level of lightning protection for the power system.
⑵Oples PC40-385/4 (ln=20KA,Up=1.7KV,Uc=385V) power supply three-phase surge protector can be used at the power distribution cabinet. The test category is Type II test as the power supply system The second level of lightning protection.
⑶Oples PD20-275/4 (ln=10KA, Up=1.2KV, Uc=275V) power supply three-phase surge protector is selected at the power distribution box of the equipment and the UPS power inlet end that needs to be protected. The test category is Class Ⅱ test. As the third level lightning protection of the power system.
⑷Choose Opelei PC40-85VDC (ln=20KA,Up=0.5KV,Uc=85VDC) DC power surge protector at the DC screen, and the test category is Class II test, as the lightning protection of the DC power supply system.
⑸ Choose Opu Lei PDU1-J1G08/16 (ln=5KA,Up=1.2KV,Uc=275V) power distribution unit surge protector at the equipment power supply in the computer room, and the test category is Type II test as the end of the power system Lightning protection.
The SPD connecting wire should be short and straight. The SPD connecting wire should not be larger than 0.5m. When the length is larger than 0.5m, the wire diameter should be thickened appropriately. When the line spacing of SPD1 ~ SPD2 is less than 10m, the line spacing of SPD2 ~ SPD3 is less than 5m, and the line spacing of SPD3 ~ SPD4 is less than 5m, a decoupling device should be installed between the two SPDs.
Install PBX-40/220 (ln=20KA, Up=1.7KV, Uc385V) single-phase power lightning protection boxes on the power supply lines in the toll booths to protect the toll computers, receipt printers, toll indicator boards, indicator lights, Automatic barriers, lane controllers, voice prompt systems, walkie-talkies and other power lines are safe.
Both ends of the low-voltage DC power supply line of the square camera head are installed with Opelei PC40-85VDC (ln=20KA, Up=0.5KV, Uc=85VDC) power surge protectors to protect the safety of the low-voltage DC power supply line.
Install PB25-385/B+C/2 (limp=25kA, ln=25KA, Up=1.8KV, Uc=385V) single-phase power surge protection at the output end of the power distribution panel of the pan/tilt camera power supply line along the highway. The test category is Type I test. As the primary lightning protection of the power supply system to protect the safety of the camera power supply line.
Install PB25-385/B+C/2 (limp=25kA, ln=25KA, Up=1.8KV, Uc=385V on the large-scale electronic display power line distribution boards at both ends and the middle of the highway entering and exiting. ) Single-phase power surge protector, the test category is Type I test. As the primary lightning protection of the power system,
4.2 protective measures for video signal transmission lines
(1) At both ends of the video transmission cable from the square camera to the control center and the toll booth lane from the surveillance camera to the control center should be installed Opelei SV-BNC (ln=3KA, Up≤40V, Uc=12V) video signal lightning protection The test category is Type II test. As a lightning protection on the transmission line of the monitoring system.
(2) Install OP-SV3/24 three-in-one surge protectors on the cameras of the pan/tilt along the highway. The power supply parameters are (ln=5KA, Up≤900V, Uc=275V), and the control signal part The parameters are (ln=3KA, Up≤40V, Uc=12V), and the test category is Type II test, which is used as lightning protection for the camera’s power line, signal line and control line.
(3) Install a set of Opelei SV-BNC (ln=3KA, Up≤40V, Uc=12V) video signal lightning protection devices on the video input and output BNC ports of the video card of the toll computer to protect the toll computer.
4.3 Protective measures for the signal line of the toll system
(1) Install Opelei SNH-RJ45 (ln=3KA, Up≤25V, Uc=6V) network signal surge between the computer network server in the monitoring center computer room and the network switch (HUB) Protector, the test category is Type II test. To protect the server.
(2) Install an Oupre SNH-RJ45 (ln=3KA, Up≤25V, Uc=6V) network signal surge protector at both ends of the data line between the computer room network switch of the monitoring center and the computer of the toll booth. , The test category is Type II test to protect the network switch and toll booth computer network port.
(3) Install one Oupulei PUC-24 (ln=5KA, Up≤60V, Uc=30V) data line signal surge protection after the optical and electrical terminal encoders of the electronic display to the two ends of the controller. To protect optical and electrical terminals, encoders and controllers.
(4) Toll booths and monitoring center wired intercom systems are each installed with 1 audio lightning protection device: Oupulei SN-RJ45 (ln=3KA, Up≤25V, Uc=6V) network signal surge protector.
(5) It is advisable to install a program-controlled telephone surge protector at both ends of the program-controlled telephone and emergency telephone transmission line: Oupulei SN-RJ45 (ln=3KA, Up≤25V, Uc=6V) network signal surge protector.
V. Shielding and equipotential connection
1. Shielding is the basic measure to reduce electromagnetic interference. The following measures should be taken: external shielding measures, wiring in a suitable path, and wiring shielding. These measures should be used in combination. The metal surface of the roof, the metal surface of the facade, the steel bars in the concrete and the metal door and window frame must be connected to the ground after equipotential bonding.
2. In practice, the large-space shielding of buildings or rooms is composed of natural components such as metal supports, metal frames or reinforced concrete. These components constitute a grid-shaped large-space shield. Conductive metal objects penetrating into this type of shielding should be connected to the nearest equivalent potential and grounded.
3. The location of the equipment room of the monitoring system should be in the highest level of LPZ and should not be located in the top three floors of the building; when the size of the lightning protection grid of the building’s sky part does not meet the system’s anti-interference requirements, it should be in the sky Install shielding layer. Use unshielded cables, wear metal pipes and bury them in the ground at a horizontal distance of more than 10m before entering the house. If it is not possible to penetrate the metal pipe and enter the house under the ground due to conditions, the length of the door shielding pipe or trestle should be lengthened, and the two ends of the metal pipe or trestle bridge and the junction of the lightning protection zone should be equipotentially connected and grounded.
4. When the monitoring system equipment is a metal enclosure, the shortest wire should be used to connect it to the equipotential bonding belt. If it is a non-metal housing, when the shielding of the building where the equipment is located does not meet the electromagnetic compatibility requirements of the equipment, a metal mesh or other shielding body should be installed to shield the equipment, and the metal mesh should be equipotentially connected with the equipotential bonding belt.
5. The equipment in the computer, communication, and monitoring room should be about 1m away from the outer wall of the building. In order to prevent the strong electromagnetic field around the down conductor that leaks into the ground along the outer wall when the building is directly struck by lightning, the microelectronic equipment is damaged.
Equipotential bonding is one of the important protection measures of modern lightning protection technology. Connect the outer layer of the coaxial cable output by the square camera and the outer layer of other pipelines before entering the building with equipotential bonding and then grounding. The metal outer layer of various water pipes, heating and air-conditioning pipes and other metal pipes entering the building where the system is located should be equipotentially connected when entering the building. After the gas pipe enters the house, a piece of insulation should be inserted at the flange connection. After the switch-type SPD is connected, the indoor metal pipeline can participate in the equipotential connection, and connect it with the large-size metal parts combined with the building. After the total equipotential connection is made according to the requirements of GB50057, it is connected to the total equipotential bonding belt And reliable connection and grounding.
Sixth, the grounding system
should be reinforced using a network of the building foundation as a common grounding system. If the building does not have a foundation reinforced ground network, it is advisable to bury artificial vertical grounding bodies and horizontal ring grounding bodies around the building. The grounding resistance of the grounding body should not be greater than 1Ω. In principle, equipotential connections should be made at the interface of each lightning protection zone. However, due to process requirements or other reasons, the installation position of the protected equipment will not be set exactly at the surge voltage that may occur at the interface, and the surge protector should be installed on the Protect the equipment, and the metal protective layer or shielding layer of the circuit should first make an equipotential connection at the interface to ground.
The lightning arrester is first of all a discharge channel for lightning discharge current, and it is also an equipotential connector. The protection principle of all lightning arresters is to ensure that the equipotential body is formed between the equipment, the ground, the building and its auxiliary equipment at the moment of lightning strikes, so as to avoid damage from overvoltage. The most important thing is the grounding system.
The ideal grounding device (including the lead from the air terminal to the ground) has no resistance. When a lightning strikes, no matter how large the lightning current is, the potential difference of any point on the grounding device to the ground is zero, which is absolutely safe for people and equipment of. However, such a grounding device does not actually exist. Therefore, the grounding resistance value should be as small as possible. According to the “Computer Room Grounding Code” and other relevant national lightning protection standards, the machine room should be grounded together, and the grounding resistance value of the machine room should not be greater than 1 ohm.
In order to ensure the stable and reliable operation of network equipment, prevent capacitive coupling interference, protect equipment and personal safety, and solve environmental electromagnetic interference and electrostatic hazards, a good grounding system must be provided.
According to the grounding requirements of IEC overall lightning protection technology, ensure that the equipment should be in an equipotential state at the moment of lightning strike. Since the signal grounds and protection grounds of some equipment are relatively independent, from the principle of “saving and effective”, the local networks are simply connected. At present, the ground grid structure under the toll station has basically constituted a joint grounding form, but it has not yet achieved complete equipotential connection.
At the moment of a lightning strike, due to the rapid conduction of lightning protection devices and the discharge of large currents, the internal circuit devices, casings, towers, and building wall metal components and metal shields of the equipment are all connected to the ground network at the same time. In this way, at the moment of thunder and lightning, various objects inside and outside the computer room are at the same potential as the ground network, and each part reaches an equipotential, thus avoiding the equipment from being damaged due to the potential difference between the objects.
According to the current grounding situation of each system, it is recommended that under the premise that each grounding system forms a joint grounding, the distance between each grounding point shall be strictly maintained in accordance with the specifications, and all exposed metal parts in the management center shall be short-circuited, and the iron pipe of the wire shall be passed Connect in the same way. The power supply system and signal system are equipped with a dedicated grounding busbar, and each grounding wire should be as short and straight as possible.
Around the monitoring center building, a ring-type closed grounding resistance of the compound hybrid grounding network should be made less than 1Ω, and a long-lasting resistance reducer should be poured to ensure that the ground resistance is stable all year round. This ground network is mainly used for the safety protection grounding of the monitoring center building and toll booths, and is connected to the grid as a shared grounding system. Grounding grid: down line 50 square 800 multi-core grounding wire + grounding body. Grounding body: It is buried in the ground and connected to the down conductor to the ground, and the lightning current is dissipated to the ground from this. The vertical grounding body is usually composed of TG-A500*400*60mm and 50 mm×50 mm×5mm×L2000 mm hot-dip galvanized angle steel, and then connected with 40 mm×4 mm hot-dip galvanized flat steel copper-iron joints Lead down the wire to meet the national lightning protection standard grounding resistance. One is introduced into the grounding busbar of the main computer room with the shortest path for the purpose of grounding the computer room.
Make a combined grounding net less than 4Ω under the gimbal poles along the highway, each ground net shall be made of two lead poles, the distance between the poles should be greater than 5m, one lead pole is used for direct lightning protection grounding, and the other lead pole is used for equipment safety For grounding. After each ground wire is shielded by 1.5 inches galvanized steel pipe, it is led to the top of the pan/tilt pole and the equipment room for two types of grounding.