In the frequent thunderstorm season, lightning protection has become an important task of wireless communication stations. It is of great significance to do a good job of system grounding in lightning protection and lightning protection of wireless communication equipment. Aiming at the most basic grounding work of wireless communication system, analyze and discuss the communication lightning protection work and reduce the accidental failure factors of the communication machine.
As the automation equipment of wireless communication systems becomes more and more advanced, the precision integration of equipment circuits is increasing day by day. The intrusion of induced lightning and lightning electromagnetic pulse is easy to damage the corresponding electronic and electrical facilities. In addition to the exposed outdoor antennas and cable feeders of the wireless communication equipment, the hazards of induced lightning strikes have increased significantly. Lightning rods alone are far from satisfying wireless The actual lightning protection requirements of the communication station equipment, therefore, the requirements for the system work and protection ground are more stringent. We must start from the details, manage from the source, and start from all directions. On the basis of grasping the system grounding work, The station equipment implements a comprehensive lightning protection project. The lightning protection of the equipment must be carefully planned, designed, and constructed. The grounding of the equipment must be strictly required and highly valued. The grounding of the system must be closed: the connection is solid, the ground network is reliable, and the leakage is smooth. In general, in a In the working area, try to consider the neighboring computer room, iron tower, antenna, transformer, power distribution cabinet, and communication cable as a whole. According to the principle of voltage equalization and equipotentiality, the working ground, protection ground and lightning protection ground form a joint grounding network. Various grounding wires in the station should be introduced separately from the grounding collection line or grounding network to expand the range of the grounding network and enhance the overall lightning protection capability.
1. Grounding work for direct lightning protection of wireless communication For direct lightning protection, we generally mainly use traditional lightning protection devices such as lightning rods, lightning protection belts, lightning protection nets, etc. As long as the design specifications and installation are reasonable, these lightning protection facilities can effectively carry out direct lightning protection. Defense, this method is economical and simple, but it should be noted that the lightning rod should be installed a few meters above the antenna tip, and there should be a certain distance between the lightning rod and the antenna to prevent the radiation pattern that damages the antenna due to the presence of the lightning rod to affect the communication effect . The general method is that the lightning rod becomes the main pole of the antenna tower, and the communication antenna is installed outside the lightning rod about 1.5 wavelengths. Due to the greater intensity and wider range of lightning strikes, the first step is to ensure that they have a good current release channel. The main grounding standards should be:
1. The resistance of the DC path of the lightning conductor is sufficiently low, generally 10-500, less than 50 is best. Due to the large lightning surge current, the frequency spectrum is wide and the duration is short, so the inductance must be as small as possible .
2. Flat braided wire or stranded wire cannot be used for the ground wire, because this wire has a large inductance, which is not conducive to the discharge of lightning current and is easily corroded. It is necessary to use solid wires of more than 3mm, and preferably the same metal material.
3. In order to increase the discharge area of ​​the ground surface, multiple grounding bodies buried at a certain interval may be used and welded to each other. For example, bury about 10 copper pipes at intervals of 1 to 2 meters around the building and weld them together.
The grounding body should be made of hot-dip galvanized steel, and its specifications are as follows:
The wall thickness of steel pipe φ50mm shall not be less than 3.5mm. Angle steel should not be less than 50mm × 500mm × 5mm. Flat steel should not be less than 40mm × 4mm.
However, due to the different environmental conditions of the wireless communication station, its ground network is often difficult to form a closed ring ground network around the house. Therefore, flexible consideration is given to the composition of the ground network, but the lightning protection of the working room, protection ground, and tower of the computer room The three grounds should be connected to the common ground network, and the tower should be connected to the building (including the underground and the roof). When there is difficulty, the lightning protection belt on the roof should also be connected to the tower ground network. For stations located on the outskirts of a city, in a thunderstorm area (annual thunderstorm days greater than 20 days or more), or in buildings that are too high to be protected by the lightning protection facilities of surrounding buildings, the ground network should be made multiple points underground and on the ground ( (Two points or more) Welding connection, especially pay attention to disconnecting the equipment during the welding connection of the ground net to ensure the safety of the system. [
In addition to the effective grounding of outdoor lightning protection facilities, from the perspective of systemicness and comprehensiveness of lightning protection projects, we should also pay attention to the joint grounding of related facilities in the communication equipment room, that is, the cable racks, hanging iron racks, and machines in the equipment room. Frames or cabinets, metal ventilation pipes, metal doors and windows should be grounded for protection. It is generally advisable to use multi-strand copper wires with a cross-sectional area of ​​not less than 35 mm2 for the protective grounding wire. According to the requirements of the "Code of Design for Lightning Protection and Grounding of the Communication Bureau (Station)", the length of the grounding inlet of the equipment room should not exceed 30m. Its material is galvanized flat steel, and the cross-sectional area should not be less than 4mm × 40mm or not less than 95-2 Yin copper wire. The grounding lead-in wire should be treated for anti-corrosion and insulation, and should not be laid in the heating or trenches. When buried, the sewage pipes and drains should be avoided, and the parts above the ground should be exposed, and measures should be taken to prevent mechanical damage.
Second, no matter how perfect the lightning rod of the wireless communication anti-induction lightning is, it is incapable of inducing lightning strikes. Due to the induced current from the line, coupled with the poor system shielding, and the failure to take effective equipotential connection measures, comprehensive wiring is not Reasonable and non-standard grounding causes ground potential counterattack, etc. Therefore, it is necessary to use a comprehensive comprehensive lightning protection method to install relevant SPDs on the power supply and feeder lines, and organically combine and complement each other with qualified lightning rods to form a complete set of lightning protection. Mine system. For any advanced and scientific lightning protection device, the grounding of the equipment itself and the grounding of the lightning protection device are particularly important. Generally, the ground resistance of the communication equipment room is not more than 10, which is also the premise and key to ensure the function of lightning protection equipment.
1. The equipment in the equipment room should first be connected to the protective ground and the working ground with equipotential connection, especially the casing of the related equipment must be grounded to minimize the hazard of secondary induction lightning strikes. The requirements for the grounding collection line and grounding row are relatively high. It is generally designed in a ring or row shape. The material is copper and the cross-sectional area should not be less than 120mm2. Galvanized flat steel with the same resistance value can also be used. The grounding collection in the machine room The line can be installed in the ground trough, on the wall or on the wire rack. The grounding collection line should be insulated from the building reinforcement.
2. The coaxial cable feeder of the communication station transmitting the RF signal generally has a metal outer sheath, which should be grounded at the upper profile, the lower part, and the entrance of the equipment room through the cable rack, and the grounding at the entrance to the equipment room should be derived from the ground network. The ground wire is directly connected to discharge the lightning current induced by the cable in the outside world. When the height of the tower is greater than or equal to 60m, the metal outer sheath of the coaxial cable feeder should also be added to the middle of the tower for grounding. Pay attention to the following grounding issues when installing lightning arresters in antenna feed systems. First, the grounding resistance of the grounding terminal of the lightning arrester must not be greater than 50, otherwise it will affect the lightning protection effect; second, when installing the communication antenna, the antenna support rod must be reliably connected to the tower, the connection resistance is equal to zero, and the feeder should hang down from the inside of the tower, and every interval Use copper wire to fix the iron tower.
3. In order to effectively prevent the induction of lightning strikes on the power supply and signal lines, the grounding conditions of the various lightning arresters provided are directly related to the lightning protection effect. For the grounding wire of the power supply arrester in the power distribution cabinet, the cross section should be at least 16mm2, and the grounding wire of the lightning arrester of the signal line should also reach a cross section of 6 to 2 and the shorter the distance to the terminal block, the better. Within the range of less than 1m, in this way, once the lightning strikes, it can ensure that the strong current on the surge arrester is discharged in the shortest time, and the effective lightning protection of the power supply and the signal line is achieved.
4. In order to prevent the secondary damage effect of induced lightning strikes, we must pay attention to the layout of the ground wire. Remember not to mix the ground wire of the surge arrester with the power supply or signal line. Although it usually seems that the lines do not interfere with each other and are concise and beautiful, but once When a lightning strike occurs, the powerful discharge current will immediately sense the adjacent line in the same direction when the lightning arrester is acting, causing damage to the connected equipment. This is often easy to ignore, but the fact reminds us that we must not be sloppy in lightning protection work. Otherwise, the consequences will be unbearable.
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