As we all know, lightning is a natural phenomenon. The lightning strikes a lot of energy. Its discharge time is very short, but the discharge current can reach tens of thousands or even hundreds of thousands of amps. Therefore, it is directly destroyed by lightning and is extremely damaging on the discharge channel. Even if it is not a direct lightning strike, but a building near the lightning point, due to electromagnetic induction, high-voltage shock waves are generated on the building body or on the overhead line, and the induced voltage can be as high as several thousand volts or even tens of thousands of volts. This high-voltage shock wave propagates rapidly along the building body or along the conductor, which can damage various electrical equipment and endanger personal safety. In the CATV system, once lightning strikes, systems without good lightning protection measures will be severely damaged or even embarrassed. For large systems with long trunk lines, lightning protection design is an important task. This paper describes the lightning mechanism from the generation mechanism of lightning and the destructiveness of lightning to CATV system, in order to readers have a general understanding of lightning strikes, and then strengthen and improve the lightning protection measures of CATV system. Lightning is a phenomenon of discharge in the atmosphere, which is formed in the cumulonimbus cloud. The cumulonimbus will stop moving with the change of temperature and airflow. When the friction generates electricity during the movement, a charged cloud layer is formed, and some cloud layers are formed. There is a positive charge, and some clouds have a negative charge. In addition, due to electrostatic induction, buildings, trees, and the like below the cloud layer are often subjected to an opposite charge. With the accumulation of electric charge, the voltage of the thundercloud gradually increases. When the thunderclouds with different charges and the earth protrusions approach each other to a certain temperature, the electric field between them exceeds 25-30 kv/cm, and intense discharge will occur. At the same time there is a strong flash. Since the temperature during discharge is as high as 2000 ° C, the air is rapidly expanded by the heat, and the roar of the explosion occurs, which is lightning and thunder. The size and amount of lightning and the activity are related to the terrain, meteorological conditions and latitude of each area. Generally, there are more mountain mines than plains, and there are more coastal areas than the hinterland of the mainland. The higher the building, the more opportunities for lightning strikes. There are two main types of lightning: "direct lightning" and "induction lightning." Direct lightning strikes only about 10% of the lightning strike rate, and the damage range is generally small. You can use lightning rods, lightning protection lines and lightning protection nets to prevent them. However, after installing the lightning rod, the electronic equipment of the CATV system may be damaged by lightning even if it is within its protection range. Most of them are burned fuses, power transformers, rectifying components, etc., and serious components may be damaged. This shows that the lightning strike is not introduced from the antenna, but is introduced from the power line. It can be seen that although the lightning rod protects the building, it cannot protect the CATV electronic equipment placed therein, which is mainly caused by the induced lightning. The "inductive thunder", which is much more harmful, accounts for nearly 90% of the lightning strike rate. The damage range is very wide. The electronic equipment of the CATV system is damaged by lightning, mainly caused by lightning. The introduction of lightning into the CATV system is mainly introduced from lightning rods, antennas, down cables and overhead cables. First, because the tip of the lightning rod has a small radius of curvature, when the thundercloud approaches, the tip charge concentrates to form an ionization zone around the electric field. When the lightning meets, the lightning rod is first connected. Secondly, although the lightning rod is generally higher than the antenna, sometimes the height is not enough, the protection angle is not large, and the high voltage is induced on the outer conductor of the antenna and the connected coaxial cable. If the outer conductor is not grounded or the grounding is improper, the core wire is Being shielded will cause high voltage between the inner and outer conductors of the cable, damaging equipment and televisions. In addition, when a lightning strike occurs near the CATV system, a strong electromagnetic field acts on the exposed overhead cable, causing a high voltage between the inner and outer conductors of the cable, damaging the device and the television. 1. The lightning protection grounding of the antenna. The receiving antenna and the vertical rod of the cable TV are generally installed at the top of the building. All the receiving antennas, including the grounding of the satellite receiving antenna, should be welded together. The lightning rod should be installed on the vertical rod (frame) of the antenna. The height of the lightning rod should be installed. Should be able to meet the protection of the antenna facilities. When installing a separate lightning rod, the protection range of a single lightning rod is tent-like and the boundary line is hyperbolic. Therefore, the length of the lightning rod above the top of the antenna should be greater than the maximum size of the antenna. The minimum horizontal spacing between the lightning rod and the antenna should be greater than 3M. . When the building has a lightning protection grounding system, the grounding of the lightning rod and the antenna vertical rod should be connected to the lightning protection grounding system of the building. Whether it is a new ground wire or the ground wire of the original building, the grounding resistance should be less than 4 ohms. 2. Lightning protection and grounding of the front-end equipment. If a lightning strike occurs near the front end, high voltage is induced in the metal case and the outer casing of the equipment room, which jeopardizes equipment and personal safety. The power leakage of the front-end equipment will also endanger the safety of personnel. Therefore, all equipment in the equipment room, the shielding layer of the input and output cables, metal pipes, etc. need to be grounded, and cannot be connected with the grounding of the antenna. The grounding and grounding of the AC power supply system should be connected together at the main ground. The grounding device of the electrical equipment and the buried metal pipe in the system shall be connected with the lightning protection grounding device. When the connection is not connected, the distance between the two should be more than 3 meters. The surface of the grounding busbar in the equipment room should be complete. There should be no aging turtle in the aging layer of the insulated wire. Crack phenomenon. Some front-end devices, such as modulators, receivers, etc., do not have over-voltage protection, but only over-current protection. In case of lightning strikes, power supply burnout will occur and insurance will continue. For this case, a lightning arrester should be installed at the main power supply. Better protection of front-end equipment. 3. Lightning protection grounding of the mains system. Underground cables laid in open areas. When the annual thunderstorm days in the area is greater than 20 days and the soil resistivity is greater than 100 ohms, the shield or metal sheath of the cable should be grounded once every 2KM. To prevent the influence of inductive electricity. The shield of the overhead cable and the metal sheath and steel strand are grounded once every 250M. The metal sheath of the overhead cable at the cable junction box, the shield layer and the steel strand should share the grounding device with the cable puller. In addition, the cable can not be ignored for lightning protection, because in the manufacturing process, in order to increase the tensile strength of the cable, the wire is added to the cable. When setting up the connection box, only pay attention to the fusion of the cable. Using the usual method, the wires of the two sections of the optical cable are respectively fixed on the brackets at both ends of the connection box, and a gap is naturally formed. Thus, when the wire in any section of the cable induces a high lightning voltage, it will discharge to the other end of the wire, and a large spark generated during the discharge process will break the fiber in the connection box. In order to prevent this from happening, during the construction of the optical cable, attention should be paid to connecting the ends of the optical cable wires in the connection box with wires, and connecting them with the steel strands of the hanging optical cables by wires, so as to effectively avoid the optical cable being damaged. Lightning violations. 4. Lightning protection grounding of the distribution system. When the cable enters the building, the outer conductive shield of the cable should be grounded near the building. When the overhead cable is directly introduced, a lightning arrester should be installed at the entrance and the outer conductor of the cable should be connected to the grounding device of the electrical equipment. When the cable is directly buried, the metal sheath of the cable should be connected to the grounding device at the entrance end. Do not lay cables directly between the roofs of the two buildings. The cables can be lowered along the wall into the lightning protection zone, but the traffic should not be prevented. The steel wires should be grounded. The coaxial cable shielding mesh in the CATV system and the galvanized iron wire for the overhead support cable have good grounding. The input and output terminals of the equipment in the system should have a discharge protector. The power supply end of the 220V power supply amplifier should have an overvoltage protection device, or try to change the 220V power supply amplifier in the system to the main circuit 60V centralized power supply to ensure the independence of the wired network. Sex and self-sufficiency to reduce the possibility of direct lightning intrusion, which is the primary measure to prevent the formation of lightning. Square Sunglasses,Square Frame Sunglasses,Square Shades,Square Shape Sunglasses Danyang Hengshi Optical Glasses Co., Ltd. , https://www.hengshi-optical.com