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Lightning protection principle and engineering design of wireless communication base station (1)
Lightning and thunder is a natural phenomenon. The communication stations and stations caused by the enormous energy released are interrupted, and the communication facilities are damaged. Their destructive and economic losses are very huge and catastrophic; the competition in the communications industry is intensifying. Today, lightning strikes have caused communication disruptions, system paralysis, and the impact on corporate social benefits are even more difficult to assess. Fortunately, from 1749, American scientist Flinn researched lightning and invented lightning rods. As far as humans are concerned, the research and exploration of the destructiveness of lightning strikes has already established a more mature theory in taking precautionary measures. Design can minimize the harm of lightning. The mobile communication system includes wireless devices: a computer room, a station, an iron tower, an antenna feeder, etc., and the antenna feeder system is set up high, and it is easy to introduce lightning. Therefore, the lightning protection of mobile communication base stations is particularly important.
1. The main ways for mobile communication base stations to introduce lightning
Taking a negative thundercloud as an example, due to the induction of negative clouds in the electric cloud, positive charges are accumulated on the nearby ground and a strong electric field is formed between the ground and thunderclouds. When the density of charges accumulated in a certain place is large, the strength of the excited electric field reaches an air-free state. When the critical value of (air breakdown) is reached, the thundercloud starts to discharge downwards, and when the ground object reaches a certain distance, the ground object generates a tip discharge under the action of a strong electric field, forming a gradual upward discharge in the direction of the thundercloud. The combination of the two forms a thunderbolt path, and the heterogeneous charge violently neutralises to form a large lightning current and emits intense lightning and lightning strikes. The lightning damage usually has the following manifestations: direct lightning strikes - discharges between charged clouds and the earth, trees, buildings or other facilities, so that lightning currents generate thermal effects and electrodynamic forces on buildings or facilities Inductive lightning - In the direct lightning strike discharge process, the lightning current will produce electrostatic induction and electromagnetic induction. The powerful pulsed current generates a transient strong magnetic field around it, generates electromagnetic induction on the surrounding wires or metal objects, and induces electromotive force. The lightning current is related to the steepness of the lightning current, and the induced high voltage results in the occurrence of an occultation; lightning intrudes into the wave. When the lightning occurs, the lightning current generates an impulse voltage through metal objects such as overhead lines or metal pipes in the sky, and rapidly spreads as the object moves. , forming a hazard. In the lightning protection of mobile communication sites, there should be a targeted understanding of the causes and hazards of lightning, and find out the main ways for the base station to introduce lightning.
1.1 The introduction of lightning in power lines or other overhead lines: Overhead cables in base stations of mobile communication systems are one of the important ways to introduce lightning. On the one hand, when the overhead power line is near the terminal, the main component is the horizontal electric field. According to the electrostatic theory, the relationship between the surface charge distribution and the radius of curvature is "", that is, the surface has a smaller radius of curvature and the surface charge density is relatively large. The protruding objects in the electric field are most susceptible to the concentration of induced electric charges, which causes the electric field strength around them to increase significantly. Overshoots of overhead power lines or other overhead lines will cause tip discharges and be struck by lightning, introducing lightning overvoltages. The base station room is likely to burn the base station master. On the other hand, when a lightning strike occurs, even if it discharges to ground, a higher voltage will be induced on the overhead power line according to the theory of electromagnetic field, which poses a threat to the equipment and is particularly likely to cause damage to the AC/DC power supply base of the base station; Reasonably, similar over-voltages may be generated when there are other overhead lines.
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