With the rapid development of the communication industry, microelectronic devices have been widely used, the integration of communication devices is getting higher and higher, and the withstand voltage level is getting lower and lower [1]. Due to the wide distribution of mobile communication base stations, the location is at the commanding height and is vulnerable to lightning strikes. Lightning is very destructive. Once the communication base station is struck by lightning, it is easy to cause damage to the communication equipment and the communication signal is interrupted, which brings great economic impact to the society. Therefore, it is an important task to do lightning protection for the mobile communication base station.
1 The main route of lightning strike mobile communication station1.1 Lightning intrusion through base station towers and antenna feeders
The average base station tower height is 40~60 m, and some are as high as 70~90 m. When the lightning rod of the tower is subjected to direct lightning strike, the lightning current passes through the iron tower and flows into the ground through the grounding device, causing the ground potential to rise, resulting in a high potential difference between the grounding network and the equipment of the base station to form a ground potential counterattack. Damage to the communication device. If the antenna feeder is a coaxial cable, a strong induced current is induced on the conductor, which is the induced current of the coaxial cable. The induced current enters the base station room through the coaxial cable from the tower antenna, enters the transceiver, and burns out the mobile communication device.
1.2 Lightning intrusion through overhead pipelines
The overhead pipeline of the mobile communication system base station is an important way to introduce lightning damage. When the thundercloud discharges, its space forms a strong electric field. When the overhead pipeline is close to the terminal, the main component is the horizontal electric field. The prominent objects appearing in the electric field are most likely to concentrate on the induced electric charge, so that the surrounding electric field intensity increases remarkably. Overhead pipelines are prone to tip discharges and are struck by lightning. When the overhead pipeline encounters lightning strikes, the overvoltage is introduced into the base station room, which is likely to burn out the communication equipment of the base station. Thundercloud's discharge to ground also induces an overvoltage on the overhead line, which also poses a threat to the power supply.
1.3 lightning electromagnetic induction effect
During the lightning process, the lightning current is high and the discharge time is short. A large instantaneous electromagnetic field will be generated around the lightning receptor and the down conductor. Under the action of a strong magnetic field, a conductor in a magnetic field will generate an induced voltage of up to several thousand to several tens of thousands of volts, and such a high induced voltage potential may cause damage to the communication device. The mobile communication device is a highly integrated device, and the impact resistance is relatively poor, so it is greatly affected by lightning induction.
1.4 Introduction of lightning into the base station equipment room
When the mobile base station room is built on the top of the mountain and the altitude of the computer room is high, the direct lightning strike may bypass the lightning rod and hit the protected object from the lateral and inclined surfaces. This phenomenon is called lightning strike. In this case, isolated lightning rods are often unable to defend against direct lightning strikes on the equipment room. Therefore, the base station equipment room must take the necessary lightning protection measures.
2 Comprehensive lightning protection measures for communication base stations2.1 lightning protection of the tower
At the antenna platform at the top of the tower, a grounding hole should be reserved at the center of the tower and at the base of the tower, or the fastening bolts of the nearby tower should be replaced with long fastening bolts as the grounding point. When the distance between the two adjacent grounding points exceeds 60 m due to the high height of the iron tower, one grounding point should be added between the two points. It is necessary to ensure the number and dispersion of connection points to facilitate the dispersion of lightning current. When the iron tower is a floor tower, the ground network of the tower and the ground network of the equipment room shall be welded and connected to each other at intervals of 3 to 5 m, and at least two places are connected to each other. The four legs of the tower are welded to other ground nets. Mobile communication antennas should have protection against direct lightning strikes. The antenna tower is equipped with a lightning rod and welded to the tower. The antenna should be installed in the lightning protection zone of the lightning rod. The purpose of welding the lightning rod and the iron tower is to ensure that the lightning rod has a good grounding wire to ensure that the lightning current flows into the earth in time.
2.2 lightning protection of overhead pipelines
The overhead lines such as power lines and optical cables connected to the equipment room cannot be directly accessed. They should be classified into the metal tube and buried in the equipment room. If the distance is long, protective devices should be installed at both ends of the power line and cable. The two ends of the metal pipe are respectively welded to the ground wire, and the solder joints are to be treated for anti-corrosion treatment, and the power line and the signal line cannot be mixed. The grounding of each system should be connected to the respective grounding busbars according to the installation requirements, and then connected to the indoor grounding bar. The DC power grounding cable in the equipment room is introduced from the indoor grounding line, independent of the protection ground, and then connected to the grounding busbar, and the leads are not shared.
2.3 lightning protection of the antenna feeder
The feeder shielding layer should be properly grounded at the top of the tower, the feeder from the tower body to the turning point of the machine room 0.5~1.0 m, and the inner side after entering the entrance of the machine room. When the length exceeds 60 m, the grounding point should be increased in the middle, so that the distance between two adjacent grounding points should not exceed 60 m, and the indoor wiring frame should be grounded once every 5~10 m. Some manufacturers require the feeder to enter the room and install a lightning arrester. The installation position of the arrester should be as close as possible to the entrance of the building.
2.4 lightning protection of communication equipment room
The lightning protection problem for the communication equipment room should include the lightning protection grounding of the building in the equipment room, the lightning protection grounding of the equipment room and the power supply system. One is lightning protection and grounding of buildings. The lightning protection network shall be set up in the sky surface of the communication equipment room. The lower corners of the equipment room shall be provided with the down conductor line. The metal facilities on the roof of the equipment room shall be welded to the lightning protection belt respectively. When the antenna tower of the communication station is located next to the equipment room, the ground between the tower and the ground of the equipment room shall be welded and connected to each other at intervals of 3 to 5 m, and at least two of them shall be connected to each other. When the communication station antenna tower is located on the roof of the equipment room, its four feet should be connected to the roof and the lightning current down-conductor respectively. Metal window frames, cable shields, equipment casings, etc. of buildings should also be reliably connected to the main steel bars to form equipotential bodies [4-5]. The second is lightning protection and grounding of the power supply system. Bolted connections shall be made between the equipotential grounding terminal plates in the communication equipment room. The cross-sectional area of ​​the connecting wires shall be multi-strand copper conductors of not less than 16 mm2 and shall be laid through the steel pipes. The cable metal sheath entering and exiting the equipment room should be protected and grounded at the inbound station. The inner core of the cable should be equipped with a lightning arrester at the inbound station. The empty wire pair in the cable should also be protected and grounded. The cable trays in the equipment room should be grounded once every 5 m. The cable trays, hanging irons, racks (or chassis), metal ventilation pipes, metal doors and windows, and other metal pipelines should be well grounded and connected to each other. The power supply transformer of the communication equipment room should not be in the same building as the communication equipment room. If it is installed in the communication equipment room, the length of the high-voltage power cable should be no less than 200 m. At the joint with the overhead power line, the cable metal outer sheath should be near. Grounding, the three phase lines in the cable should be equipped with zinc oxide gapless arresters respectively.
2.5 equipotential bonding
The grounding network of the mobile communication base station shall form a joint grounding network according to the principle of voltage equalization and equipotentiality, and the grounding lines of various types in the base station shall be respectively introduced from the grounding collection line or the grounding network. For the high-altitude resistivity area of ​​the alpine base station ground network, in addition to lowering its ground resistance value, the most important thing is to equipotential bonding, shielding and voltage equalization treatment to achieve uniform potential distribution between the various parts, so that the potential difference It is “zero†to ensure that lightning current will not cause high voltage counterattack to all parts and reduce electromagnetic interference.
2.6 Reduce the grounding resistance value
The national standard requires that the resistance value of the mobile base station should be less than 5 Ω. In the high soil resistivity area, the common methods for reducing the grounding resistance are as follows: First, the multi-branch external grounding device is adopted, and the external lead length should be no more than the effective length; Second, the grounding body is buried in the deep low-resistivity soil; the third is to use a resistance-reducing agent; the fourth is to change the soil. Practice has proved that the method of soil replacement is the best way to improve the soil and reduce the value of grounding resistance. The method is to replace the soil with higher resistivity in the ground net with powdery ore, pond mud, field mud, black soil, clay and other materials with lower resistivity.
Laptops,windows Laptops,win11 Laptops,win10 Laptops
Jingjiang Gisen Technology Co.,Ltd , https://www.jsgisengroup.com