Most mobile base stations are built in high places, such as high mountains, suburbs, and buildings. The antenna of the base station is often higher than the existing lightning arrester of the building, which becomes a high incidence of lightning strikes. Therefore, for the lightning protection of mobile base stations, not only the protection against direct lightning strikes, but also the protection against lightning induction and the protection against lightning wave invasion, shielding of communication lines and establishing a good grounding system, reducing grounding resistance, Equipotential bonding to avoid ground potential counterattack.
In order to prevent the smart antenna of the mobile base station from being struck by lightning, a highly suitable lightning rod can be welded on the main pole of the base of the mobile base station, so that the lightning rod sufficiently protects the smart antenna scattered at a 90-degree angle, and the lightning rod and the sky are welded with 95 mm twisted pairs Lightning protection zone. If conditions permit, an optimized lightning rod can be set at a position about 3 meters away from the antenna support. The height of the lightning rod should keep the base station antenna within its protection range. The specific calculation method can be based on the antenna height and refer to the rolling ball method. In this way, the lightning rod is separated from the antenna. Before the lightning develops into a discharge, due to the strong electric field strength near the lightning rod tip, a continuous discharge path can be generated in time and merged with the downward leader of the thundercloud to attract the lightning current to itself and pass The down-conductor and grounding device safely discharge the lightning current into the ground, effectively protecting the base station antenna and the main equipment. The material selection and technical specifications of the lightning rod can be determined according to the surrounding environment of the mobile base station and the local climate.
Inductive lightning is that when lightning is discharged between thunderclouds and thunderclouds to the ground, electromagnetic induction occurs in nearby outdoor power lines, transmission signal lines, and equipment connection lines and invades the equipment, causing serial connection in the middle or damage to terminal equipment. . Lightning wave intrusion refers to the lightning wave that intrudes along the transmission line by direct strike or electromagnetic induction and electrostatic induction. According to the wave transmission theory, the change in the wave impedance of a lightning wave during transmission will cause reflection and refraction, which can cause the voltage at the sudden change of the wave impedance to increase, generate surges, and increase the damage to the equipment. The hazards of mobile base stations from inductive lightning and lightning waves are mainly induced overvoltage waves and lightning electromagnetic pulses that enter the device through the electromagnetic coupling or electrostatic induction of power lines, signal lines, antenna feeders connected to the base station's main equipment. Therefore, it is necessary to install corresponding lightning arresters on various interfaces of the power line, signal line and antenna feeder of the base station equipment.
At present, the AC power of mobile base stations is mainly provided by the municipal power grid. Due to the instability of the municipal power grid and power outages, as well as the harsh working environment of the mobile base station and harsh conditions, the possibility of surges and lightning overvoltage damage to the municipal power grid is relatively high. Big. Therefore, the power system in the base station must be protected in stages. First, install a 80-120kA power lightning protection box at the base station mains entrance, and then install a 40-60kA power lightning protection module in the AC power distribution cabinet, so that the residual voltage is minimized and communication is protected. The equipment power system is safe.
In order to avoid the inductive lightning current and lightning waves from the base station antenna feeder line intruding into the base station main equipment and damaging the electronic board of the equipment, the antenna feeder line should be connected in series with the antenna feeder lightning arrester. The working frequency and interface mode of the arrester should be compatible with the working requirements of the antenna feeder of the station, and a high-pass filter design should be used to effectively reduce the insertion loss without affecting the base station's signal transmission and reception. A general mobile base station has six antenna feeders that receive signals from different angles. Therefore, each line needs to be connected with a lightning arrester in series.
The signal lines of the mobile base station are laid over a long distance in the sky before entering the main equipment of the base station, thereby increasing the probability of inductive lightning intrusion. In order to avoid the intrusion of inductive lightning from the signal line, a signal arrester can be installed in some base stations. The arrester should have a two-stage protection device that can be protected from induced overvoltage and transient surge voltage caused by lightning strikes, which can minimize the residual voltage and parasitic capacitance. And quick response capabilities. At the same time, the signal line should be shielded with a certain length of metal tube on the sky.
Grounding is the most important part of lightning protection technology. Whether it is direct lightning protection, side lightning protection or induction lightning protection, the lightning current is finally introduced into the ground safely. Therefore, it is impossible to avoid lightning without a reasonable, proper and good grounding device. The mobile base station connection system should adopt joint grounding, that is, antenna lightning protection grounding, base station equipment protection ground, base station equipment working grounding, various lightning arrester grounding and other grounding systems are combined into one grounding system, but the lightning rod grounding should be introduced separately from other grounding and combined grounding devices The distance between the two grounding points should be up to 5 meters. The grounding resistance of the joint grounding network must not be greater than 10Ω.
(1) Lightning rod lightning protection grounding can be made of -40 × 4 galvanized flat steel, which is led to the lightning protection belt from the two directions on the base of the lightning rod; and reliable electrical welding with the lightning protection belt, the down conductor of the lightning protection grounding is also It should be connected to the lightning protection zone by welding.
(2) Install a joint grounding copper bar on the metal member of the antenna base. Connect the metal shields of signal and power lines, the metal case of the base station equipment, the grounding of antennas, power supplies, and signal arresters, and the grounding of the metal parts of the antenna frame to the joint grounding copper with a cross-sectional area of 10 mm2. On the row.
(3) The 35mm2 insulated copper core wire (or -40 × 4 galvanized flat steel) from the joint grounding bus bar is welded to the ground point of the joint grounding grid. This 35mm2 copper core wire (or -40 × 4 galvanized flat steel) is called the base station equipment ground lead-in wire.
(4) In some rented residential houses, if there is no grounding, a qualified joint grounding grid must be built. The grounding resistance of the grounding grid must be less than 4Ω.
If the ground resistance does not meet the requirements, a ground resistance reduction module can be used; in areas with high soil resistivity, the use of a resistance reduction module can effectively reduce the ground resistance, and can also effectively reduce the engineering cost.
The resistance reduction module is mainly composed of non-metallic materials with good electrical conductivity and stable chemical properties, and conductive electrolytic media. Its built-in galvanized metal rods are connected to the protected ground wire, and the effective contact area between the metal ground body and the ground It will greatly increase, and because the resistance reducing module is connected to the metal ground wire, the contact resistance between the metal grounding body and the ground will be greatly reduced, so that the resistance reducing function of the grounding module is fully exerted, and the lightning current can be quickly discharged into the ground.
Due to the diverse construction environment of mobile base stations, the environment of each base station is different, and the number of mobile base stations is large. The lightning protection installation of base stations should be implemented in accordance with the principles of high efficiency, science, security, and local conditions to ensure that customer needs are met.
Before the lightning protection installation and construction, check whether the mobile base station works normally. If it is normal, perform the installation and construction according to the following steps. Otherwise, the fault of the base station equipment must be eliminated before installation and construction can be performed.
(1) Test the grounding resistance of the building where the base station is located and make a test record (the grounding resistance should be less than 4Ω).
(2) Install a lightning rod.
(3) Determine the specific location of the optimized lightning rod according to the base station antenna.
(4) Tighten the lightning rod base and the roof floor with expansion screws, and install the lightning rod bracket and the lightning rod body at the same time.
(5) Use -40 × 4 flat steel to weld the lightning rod base to the lightning conductor to the lightning protection zone of the building or weld it to the joint grounding grid.
(6) Install the grounding copper busbar at an appropriate position on the antenna base, or connect the grounding wire directly to the grounding hole of the bracket without the busbar.
(7) Disconnect the power of the base station (unplug the power switch of the base station power), and at the same time disconnect the power protective ground wire connected to the chassis in the base station.
(8) Shield the metal tubes of the power and signal cables, and at least two points of the shielding tube are grounded, and they can be soldered to the lightning protection tape.
(9) Disconnect the 220V power line, install the UPS power supply, and then combine the power supply signal with a lightning arrester, connect the power supply in series, and the signal line is close to one end of the device.
(10) Connect each antenna feeder lightning arrester string into the antenna feeder close to the device.
(11) Connect the antenna feeder, power supply, signal arrester ground wire, and equipment protective ground wire to the ground bus bar.
(12) Seal the connection of the lightning arrester of the antenna feeder with waterproof tape, and seal the power supply signal lightning arrester in and out of the cable and the interface with the outside.
(13) Organize the protective ground wire with cable ties or plastic sleeves.
(14) Coat each solder joint with an anti-rust material.
(15) Turn on the power of the base station, wait for the base station to resume work, and perform testing for the calling and called parties. If the operation is normal, clean the installation site and clean up the installation tools to complete the installation of the arrester device.
(16) If the base station equipment works abnormally, check the arrester grounding sequence and line correspondence and contact the relevant technical personnel of the telecommunications company.
(1) The location of the optimized lightning rod should be about 3 meters from the base station antenna, and the base station antenna should be within the protection range of the lightning rod.
(2) All solder joints should be rust-proofed.
(3) The power supply, signal, antenna feeder grounding cables and equipment working grounding cables must be connected reliably. When multiple strands of ground wires are connected together, they are crimped together with cold copper ears and soldered, and then fixed to the grounding copper bus bar through the copper ears with bolts.
(4) It is strictly prohibited to use roof water pipes, outdoor air-conditioning units, solar water heaters, metal cooling towers and other metals as the base station ground. For mobile base stations that do not have a ground network or a substandard ground network, a new ground network or a rectification of the base station ground network should be passed.
(5) For the interfaces of antenna feeder arresters, each interface should be waterproofed in the same way as the base station equipment. The input and output terminals of the power supply and signal lightning arresters should also be waterproofed.
(6) Separate power lines and signal lines.
(7) The power arrester and the signal arrester should be assembled together in a sealed iron box that is waterproof and sunproof.
Lightning protection engineering is a systematic project, so effective protection cannot be based on a single protection measure. If only the protection against direct lightning is considered, and other induction lightning parts are not protected or the protection measures are insufficient, the lightning induced overvoltage and lightning electromagnetic pulses will invade the base station equipment from various lines. In addition, if the grounding system is not processed well, then The entire lightning protection system did not play a safety role. Therefore, we should carry out comprehensive lightning protection design for the mobile base station's lightning protection design principles, and adhere to measures such as "flashover, shielding, equipotential connection, voltage equalization, shunting, grounding, and reasonable wiring" for comprehensive lightning protection.