With the progress of society, the rapid popularization of mobile communication technology and development, in every corner of the globe, mobile communication base stations have mushroomed straight into the sky, intervention into people’s daily lives, more and more fast and stable communication Become an important indicator of communication equipment. Mobile communication base station equipment is a cutting-edge microelectronic product, and its electromagnetic compatibility is relatively low, and its anti-lightning and anti-electromagnetic interference capabilities are relatively weak. As the climate changes, thunderstorms and severe weather have become more and more abnormal, resulting in frequent lightning damage to mobile communication base station equipment in various places, communication interruption, and immeasurable losses to people’s lives and various industries. It is more and more important to do a good job in lightning protection of mobile communication base stations and ensure the normal and stable operation of communication equipment. Mobile communication base stations are mainly composed of infrastructure, power supply facilities and communication equipment.
Infrastructure includes: houses, iron towers.
Power supply facilities include: power transformers, power distribution panels, DC panels, UPS power supply systems, and distribution boxes.
Communication equipment includes: antennas, feeders, communication equipment, etc.
2. Design Idea
2.1 Features of Communication Base Station
① Geographical location: It is usually located on the higher floors of tall buildings in urban areas, and is often located in open areas or mountainous areas in suburbs and villages.
②Computer room conditions: Whether in urban or rural areas, a large number of buildings are built in non-dedicated communication buildings. These buildings often do not have the required lightning protection implementation (including external lightning protection devices, internal lightning protection devices, and ground networks, etc.). In addition, the area of the equipment room is generally very small, which is not convenient for the implementation of multi-level lightning protection schemes.
③ AC power supply: Especially in rural and mountainous areas, the AC power supply in the computer room is usually introduced overhead.
④ Communication signal: The communication line of the base station equipment is usually also introduced overhead.
2.2 Several channels for the introduction of lightning to mobile communication base stations
①Lightning damage introduced by the tower antenna feeder and grounding system; ②Lightning damage
introduced by the power supply system;
③ Lightning damage introduced by signal transmission lines.
2.3 Base Station mine design
a mobile communication base station is a power system, an integrated system configuration of receiving / transmitting system, a relay antenna feeder systems and transmission systems, the purpose of lightning protection system is to ensure that each can work, without The interference and destruction of thunder and lightning.
Lightning protection is finally realized through equipotential connection. The position of equipotential connection is selected on the interface of different lightning protection zones, and the energy of lightning strikes is introduced into the earth through the grounding system. The electromagnetic intensity of different lightning protection zones is different, except for the direct strike zone, the internal lightning protection zone is different from the external lightning protection zone due to electromagnetic attenuation. Therefore, appropriate shielding measures can prevent the entry of lightning electromagnetic pulses to a certain extent. Then, the line that crosses the interface of the lightning protection zone becomes the main channel for lightning intrusion. Doing a good job of lightning protection for the line crossing the interface of the lightning protection zone is undoubtedly the focus of overall lightning protection.
In addition to line intrusion and electromagnetic induction, there is also a grounding system through which lightning electromagnetic pulses enter the internal lightning protection zone. When a lightning strike occurs near the grounding grid, the lightning current enters the ground through the grounding wire, and the instantaneous high potential of the grounding grid may strike the equipment through the grounding wire and cause damage. It can be concluded that comprehensive lightning protection not only includes air-termination, but also includes shielding and grounding and other measures that help to safely and reasonably leak lightning current to the earth.
Comprehensive lightning protection is a combination of the four technologies of shunting, voltage equalization, grounding and shielding. However, some base stations are non-standard computer rooms, which are just rented ordinary buildings. The shielding and grounding measures cannot meet the requirements, and it is not realistic to rectify and strengthen the shielding. At this time, the problem of lightning electromagnetic pulse can only be solved from the perspective of rational installation of air-termination and improvement of the grounding system.
According to the principle of comprehensive protection and comprehensive management, a six-point solution for the overall lightning protection of the base station has been explored.
①Control the lightning strike point;
②Safely guide the lightning current into the ground grid;
③Add a complete low-impedance ground grid;
④Make equipotential connection to avoid ground potential counterattack;
⑤Protect power surge impact;
⑥ Surge protection data lines, communication lines and signal lines;
3.1 lightning protection
for the direct lightning protection, diversion may take measures by lightning rods, lightning belts, lightning lightning current network Lead into the ground along the down conductor to prevent direct lightning from hitting the tower or system equipment.
3.1.1 room LPZO
room roof with lightning tape, net or lightning rod receptor as the receptor. The air-termination net (belt) should be laid along the corners, ridges, eaves and corners of the roof that are vulnerable to lightning strikes, and should form a grid that should not be larger than 10m×10m or 12m×8m on the entire roof. The lightning net (belt) and the lead-down connecting line are made of Φ12 galvanized round steel and -40×4mm galvanized flat steel. There should be no less than two down conductors, and they should be arranged evenly or symmetrically along the building’s circumference, and their spacing should not be greater than 18m.
For the newly-built equipment room, the ground wire of the lightning net (belt) should use the diagonal steel bars in the structural column. If the diameter of the steel bars in the column is not less than Φ16, use two diagonal steel bars in the column as the down conductor; if the diameter of the steel bars in the column is less than Φ16, use four diagonal steel bars in the column as the down conductor.
3.1.2 The base station tower LPZO
tower base is at the highest point, is the preferred target of lightning, lightning protection for the tower can be installed OP-B1-type overhead lightning rod, preventing direct lightning hit other devices, lead devices damage.
The air-termination pole should be provided with a special down conductor directly connected to the ground network, when the lightning strikes, the lightning can be quickly introduced into the earth. Down-conductor can use -40×4mm galvanized flat steel. Because the tower is on the top of the building, lightning will be directly introduced into the machine room after lightning strikes. Therefore, the tower ground should be connected to the steel wire mesh on the roof or use more than three galvanized steel. The flat steel is welded to the lightning belt around the machine room.
3.2 Protection of induction mine
Inductive lightning refers to the electromagnetic pulse current generated by the direct coupling between the electromagnetic field generated during the lightning process and the signal lines, power lines, and antenna feeders of various electronic equipment. It also refers to the electrostatic induction current generated by charged thunderclouds on ground objects. The purpose of lightning protection is achieved, and the induced lightning current on the power line, signal line and antenna feeder of the electronic equipment can be guided into the ground through the corresponding induction lightning air-termination device to achieve the purpose of venting the lightning current.
3.2.1 Antenna System lightning protection
Antenna system is an important part of the microwave relay communication, the antenna plays an electromagnetic wave transmitted to the feeder converting the free space propagation of electromagnetic waves or converting the free space propagation It is the effect of electromagnetic waves transmitted in the feeder. The feeder is the transmission channel of electromagnetic waves. In the communication base station, the signal transmission of the antenna feeder directly affects the normal operation of the base station. Therefore, it is very important to protect the antenna and feeder from lightning. The coaxial cable from the base station to the antenna can be led down from the center of the tower, which can reduce the induced current to the coaxial cable when the lightning current after the lightning rod flashes is discharged along the tower, because the four iron pillars of the base station tower discharge lightning at the same time When flowing into the ground, the induction field in the center of the iron tower generated by the induction mine is the weakest. The lightning protection measures for the antenna feeder mainly include:
① The lightning protection of the antenna feeder is three-point grounding from the engineering point of view. The waveguide feeder and the metal outer sheath of the coaxial cable erected on the tower should be at the upper and lower ends, and enter the computer room respectively. The entrance is grounded nearby. When the length of the feeder and coaxial cable is longer than 60m, the shielding layer should be added a grounding connection point in the middle of the tower, and both ends of the outdoor cabling frame should be grounded.
②For isolated tall buildings in cities or wireless communication bureaus (stations) built in suburban and mountainous areas above the minefield, when the feeder adopts coaxial cable, a nominal discharge should be installed at the entrance of the coaxial cable introduction machine room. For the coaxial SPD with current not less than 5KA, the ground lead of the coaxial SPD ground terminal should be connected from the ground wire, lightning belt or ground net outside the entrance of the antenna feeder.
The lightning protection device of the antenna feeder line can adopt PR-F, PR-N, PR-BNC, PR-DIN/4 and other antenna feeder line lightning protection devices according to the interface form, the nominal discharge current ln=10KA, the voltage protection level Up≤600V , Insertion loss≤3dB, standing wave ratio≤1.2.
3.2.2 lightning protection system power
supply system of the base station is an important part of the base station. The power supply of the base station can be entered by an external overhead line, or can be buried in the base station through a tunnel. Because the power cord frame is very long, the line trend is also quite complicated, and it is easy to sense strong lightning current. Therefore, no matter what kind of connection, the power cord should be installed in the LPZ0B area to enter the LPZ1 area with a first-level lightning protection device, and a second-level lightning protection device should be installed in front of the rectifier equipment of the switching power supply, at the UPS power input end And the DC output terminal is equipped with a third-level lightning protection device, and a power supply precision protection is set.
①The PB25-385/B+C/4 power three-phase surge protector can be used at the main power distribution cabinet where the power line enters from the LPZ0B zone into the LPZ1 zone. The test category is Type I test (limp=25kA, ln =25KA, Up=1.8KV, Uc=385V). The front end is connected in series with a 63A power circuit breaker, the length of the PE wire of the surge protector should not be greater than 0.5m, and the 16mm2BVR copper core wire is used for the nearest grounding.
②PC40-385/4 power supply three-phase surge protector can be used at the power distribution cabinet, and the test category is Type II test (ln=20KA, Up=1.7KV, Uc=385V). The front end is connected in series with a 32A power circuit breaker, and the length of the PE wire of the surge protector should not be greater than 0.5m, and the 10mm2BVR copper core wire is used for the nearest grounding.
③ PD20-275/4 power supply three-phase surge protector can be selected at the UPS power inlet end, and the test category is Type II test (ln=10KA, Up=1.2KV, Uc=275V). The front end is connected in series with a 32A power circuit breaker, the length of the PE wire of the surge protector should not be greater than 0.5m, and the 6mm2BVR copper core wire is used for nearby grounding.
④PC40-85VDC DC power surge protector can be used at the DC screen. The test category is Type II test (ln=20KA, Up=0.5KV, Uc=85VDC). The length of the PE wire of the surge protector should not be greater than 0.5m, and the 6mm2BVR copper core wire should be grounded nearby.
⑤The PDU1-J1G08/16 power distribution unit surge protector can be used at the equipment power supply in the computer room, and the test category is Type II test (ln=5KA, Up=1.2KV, Uc=275V). The length of the PE wire of the surge protector should not be greater than 0.5m, and the 6mm2BVR copper core wire should be grounded nearby.
3.2.3 Signaling System lightning protection
signals given a major system functions of the base station signal transmission, good lightning signal system is also very important. The lightning protection measures of the signal system mainly include:
① For optical cables or cables entering and leaving the communication bureau (station), the metal armor outer sheath should be grounded in the entry room, and the metal components in the cable should be grounded at the terminal;
②The signal line entering the communication bureau (station) should be equipped with SPD at the terminal, and the empty line pair must be grounded nearby.
The communication system is restricted by the working level, interface rate, transmission performance (insertion loss), line impedance and other indicators, and cannot be divided into several levels of lightning protection like the power supply system. Therefore, the signal line lightning protection should be at the interface of the communication line and the device. That is, the LPZ1-LPZ2 zone uses a fine-level lightning arrester with its communication interface, working level, speed matching, and line impedance matching. At the same time, the communication line should be grounded nearby.
SNH-RJ45/16 network signal surge protector can be used for signal line lightning protection, and the test category is Type II test (ln=3KA, Up≤25V, Uc=6V). The length of the PE wire of the surge protector should not be greater than 0.5m, and the 6mm2BVR copper core wire should be grounded nearby.
3.2.4 Inductive lightning protection of the monitoring system
In recent years, China Mobile base stations have generally adopted intelligent monitoring systems. According to statistics, the monitoring system equipment has become the most frequently damaged equipment in mobile base stations by lightning, and it is also the most severely damaged system. There are no lightning protection measures for the power and signals of the monitoring equipment, and the withstand voltage level is low; the monitoring system has a large number of data collection lines, which are not standardly laid out, and are often bundled together, and many data collection lines are not shielded cables; It is said that the complicated wiring of the monitoring system provides more channels for lightning current intrusion, which forms a huge contrast with its weak protection ability. Therefore, the main lightning protection measures for the mobile base station monitoring system are:
①The monitoring data collection line The layout should be reasonably planned. All data collection lines should use shielded wires, and the shielding layer should be grounded to reduce the lightning current induced by lightning electromagnetic pulses on the data collection lines as much as possible;
②Set a small under the main monitoring device The grounding reference point of the monitoring equipment is used as the grounding of all monitoring equipment, and the grounding wire exceeding 16mm2 is used to connect to the total equipotential row of the base station. The purpose is to reduce the potential difference between the monitoring equipment due to grounding, and install the corresponding power surge protector at the monitoring equipment end to release the lightning current introduced from the ground or power line;
③In some equipment with high frequency of damage The communication port between the monitoring equipment is equipped with a suitable signal line lightning protection device. The data acquisition line and control line of the monitoring system are signal lines. Therefore, when choosing a lightning protection device, consider the interface type and work of the signal line lightning protection device. The voltage, transmission rate, and line impedance are matched with the system equipment;
④SV-BNC video signal lightning protection device is installed at the front end of the monitoring host, and the test category is Type II test (ln=3KA, Up≤40V, Uc=12V). The length of the PE wire of the surge protector should not be greater than 0.5m, and the 6mm2BVR copper core wire should be grounded nearby;
⑤Install the OP-SV3/24 three-in-one surge protector in front of the camera to protect the power line, signal line and control line of the camera against lightning. The test category is Type II test, and the power supply parameters are (ln=5KA, Up ≤900V, Uc=275V), the control signal parameters are (ln=3KA, Up≤40V, Uc=12V). The length of the PE wire of the surge protector should not be greater than 0.5m, and the 6mm2BVR copper core wire should be grounded nearby.
3.3 and equal potential shield room
in the engine room are set around a pressure ring, as the ground lines of the communication device and the lightning discharge convergence and reliable grounding device connected to the outdoor. The material of the equalizing ring is 30*3 copper bar. Equipotentially connect all metal objects around the computer room, such as the doors, windows, and the steel bars inside the walls of the computer room, to make it a shielding net, which can reduce the occurrence of lightning to a certain extent, the external induced lightning, lightning electromagnetic pulse Damage to various equipment in the computer room.
3.4 Ground station system
of the mobile communication base station shall equalizing, equipotential principle, joint grounding system, grounding lightning protection, low voltage distribution system (protection) ground, grounding, the grounding shield, an equipotential grounding system common grounding. For base stations with iron towers, the ground grid of the tower should be welded to the ground grid of the machine room. When connecting the ground wire of the general ground bar of the machine room to the ground grid, avoid the dedicated down conductors of the tower and the air-termination rod. The distance between the two should be greater than 5 Meter, so as to prevent the lightning current on the tower and air-termination pole from flowing into the equipment room along the lead-in line of the general ground wire. For some base stations of rented buildings or civil buildings, the reinforced concrete foundation is generally used as the ground network for the grounding of the building. The reinforced concrete foundation of the building is buried deep, and the grounding resistance of the building can basically meet the requirements, so it can be used The main steel bar of the building serves as a lightning protection grounding system. The power frequency grounding resistance should be controlled within 10 ohms. If the grounding resistance of base stations in mountainous areas is difficult to meet the requirements, the resistance can be reduced by using resistance-reducing materials.
Set up a grounding bar at the external wire hole of the mobile base station and connect it to the base station ground network. Connect the grounding of all cables that enter the base station, such as the grounding of the antenna feeder, the grounding of the wire rack of the tower, the grounding of the fiber optic cable reinforcement core, and the grounding of the shielded pipe of the power supply line. The power cables (lines) and communication cables entering and exiting the communication bureau (station) should be metal sheathed cables or laid in metal pipes, and should be buried in the ground, and the buried depth of the cables should not be less than 0.7m. Especially the low-voltage power cables entering the communication bureau (station) should be buried in the whole process, and the buried length of the cable should not be less than 15m. These engineering measures have a certain lightning protection effect.
The material selection of the grounding device, the metal grounding body should be made of hot-dip galvanized material. Since the original hot-dip galvanized layer has been destroyed at each welding point, anti-corrosion treatment must be done. The length of the vertical grounding body is 1.5-2.5m, and the interval of the vertical grounding body is 1.5-2 times of its own length. The upper end of the grounding body is not less than 0.7m from the ground, and it should be under the frozen soil layer. The vertical grounding body can be made of ∟50*50*5mm angle steel or grounding copper rods, and the horizontal grounding body and grounding lead-in can be made of -40*4mm flat steel and grounding modules, and materials such as resistance reducing agents can be added to reduce the grounding resistance.
Schematic diagram of lightning protection for mobile communication base stations