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1. The AC power supply system of the mobile communication station should adopt the three-phase five-wire system power supply mode.
2. The mobile power station should be equipped with special power transformers. The power lines should be metal piped or insulated jacketed steel pipe buried in the ground and introduced into the mobile communication station. Both ends of the power cable metal sheath or steel pipe should be reliably grounded.
3. When the power transformer is installed outside the station, the lightning resisting line (except for the terminal rod) shall be within the protection range of the lightning protection line within 25° when the annual thunderstorm day is more than 20 days and the earth resistivity is greater than 100Ω·m. Each pole should be grounded as shown.
To ensure safety, a group of zinc oxide surge arresters should be added to the front pole of the lightning protection terminal rod. If it is difficult to use the lightning protection line for lightning protection reconstruction of overhead high-voltage power lines that have been established, a set of zinc oxide surge arresters may be added to the first, third, or fourth rod in front of the terminal Rods of the overhead high-voltage power lines. The third or fourth rod adds a set of high voltage fuses. The grounding body of the lightning conductor and the arrester should be designed to be radial or annular.
4. When the power transformer is installed in the station, the high-voltage power line should use the power cable to enter the station from the ground. The length of the cable should not be less than 200m. The three phases of the connection between the power cable and the overhead power line should be installed with a zinc oxide surge arrester. Cover should be grounded nearby.
5, mobile communication base station AC power transformer high voltage side of the three phase line, respectively, should be installed on the ground near the zinc oxide arrester, power transformer low voltage side of the three phase line should be installed on the ground without gaps zinc oxide arrester, transformer low voltage side of the chassis The AC neutral wire, and the metal outer sheath of the power cable connected to the transformer, should be grounded nearby. All power lines entering and exiting the base station should be equipped with surge arresters at the exit.
6. The low-voltage power cable entering the mobile communication base station should be introduced into the equipment room from the underground, and its length should not be less than 50m (when the transformer high-voltage side has adopted the power cable, the length of the low-voltage side power cable is not limited). The arrester should be installed on the power cable into the AC screen of the equipment room, and the zero line drawn from the screen should not be grounded repeatedly.
7. The ground terminal of the normal uncharged metal partial arrester of the mobile communication base station power supply equipment should be used as the protection grounding. It is forbidden to perform zero protection.
8. The DC ground of the mobile communication base station should be connected from the indoor ground collection line. The cross-sectional area of ​​the grounding line should meet the requirements of the maximum load, generally 35-95m2. The material is a multi-strand copper wire.
9, mobile communication base station power supply equipment should meet the requirements of the relevant standards and regulations on lightning impulse indicators, AC screen rectifier (or high frequency switching power supply) should be provided with graded protection device, as shown in the figure.
10. It is recommended to use the power supply lightning protection box DS150E (140KA8/20us) produced by CITFL in France for the three phase lines and neutral lines led to the distribution panel. The response time is fast (25ns) and the residual voltage is low (700V-800V). The internal structure of the box is a composite lightning arrester with two poles and MOVs connected inductively. It is generally installed in a low-voltage power distribution cabinet. Do not emphasize that the neutral line in the screen is not grounded repeatedly. The neutral line (neutral line) in the AC power supply line laid in the building shall be insulated from the normal uncharged metal part of the rack.
11. Each shunt switch in the power distribution panel should also be connected with the corresponding type of power lightning arrester. The rated load of the switch exceeds 200A. It is recommended to use DS150E (140KA) or LA60-B (10/350us70KA); DS100R is recommended between 100A-200A. For V25B (100KA), 100A-63A is recommended to use DS70B or V20C/4 (70KA); below 50A, DS44 or V20C/2 (40KA) is recommended.
12. The AC input terminals of important electrical equipment (such as UPS rectifier high-frequency switching power supply precision air conditioner) also use different types of power surge arrestors (DS150E-DS44 or LA60-B-V20C/2) according to their capacity.
13. The DC side of communication power supply or high-frequency switching power supply is recommended to be protected by the national OBO product V20C/0-75V low voltage arrester.
Lightning Protection Engineering Step 2. Lightning Protection and Grounding Requirements of Antenna Feeder System for Mobile Communication Base Stations
1. Within the protection range of the air-termination device of the mobile communication base station antenna, the lightning receptor shall be provided with dedicated lightning current down conductor. The material should adopt 4×40 galvanized flat steel.
2. The metal outer sheath of the base station coaxial cable antenna feeder should be grounded at the entrance of the upper part, the lower part, and the cable rack into the machine room. The grounding at the entrance of the machine room should be properly connected to the grounding wire drawn from the ground network. When the tower height is greater than or equal to 60m, the metal sheath of the coaxial cable antenna feeder should also be grounded in the middle of the tower.
3. The lightning arrester for the feeder should be installed at the connection point of the coaxial cable antenna feeder and the communication equipment after entering the equipment room. In case of induced lightning from the antenna feeder. The feeder lightning arrester grounding terminal should be connected to the outdoor to the feeder grounding line. When selecting the lightning arrester for the feeder, the indicators such as impedance, attenuation and operating frequency band should be matched with the communication equipment. The COAX series of coaxial cable protectors produced by British MARSE Co., Ltd. is designed and manufactured to protect equipment connected to antenna feeders. Its operating frequency can be as high as 2.5GHZ, loss 0.5dB, residual voltage is 20V, 35V, 65V, etc. 50Ω, 75Ω, as shown in the figure.
Lightning Protection Engineering Step 3, Lightning Protection and Grounding Requirements for Signal Lines of Mobile Communication Stations
The signal cable shall be moved underground and out of the mobile communication base station. The cable inner core shall be equipped with a corresponding signal lightning arrester at the entry and exit points. The arrester and the empty line in the cable shall be protected. It is forbidden to place overhead cables in the station area.
For new signal cables located on the annual thunderstorm day of more than 20 days and the earth resistivity greater than 100Ω.m, the drainage line or the cable with metal sheathing above the cable should be adopted, or the cable can be used to prevent lightning strikes. .
For paging station GSM station communication equipment, at present, the local area long-range wide area network has been generally applied, and more Norwegian networks and Ethernet are used, and the speed has reached 10Mbaud. Soon it will be expanded to 60M and even over 100M baud. For devices that are often exposed to lightning and overvoltage hazards, such as: digital encoders, network cards, modems, automatic queues, AT multifunction cards, transmitters, antenna converters, program-controlled switches, terminals, servers, etc., signal input terminals or The network connection should be protected according to its transmission speed, impedance characteristics, and interface characteristics.
Lightning Protection Engineering Step Four: Lightning Protection and Grounding Requirements for Mobile Communication Base Towers
1. The mobile communication base station tower should have perfect lightning protection devices against direct lightning and secondary induction lightning.
2. Mobile lightning protection engineering steps Step 4: Lightning protection and grounding requirements of the mobile communication base station tower 1. The mobile communication base station tower should have perfect lightning protection devices against direct lightning and secondary induction lightning.
2. Towers of mobile communication base stations should use solar tower lights. For aeronautical obstruction signal light using AC feeders, the power cord should be used with a cable with a metal outer sheath. The outer metal sheath of the cable should be grounded on the outside of the tower top and the entrance to the machine room. The tower light control line and power line should be installed on the ground at the entrance of the machine room respectively. The neutral line should be directly grounded. as the picture shows.
Lightning Protection Engineering Step 5, Lightning Protection and Grounding of Other Facilities
1. The building of a mobile communication base station should have perfect lightning protection and lightning protection devices (lightning protection network, lightning protection zone, and lightning receptor) that can prevent secondary lightning.
2. All kinds of metal facilities on the top of the equipment room should be connected to the roof lightning protection belt respectively. The lantern on the top of the house should be installed under the lightning protection zone.
3. The cabling racks, wire racks, racks or cabinets, metal ventilation ducts, and metal doors and windows in the equipment room should all be protected and grounded. Protective grounding wire should generally use multiple copper conductors with a cross-sectional area of ​​not less than 35mm2.
Lightning Protection Step 6 Joint Grounding System of Mobile Communication Base Stations
(1) Composition of the ground network 1. The mobile communication base station shall form a joint grounding network with the working ground, the protection ground and the lightning protection ground in accordance with the principles of voltage equalization and equal potential. All types of grounding wires in the station should be separately introduced from grounded collection lines or grounding nets.
2. The ground network of the mobile communication base station consists of the equipment room ground network, the iron tower ground network and the transformer ground network. The composition of the ground network is shown in the figure. The base station ground network should make full use of the foundation of the equipment room building (including ground piles), the main steel Bars in the iron tower foundation and other underground metal facilities as part of the grounding body. When the tower is installed on the roof of the engine room and the power transformer is installed in the engine room, the ground network can be used in the ground of the equipment room.
3, the computer room ground network composition: room ground network should be along the computer room building water point peripheral ring grounding device, but also should use the room building structure horizontal and vertical beams within the two main reinforcements together to form the engine room network. When there are ground piles in the building of the equipment room, two or more main steel bars in the ground pile should be welded to the ground of the equipment room.
When the equipment room is equipped with an anti-static floor, a closed ring-shaped grounding wire should be laid around the equipment room under the floor as the grounding wire of the floor metal bracket. The material is copper wire and the cross-sectional area should not be less than 50 mm2. No less than two copper grounding conductors with a cross-sectional area of ​​50 to 75 mm2 are connected to the south, north or east and west sides of the lead row.
4. For mobile communication base stations that use commodity housing as the engine room, they should try to find out the building lightning protection grounding network or other special ground network, and then set up a set of ground networks nearby. The three are connected to each other in the underground and can communicate with each other in case of difficulty. The ground can be seen as part of the welding as a room network. When the original ground network cannot be found, a group of ground networks should be set up nearby for local conditions as the work place of the engine room, the protection site and the lightning protection tower. The distance between the contact points on the work place and lightning protection ground shall not be less than 5m, and the tower should be connected to two or more nearby lightning protection zones of the building.
5. The composition of the tower network: When the communication tower is located next to the machine room, the tower network should extend to the foot of the tower at a distance of 1.5m away. The grid size should not exceed 3m × 3m, and its perimeter is closed. It is also necessary to use two or more main steel bars in the tower base pile as the vertical grounding body of the iron tower ground net. The iron tower ground net and the machine room ground net should be welded and connected once every 3~5m. The connection point should not be less than two points. When the communications tower is located at the top of the engine room, the four legs of the tower should be connected to at least two nearby lightning protection belts. At the same time, radiation grounding devices should be installed at the four corners of the machine room network to distribute the current.
6, the composition of the transformer ground network: when the power transformer is installed in the engine room, the ground network can be used in conjunction with the ground network consisting of the engine room and the tower network; when the power transformer is installed outside the machine room and within 30m from the edge of the computer room network Between the transformer ground network and the equipment room ground network or the iron tower, they shall be welded and connected once every 3~5m (at least two places are connected) to form a perimeter-closed ground network.
7. When the grounding resistance value of the local network does not meet the requirements, the area of ​​the ground net can be expanded, that is, one ring or two ring grounding devices can be added to the periphery of the ground net. The ring grounding device is composed of a horizontal grounding body and a vertical grounding body. The horizontal grounding body and the grounding network should be on the same horizontal plane. The ring grounding device and the ground network and the ring grounding device should be welded and connected once every 3 to 5 m. Can also be set in the four corners of the tower radiation extended grounding body, the length of the extended grounding body should be limited to within 10 ~ 30m.
(b) grounding body
1. The grounding body should adopt hot dip galvanized steel. The specifications are as follows:
Steel pipe Φ50mm, wall thickness should not be less than 3.5mm
Angle steel should not be less than 50mm × 50mm × 5mm
Flat steel should not be less than 40mm x 4mm
2. The length of the vertical grounding body should be 1.5~2.5m, and the vertical grounding body spacing should be 1.5~2 times of its own length. If you encounter uneven soil resistivity, the lower soil resistivity can be properly lengthened. When the vertical grounding body is difficult to bury, a plurality of ring-shaped horizontal grounding bodies may be provided, spaced from each other by 1 to 1.5 m, and each of the rings should be welded and communicated with each other every 3 to 5 m.
3, in the coastal areas with strong salinity corrosion or high earth resistivity is difficult to meet the resistance requirements of the area, the grounding body should adopt a non-metallic grounding body with corrosion resistance, good moisturizing performance.
4. All welding points between grounding bodies shall be treated with anti-corrosion treatment except pouring into concrete. Welding length of the grounding device: 2 times the width of flat steel and 10 times the diameter of round steel.
5. The upper end of the grounding body should not be less than 0.7m above the ground. In cold regions, the grounding body should be buried below the frozen soil layer.
(c) Ground and ground lead-in
1, the grounding line should be short, straight, load area of ​​35 ~ 95mm2, material for multiple strands of copper wire.
2, the length of the grounding lead should not exceed 30m, the material is galvanized flat steel, cross-sectional area should not be less than 40mm × 4mm or not less than 95mm2 stranded copper wire. The grounding lead-in line shall be treated with anti-corrosion and insulation, and shall not be placed in the heating trench. When burying, the sewage pipeline and the ditch shall be avoided, and exposed to the above-ground part, and measures shall be taken to prevent mechanical damage.
3. The grounding lead-in line is led from the center of the ground network to the nearby grounding collection line in the equipment room. For new stations, it should not be less than two. See the figure for details.
(four) grounding collection line
The grounding collection line is generally designed as a ring or a row, and the material is copper. The cross-sectional area should not be less than 120 mm2. Galvanized flat steel with the same resistance value can also be used.
The grounding collection line in the equipment room can be installed in the ground tank, wall or cable rack, and the grounding collection line should be insulated from the building rebar.
(five) grounding resistance
1. The grounding resistance of the base station network of mobile communication base stations should be less than 5Ω. For areas where the annual thunderstorm day is less than 20 days, the grounding resistance can be less than 10Ω.
2. The protective grounding at the interface between the overhead power line and the power cable and the grounding resistance value of the power transformer (below 100KVA) protective earthing should be less than 10Ω.
3. The grounding resistance value of the lightning protection line above the overhead power line and the arrester installed on the high-voltage line should be less than 10Ω at the head end (ie, the inbound side) and 30Ω at the middle or end.
(6) Measures to prevent SPG from counterattacking DCG ground potential
At present, the IEC standard and the international GB50057-94 all recommend the use of a comprehensive ground network. However, some units and certain equipment manufacturers still emphasize the use of an independent DC grid. According to statistics from relevant international experts, microelectronic equipment has suffered lightning damage, and about 60% is counterattacked from the ground potential. Therefore, for the current specific situation, the following measures to prevent the SPG from counterattacking the DCG ground potential are proposed.
Assume that the SPG grounding resistance value of the common lightning protection ground of the building is 4Ω. A medium (40KA) direct lightning strike hits the building's roof lightning protection needle system, and the 40KA lightning surge current passes through the lightning conductor and the down conductor (possibly the building structural reinforcement). The ground net leaked into the earth and formed an instantaneous voltage drop of 4×40000=160kv on the grounding wire grounding resistance (4Ω), ie 160,000 volts high voltage. The microelectronic equipment in the equipment room is normally uncharged with metal housing protection ground (SPG). At this time, the potential is 160KV, and the internal circuit of the microelectronic equipment is connected to DC ground (DCG). Its potential is "0" volt, both inside and outside the microelectronic equipment. Potential difference of 160KV high voltage, will destroy no doubt! And it is the destruction of a large number of equipment in the engine room.
It is necessary to maintain the superiority of the anti-interference of the DC working ground network that is independently set, but also to prevent the destructive ground potential counterattack when the building is hit by lightning. The most reasonable measure is to connect the protector at the point where DCG enters room C. SGP1 (100KA) or low-voltage power supply arrester DC98 (220V), whose grounding point is connected to point D of the SPG system. In the vast majority of situations without direct lightning strikes, because the gas discharge tube of the grounding connector plays a role in isolating or the DS98 is open circuit, SPG and DCG are two sets of mutually independent ground nets, and the DC ground net can exert its anti-jamming as usual. Advantages: Under the special circumstances of direct lightning strikes, the discharge of the gas discharge tube in the ground connector or the internal MOV element of the DS98 is turned on (ignoring the residual voltage), so it is equivalent to the SPP and DCG forming an instantaneous equipotential body, all micro-machine room Electronic equipment can avoid damage due to elevated ground potential.
Lightning grounding engineering attention methods and steps
I. General requirements for lightning protection and grounding of AC power supply systems for mobile communication stations