First, the reasons for lightning strikes on communications equipment and common problems
In recent years, with the development of communication technologies, especially mobile communication technologies, communication stations (station) in various places have frequently experienced lightning strikes on communication equipment, which has seriously affected the smooth communication and equipment and personal safety. After analysis, it is found that the causes of lightning strikes and the current problems are as follows:
First, many old bureaus (stations) have been expanded several times. The original communication equipment room, protection ground, and building lightning protection ground in the ground network have not been grounded in accordance with the requirements of â€œequal pressure equipotentialâ€. Some communication stations (stations) have been corroded for a long time and the grounding resistance is unqualified.
Second, some mobile base station tower heights exceed the height of other buildings in the urban area, resulting in an increased possibility of lightning discharge through the tower. Some towers were built in the county and branch offices. Although they have made independent ground lines and are self-contained, some have not connected with the network of the original intra-office communication, resulting in a ground potential difference between the local lines.
Third, some of the microwave stations, mobile base stations, and feeders of the wireless paging base warfare have no grounding or grounding that does not meet the requirements, and lightning is introduced from the feeder.
Fourth, some communication stations (station) or microwave station power systems have not taken effective protective measures or grounding measures are unreasonable, resulting in lightning being introduced into the equipment room from the power system.
Fifth, some local telephone cables are not grounded, the distribution frame security unit does not meet the requirements, and lightning is introduced into the equipment room from the cable.
Sixth, modern communication equipment has high technical content and is sensitive to increasingly complex electromagnetic environments. Especially the influence of lightning induction is particularly prominent. Since the control and management of communication systems are heavily introduced into microelectronic devices such as computers, strong electromagnetic interference generated by lightning often causes communication systems. The fault is prevented by the protection methods and devices previously composed of separate components, regardless of the main indicators such as operating voltage, response speed, and flow capacity.
Second, communication lightning protection grounding technology renovation project
In order to ensure the smooth communication and prevent the intrusion of lightning strikes, the communication lightning protection should follow the overall consideration, coordinate the design, coordinate the construction, coordinate the acceptance, and comprehensively manage the principle of comprehensive system protection. The lightning protection and grounding technology transformation of the Communication Bureau (station) involves a wide range of areas, strong professionalism, and a wide variety of equipment in the bureau. In order to ensure the safety and reliability of communication, the lightning protection grounding technology transformation project should be carried out by the design unit holding the first-class design qualification, and it must be reviewed by the provincial and municipal bureaus. Generally, it includes two parts: the original bureau (station) lightning protection and grounding technical transformation; the new bureau (station) lightning protection and grounding technology considerations.
The following focuses on the original bureau (station), especially the original bureau (station) lightning protection and grounding technology transformation.
The original communication bureau (station) lightning protection and grounding technology transformation is a system engineering, should be based on the principle of comprehensive management, lightning protection of the power system, communication station (station) building lightning protection grounding and grounding network. The lightning protection and grounding of microwave and wireless base station towers and antenna feeders, and the lightning protection and grounding of signal lines and interface equipment and computer networks are comprehensively controlled. If only the transformation is carried out in some aspects without comprehensive comprehensive management, the lightning protection effect is not very satisfactory.
(1) Lightning protection of power system
The lightning protection of the power system includes: low-voltage system, DC system, special office (station) power system and lightning protection of high-voltage system.
1. Requirements for low voltage systems
(1) Install a lightning arrester on the low voltage side of the power transformer.
(2) Where the low-voltage line of the power room in overhead form shall be changed to a direct buried circuit cable, the length of which shall be greater than 15 meters, and the metal sheath of the power cable shall be grounded at both ends.
(3) Add a first-level arrester to the core of the power cable at the first terminal of the power room, and install a lightning arrester at the corresponding position for the hub of the power supply system.
(4) In the AC power supply system, install a corresponding lightning arrester for the power supply line of some vulnerable equipment.
(5) Before the arrester, connect the fuse or circuit breaker in series. The capacity of the fuse should be less than 1.6 times that of the upper fuse. The rated capacity of the circuit breaker should be two levels lower than the upper circuit breaker.
2. DC system requirements
(1) The DC lead-in terminal of the equipment room should be equipped with a lightning arrester with more lightning strikes (station), professional.
(2) The fuse should be connected in series within the arrester.
(3) The operating voltage of the arrester should be greater than 70v, less than 90v (-48v system).
3. Requirements for special office (station) power system
(1) Install a lightning arrester on the ground power cable core of the electric power station of the mountain microwave station. The nominal discharge current should be greater than 40KA (8/20uS).
(2) When the power supply of the base station is used with other users or 220v/380v direct power supply, the arrester should be installed according to different power supply systems. The installation of the TT system arrester should be relatively medium and medium to ground (the arrester should meet the requirements) Power supply requirements).
3. Requirements for high voltage systems
(1) For communication stations (stations) that are introduced from high-voltage power lines and are often struck by lightning, a set of zinc oxide arresters shall be added to the first, third or second and fourth poles of the overhead high-voltage power line terminal rods. Add a set of high voltage fuses.
(2) For overhead high-voltage lines that supply power to the communication station (station), a lightning arrester shall be installed at the junction of the terminal bar and the cable, and the outer sheath of the cable shall be grounded.
(3) Install a lightning arrester on the high voltage side of the power transformer.
(4) The transformation of the high-voltage system is negotiated with the grounded power department.
(II) Reconstruction of lightning protection grounding and grounding grid for communication bureau (station) buildings
1. Grounding grid and grounding resistance requirements
(1) When the grounding resistance of the grounding station (station) ground network does not meet the requirements, the grounding area should be expanded. Non-metallic grounding modules should be used with caution.
(2) In the same bureau (station), the old and new ground networks (including towers, buildings, etc.) must be transformed into a joint grounding network. Other metal facilities in the station (station) should be connected to the ground network to reach the equalization equipotential. The purpose is to work the ground line, protect the ground line, and the lightning protection ground line should share a ground net according to the principle of equalizing the equipotential.
2. Requirements for building roof and lightning current down conductor
(1) A sign light on the roof of a building. Festival lanterns, air-conditioning accessories and other facilities, the metal frame, the metal sheath of the power cord, the lower end should be welded with the lightning protection net on the dark-mounted lightning protection net or the top daughter wall, and the solder joints are treated with anti-corrosion treatment. The lightning protection belt of the building is set on the wall of the daughter. It is connected to the hidden lightning protection net every 5 to 10 meters and welded firmly. The solder joints exposed to the air are treated with anti-corrosion treatment. A microwave antenna is arranged on the roof, and a lightning rod is arranged on the mobile communication antenna, and the down conductor should be soldered to the dark lightning protection network in two opposite directions. In the tower, a lightning rod should be installed on the tower, and the two main steel bars in the tower column should be used as the down conductor and connected to the hidden lightning protection net.
(2) The lightning current down-conductor line starts from the top of the building and leads to the ring-shaped grounding body of the building to form a cage structure. The bottom layer of the building should be connected with the galvanized flat steel every 5 to 10 meters around the ring body around the building. Once and soldered, the solder joints should be treated with anti-corrosion treatment.
(3) The lightning current down-conductor of the tower shall be connected by flat steel or copper row and directly introduced into the joint grounding body.
(4) Lightning rod. Should be used in accordance with the national standard GB5 printed 57-94 "Building Lightning Protection Design Code" lightning receptors, that is, conventional lightning rods, other non-conventional lightning rods or lightning arresters with caution.
(5) Grounding body. The vertical grounding body length should be 1.5 to 2.5 m, and the vertical grounding body spacing should be 1.5 to 2 times its own length. All solder joints between the grounding bodies shall be treated with anti-corrosion treatment except for casting in concrete. The upper end of the grounding body should not be less than 0.7m from the ground.
(6) Ground wire and ground lead. The grounding wire should be short, straight, and the cross-sectional area is 35~95mm. The material is multi-strand copper wire. The length of the grounding lead-in wire should not exceed 30m, and the material is a multi-strand copper wire with a cross-sectional area of â€‹â€‹not less than 40Ã—4 and a galvanized flat steel of not less than 95mm. The grounding lead is connected from the ground in two directions and connected to the assembly line of the equipment room to avoid the lead-out from the lightning current down-conducting line.
(7) Grounding collection line. The grounding collection line is generally designed to be ring-shaped or row-shaped, the material is copper, the cross-sectional area should be no less than 120mm, and galvanized flat steel can also be used. The grounding collection line of the equipment room can be installed in the reading slot, on the wall or on the cable rack.
3. Equipotential bonding and grounding requirements for other facilities
(1) Cable racks in the equipment room, hanging iron racks, racks over the casing, metal ventilation ducts, metal doors and windows, etc. should be equipotential bonding and grounding.
(2) The grounding lead-in of the equipment should be introduced from the grounding busbar.
(3) The neutral point of the transformer, the grounding end of the foreign passenger and the arrester and the metal sheath of the cable should be connected to the ground.
(III) Retrofit of lightning protection and grounding of microwave and wireless base station towers and feeders
1. Microwave antenna. Microwave antennas and other antennas should be within the protection range of the lightning rod.
2. The lightning current limit of the lightning rod of the iron tower
The lightning current down-conductor line that introduces the iron tower lightning rod is uniformly connected by flat steel or copper row, and directly connected to the ground net.
3. Sky feeder requirements
The antenna feeder should be grounded at the upper part of the tower, at the lower part or at the entrance of the machine room through the cable rack. The grounding at the entrance of the equipment room should be properly connected to the grounding wire drawn from the ground grid. When the height of the tower is greater than 60m, the metal outer sheath of the feeder should also be grounded in the middle of the tower. When mobile communication, the coaxial cable used by the wireless home search antenna feeder is greater than 30m, the corresponding coaxial lightning arrester should be installed at the entrance of the equipment room.
4. Iron tower ground network and computer room network
The iron tower ground network and the machine room ground network must be connected with the flat steel and the machine room ground net at two or more points.
5. Tower marking lamp requirements
It is advisable to use a solar tower lamp. For the sign lamp using AC feed, the power line should be a cable with a metal outer sheath. The metal outer sheath of the cable should be grounded near the top of the tower and the entrance of the machine room. Each phase line of the tower light control line and the power line shall be respectively installed with lightning arresters at the entrance of the equipment room, and the neutral line shall be directly grounded.
6. Requirements for cable entry in the equipment room
Cables and solar cell wires that enter the equipment room from the roof of the equipment room shall be made of metal sheathed steel. The metal sheath shall enter the entrance of the equipment room and be connected to the lightning protection belt on the roof of the daughter's wall. The inner core of the cable shall be Install a lightning arrester on the ground.
(IV) Reconstruction of lightning protection and grounding of signal lines and excuses equipment and computer networks
1. It is the introduction of all kinds of signal cables, and the metal sheath should be grounded in the incoming room.
2. The incoming cable should be connected to the device after passing through the security device.
3. The empty line in the incoming cable corresponds to the ground.
4. It is the data line of the incoming and outgoing computer. The arrester should be equipped with lightning arresters at both ends of the equipment.
5. It is the measurement room MDF distribution frame is connected to the ground net in two directions.
6. When the computer control line is greater than 50m, the data line arrester should be installed at the equipment terminal.
7. It is a data line connected to the antenna device, and a signal line arrester is installed in front of the terminal device.
8. After the optical cable enters, the metal components should be grounded before entering the equipment.
9. It is strictly forbidden to use the external wall power socket for computers and meters.In order to minimize and avoid lightning strikes on communication equipment and to ensure the normal operation of communication equipment, in practice, we cannot ignore and relax the inspection and maintenance of it (especially the old communication station). In routine maintenance, the following aspects should be done: Always check whether the mains voltage fluctuation range is normal, whether the three-phase AC load is balanced, whether the zero-to-ground voltage is greatly drifted, etc.; Carefully check whether the grounding system is good, and whether the grounding resistance value meets the requirements; should always check whether the lightning arrester wiring is secure, loose or not, whether the lightning protection grounding is well connected, whether the lightning protection device is deformed or cracked; The lightning arrester of the green indicator window (green when it is normal and red when it is faulty) should also check whether the color of the indicator window changes. For a lightning arrester with an alarm contact or a lightning protection device with an alarm circuit installed, it should be simulated. If the lightning arrester is damaged, check whether the alarm is normal.
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