Lightning protection and overvoltage problems of communication equipment

May 23, 2022

Since the lightning protection of communication equipment is not well considered during the construction of the communication network, especially most of the equipment is installed in the main control room of the substation, lightning damage and overvoltage cause damage to communication equipment every year. The lightning protection and overvoltage problems of communication equipment are imminent. In recent years, the lightning protection of electric power communication has been investigated and analyzed, and the comprehensive lightning protection facilities of communication have been improved in combination with the transformation of the communication network, and remarkable results have been achieved.

Ways for lightning or overvoltage to penetrate into communication equipment

In the communication network in recent years, the damage to the communication equipment by lightning strikes, the communication power supply, the microwave communication equipment transceiver, the communication equipment user circuit or the interface circuit damage accounts for the vast majority. Statistical results show that there are no more than the following ways for lightning or overvoltage to penetrate into communication equipment:

1 The lightning strikes directly or strikes the transmission and distribution lines nearby, and the lightning wave penetrates into the power equipment in the computer room along the power line, and damages the power switch, insurance, rectification and conversion module, communication power panel, etc.

2 The lightning strikes the microwave antenna tower directly, and the lightning wave quickly invades the communication equipment along the antenna feeder, directly damaging the transceiver unit part connected to the feeder, causing communication interruption.

3 Lightning strikes or strikes directly on the communication overhead optical cable or cable line, and the instantaneous overvoltage generated on the line rapidly expands along the optical cable or cable metal sheath or strengthening core to both ends of the line into the equipment room, damaging the machine panel directly connected to the optical cable, or Damage to the security patch panel, user circuit board or interface circuit board directly connected to the communication cable.

4 The lightning strikes the lightning rod in the tower or the substation directly, and the lightning current flows into the grounding grid through the down-conductor of the lightning rod, causing the ground potential to rise. When the equipment is poorly grounded and the resistance of the grounding resistance is large, it will cause damage to the microelectronic equipment.

5 When a line or busbar grounding accident occurs in the substation, the fault current discharges to the grounding grid, and the huge grounding current flows into the grounding grid, causing the ground potential to rise rapidly in a short time, and also causing damage to the microelectronic equipment.

6 When the communication line is added under the power line, when the insulation of the power line porcelain bottle breaks down, the power line discharges to the communication line, or the power line is overlapped on the communication line, causing the strong current to invade the computer room along the metal strength core of the optical cable or the audio communication cable. , causing damage to communication equipment or personal injury.


Deficiencies in Lightning Protection of Communication Stations

For the lightning protection of electric power communication, we conducted lightning protection inspections one by one according to the "Management Regulations for Lightning Protection Operation of Power System Communication Stations". The inspection results show that individual communication stations still have deficiencies to varying degrees, and the common problems are mainly manifested in the following aspects:

1. Most of the communication rooms in the office buildings are transformed from offices. The grounding grid is not standardized, the individual grounding resistance is greater than 5Ω, and there is no annular grounding bus. The diameter of the equipment grounding wire is thin.

2. Some AC power supplies are equipped with overvoltage protectors, while others are not. Most communication stations are not equipped with DC power supply overvoltage protectors, and the power inlets of communication equipment are not equipped with varistors.

3 Due to the limitation of on-site environmental conditions, individual communication cable lines are directly overhead into the equipment room and are not directly buried. The new type of clip-on distribution frame is inconvenient to connect, and the empty wire pair of the cable is not grounded.

4 The digital wiring and audio security wiring frame in the substation are assembled in the frame of the optical transceiver, and the grounding wire of the security wiring unit is not connected to the grounding bus.

5 Most of the RTU remote control devices in substations use RS232 interfaces to connect with communication equipment such as "one point multiple access" microwaves, optical transceivers, etc. It often occurs that the RS232 interface board is burned out after thunderstorms. Most of the grounding of RTU devices is directly fixed on the channel steel of the trench with screws (channel steel is welded with the ground grid) and the grounding is poor.

Application of Comprehensive Lightning Protection Measures for Communication Stations

In view of the shortcomings of the above-mentioned lightning protection of communication stations, in recent years, we have adopted comprehensive lightning protection according to the general principles and common protection measures of lightning protection of communication stations, and transformed and improved the lightning protection facilities of communication stations.

1 The general principle of lightning protection is:

(1) Use external protection to direct most of the lightning current into the ground for discharge.

(2) Use an overvoltage protector to block overvoltage waves introduced along power lines, data lines, and signal lines (internal protection).

(3) Use an overvoltage protector to limit the surge voltage amplitude on the protected equipment.

(4) Use an optoelectronic isolator to isolate the RS232 interface between the communication and the RTU to avoid electrical connection of the interface equipment.


2 General methods and techniques of lightning protection:

(1) Set up a set of good building lightning protection belts and lightning protection nets, and ground them together with the main steel bars;

(2) External equipment (antenna, etc.) should be placed within the protection angle of the building lightning protection net as much as possible:

(3) Adopt common grounding measures;

(4) Install a special lightning arrester with reliable performance at each inlet and outlet of the power supply, signal or data line;

(5) Indoor equipment should be kept away from lightning conductors as far as possible;

(6) Indoor wiring, including all kinds of transmission lines, should minimize loops, preferably with shielded wires and grounded at both ends.

3 Retrofit of lightning protection grounding system.

(1) The grounding grid of the dispatching and communication building was reconstructed, and it was found that some grounding belts had been broken due to the disrepair of the original grounding grid for many years. Re-embed four grounding grids on the four sides of the communication building. The grounding electrodes are made of 50mm×50mm×5mm galvanized angle steel. Galvanized flat steel is welded to form a mesh grounding device. The four grounding grids are respectively connected to the symmetrical grounding grids in the computer rooms on each floor of the communication building with a flat steel. After the transformation, the grounding resistance is 0.5Ω, which meets the requirements.

(2) Transform the grounding of the communication equipment room in each office building, extend the grounding grid, increase the number of grounding poles or lay more than two grounding grids. Reduce the ground resistance to less than 1Ω.

(3) The 40mm×4mm galvanized flat steel is used to form a ring grounding bus in the communication room, and the four corners are connected to the grounding grid. All metal components such as equipment shells, heating, and cable trays in the equipment room are connected to the grounding grid nearby with 35mm2 copper wires.

(4) The communication equipment in the substation and the housing of the RTU remote control device are connected to the same point of the grounding bus of the substation with 35mm2 multi-strand copper wires to eliminate the potential difference.

(5) Connect the upper, middle and lower ends of the metal sheath of the "one-point-multiple-access" microwave feeder to the iron tower as close as possible, and to the grounding bus at the entrance of the machine room. The grounding resistance test of each microwave tower meets the requirements.

(6) For the dispatching communication building, since there are computer rooms such as telecontrol, dispatch, switch, optical fiber, microwave, and power supply in the building, there are many connections between the computer rooms, and the connection between various audio cables and coaxial cables is complicated. If the potential of the equipment room rises, it will pose a threat to other equipment in the equipment room. Therefore, the grounding of these equipment rooms should be unified to a common grounding system to realize the equipotential bonding of the grounding of each equipment room.


4 Lightning protection of power system

(1) The power line introduced into the communication room adopts underground power cable, and both ends of the cable metal sheath are well grounded.

(2) The high-voltage side of the distribution transformer is connected to the high-voltage zinc oxide arrester, and the low-voltage side is connected to the power supply arrester. The transformer casing and arrester grounds are uniformly connected to the grounding grid and are well grounded.

(3) The power supply in the communication room adopts multi-level surge protection measures. The AC bus is connected in parallel with a 380V overvoltage protector; the AC input of the high-frequency switching power supply is connected in parallel with a 380V overvoltage protector; the -48V power inlet is connected with a first-level varistor. The positive pole of the power supply of the communication equipment is connected to the grounding bus on the power supply side and the equipment side respectively.

(4) The power supply of the communication equipment in the substation is installed in the main control room together with other substation equipment due to the lack of communication equipment. The DC power supply is taken from the 220V DC operating power supply of the substation, and is converted into -48V power supply by the DC/DC module for communication equipment. Therefore, a first-level 380V/100G AC overvoltage protection device is installed on the AC bus of the electric cabinet used in the substation as a first-level lightning protection; A 48V DC surge protection is installed on the 48V output side of the DC/DC module; finally, a 48V varistor is installed at the 48V inlet of the communication equipment.

(5) All AC and DC power distribution cabinets in the equipment room are grounded. The AC protective grounding wire is directly drawn from the grounding bus. It is strictly forbidden to use the neutral wire as the AC protective grounding wire.


5 Lightning protection of various signal lines

According to the actual situation of each communication station, measures such as surge protection and photoelectric isolation are adopted to protect all signal lines entering and leaving the communication room and the interface between communication equipment and other equipment. In order to prevent the intrusion of lightning induced voltage or overvoltage from damaging communication equipment.

(1) Renovate the communication cable lines of individual communication stations that enter the computer room directly, ground the steel wire at the line terminal pole, and bury the communication cable horizontally for more than 10m and enter the computer room. The metal sheaths of communication cables entering the equipment room are well grounded.

(2) Common overhead optical cables, pipeline optical cables, and self-supporting optical cables are all non-metallic optical cables. For optical cables with metal reinforced cores or metal sheaths, before entering the equipment room, the terminal rods or terminal cable wells should be changed to non-metal optical cables to transition into the equipment room.

(3) All audio cables, telephone lines, and signal lines should be connected to the audio security device first when they enter the computer room to suppress the horizontal and vertical overvoltage of the cable pairs. The grounding end of each patch panel security unit must be well grounded to ensure the normal function of the security device.

(4) Conscientiously implement the grounding protection measures for the cable sheath and empty wire entering the equipment room. The cable empty wire pair should be grounded on the distribution frame in time to prevent the introduction of lightning induced voltage from counterattacking at the end of the open wire and damaging the equipment. Conditional distribution frames can use short-circuit grounding plugs, which can be directly inserted into the overhead wiring pairs, which is convenient and flexible. After the change of the line pair is usually inspected, the grounding condition of the air pair should be checked in time.

(5) For other professional signals such as telecontrol, isolation measures should be taken before entering the communication equipment: the audio analog signal output by the modem is electrically isolated by an audio transformer; the data signal using the RS232 interface is isolated by an optoelectronic isolator to eliminate the The ground potential difference may be connected in series through the common ground wire in the interface, resulting in the phenomenon of counterattack damage to the interface circuit.

In addition, judging from the damage to the interface of Chaoyang communication equipment, the RS232 interface is often damaged, and the RS422 interface has never been damaged. It can be seen that the anti-interference ability of the RS232 interface chip is not as good as that of the RS422 interface chip. Therefore, where we have the conditions, we have changed to RS422 channel transmission instead of RS232 interface. It is recommended that the new equipment should be changed to 64K, RS422, or 2M interface instead of RS232 as much as possible in the future.

(6) The network signal using the RJ45 interface first passes through the network surge protector and then connects to the communication equipment interface. For power acquisition, relay protection, integrated automation, MIS, and load control, signals that use 2Mbit/s interfaces must first pass through a 2Mbit/s coaxial signal surge protector, and then connect to communication transmission equipment to prevent surges. Voltage intrusion. In some places, the MIS, negative control and other computer rooms are not together with the communication computer room, and the distance is relatively long. Optical fiber transceivers can be used for photoelectric isolation. First, the transmission distance is long, and second, signal isolation is required. Third, optical fiber transmission is anti-interference and lightning protection. Better results.

(7) After the "one point multiple access" microwave feeder enters the machine room, install a coaxial high-frequency signal lightning protector at the feeder input end, and the protector shell should be well grounded. The selection of the protector should consider the appropriate bandwidth.