We have found that not only are outdoor cameras damaged by lightning, but the equipment in the monitoring center room is also “damaged†by lightning strikes. So, what areas can we start from "to get" lightning to protect the monitoring system? In general, the monitoring system is divided into front-end camera, intermediate transmission, and back-end monitoring center. From the above analysis of several major problems, it can be seen that the lightning protection of the monitoring system can also be started from three places.
1. Lightning protection of front-end equipment
The installation position of the front-end camera is often divided into indoor and outdoor, and the camera installed in the room is generally not subject to direct lightning. However, lightning overvoltage may also cause infringement on the camera, and outdoor equipment needs to be considered to prevent direct lightning strikes. Faced with this situation, how do we conduct lightning protection?
The usual method is that we will place the front-end equipment such as the camera within the effective protection range of the lightning receptor (lightning rod or other lightning conductor). When the camera is set up independently, in order to prevent the transient high potential of the lightning rod and the down conductor, the lightning rod is preferably 3-4 meters away from the camera.
In addition, in order to prevent electromagnetic induction, the camera power cord and signal line led along the telephone pole should be put in the metal tube to achieve the shielding effect. Both ends of the shielding metal tube should be grounded.
To prevent lightning waves from entering the front-end equipment along the line, we usually install appropriate lightning arresters on each line in front of the device, such as power lines (DC24V or 220V), video lines, signal lines, and PTZ control lines; Should also install B, C-level lightning protection device.
The signal line has a long transmission distance and a low withstand voltage level. It easily induces lightning current and damages the equipment. In order to conduct the lightning current from the signal transmission line to the ground, the signal overvoltage protection device must respond quickly. When designing the signal transmission line, the protection must be considered. Situation, according to the signal transmission rate, signal level, starting voltage and lightning flux and other parameters to choose the right lightning protection equipment.
2. Lightning protection of transmission lines
For analog systems, the lines are mainly transmission signal lines and power lines. The power of the outdoor camera may be introduced from the terminal equipment or may be introduced from the power source near the monitoring point. The control signal transmission line and the alarm signal transmission line are generally selected from reinforced core shielded soft wires, which are erected (or laid) between the front end and the terminal, and both the reinforcing core and the shielding layer should be well grounded.
According to the regulations, when the transmission line is laid in the suburbs and villages of the city, it can be laid directly. When the conditions are not allowed, communication channels or overhead can be used. From the point of view of lightning protection, the direct burial laying method has the best lightning protection effect, and the overhead line is most vulnerable to lightning strikes, and has a large destructive effect and has a wide spread range. To avoid damage to the head and tail end equipment, the overhead transmission line should be on each pole. Ground handling is required. The overhead cable overhead line and overhead line cable should be grounded. The signal source and the power supply at the input of the intermediate amplifier should be respectively connected to the appropriate arresters.
However, it should be noted that the laying of the transmission line does not prevent the occurrence of a lightning strike. A large number of facts show that the failure of a buried cable caused by a lightning strike accounts for about 30% of the total failure. Even if it is far from the lightning strike, it still will Some lightning current flows into the cable. Therefore, if a shielded cable or cable is laid through a buried steel pipe, we need to pay attention to maintaining the electrical continuity of the steel pipe. This is very effective for shielding electromagnetic interference and electromagnetic induction. This is mainly due to the shielding effect of the metal pipe and the thunder. The skin effect of the current. Of course, if the cable is difficult to pass through the metal pipe, it can be introduced before the cable enters the terminal and the front-end equipment. However, the length of the buried shall not be less than 15 meters. The metal sheathing of the cable and the steel pipe shall be grounded to the lightning protection at the entrance end. The device is connected.
3, monitoring center's lightning protection
In the surveillance system, the monitoring center is often the place where surveillance video is processed, so its lightning protection is also very important. In brief, the lightning protection of the monitoring center shall be carried out in various aspects from direct lightning protection, lightning wave intrusion, equipotential bonding and surge protection.
From the standpoint of direct lightning protection, the building where the monitoring center is located should have lightning rods, lightning conductors, or lightning protection nets that prevent direct lightning strikes. The measures for direct lightning protection shall comply with Article 3.1.2 of Article 3.1.2 of the provisions of GB50057-94 (2000 Edition): "In order to reduce the risk of fire, explosion and death in the space where lightning protection is needed, "Equipotentiality is an important measure"; Section 3.3: "The most important measure to prevent the danger of life in a space requiring lightning protection is the use of equipotential bonding".
From the point of view of lightning wave intrusion protection, various metal pipelines entering the monitoring center should be connected to grounding devices that prevent lightning induced lightning. When the overhead cable is directly introduced, an arrester shall be installed at the entrance to the house, and the cable outer sheath and the self-supporting steel cable shall be connected to the grounding device.
Because 80% of the lightning high potential is invaded from the power line, in order to ensure the safety of the equipment, three levels of lightning protection should be installed on the general power supply. The lightning protection module must be installed at the last stage to limit the voltage to less than 1200V. ).
To explain the equipotential bonding problem of the monitoring center, in general, the monitoring center should be equipped with an equipotential bonding bus (or metal plate). The equipotential bonding bus should be connected to the building lightning protection grounding, PE line, and equipment protection ground. , ESD ground, etc. are connected together to prevent dangerous potential differences. The grounding wires of various surge protectors (arresters) should be electrically connected to the equipotential bonding busbars at the straightest and shortest distances. The equipotential bonding is part of the internal lightning protection device and its purpose is to reduce the potential difference caused by lightning currents. The equipotential is the use of connecting wires or overvoltage (surge) protectors to connect lightning protection devices in spaces requiring lightning protection, metal structures, metal devices, external wires, electrical devices, telecommunication devices, etc. of buildings. An equipotential bonding network is formed to achieve equal potential equipotentiality to prevent fire, explosion, life hazards and equipment damage in the lightning protection space.
It should be said that the lightning protection of the surveillance system is a more complex issue, not only the protection of outdoor monitoring equipment, but also consider the lightning protection issues of transmission cables and monitoring centers. The lightning protection design of the safety monitoring system not only depends on the performance of the lightning protection device, but more importantly, before the design and construction of the monitoring system, the geographical environment of the monitoring system must be taken into consideration, and a suitable cable deployment method should be designed. Shielding and grounding methods.
1. Lightning protection of front-end equipment
The installation position of the front-end camera is often divided into indoor and outdoor, and the camera installed in the room is generally not subject to direct lightning. However, lightning overvoltage may also cause infringement on the camera, and outdoor equipment needs to be considered to prevent direct lightning strikes. Faced with this situation, how do we conduct lightning protection?
The usual method is that we will place the front-end equipment such as the camera within the effective protection range of the lightning receptor (lightning rod or other lightning conductor). When the camera is set up independently, in order to prevent the transient high potential of the lightning rod and the down conductor, the lightning rod is preferably 3-4 meters away from the camera.
In addition, in order to prevent electromagnetic induction, the camera power cord and signal line led along the telephone pole should be put in the metal tube to achieve the shielding effect. Both ends of the shielding metal tube should be grounded.
To prevent lightning waves from entering the front-end equipment along the line, we usually install appropriate lightning arresters on each line in front of the device, such as power lines (DC24V or 220V), video lines, signal lines, and PTZ control lines; Should also install B, C-level lightning protection device.
The signal line has a long transmission distance and a low withstand voltage level. It easily induces lightning current and damages the equipment. In order to conduct the lightning current from the signal transmission line to the ground, the signal overvoltage protection device must respond quickly. When designing the signal transmission line, the protection must be considered. Situation, according to the signal transmission rate, signal level, starting voltage and lightning flux and other parameters to choose the right lightning protection equipment.
2. Lightning protection of transmission lines
For analog systems, the lines are mainly transmission signal lines and power lines. The power of the outdoor camera may be introduced from the terminal equipment or may be introduced from the power source near the monitoring point. The control signal transmission line and the alarm signal transmission line are generally selected from reinforced core shielded soft wires, which are erected (or laid) between the front end and the terminal, and both the reinforcing core and the shielding layer should be well grounded.
According to the regulations, when the transmission line is laid in the suburbs and villages of the city, it can be laid directly. When the conditions are not allowed, communication channels or overhead can be used. From the point of view of lightning protection, the direct burial laying method has the best lightning protection effect, and the overhead line is most vulnerable to lightning strikes, and has a large destructive effect and has a wide spread range. To avoid damage to the head and tail end equipment, the overhead transmission line should be on each pole. Ground handling is required. The overhead cable overhead line and overhead line cable should be grounded. The signal source and the power supply at the input of the intermediate amplifier should be respectively connected to the appropriate arresters.
However, it should be noted that the laying of the transmission line does not prevent the occurrence of a lightning strike. A large number of facts show that the failure of a buried cable caused by a lightning strike accounts for about 30% of the total failure. Even if it is far from the lightning strike, it still will Some lightning current flows into the cable. Therefore, if a shielded cable or cable is laid through a buried steel pipe, we need to pay attention to maintaining the electrical continuity of the steel pipe. This is very effective for shielding electromagnetic interference and electromagnetic induction. This is mainly due to the shielding effect of the metal pipe and the thunder. The skin effect of the current. Of course, if the cable is difficult to pass through the metal pipe, it can be introduced before the cable enters the terminal and the front-end equipment. However, the length of the buried shall not be less than 15 meters. The metal sheathing of the cable and the steel pipe shall be grounded to the lightning protection at the entrance end. The device is connected.
3, monitoring center's lightning protection
In the surveillance system, the monitoring center is often the place where surveillance video is processed, so its lightning protection is also very important. In brief, the lightning protection of the monitoring center shall be carried out in various aspects from direct lightning protection, lightning wave intrusion, equipotential bonding and surge protection.
From the standpoint of direct lightning protection, the building where the monitoring center is located should have lightning rods, lightning conductors, or lightning protection nets that prevent direct lightning strikes. The measures for direct lightning protection shall comply with Article 3.1.2 of Article 3.1.2 of the provisions of GB50057-94 (2000 Edition): "In order to reduce the risk of fire, explosion and death in the space where lightning protection is needed, "Equipotentiality is an important measure"; Section 3.3: "The most important measure to prevent the danger of life in a space requiring lightning protection is the use of equipotential bonding".
From the point of view of lightning wave intrusion protection, various metal pipelines entering the monitoring center should be connected to grounding devices that prevent lightning induced lightning. When the overhead cable is directly introduced, an arrester shall be installed at the entrance to the house, and the cable outer sheath and the self-supporting steel cable shall be connected to the grounding device.
Because 80% of the lightning high potential is invaded from the power line, in order to ensure the safety of the equipment, three levels of lightning protection should be installed on the general power supply. The lightning protection module must be installed at the last stage to limit the voltage to less than 1200V. ).
To explain the equipotential bonding problem of the monitoring center, in general, the monitoring center should be equipped with an equipotential bonding bus (or metal plate). The equipotential bonding bus should be connected to the building lightning protection grounding, PE line, and equipment protection ground. , ESD ground, etc. are connected together to prevent dangerous potential differences. The grounding wires of various surge protectors (arresters) should be electrically connected to the equipotential bonding busbars at the straightest and shortest distances. The equipotential bonding is part of the internal lightning protection device and its purpose is to reduce the potential difference caused by lightning currents. The equipotential is the use of connecting wires or overvoltage (surge) protectors to connect lightning protection devices in spaces requiring lightning protection, metal structures, metal devices, external wires, electrical devices, telecommunication devices, etc. of buildings. An equipotential bonding network is formed to achieve equal potential equipotentiality to prevent fire, explosion, life hazards and equipment damage in the lightning protection space.
It should be said that the lightning protection of the surveillance system is a more complex issue, not only the protection of outdoor monitoring equipment, but also consider the lightning protection issues of transmission cables and monitoring centers. The lightning protection design of the safety monitoring system not only depends on the performance of the lightning protection device, but more importantly, before the design and construction of the monitoring system, the geographical environment of the monitoring system must be taken into consideration, and a suitable cable deployment method should be designed. Shielding and grounding methods.
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