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1. What are the reasons why the video surveillance system is damaged by lightning?
(1) The composition of the video surveillance system generally consists of the following three parts 1. The front end part: mainly composed of the camera, lens, gimbal, protective cover, bracket, decoder, etc.
2. Transmission part: Use cables and wires to transmit video, audio or control signals by overhead, underground or laying along the wall.
3. Terminal part: It is mainly composed of picture splitter, monitor, control equipment, video storage equipment, etc.
(B), the main reason for the video surveillance system to suffer lightning damage 1. Direct lightning: lightning strikes directly on the open-air camera to cause equipment damage or lightning strikes directly on the overhead cable to cause cable damage. The damage caused by this type of lightning strike is the most serious, but the probability of occurrence is relatively small.
2. Induction lightning: Also called secondary lightning, it is divided into electromagnetic induction and electrostatic induction. When there is a lightning strike in the nearby area, a strong transient electromagnetic field will be generated around the lightning strike implementation channel. The monitoring equipment and transmission lines in the electromagnetic field will induce a large electromotive force. This phenomenon is called electromagnetic induction; when a charged thundercloud appears, the buildings and transmission lines below the thundercloud will be induced with the thundercloud. The opposite charge, this phenomenon is called electrostatic induction. The damage caused by induction lightning is not as great as the damage caused by direct lightning, but the probability of occurrence is very high, accounting for more than 80% of modern lightning strikes.
3. Lightning Intrusion Wave: When the power line, signal transmission line of the monitoring system or other metal cables entering the monitoring room are struck by lightning or induced by lightning, the lightning wave intrudes into the equipment along these metal wires / conductors, resulting in high potential difference causing damage to the equipment.
2. What are the measures for video surveillance system lightning protection?
(1) Lightning protection of the front-end equipment: the front-end equipment has two distribution modes: outdoor and indoor. The indoor distribution is generally not subject to direct lightning strikes, but it is necessary to consider preventing the lightning overvoltage from damaging the equipment, while the outdoor equipment needs at the same time. Consider preventing direct lightning strikes.
Front-end equipment such as cameras should be placed within the effective protection range of the lightning rod. For front-end equipment that is already within the protection range of other lightning rods or the original lightning protection system of high-rise buildings, direct lightning protection is generally no longer considered; for front-end equipment that is not within the protection range of any lightning protection system, direct strike should be considered Lightning protection problem.
(2) Lightning protection of the transmission line: More than half of the lightning damage accidents in the monitoring system are caused by the lightning overvoltage induced on the line connected to the system. Therefore, the protection of the lines connected to the system is a part of the overall lightning protection that cannot be ignored. The video monitoring system mainly transmits signal lines and power lines.
The safest wiring method should be laid through the metal pipe through the whole process, and pay attention to the fact that both ends of the metal pipe must be effectively grounded. The camera power supply generally uses AC220V or DC12V. If the camera is powered by a DC transformer, the single-phase power surge arrester should be connected in series or parallel to the front end of the DC transformer. If the transmission distance of the DC power supply is greater than 15 meters, the low-voltage DC surge arrester should also be connected in series at the camera end.
(3) Lightning protection of terminal equipment: The lightning protection of the monitoring room is the core of the lightning protection of the monitoring system. It should be carried out from direct lightning protection, lightning intrusion wave, equipotential connection, and surge protection.
The main equipment of the monitoring room includes the monitoring center computer, video matrix, hard disk recorder, intercom system, and monitoring room power supply. The location of the monitoring system equipment room should be selected in the highest level of the LPZ and avoid being located in the top three floors of the building; when the size of the lightning protection grid of the sky surface part of the building does not meet the requirements of the system anti-interference, it should be installed on the sky surface Shield. Use unshielded cables. Before entering the house, wear metal pipes and bury them in the ground with a horizontal distance of more than 10 meters. If restricted by conditions and unable to bury the metal pipe into the house, the length of the house shield pipe or trestle should be lengthened. Both ends of the metal pipe or trestle and the junction of the lightning protection zone should be connected to the equipotential and ground. When the monitoring system equipment is a metal shell, the shortest wire should be used to connect it to the equipotential bonding band. If it is a non-metallic enclosure, when the shielding of the building where the device is located does not meet the electromagnetic compatibility requirements of the device, a metal mesh or other shielding body should be installed to shield the device. The equipment of computer, communication and monitoring equipment room shall be protected about 1 meter from the outer wall of the building. In order to prevent the building from being subjected to direct lightning, it will leak into the ground along the outer wall and generate a strong electromagnetic field around the downline to damage the microelectronic equipment.
1. Lightning protection measures for the power supply system of the monitoring room Since 70% of the high lightning strike potential is invaded from the power cord, in order to ensure the safety of the equipment, the general power supply should be equipped with three-level lightning protection.
Install a three-phase surge protector at the general power distribution point of the building where the monitoring room is located, with a flow capacity of 80KA (waveform 8 / 20μs), as the first level of power protection.
Install a three-phase modular power surge protector at the distribution box of the monitoring room, with a maximum flow capacity of 40KA, as a second-level protection.
Install single-phase series lightning arresters in front of the UPS power supply or monitoring equipment in the monitoring room and install them in series as the third-level protection of the power line.
Install a single-phase lightning protection socket with a flow capacity of 10KA in front of the equipment in the monitoring room, as a fine power supply lightning protection, clamping and filtering the power supply.
If the power surge protection cannot be done in stages, it is recommended to install a BC compound three-phase power surge protector in the monitoring room. Install a single-phase series power supply surge arrester in front of the UPS power supply in the monitoring room as the third-level protection of the power line. Install a lightning protection socket with 10KA single-phase power supply in front of the equipment in the monitoring room. As a fine power supply lightning protection, it clamps and filters the power supply.
2. Lightning protection measures of control room control and intercom system The video of the control room adopts 16-port combined video lightning arrester to protect the video input port of the hard disk recorder from being damaged by surge voltage. Video guns that transmit signals through optical fibers do not consider installing video arresters.
The RS232 interface of the hard disk video recorder adopts an RS232 interface lightning arrester to protect the serial port of the hard disk video recorder from being damaged by surge voltage.
All control lines entering the control room are equipped with control line arresters.
The wired intercom system is equipped with a lightning arrester for audio lines, and the arrester is installed only at the end of the intercom host.
The above are just some basic lightning protection measures. The real lightning protection of the video surveillance system requires comprehensive consideration of all aspects, and the lightning protection technology is also very complicated. The performance requirements of various lightning protection devices are also relatively high, but you can use the above The lightning protection method is used as a foundation. In-depth in all links, the monitoring system can be protected from lightning strikes to the maximum extent, and the purpose of lightning protection and disaster reduction can be effectively achieved.
Thunderstorm season video surveillance system lightning protection facilities tested
Thunderstorms occur frequently in summer, and lightning protection becomes the key. In order to take effective lightning protection measures for the video surveillance system, first of all, we should accurately understand the composition of the video surveillance system and the cause of lightning damage.