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In recent years, with the accelerating pace of urbanization in China, banks have increased the number of new outlets and demand for the renovation of existing outlets. Major banks have invested a lot in the construction of bank network security monitoring systems, among which the lightning protection device detection of the security monitoring system is a must for bank outlets. The author combines the problems found in the lightning protection device detection process of the bank network security monitoring system, and mainly analyzes the causes of lightning strikes in the security monitoring system, and proposes lightning protection measures for the security monitoring system.
Second, the composition of security monitoring system and causes of lightning and existing problems 1. The basic composition of security monitoring system
The security monitoring system is generally composed of three major components: front-end equipment, transmission equipment, and terminal equipment (including control equipment, display and recording equipment, and power console equipment). The front-end part includes the camera and the lens, the head, the protective cover, etc.; the transmission part includes the cable or the optical cable, and possibly the wired/wireless signal modulation and demodulation equipment; the terminal part control equipment mainly includes the video switcher, the lens controller, various types Control communication interfaces, power consoles, monitor cabinets, etc.; terminal parts display recording equipment mainly includes monitors, multi-screen splitters, etc.
2. Causes of Lightning Strike in Security Surveillance System
Direct lightning: Thunder strikes directly on the open camera to cause equipment damage; lightning strikes the overhead cable (power line and signal transmission line) causing the cable to blow.
Lightning wave intrusion: refers to the lightning surge or lightning induced by the power line, signal transmission line of the security monitoring system or the metal pipeline entering the monitoring room. The lightning wave invades the equipment along these lines and metal pipelines, causing a potential difference and damaging the equipment. .
Lightning electromagnetic pulse: (1) Lightning induction: When a lightning strikes a lightning rod (a lightning protection zone), a strong transient electromagnetic field is generated around the down conductor. The monitoring equipment and transmission line in the electromagnetic field will induce a large The electromotive force, this phenomenon is called electromagnetic induction. (2) Electrostatic induction: When a charged lightning cloud appears, a charge opposite to that of a thundercloud will be induced on the buildings and transmission lines below the thundercloud. This induced charge can reach 100kV on low-voltage overhead lines. Up to 40 ~ 60kV, this phenomenon is called electrostatic induction. Electromagnetic induction and electrostatic induction are collectively referred to as lightning induction. The damage caused by lightning inductance to the equipment is not serious, but it is more likely to occur than direct lightning, resulting in a wider range of losses.
Ground potential counterattack: direct lightning protection devices (such as lightning rods) generate a very high instantaneous voltage on the down conductor, the grounding body, and the metal conductors connected to them when guiding powerful lightning currents into the earth. (Generally referred to as within 20m) There is a huge potential difference between metal objects, equipment, lines, and human bodies that are not connected by equipotential bonding. The electric shock caused by this potential difference is the counter-attack of the ground potential. This counterattack is not only enough to damage electrical appliances and equipment, but also cause personal injury or fire and explosion.
At present, lightning protection devices for bank network security monitoring systems mainly have the following problems: (1) Lightning wave intrusion protection measures are not provided or only one-level SPD is simply installed for protection; (2) Thunderbolt electromagnetic pulse protection measures are not in place, The location of the equipment room and the electromagnetic shielding measures of the equipment room do not meet the relevant requirements: (3) For counter-attack of the ground potential, the safety distance between each line and the lightning protection ground lead wire is insufficient; second, the metal pipeline near the lightning protection device The equipotential connection is not made close to the lightning protection device and the two ends are grounded.
Due to the above problems, bank outlet monitoring equipment is often damaged by lightning strikes, which greatly reduces the application effectiveness of the security system.
Third, lightning protection measures of security monitoring system
At present, the direct lightning protection device and the PE system grounding of the electrical system of the building where the bank outlet is located have obtained the acceptance certificate from the local meteorological authority. The security monitoring system is a built-in system in a building. Its lightning protection is mainly considered from the aspects of the lightning protection electromagnetic pulse and lightning protection. In the case of front-end equipment such as cameras installed outdoors, it should also be protected by direct lightning protection. Measures.
1. Lightning protection measures for front-end equipment
There are two kinds of idle conditions for outdoor and indoor installations on the front-end equipment: indoor equipment will not suffer direct lightning strikes, but it is necessary to consider the prevention of damage caused by lightning wave intrusion into the equipment; when the outdoor equipment is not within the protection scope of the direct lightning protection device Direct lightning protection measures must be taken. In order to prevent lightning waves from invading the front-end equipment along the line, a surge protection device for transportation shall be installed on each line in front of the device. The signal surge protector must be able to respond quickly and the transmission rate and other parameters must be matched. Outdoor equipment should have good grounding. When connecting to her busbar, a copper wire with a cross-sectional area of ​​not less than 25mm2 should be used. There should be a grounding mark. The grounding resistance should be determined when the common grounding is connected to the minimum value in the access equipment. Greater than 4 omega.
2. Lightning protection measures for transmission equipment
Transmission equipment is mainly transmission signal lines and power lines. In order to avoid damage to the head and tail end equipment, grounding should be done on each pole when transmitting the overhead lines. The overhead wires of the overhead cables and the metal pipes in the overhead cable lines should be grounded. The signal source and the power supply at the input of the intermediate amplifier should be respectively connected to the adapted surge protector. The transmission line uses a cable or cable with a shielding layer laid through the steel pipe to keep the electrical connection of the steel pipe and both ends of the steel pipe must be grounded. If the cable is difficult to pass through the metal pipe all the time, it can be introduced through the metal pipe before the cable enters the terminal and the front-end equipment. The length of the buried shall not be less than 15 meters. The metal sheathing of the cable, the steel pipe, and the lightning protection grounding device are located at the entrance end. Do equipotential bonding.
3. Lightning protection measures for terminal equipment
The terminal equipment is placed in the monitoring room. The lightning protection of the monitoring room should be carried out in various aspects such as direct lightning protection, lightning electromagnetic pulse protection, shielding of buildings or monitoring rooms, equipotential bonding and surge protection. The direct lightning protection measures of the building in which the monitoring room is located shall comply with the provisions in GB50057. The location of the monitoring room shall be located in the LPZ1 zone, LPZ2 zone, at the center of the bottom floor of the building, and shall be far from the external wall of the lightning deflector, and shielding measures shall be taken in the machine room. . All kinds of metal pipelines entering the monitoring room shall be connected to the lightning protection grounding device. When the overhead cable line is directly introduced, an appropriate surge protector shall be installed at the entrance to the house, and the metal outer sheath of the cable shall be self-supported. The cable is connected to the grounding device. The monitoring room shall be provided with an equipotential bonding bus and a common lightning protection ground for the building lightning protection grounding, PE line protection grounding, equipment protection grounding, anti-static grounding, etc. to prevent ground potential counterattack damage equipment. For all kinds of surge protectors installed, the grounding wire should be connected to the equipotential bonding bus for the equipotential bonding with the straightest and shortest path. The specifications of the surge protection device connecting lead should be in accordance with Table 1, and the length of the connection line should not be greater than 0.5m.
IV. Conclusion
The security monitoring system of bank outlets is based on buildings as a carrier. Doing a good job of building false lightning protection is the prerequisite for lightning protection of the security monitoring system. The security monitoring system is generally set up during the second decoration process, so its lightning protection should mainly be protected from lightning electromagnetic pulse radiation and lightning protection, and it should be taken to the front-end equipment installed outdoors. Direct lightning protection. In short, before designing and constructing the lightning protection device of the security monitoring system, it is necessary to fully consider the geographical, environmental, and characteristics of the object to be protected of the monitoring system, and to study and determine in detail the form and arrangement of the lightning protection device in order to obtain good results. Lightning protection effect.
Bank security monitoring system lightning protection measures
I. Introduction