The monitoring system mainly monitors the incidents that may affect social public safety and property, etc., mainly for post-mortem investigation and evidence collection. In this thunderstorm season, if the front-end camera does not have a good anti-lightning surge, it will bring hidden dangers for the occurrence of late-stage accidents. Because the camera's damage may cause the entire system to appear unconventional, posing a potential threat to public safety and personal property. However, many "professional lightning protection manufacturers" introduced that they should install their "lightning arresters" or surge protectors at the pole lightning camera and the host video input. Is this useful? The case of exposure is: even the lightning protector is burned together.
Aside from the lightning protection installation design of the camera, consumers must first understand the structure of the lightning arrester.
First, the size of the arrester. The arrester is made according to the internal and external conditions to determine the insulation strength of the porcelain sleeve, and its dimensions are related to the valve sheet material. When it is used for overhead lines or outdoor power distribution equipment, due to its large phase spacing, the external dimensions of the arrester do not have adverse effects. Indoor handcart type switchgear has a small size, and the arrester has an adverse effect when its external dimensions are large.
The SiC valve of silicon carbide arrester has a unit current capacity of only 1/4 of the ZnO valve. Under the same flow capacity (5kA), the SiC valve has a larger diameter and the outer diameter of the arrester is larger; at the same rated voltage And under residual pressure conditions, silicon carbide arrester height is greater than zinc oxide surge arresters. Especially in the 35kV class more significant. Such as JYN1-35 handcart cabinet 112 program, the original use of FYZ1-35 type gapless zinc oxide arrester, only 650mm high, mounted on the back of the cabinet compartment interior simple handcart, the upper isolating plug, because the product has been discontinued The design of the project insisted on using the FZ3-35 silicon carbide surge arrester with a height of 1500mm. The height of the compartment was not enough. The busbar compartment and the compartment partition board had to be eliminated. The arrester was directly connected to the main busbar. The arrester must be tested or replaced in the entire process. The main busbar section is under power off, and operation and maintenance are difficult. The outer diameter of the arrester is relatively large, and the gap between the air on the other side is not enough. The phase-to-phase insulation partitions installed in the main busbar have potential hazards of aging and damp insulation. The outer diameter and height of the zinc oxide surge arrester are relatively small, and the 35kV grade can also be made into hanging type, such as the Y5CZz-42/110L series gap zinc oxide surge arrester, the height is only 640mm. Miniature arresters are more conducive to installation and use in handcart cabinets.
Second, the performance and price ratio of arresters. The gap-free zinc oxide surge arrester operates in the long-term grid voltage, and the working conditions are severe. The product must be strictly tested and screened during manufacture, and the qualification rate is low cost and high, so the price is high; because of its transient overvoltage tolerance The fatal weakness of the poor is not suitable for promotion in China's 3 ~ 35kV power grid. Interstitial gap zinc oxide surge arresters due to gaps, greatly improve the long-term operating conditions of the valve, the product manufacturing requirements of the valve test screening is relatively low, the qualified rate is high, the cost is low, the price is also cheaper, the series gap of zinc oxide arrester price than no gap Zinc Oxide arresters are generally cheaper and sometimes cheaper than silicon carbide surge arresters (such as the 3 to 10 kV FZ type). At the same time, they have advantages for other lightning protection devices. They are actually the most advanced lightning protection devices in the world and have a high performance-to-price ratio. , is the popularization and promotion of arrester replacement.
Thirdly, the service life of the arrester is related to many factors. In addition to manufacturing quality, moisture in the seal failure and other external factors, the aging speed of the arrester valve is a key factor affecting the service life. Silicon carbide arrester due to its action and heavy load, continued flow, poor stability of the operating characteristics, may be subject to transient overvoltage hazards and other reasons, accelerating valve aging, life is not long, generally 7 to 10 years, even only 3 ~ 5 years. The gap-free zinc oxide surge arrester valve can withstand long-term grid voltage, harsh working conditions, low inflection point voltage, large frequency of operation, and may be subject to transient overvoltage hazards, thermal damage and other reasons, quickly accelerating the aging of the valve, the short life span Some are shorter than SiC arresters. The gap of the zinc oxide arrester in the series gap gap can guarantee that the valve plate only withstands high voltage during the overvoltage protection action, and the time is very short (within 100μs). In other cases, the valve plate is for grid voltage, or is isolated (pure clearance), Or in a low potential state (combined gap resistance voltage divider), which greatly improves the long-term operating conditions of the valve, and also protects against transient over-voltage hazards and thermal damage to ensure that the temperature of the valve does not exceed 55°C, thus ensuring the lifetime of the arrester is up to 20 More than a year.
Then, after understanding the inherent information of the lightning arrester, it can be relatively recognized when the camera is installed.
1) Look at the front end of the video signal lightning protection device connected in series at the output end of the camera: The lightning protection device is connected to the input and output of the video cable, and another grounding point is normally open to the video line (some products have made a normal short circuit). At high voltage, the internal component short-circuits the video line and discharges the lightning current.
It should be noted here that when the camera pole is connected to the flash, the discharge channel of the video signal lightning protector is: "Lightning rod body - camera - video short-line - lightning protection device internal discharge element short circuit - grounding point - grounding net"; when lightning, lightning rod Body and lightning arrester These two "leakage current discharge channels" are discharged in parallel to the ground grid.
2) When the pole lightning rod catches the flash, a huge discharge current will form a huge “thunderbolt counterattack voltage†on the lightning rod body; the “lightning counterattack voltage†is also added to the upper end of the video signal lightning protector. If this SPD can reduce the "thunder voltage" above 400,000 volts to more than ten volts and several volts, the ability of this SPD to discharge the lightning current must greatly exceed the lightning rod, making the lightning current "mainly through the The discharge of the mine device" is not mainly through discharge of the lightning rod. It is hard to imagine that "the lightning protector is connected to the ground net with an insulated multi-strand copper core yellow-green flexible wire of ≥2.5mm2", and its discharge capacity can far exceed that of the metal pole. Obviously impossible, the consequences can only be "leisure self-destruction."
3) The lightning protection devices introduced by “Professional Lightning Protection Manufacturers†are all anti-lightning devices. Without introduction, they can effectively prevent “thunderbolt counter-attack voltages†from being burned. However, the "security and lightning protection system design" that they actively launched is daunting for such applications, indicating that such designs lack the minimum security system concept. If there is such a powerful lightning arrester, then the lightning rod can be used.
4) Directly introduce the "lightning counterattack voltage" into the security system. Is it lightning protection or lightning? For this issue, the Security Forum tracked for more than two years, no one "professional lightning protection factory" can make a positive explanation, they all take a evasive attitude. So far, only some “professional lightning protection manufacturers†have been seen, actively promoting the design and application of security projects, and have not seen any professional manufacturer of lightning protection devices (surge protector) products dare to publicize “the ability to discharge lightning currents. Can exceed the lightning rod, can safely limit the "lightning counterattack voltage."
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