[ Huaqiang Security Network News ] The security industry is developing rapidly, and people's living standards are constantly improving. All areas need to use closed-circuit television monitoring systems to protect national production and life. CCTV monitoring systems are widely used in campus and outdoor parking lots. , large enterprises, mines, docks and other fields. The front-end equipment of these CCTV surveillance systems, such as cameras, are mostly installed outdoors, in relatively open areas, and the risk of lightning strikes is relatively large. The electronic equipment in the CCTV monitoring system is very sensitive to various electromagnetic interferences such as lightning overvoltage, power system operation overvoltage, electrostatic discharge, etc., making the monitoring system equipment extremely vulnerable to lightning and voltage overvoltage, resulting in the entire closed circuit television monitoring system. . Therefore, these CCTV monitoring systems must consider transient over-voltage protection (lightning protection) measures when designing and constructing. 
First, the closed circuit television monitoring system has three common problems of transient overvoltage (lightning strike)
1. It has been equipped with lightning rods, grounding grids, and joint grounding. Why are closed-circuit television monitoring system equipment sometimes damaged by lightning?
When the lightning current passes through the lightning rod and is introduced into the ground into the ground, the ground potential instantaneously rises. Assume that the lightning current I=50KA, the grounding resistance R=1Ω, the ground potential ΔU=I×R=50KA×1Ω=50KV.
Because the joint grounding is adopted, the ground potential of the device is also increased by 50KV, and the power supply line and the signal transmission line are led from a distance, and the remote ground potential is still at zero potential, so the ground potential of the device casing will be between the power input terminal of the device. A large potential difference of 50KV occurs between the signal input terminal (referred to as "counter-attack" or "negative potential introduction" in lightning protection technology), causing damage to the corresponding parts of the device.
If the grounding of the grounding network is not good enough, the counterattack voltage will be higher and the damage may be more serious.
2. The monitoring center computer room is not affected by lightning, but there is lightning in the distance. Why is the equipment in the monitoring center machine room sometimes damaged?
The transmission line of the camera of the front-end equipment of the CCTV surveillance system is drawn from the remote computer room. Assume that there is a lightning strike near the transmission line, and an instantaneous overvoltage is induced on the transmission line. This induced high voltage extends along the transmission line to both ends. If the monitoring center room is not too far from the lightning point, the induced voltage may still have a certain strength when it is transmitted to the equipment room, which may damage the equipment in the equipment room.
3. In the days when there is no thunder, why is the power module of the monitoring center room equipment still damaged?
For the power supply line, we always mistakenly believe that a very clean sine wave flows through the line. In fact, due to the switching of the power grid, the start and stop of the inductive load in the same power grid, etc., various voltage interferences may occur in the power supply line. Among the harmful interferences of the power grid, the incidence of instantaneous oscillations and transient pulses is high.
This transient voltage duration is very short, only a few microseconds short, non-dedicated instruments are not easy to find, but their damage to the equipment can not be underestimated. Because modern surveillance security devices are microelectronic products, these monitoring devices have the characteristics of high density, high speed, low voltage and low power consumption. The more advanced the devices, the higher the degree of circuit integration, and the distance between devices is only A few tenths of a micron, so as long as there is a slight pulse impact in the power supply, it may cause damage to the components in the circuit. However, they are more concealed, and they are gradually causing damage. The damage is not as serious as lightning. It is mainly reflected in the shortened life, so it is not easy to attract attention.
For this transient overvoltage in the power supply, the UPS and the regulator not only do not protect, but instead they themselves become objects of protection.
Second, the working principle and choice of instantaneous overvoltage protector
For the three types of overvoltage damage mentioned above, we should install overvoltage protection at all ports where the CCTV monitoring system equipment is connected to the outside world (such as power cable, video signal transmission line, control signal transmission line, etc.). Bypassing the overvoltage that appears at the port to the ground so that it does not damage the equipment in the equipment room. This kind of protector is still used to be called "arrester arrester" in China, and is called "overvoltage limiter" or "surge suppressor" (SURGEARRESTER) and "transient voltage surge suppressor" (TRANSIENTVOLTAGESURGESUPPRESSION) abroad. )Wait.
The working principle is: when the voltage on the line is within the normal range, the protector (TVSS) exhibits high impedance, which is equivalent to an open circuit. When the voltage on the line exceeds the set range, the protector quickly exhibits a low impedance, venting all or most of the instantaneous over-voltage energy. Thereby achieving the purpose of protecting the equipment.
It is necessary to install a protector to prevent overvoltage. For those who have suffered such damage, install a protector to prevent further damage; for those who have not suffered such damage, the equipment can be protected from damage after the device is over-voltage protector, and it can be prevented beforehand. Extend the life of the equipment to ensure the normal operation of the entire CCTV monitoring system. Due to the large size caused by lightning, the selection of overvoltage protector can focus on lightning wave intrusion:
1. The overvoltage protector should be selected to withstand a larger current (ie, the flow capacity is large)
In most cases, the lightning current is not large, and the probability of a large current is low. For example, the probability of a 100KA lightning current is about 12%. Although the probability is low, it may appear after all, and when it is unpredictable. of. Therefore, if economic conditions permit, the protector can be used to withstand larger currents.
2, overvoltage protector must choose low residual voltage
The residual voltage at both ends of the protector is the lowest voltage applied to the device (taking into account the additional voltage of the lead). Under the same inrush current, the lower the residual voltage, the better the protection performance, and the more effective the device can be.
3, overvoltage protector to choose performance / price ratio
The price of overvoltage protectors with different performance indicators will vary greatly. Therefore, you can't just look at the price, you should also make a performance comparison.
At present, the most common overvoltage protectors (arrest arresters) on the market are: Thunder Sky LKWX protector, Miyazaki (HYC1) protector, ESPfurse protector, DEHN protector, TVS of North American Technology Corporation.
Third, how to suppress transient overvoltage in CCTV surveillance system
The building where the CCTV monitoring system monitoring center is located shall have lightning rods, lightning protection belts or lightning protection nets for direct lightning protection. The measures against direct lightning shall comply with the provisions of GB50057-94 on direct lightning protection. The grounding system is one of the necessary components of the lightning protection system. All lightning protection systems should have reliable and effective grounding. Good grounding is a vital part of lightning protection. The front-end and terminal equipment of CCTV monitoring system should have good lightning protection grounding. The smaller the grounding resistance value is, the lower the voltage value is. When the monitoring center room is equipped with a dedicated grounding device, the grounding resistance shall not exceed 4 Ω. When using a comprehensive grounding grid, the grounding resistance shall not exceed 1 Ω. Front-end equipment such as cameras should be placed within the effective protection range of the lightning receptor (lightning rod or other lightning conductor). The various metal lines entering the monitoring center room should be connected to the grounding device.
Since the energy of the lightning strike is very large, it is necessary to gradually discharge the lightning energy to the earth through the staged discharge. Therefore, it is not enough to install lightning protection pins and grounding grids in the CCTV monitoring system. It is also necessary to take the intrusion path of the closed circuit television monitoring system (power line, video signal transmission line, control signal transmission line, etc.). Measures.
1. Protection of transient overvoltage on the power line in CCTV monitoring system
Since 80% of lightning strikes are intruded from the power line, in order to ensure the safety of the monitoring security system equipment, all the AC power incoming lines of the monitoring security system are effectively protected against lightning. The corresponding power overvoltage protector should be installed at the AC power inlet of the front-end equipment. The power cord that enters the monitoring equipment room should consider three-level protection. Install a primary power over-voltage protector at the power incoming line of the building's main power distribution room, and install it at the power incoming line of the distribution box on the floor where the monitoring room is located. The secondary power overvoltage protector is installed with a three-level power overvoltage protector at the power incoming line of the important equipment in the monitoring room.
1. It has been equipped with lightning rods, grounding grids, and joint grounding. Why are closed-circuit television monitoring system equipment sometimes damaged by lightning?
When the lightning current passes through the lightning rod and is introduced into the ground into the ground, the ground potential instantaneously rises. Assume that the lightning current I=50KA, the grounding resistance R=1Ω, the ground potential ΔU=I×R=50KA×1Ω=50KV.
Because the joint grounding is adopted, the ground potential of the device is also increased by 50KV, and the power supply line and the signal transmission line are led from a distance, and the remote ground potential is still at zero potential, so the ground potential of the device casing will be between the power input terminal of the device. A large potential difference of 50KV occurs between the signal input terminal (referred to as "counter-attack" or "negative potential introduction" in lightning protection technology), causing damage to the corresponding parts of the device.
If the grounding of the grounding network is not good enough, the counterattack voltage will be higher and the damage may be more serious.
2. The monitoring center computer room is not affected by lightning, but there is lightning in the distance. Why is the equipment in the monitoring center machine room sometimes damaged?
The transmission line of the camera of the front-end equipment of the CCTV surveillance system is drawn from the remote computer room. Assume that there is a lightning strike near the transmission line, and an instantaneous overvoltage is induced on the transmission line. This induced high voltage extends along the transmission line to both ends. If the monitoring center room is not too far from the lightning point, the induced voltage may still have a certain strength when it is transmitted to the equipment room, which may damage the equipment in the equipment room.
3. In the days when there is no thunder, why is the power module of the monitoring center room equipment still damaged?
For the power supply line, we always mistakenly believe that a very clean sine wave flows through the line. In fact, due to the switching of the power grid, the start and stop of the inductive load in the same power grid, etc., various voltage interferences may occur in the power supply line. Among the harmful interferences of the power grid, the incidence of instantaneous oscillations and transient pulses is high.
This transient voltage duration is very short, only a few microseconds short, non-dedicated instruments are not easy to find, but their damage to the equipment can not be underestimated. Because modern surveillance security devices are microelectronic products, these monitoring devices have the characteristics of high density, high speed, low voltage and low power consumption. The more advanced the devices, the higher the degree of circuit integration, and the distance between devices is only A few tenths of a micron, so as long as there is a slight pulse impact in the power supply, it may cause damage to the components in the circuit. However, they are more concealed, and they are gradually causing damage. The damage is not as serious as lightning. It is mainly reflected in the shortened life, so it is not easy to attract attention.
For this transient overvoltage in the power supply, the UPS and the regulator not only do not protect, but instead they themselves become objects of protection.
Second, the working principle and choice of instantaneous overvoltage protector
For the three types of overvoltage damage mentioned above, we should install overvoltage protection at all ports where the CCTV monitoring system equipment is connected to the outside world (such as power cable, video signal transmission line, control signal transmission line, etc.). Bypassing the overvoltage that appears at the port to the ground so that it does not damage the equipment in the equipment room. This kind of protector is still used to be called "arrester arrester" in China, and is called "overvoltage limiter" or "surge suppressor" (SURGEARRESTER) and "transient voltage surge suppressor" (TRANSIENTVOLTAGESURGESUPPRESSION) abroad. )Wait.
The working principle is: when the voltage on the line is within the normal range, the protector (TVSS) exhibits high impedance, which is equivalent to an open circuit. When the voltage on the line exceeds the set range, the protector quickly exhibits a low impedance, venting all or most of the instantaneous over-voltage energy. Thereby achieving the purpose of protecting the equipment.
It is necessary to install a protector to prevent overvoltage. For those who have suffered such damage, install a protector to prevent further damage; for those who have not suffered such damage, the equipment can be protected from damage after the device is over-voltage protector, and it can be prevented beforehand. Extend the life of the equipment to ensure the normal operation of the entire CCTV monitoring system. Due to the large size caused by lightning, the selection of overvoltage protector can focus on lightning wave intrusion:
1. The overvoltage protector should be selected to withstand a larger current (ie, the flow capacity is large)
In most cases, the lightning current is not large, and the probability of a large current is low. For example, the probability of a 100KA lightning current is about 12%. Although the probability is low, it may appear after all, and when it is unpredictable. of. Therefore, if economic conditions permit, the protector can be used to withstand larger currents.
2, overvoltage protector must choose low residual voltage
The residual voltage at both ends of the protector is the lowest voltage applied to the device (taking into account the additional voltage of the lead). Under the same inrush current, the lower the residual voltage, the better the protection performance, and the more effective the device can be.
3, overvoltage protector to choose performance / price ratio
The price of overvoltage protectors with different performance indicators will vary greatly. Therefore, you can't just look at the price, you should also make a performance comparison.
At present, the most common overvoltage protectors (arrest arresters) on the market are: Thunder Sky LKWX protector, Miyazaki (HYC1) protector, ESPfurse protector, DEHN protector, TVS of North American Technology Corporation.
Third, how to suppress transient overvoltage in CCTV surveillance system
The building where the CCTV monitoring system monitoring center is located shall have lightning rods, lightning protection belts or lightning protection nets for direct lightning protection. The measures against direct lightning shall comply with the provisions of GB50057-94 on direct lightning protection. The grounding system is one of the necessary components of the lightning protection system. All lightning protection systems should have reliable and effective grounding. Good grounding is a vital part of lightning protection. The front-end and terminal equipment of CCTV monitoring system should have good lightning protection grounding. The smaller the grounding resistance value is, the lower the voltage value is. When the monitoring center room is equipped with a dedicated grounding device, the grounding resistance shall not exceed 4 Ω. When using a comprehensive grounding grid, the grounding resistance shall not exceed 1 Ω. Front-end equipment such as cameras should be placed within the effective protection range of the lightning receptor (lightning rod or other lightning conductor). The various metal lines entering the monitoring center room should be connected to the grounding device.
Since the energy of the lightning strike is very large, it is necessary to gradually discharge the lightning energy to the earth through the staged discharge. Therefore, it is not enough to install lightning protection pins and grounding grids in the CCTV monitoring system. It is also necessary to take the intrusion path of the closed circuit television monitoring system (power line, video signal transmission line, control signal transmission line, etc.). Measures.
1. Protection of transient overvoltage on the power line in CCTV monitoring system
Since 80% of lightning strikes are intruded from the power line, in order to ensure the safety of the monitoring security system equipment, all the AC power incoming lines of the monitoring security system are effectively protected against lightning. The corresponding power overvoltage protector should be installed at the AC power inlet of the front-end equipment. The power cord that enters the monitoring equipment room should consider three-level protection. Install a primary power over-voltage protector at the power incoming line of the building's main power distribution room, and install it at the power incoming line of the distribution box on the floor where the monitoring room is located. The secondary power overvoltage protector is installed with a three-level power overvoltage protector at the power incoming line of the important equipment in the monitoring room.
Bathroom Vanity,Bathroom Vanity Units,Bathroom Vanities With Tops,Double Sink Vanity
Ningbo Oulin Import&Export Co.,Ltd. , https://www.oulinfurniture.com