In the domestic security industry, there is a common practice and point of view is that lightning protection should be grounded, as long as the ground can be lightning, grounding can prevent interference. Taking grounding as the main measure of lightning protection and anti-interference of the security system has led to frequent occurrence of multi-point grounding security systems. According to a large number of engineering cases, it can be seen that such an approach can cause inexplicable burning of equipment when it does not rain or when it does not rain. So how does the security monitoring system take lightning protection measures?
Let us first understand that the hazards caused by lightning are divided into direct-once-lightning and induced-lightning. Direct lightning can only release current through the lightning rod to the earth to protect the object, which is the situation mentioned above. The security industry is receiving lightning from lightning. Induced lightning refers to the thunder and lightning in the discharge process, due to strong lightning electromagnetic pulse, through the conductive body, so that all 3-5 km of electronics, communications equipment has been severely damaged. This type of damage does not necessarily have a clear lightning strike, but once it occurs, it will seriously affect the normal operation or outage of engineering equipment. Sudden security incidents cannot be recorded, and it has an impact on our society and personal safety. Major influence. So you also need to install lightning protection devices.
In fact, lightning protection is not as simple as grounding. The premise of doing lightning protection and grounding is to do a good job in basic safety. How to make lightning protection for security systems? Actually, measures should be taken based on the characteristics of the Earth's electromagnetic environment and wide-area systems:
1. The monitoring system of a residential area is a wide-area system that connects to each building and external camera. Each building has its own joint grounding device, including lightning protection grounding of the building, power grid grounding, and equipment safety grounding, etc., all connected to a unified “equipotential earthing body”, and strive to make the entire grounding point in the building do “etc. Potential float". The lightning protection system of any building will cause sudden changes in the ground potential at the ground contact point of the building. If the host is connected to the ground in one building, the second building is connected to flash, and the ground potential of the second building is abrupt. The ground potential of the monitoring system here also mutates with “equipotential floating”, and the monitoring system cable takes the “abrupt ground potential” here. Lead to the grounding point of the main building of the No. 1 building, and conduct it to the entire system. Causes extensive damage to the system; this is the basic concept of "lightning ground potential."
2. Both the first floor and the second floor have their own "equipotential grounding body", but there is no, or impossible, effective equipotential bonding between the two floors. This is an objective reality. It's called the electromagnetic environment. The meaning of the "wide area" of the so-called wide-area information system is, in this case, the system is connected to a number of "independently grounded equipotential areas" of the equipment, and these "independently grounded equipotential areas" are not done or are impossible. An effective "equipotential bonding" is achieved, but monitoring equipment installed in these different equipotential areas has an effective cable electrical connection. If the system is grounded at multiple points, these cables can be connected to each other independently of one another. The fluctuation or abrupt change of the ground potential in the equipotential zone is transmitted to the system in a larger range and causes damage. This causes safety hazards in the system ground potential loop.
3. The simple understanding of “grid ground potential” is that there are many types of grounding methods and functions for power grids and electrical equipment, and weak information systems are designed. These grounding methods and functions may not be carefully studied, but it must be known that: In the event of a fault or equipment failure, the "essence of grounding" is to ground the high potential of the fault point. "High-potential grounding" will cause "ground current", and "ground potential fluctuation" will also form on the ground resistance - " The "equipotential bonding body" conducts this "potential fluctuation" to a wider range, including conduction to the grounding equipment of the monitoring system, and affects the safety of the entire monitoring system through the system cable. This is the basic "grid ground potential". concept.
4. The "grid ground potential" and "lightning ground potential" are the two major factors that make up the "magetic environment." Its characteristics are: “Lightning ground potential” has high transient voltage, short duration, and low probability of occurrence. “Ground potential” is not as high as lightning ground potential, but its duration is long, mostly in the second. (that is, troubleshooting time). The “ground potential difference” of a few volt can constitute the interference of the monitoring system. The potential difference of tens of volts or more can burn down the IC circuit, breakdown or even burn the signal lightning protector. Non-thunderstorm weather can still cause grid fault and power grid. Ground potential; high probability of occurrence, wide distribution area, long duration is the main characteristics of "grid ground potential";
5. The "magnet electromagnetic environment" is a problem that must be paid serious attention to the safety design of surveillance (information) systems, but it has always been a problem that has been widely overlooked. For many years, the “grounding and lightning protection” caused a large number of damages to the monitoring system, which led us to gradually realize the objective reality of the “magnetism electromagnetic environment”. Only then can we understand the nature of the “potential hazard of the ground potential loop” and understand the grounding lightning protection. The lightning protection is invalid, and the introduction of system security hidden dangers is 100% effective. It can also be proposed that the system single-point grounding is the basic principle of the wide area information system security design.
6, cable lightning EMF is a high-frequency alternating voltage, the location of the equivalent in the middle of the cable. The basic practice of inductive lightning protection is to set a “voltage limiting protection circuit” for the input and output interfaces of the equipment.
After the above analysis and conclusion, the security system can not be grounded to prevent lightning, grounding can prevent interference, but must take the actual characteristics of the corresponding measures taken.
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