Basic principle of lightning protection

The basic principle of lightning protection:

The so-called lightning strike protection: is to introduce the energy of the lightning current into the earth as much as possible through reasonable and effective means, which is to divert, not to block or eliminate lightning. A complete lightning protection system consists of two aspects: direct lightning protection and inductive lightning protection. The lack of either side is incomplete, flawed, and potentially dangerous. Generally we divide it into two parts: external lightning protection and internal lightning protection. The lightning protection system consists of lightning rods (or lightning protection belts, lightning protection nets), down conductors and grounding systems, mainly to protect buildings from fire accidents and personal safety accidents caused by lightning strikes, while internal lightning protection systems prevent lightning and Other forms of overvoltage intrusion into the equipment cause damage, which is not guaranteed by the external lightning protection system. In order to achieve internal lightning protection, the installation of overvoltage protectors for cables and metal pipes entering and leaving the protection zones of the buildings shall be protected and well grounded. .

A. Multi-level classification (class) protection principle : that is, according to different functions of electrical and microelectronic equipment, protected procedures and protected areas, the protection points are classified and protected; according to the possible channels of lightning and operation transient overvoltage hazard, Power lines, data, and communication lines should be protected by multiple levels.

B. External passive protection : passive protection is provided in the 0-level protection zone, which mainly relies on lightning rods (net, wire, belt) and grounding devices. Protection principle: When the thundercloud discharge is close to the ground, it causes the ground electric field to be distorted. At the top of the lightning rod (wire), a local electric field intensity distortion is formed to affect the development direction of the lightning pilot discharge, guide the lightning to discharge the lightning rod (wire), and then pass the grounding down conductor, and the grounding device introduces the lightning current into the earth, thereby being protected. The object is protected from lightning strikes. This is an effective method for preventing direct lightning strikes that has been proven by people for a long time. All exposed metal components (pipes) of the building should be well connected to the lightning protection net (belt, wire).

C , internal protection

(1), power supply part protection: lightning infringement is mainly through the line intrusion. There is a dedicated high-voltage lightning protection device for the high-voltage part of the power station. The power transmission line limits the power to the ground to less than 6000 volts (IEC 62.41), while the line-to-line is uncontrollable. Therefore, the 380v low-voltage line should be over-voltage protected. It should be divided into three parts according to the national standard: It is recommended to install a surge protector at both ends of the high-voltage transformer to the cable core at the front end of the main switchboard. Protection; install a surge protector at both ends of the cable inner core between the building's main switchboard and each floor distribution electrical box for secondary protection; cope with all important, sophisticated equipment and front end of the UPS Install a surge protector as a three-level protection. The purpose is to use the shunt (limited) technology, that is, the high-absorption energy shunt device (surge protector) to divert the energy of the lightning over-voltage (pulse) into the earth for protection purposes. Therefore, the shunt and equipotential technology are adopted. The quality and performance of the protector is the key to the network protection. Therefore, it is important to choose a qualified surge protector.

(2), signal partial protection:

For information systems, it should be divided into rough protection and fine protection. The coarse protection level is determined according to the level of the protected area, and the fine protection is determined according to the sensitivity of the electronic device. The main considerations are: satellite receiving system, dian system, network dedicated line system, monitoring system, etc. It is recommended that all information systems enter the cable inner core end of the building, and install a surge protector. The empty wire in the cable should be grounded and shielded and grounded. Pay attention to the online voltage, transmission rate and press of the system equipment. Port type, etc., to ensure the normal operation of the system.

(3), grounding treatment

In the construction of the computer room, a good grounding system is required, because all lightning protection systems are required.

The grounding system is used to discharge lightning current into the earth to protect equipment and personal safety. If the grounding system of the equipment room is not well done, it will not only cause equipment failure, but also burn out the components, which will seriously endanger the safety of the workers. There is also an anti-interference shielding problem, and the anti-static problem needs to be solved by establishing a good grounding system. Generally, the grounding system of the whole building includes: building ground network (connected with Faraday network), power ground (required ground resistance is less than 10 ohms), logical ground (also called signal ground), lightning protection ground, etc. IBM) requires a separate, independent, required ground resistance of less than 4 ohms (may be less than 1 ohm depending on the actual situation). However, when the localities must be independent, if the distance between them does not meet the requirements of the specification, the ground potential counterattack is likely to occur. Therefore, when the distance between the grounding systems does not meet the requirements of the specification, they should be connected as much as possible. If the actual situation does not allow direct connection, the potential connection can be achieved by the ground potential equalizer. In order to ensure the normal operation of the system, the precision resistance meter should be used regularly to detect the ground resistance value every year. The grounding device consists of a grounding electrode and some accessories and auxiliary materials. The selection and construction of the grounding device is mainly determined by the soil structure, that is, the earth resistivity ρ of the soil. Different layers of soil structure are different, so the ground resistance rate ρ is different. In order to increase the efficiency of the grounding device, a long-term resistance reducing agent can be used.

D. There are external lightning protection measures and it is necessary to improve internal lightning protection measures.

We know that the lightning down of the lightning protection facilities in the external lightning protection measures will have a large transient current after the lightning is connected, which means that a large transient electromagnetic field (LEMP) will be generated around. Therefore, the installation of external lightning protection measures is not a substitute for internal lightning protection measures. Furthermore, we all know that the working principle of the lightning rod is to attract lightning. Therefore, after the lightning rod is installed, the lightning protection system of the building will be more likely to be struck by lightning, which means that the probability of LEMP will increase. The distance from the overvoltage generating point will be shortened (down to the line), so buildings with computer networks such as external lightning protection measures require internal lightning protection measures.