Lightning is the phenomenon of natural discharge in the atmosphere. The intensity of lightning activity is usually represented by the average annual thunderstorm day. According to the statistics of the state's meteorological data, the city belongs to a multi-relief area. The so-called thunderstorm is the day when there is a lot of electromagnetic thunderclouds in the sky, or the clouds are rapidly discharged to the earth, and they produce a strong flash of light, accompanied by a huge lightning strike. The discharge between clouds mainly causes damage to the aircraft. The discharge of clouds to the earth is extremely harmful to buildings and people. The technical principle of modern lightning protection is to emphasize comprehensive protection, comprehensive management, and multi-layered defense, and design lightning protection as a systematic project. As the danger of lightning is pervasive, the destructive effects of lightning are mainly caused by the following aspects:
1, direct lightning:
Direct lightning strikes lightning directly on the building. Since lightning strikes, the lightning voltage is as high as several million to tens of millions of volts, and the lightning current is as high as tens of thousands to several hundred thousand amps. The moisture on the objects through which strong lightning currents pass is vaporized and expanded, resulting in strong thermal effects and mechanical The effect of destroying buildings and causing fires.
2. Inductive Ray:
Inductive lightning refers to all objects on the ground when a cloud strikes, especially conductors. Because of electrostatic induction, a large number of binding electric charges of the opposite polarity of lightning are gathered. After the thundercloud hits the ground or is struck by another thundercloud, The charge in the cloud becomes a free charge, resulting in a very high electrostatic voltage (induction voltage). Its overvoltage amplitude can reach tens to hundreds of thousands of volts. This overvoltage tends to cause wires in the building. , The poorly grounded metal conductors and large metal devices cause electric sparks due to discharge, which can cause fires, explosions, endangering personal safety, or damage to the power supply system. In another case, when lightning strikes, a strong induced electromagnetic field is formed near the passage of the lightning current due to a large rate of change of the lightning current, which causes interference or destruction to the electronic equipment in the building, or causes The surrounding metal components generate inductive currents that generate large amounts of heat and cause fires. In addition, when overhead lines are subjected to direct lightning strikes or induced lightning, high potentials can enter the substations or buildings along the power lines and signals of the conductors. This type of lightning surge can also cause damage to electrical equipment or make it inside buildings. Discharge of metal equipment, causing damage. Therefore, the fundamental method to prevent the internal equipment of the building from being damaged by lightning is to make the building have a complete set of lightning protection facilities. In order to achieve its protection against different lightning damages, it is necessary to adopt lightning protection, shunting, shielding and pressure equalization. Technical measures such as grounding and grounding, therefore, the lightning protection facilities of a building shall include eight technical links: earthing body, down conductor, lightning protection grid, lightning protection zone, lightning arrester, pressure equalizing ring, equal potential and arrester. Effectively use the building structures to weld each other into a net, perform cage shielding and equipotential processing. This design is not only economical but also accords with the idea of modern lightning protection. It provides basic conditions for the prevention of lightning and electromagnetic pulse (LEMP) destruction in electrical and electronic equipment. It utilizes the structural reinforcements such as foundation piles and beams and columns of buildings to serve as lead wires and cables. The grounding device has the advantages of economy, estheticity, and facilitates the flow of lightning currents, and does not require maintenance and long life. The building ribs, the main ribs in the ground beam and the main ribs in the column are welded together, and the middle (grid) of the ground beam outer beam is welded into a closed loop to form a complete grounding system. This grounding system has a wide contact area with the earth and low grounding resistance, and the steel bars are protected by concrete, reduced by erosion, and the grounding resistance is relatively stable.
The comprehensive protection of modern thunder and lightning not only solves the direct thunder and thunder protection of buildings, but also the LEMP protection for various metal pipes, power lines and letterhead lines entering the building to ensure the electrical and electronic equipment in the building. Safety. The use of lightning protection strips, nets, and column reinforcements in the surrounding walls of the building as deflectors, and the welding of beam reinforcements, makes good electrical connections to metal components such as pipes and metal pipes entering the building. In this way, the entire building forms an ideal "Faraday cage" shielding net. Not only can make the lightning current have a good flow path, the pressure distribution and shunt, grounding resistance is small, and the entire building forms a uniform equipotential system to maintain the pressure equalization. With the use of the grounded body of the underground building, the grounding resistance is greatly reduced due to the large area of the grounding body. Column bars are used as deflectors. Due to the multiple deflectors, the diversion effect is good, and the current value of the deflectors can be greatly reduced. Therefore, lightning strikes or counterattacks can be avoided when lightning strikes. In the lightning protection of high-rise buildings, it is considered that there is a long flow of lightning current. The potential gradient from the air receiver to the down conductor to the grounding device is large. In order to equalize the potential and reduce the potential gradient, the reinforcement of the high-rise outer ring beam is welded into a closed loop to form a horizontal lightning protection belt, which can effectively prevent side-impact lightning. But it has greatly weakened it. With the rapid development of information technology, modern high-tech electronic devices are widely used. Due to their high sensitivity and low voltage, they are easily induced by lightning electromagnetic pulses. Therefore, buildings should be equipped with low-voltage lightning arresters on the low-voltage side and lightning arresters and electrical busbars on various floors to minimize damage to the shortest path and electronic equipment. Practice has proved that the safety effect is quite significant.
Therefore, engineering and technical personnel engaged in lightning protection design, auditing, and lightning protection quality must increase the publicity of policies and regulations, comply with laws and regulations, and do all appropriate lightning protection measures in accordance with the classification requirements of building lightning protection, and pay attention to all aspects. Quality ultimately makes the building's lightning protection facilities truly play a role in protecting the safety of people and equipment in buildings and buildings.