1) Lightning strike is a natural phenomenon, which can release huge energy and have great destructive power. The main ways of lightning strike ginseng, equipment and facilities are: lightning strike, lightning induction and lightning electromagnetic pulse. Lightning protection mainly adopts the following measures: conduction, lap joint, grounding, shunt, shielding and avoidance.
2) Lightning can cause many different forms of harm, and there is no way to completely prevent the harm of lightning.
3) Direct lightning: It is a phenomenon of rapid discharge between charged clouds (Lei Yun) and building frames, other objects, the earth or lightning protection devices, and a series of destructive effects such as electric effect, thermal effect or mechanical force, which do harm to buildings, electronic equipment and people in buildings. The peak voltage of direct lightning can usually reach tens of thousands or even millions of volts, and the peak current can reach tens or even hundreds of kA. It is extremely destructive because the energy contained in thunderclouds is released in a very short time (its duration is usually only a few microseconds to hundreds of microseconds), and it is extremely powerful in an instant.
Defense against direct lightning: usually, structural steel bars such as foundation piles, beams and columns of buildings are fully used as down lead and grounding devices, and lightning rods, lightning strips, lightning wires, lightning nets or metal objects are used as lightning receptors to receive lightning current, and then the lightning current is guided to underground grounding devices and scattered underground through metal conductors as down lead.
4) Lightning induction: When thunder clouds come, all objects on the ground, especially conductors, gather a lot of bound charges with the opposite polarity to lightning due to electrostatic induction. After Lei Yun landed or released another Lei Yun, the charge in the cloud turned into free charge, resulting in extremely high electrostatic voltage (induced voltage), and its overvoltage amplitude can reach tens of thousands to hundreds of thousands of volts. This overvoltage often causes the discharge of nearby outdoor transmission signal lines, buried power lines, connecting lines between equipment, poorly grounded metal conductors and large metal equipment, resulting in fire, explosion, personal safety or harm to power supply system. In addition, when lightning strikes, due to the large change rate of lightning current, a strong induced electromagnetic field is formed near the passage of lightning current, which causes interference and damage to the electronic equipment in the building, or generates induced current to the surrounding metal components, thus generating a lot of heat and causing a fire.
Although induction lightning is not as violent as direct lightning, its probability of occurrence is much higher than direct lightning. The effective means to prevent induced lightning is shielding, which connects the steel bars, metal doors and windows, metal pipes leading into buildings and structures in the roof and wall of buildings. And can defend against lightning induction when reaching a certain grid distance.
5) Lightning surge: When the line is subjected to direct lightning or lightning induction, high potential will invade the substation or building along the conductor power line and signal, and this lightning wave intrusion will also cause harm to electrical equipment or discharge metal equipment in the building, causing damage. The most common harm of electronic equipment is not caused by direct lightning strike, but the current surge induced in power supply and communication lines during lightning strike. On the one hand, due to the high integration of the internal structure of electronic equipment, the withstand voltage and overcurrent level of the equipment decrease, and the ability to resist lightning (including induced lightning and operating overvoltage surge) decreases. On the other hand, due to the increase of signal source path, the system is more vulnerable to the invasion of lightning waves than before. Surge voltage can jump into computer equipment from power line or signal line. The main sources of surge voltage in signal system are induced lightning strike, electromagnetic interference, radio interference and electrostatic interference.
Lightning protection electromagnetic pulse: when the line enters the building, it is connected with grounding device and equipped with surge protector.