We are currently experiencing thunderstorms. We sometimes see some towering trees knocked down by lightning, while some surrounding towers, high-rise buildings and other high-rise buildings are safe and sound. What is the reason for this?
These towering trees are induced by the clouds that carry a large amount of charge, and they also carry a large amount of charge. When the accumulated charge is too much, the tree will be knocked down.
Under the same circumstances, the safety of high-rise buildings may be attributed to lightning rods. On many high towers, there is something made of metal, shaped like an embroidery needle, with the needle pointing upright. This is a lightning rod.
So, why does this unassuming thing like an embroidery needle have such a great effect in "lightning protection"? In fact, the lightning rod should be called a "lightning rod".
The working principle of a lightning rod
The entire working process of a lightning rod is to attract lightning, and then conduct the lightning to the earth, so that the earth absorbs the lightning.
To complete this process, three things are needed - air terminal, down conductor, and grounding body.
So, the lightning rod attracts all the lightning within a certain range to itself, and then guides it underground to nip it in the bud. The protection range of a lightning rod is related to its height and size.
What we call lightning rods every day is a type of air terminal. In addition to lightning rods, there are also lightning protection wires, lightning protection belts, lightning protection nets, etc. The function of the air terminal is to attract lightning.
When the lightning rod is working, it is connected to the earth through the down conductor and the grounding body, so that the potential on the lightning rod is the same as the earth (the earth potential is extremely low). Because the height of the lightning rod is high, its potential is low. Lightning with extremely high potential is naturally attracted to the lightning rod. After the lightning rod attracts the lightning, the potential at the top increases and the current begins to flow to the earth.
Due to the large current generated by lightning, a strong electromagnetic field will be generated on the lightning rod, which will form a path between the lightning rod and the lightning, and the lightning will be continuously directed into the earth.
The role of lightning rods
Installing lightning rods is an effective way to avoid lightning strikes. A metal rod is erected at the highest point of the house. The lower end of the rod is connected to a thick enough copper wire. The lower end of the copper wire is connected to a metal plate and buried deep in the ground in a moist place. The upper end of the metal rod must be a pointed end or be bifurcated into several pointed ends. With such a device, when there are charged clouds in the sky. The tip of the lightning rod concentrates heterogeneous charges due to electrostatic induction, resulting in tip discharge, which neutralizes the electricity in the cloud to avoid violent lightning. This is one aspect of the lightning rod's ability to protect against lightning. But this effect is quite slow. If the electricity accumulates quickly in the cloud, or a cloud with a large amount of charge suddenly flies over, sometimes there is no time to neutralize it in the above way, so there is a strong discharge and thunder and lightning will still occur. But at this time, because the lightning rod is higher than the surrounding objects, its tip concentrates charges that are different from the electricity in the cloud. If lightning occurs between the cloud and the ground object, the discharge current mainly flows into the earth through the lightning rod, so there will be no strike. If it hits the house or people nearby, it will only hit the lightning rod.
It can be seen that the tip discharge of the lightning rod will reduce the possibility of lightning between ground objects and clouds; when it is inevitable, it will bear the lightning strike itself, and houses and people will be safe. Due to the structure and function of the lightning rod, we must pay special attention to maintaining good electrical conductivity of the lightning rod. Once there is a bad connection or break, the section above the break becomes an isolated conductive system. When there is charge in the cloud, the upper part of the separated part induces a charge with a different sign from the electricity in the cloud, while the lower part induces a charge with the same sign as the electricity in the cloud. If the upper part and the electricity in the cloud act to discharge, a powerful The discharge current can only release a large amount of heat through the building, thus causing lightning strikes. This not only fails to protect against lightning, but also causes lightning disaster.
To prevent accidents, it is best to erect several lightning rods on tall buildings. In addition, each lightning rod can only protect a certain building area. For larger buildings, several lightning rods also need to be erected