What is a Lightning Rod?

Lightning rods, also known as lightning rods and lightning rods, are devices used to protect buildings and tall trees from lightning strikes. An air-termination device is installed on the top of the object to be protected, and connected to the underground drain network buried in the ground with a wire conforming to the specifications. Lightning rod specifications must meet GB standards, and the lightning rod height specifications required for each lightning protection category are different. ^[1]

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The lightning rod is a former name. In the national standard GB50057-2010 "Code for Design of Lightning Protection of Buildings" of the People's Republic of China, this title has been abandoned and replaced by '

If a building has an air-termination system but it is not grounded or the grounding effect is not good, it will cause greater damage to the building or its personnel when the air-termination system is connected, compared with a building without an air-termination system. Safety. Occurred in Chongqing County in 2007

Franklin

Modern lightning rods are

During a thunderstorm, a large amount of charge is induced on both the lightning rod and the top of the high-rise building when a charged cloud appears over it. Because the needle of the lightning rod is pointed, the conductor tip always collects the most charge during electrostatic induction. In this way, the lightning rod collects most of the charge. The lightning rod forms a capacitor with these charged cloud layers, because it is sharp, that is, the area of the two plates of the capacitor is very small, and the capacitance is very small, which means that it can hold very little charge. And it collects most of the charge, so when there is more charge on the cloud layer, the air between the lightning rod and the cloud layer can be easily penetrated and become a conductor. In this way, the charged cloud layer forms a path with the lightning rod, and the lightning rod is grounded. The lightning rod can introduce the charge on the cloud layer to the ground, so that it does not pose a danger to high-rise buildings and ensure its safety.

The lightning protection effect of the lightning rod is that it can lead the lightning from above the protective object to itself and safely leak into the earth through itself. Therefore, its lightning performance and discharge performance are of vital importance. The experimental and theoretical analysis of the lightning performance of lightning rods is as follows:

The lightning protection airspace of a lightning rod erected on a flat ground is shown in Figure 1. The simplified envelope is a parabola. This line is the average of 50% of the lightning stroke of the lightning rod under the positive and negative thunder clouds.

1. All metal parts must be

The welding place is not full, the flux is not clean, and the anti-rust paint is leaked. Should be repaired in time, knock off the skin, brush with anti-rust paint.

Conventional lightning protection can be divided into direct lightning protection, induction lightning protection and comprehensive lightning protection. Lightning protection devices against direct lightning strikes generally consist of three parts, namely the lightning receptor,

1. Reasonable selection of the calculation method for the protection range of lightning rods. The calculation methods for the protection range of commonly used lightning rods (here, only single needle) are mainly the folding line method and the rolling ball method. The main feature of the "folding line method" is that the design is intuitive, the calculation is simple, and it can save investment, but it is not suitable for buildings greater than 20m in height. The main feature of the "rolling ball method" is that it can calculate the lightning rod or the combination of the lightning rod and the grid. The scope of protection is relatively complex, but the investment cost calculated by this method is relatively large.
Among these two calculation methods, the "folding line method" is a relatively mature method. In the power system, it is also called the "rule method". That is, the protection range of a single lightning rod is a broken line cone with the lightning rod as its axis. The protection range of a single lightning rod is specified in the DL / T620-997 "Overvoltage Protection and Insulation Coordination for AC Electrical Installations" standard; the "rolling ball method" is a calculation of the lightning protection range recommended by the International Electrotechnical Commission (IEC) One way. China's building lightning protection code GB50057-1994Z also uses the "rolling ball method" as a method to calculate the protection range of lightning rods. The rolling ball method is a sphere with a radius of hR rolling along the part to be protected from lightning. When the earth touches a metal object that can withstand lightning strikes), but does not touch the part to be protected, the part is protected by the air-termination device. In recent years, the "rolling ball method" stipulated in the national standard has also begun to be recognized by the industry, but in practice, the "rolling ball method" also encountered some problems, especially when calculating the protection range of lightning rods in the sky. Generally speaking, these two algorithms have their own characteristics. Generally, high-rise buildings use the "rolling ball method".
2. Is it safe to use a lightning rod in advance?
In fact, no lightning protection equipment is foolproof. There is no lightning strike in the protection range, but the lightning strike energy is small. From an economic point of view, it is also very wasteful to be foolproof. Therefore, the "Lightning Protection Design Code for Buildings" and other design codes and standards have "reduced" lightning strikes as a requirement. Therefore, the lightning protection device designed according to national and international standards is not 100% safe. In addition to direct lightning strikes, high-rise buildings may also be affected by side strike and induction lightning.
There are two main advantages of early discharge lightning rods. One is that they can "discharge ahead" and have better lightning performance than ordinary lightning rods. The second is that after converting its pre-discharge time to pre-discharge distance, it is equivalent to increasing the height of the lightning rod, which can increase the protection radius. However, there is still no way to protect against side strike lightning and induction lightning.
3. It is important to ensure the lightning discharge capacity of the lightning rod. <br /> Various lightning protection specifications require the lightning rod to have an independent down-conducting ground, so that lightning current can be quickly discharged into the ground. When purchasing, you must not listen to the suggestions of some irregular manufacturers, and connect the lightning rod to the grounding system of the building itself to save costs.
4. It is very important to choose a regular lightning protection manufacturer. Lightning rods are actually lightning rods, so the lightning protection project needs to undergo rigorous scientific calculations, and it may be "induced into the room" by accident. Therefore, when choosing a lightning rod supplier, you need to check whether it has the professional design qualification of lightning protection engineering and the professional construction qualification of lightning protection engineering. The domestic lightning rod market is mixed, and some dealers who represent foreign brands advertise their products in accordance with advanced foreign standards. Among them, it is difficult to distinguish between genuine and fake.

The lightning rod is composed of a lightning receptor, a grounding down conductor and a grounding body. The air-termination device usually adopts round steel or steel pipe with a diameter of 15-20mm and a length of 1-2m, which is fixed on the upper end of the pillar and connected to the grounding body through a grounding down conductor.

When the thundercloud discharge path to the ground is close to the ground, the tip of the lightning rod protrudes from the ground and is well grounded.

According to the "Han Han Book", an important palace of the time, Weiyang Palace and Bailiangtai, was

(1) There should be a distance of not less than 5m between the independent lightning rod and the protected object to avoid counterattack when the lightning rod strikes. The independent lightning rod should be provided with an independent grounding device, and the distance between the ground and the grounding network should not be less than 3m.

(2) Lightning rods should not be installed on the structure and roof of high-voltage power distribution devices of 35kV and below. The lightning rod installed on the structure should be connected to the grounding grid and a centralized grounding device should be installed.

(3) Lightning rods should not be installed on the door frame of the transformer.

(4) The distance between the lightning rod and the grounding device and the road and the exit should be greater than 3m, otherwise the gravel or asphalt surface should be paved 5 to 8cm thick to protect the person from step voltage hazards.

(5) It is strictly forbidden to install overhead lighting lines, telephone lines, broadcasting lines, antennas, etc. on lightning rods or structures.

(6) If a lighting lamp is installed on an independent lightning rod or frame, its power cord must be a lead cable or run through a steel pipe and directly buried in the ground with a length of more than 10m.