Technical Specification for Lightning Protection of Buildings _ Electrical Technical Paper on Lightning Protection of Buildings

With the economic development and social needs, high-rise buildings have mushroomed in various cities and regions, and lightning protection electrical technology is becoming more and more important. The following is my paper on lightning protection and electrical technology for buildings. I hope you like it. Lightning protection technology for buildings

Lightning protection technology in electrical design of high-rise buildings

Abstract In electrical design of high-rise buildings, lightning protection and grounding design is an important link. This paper briefly introduces the classification of lightning protection for buildings and the lightning protection measures that should be taken for different types of buildings. Several lightning protection measures for high-rise buildings are analyzed in detail, including lightning arrester, down conductor, grounding device, lightning protection counterattack measures, measures to prevent high potential from entering, and problems in construction and design of foundation grounding body.

Keywords high-rise building; Electrical design; Lightning protection; Lightning receptor; Down lead; Grounding device

1. Introduction

With the economic development and social needs, high-rise buildings have mushroomed in various cities and regions, and with the increase of building height, lightning protection has been paid more and more attention. In order to meet the needs of people's life, there are more and more electrical equipment of various types and functions. When using these appliances, it will inevitably bring some safety problems to high-rise buildings. Therefore, it is of great significance to study the lightning protection technology in electrical design of high-rise buildings.

ii. lightning protection level of buildings and lightning protection measures

(I) lightning protection level of buildings

according to the requirements of lightning protection for buildings, according to their nature of use, importance, possibility and consequences of lightning strikes, the lightning protection level of buildings can be divided into three levels.

the first type of lightning-proof buildings refer to buildings that manufacture, use or store a large number of explosive substances such as explosives, gunpowder, initiating explosive and initiating explosive, or buildings that are in danger of explosion, which will be caused by electric sparks, and will cause casualties and huge destroyers.

the second type of lightning protection buildings refer to national key buildings, buildings with a large number of electronic equipment that are of great significance to the national economy, important office buildings and crowded public buildings with an estimated lightning strike frequency of more than .6 times /a, and general buildings with an estimated lightning strike frequency of more than .3 times/a.

the third category of lightning protection buildings refers to buildings that are not as high as the first two, but also have a certain risk of lightning strike.

(II) Lightning protection measures for buildings

According to the general provisions in Code for Lightning Protection Design of Buildings (GB 557-21), all kinds of buildings should take measures to prevent lightning wave intrusion and direct lightning.

in the lightning protection buildings of category I and category II, measures should be taken to prevent lightning induction, lightning wave invasion and direct lightning strike in places with explosion danger. In addition to places with explosion danger, lightning protection buildings of Category II and Category III should take measures to prevent the invasion of lightning waves and direct lightning. Refer to Articles 3.2.1 to 3.4.1 of the specification for specific lightning protection measures.

according to research and observation, the slope of the roof can affect the parts of the building that are prone to lightning strike.

building roofs are rarely struck by lightning. When designing, we should analyze the actual situation of the roof, determine the parts that are most vulnerable to lightning strike, and then install lightning rods, lightning belts or lightning protection nets in these parts for key protection as required.

3. Lightning protection measures for high-rise buildings

(1) Lightning receptor

Lightning receptor is a metal object specially used for receiving direct lightning strikes. The metal rod that meets the lightning is called a lightning rod. The metal wire that meets the lightning is called lightning protection wire, also known as overhead ground wire. The metal belt and metal net connected with lightning are called lightning protection belt and lightning protection net. The lightning receptor should be composed of one or more independent lightning rods, overhead lightning wires or overhead lightning nets or lightning rods, lightning belts and lightning nets directly installed on buildings.

the lightning arrester should be connected to the grounding body (grounding device) through the grounding down lead.

grounding body is used to lead lightning current to the earth, which is the general name of all kinds of grounding electrodes buried in underground soil.

At present, in China, except for only a few high-rise buildings (such as Beijing Great Wall Hotel and Guangzhou Garden Hotel) that use the radiation electrodes in E and F radioactive lightning protection systems, lightning protection belts or lightning protection nets are mostly used as lightning receptors in other high-rise buildings, and lightning rods are rarely used. Some high-rise buildings with a building area as high as tens of thousands or even hundreds of thousands of square meters, but the aspect ratio is generally relatively large and the building ceiling area is relatively small, usually as long as lightning protection belts are set around the ceiling and the top of the pool, and some lightning protection nets are added locally.

(2) Down lead

In high-rise buildings, the common method in the construction of construction projects in China is to use the steel bars of columns or shear walls as lightning protection down lead. This method has been written into the national standard "Code for Lightning Protection Design of Buildings". According to the specification, the cross-sectional area of down lead should not be less than that of steel bars with a diameter of 1mm, while the cross-sectional area of main reinforcement is more than 2mm in high-rise buildings, so it is not difficult to achieve this requirement. For the sake of safety, the main reinforcement with a cross-sectional area of at least 16mm is usually used as lightning protection downlead in construction, and generally two are used. During construction, indicate the position of down lead to prevent dislocation of upper and lower welding.

in the construction of high-rise building against side lightning, the lightning protection downlead is linked with the ring beam and the girder, and then it is especially led out to the embedded iron parts, and then the embedded iron parts are welded with the metal doors and windows. However, this process has a large amount of work and some difficulties. How to solve the grounding of aluminum alloy doors and windows is still a problem worthy of study and discussion in lightning protection design. If the building adopts glass curtain wall, it will be much more convenient.

(3) grounding device

At present, the grounding device of high-rise buildings in China mostly adopts the method of taking the deep foundation of the building as the grounding electrode. This method has many advantages, such as low grounding resistance, uniform potential distribution, good voltage equalizing effect, convenient construction, less maintenance work and material saving.

High-rise buildings are mostly based on reinforced concrete, so there are many pores after solidification, and groundwater penetrates into them. Because it is silicate concrete, the conductivity is enhanced. In the concrete foundation, the steel bars are dense and criss-crossed, and directly contact with conductive silicate concrete after binding and welding, which makes the grounding resistance very low. The grounding of pile foundation is like forming a large-scale pressure equalizing net for the whole building underground, and the pressure equalizing effect is remarkable. At the same time, the main reinforcement is used for grounding, which saves a lot of steel.

(4) prevent lightning strike back

in the construction of high-rise buildings, the structural steel bars of buildings have actually been loosely or tightly connected with grounding devices. However, in order to prevent lightning counterattack, all metal conduits, metal components and supports in the building should also be connected to the grounding device. For electrical lines laid vertically, voltage breakdown protection devices can be installed at appropriate positions. It is best to connect all kinds of grounding devices into a whole. The above methods are based on the principle of equipotential, so as to make the potential uniform and avoid the damage of lightning counterattack to buildings.

(5) prevent the introduction of high potential

lightning wave invasion, which may easily lead to the introduction of high potential indoors. In order to prevent such problems, the overhead metal pipes entering the building should be connected to the grounding device at the entrance. All cables should be used as far as possible. If it is really difficult for all cables to enter the line, the overhead lines should be replaced with cables 5 meters before entering the house, and lightning arresters should be installed at the replacement place. At the same time, the lightning arresters, the iron feet of overhead line insulators and the cable sheath should be grounded, and the impact resistance when grounded should be less than or equal to 1? . For metal pipes or low-voltage directly buried cable lines entering the building, the cable sheath, cable metal entrance conduit, etc. should be connected with the grounding device at the entrance.

(VI) Design and construction of foundation grounding electrode

In the process of construction, the foundation piles of high-rise buildings (whether digging piles, punching piles or drilling piles) all extend reinforced concrete columns into the ground and reach the rock stratum with a depth of tens of meters. The pile foundation is used as the bearing platform of the building to connect the pile foundation into a whole. The cap is also made of reinforced concrete, generally more than one meter thick. Above the cap are the shear walls and columns of the building, and the ground part of the building is located on the cap.

IV. Conclusion

The lightning protection of high-rise buildings directly affects the use safety of buildings and threatens the safety of people's lives and property, so it should be paid enough attention. As the height of high-rise buildings is getting higher and higher, there are more and more buildings, and there are some problems and defects in its lightning protection design, which needs further research and discussion by people in the industry and related personnel.

References:

[1]GB 557-21, Code for Lightning Protection Design of Buildings [S]. Beijing: China Planning Press, 21.

[2] Liu Siliang. Power supply and distribution of buildings [M]. Beijing: China Building Industry Press, 1998.

[3] > > Paper on electrical technology of building lightning protection