Six elements of building lightning protection design

 Lightning protection is a systems project. As early as 1960, when Mr. Wang Shizheng summarized the electrical engineering of the Great Hall of the People and wrote the book "Lightning Protection Design of Buildings", he proposed six important factors for building lightning protection design, which played an important role in the standardization of building lightning protection in China. .
一 、 Flash function
Refers to the conditions required to realize the air-termination function, including the form of the air-termination device (lightning rod, lightning protection belt and lightning protection net), current and pressure resistance, continuous air-termination effect, cost, and aesthetic unity of the air-termination device and the building Wait.
Second, the impact of diversion
Guide the impact of offline on the shunting effect. The thickness and number of down-conductors directly affect the shunting effect. With more down-conductors, the lightning current passed by each down-conductor is small, and its induction range is small. The distance between the down-conductors should not be less than specified in the specification. When the building is tall and the down-conductor is long, a voltage equalizing ring should be added in the middle of the building to reduce the inductance voltage drop of the down-conductor. Not only does this shunt, but it also reduces the counterattack voltage.
Three, equilibrium potential
Make all parts of the building an equal potential, that is, equipotential. If the structural steel bars in the building can be connected with various metal settings and metal pipelines to form a unified electrical conductor, of course, different potentials will not be generated in the building, so that it can ensure that there is no counterattack and endanger people Safe contact voltage or step voltage also has great benefits in preventing lightning electromagnetic pulses from interfering with microelectronic equipment. Buildings with reinforced concrete structures are best equipped to achieve equipotential conditions, because most of the internal structural steel bars are welded or tied together naturally. In order to meet the requirements of lightning protection devices, the air-termination device should be reliably welded, tied, or overlapped with beams, plates, columns, and foundations, and various metal equipment and metal pipelines should be welded or clamped together. Connected together, this makes the entire building a good equipotential body.
Shielding effect
The main purpose of the shielding is to protect the communication equipment, electronic computers, precision instruments and automatic control systems in the building from the electromagnetic pulses of lightning. These facilities in the building will not only be subject to electromagnetic interference when the lightning protection device is flashed, but because of their high sensitivity and low voltage resistance level, sometimes when lightning or lightning strikes nearby, they will also be exposed to electromagnetic radiation from lightning waves. The influence, even when other buildings are flashed, will be affected by the electromagnetic waves from there. Therefore, we should try to use the steel bars in the reinforced concrete structure, that is, the steel bars in the floor, roof, wall, and beams and columns of the building, so that it forms a hexahedral cage, that is, a cage type lightning protection net, so as to achieve shielding. . Due to the different structural structures, the steel bars in the walls and floors are dense and dense. When the steel bars are not dense enough, the designer should increase the density of the grid according to the different needs of various equipment. Good shielding not only solves the two problems of equipotential and shunt, but also is the most effective measure to prevent lightning electromagnetic pulses. In addition, the building's overall shielding also protects against ball, side, and orbit lightning.
V. Grounding effect
Refers to the quality of the grounding effect. A good grounding effect is also an important guarantee for the success of lightning protection. Every building must consider which grounding method is the best and most economical. Mr. Wang Shikun believes that when the buildings of reinforced concrete structures meet the requirements of the code, the steel bars in the foundation should be used as grounding devices. When the conditions stipulated in the specification are not met or the foundation is enclosed in a waterproof membrane layer, a peripheral grounding device can be used. other than). The ground bar close to the steel bars in the foundation is good for equalizing the potential, and it can also save manpower and material resources for digging deep trenches. Digging deep trenches after the foundation is completed can easily affect the stability of the foundation.
For wooden structures and brick-concrete structures, separate down conductors must be made and independent grounding methods used. When the soil resistivity is large and more grounding electrodes are used, it can also be used as a surrounding grounding device. Because the impact resistance of the peripheral grounding device is smaller than the impact resistance of the independent grounding device, it is also helpful to improve the ground potential distribution in the building and reduce the step voltage. When the independent grounding method is adopted, the effect of drilling a deep buried ground electrode (about 4-12m) is the best. The deep hole ground electrode can easily reach the groundwater level and can reduce the amount of steel used for the ground electrode.
Reasonable wiring
Refers to how to get the best overall results. Modern buildings are inseparable from the pipelines of lighting, power, telephone, television, and computer equipment. In the design of lightning protection, the relationship between the lightning protection system and these pipelines must be considered. In order to ensure that these pipelines are not affected when the lightning protection device is flashed, first of all, these wires should be routed in metal pipes to achieve reliable shielding;
Secondly, the vertical part of the trunk lines of these lines should be set at the center of high-rise buildings, and avoid close to the pillars used as down-conductors, in order to minimize the scope of induction. On long routes or long facilities such as bridges, both ends need to be grounded.
Third, attention should be paid to the introduction of power lines, antennas, and colored lights on the roof and aviation obstruction lights to prevent lightning waves from entering. In addition to considering the wiring location and shielding, surge protection devices such as lightning arresters and varistors should also be installed on the required lines. Therefore, when designing various indoor pipelines, it must be considered with the lightning protection system.

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Mar. 02, 2020