Students are the future of the motherland. Therefore, it is particularly important for the school to design mine protection engineering. How to make school lightning protection? Next, Zhengzhou Leidi Electronic Engineering Co., Ltd. technical personnel through their own work experience for everyone to sum up.
First of all, the risk assessment of the various buildings of the school is carried out. Based on this, the overall design of the lightning protection project is carried out from the aspects of direct lightning strike prevention and lightning protection intrusion to minimize the lightning disaster.
School technical regulations for lightning protection. The lightning protection work in school was divided into three categories: direct lightning (side impact), inductive lightning, and lightning surge; according to related technical requirements such as “Building Protection Design Specification†and “Building Electronic Information System Lightning Protection Technical Specificationâ€, combined with school personnel Intensity, the existence of outdoor activities, the relative concentration of information systems, and the provision of lightning protection and safety hardware facilities for school premises and buildings should meet the following basic requirements:
External lightning protection facilities and requirements: School buildings, dormitories, office buildings, canteens, gymnasiums, chimneys, satellite receiving antennas and other structures should have lightning protection strips or lightning rods. The scope of protection of lightning rods should comply with relevant standards and effectively protect buildings. Buildings; lightning protection zone should be flat, straight, solid, no inverted, fracture. Grounding system should be complete, grounding resistance in line with relevant requirements; isolated large metal objects should have reliable grounding; school cable broadcasting, network cable, telephone line, etc. It is forbidden to wind lightning conductors and lightning rods on metal wires.
Internal lightning protection facilities and requirements: The metal stair handrail should be reliably grounded; the school's total power distribution room, office, teaching network room, program-controlled switch room, audio-visual teaching network center room, and monitoring room should have two or more power surge protection devices ( Power surge arresters); indoor metal components should be equipotential bonding; anti-static floor to achieve multi-point grounding; classrooms with electrified classroom terminal schools, teaching building floors need to have two power surge protectors; satellite receiver indoor and outdoor feeder ports (IDU, ODU), information network external network interface (metal wire), network switch important port should be corresponding signal surge protector (signal arrester) should have anti-lightning electromagnetic pulse measures.
The specific plans for the school's lightning protection design and planning are shown below. The plan is designed by Zhengzhou Leidi Electronic Engineering Co., Ltd.
The lightning receptor is equipped with lightning protection strips around roofs, parapet walls and ridges, etc., which are vulnerable to lightning strikes. Φ10 hot-dip galvanized round steel is used for lightning protection materials, and Φ12 hot-dip galvanized round steel is used for lightning protection short pins. The height of the lightning protection belt is 0.15m, the support spacing is 1m, and the suspended section at the corner is 0.3m. No support clips are allowed on the corners. The lightning conductor must form a closed circuit. Lightning belts with deformation joints should be compensated. The welding between the lightning protection belts adopts double-sided welding. The welding length is more than 6 times of the diameter of the round steel, and the welding place should be treated with anti-corrosion. When the parapet is wide, the lightning protection zone should be laid along the outside of the parapet and no more than 0.1m away from the outer edge. All metal objects and metal devices protruding from the roof should be connected with lightning protection strips. The non-metallic objects protruding from the roof are protected by short lightning protection needles. All short lightning rods should be connected with lightning protection strips.
For the reconstructed project, the downtrodden line was applied along the outer wall of the building and the material was 25mm × 4mm hot dip galvanized flat steel. The downleads are evenly arranged along the perimeter of the building. The second type of lightning protection building is set off at no more than 18m. The third type of lightning protection building is set off at no more than 25m. The deflector support height is 0.1m and the fixed spacing is 2m. Each deflector shall be provided with a disconnect card at a height of 1.8m from the ground, protected by a modified plastic tube between 0.3m below the ground and 1.7m above the ground. The downleads and the lightning protection and grounding wires are double-sided soldered. The welding length is more than 6 times the diameter of the round steel.
For newly-built projects, use the four main steel bars with a diameter of ≥ φ12 in the structural column, or two main steel bars with a diameter ≥ φ16 in the diagonal as the downline, and the down-conductor steel bars should be long welded and should be evenly symmetrical along the perimeter of the building. The distance between the downlights of the second type of lightning protection building shall not exceed 18m, and the spacing of the third type of lightning protection downconduct shall not exceed 25m. The main positive angle of the building shall be set off.
Lightning protection grounding device For the reconstruction project, use A-type grounding device, that is, set a group of grounding body at each lead. Each group of grounding bodies uses two galvanized angle steels with a length of 2.5m, L50×50×5, a galvanized angle steel spacing of 5m, and a -40×4 hot galvanized flat steel connection between them. Grounding body buried depth of 0.8m, and from the building entrance or sidewalk is not less than 3m. Each group grounding building exterior wall is 1m. The connection between the down conductor and the grounding body is -40 x 4 hot galvanized flat steel. The impact grounding resistance at each down conductor is no more than 10Ω, otherwise a grounding body should be added. The connection between the grounding wire, the grounding body and the grounding body is welded on three sides, and the welding length is twice the width of the flat steel.
For newly-built projects, the steel bars in piles, platforms, and ground beams should be fully utilized as natural grounding bodies. For the pile foundation, each pile uses the two diagonal main reinforcements in the main structure of the peripheral structure as the vertical grounding body, and the pile foundations at the points where the lightning is directed down shall be used as the vertical grounding body. No less than two main bars of the platform platform and the bottom beam are horizontally and horizontally welded to form a horizontal grounding grid. The average size of the grid of the grounding grid is no more than 20m×20m or 24m×16m. When there is no steel bar in the foundation beam to be used, use - A 40×4 galvanized flat steel is laid in the foundation as a grounding net. The horizontal grounding body and the vertical grounding body should be reliably welded. Grounding resistance test terminals should be installed near the down conductor at the main sun corner of the grounding device. The height from the ground should not be less than 300mm. The specification is -40 x 4 hot dip galvanized flat steel or L50 x 50 x 5 galvanized angle steel. Sign.
If there is a tree outside the building outside the building, if the tree is not within the protection scope of the lightning protection device of the building, when the lightning strike occurs, the lightning current may be the first contact with the tree, when the lightning current flows down the trees. In case of induction of good conductors such as steel bars, power lines, and signal lines in buildings, it is possible to break through the wall and “break†new conductors. If the human body is very close to these metal objects at this time, it is likely to be counterattacked; When lightning currents descend under the trees, they may also directly sense the human body. Thunder currents may break through the walls and cause serious consequences through the human body entering the ground.
According to the relevant requirements of GB50057-94 (2000 edition), when the outdoor trees are higher than the buildings and are not within the protection scope of the air-termination device, the clear distance between the trees and the buildings shall not be less than 5m. However, when the situation is limited due to specific circumstances and the safety distance cannot be met, measures should be taken against these trees. From the perspective of economy and convenience, put forward the following measures:
1) When selecting greenery, consider selecting low-level trees.
2) To ensure safety, it is recommended that the tree top should be at least 1m below the surrounding buildings. When the requirements are not met, the canopies should be regularly cut to keep the height 1m below the surrounding buildings.
3) Use lightning rod protection for tall trees and set down the trunk along the trunk, and set the grounding device. The grounding resistance should not exceed 10Ω. Take measures such as insulation on the ground above the grounding device and set up warning signs.
The lightning surges invading the low voltage cables shall be buried. The power surge protectors shall be installed in the distribution cabinets of the school power distribution room as the first level of protection. The maximum flow capacity of the lightning arrester is not less than 60KA (8/20us) and the residual voltage is less than 1.7KV (25KA, 8/20us). The introduction cable of the equipment room is generally laid along the inner wall. The probability of lightning strike and the intensity of lightning strike are not large. Therefore, power surge protection devices are installed in the power distribution boxes that are introduced into the equipment rooms and are used as secondary protection. The maximum flow capacity of the arrester is 40KA (8/20us), and the residual voltage is less than 1.5KV (15KA, 8/20us).
The air switch position should be reserved in the distribution box. If there is no installation position, the lightning arrester box should be installed separately near the switch box. The distance between the installed SPDs should meet the requirements of the specification: The length between the voltage switch SPD and the SPD should not be less than 10m, and the length between the SPDs should not be less than 5m. Corresponding decoupling measures should be taken.
School personnel are intensive, and microelectronic equipment is widely used. If the protective measures are improper, once a lightning strike accident is caused, it will have unpredictable consequences. School lightning protection systems should be adapted to local conditions. Based on a comprehensive assessment of the risk of lightning disasters in schools, from the perspective of the overall lightning protection, in strict accordance with the requirements of national standards, careful study of lightning protection device design layout, careful construction supervision and acceptance, effectively prevent or Reduce the harm of lightning on the campus.
The joint grounding of buildings can effectively solve the impact of ground potential elevation. Qualified ground nets are the key to effective lightning protection. The joint ground network of buildings is usually composed of building foundations (including ground piles), ring grounded (body) devices, working (power transformers) ground nets, and the like. For the lightning protection of sensitive data communication equipment, the soundness of the grounding system is directly related to the effect and quality of lightning protection. If the ground network does not meet the requirements, the conditions of the ground network should be improved, the area of ​​the ground network should be appropriately expanded and the structure of the ground network should be properly improved so that the lightning current can be discharged as soon as possible and the holding time of the high overvoltage caused by the lightning current can be shortened to meet the lightning protection requirements.
First of all, the risk assessment of the various buildings of the school is carried out. Based on this, the overall design of the lightning protection project is carried out from the aspects of direct lightning strike prevention and lightning protection intrusion to minimize the lightning disaster.
School technical regulations for lightning protection. The lightning protection work in school was divided into three categories: direct lightning (side impact), inductive lightning, and lightning surge; according to related technical requirements such as “Building Protection Design Specification†and “Building Electronic Information System Lightning Protection Technical Specificationâ€, combined with school personnel Intensity, the existence of outdoor activities, the relative concentration of information systems, and the provision of lightning protection and safety hardware facilities for school premises and buildings should meet the following basic requirements:
External lightning protection facilities and requirements: School buildings, dormitories, office buildings, canteens, gymnasiums, chimneys, satellite receiving antennas and other structures should have lightning protection strips or lightning rods. The scope of protection of lightning rods should comply with relevant standards and effectively protect buildings. Buildings; lightning protection zone should be flat, straight, solid, no inverted, fracture. Grounding system should be complete, grounding resistance in line with relevant requirements; isolated large metal objects should have reliable grounding; school cable broadcasting, network cable, telephone line, etc. It is forbidden to wind lightning conductors and lightning rods on metal wires.
Internal lightning protection facilities and requirements: The metal stair handrail should be reliably grounded; the school's total power distribution room, office, teaching network room, program-controlled switch room, audio-visual teaching network center room, and monitoring room should have two or more power surge protection devices ( Power surge arresters); indoor metal components should be equipotential bonding; anti-static floor to achieve multi-point grounding; classrooms with electrified classroom terminal schools, teaching building floors need to have two power surge protectors; satellite receiver indoor and outdoor feeder ports (IDU, ODU), information network external network interface (metal wire), network switch important port should be corresponding signal surge protector (signal arrester) should have anti-lightning electromagnetic pulse measures.
The specific plans for the school's lightning protection design and planning are shown below. The plan is designed by Zhengzhou Leidi Electronic Engineering Co., Ltd.
The lightning receptor is equipped with lightning protection strips around roofs, parapet walls and ridges, etc., which are vulnerable to lightning strikes. Φ10 hot-dip galvanized round steel is used for lightning protection materials, and Φ12 hot-dip galvanized round steel is used for lightning protection short pins. The height of the lightning protection belt is 0.15m, the support spacing is 1m, and the suspended section at the corner is 0.3m. No support clips are allowed on the corners. The lightning conductor must form a closed circuit. Lightning belts with deformation joints should be compensated. The welding between the lightning protection belts adopts double-sided welding. The welding length is more than 6 times of the diameter of the round steel, and the welding place should be treated with anti-corrosion. When the parapet is wide, the lightning protection zone should be laid along the outside of the parapet and no more than 0.1m away from the outer edge. All metal objects and metal devices protruding from the roof should be connected with lightning protection strips. The non-metallic objects protruding from the roof are protected by short lightning protection needles. All short lightning rods should be connected with lightning protection strips.
For the reconstructed project, the downtrodden line was applied along the outer wall of the building and the material was 25mm × 4mm hot dip galvanized flat steel. The downleads are evenly arranged along the perimeter of the building. The second type of lightning protection building is set off at no more than 18m. The third type of lightning protection building is set off at no more than 25m. The deflector support height is 0.1m and the fixed spacing is 2m. Each deflector shall be provided with a disconnect card at a height of 1.8m from the ground, protected by a modified plastic tube between 0.3m below the ground and 1.7m above the ground. The downleads and the lightning protection and grounding wires are double-sided soldered. The welding length is more than 6 times the diameter of the round steel.
For newly-built projects, use the four main steel bars with a diameter of ≥ φ12 in the structural column, or two main steel bars with a diameter ≥ φ16 in the diagonal as the downline, and the down-conductor steel bars should be long welded and should be evenly symmetrical along the perimeter of the building. The distance between the downlights of the second type of lightning protection building shall not exceed 18m, and the spacing of the third type of lightning protection downconduct shall not exceed 25m. The main positive angle of the building shall be set off.
Lightning protection grounding device For the reconstruction project, use A-type grounding device, that is, set a group of grounding body at each lead. Each group of grounding bodies uses two galvanized angle steels with a length of 2.5m, L50×50×5, a galvanized angle steel spacing of 5m, and a -40×4 hot galvanized flat steel connection between them. Grounding body buried depth of 0.8m, and from the building entrance or sidewalk is not less than 3m. Each group grounding building exterior wall is 1m. The connection between the down conductor and the grounding body is -40 x 4 hot galvanized flat steel. The impact grounding resistance at each down conductor is no more than 10Ω, otherwise a grounding body should be added. The connection between the grounding wire, the grounding body and the grounding body is welded on three sides, and the welding length is twice the width of the flat steel.
For newly-built projects, the steel bars in piles, platforms, and ground beams should be fully utilized as natural grounding bodies. For the pile foundation, each pile uses the two diagonal main reinforcements in the main structure of the peripheral structure as the vertical grounding body, and the pile foundations at the points where the lightning is directed down shall be used as the vertical grounding body. No less than two main bars of the platform platform and the bottom beam are horizontally and horizontally welded to form a horizontal grounding grid. The average size of the grid of the grounding grid is no more than 20m×20m or 24m×16m. When there is no steel bar in the foundation beam to be used, use - A 40×4 galvanized flat steel is laid in the foundation as a grounding net. The horizontal grounding body and the vertical grounding body should be reliably welded. Grounding resistance test terminals should be installed near the down conductor at the main sun corner of the grounding device. The height from the ground should not be less than 300mm. The specification is -40 x 4 hot dip galvanized flat steel or L50 x 50 x 5 galvanized angle steel. Sign.
If there is a tree outside the building outside the building, if the tree is not within the protection scope of the lightning protection device of the building, when the lightning strike occurs, the lightning current may be the first contact with the tree, when the lightning current flows down the trees. In case of induction of good conductors such as steel bars, power lines, and signal lines in buildings, it is possible to break through the wall and “break†new conductors. If the human body is very close to these metal objects at this time, it is likely to be counterattacked; When lightning currents descend under the trees, they may also directly sense the human body. Thunder currents may break through the walls and cause serious consequences through the human body entering the ground.
According to the relevant requirements of GB50057-94 (2000 edition), when the outdoor trees are higher than the buildings and are not within the protection scope of the air-termination device, the clear distance between the trees and the buildings shall not be less than 5m. However, when the situation is limited due to specific circumstances and the safety distance cannot be met, measures should be taken against these trees. From the perspective of economy and convenience, put forward the following measures:
1) When selecting greenery, consider selecting low-level trees.
2) To ensure safety, it is recommended that the tree top should be at least 1m below the surrounding buildings. When the requirements are not met, the canopies should be regularly cut to keep the height 1m below the surrounding buildings.
3) Use lightning rod protection for tall trees and set down the trunk along the trunk, and set the grounding device. The grounding resistance should not exceed 10Ω. Take measures such as insulation on the ground above the grounding device and set up warning signs.
The lightning surges invading the low voltage cables shall be buried. The power surge protectors shall be installed in the distribution cabinets of the school power distribution room as the first level of protection. The maximum flow capacity of the lightning arrester is not less than 60KA (8/20us) and the residual voltage is less than 1.7KV (25KA, 8/20us). The introduction cable of the equipment room is generally laid along the inner wall. The probability of lightning strike and the intensity of lightning strike are not large. Therefore, power surge protection devices are installed in the power distribution boxes that are introduced into the equipment rooms and are used as secondary protection. The maximum flow capacity of the arrester is 40KA (8/20us), and the residual voltage is less than 1.5KV (15KA, 8/20us).
The air switch position should be reserved in the distribution box. If there is no installation position, the lightning arrester box should be installed separately near the switch box. The distance between the installed SPDs should meet the requirements of the specification: The length between the voltage switch SPD and the SPD should not be less than 10m, and the length between the SPDs should not be less than 5m. Corresponding decoupling measures should be taken.
School personnel are intensive, and microelectronic equipment is widely used. If the protective measures are improper, once a lightning strike accident is caused, it will have unpredictable consequences. School lightning protection systems should be adapted to local conditions. Based on a comprehensive assessment of the risk of lightning disasters in schools, from the perspective of the overall lightning protection, in strict accordance with the requirements of national standards, careful study of lightning protection device design layout, careful construction supervision and acceptance, effectively prevent or Reduce the harm of lightning on the campus.
The joint grounding of buildings can effectively solve the impact of ground potential elevation. Qualified ground nets are the key to effective lightning protection. The joint ground network of buildings is usually composed of building foundations (including ground piles), ring grounded (body) devices, working (power transformers) ground nets, and the like. For the lightning protection of sensitive data communication equipment, the soundness of the grounding system is directly related to the effect and quality of lightning protection. If the ground network does not meet the requirements, the conditions of the ground network should be improved, the area of ​​the ground network should be appropriately expanded and the structure of the ground network should be properly improved so that the lightning current can be discharged as soon as possible and the holding time of the high overvoltage caused by the lightning current can be shortened to meet the lightning protection requirements.
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