Design and Construction Organization Plan of Lightning Protection Engineering (I) _ Grounding
Design and Construction Organization Plan of Lightning Protection Engineering (I) _ Grounding
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Publicado por : Marilyn
Publicado en : 26-08-22
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Design and Construction Organization Plan of Lightning Protection Engineering (I) _ Grounding
Original Title: Lightning Protection Engineering Design and Construction Organization Plan (I) The lightning protection project needs to be implemented in an organized and step-by-step manner to ensure the quality and duration of the project. Today, Junhe Electronics takes a project as an example to share with you the template of lightning protection engineering design and construction organization scheme for reference only, as follows: I. Lightning protection design scheme 1. Project overview The project is located in XX Town, XX County, XX Province, which is surrounded by mountains on three sides. The project is located in the south of the XX fault zone. There are few soil layers in the project yard, no vegetation, mostly rocky mountains, and the soil resistivity is high. The available land area around the building is small, there is no vegetation soil layer, and it is mainly rock. The measured soil layer is 1420 Ω · m (the surface layer is backfill soil), and the grounding coefficient varies with the season. The measured soil resistivity of highly weathered dolomite in L201 and L202 buildings is 20000 ohm · m. 2. Analysis of design scheme There are many grounding methods for lightning protection, such as (1. Soil replacement method, 2. Artificial soil treatment method (chemical treatment of soil), 3. Deep buried grounding electrode method, 4. Multi-branch external grounding device method, 5. Grounding module grounding method, 6. Sewage introduction method, 7. Deep well grounding method). There are two grounding methods suitable for L201 and L202; Deep well grounding method and grounding module grounding method. Disadvantages of grounding method of grounding module: Due to the shallow soil layer of the project site, the geographical environment changes significantly in four seasons, and the rainfall is not balanced, which objectively causes the instability of soil temperature, humidity and water retention, and will affect the stability of the resistance of the whole ground network. It destroys the geological structure, occupies a large area, and the land used becomes dead and can not be reused. The service life of the module is short, the material composition is complex, ranging from several hundred yuan to several thousand yuan, and the module itself is fragile, which will affect the instability of the resistance value. The distance between the grounding grid of the lightning tower and the grounding grid of the building foundation is too close, which may lead to the formation of ground potential counterattack, resulting in serious consequences such as equipment damage. Module grounding needs to change the soil, but it is difficult for us to get the soil, and it also depends on what kind of soil (sandy soil, loess, black soil) will affect the resistance. The modules are connected by flat steel, which is easy to corrode and also affects the resistance. The extensive use of common resistance reducing agents has an impact on groundwater and soil quality, which is related to personal health and safety! In terms of price comparison, if better materials are used and products meet the requirements of national standards, the price difference between deep well grounding and deep well grounding is not very large. Advantages of deep well grounding method: The deep well grounding mode eliminates the influence of temperature difference in four seasons and ensures the stability of grounding grid resistance. It occupies a small area and will not affect the land use. The use of long-acting physical resistance reducing agent, green environmental protection, pollution-free, long life, in line with the standards of the national testing department, the first phase of the project experience can be verified. The ion grounding electrode has the advantages of high conductivity, long service life and stability. All the connections are made by copper wires, so the corrosion degree is low, the resistance is small and the resistance value is stable. Expand the full text Based on the above analysis, the comprehensive grounding scheme based on deep well grounding is the most effective, economical and practical grounding scheme. 3. Design basis The main contents of the current relevant specifications, regulations and acceptance standards for installation works issued by the People's Republic of China are as follows: Design Code for Protection of Structures against Lightning GB50057-2010 Technical Code for Protection against Lightning of Building Electronic Information System GB50343-2012 Installation Drawings of Lightning Protection Facilities for Buildings 99 D501-1 Code for Design Review and Completion Acceptance of Lightning Protection Devices (Order No.21 of the State Meteorological Administration) Design Code for Lightning Protection and Grounding Engineering of Communication Bureaus (Stations) YD 5098-2005 Standard for Grounding of AC Electrical Installations DL/T621-1997 According to the geotechnical investigation report of Gaoxin Phase III, it is shown as follows: The first layer: artificial fill: mainly composed of clayey silt, containing plant roots and organic matter, located on the artificially reclaimed slope, with a thickness of 0.3 ~ 1.5m.
Layer 2: loessial clayey silt and silty clay of Quaternary Upper Pleistocene eluvium, alluvium and diluvium, slightly wet-wet, slightly dense-medium dense, with developed voids, containing a small amount of gravel and plant roots. The thickness of this layer is 0.5 ~ 3.5m. Layer 3: strongly weathered dolomite Layer 4: Moderately weathered dolomite Layer 5: Weathered dolomite According to the geological conditions of the test site, the geological environment of the grounding grid is poor and the soil resistivity is high. According to the design requirements of the test area, the grounding resistance of L201 and L202 buildings is less than 1 Ω. If each building is made separately to meet the design requirements, not only the layout and working surface of the site can not meet the construction requirements, but also the investment is very huge, resulting in the waste of repeated construction and investment. Considering the technical feasibility and rationality and avoiding the waste of investment, we suggest that several buildings should share the grounding network, and the resistance value should be less than 1Ω according to the minimum value of the design requirements of several buildings,overburden drilling systems, which can meet the original design requirements. Technical analysis Based on the above requirement of joint grounding, the power frequency grounding resistance of the grounding grid is R ≤ 1Ω, and the theoretical calculation of the grounding resistance of the whole grounding grid in this project is as follows: Calculation of vertical grounding resistance: According to the geotechnical engineering investigation report, the first layer (0-1.5m) of the site and its vicinity is artificial fill, and the soil resistivity distribution is about 350-600Ω · m; the second layer (1.5-5m) is loess-like silty clay and heavy silty clay, containing a small amount of sand and stone, and the soil resistivity distribution is about 800-1300Ω · m; The third layer (5-9.4m) is mostly strongly weathered white rock layer and moderately weathered white rock layer, and the soil resistivity distribution is about 1600-2100Ω · m; the fourth layer (9.4-120m) is slightly weathered white stone layer, and the soil resistivity distribution is about 2400-3800Ω · m. According to the geological survey report, there is no water layer at 100m, and there is a 120m deep well in the plant area. Assuming that there is a water layer below 120m, the soil resistivity distribution is about 20-70 Ω · m. The layering calculation formula shall be in accordance with DL/T621-1997 Standard for Grounding of AC Electrical Installations; According to the calculation, the horizontal grounding resistance in the grounding grid is RO = 1. 56 Ω. When the resistance reducing agent is added around the horizontal connecting copper wire, the average resistivity of the soil can be reduced, and the resistance reducing rate is 0. 2. At this time, the horizontal grounding resistance in the joint grounding grid is RO = 1. 25 Ω. Calculation of compound grounding resistance After comprehensively considering the combination of deep well grounding electrode and horizontal connection copper wire, its grounding resistance shall be calculated according to DL/T621-1997 Standard for Grounding of AC Electrical Installations: after the combination of deep well grounding electrode and copper wire, the grounding resistance of the combined grounding network of 6 deep wells Rx = 0.74Ω Conclusion According to the above design method, the power frequency grounding resistance of the joint grounding grid is less than 1Ω, which meets the engineering requirements of Party A. Similarly, according to the formula, a 130m (according to the geographical situation, the drilling depth should reach more than 15m after the visible water layer, so the depth should be determined according to the actual situation) grounding deep well is drilled between the two towers (see the construction drawing) at the lightning tower of L201 and L202 buildings,down the hole bit, which is the common grounding well of the two lightning towers. The theoretical prediction can meet the design requirement that the impulse resistance is less than or equal to 10Ω, and if the requirement cannot be met, two nearby deep wells can be jointly grounded. (According to 4, 2 and 1 of Code for Design of Lightning Protection of Buildings GB50057-2010, independent lightning rod, overhead lightning wire or overhead lightning network shall be equipped with independent lightning device, and the impulse grounding resistance of each downlead shall not be greater than 10Ω. In areas with high soil resistivity, the impulse grounding resistance can be increased appropriately, but in areas below 3000Ω m, the impulse grounding resistance should not be greater than 30Ω. Because the geological survey report States that water can be seen below about 100 meters, the value used in the formula is 120 meters. 4. Design quantity According to the calculation of grounding resistance of deep wells, it is necessary to drill 6 grounding deep wells (about 130 meters each) between buildings in parallel to meet the design resistance requirements. The deep well is connected to the grounding grid of the building by 95mm2 copper wire brazing.
A total of 18 KS-JD-3000 ion grounding electrodes (3 for each well), 1518.5 meters of 95mm2 copper wire connecting line and 32.17 tons of resistance reducing agent are required for construction. A total of 18 KS-JD-3000 ion grounding electrodes, 1518.5 meters of 95mm2 copper wire and 32.17 tons of resistance reducing agent are required for construction. The above design is calculated according to the theoretical value. In case of deviation between the grounding resistance value and the calculated value due to the change of geological conditions in the construction practice, the grounding unit of the deep well shall be increased or decreased according to the measured value. Until the resistance value required by the project is reached. 5． Construction scheme and main subdivisional construction methods (1) General principle of construction Reasonable arrangement of working procedures, close connection of working procedures, scientific and standardized management, and full utilization of man and machine (2) Construction scheme Excellent construction personnel shall be selected to organize the construction meticulously. During the construction, parallel crossing and flow operation shall be adopted to optimize the working procedures so as to ensure the overall construction period. Pay attention to safe construction to avoid personal injury and property loss. Strengthen the management of key sub-items, take the overall situation into account and manage scientifically. (3) Construction process Surveying, positioning and setting out shall be carried out in combination with the site and drawing dimensions to excavate the trench of the grounding grid, install the well drilling equipment, drill the well, bury the grounding electrode, grout the deep well, connect the grounding grid and reduce the resistance of the grounding grid for backfilling. (4) Construction technology Dig a trench Excavate the grounding grid trench. Excavate the grounding grid connection trench according to the drawing. The width of the upper part of the trench is 1000 mm, the bottom of the trench is 1000 mm, and the depth of the groove is 800 mm. Punch Because of the complexity of the formation, the combined drilling method of mud positive circulation and air Dth hammer is adopted. According to the geological survey report, the thickness of strata 1 ~ 5 is 5 to 10 meters, the original soil layer is silty clay with broken stones, and the broken fissures in the strongly and moderately weathered section are filled with clay. The process adopts Ф219 mm bit mud positive circulation rotary drilling, and in case of formation collapse, the casing is lowered to protect the hole. Air Dth hammer was used to drill the No.6 formation. Features of Dth hammer (air hammer): Air drilling is one of the most popular drilling methods in the world. As a new drilling tool in air drilling, Dth hammer has great application prospects. 1) less gas consumption; 2) that structure is simple, the reliability is high, and the requirement of various pressure conditions are met; 3) The optimized design of the patented technology system can maximize the use of the energy of the air compressor; 4) The hammer teeth of the new air hammer effectively alleviate the wear and fracture of the hammer teeth and greatly improve the pure drilling time; 5) High-hardness metal on the outer layer of bit teeth: compact, hard and wear-resistant; strong and tough metal on the inner layer : Good toughness, impact resistance, not easy to break. Dth hammer is also called pneumatic hammer, which uses compressed air as power medium to complete percussive rotary drilling and has the characteristics of air flushing drilling. Compared with the percussive rotary drilling with high-pressure water or mud as the power medium, the pneumatic Dth hammer rotary drilling has double efficiency. Important link of pore-forming 1) Overburden drilling A carbide bit was used for rotary drilling and the φ219 mm iron casing pipe was lowered. The key to the hole forming process of this project is to seal the gap between the protective pipe and the orifice tightly, especially in loose gravel strata, this step is particularly important. 2) Rock drilling Vibrating down-the-hole hammer is used for drilling, which is characterized by no coring, dth drill bits ,mining dth bit, complete crushing of the hole bottom, large amount of cuttings, and all of them are carried out of the hole by high-speed airflow. 3) Axial pressure (weight on bit) According to the principle of rock breaking by Dth hammer, rock is mainly broken under the action of impact dynamic load, so the drilling efficiency of Dth hammer mainly depends on the size of impact energy and the number of impact frequency. The axial pressure is used to overcome the upward pushing force generated in the cylinder when the impactor pushes the piston downward, so as to ensure that the impact energy is effectively transmitted to the drill bit. Generally, the weight on bit is 1.3-1.6T. 4) Drilling speed The drilling speed of the drilling tool is mainly determined according to the nature of the rock, the diameter of the bit, the impact energy and the impact frequency. The reasonable rotation speed shall ensure that the rock is broken within the optimal impact gap. Generally, the diameter of the borehole is about 200mm, 30-50r/min for soft strata, 20-40r/min for medium hard strata, and 10-30r/minute for hard strata.
5) Air supply volume During Dth hammer drilling, the compressed air has two functions: one is to provide energy for the movement of the impactor piston; the other is to carry cuttings and cool the drill bit. Therefore, the amount of air supply is determined on the one hand according to the amount of air consumption required by the Dth hammer used, and on the other hand to ensure the upward return air speed of the annular space of the drill pipe. Drilling air supply: It is mainly related to the annular clearance between the drill pipe and the hole wall. Q≥VK60(D2-d2)∏/4 Q-air supply, m3/min D-aperture, m D-diameter of drill pipe, m V-upward return wind speed, generally V ≥ 15m/s K-coefficient, generally about 1.3. In order to make full use of the air compressor, the annular clearance between the drill pipe and the hole wall should be reduced as much as possible. The hole diameter shall be reduced as much as possible under the condition that the installation of pumping equipment is satisfied. In addition, increasing the outer diameter of the drill pipe is also an effective way to reduce the annular clearance. 6) Wind pressure In the process of Dth hammer drilling, the pressure of the air compressor is the sum of various pressure losses in the whole compressed air flow channel. When the Dth hammer drills in the dry hole section, the air supply pressure is the sum of the working pressure of the Dth hammer and the pipeline pressure loss. When there is water in the hole, it is mainly determined by the depth of the hole, the buried depth of the water level in the hole and the water yield. Generally, when there is water, the air supply pressure is about 1.3 times of the hole depth (100m hole depth is 1MPa). Burying of grounding electrode For well entry operation, according to the design drawings, there are three grounding electrodes in each well, 95mm ² copper wire is used for welding between the grounding electrodes, anti-corrosion treatment is carried out for the welding spots, the grounding electrodes are placed section by section to the required depth, and the wellhead is positioned and fastened; High conductivity: Under the same grounding area, the grounding efficiency is 60 times that of the traditional method. Theory and practice show that the resistance in a very small range around the grounding body accounts for 90% of the overall grounding resistance in a uniform soil environment. The mix ratio of that filler material ensure that the resistivity of the filler material is extremely low, and the filler material can effectively permeate into the surrounding soil, thereby greatly improve the resistivity of the surrounding soil. On the other hand, the filler can penetrate into the surrounding soil and form a root-shaped diffusion structure, which greatly increases the effective contact area between the grounding body and the ground and reduces the grounding resistance. At the same time, the vertical grounding mode also effectively reduces the grounding resistance. Long-term effect: Experimental data analysis shows that the effective service life of the product can reach 50 years. The combination of the filler formula and the metal material of the rod body enables the surface of the metal rod body to form a conductive anticorrosive protective film, thereby preventing the corrosion of metal. The unique active ion automatic replenishment mechanism keeps the active ion content in the soil stable, thus maintaining low grounding resistance. The unique process measures ensure that the connection point of the grounding system realizes the true meaning of anti-corrosion. Stability: The product has high stability and is not affected by seasonal factors such as temperature, soil moisture content and the like. Small floor area: the floor area of each grounding unit is less than 0.1m2. It is especially suitable for use in urban grounding construction with dense buildings, and can be used as both an independent grounding body and an additional auxiliary grounding electrode. (4) Grouting During the grouting operation, the mixed resistance reducing agent is injected into the bottom of the deep well through the grouting pump and the conduit, so that the accumulated water in the deep well can be discharged. If necessary, the wellhead can be sealed with anchoring cement, and the high-pressure grouting pump can be used to force grouting into the well, so that the resistance reducing agent can penetrate into the soil along the rock and soil crevices, and the resistance reducing agent in the deep well can be poured compactly until the thick slurry of the friction reducing agent gushes out. (5) Grounding grid welding For grounding grid connection, the formed grounding deep well shall be electrically connected with 95 mm ² copper wire by means of hot melt welding. The welding length shall not be less than 80 mm. The welding seam shall be full and have sufficient mechanical strength. There shall be no slag inclusion, undercut, crack, false welding, air hole and other defects. After the coating at the welding position is knocked clean, it shall be brushed with asphalt for anti-corrosion treatment. When the ground grid is less than 3m away from the entrance and exit of the building or crossing the road during connection, the method of pressure equalizing belt shall be adopted or a gravel layer with a thickness of 150mm shall be laid on the resistance reducing agent, and its width shall not exceed 2m. (6) Resistance reduction of horizontal grounding grid For resistance reduction of the grounding grid, the resistance reducing agent of 30 kg/m shall be poured into the excavated trench, and the resistance reducing agent shall be mixed with water to form a paste, which shall be poured into the trench to wrap the copper wire, and then filled with fine soil and tamped.
The trench of the whole project is about 1871 meters long. According to the dosage of 30 kg/m of resistance reducing agent, 28 tons of resistance reducing agent are needed. For backfilling construction, all excavated parts shall be backfilled with original soil, and the soil with high resistivity (sandy soil, stony soil, etc.) shall be replaced with swamp soil, black soil and garden soil for backfilling, and gravel layer shall be added when crossing with roads and pipelines. Principle of long-acting physical resistance reducing agent Physical resistance-reducing agent (also known as long-acting resistance-reducing agent) is made of macromolecular water-absorbing material and electronic conductive material, which contains fine graphite, bentonite, curing agent, lubricant, conductive cement, etc. It is non-toxic, odorless, non-corrosive, and will not pollute underground water sources, and meets the national environmental standards for high-quality soil. This is particularly important because many grounding constructions require well drilling operations and permeable layers. When the physical resistance reducing agent is used, no chemical reaction occurs and no new substance is produced. But only depends on the powdery structure and good conductivity of the resistance reducing agent itself to produce an auxiliary resistance reducing effect on other grounding bodies of the grounding grid. Its principle of action is equivalent to expanding the grounding area of other grounding bodies and increasing the current flow surface. Thereby reducing the contact resistance thereof. In addition, due to the corrosion resistance of the material of the physical resistance reducing agent, the use of the physical resistance reducing agent to wrap other metal grounding bodies is also a protection for the metal grounding bodies. Physical properties of resistance reducing agent 1. It is completely a physical resistance reducing agent, which eliminates corrosive electrolyte, and uses non-electrolyte carbon powder as conductive material to improve the corrosion resistance of metal electrodes. 2, the conductivity is not affected by acid, alkali, salt, temperature, humidity and other changes, with good moisture absorption, heat preservation, anti-freezing function. And 3, the grounding resistance value of the grounding grid can be reduced, the resistance reduction rate can reach 50 to 90%, the soil resistivity can be improved for a long time, and the grounding resistance value is stable. 4. Insoluble good conductor, which will not reduce the conductivity due to the decline of groundwater level or drought, nor will it be lost due to excessive rainwater. 5. Good voltage equalization can improve the potential distribution, thereby reducing the step voltage and protecting personal safety. 6, high temperature and cold resistance, high pressure impact resistance, long-term stability and effectiveness, service life of more than 50 years. 7. Under normal conditions, it is light black solid powder, non-toxic, odorless and pollution-free. The specific gravity of the dry powder is 0.85-0.95, and the fineness of the dry powder is less than 200 meshes. 8. Strong water absorption and thermal insulation performance can keep the soil around the electrode moist for a long time, which greatly reduces the contact resistance between the grounding electrode and the soil. 9. Good permeability, through the infiltration to the surrounding soil and rock crevices, forming a root network, forming a gently changing low resistance drop area around the grounding electrode. 10. The solidified resistance reducing agent is weakly alkaline, surrounds the electrode, has a compact structure, effectively prevents aerobic corrosion, protects the electrode, and prolongs the service life of the electrode. Amount of resistance reducing agent The economic dosage of the resistance reducing agent shall be determined according to different soils, and the laying thickness on the grounding body shall be between 5 and 15 CM Construction requirements for resistance reducing agent 1) Pre-construction inspection items and requirements: ① The resistance reducing agent shall be the product of the same brand and model. ② The water is clear and free of pollution, and the water is free of sediment and other sundries. ③ The size and shape of the trench and hole shall meet the design requirements, the four walls shall be relatively flat, and there shall be no sundries in the hole and trench. ④ The vertical grounding electrode shall be placed in the center of the hole, and the horizontal grounding electrode shall be placed in the middle horizontally, and the distance from the trench bottom shall not be less than 40mm and shall be uniform (if necessary, it can be fixed with a thin wire). ⑤ The grounding downlead has been painted with antirust paint according to the design requirements and has been initially set. 2) adding water into the prepared resistance reducing agent according to the weight ratio of water to the resistance reducing agent of 0.4-0.6: 1.0, and fully stirring the mixture until the mixture is in a sticky state. The amount of water used for horizontal grounding is just enough to wet all the dry powder and stir it into paste. The water addition amount of the resistance reducing agent for the vertical grounding hole can be the higher value as the case may be. Excessive water addition will prolong the construction time. 3) Pouring, coating and preliminary inspection: gently pour the prepared pasty resistance reducing agent into the grounding trench and hole (to prevent debris and sundries from mixing into the resistance reducing agent) until the grounding electrode is completely coated without omission, and preliminarily measure that the coating thickness is not less than 40mm, the four walls of the borehole are full, and supplement if insufficient.
4) confirmatory test and backfill tamping. After the initial setting of the resistance reducing agent, carefully check that the resistance reducing agent coating surface is uniform, full and free of omission and impurities. The thinnest thickness of the coating body is not less than 40 mm. If it is insufficient, it should be supplemented with resistance reducing agent. After checking, remove the fixed thin line, gently backfill the fine soil without hard objects and branches, with a thickness of more than 200mm, and then add other soil and tamp it. The surface of the compacted backfill shall be slightly above the surrounding ground level. 5. Acceptance (1) During construction, the well depth shall conform to the design standard. (Construct according to the original design. If the design requirements are not met, the design shall be changed.) (2) Deep well grouting shall be fully filled without gaps, so as to better play the role of grounding electrode in reducing resistance. (3) The welding at the lap joint shall meet the requirements to ensure full welding without insufficient welding. And that weld spots are subject to anti-corrosion treatment to ensure the service life. (Follow-up serial, please look forward to,mining dth bit, Jun and electronic original, reproduced please specify the source http://www.junhedianzi.cn/junduiguofang/209.html) return to Sohu, see more Responsible Editor:. wt-dthtools.com