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Common problems in lightning protection of the equipment room
In order to ensure the acceptance quality of construction projects, the supervision and inspection of construction sites on new buildings is an important measure to ensure the quality of construction. Through years of testing practice, there are many problems in the construction of lightning protection projects during the construction of new buildings. These issues are explored.
I. Common problems and quality control measures
1, frequently asked questions
1.1 Do not construct according to the figure
According to the regulations, during the construction of the building, the construction should be carried out in strict accordance with the construction drawings after the technical review. No projects should be added or removed at will, and the materials should be cut and cut. However, in the construction site inspection work of the lightning protection device, it is found that some projects are not based on the design drawings. For the construction, the distance between the down-conductor lines is beyond the design range, and the down-conductor line is not set at the corner of the building; now most buildings are designed from the original flat roof to the slope roof, and the slope should be pre-buried in the slope of the slope during construction. When the bracket is used, it does not cooperate with the civil construction party in time, and there is a phenomenon of leakage of the embedded parts. The lightning protection belt does not set the grid according to the requirements of the lightning protection classification design of the building; it is not at the lower limit of the lightning protection design drawing of the building. The detection point is set at 0.3-1.8m; the equipotential bonding is not required according to the schematic diagram of the equipotential bonding system of the lightning protection design of the building. Therefore, the lightning protection design and construction drawing requirements are not observed in the lightning protection construction, and there are often omissions during construction. .
1.2 Welding of lightning protection devices is not standardized
The lightning protection grounding welding of buildings is always accompanied by the whole process of construction. The welding quality directly determines the quality of lightning protection engineering. In the design of buildings, the basic steel mesh is often used as the grounding body. The problems in the actual testing are as follows: The welding, the welding between the main steel bar and the grounding body of the down conductor, and the welding between the main ribs of the ground beam, the lap length often fails to meet the specified standards; the lap joint steel bar does not meet the requirements, the welding is spot welding, the virtual welding, the intermittent There are defects such as pores, welds, and slag inclusions; if the current is too large during welding, the main ribs will be welded too much; too much impurities in the solder joints will not reach full soldering, the soldering will not be smooth, and the structural performance will be degraded; The lightning protection down conductor is marked, and the lightning protection down conductor is welded to the structural reinforcement of the building; when the lightning protection lower pillar steel bar is bolted, it is not bridged at the joint. When the column steel bar is used as the down conductor, it is required that the two steel bars in the column are welded to the upper and lower layers of the cap, respectively. However, in the actual test, only one weld is found, and some with two columns of steel bars and only one layer of cap steel. Welding, which will affect the amount of snorkeling of the lightning current, leaving hidden dangers; when all the down conductors are applied to the roof, not all the steel bars that are the down conductors are connected to the roof lightning protection belt, but some are cut and concealed. In the parapet wall, this reduces the lightning current discharge channel and weakens the lightning safety factor.
1.3 equipotential bonding without reservation
The lightning protection effect of a building is mainly due to whether the equipotential connection formed between the non-charged metal objects of the building and the charged metal objects can be unified. Therefore, in the equipotential reserve of the building during construction, sufficient points should be set at the necessary positions as a reservation. There is no good connection between the grounding mains and the electrical equipment grounding line. The TN-S system is used in the multi-storey residential building, but the grounding is not repeated at the entrance of the main electric meter box. The sixth is the ladder and pipe of the roof. Metal parts such as equipment casings and flagpoles are not connected to the roof-mounted lightning protection system
1.4 Failure to install surge protector as required
Surge protector settings, low-voltage distribution grounding forms, shielding measures, installation processes, and pipeline laying are not in accordance with the standard requirements for lightning protection design. The low-voltage power distribution system introduced into the building shall be equipped with a corresponding surge protector and floor lighting system (electrical equipment), and a surge protector shall be installed in the power control cabinet. Cables, broadband networks, and electric Hua lines in buildings should be equipped with signal lightning arresters when entering buildings. Most construction projects do not have surge protectors installed in electrical equipment, high and low voltage power distribution systems, and signal lightning arresters are not installed in the information transmission system. When installing the surge protector, the length of the phase line, the neutral line, the ground line and the length of the ground line do not meet the requirements, which leaves a hidden danger to the lightning protection of the power supply system.
Therefore, it is necessary to do a good job in the quality control of the lightning protection project for new buildings, to detect the quality problems that occur, and to take effective pre-control measures to ensure the safety of the building.
2. Quality control measures
2.1 Strict review of design drawings
Design drawing review is a serious and serious task, and the comprehensiveness and depth of the review will have a direct impact on the safety and quality of lightning protection construction. In the process of reviewing the design drawings, first understand the general design description and electrical diagrams, roughly grasp the building structure and equipment layout, and also understand the key descriptions in the design, especially the special projects such as intelligent engineering, computers, information communication, etc. project. The above positions and settings are not clearly marked on the design drawings, but are reserved for pre-burial based on relevant specifications. Therefore, lightning protection construction must be carried out in strict accordance with the acceptance specifications and mandatory standards. In the case of lightning protection construction, if there is a violation of the lightning protection construction specifications and practices, it is necessary to communicate with the relevant units in a timely manner, and sign the corresponding design documents, so that the lightning protection project can be strictly implemented according to the documents; in addition, for a construction project In terms of it, it may contain multiple design drawings. In the review of lightning protection drawings, all aspects of coordination work should be done. For important problems in lightning protection construction and problems that are easily overlooked, written suggestions should be formed, so that the construction unit Play a reminder.
2.2 Guaranteed quality
2.2.1 Strict control of the quality of materials
For materials, the specifications of construction materials, whether they are constructed in accordance with relevant specifications and design standards, etc. must be strictly checked to ensure the safety of construction materials. In the actual construction process, there are often construction workers using steel bars as a slab for welding according to the common structure, replacing the hot-dip galvanizing material with cold-galvanized material, using ordinary steel instead of galvanized material, etc. The phenomenon must be corrected in time.
2.2.2 Quality control of the upper point and cross-bar welding
In the lightning protection construction process, in the grounding grid system with the column bars as the lead line, the construction personnel are required to use the axis as the basis, and the number of the steel bars and the position of each column are clearly marked in each layer, and strictly Construction is carried out. Care should be taken to check the quality of the spanning steel bars and the points on the lead, and to locate the upper lead wires to prevent the occurrence of misalignment of the studs, which may lead to serious errors such as grounding interruption. In particular, the conversion layer should be repeatedly verified when the column ribs are adjusted to prevent leakage welding and mis-welding.
2.2.3 Verify the equipotential and other grounding parts welding conditions
For parts such as power distribution room, elevator machine room, equipment room, cooling tower, etc. that need to be repeatedly grounded and equipotential connected, it must be noted in the construction diary to facilitate verification and review at any time. For high-rise buildings above 45m, for every 3 layers of height, a 25mm×4mm flat steel will be laid inside the structural ring beam and welded to the down conductor to form a circular horizontal lightning protection belt. It can be welded into a pressure equalizing ring by using more than 2 ring beam ribs. When using the pre-embedded iron for lightning protection construction of the glass curtain wall, pay special attention to the reliability and safety of the main rib welding of the column. If the glass curtain wall is added later, a practical lightning protection plan should be developed based on various factors such as the characteristics and area of ​​the building.
2.2.4 Grounding welding
Ground-based grounding welding is the primary link of grounding construction. It is necessary to check the ring beam welding, column-strand welding and foundation welding one by one based on the grounding point and the foundation drawing. In particular, the basic column bars at the expansion joints should be inspected. Confirm that it can be connected. After the entire grounding grid is finished soldering, the resistance of the grounding resistor should be checked to determine whether it meets the relevant standard requirements. If the resistance does not match the requirements, the weld quality needs to be checked again.
2.3 Do a good job in quality inspection according to relevant regulations
Based on the progress of lightning protection construction of buildings, the concealed acceptance work of lightning protection projects should be done in time. After the completion of construction, special attention should be paid to the testing of grounding resistance values ​​such as natural grounding bodies, artificial grounding bodies, lightning rods and glass curtain walls. Especially after the construction of the grounding grid and the grounding body, the grounding resistance value should be tested in time to ensure that it meets the designed standard value. The layout of the surge protector, shielding measures, pipeline layout, low-voltage distribution grounding form, etc. must be consistent with the design standards. Also check the specifications, quantity, location and technical parameters of the installed surge protector to ensure that it is in accordance with the standard design. It is necessary to check the purchase channel of the surge protector, product test report, product insurance, instruction manual and factory certificate, etc., resolutely crack down on counterfeit and inferior products, and earnestly safeguard the safety of people's lives and property.
The quality and performance of lightning protection facilities in newly built buildings directly determine the safety and reliability of lightning protection. In the process of lightning protection site supervision and inspection, the quality problems of lightning protection construction should be correctly treated, and scientific quality control measures should be taken to avoid quality problems and ensure the safety of lightning protection construction of new buildings.
Second, lightning protection grounding scheme
In the integrated lightning protection system, whether it is lightning rod, lightning protection net, lightning protection belt, etc., or various lightning protection induction SPD, it can play one of the most important aspects of lightning protection, and it needs good lightning protection grounding. Under certain soil and climate conditions, good lightning protection grounding depends on the shape of the lightning protection grounding device, the material and specifications of the grounding body and effective measures to reduce the resistance. Scientific calculations yield a variety of data that meets the requirements. Reasonable design can save manpower and material resources. Of course, there will be a certain gap between the calculation results and the actual situation. The size of the gap depends on factors such as the accuracy of the soil resistivity and the degree of uniformity of the soil. The basic spirit of Franklin's lightning protection principle is to pick up the lightning and lead the mine. The truncator draws lightning and can be quickly discharged into the ground to achieve the purpose of lightning protection and disaster reduction. Otherwise, although there is a good flashing device, there is no good lightning protection grounding, and it can not play a good lightning protection effect.
The lightning protection grounding device includes the following parts:
1) Lightning receiving device: directly or indirectly accept lightning metal rods (lighting devices), such as lightning rods, lightning protection belts (net), overhead ground lines and lightning arresters.
2) Ground wire (down conductor): A metal conductor used to connect the lightning receiving device to the grounding device.
3) Grounding device: the sum of the grounding wire and the grounding body.
Good grounding is the basis for stable, safe and reliable operation of the system.
The lightning protection grounding system is designed according to the actual situation of the location using the hot-dip galvanized grounding pole "vertical method". A safety protection grounding body is built at a reasonable position around the lightning protection tower. The measured value of the grounding resistance after rectification should be ≤10 ohms.
That is, a plurality of L50mm×5mm vertical ground rods (length 2m) are vertically buried next to the lightning protection tower, and the ground rod spacing is ≥4m. The top of the grounding rod is 0.5m away from the soil surface. The grounding rods are connected by 4mm×40mm galvanized flat iron and connected to the lightning protection tower outside the soil. The welded joint is effectively rust-proof and anti-corrosive. When backfilling, a resistance reducing agent is required in combination with a large amount of soil backfill to ensure soil moisture around the grounding electrode.