Chen Hao (Kerry Power Supply Bureau of Guizhou Province, Kaili 556000, Guizhou Province) focused on the analysis, research and application of power cable laying, installation and handover test, and explained the application of cable in production. In the construction of cities and towns in China, the construction of distribution networks is a crucial link. Effectively improving the construction quality of power cable projects is an important factor in the safe and reliable operation of the power grid. 1 The cable laying method of the cable includes direct burial laying, cable trench laying, pipe laying, cable tray laying and cable laying of concrete pipe. The method of laying is as follows: Firstly, it is necessary to check whether the cable laid is wet or not, and whether it is damaged by machinery. If the cable is in both cases, it cannot be laid. Compliance with the various tools and materials required for inspection and laying. After the preparation is completed, the power cable can be transported to the job site for laying. Now take the direct buried cable installation as an example: according to the design drawings, site conditions to determine the direction of the power cable, measure the path length of the cable, and then intercept the power cable according to the length of the path, usually need to leave 12m for easy laying; then scribe Use white lime to mark the position of the cable trench and the width of the excavation on the ground. The width is determined according to the width of the human body and the number of cables. The width of the excavation is usually 0.50.6m and the depth is 0.8m. When digging, it should be vertical. Excavation, the excavated soil is piled on both sides of the ditch for easy backfilling. After the cable trench passes the acceptance, a 10 cm thick sand layer is placed on the bottom to protect the cable. Finally, use mechanical gravitation or manpower to lay the cable, put the cable into the ditch, and after passing the inspection, cover the 10cm soft soil fire sand layer around the cable, cover the protective cover, and backfill the soil on both sides of the ditch to the ditch. Inside, the laying is over. 2 When installing and installing the power cable, ensure that the ambient temperature and the temperature of the power cable are above C. It can be installed after 24 hours. Especially PVC plastic, it will become harder and more brittle with the decrease of ambient temperature. If it is subjected to violent impact below 0C, PVC plastic will be broken. The plastic sheath is cut according to the length of the power cable bracket to the electrical connector. Saw the steel armor at a distance of 3 cm from the plastic forming port, tie the steel armor with a plastic bag, cut the inner sheath 1 cm away from the steel armor, then heat the anti-corrosion layer with a blowtorch, and then clean the anti-corrosion layer with gauze. Insert the PVC gloves, seal the lower mouth of the glove with a heat-shrinkable tube, leave a 2cm shield on the fingertips of the glove, loosen the semi-conductive layer, and use a self-adhesive rubber tape to separate the semi-conductive layer from the nozzle. A stress hammer is placed at 0.5 cm, and two layers of rubber tape are wrapped on the stress hammer to seal the finger mouth. Mark the phase sequence and put a yellow, green and red color plastic tube on the three-phase core. Put a rain cover on the end of the outdoor cable, and fix it with a self-adhesive rubber band. This cable can be omitted. According to the depth of the wire nose increased by 0.5cm, the wire core insulation is stripped, the wire nose is put on, and the air pressure clamp is used to clamp the cable to the electrical connection. If necessary, cover the protective cable of the power cable to prevent corrosion and mechanical damage. The main points that need attention in the installation of power cables are as follows: (D) Check whether the cables are damp before construction. The specific method is to ignite the cable insulation paper or put it into the cable oil of about 150C for inspection. The power cable can not be sharply bent. According to the standard of GB/T127062002, the laying process must be strictly in accordance with the standard requirements, and a large bending radius should be used as much as possible during the laying process. Control cable, plastic power cable, rubber insulation and plastic sheathed power cable can not be less than 10D (D is the cable outer diameter) oil-impregnated paper extruding power cable, rubber insulation, bare lead-package power cable not less than 15D, rubber insulated lead package Armored power cables must not be less than 20D. When burying power cables in cold areas, the power cables should be buried below the frozen soil. When the power cable passes through various places subjected to pressure and vibration, the construction shall be protected by pipe. It includes: the foundation of the building, the floor, the wall; the section of the railway and the road that may be subjected to mechanical damage; the cable is perpendicular to the ground 2m to the ground 0.2m, which is easy to come into contact with pedestrians and may be subject to mechanical damage. If the power cable is parallel to the building during laying, the cable must be buried outside the building's scattered water. When entering the building, the protective pipe must be 10cm away from the scattered water of the building. When the direct buried power cable crosses the railway and the road, the protective pipe should be extended 1m. When the power cable crosses the heat pipe, such as The cable shall be protected by asbestos cement pipe. The length shall extend 2m on both sides of the heat pipe trench and shall be protected by the heat insulation layer. It shall exceed 1m of the heat pipe trench and each side of the cable. When laying the power cable, the lower part of the joint box The foundation board of the concrete must be placed, and the length should extend 0.60.7m on both sides of the joint protection box. 3 The handover test of the power cable project is to carry out the handover test of the power cable. It is an important work to ensure the safe operation of the power grid. It is stipulated that the DC withstand voltage test should be used. During the test of DC withstand voltage, there may be electron injection into the interior of the cross-linked cable dielectric polymer, so that the space charge at the convex portion or the tiny gap of the semi-conductive layer accumulates, and the cable is put into operation and sent with AC voltage. Superimposed on each other to cause insulation breakdown. After the test of DC withstand voltage, there will still be a lot of residual charge in the power cable. In order not to affect the measurement of insulation resistance and absorption ratio, the cable should be fully discharged in time. The first time the cable passes the DC withstand voltage test, the discharge time is short. If the insulation resistance test is performed without discharging the remaining charge, the absorption current and the charging current will be reduced compared with the first time. The result is insulation. The resistance increases falsely and the absorption ratio decreases. According to the experimental research at home and abroad, the DC withstand voltage test has obvious shortcomings: in the DC voltage, the electric field distribution of the cable insulation and the electric field distribution under the AC voltage are different, which reflects the actual operation. The space charge formed by the DC voltage during the test will cause creeping and breakdown of the cable during use. The increasingly sophisticated test equipment makes AC withstand voltage testing possible. The voltage value of the 30300Hz variable frequency withstand voltage test of the power cable is shown in Table 1. It should be noted that the above data is the test data of rubber-plastic cable. The test data of paper-insulated cable and rubber-plastic cable are different. It is necessary to judge according to the construction environment and use rubber-plastic cable as the test for paper-insulated cable. 4 Cable development trend and application in production 4.1 Construction of large-scale power grid to promote industry development During the “Eleventh Five-Year Plan†period, China’s investment in power grids amounted to 1.2 trillion yuan, and “10th Five-Year Plan†Compared to the period, it increased by 2.4 times. The wide application of cables in power grid construction has also ushered in a new round of rapid development in this industry. During the “Eleventh Five-Year Plan†period, the deformation characteristics of the new 330kV (down to page 136) specimens in China were firstly elastic deformation, then uniform plastic deformation, and after plastic deformation reached a certain degree, necking occurred, and plasticity occurred locally. Deformation, the last break occurs, and the fracture occurs near the weld line of the joint. The tensile mechanical tests of TIG welding and conventional TIG welding head specimens show that the tensile strength of A-TIG welding specimens is about 590 MPa, the tensile strength of conventional TIG welding specimens is about 560 MPa, and the resistance of A-TIG welding specimens. The tensile strength is increased by about 5% compared to the conventional TIG welding specimen, the elongation is increased by about 27%, and the strength and plasticity are both increased. 2.2A-TIG welding stress corrosion cracking improvement factor Stress corrosion cracking has three influencing factors, these three elements can be roughly summarized as: stress corrosion cracking can only be caused by tensile stress. The tensile stress may be a stress caused by an applied load; or may be various residual stresses such as welding residual stress, heat treatment residual stress, and assembly stress. Corrosive media are always present in stress-corrosive environments. These corrosive media are generally weak. If there is no tensile stress, the material will corrode slowly in various media. The medium that produces stress corrosion is specific, that is, each material is only sensitive to a medium that may not have a significant effect on other materials. Austenitic stainless steels are prone to stress corrosion in corrosive environments containing chloride ions. Generally, only alloys produce stress corrosion, which is not caused by pure metals. Alloys can also produce stress corrosion cracking only when combined with tensile stress and specific corrosive media. The difference of the stress corrosion cracking resistance between the A-TIG welding specimen and the ordinary TIG welding specimen was analyzed from the above three factors. In the 41% magnesium chloride stress corrosion test method, the A-TIG welding sample and the ordinary TIG welding sample are in the same corrosion solution, the materials are the same, the corrosion medium is the same, so the resistance to stress corrosion cracking The difference is mainly due to the difference in tensile stress. During the processing of stress corrosion specimens, external tensile stress is applied, but the specimens are processed strictly according to national standards, and the degree of bending and clamping are basically the same. Therefore, the influence of the difference of welding residual stress is mainly considered in the analysis process. . According to Ye Song's research, the conventional TIG specimens have a higher cracking speed under a larger tensile stress and a weaker resistance to stress corrosion cracking. A-TIG weld cracks occur later than conventional TIG welds, and crack propagation depth is lower than conventional TIG welds. It shows that the active agent welding improves the stress corrosion cracking resistance of the workpiece to a certain extent. During the formation and expansion of stress corrosion cracks, since the tensile stress in the overheated zone of the conventional TIG welding specimen is larger, the crack is formed earlier and the expansion speed is faster, so the crack quickly penetrates the metal in the superheated zone and brittle fracture occurs. 3 Conclusion Active agent welding is a special TIG welding method that adds active agent in the welding process. Its outstanding advantage is that it can greatly improve the weld penetration and reduce defects such as infusibility. The stress corrosion mortar shows that under the same test conditions, the crack initiation time of A-TIG welding specimens is later than that of conventional TIG welding, and the penetration depth of cracks is smaller than that of conventional TIG welding specimens. The overall quality of A-TIG after welding is significantly better than conventional TIG welding. Liu Fengqi. Study on the mechanism of welding and penetration increase of stainless steel and alloy active agents. Harbin Institute of Technology, 200 (1): 17 Zhang Ruihua, Fan Ding, Yin Yan. Study on active agents for high-efficiency TIG welding of mild steel. Gansu Gong Yang Chunli, Lin Sanbao. Arc Welding Foundation Harbin Institute of Technology Press, welding and assembly of force equipment. (Continued from page 129) Table 1 30300Hz variable frequency withstand voltage test voltage cable for power cable rated voltage transfer test multiples CUo) The above AC line is about 36,000 km, and the capacity for substation is 180 million kVA. According to 7000km per year The speed is increasing, and the substation capacity is also increased. 3 4.2 Optimizing large-scale enterprises and accelerating the development speed At present, the concentration of the cable industry is not high. Therefore, the integration of industry resources is imminent, and smaller enterprises will gradually be kicked out of the market. Once the concentration of the industry is improved, large-scale high-quality enterprises will surely develop rapidly and become the leader in the industry. Under such a trend, the application range of the cable will be wider and the demand will be larger. Rubber-plastic cable is one of the most common cables in daily life. It is applied to various electrical equipment (such as electric machinery, household appliances, etc.), and can adapt to various outdoor environments and is extremely durable. Rubber and plastic cables have a complete range of specifications, versatility and stable performance. Whether it is the climatic conditions in the north or the south, the temperature outside is poor, and the rubber-plastic cable can handle it with its excellent durability. The rubber and plastic materials also greatly increase the service life of the cable, which not only reduces the probability of accidents caused by cable breakage, but also saves the funds spent on maintenance and repair of the cable. Therefore, the rubber-plastic cable becomes the conclusion of the cable production. With the continuous development of society, the process of urban and township construction is gradually accelerating. In this process, the distribution network is an essential construction project. How to effectively improve the construction quality of power cable engineering has become an important factor to improve the safety of the power grid and ensure its reliable operation. Therefore, it is necessary to study the laying, installation and handover test of power equipment cables. Only under the guidance of scientific theories and predecessors' experience, combined with specific actual conditions, flexibly mastering and applying technology in practice, and continuously improving the level, can better serve socialist construction. Xia Xinmin. Power cable selection and laying. Chemical Industry Press, 2008.5 GB50150-1991 Electrical installation engineering electrical equipment handover test standard DL/T5961996 power equipment preventive test procedures Wei Weicheng. Power cable laying method selection. China Power Enterprise Management, 2009 Li Shijun. Power engineering cable quality control technology. China Construction Information, 2007 (22) Electrical Test. Knitted Polar Fleece,Bonded Polar Fleece,Yarn Dyed Polar Fleece,Polyester Micro Polar Fleece SHAOXING SHUKE IMPORT AND EXPORT CO.,LTD , https://www.shuketex.com
Laying, installation and handover test of power equipment cables