Several problems that should be paid attention to

Several problems that should be paid attention to in the construction of high-voltage cables

Abstract: This paper summarizes the experience and achievements in the construction of high-voltage cables in Beijing, analyzes some problems that should be paid attention to, and puts forward some own views and opinions

key words: high voltage cable construction problems the cable construction Department of Beijing power supply engineering company is responsible for the construction of 110 kV and above high voltage power cables in Beijing. Since 1994, with the rapid development of Beijing electric power, a large number of cables (mainly high-voltage XLPE insulated power cables) have been put into operation every year. The cable construction department has also accumulated a lot of experience in cable construction and achieved some results. Now let's introduce some of our construction experience. I Technical requirements for cables: basically according to the technical conditions of the order (formulated according to the standards IEC, GB, etc.), according to the problems encountered in our construction, we especially require the following items: the eccentricity of the main insulation is 8% (new IEC regulations), the measurement accuracy is high, the outer sheath is made of flame-retardant RED PVC, the sheath should be firmly wrapped on the metal, and the cable should not be loose or slip during construction and operation. The outer sheath shall be coated with graphite conductive layer, and the coating shall be smooth and firm without falling off during laying and long-term operation. The traction head and lead sheath (aluminum solder for aluminum sheath) shall be firmly welded to ensure sealing and no water ingress. The overlapping length of the heat shrinkable sleeve of the traction head to the traction head and the cable shall not be less than 200mm respectively. The flame retardant test shall be conducted according to iec-332-c and IEC or IEC. The halogen content is 330mg/g (reference value), and the smoke density shall be provided according to astme. The light transmittance of the smoke density is 20% (reference value), and the test report shall be provided. For the cable with lead metal sheath and semi conductive resistance hose as the inner lining, the carbonization of the hose due to the lower carbonization temperature (230 ℃) than the lead pressing temperature (290 ℃) should be avoided to adhere to the cable insulation shield. The semi conductive resistance hose is easy to absorb moisture. When wrapping the semi conductive resistance hose, the cable manufacturer should pay attention to the exposure time as short as possible to prevent moisture absorption and water inflow in the manufacturer. When checking the on-site cable after breaking the cable, we must pay attention to check whether the semi conducting resistance hose is dry. We once found that there seems to be a colloid on the semi conducting resistance hose of a manufacturer's cable, and finally confirmed that there is serious water inflow in the manufacturer. II. The best graded plate Cable joint installation 1 Domestic construction units generally do not pay much attention to the environmental humidity and dust at the joint site. In fact, for the long-term operation of cables, moisture and small impurities are very harmful, which is easy to cause water trees and partial discharge. Therefore, attention must be paid to the environmental humidity and dust during the joint construction. Before construction, attention should be paid to cleaning the environment. In summer, construction joint personnel should wear gloves. If the environmental humidity is too high, dehumidification treatment should be carried out (increase the ambient temperature or use dehumidifier), Before inserting the stress cone, the insulating surface shall be dried with a blower. 2. Before the cable joint, the cable should be heated and straightened. Sometimes the construction personnel think that the cable can not be heated without bending. In fact, this view is incorrect. There are two reasons why the cable should be heated and straightened: one is to eliminate the mechanical stress in the cable caused by distortion during cable laying; The second is to eliminate the size change caused by insulation thermal shrinkage after the cable is put into operation. Therefore, the cable must be heated and straightened before the cable joint. 3. Insulation shielding end treatment insulation shielding end treatment is an important step in the work of cable joints. This step has the highest technical and technological requirements and should not be sloppy. If the process is not well mastered, it is easy to grind pits, steps or semi conductive tips at the end of the insulation shield, which are very dangerous. The methods generally adopted by cable accessory manufacturers include painting semiconducting paint (elastimold in the United States, C.C in Switzerland, etc.), molding semiconducting layer (made in Japan), covering semiconducting tube (GW in the United States), and scraping the end of semiconducting shield only to form a smooth and excessive slope (Brugg in Switzerland, K.P company in Germany). Compared with this method, molding semiconducting layer is more safe. 4. Insulation surface treatment because the wrapped cable joint is no longer in operation, the total production capacity of the product is now mainly expanded to 9000 tons. The two types of cable accessories are prefabricated cable joints (Japanese manufacturers, Korean manufacturers, Changsha cable accessories factory terminal, Shenyang Guhe intermediate joint), prefabricated cable joints (European manufacturers, American manufacturers, Shenyang outdoor terminal). Assembled cable joint cable joint has high requirements for insulation outer diameter (outer diameter error is within 10kw0.5 mm of power supply), insulation surface flatness (the sand paper used is generally not less than 600 #), and size requirements are also relatively strict (size error is within 1 mm). In a project in Beijing, Japanese construction personnel feel that the size of one of the joints is not well controlled after the joints have been completed, Not sure, take it apart and reconnect it. In comparison, the prefabricated cable joint technology is relatively advanced, and the requirements for the insulation outer diameter (the allowable variation range of the outer diameter of the EPDM type stress cone is within 4.5mm, and the allowable variation range of the outer diameter of the silicone rubber type stress cone is within mm), the flatness of the insulation surface are not high (the sand paper used is generally required to be up to 400 #), and the requirements for the size are relatively loose (the size error is required to be within 15 mm). The above is the schematic diagram of prefabricated (a) and fabricated (b). The shapes of prefabricated terminals and intermediate joint stress cones are shown in the above figure respectively. After grinding, clean them with lint free cleaning paper and dry them with an electric hair dryer. Some manufacturers also use a high thermal electric hair dryer to heat the insulation surface for a short time to ensure that the surface is smooth. Before installing the stress cone, use an electric hair dryer to remove moisture from the stress cone and the cable insulation surface. 5. Conductor connection high voltage cable conductor connection generally adopts crimping, and sometimes adopts welding (Shenyang cross-linked terminal used in 1996) or bolt crimping (Swiss Brugg middle)