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Cable connector installation precautions

1566800225-主图1

Cable connector installation precautions
1. Domestic construction units generally do not pay much attention to the environmental humidity and dust conditions at the joint location. In fact, for long-term operation of the cable, moisture and small impurities are very harmful, which may cause water trees and partial discharge. Therefore, it is necessary to pay attention to the environmental humidity and dust in the joint construction. Pay attention to clean the environment before construction. In summer, joint personnel should wear gloves. If the ambient humidity is too high, dehumidification should be carried out (increasing the ambient temperature or using a dehumidifier). Dry the insulating surface with a blower before inserting the stress cone.
2. The cable should be heated and straightened before the cable joint. Sometimes the construction personnel think that the cable is not bent and can not be heated. In fact, this view is incorrect. There are two reasons for the cable to be heated and straightened: one is to eliminate the mechanical stress caused by the distortion in the cable when the cable is discharged; the other is to eliminate the dimensional change caused by the insulation heat shrinkage after the cable is put into operation. Therefore, the cable must be heated and straightened before the cable connector.

3. Insulation shield 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 must not be sloppy. If the process is not well controlled, it is very dangerous to insulate the end of the shield to grind the pit, step or semi-conductive tip.
Cable accessory manufacturers generally use semi-conductive paint (ELASTIMOLD, Swiss CC, etc.), molded semi-conductive layer (made in Japan), semi-conductive tube (G&W), and only the semi-conductive shield ends are scraped. Forming a smooth over-slope (Swiss BRUGG, KP, Germany), in comparison, the method of molding semi-conductive layers is more secure.
4. Insulation surface treatment
Since the wrap-around cable joints are basically not put into operation, the main two types of cable accessories are now assembled cable joints (Japanese manufacturers, Korean manufacturers, Changsha cable accessories factory terminals, Shenyang Fuhe intermediate joints), prefabricated cable joints ( European manufacturers, American manufacturers, Shenyang outdoor terminals). Assembled cable joint cable joints have high insulation outer diameter (outer diameter error within 0.5 mm), high insulation surface flatness (the sandpaper used is generally not less than 600#), and the dimensional requirements are strict (size error is Within 1 mm), in a project in Beijing area, the Japanese construction personnel had finished the joints, but felt that the size of one of the joints was not well controlled, and the mind was not sure, and the joints were disassembled. In comparison, the prefabricated cable joint technology is more advanced, the outer diameter of the insulation (EPDM type stress cone outer diameter is allowed to vary within 4.5 mm, the silicone rubber type stress cone outer diameter is allowed to vary within 8-16 mm), and insulation The surface flatness requirement is not high (the sandpaper used generally requires a maximum of 400#), and the size requirements are also loose (the size requirement error is within 15 mm).
After the sanding is completed, it is cleaned with a lint-free cleaning paper and air-dried with a hair dryer. Some manufacturers use a high-heat hair dryer to heat the insulating surface for a short time to ensure a smooth surface. Before the stress cone is installed, the stress cone and the cable insulation surface are dehumidified by a hair dryer.
5. Conductor connection
High-voltage cable conductor connections are generally crimped, and sometimes welded (Shenyang cross-linking terminal used in 1996) or bolted (Swiss BRUGG intermediate joint), but high-voltage cable conductor crimping has no national standard (only in GB14315-1993) It is mentioned that other wires and cables for fixed laying can also be referred to.) There are no written standards in the world, and the standards of various manufacturers are different. In Beijing, the hexagonal die is used for confining pressure and the indentations overlap. (The matching dimensions of hydraulic pipe and compacted conductor are shown in Table 1)
The crimping sequence is to press the middle final crimping edge first. Each time the stamper is pressed once, after the stamper is closed in place (the pressure gauge indicates 700kg/mm2), it should stay 10-15S, so that the metal plastic deformation of the crimping part can be basically stabilized before the pressure can be eliminated. Before crimping, the cable should be leveled first, and the height of the clamp die should be appropriate. The rise of the mold during the crimping process should be considered to ensure that the take-up is in line with the cable after crimping. The maximum allowable value for the margin size S after crimping various hydraulic pipes is: S = 0.866 × (0.993D) + 0.2mm D - tube outer diameter mm. Generally, the compression ratio of the manufacturers is about 15%. Some manufacturers have a larger compression ratio. For example, the compression ratio of the US G&W is 25-30%. When the actual crimping is required, the pressure is twice. First, press the larger mold once. Then use the selected mold to crimp, otherwise there will be a large flash.
There is generally a shield cover outside the intermediate joint, which has two main functions: maintaining good contact with the stress cone shield and dissipating heat. European manufacturers also use the method of trenching the insulation, which not only ensures good contact with the stress cone shield and also acts as a heat sink, but also prevents thermal shrinkage of the insulation.
6. Stress cone size positioning
Generally, the method of positioning at both ends is adopted: before the sleeve stress cone, a mark is made at an appropriate position on the two semi-conductive layers of the cable, and the distance between the two ends and the two ends is required to be substantially the same when the stress cone is set to the final position. This method is more accurate and the error is small.

7. Joint seal
Considering that plastic products cannot guarantee the long-term infiltration of water, there is often water accumulation in the rainy season in cable tunnels in Beijing. Therefore, when the intermediate joints are ordered, copper shells are generally required outside the joints, and lead shells and copper shells are used between the copper shells and the metal sheath of the cables. A heat-shrinkable tube is used externally, such a double-layered structure. The lower part of the terminal head is also generally used to reheat and shrink the tube. Some manufacturers also use a glass fiber belt with epoxy sealant or a mixture of two kinds of glue (such as Japanese manufacturer, Changsha Cable Accessories Factory).
Because the cross-linked cable can not be used to check the quality of the seal according to whether the oil is leaking or not, so to ensure the quality of the seal, the seal should be carried out twice, the first seal, the second build and strengthen, lead The seal must be dense and free of pores. Then, according to the manufacturer's process requirements, the waterproof layer is wrapped, the anti-corrosion and insulation layers are made, and the outer sheath of the cable is restored. There are also some manufacturers that require the addition of an insulating agent or a heat sink (such as Sumitomo Corporation of Japan).