Failure And Solution Of Cold Shrink And Heat Shrinkage Cable Joints

The main function of the cable joints is to make the line unobstructed, to keep the cable sealed, and to ensure the insulation level at the cable joint for safe and reliable operation. Therefore, it is necessary to analyze the failure carefully, find out the cause and take preventive measures to ensure the safe operation of the cable line.

Common Failure and Solutions for Heat Shrinkable Cable Joints

(1) During the cutting process of the cable joints, the cutting edge should not be too deep. In the process of removing the semiconductor ring cutting, it is necessary to grasp the appropriate strength, and it is not allowed to cut into the polyethylene-insulated insulating layer of the cable to destroy the main insulation of the cable, otherwise it will become a weak link of the cable insulation. Try to ensure the overall main structure, and stabilize the cable strap and copper shield tape. When cutting, you should prevent damage to the inner structure of the cable. Each cutting surface should be as close as possible to the ideal 45* angle, without leaving any knife marks and burrs, ensure the quality of the stripping process. Evenly polished in the radial direction, and then apply a thin layer of silicone grease.

(2) Correctly using flame shrinkage and heat shrinkable materials. The shrinkage heating temperature is generally 110-140C, and the shrinkage depends directly on the control degree of the fire hall. In order to ensure uniform shrinkage, keep distance and control temperature properly according to the size of the flame to prevent the heat shrink tubing from being over-contracted or cracked. When heated, the flame moves slowly around it, and the flame faces the direction of contraction to preheat the tube. In order to facilitate the exclusion of gases and seals, the initial shrinkage site and direction are specified. The insulating tube wall of the shrink layer should be smooth and wrinkle-free, and the inner contour can be clearly seen. A small amount of glue is extruded at the end of the heat-shrinkable tube sealing, indicating that the seal is good and reliable. Whenever possible, the liquefied gas is used instead of the gasoline burner. The liquefied gas can be fully burned, and the carbon particles generated by the incomplete combustion are not left on the surface of the heat-shrinkable tube, and the creepage passage generated can be avoided.

Prevention Countermeasures of Cold Shrink Cable Joints

To prevent the failure of the cold shrinkable cable joint, the key is to improve the construction quality, which should be strictly checked in the following aspects:

1) After stripping the insulation of the cable, carefully polish the surface of the main insulation layer with fine sandpaper to make it smooth without knife marks and semiconductor residue. The cleaning of the insulating layer must be carried out from the core to the semiconductor shield with a cleaning solvent. Never clean the surface of the main insulating layer with a cleaning paper that has been in contact with the semiconductor shield.

2) After the core is crimped, carefully grind it with a trowel and sandpaper to eliminate the edges and the tip, and note that the metal dust must not remain on the surface of the insulation.

3) Cable joints should be carefully kept clean during the production process, while minimizing production time. The longer time the cable is exposed after being stripped, the greater the possibility of intrusion of dust, moisture, gas, etc., which affects the quality of the joint. Therefore, it is required to fully prepare all the preparations before the construction to ensure uninterrupted production.

4) Before the production of the cold shrink cable joint, carefully check the cable accessories to make sure that they match the cable, so that the interference of the cold shrinkable silicone rubber bushing can be strictly controlled to ensure that it has sufficient grip force to make the interface close and no gas gap.

5) After shrinking, the two ends of each phase of the silicone rubber sleeve are respectively wrapped with a semiconductor self-adhesive tape, so that the outer semiconductor layer of the silicone rubber sleeve and the outer semiconductor shielding layer of the XLPE cable can be well integrated and can prevent the intrusion of moisture, gas, and dust in the axial direction.

6) Wrap 228 self-adhesive waterproof tape, which is the key link of moisture-tight sealing of cold shrink cable joint. It should be wrapped from one end of the joint to the other end by semi-overlapping method, and then wrapped in the opposite direction from the end to the starting end. Wrap two layers. After each layer is wrapped, it should be gripped with both hands in order to make it adhere firmly. When wrapping, it is necessary to pull the tension properly, so that the wrapping is tight and seamless.