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1. Causes of manufacturing of cable body Generally, the problems that are likely to occur in the cable production process include eccentricity of insulation, uneven thickness of insulation shield, impurities in insulation, protrusions inside and outside shielding, uneven degree of cross-linking, moisture in cable, and sheathing of cable metal sheath. Poor, etc., Some situations may be more serious. Failures may occur during or shortly after completion of the test, and most of them are in the form of defects in the cable system, causing serious hidden troubles in the long-term safe operation of the cable.
2. Reasons for the manufacture of cable joints High-voltage cable joints have previously used wrap-around type, die-cast type, and molded type, and require a large amount of work to be produced on site. Because of the limitations of on-site conditions and the manufacturing process, insulation layers are not allowed. Avoid air gaps and impurities, so problems can easily occur. The types commonly used in China are assembly and prefabrication.
The cable joints are divided into cable end connectors and cable intermediate joints. No matter what the joint type is, the cable joint failure usually occurs at the fracture of the cable insulation shield because it is the site where the electrical stress is concentrated and the cause of the cable joint failure due to manufacturing reasons is stress. Cone body manufacturing defects, insulation filler problems, oil leaking seals and other reasons.
3. Cable Grounding System The cable grounding system includes the cable grounding box, the cable grounding protection box (with protective layer protector), the cable cross-connection box, and the protection layer protector. The general problem that is easy to occur is mainly because the poor sealing of the box body leads to multi-point grounding, causing the metal sheath induction current to be too large. In addition, the selection of protective layer protector parameters is unreasonable or the quality of the zinc oxide crystal is unstable, and the protective layer protector is easily damaged.
Second, the construction quality reasons
There are many cases of high-voltage cable system failure due to construction quality. The main reasons are as follows:
1, the site conditions are relatively poor, cables and joints in the factory manufacturing environment and process requirements are high, and the construction site temperature, humidity, dust are not well controlled.
2. In the course of cable construction, it will inevitably leave tiny sliding marks on the insulating surface. The semi-conductive particles and sand on the abrasive cloth may also be embedded in the insulation. In addition, during the construction of the joint, the insulation is exposed to the air and the insulation is also inhaled. Moisture, these all leave hidden dangers for long-term safe operation.
3, the installation did not strictly in accordance with the process of construction or process regulations did not take into account the possible problems.
4. Acceptance and acceptance of the DC voltage withstand test results in the formation of a back-EMF within the connector resulting in insulation failure.
5, due to poor sealing caused. The middle joint must adopt the sealed structure of metal copper shell plus PE or PVC insulation coating to ensure the solidity of the seal during construction on site, which effectively ensures the sealing and waterproof performance of the joint.
Third, the design reason
Cable breakdown caused by thermal expansion of the cable causes breakdown. When the cross-linking cable load is high, the temperature of the core is increased, the cable is heated to expand, and the cable is turned on the bracket elevation at the turning point in the tunnel. The long-term heavy-duty operation of the cable has a large amount of peristaltic force, which causes the bracket facade to crush the outer jacket of the cable. , Metal sheathing, intrusion into the cable insulation leads to cable breakdown.
YJV high voltage cable common problems and causes
A, factory for manufacturing reasons <br> <br> factory manufacturing reasons occurred according to different parts of the body is divided into cable reasons, the reason connector cable, grounding cable system three reasons.