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First, manufacturers make reasons
According to the different parts, the manufacturer's manufacturing reasons are divided into three categories: cable body reason, cable joint reason, and cable grounding system reason.
Reasons for manufacturing cable bodies are generally caused by problems such as eccentricity of insulation, uneven insulation shield thickness, impurities in insulation, protrusions inside and outside shielding, uneven degree of cross-linking, moisture in cables, poor sealing of cable metal sheaths, etc. In some cases, serious failures may occur during or shortly after the completion of the completion test, and most of them exist in the form of defects in the cable system, causing serious hidden troubles in the long-term safe operation of the cable.
Reasons for the manufacture of cable joints High-voltage cable joints have previously been of the wrap-around type, die-cast type, molded type, etc., requiring a large amount of work on site, and due to the limitations of on-site conditions and manufacturing processes, the insulating tape layers are inevitably There will be air gaps and impurities, so it is prone to problems. 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 location 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.
Cable Grounding System The cable grounding system includes the cable grounding box, the cable grounding protection box (with protective layer protector), the cable cross-interconnect box, and the protective 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 it is easy to cause damage to the protective layer protector.
Second, the reason for construction quality
There are many cases of high-voltage cable system failure due to construction quality. The main reasons are the following: First, the site conditions are relatively poor, the environment and process requirements are very high when the cables and connectors are manufactured in the factory, and the construction site temperature, humidity, dust Not well controlled. Secondly, during the cable construction, it is inevitable that tiny scratches will be left on the insulating surface. The semi-conductive particles and the 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. Third, the installation did not strictly follow the process of construction or process regulations did not take into account the possible problems. The fourth is that the DC voltage withstand test results in the formation of a back-EMF in the joint resulting in insulation failure. The fifth is due to poor sealing. 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 thermally expanded, 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.
A high-voltage cable is a kind of power cable and refers to a main road used to transmit power cables between 10KV-35KV (1KV=1000V) and is mostly used for power transmission. The cable is the bridge between the power supply equipment and the electrical equipment, and plays the role of transmitting electrical energy. Because of its wide application, faults often occur. The following briefly analyzes the causes of the common problems of high-voltage cables. The classification based on the causes of faults can be roughly divided into the following categories: manufacturer's manufacturing reasons, construction quality reasons, and design unit design reasons.