Discuss the causes of common problems in high-voltage cables
2017-04-25
The cable is the bridge between the power supply equipment and the electrical equipment, which plays the role of transmitting electric energy. Widely used, so failures often occur, the following brief analysis of the causes of common problems of YJV high-voltage cable, according to the causes of failure classification is roughly divided into the following categories: manufacturers manufacturing reasons, construction quality reasons, design unit design reasons, external damage four categories.
The cable is the bridge between the power supply equipment and the electrical equipment, which plays the role of transmitting electric energy. Widely used, so failures often occur, the following brief analysis of the causes of common problems of YJV high-voltage cable, according to the causes of failure classification is roughly divided into the following categories: manufacturers manufacturing reasons, construction quality reasons, design unit design reasons, external damage four categories.
1. manufacturer manufacturing reasons
According to the different parts, the manufacturer's manufacturing reasons are divided into three categories: cable body reasons, cable joint reasons and cable grounding system reasons.
1. Reasons for cable body manufacturing
Generally, the problems that are easy to occur in the cable production process include insulation eccentricity, uneven thickness of insulation shield, impurities in insulation, protrusions in internal and external shields, uneven crosslinking degree, cable moisture, poor sealing of cable metal sheath, etc. In some cases, faults may occur during the completion test or shortly after commissioning. Most of them exist in the form of defects in the cable system, causing serious hidden dangers to the long-term safe operation of the cable.
2. Reasons for cable joint manufacturing
High-voltage cable joints used to be wrapped, die-cast, molded and other types, requiring a large amount of work to be produced on site, and because of the limitations of on-site conditions and the reasons for the production process, there will inevitably be air gaps and impurities between the insulating tape layers, so problems are prone to occur. The types commonly used in China are assembled and prefabricated.
Cable joints are divided into cable terminal joints and cable intermediate joints. No matter what joint form, cable joint faults generally occur at the cable insulation shielding fracture, because this is the place where electrical stress is concentrated. The causes of cable joint faults due to manufacturing reasons include manufacturing defects of stress cone body, insulation filler problems, oil leakage of sealing ring, etc.
3. Cable grounding system
Cable grounding system includes cable grounding box, cable grounding protection box (with sheath protector), cable cross interconnection box, sheath protector and other parts. Generally, the main problem that is easy to occur is that the box is not well sealed and water enters the multi-point grounding, which causes the induced current of the metal sheath to be too large. In addition, the parameter selection of the sheath protector is unreasonable or the quality is not good. The instability of zinc oxide crystal is also easy to cause the damage of the sheath protector.
2. construction quality reasons
Because the construction quality leads to a lot of cases of high-voltage cable system failure, the main reasons are the following aspects:
1, the site conditions are relatively poor, cables and joints in the factory manufacturing environment and process requirements are very high, and the construction site temperature, humidity, dust are not easy to control.
2, the cable construction process in the insulation surface will inevitably leave small slip marks, semi-conductive particles and sand on the emery cloth may also be embedded in the insulation, in addition to the joint construction process due to the insulation exposed to the air, the insulation will also inhale moisture, these are to the long-term safe operation of the hidden dangers.
3. The installation did not strictly follow the process construction or the process regulations did not take into account the possible problems.
4. DC withstand voltage test is adopted for completion acceptance, resulting in insulation damage caused by anti-electric field formed in the joint.
5. Caused by poor sealing treatment. The intermediate joint must adopt the sealing structure of the metal copper shell plus PE or PVC insulation anti-corrosion layer to ensure the compactness of the lead seal in the field construction, which effectively ensures the sealing and waterproof performance of the joint.
3. design reasons
Breakdown due to cable extrusion caused by thermal expansion of the cable. When the load of the cross-linked cable is high, the core temperature rises and the cable expands due to heat. The cable is topped on the elevation of the bracket at the bend in the tunnel. The creep force of the cable during long-term heavy load operation is very large, which causes the elevation of the bracket to crush the outer sheath and metal sheath of the cable and squeeze into the cable insulation layer, resulting in cable breakdown.
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