Cable is the bridge between power supply equipment and electrical equipment, which plays the role of transmitting electric energy.
It is widely used, so faults often occur. The following is a brief analysis of the causes of common problems of YJV high-voltage cables, which are roughly divided into the following categories according to the causes of faults: there are four categories: Manufacturer's manufacturing reasons, construction quality reasons, design reasons of design units and external force damage.
First, the manufacturer's manufacturing reasons, the manufacturer's manufacturing reasons are divided into three categories according to the location of the cable body, cable joint reasons, cable grounding system reasons.
1, Cable body manufacturing reasons, generally, problems that are easy to occur in the cable production process include insulation eccentricity, uneven thickness of insulation shielding, impurities in insulation, protrusion in internal and external shielding, uneven crosslinking degree, cable moisture, cable metal poor sealing of sheath, etc, some serious cases may occur in the completion test or shortly after the operation, most of which exist in the cable system in the form of defects, causing serious hidden dangers to the long-term safe operation of the cable.
2. The manufacturing reason of the cable connector, the high-voltage cable connector used the winding type, the mold type, the mold type and other types before, which requires a large amount of work to be made on site, and because of the limitation of the field conditions and the reason of the manufacturing process, there will inevitably be air gaps and impurities between the insulating tape layers, so it is easy to happen.
The commonly used types in China are assembly type and prefabrication type.
Cable joints are divided into cable terminal joints and cable intermediate joints. No matter what type of joints, cable joint faults generally occur at the fracture of cable insulation shielding, because this is the part where electrical stress is concentrated, the causes of cable joint failure 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 and cable grounding protection box (With protective layer Protector)
, Cable cross interconnection box, sheath protector and other parts.
Generally, the problem that is easy to occur is mainly due to the poor sealing of the box body, which leads to multi-point grounding and causes excessive induced current in the metal sheath.
In addition, the parameter selection of the protective layer protector is unreasonable or the quality is not good. The instability of the zinc oxide crystal is also easy to cause damage to the protective layer protector.
Second, the construction quality reasons, because the construction quality leads to many cases of high voltage cable system failure, 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 very high, and the construction site temperature, humidity, dust are not good control.
2. In the process of cable construction, fine slip marks will inevitably be left on the insulation surface, and semi-conductive particles and sand particles on the emery cloth may also be embedded in the insulation, in addition, during the construction of the joint, due to the exposure of the insulation to the air, the insulation will also absorb moisture, which will leave hidden dangers for long-term safe operation.
3, the installation did not strictly follow the process construction or process regulations did not take into account the possible problems.
4. DC withstand voltage test is adopted for completion acceptance, resulting in the formation of anti-electric field in the joint, resulting in insulation damage. 5, due to poor sealing treatment.
The middle joint must adopt the sealing structure of metal copper shell plus PE or PVC insulation anticorrosive coating to ensure the compaction of the lead seal during on-site construction, thus effectively ensuring the sealing and waterproof performance of the joint.
Third, the design reasons, due to cable thermal expansion caused by cable extrusion damage caused by breakdown.
When the load of the cross-linked cable is high, the temperature of the cable core rises, and the cable expands with heat. At the turning point in the tunnel, the cable is topped on the bracket facade, and the cable peristalsis force is great when running under heavy load for a long time, cause the bracket facade to break the outer sheath and metal sheath of the cable, and squeeze into the cable insulation layer to cause the cable to break down.