Discuss the causes of common problems with high-voltage cables
The cable is the bridge between the power supply equipment and the electrical equipment, and plays the role of transmitting electric energy. It is widely used, so faults often occur. The following briefly analyzes the causes of common problems of YJV high-voltage cables. According to the causes of faults, they are roughly divided into the following categories: manufacturer's manufacturing reasons, construction quality reasons, design unit design reasons, external forces Destroy four categories.
1. Reasons for manufacture
According to the different parts of the manufacturer, the reasons for the manufacture are divided into three categories: the reasons for the cable body, the reasons for the cable joints, and the reasons for the cable grounding system.
1. Reasons for the manufacture of the cable body
Generally, the problems that are easy to occur in the cable production process are insulation eccentricity, uneven thickness of insulation shielding, impurities in insulation, protrusions in inner and outer shielding, uneven cross-linking degree, cable damp, poor sealing of cable metal sheath, etc. In severe cases, failures may occur during the completion test or shortly after being put into operation, and most of them exist in the form of defects in the cable system, causing serious hidden dangers to the long-term safe operation of cables.
2. Reasons for the manufacture of cable joints
High-voltage cable joints used to be of wrapping type, die-casting type, molding type, etc., which required a large amount of work to be produced on site, and due to the limitations of site conditions and the production process, there would inevitably be air gaps between the insulating tape layers. and impurities, so it is prone to problems. The commonly used types in China are the assembled type and the prefabricated type.
Cable joints are divided into cable terminal joints and cable intermediate joints. Regardless of the joint form, cable joint failures generally occur at the cable insulation shielding fracture, because this is the place where electrical stress is concentrated, and the cause of cable joint failure due to manufacturing reasons is stress. Cone body manufacturing defects, insulation filler problems, oil leakage from the sealing ring, etc.
3. Cable grounding system
The cable grounding system includes cable grounding box, cable grounding protection box (with sheath protector), cable cross-connection box, sheath protector and other parts. Generally, the problem that is easy to occur is mainly because the box body is not well sealed and water enters, which leads to multi-point grounding, which causes the induced current of the metal sheath to be too large. In addition, the unreasonable selection of the parameters of the protective layer protector or the poor quality of the zinc oxide crystal is also easy to cause damage to the protective layer protector.
2. Reasons for construction quality
There are many cases of high-voltage cable system failures due to construction quality. The main reasons are as follows:
1. The site conditions are relatively poor. The environment and process requirements for cables and connectors are very high when they are manufactured in the factory, and the temperature, humidity and dust on the construction site are not well controlled.
2. Small slip marks will inevitably be left on the insulating surface during the construction of the cable, and the semiconductive particles and sand on the emery cloth may also be embedded in the insulation. In addition, the insulation will be inhaled due to the exposure of the insulation to the air during the construction of the joint. Moisture, these leave hidden dangers for long-term safe operation.
3. The installation did not strictly follow the process construction or the process regulations did not take into account the possible problems.
4. The DC withstand voltage test is adopted for the completion acceptance, resulting in the formation of a reverse electric field in the joint, resulting in insulation damage.
5. Caused by poor sealing. The intermediate joint must be sealed with a metal copper shell and a PE or PVC insulation and anti-corrosion layer, and the tightness of the lead seal is ensured during the on-site construction, which effectively ensures the sealing and waterproof performance of the joint.
3. Design reasons
Breakdown due to cable crushing caused by thermal expansion of the cable. When the cross-linked cable is under high load, the core temperature rises, the cable expands due to heat, and the cable rests on the vertical surface of the bracket at the turn in the tunnel. The cable has a large creep force during long-term heavy-load operation, which causes the vertical surface of the bracket to crush the outer sheath of the cable. , Metal sheath, squeeze into the cable insulation layer to cause cable breakdown.