Cables are the bridge between power supply equipment and electrical equipment, playing a role in transmitting electrical energy. Due to the wide application of high-voltage cable joints, various problems often occur. Below is a brief analysis of the causes of common problems with high-voltage cable joints:

There are four major categories: reasons for manufacturing, reasons for construction quality, reasons for design by the design unit, and external damage.

1、 Reason for manufacturer's production

According to the different locations where high-voltage cable joint problems occur, the reasons for manufacturer production can be divided into cable body reasons, cable joint reasons, and cable grounding system reasons.

1. Reasons for the production of cable body

The common problems that arise during cable production include insulation pain, uneven insulation shielding thickness, impurities inside the insulation, protrusions on the inner and outer shielding, uneven cross-linking, cable moisture, and poor sealing of the cable metal sheath. Some of the more severe conditions may present problems during completion testing or shortly after commissioning, and most of them exist in the cable system in a defective manner, posing a serious danger to the long-term safe operation of the cable.

2. Reasons for the production of cable joints

High voltage cable joints used to be wrapped, molded, and molded, which required a large amount of on-site production work. Due to the constraints of on-site conditions and production processes, there were inevitably air gaps and impurities between the insulation tape layers, resulting in simple problems. The commonly used types in China now are assembled and prefabricated.

High voltage metal cable joints are divided into cable terminal joints and cable intermediate joints. Regardless of the joint method, cable joint problems generally occur at the insulation shielding fracture of the cable, because this is the location where electrical stress gathers. The reasons for cable joint problems due to manufacturing reasons include defects in the stress cone body, insulation filler problems, and sealing ring oil leakage.

3. Cable grounding system

The cable grounding system includes cable grounding box, cable grounding maintenance box (with protective layer maintainer), cable cross interconnection box, protective layer maintainer, and other parts. The common and simple problems are mainly caused by poor sealing of the box, which leads to water ingress and multiple grounding points, resulting in excessive induced current in the metal protective layer. Improper parameter selection or poor quality of other protective layer maintainers can also easily cause damage to the protective layer maintainer due to unstable zinc oxide crystals.

2、 Construction quality reasons

There are many cases of high-voltage cable system problems caused by construction quality, mainly including the following five reasons:

1. The on-site conditions are relatively poor, with high environmental and process requirements for cable and joint manufacturing in the factory, and inadequate control of temperature, humidity, and dust on the construction site.

During the cable construction process, it is inevitable that small slip marks will be left on the insulation surface, and semi conductive particles and sand particles on the sand cloth may also be embedded in the insulation. In the construction process of other joints, due to the insulation being exposed to the air, moisture will also be inhaled in the insulation, which poses a danger to long-term safe operation.

3. The installation did not strictly follow the construction process or did not take into account the possible problems that may arise.

4. The completion acceptance adopts DC withstand voltage test to form a reverse electric field inside the joint, which causes insulation damage.

5. Caused by poor sealing treatment. The intermediate joint must adopt a sealing structure with a metal copper shell and PE or PVC insulation anti-corrosion layer to ensure the compactness of the lead seal during on-site construction, which effectively ensures the sealing and waterproof performance of the joint.

3、 Design reasons

Cable compression caused by excessive thermal expansion resulted in breakdown. When the load of cross-linked cables is high, the temperature of the core increases, causing the cable to expand due to heat. At the turning point in the tunnel, the cable is placed on the support facade, and the cable has a strong movement force during long-term high load operation, resulting in the support facade crushing the outer sheath and metal sheath of the cable, squeezing into the cable insulation layer and causing cable breakdown.

In addition, there are also external forces that can cause problems with high-voltage metal cable joints, which objectively cannot be controlled by human intervention.