Cable is the bridge between power supply equipment and power consumption equipment, and plays a role in transmitting electric energy. Because of the wide range of applications, faults often occur. The following briefly analyzes the causes of common problems of high-voltage cables and classifies them into the following categories according to the causes of faults:

　　I The manufacturing reasons of wire and cable manufacturers are divided into three categories according to the location: cable main body reason, cable joint reason and cable grounding system reason.

　　1. Cable grounding system the cable grounding system includes cable grounding box, cable grounding protection box (with protective cover), cable cross interconnection box, protective cover and other components. The common problems are mainly due to the poor sealing of the water tank and the entry of water, which leads to multiple grounding points and excessive induced current in the metal sheath. In addition, the unreasonable parameters of the protective layer protector or the poor zinc oxide crystal are unstable, which is easy to damage the protective layer protector.

　　2. The manufacturing reasons of the cable body are usually prone to problems in the cable production process: insulation eccentricity, uneven thickness of the insulation shield layer, impurities in the insulation layer, protrusions inside and outside the shield layer, uneven crosslinking degree, moisture in the cable, sealing defects of the cable metal sheath, etc. In some serious cases, faults may occur during the completion test or shortly after commissioning, and most of the faults are defects in the cable system, thus causing serious hidden dangers to the cable.

　　3. Manufacturing reasons of cable joints: high voltage cable joints are usually used for wrapping, molding, molding, etc., which requires a lot of on-site work. Due to the limitations of on-site conditions and manufacturing processes, the insulating tape is not allowed to be coated to avoid air gaps and impurities, so it is easy to cause problems. The types commonly used in China are assembled and prefabricated. Cable connectors are divided into cable terminal connectors and cable intermediate connectors.

　　II Reasons for construction quality there are many failures of high-voltage cable system due to construction quality. The main reasons are as follows:

　　1. The site conditions are relatively poor. When leaving the factory, the environment and process requirements of cables and connectors are very high. The temperature, humidity and dust at the construction site are not easy to control.

　　2. During cable construction, small slip marks will inevitably be left on the insulation surface. The semi conductive particles and sand particles on the abrasive cloth can also be embedded in the insulating material. In addition, during the construction of the connector, moisture will be inhaled due to exposure to the air, which leaves hidden dangers for long-term safe operation.

　　3. The installation did not strictly follow the process structure or process regulations, and did not consider possible problems.

　　4. DC voltage test is used in the acceptance inspection to form a reverse electric field in the joint and damage the insulation.

　　5. Due to improper sealing treatment. The intermediate joint must adopt the sealing structure of metal copper shell plus PE or PVC insulation and anti-corrosion layer. The lead seal shall be compact in the field construction, effectively ensuring the sealing and waterproof performance of the joint.

　　3、 Design reason: cable extrusion is the breakdown caused by thermal expansion of the cable. Guangxi low smoke zero halogen cable indicates that when the load of cross-linked cable is high, the core temperature rises and the cable expands due to heat. The cable is located on the vertical surface of the support at the turning point of the tunnel. The long-term heavy-duty cable has a great creep capacity, which will cause the vertical surface of the support to break the jacket and metal sheath, and squeeze into the cable insulation layer, which will lead to cable breakdown.