With the development of China's industry, it is almost said that the wires and cables are everywhere, and the construction and development of cable entering the ground in recent years is also very rapid. However, with the increasing number of cable lines and the increase of operation life, cable failures also gradually increase, and the failures of cable body, cable accessories, cable accessories and auxiliary equipment also increase significantly, Now take a look at the causes of these failures.

With the increase of cable usage time and accumulation, the most likely problem of cable is insulation aging. The reason for this situation may be that the cable is not selected for the suitable model when laying at that time, which may lead to the long-term operation of the cable under overvoltage or close to heat source around the cable line, which causes the cable to be partially or the whole cable line aging prematurely due to long-term heating. The working environment of the cable is also a factor affecting the life of the cable insulation. If it is used in the environment with adverse chemical reaction, or if multiple cables are running in parallel, but one or several of them are in bad contact, it will cause overload operation of other parallel cables, which will lead to failure. When the cable accessories are made, the cable connection pipe is not crimped, The reason of the insulation failure is that the contact resistance increases and causes overheating. Therefore, it is necessary to avoid it reasonably.

Accessories are also very easy to have problems, and this proportion is also very high, because the middle connector and terminal head of cable are usually completed by the installation personnel on the site. If the installation is not paid attention to, it will be easy to slip. The problem of accessories will affect the discharge of composite interface and aging of accessory materials. The problem of accessories is often due to the poor manufacturing process and poor product quality. In the process of manufacturing, the defects such as bubbles, moisture and impurities appear in the accessories, which lead to partial discharge and lead to insulation breakdown. Not only high-quality accessories should be selected, but also can not be neglected during installation.

The outer sheath is also common. In the medium and high voltage power grid, the outer sheath of the electric wire and cable is the first defense line to protect the cable. Its integrity directly affects the safety of the internal structure and the length of the cable service life. The reasons for the problems of the outer sheath are: the hard objects and sharp corners directly contact the outer sheath on the buried cables, especially in the road sections where vehicles pass, the road vibrates for a long time, and the sharp angle of hard objects may pierce the outer sheath, which leads to the damage of internal structure. In addition, the cable load changes, the thermal expansion and contraction of the cable itself and the uneven distribution of electric field in the damaged part, which leads to the damage of the insulation layer; When laying the pipes, the steps or inner walls of the connecting parts of the pipes may cause damage to the outer protective layer; Mechanical construction or pipe jacking around cable path, causing damage to outer sheath.

The damaged and cracked parts of the protective layer in the laying process and in the pipe arrangement will not be found in time; After a period of operation, cracks occur, the insulation of outer sheath decreases, metal sheath is grounded at multiple points, and circulation increases, which leads to insulation aging and breakdown. Termite decay is also one of the reasons for the appearance of the outer sheath. Once a termite cavity is found, there should be more than one decay part on the cable line, so we should pay enough attention to it. Termites are very dangerous to decay, and relatively less in the north.