The construction of power cable into the ground is the direction of urban modernization. With the increase of the number of cable lines and the extension of service life, cable faults gradually increase, and the faults of cable body, cable accessories and cable accessory equipment also increase significantly. According to the maintenance practice of Xiaobian for many years, the fault location of power cable is mainly concentrated on insulation, accessories and outer sheath.
1. Insulation failure. The insulation aging of power cables mainly occurs in the later stage of operation, generally in cable lines that have been operating for more than 15 years, resulting in a significant increase in cable failure rate. Insulation aging is mainly divided into insulation material aging, electrothermal aging and dendritic aging. Under the action of electric field, the air gap in the cable insulation medium is dissociated, which reduces the insulation. When the insulating medium is ionized, ozone, nitrate drum and other chemicals are generated in the air gap to corrode the insulating layer. At the same time, the moisture in the insulation leads to the decomposition of insulating fibers, resulting in the decline of insulation strength.
2. Annex issues. The intermediate joints and terminal heads of power cables are usually completed by the installation personnel at the laying site. If they are not careful, they are easy to make mistakes. Power cable accessory failure is the main part of cable line failure. Its macroscopic performance is composite interface discharge and accessory material aging. The failure of cable accessories is often caused by poor manufacturing process and carelessness of personnel. During the manufacturing process, there are defects such as moisture, bubbles and impurities in the accessories, resulting in partial discharge and insulation breakdown.
3. Outer protective layer. In medium and high voltage power grid, power cable is more and more widely used. The outer sheath of power cable is the first line of defense to protect the cable, and its integrity is directly related to the safety of the internal structure and the service life of the cable.
Measures to prevent power cable failure: 1. Starting from the design, select the cable that meets its voltage level, fully understand the grounding system used by the cable, and avoid the cable working under long-term overvoltage conditions. The selection of outer sheath shall meet the requirements of service life and service environment, and the selection of cable sheath protector shall meet the principle that the protector can reliably pass through the grounding current without damage when it is relatively grounded. 2. Cable routing shall avoid the influence of external environment, such as overheating, corrosion, external force damage, etc. And avoid the influence of internal factors, such as excessive concentration of cable laying, which may lead to timely diffusion of heat and overheating. In addition, in order to prevent the cable path from being damaged at the same time, it is not recommended to lay the cable path of double circuit power supply in the pipeline of the same path, resulting in large-scale power failure. 3. Personnel training shall be strengthened, and cable head production personnel shall work with certificates. And necessary business qualification and technical assessment shall be carried out. 4. Advanced on-line monitoring technologies such as on-line optical fiber temperature measurement technology, on-line monitoring technology and on-line partial discharge detection technology are used to strengthen the real-time on-line operation monitoring of cables, find hidden dangers in advance and avoid power failure.
The safe operation of power cable line is directly related to the safe operation of the whole power grid and the stability of the system. Only by strengthening the quality control and acceptance from the aspects of power cable production, transportation, laying, installation, test and inspection, can the cable fault be reduced as much as possible and ensure the long-term safe operation of cable line.

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