Fault analysis is an important work to ensure the safe operation of the cable line system. Attaching importance to this work is the basis for eliminating the causes of cable faults and the strong basis for improving cable technology, including line design, cable manufacturing and operation. Although the cable structure, including the design of accessories, has been carefully studied in the production process and passed a series of relevant tests before it was put into operation, these are not all realistic simulations of the long-term operation of individual actual cable lines. Therefore, the occurrence of cable line failures can be determined in which links it is necessary to improve. If you only meet the rush to repair the cable fault and ignore the analysis of the cause of the fault, you will always be in a passive state and exhausted.

1. Fault classification

After the cause of the failure is found out, the number of times it is classified and counted year by year, which is helpful to formulate the degree of urgency of the countermeasures to eliminate the accident, and sometimes feedback whether the measures are effective or not. Obviously, each failure must find the real cause, otherwise it will lead to wrong countermeasures, not only can not eliminate or reduce the accident, but also cost manpower and financial resources, so we should be cautious. The classification of various faults can be divided into two categories, one is congenital defects, such as normal aging of insulation, manufacturing defects, etc.; the other is acquired defects, such as mechanical damage, corrosion or construction defects. The former can be used as a basis for providing manufacturers to improve product quality, while the latter can be used as an annual overhaul plan for cable management to reduce accidents. Some accidents cannot find out the real cause at the moment, so it is not advisable to rush to qualitative classification, and it is necessary to accumulate data on the number of accidents, including the physical objects of the fault parts. The causes of accidents that have accumulated throughout the years but have not been properly resolved may be listed as special topics for research by the research department. In order to facilitate analysis, research and classification, the causes of failures are divided into the following: manufacturing defects, poor construction, poor design, mechanical damage, insulation aging, water branches, corrosion, ant damage, unknown causes and others. The number of accidents shall be counted every year, and the failure rate of 100km/year shall be calculated.

2. Field analysis

Many cable accidents are related to the on-site environment, so to find out the real cause of their occurrence, it is necessary to understand the on-site situation clearly. For example, if the lead package is corroded, it is necessary to analyze the pH value of the adjacent soil or whether the potential of the cable lead package is in the anode area or the cathode area. Another example is mechanical damage. It is necessary to check whether there is any excavation project nearby in the past. If there is some slight mechanical damage, only the metal sheath is damaged and the insulation is intact. It takes a long time for moisture in the soil to gradually penetrate into the insulation before it develops into an accident. When no obvious corroborative reasons can be found for the damaged parts of the cable on site, the damaged fragments, including some cables, shall be sawed back for further experimental research in the laboratory.

3, Laboratory Analysis

The cause of some cable accidents cannot be identified from the appearance, such as the determination of groundwater and soil corrosivity and the molecular crystallization of water branches or metal sheath in plastic insulation, and the characterization of corrosion. This requires the use of sophisticated instruments to conduct a comprehensive physiological and chemical analysis of the damaged fragments of the accident cable, and make detailed records for future inspection. The damaged fragments of cables whose cause of the accident is not confirmed shall also be properly preserved, which is of reference value for similar analysis in the future.