The underground construction of power cables is the direction of urban modernization. With the increase in the number of cable lines and the extension of service life, cable faults gradually increase, and the faults of cable bodies, cable accessories, and cable accessory equipment also significantly increase. According to my years of maintenance practice, the location of power cable faults is mainly concentrated in insulation, accessories, and outer sheaths.
1. Insulation fault. The insulation aging of power cables mainly occurs in the later stage of operation, usually in cable lines that have been in operation for more than 15 years, leading to a significant increase in cable failure rate. Insulation aging is mainly divided into insulation material aging, electric heating aging, and dendritic aging. Under the action of an electric field, the air gap in the cable insulation medium dissociates, causing insulation to decrease. When the insulation medium is ionized, chemicals such as ozone and nitrate drums are generated in the air gap, which corrodes the insulation layer. At the same time, the moisture in the insulation causes the decomposition of insulation fibers, leading to a decrease in insulation strength.
2. Attachment issues. The intermediate joints and terminal heads of power cables are usually completed by installation personnel on the laying site, and if not paid attention, it is easy to make mistakes. The failure of power cable accessories is the main part of cable line failure, which is manifested macroscopically as composite interface discharge and aging of accessory materials. The failure of cable accessories is often caused by poor manufacturing process and carelessness of personnel. During the manufacturing process, defects such as moisture, bubbles and impurities occurred inside the accessories, which led to partial discharge and insulation breakdown.
3. External protective layer issues. In medium and high voltage power grids, the application of power cables is becoming increasingly widespread. The outer sheath of power cables is the first line of defense to protect cables, and its integrity directly affects the safety of the internal structure and the service life of the cables.
Measures to prevent power cable failure: 1. From the beginning of the design, select the cable that meets its voltage level, fully understand the earthing system used by the cable, and avoid the cable working under long-term overvoltage conditions. The selection of outer sheath should meet the requirements of service life and usage environment, and the selection of cable sheath protector should meet the principle of reliable passage of grounding current without damage when the protector is relatively grounded. 2. The selection of cable routing should 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 cause overheating. In addition, to avoid simultaneous damage to cable paths, it is not recommended to lay dual circuit power supply cable paths in pipelines along the same path, resulting in large-scale power outages. 3. Strengthen personnel training, and ensure that cable head production personnel hold certificates to work. And necessary business qualifications and technical assessments must be conducted. 4. Advanced online monitoring technologies such as online optical fiber temperature measurement technology, online monitoring technology and online partial discharge detection technology of outer sheath circulation are used to strengthen real-time online operation monitoring of cables, identify hidden dangers in advance and avoid power failure accidents.
The safe operation of power cable lines is directly related to the safe operation of the entire power grid and the stability of the system. Only by strengthening quality control and acceptance from the aspects of power cable production, transportation, laying, installation, testing, inspection, etc. can cable faults be minimized as much as possible, ensuring the long-term safe operation of cable lines.