Used for previous construction 70 year long life wire and cable Mainly YJLV22 series cross-linked aluminum core cable and YJV22 series cross-linked copper core cable. Compared with overhead lines and old oil filled cables, this type of cable has good insulation performance, high allowable working temperature and good mechanical strength. The extensive application of cables not only improves the reliability of power supply, but also beautifies the city appearance, which is worth promoting. However, in the long-term construction process, combined with a large number of feedback from the operation unit, we found that the phenomenon of cable moisture and water ingress has increasingly become a potential hazard affecting the safe operation of cables. According to our current technical strength and existing equipment, it is very difficult to deal with the inlet cable. In actual operation, if the cable head is found to have water ingress, we can only saw off the front several meters to see if it is dry inside. If not, we can continue to saw forward. But if the whole cable has been flooded, there is nothing we can do.
Therefore, water ingress of cables should be mainly prevented. Through long-term practice, we have summarized the following countermeasures: at present, we have adopted 8.7/10kV cables in the urban power grid 6kV system transformation. The insulation thickness of cables of this level is 4.5mm, while that of 6/10kV cables is 3.4mm. Due to the increase of cable insulation thickness, the field strength is reduced, which can prevent the aging of water trees. At the same time, when the 6kV neutral point small current grounding system is single-phase grounded, the cable must withstand 1.73 times the phase voltage, and operate for 2 hours as required. Therefore, it is necessary to thicken the cable insulation layer. Since impurities and pores in insulation are the starting point of water tree, the quality of cable is crucial to prevent water tree aging. When purchasing cables, we must select manufacturers with excellent quality. We must conduct strict tests on the samples submitted by various manufacturers for inspection, and require all manufacturers to bid to select products with high quality and low price.
Ensure that the cable head is well sealed. For sawn cable ends, whether stacked or laid, they should be sealed with plastic. It is better to use special cable glands to prevent moisture infiltration. After laying wires, the cable head shall be made in time. If it is impossible to make the cable head immediately due to limited conditions, the cable head shall be sealed and wrapped before being placed overhead. Improving the technical quality of the construction personnel and strengthening the management of the cable head production process can effectively prevent the cable head from entering water during the production process. When the cable is directly buried, we use PP-R new plastic pipe as the casing. The pipe has corrosion resistance, smooth inner wall, good strength and toughness, which can greatly reduce the occurrence of cable outer sheath damage.
Due to the limitation of conditions, the local cable laying is in the form of direct burial or cable trench. We are located in the coastal area, and the local area is mostly saline and alkaline land. In addition, the drainage is not smooth, resulting in frequent ponding in the cable trench or cable well. Therefore, in the early planning, the design of cable trench, culvert and cable well shall be timely coordinated with the civil construction company to facilitate the drainage of cable trench. At the same time, the support shall be embedded in the cable trench to support the cable with the support. In addition, in view of the current situation of numerous petrochemical enterprises within the jurisdiction of Shengli Oilfield, the nearby cable trench must have perfect drainage facilities. In the design of cable culvert pipe, try to be straight and reduce bends to make the cable easy to lay; After the cable is laid and the cable head is made, a DC withstand voltage leakage test shall be carried out as required before the cable is handed over to the operation management department for formal operation, and the cable can be put into operation only after everything is qualified. When cable problems are found during operation, management personnel shall strengthen monitoring and timely handle them.
Strengthen cable quality inspection. In order to improve the quality of cable manufacturing in Shanghai, personnel were sent to supervise the manufacturing in the manufacturer. Many problems were found in the process of supervision, and good results were achieved. Beijing has always carried out on-site cable quality inspection before connection, and found many problems, but this measure also has limitations, that is, only the appearance inspection can be carried out on site, and the internal condition of insulation cannot be understood. For this reason, Beijing now adopts the method of regularly sampling cables and sending them to Wuhan High tech Research Institute or Shanghai Cable Research Institute for inspection to ensure cable quality. At the same time, cable manufacturers should also strengthen quality management, improve quality awareness, strictly carry out test and inspection before leaving the factory, and prevent unqualified products from entering the market. Improve cable installation quality. To improve the quality of cable installation, we must first attach great importance to this problem. Using professional construction teams, strengthening the technical level and quality awareness of joint installation personnel, and strictly following the installation process are important ways to reduce cable accidents. When the cable is laid, the traction method shall be used to prevent the side pressure at the turning from being too high. When installing the connector, good process measures shall be taken to ensure the installation level, which shall be summarized and improved during construction. Adopt new test means. In the completion test of cross-linked cables, DC withstand voltage can be avoided, and the method of series resonance or VLF can be adopted. If there is no corresponding equipment, 24-hour no-load operation can also be adopted. Increase the depth of design drawings. Design is the guidance of construction, and the improvement of design level is the key to the improvement of cable engineering level. Local design units should strengthen communication and learning, fully consider the possible situation of cable system in long-term safe operation, and make efforts to ensure long-term safe operation of cable system. Strengthen operation monitoring. Many people think that the cable system can be maintenance free, which is wrong. In the past, because there was no good monitoring means, the cable operation department had to strengthen patrol inspection. Now, infrared temperature measurement has been used in some places, and temperature monitoring systems have been installed in some places. Partial discharge technology has entered the practical stage. Local operation departments shall develop or adopt corresponding detection means according to the actual situation to prevent in advance.
