When Low voltage cables and middle voltage Cables are constructed in winter, because the outdoor temperature is below minus 10 ℃, the low temperature polyvinyl chloride and cross-linked polyethylene insulation and sheath materials show hard and brittle characteristics, such as accidental accidents during the laying process If bumped, the insulated core and copper shield are easily damaged. Even if the on-site completion test can pass smoothly after the cable is laid, after the cable is continuously energized, partial discharge will occur after the capacitive current flows in the damaged part, accelerating the insulation aging, and leading to breakdown of the line. This situation is not prominent in low-voltage cables, but is prominent in medium-voltage cables. Sometimes there is no problem in the cable factory test. Because of the restrictions of various conditions, the cable is directly constructed in winter without any measures. After the cable is laid, the on-site completion test is all normal, but it appears after the power-on operation in a short period of time. Failure, anatomy of the failure point, there is no trace of mechanical damage in appearance, but serious breakdown and ablation occurred in the internal insulation.
In recent years, some newly laid medium-voltage 10kV and 35kV faulty cables have not been heated on site due to various conditions, and they have been directly constructed and installed at minus 10°C in winter. In a short period of time when the cable was energized and operated, there was a phase-to-phase and relative-to-ground insulation breakdown fault (the incident time was as short as 10 days, and the length was about 1 month). After the accident investigation, the cable production and factory tests showed no abnormalities. The completion test is also smooth (26/35kV power cable AC 52kV/1h passed). However, the failure occurred in a short period of time (as short as 10 days, and as long as 1 month) after power-on operation. This is undoubtedly related to the fact that the power cables were not heated during construction in0 winter.