The Degradation Analysis of PVC Insulation Tape in 220kV Oil-filled Cable Terminal

Recent oil leakage failure cases in Guangdong Power Grid suggested possible chemical interaction between PVC insulation spiral tape and silicone oil. More attentions had been aroused to analyze the operating and aging performance. In this paper, degradation analysis were performed on PVC samples after 2 years operation in 220kV cable terminal or accelerated thermal aging in silicone oil. Two aging temperatures were set up for aging contrast. Compatibility, IR, TGA and stretching tests were operated to determine the degradation of molecular, thermal and mechanical behavior. After aging, the results showed different degrees of degradation of PVC. The weight of PVC reduced 2%~4%, additives and oil composition were observed, the decomposition temperature decreased over 10%, the tensile strength decreased over 11%, and the elongation at break reduced over 300%. Results showed that PVC reacted with the insulating silicone oil in the long run, causing aging, additives precipitation, changing composition, increasing molecular chain mobility, reducing thermal stability and mechanical strength. The degradation became more severe and faster under higher temperature or in longer aging time. The results could be used to reveal the cause of defects and propose solution for materials matching and failure preventing in high voltage transmission lines.