Key process of the defection of PET buffer layer in XLPE power cable by a case study: Thermo-oxidative degradation

Abstract

Buffer tape ablation failures in the buffer layer of high voltage XLPE cables have become a common failure mode in cable transmission system. In this work, we aimed to analyze the degradation mechanism and evolution process of the buffer tape, which mainly consists of polyethylene terephthalate (PET) fibers, based on a fault in a 110 kV cable line. First, the gas inside the cable were extracted on site, and the gas components were analyzed using gas chromatography technology. Then the mechanism of the combustion phenomenon caused by thermo-oxidative degradation of PET fibers was proposed. Subsequently, the discharge simulation experiment of the PET buffer tape under different background gas was conducted to study the effect of oxygen on the thermal-oxidative degradation process. The research results show that oxygen plays a key role in the discharge ablation process of the PET buffer tape. Due to the thermal-oxygen degradation process, the O2 concentration in the buffer layer decreases, and the CO and CO2 concentration increases, and at the same time the combustible gases such as hydrogen and methane are generated. The internal pressure of the buffer layer also increases under the influence of the gas partial pressure. The gas components mentioned above are not generated by the discharge under anaerobic conditions. Finally, a method of preventing the ablation defect of the buffer layer of the high-voltage cable according to the thermo-oxidative degradation mechanism of the buffer tape PET material is proposed.