Mechanism of Status Evaluation for Water Blocking Buffer Layer of High-Voltage Cable Based on Characteristic Gas Analysis

The corrosion and ablation of the water-blocking buffer layer of high-voltage cables are accompanied by the production of various gases. By selecting characteristic gases and analyzing the corresponding relationship between their concentration and the corrosion/ablation stages, it is possible to evaluate the status of the buffer layer. This article analyzes the time-varying characteristics of gas concentration during the corrosion and ablation of water-blocking buffer layers, reveals the mechanisms of gas production, and proposes a method for evaluating the status of the buffer layer based on characteristic gas analysis. Results indicate that both the corrosion and ablation processes of the buffer layer produce H2, CH4, and CO2, but the ablation process generates additional gases including C2H6, C2H4, C2H2, and CO. The H2 concentration is positively correlated with the amplitude of applied voltage, water content, and surface pressure and saturates after a period of generation. On this basis, the mechanism of H2 production during the corrosion stage and the decomposition of polyethylene terephthalate (PET) accompanied by hydrocarbon gas production during the ablation stage of the buffer layer are investigated. By detecting the concentration of H2 in the cable, the overall damage level of the buffer layer can be determined. Additional detection on C2H6, C2H4, C2H2, and CO gases can determine whether the buffer layer is in a corrosion state. Finally, the effectiveness of evaluating the status of the buffer layer by characteristic gas analysis is proved on new and on-site 110-kV cables.