Microstructural conduction properties of the electrical discharge channels within decay-like degraded FRP rod

Tree-like discharge erosion channels within the fiber-reinforced plastic rod are prominent feature of decay-like degraded composite insulators, and their electrical properties remain insufficiently understood. This study investigates the microstructural electrical conductivity and chemical composition of discharge erosion channels within a decay-like degraded core rod. A cross-sectional sample exposing a discharge channel was prepared using ion beam polishing. The electrical properties were characterized using tunneling atomic force microscopy (TUNA) under different humidity levels, while chemical changes were analyzed via in situ Raman spectroscopy and mapping. The TUNA results revealed a significant current increase within the discharge channel. The estimated channel conductivity is on the order of 3 × 10−8 and 10−4 S/m under low and high humidity, respectively. The porous microstructure within channel likely facilitates capillary condensation of water vapor, creating an ionic conductive path along the fiber direction via the condensed water film. Tree-like microstructure is attributed to partial discharge erosion, while humidity-dependent capillary condensation is proposed to activate ionic conduction, further facilitating discharges. Raman spectroscopy showed a substantial decrease in characteristic peaks of the epoxy resin within the channel, indicating severe polymer decomposition. Critically, the absence of D and G bands suggests that carbonization is unlikely to be the dominant conduction mechanism. Ion chromatography confirmed the presence of nitrate and multiple carboxylic acid anions, and the enhanced conductivity is therefore attributed primarily to dissolved ionic species transporting through capillary-condensed water within the porous channels.