Depth profiling of surface degradation of silicone rubber composite insulators by remote laser-induced breakdown spectroscopy

High-voltage silicone rubber composite insulators are widely used for outdoor insulation in power transmission lines. Silicone rubber, which is used as a housing material, gradually degrades with long-term use in the field. Therefore, to accurately determine the lifetime of composite insulators, it is essential to evaluate this degradation. This paper describes the results of depth profiling, which shows the change in the chemical composition caused by degradation, using laser-induced breakdown spectroscopy (LIBS). A remote LIBS system was constructed for application in in-situ degradation diagnostics. Field-aged insulators were irradiated with second harmonic Nd:YAG laser pulses at a distance of 10. The emission from the plasma was received by a telescope, and a spectroscopic analysis was performed. Energy dispersive X-ray spectroscopy (EDX) was performed for a comparative study. The emission intensity ratio of silicone to aluminum, which forms an alumina trihydrate filler, decreased by approximately 30% at the degraded surface compared to the undegraded bulk. A reduction in silicones at the degraded surface up to a depth of 300 was confirmed by LIBS and EDX measurements. These results show that remote LIBS using the ratio of silicone to aluminum as an index is a promising method for the in-situ diagnostics of composite insulators.