Influence of Air Pressure on Laser-Induced Breakdown Spectroscopy of Silicon Rubber Insulators

Abstract

Silicon rubber composite insulators are widely used in transmission lines owing to their excellent external insulation. However, the silicone rubber composite insulator gradually ages, seriously affecting its external insulation properties. Traditional silicone rubber composite insulator detection methods (such as ATH content, which affects resistance to tracking and erosion, and usually needs to cut a sample from an insulator) cannot achieve rapid in situ detection, while laser-induced breakdown spectroscopy (LIBS) is a new in situ detection technology, which has the advantages of rapid detection and remote detection, having a good application prospect in the field of electrical engineering. The ultrahigh-voltage (UHV) transmission lines pass through high-altitude areas such as Lhasa in Tibet (3658 m above sea level with 65 kPa air pressure). The low air pressure in high-altitude areas affects the accuracy of LIBS detection. Herein, the influence law and mechanism of air pressure on the laser spectral data and the influence of air pressure on the quantitative analysis ability of LIBS are studied based on LIBS. The results show that in the range of 50–101 kPa air pressure, the spectral line intensity increases as the air pressure decreases. The energy of the laser propagates in the air with a negative exponential attenuation law, the lower the air pressure is, the higher the energy attenuation curve is. The ablative morphology of samples is different under different pressures, under low air pressure, the morphology of the ablation hole is more uniform and the average depth is greater. The quantitative analysis ability of LIBS is different under different pressures, the goodness of fit of the model at 50 kPa is better than that at 101 kPa under a single linear calibration model (Al I 396.15 nm spectral line intensity-ATH content), the goodness of fit is 0.967 and 0.928, respectively, and the full-spectrum data-ATH content calibration model is established by partial least squares (PLSs) at 50 and 101 kPa. Overall, the model goodness of fit is improved to 0.995 and 0.992, respectively. Through this study, we can preliminarily understand the influence law and mechanism of air pressure on laser spectral data, which is conducive to eliminating the influence of air pressure on LIBS quantitative analysis, which is expected to be used for remote online monitoring of transmission lines insulation status.