*Case Report* **Analysis of Salt Mixture Contamination on Insulators via Laser-Induced Breakdown Spectroscopy**

#### **Shan Lu 1, Xinwei Wang 1, Tianzheng Wang 1, Xinran Qin 2, Xilin Wang 2,\* and Zhidong Jia 2**


Received: 4 March 2020; Accepted: 5 April 2020; Published: 10 April 2020

**Abstract:** The composition of contamination deposited on transmission line insulators can affect their surface flashover voltage. Currently, there is no rapid on-line method to detect this contamination composition in power grids. In this paper, we applied laser-induced breakdown spectroscopy (LIBS) to analyze contamination on insulator surfaces. Usually, Na and Ca salts are found in contamination along with various sulfate, carbonate, and chloride compounds. As an element's detection method, LIBS can only measure a certain element content, for example, Ca. The mixture of various compounds with the same cations can influence the LIBS signal. The influence of mixing ratios on the calibration curves and relative spectral intensity was studied via LIBS. Na2CO3, NaHCO3, CaSO4, and CaCO3 samples containing different proportions of Na and Ca were prepared. The linear correlation coefficients (R2) for the Na and Ca calibration curves generated using various mixing ratios were analyzed. The results showed that the mixture ratio did not dramatically affect the linear calibration curves for mixtures containing the same cations. This finding may significantly reduce the difficulty of applying LIBS analysis for complex contamination on insulators. The laser energy density had effects on the spectral characteristics of the measured elements. The partial least-square regression (PLSR) model can improve the accuracy of Na and Ca prediction.

**Keywords:** laser-induced breakdown spectroscopy; contamination; insulators; salt; calibration curves
