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Lightning strikes and pollution could cause short circuits and tripping of the overhead distribution lines. To alleviate this, a 10-kV post insulator with concentric externally gapped line arrester (EGLA) has been proposed and its performance is studied in service. However, its pollution performance has to be established. This paper studies the AC pollution breakdown characteristics of the EGLA and broaden current knowledge of pollution flashover. Compared with the flashover of the normal insulator, three kinds of specificity of the EGLA were found. Firstly, the pollution flashover process can be divided into three categories. Secondly, the wet flashover voltage, Uf_wet, of the novel insulator is higher than the dry flashover voltage, Uf_dry. Thirdly, the piecewise fitting methods with a × ESDD^−b + d and a × ESDD^−b + c × ESDD^−d are more suitable for fitting the empirical formula of flashover voltage. Furthermore, to explain specificity, the electric potential and electric field distribution are calculated based on the finite element method. Calculated results indicate that when the EGLA is covered with a 0.5mm water film, the maximum electric field intensity decreased from 2.17 kV/cm to 1.99 kV/cm. Also, U_arrester (the withstand voltage of the insulation section) was obtained from the tests and it presents a discontinuous and random increasing trend until flashover occurs, which is considered to be one of the important reasons for the specificity. Besides, based on the Obenaus’ model and Hampton's criterion, we further analyzed the arc development process by a simplified plate model. [ABSTRACT FROM AUTHOR]