In order to clarify the differences of partial arc propagation process and flashover process between uniform and un-uniform contaminated insulator strings, experiments of flashover characteristics on uniform and un-uniform contaminated insulator strings have been made in this paper. The result indicates that the partial arc initial voltage decrease with increasing ESDD in uniform contamination distribution situation, relatively, in situation of un-uniform contamination distribution, the initial voltage of partial arc not only relevant to ESDD of the whole insulator string, but also the distribution of pollution layer. In the context uniform contamination distribution, the partial arcs develop as progressive-style; and in the case of un-uniform contamination distribution, the propagating mode of partial arcs is progressive-style and leap-style alternating. Assume that ESDD value of the whole strings constant, the number and lightness of partial arcs would decrease with the reduction of ratio between upper and lower surface ESDD values, and Arc-over occurrence probability as well. High amplitude pulses of leakage circuit exist in the course of flashover duration.
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