Characterization of pre-flashover behavior based on leakage current along suspension insulator strings covered with ice

In order to clarify the features of the pre-flashover and predict ice flashover more accurately, the entire evolution of leakage current during the pre-flashover process of both AC long and short suspension insulator strings covered with ice were recorded and analyzed in this paper. It is found that the pre-flashover processes of both ice-covered long and short insulator strings could be divided into four stages based on the time domain characteristics of leakage current. Two significant parameters were proposed as characteristic parameters for the analysis of pre-flashover characteristics, namely the characteristic current (IW) which was the quasi-constant value in Stage III, and the critical current (IFT) which was the leakage current amplitude value in the last cycle before flashover in Stage IV. The relationships between these two characteristic parameters and the influencing factors including ice build-up severity, the contamination degree, and the conductivity of the freezing water were also studied. It was believed that the characteristic parameter IW could be adopted as early-warning value of pre-flashover along the ice-covered suspension insulator, and IFT as the criterion of the critical flashover.