Nonlinear characteristics of leakage current for flashover monitoring of ice-covered suspension insulators

This paper investigates nonlinear characteristics of leakage current (LC) for analyzing and monitoring AC flashover performance of ice-covered suspension insulators. The experiments were carried out in a cold climate room of CIGELE Laboratories according to the methods recommended by IEEE Std. 1783/2009. The maximum withstand voltage (V
_MW
= 81 kV
_rms
) and minimum flashover voltage (V
_MF
= 84 kV
_rms
) were obtained to reflect electrical performance of suspension insulators under a most dangerous ice type. The ice accretion process, the length, width and number of icicles associated with the appearance of partial discharges were observed and discussed to present the final formation of a relatively uniform ice layer and vertical icicles along the insulator string. This ice-covered insulator string was characterized by air gaps on the grounded-side shed space and complete ice bridging of the other shed spaces, which have significant influence on the development of arcing discharges leading to flashover. Nonlinear characteristics of LC were analyzed by using a recurrent plot (RP) technique, which graphically gives nonlinear variations of LC on RP maps as well as nonlinear indicators for quantitative prediction of the flashover. The obtained results reveal that dynamic behavior (initiation, propagation, extinguishment and re-ignition) of arcing discharges on ice-covered suspension insulators can be visually reflected by the texture transition of RP maps of LC, which correlate with different stages during the flashover process. The quantitative indicators including a recurrence rate (RR) value lower than 0.24 and a deterministic (DET) value lower than 0.965 are proposed as the predictive values to indicate the highest probability of flashover occurrence. The results obtained will be helpful to predict most hazards of ice-covered outdoor insulators; this is one of monitoring methods based on LC characteristic analysis.