Abstract
The crystallization effect during the phase transition of icing water has a significant impact on the electrical performance of an ice-covered insulator. However, the spatial distribution of conductive ions in the ice layer remains poorly understood. In this study, the crystallization effect was confirmed through a condensation test of the potassium permanganate solution. The influence of freezing water conductivity, ice thickness and equivalent salt deposit density on the spatial distribution of conductive ions was determined by a triangular ice sample, wherein the effect on the flashover characteristics of ice-covered insulator was investigated. Results show that MnO4− migrates to the unfrozen area during freezing, thus accumulating on the droplet top. The conductivity of melted water on the exterior surface of an ice sample is considerably higher than that of icing water. The former can reach a maximum of 5.7 times the latter when the freezing water conductivity method is adopted. This value is 9.7 for a polluted ice sample. A highly conductive water film forms on the insulator surface because of the crystallization effect in the melting period, thereby improving the leakage current and reducing the residual ice resistance, which results in the decrease of flashover voltage.
Highlights
Ice flashover is one of the major events that threatens the safe and stable operation of power systems
The flashover voltage of ice-covered insulators and their melting water conductivities in the flashover process when the freezing water conductivity and solid-layer methods are adopted are shown in Table 1 and Fig. 14, respectively
According to the preceding study, more conductive ions accumulated on the outer surface of the ice layer because of the crystallization effect with the increasing σ20 and equivalent salt deposit density (ESDD), thereby causing the water film conductivity rising and reducing the residual resistance in the melting period, eventually resulting in the flashover voltage decreasing
Summary
Ice flashover is one of the major events that threatens the safe and stable operation of power systems. B. INFLUENCE OF ICE THICKNESS ON THE DISTRIBUTION OF IONS The relationship between melting water conductivity and time is shown, where σ20 is 500 μS/cm and d is 5, 10 and 20 mm, respectively.
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