Equivalent surface conductivity of ice accumulated on insulators during development of AC and DC flashovers arcs

Surface conductivity of ice was investigated during the development of AC and DC arcs on ice-covered insulators. To determine this parameter, an approach based on fluid mechanics combined with experimental measurements of the water film flow rate and conductivity was used. In particular, the variation of the thickness and volume conductivity of the water film as well as the mechanisms of discharge initiation and arc development on the surface of an ice-covered post insulator were studied. The effect of ice surface conductivity on arc propagation velocity was evaluated for different freezing water conductivities using highspeed video camera techniques. Empirical models were proposed to account for equivalent surface conductivity dynamics during the flashover process. The derived equivalent surface conductivity was used to improve existing dynamic models to predict the minimum flashover voltage of the ice-covered insulator. The computed results from the models were in good agreement with those obtained experimentally.

I. Introduction

As power networks are expanding and the voltage level of transmission lines is being increased, the performance of outdoor insulators is playing an increasingly important role in assuring the secure operation of power systems. Outdoor insulators in cold climate regions subjected to the combination of pollution and atmospheric ice accumulation may result in considerable loss of their electrical performance. The power outages caused by flashover on ice- or snow-covered insulators have been reported in North America [1]–[5] as well as in many cold climate countries of Europe [6], [7] and Asia [8], [9]. Flashover of ice-covered insulator is an extremely complex phenomenon resulting from the interaction of many factors including electric field strength, voltage polarity, ice surface condition, presence of ice-free zones (air gaps), environmental conditions and insulator type and configuration [10], [11].