Improved dynamic model of DC arc discharge on ice-covered post insulator surfaces

This paper presents a self-consistent dynamic two-arc model predicting the behavior of DC arcs on ice-covered station post insulators. This model makes it possible to determine the minimum flashover voltage (VMF) as well as some characteristics of the discharge, including temporal evolution of leakage current, arc characteristics and icing severity of the insulators. The model takes into account the variation of freezing water conductivity, insulator geometry, ice layer characteristics, applied voltage polarities and some fundamental concepts of air gap formation. The model was validated in laboratory using a typical 735-kV ice-covered station post insulator under DC voltage. The VMF was experimentally determined based on IEEE Std 1783. Moreover, the influence of the number and position of air gaps on the minimum flashover voltage was investigated experimentally and mathematically. There was a good concordance between the experimental results and those predicted by the model. This model is a good foundation for the development of multi-arc models and a powerful tool for the design and selection of DC EHV insulators subjected to ice accretion.