New mathematical formulations for calculating residual resistance in a static arc model of ice-covered insulators

Abstract

This paper develops two new mathematical formulations for calculation of the residual resistance in a static arc model to predict ac and dc flashover voltages of heavy ice-covered insulators. In the first formulation, appropriate for dc with a small insulator string, the residual resistance is considered as a resistance between a small circular conductor where it models the arc root and the ground electrode. It is shown that using this new formula for a static dc arc model with heavy ice-covered insulators leads to an improved model to predict flashover voltage. In the second formulation, appropriate for ac and dc with long insulator strings, the residual resistance is considered as a resistance between two small circular conductors modeling two arc roots where the arcs are on air gaps formed near the high voltage and ground electrodes. The method of image charges is used in both formulations. The capability of this improved static arc model is confirmed when it is compared to that of previous static and dynamic models. This improved arc model has a better correspondence with the experimental results than the previous static and dynamic models. It can be used as a powerful tool for the design and selection of insulators subjected to ice accretion.