Development of a New Bi-Arc Dynamic Numerical Model for Modeling AC Flashover Processes of EHV Ice-Covered Insulators

Abstract

This paper presents the development of a new bi-arc dynamic numerical model for predicting AC critical flashover voltage (FOV) of ice-covered extra-high voltage (EHV)insulators. The proposed model is based on a generic calculation algorithm coupled with commercial finite element method software designed to solve the Obenaus/Rizk model. The proposed model allows one to implement the Nottingham and Mayr approaches and compare the results obtained as a function of the arcing distance, the freezing water conductivity, and the initial arc length. The validation of the model demonstrated high accuracy in predicting the FOV of ice-covered post-type insulators and its capability to simulate the interaction of the two partial arcs during the flashover process. In particular, the results showed that the Nottingham approach is sensibly more accurate than the Mayr one, especially in simulating the dynamic behavior of the partial arcs during the flashover process. Based on the encouraging results obtained, a multi-arc calculation algorithm was proposed using the bi-arc dynamic numerical model as a basis. The basic idea, which consists in dividing the multi-arc model in several bi-arc modules, was not implemented and validated but will serve as a promising concept for future work.Energies 2018, 11, 2792 2 of 22 applicability of the static and dynamic predictive models to insulators having an arcing distance lower than 1 m [12][13][14][15][16][17][18].To avoid such a limitation, some authors have proposed an improvement of the original Wilkins formulation in order to determine the residual resistance when several partial arcs and, consequently, several arc roots are in contact with the ice surface [14,18]. This improved formulation has been implemented in a mathematical static multi-arc model and successfully applied to full-scale extra-high voltage (EHV) post insulators [14]. More recently, this new formulation has been implemented in a dynamic mathematical multi-arc model using the same approach and is described in more detail in the next section [18]. Both multi-arc models can predict the critical flashover voltage, but the dynamic model can also predict leakage current and arc velocity during the flashover process. However, the use of Wilkins formulation requires a well-defined uniform ice layer that can only be obtained under severe icing conditions [14]. Under these specific conditions, the insulator is totally bridged by the ice deposit that can then be modelled as a half cylinder [12][13][14][15][16][17][18]. Consequently, the calculation of the residual resistance using the analytical formulation remains the main limitation of the current static and dynamic mathematical models used to predict the FOV of ice-covered insulators. However, such residual resistance formulation is more difficult to use in the case of non-uniform conductive layers with complex geometries.To deal with such geometry-related problems, new numerical predictive models using E-field calculation tools have been proposed in recent years by the author...