Developpement de modeles dynamiques de prediction de la tension critique de contournement des isolateurs recouverts de glace bases sur la methode des elements finis.

摘要

The vast majority of dynamic and static models for predicting critical flashover voltage (FOV) of ice-covered insulators during the melting period use Wilkins analytical formulation to calculate the residual resistance of ice layer. Since this formulation can be used only for well-defined uniform ice layer with simple geometrical shape, it seems difficult to adapt it to non-uniform ice layer or for insulators with complex geometries. In addition, all dynamic models being developed are restricted to arcing distance less than one meter since they can take into account only one arc in contact with the ice surface. To overcome this problem, it was decided recently to use finite element method (FEM) to develop dynamic predictive models applied to insulators covered with a non-uniform ice layer, and this, for arcing distances that can reach two meters. This last consideration requires the implementation of two partial arcs in contact with the ice surface.;The proposed models were elaborated by using the commercial software FEM COMSOL MultiphysicsRTM which was coupled with MatlabRTM in order to enable the execution of algorithms. The three FEM dynamic models mentioned above were validated with experimental and numerical results obtained in previous studies. The comparison of different results concludes that the FEM single arc dynamic models in DC and AC are able to predict the critical flashover voltage with accuracy as good as the one found by the current dynamic models. The maximum error is around 13 % regardless of the applied water conductivity, the arcing distance (less than one meter) and the air gap initial length. This latter, which is an influential parameter, was not taken into account in most of the existing dynamic models. Regarding the two-arc dynamic model which is presently, to the best of our knowledge, the only dynamic model that can be applied to arcing distance higher than one meter, the comparison of the results show that the numerical results obtained are in agreement with the experimental ones obtained in previous studies with a maximum error of 5,8 %.;The use of FEM, the implementation of Hampton criterion as a criterion of propagation and the modeling of water film and arc root allowed the development of simple dynamic models that can predict critical FOV of ice-covered insulators with a maximum arcing distance of two meters. Also, the results have demonstrated the versatility of all proposed models that can easily trace the evolution of several parameters, namely the residual resistance, the leakage current and the applied voltage versus the displacement of one or two arc roots along the ice surface.;With this objective, three predictive dynamic models were established in this research work, that is to say a direct current (DC) single arc model, an alternative current (AC) single arc model and finally an AC two-arc dynamic model. The latter is in fact an extension of the AC single arc model. All the developed models are based on the model of Obenaus and use the FEM to calculate the residual resistance of the ice layer. Because of the presence of a conductive water film thickness assumed to be constant, the ice surface is modeled by a two-dimensional conductive surface in contact with one or two arc roots considered as circular equipotential surfaces. Using Hampton criterion as a propagation condition is a very good approach for designing simple dynamic models because this criterion can be easily validated by FEM. The critical FOV of ice-covered insulators is obtained by simple iterative calculation when the arc root reaches the ground electrode (case of single arc model) or when the two arc roots meet together (case of two-arc model).