Lightning impulse flashover modelling of a typical MV porcelain insulator using ATP-EMTP: application to a MV overhead distribution line

Flashover prediction of medium voltage overhead line insulators is of great importance in insulation coordination studies . In electromagnetic transient simulations insulator flashover is modelled using experimentally obtained flashover volt-time curves, or the integration method with parameters appropriately adjusted based on experimental flashover results. However, these modelling approaches, being specifically related to the reference experimental results, cannot be easily generalised to apply to the great variety of utilized distribution line insulators, differing in geometry and material, as well as to the variability in the waveshape and polarity of the lightning surge overvoltages. In this study a modelling approach for lightning impulse flashover of typical MV overhead line insulators is introduced, based on the CIGRE leader progression model however with its model parameters appropriately adjusted. An excellent agreement between experimental and modelling flashover results has been achieved by expressing model parameters as a function of the average steepness of the applied voltage at leader inception. The developed model is implemented in ATP-EMTP environment to evaluate insulation flashover of an overhead line of the Hellenic distribution system due to direct positive lightning strikes. The main advantage of developed leader progression model is its ability to accurately describe the dynamics of discharge growth over insulators, starting from leader inception up to flashover.