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International audienceThis paper is aimed at the study of the influence of the chemical constitution of pollution on dc flashover discharge of high voltage contaminated insulators. It's shown that the type of salt and salt mixture has an influence on the critical currents for both polarities but doesn't affect significantly the critical voltages whereas the concentration of insoluble matters (Non Soluble Density Deposit, NSDD) has an influence on both critical current and critical voltage. The discharge parameters characteristics N and n depend on the chemical constitution of pollution, the concentration of NSDD and the polarity of voltage. It's also shown that the most important constituent of the discharge column are water vapour and air; and the transfer of metallic ion has no significant influence on flashover voltage

This paper presents a refinement in the residual resistance formulation used in pollution flashover model. The proposed study focused on the residual resistance calculation of the AR or open model which used the expression of the insulator factor form. The proposed modification takes into account the non-uniformity of the current density distribution inducted by the open model which is increased by the presence of the arc root at the pollution surface. A correction factor was determined based on experimental and numerical investigations. The numerical simulations confirm that the constriction and the distribution of the current lines along the open model have a significant influence on the residual resistance calculation. The proposed corrected residual resistance formulation was then implemented in a dynamic mathematical model in order to determine the critical flashover voltage (FOV) of different cap-and-pin insulators for different pollution layer levels. The results obtained with the proposed flashover model and its corrected resistance formulation show a very good agreement with the theoretical and experimental results obtained from the literature. This validates the propose refinement of the residual resistance dedicated to polluted flashover model and provide a powerful tool for insulator dimensioning.