This work aimed on optical and electrical characterization and mathematical modeling of flashover of polluted insulators, taking into account the applied voltage waveform, the distribution and chemical composition of pollutant deposit. Under lightning impulse voltage (1.2 /50μs), the morphology of the discharge and the associated currents depend on voltage (shape, amplitude, polarity), the distribution ofpollution and its conductivity. The measured average velocity of the discharge depends on the polarity applied to the tip and the pollution conductivity. The critical time corresponding to the critical conditions is about 9/10 of total flashover duration regardless of the polarity of the voltage and the pollution conductivity. The chemical composition of the pollution layer has little effect on the critical voltage unlike the critical currents. The values of the characteristic constants n and N depend on the chemical nature of the deposits and the voltage polarity.The developed model shows that the discharge constant characteristics n and N are dynamic parameters and depend on the elements of the equivalent electrical circuit system and thermal parameters of the discharge. The developed relationships of critical conditions of flashoverlink the electrical parameters and thermal equivalent circuit and the propagation condition of the discharge. This approach allows us tounderstand the effect of the chemical constitution of pollution on the values of n and N. The application of this model for various voltage waveforms and for several types of pollution, gives satisfactory results. The assumption that the column of the discharge contains only watervapor and air is a good approximation of the critical conditions. Under lightning impulse voltage, the current circulate into a effective section of the pollution surface. The introduction of the concept of critical effective thickness of pollution and its application to the calculation ofcritical parameters gives good results compared with the experimental values. We have also shown that the effective thickness of the depositis proportional to the resistivity of the pollution and depends on voltage polarity and pollution configuration. In the case of discontinuous deposit of pollution and / or non-uniform propagation conditions of discharges are local and their characteristic parameters vary dependingon the configuration and the conductivity of the deposit and the polarity of the applied voltage. The developed model gives good results
