Flashover Along Polluted Insulators Under Short-tail Waveform Impulse Voltage

When shielding failure or back striking occur, the voltage waveforms which insulatorswithstand are quite different from standard lightning wave, therefore, the insulation flashovercriterion based on standard lightning wave may be irrational. This paper studied the pollutionflashover characteristics and pollution flashover process of insulators under short tail waveform bya large number of tests; based on these test data, this paper revised and improved the insulatorsdynamic circuit analysis theory.Single and double circuit transmission line are modeled in this paper based on the ATP/EMTPsoftware, in order to get the voltage waveform under shielding failure and back striking situation.And these two waveforms are adopt as the test waveforms. Test results show that influence ofESDD (Equivalent Salt Deposit Density), NSDD(Non_Soluble Deposit Densities) to the insulationflashover characteristics under shielding failure waveform is similar with the previous studies, andin the situation of the back striking waveform，it is different: With the increase in ESDD,short-tailed wave flashover voltage decreases; with the increase in NSDD, flashover voltage isgradually increased, approaching dry flashover voltage.In the study around waveform，this paper consider the wave tail time of flashover voltage has agreater influence on the flashover voltage，then carried out tests under different ESDD. The resultsshow that the wave tail time flashover voltage will affect the action index of ESDD, the shorter thewave tail, ESDD effects on the flashover voltage smaller.Through the process of flashover discharge current, high-speed photography, still photos of theobservation under different ESDD, combined with the critical volume theory, the paper summarizesthe initial arc conditions of polluted insulator; the development of the arc and the relationshipbetween ESDD. With the date of voltage, current, static pictures，the arc development process wasanalyzed.By studying the dynamic circuit analysis theory, combined with experimental research data, theinitial arc conditions is applied to the dynamic circuit model, and test data is used to improve thedynamic circuit model for the verification, the simulation results and experimental data is basicallyconsistent. In this paper, the dynamic circuit model is more objective to the original model, it isuseful to the study of basic parameters, and it could guide the forecast of flashover voltage.