Study on impulse flashover characteristics of polluted insulators under different voltage applied methods

Pollution flashover of insulator strings is one of the most serious natural disasters in transmission line, and it is dangerous to the power grid. The three voltage applied methods of impulse voltage, power frequency pre-voltage and impulse voltage superimposed on power frequency were built to do the research, and influence of power frequency pre-voltage, partial drying effect of power frequency leakage current on impulse flashover characteristics were studied in the paper. For a fixed NSDD, the impulse flashover voltage of three test methods increased with the increasing of ESDD, the positive polarity impulse flashover voltage was lower than that of negative polarity ones. During the process of impulse voltage superimposed on power frequency test method, the power frequency voltage upraise the initial potential of impulse flashover voltage, and it was conducive to the flashover of polluted insulators. During the process of impulse voltage superimposed on power frequency test, drying effect due to power frequency current and power frequency pre-discharge effect were helpful to the form of partial discharge arc, and they provided favorable environments for the flashover of polluted insulators. Pre-discharge of power frequency and drying effect of power frequency current was contributed to the flashover of polluted insulators, and it was more and more clearly with the increasing of pollution, at a special point both pre-discharge of power frequency and drying effect of power frequency current were in a state of equilibrium.