Effect of ultrasonic fog on AC flashover voltage of polluted porcelain and glass insulators

Three wetting methods are frequently used for polluted insulators in artificial fog tests, i.e. cold fog, steam fog and mixture fog. IEC recommended the steam fog wetting method. However, experimental experience shows that, it is difficult to control wetting time with this steam input rate. In addition, the temperature in climate chamber rises over the duration of the test. Both factors make the steam fog test less representative. Porcelain and glass insulator strings of 3 units are wetted by ultrasonic fog in an artificial climate chamber. The flashover performances of polluted insulators are studied. The test results revealed that the relationships between flashover voltage and Salt Deposit Density (SDD) can be expressed as negative exponential functions for porcelain and glass insulators. However, the fitting formulas, which are simulated ac pollution flashover voltages at various pollution degrees for the same type of insulator, are consistent at various conductivities of the applied water. Moreover, the relationships between flashover voltage and conductivity of the applied water can also be expressed as a negative exponential function.