Hygroscopic properties of pollutants on HV insulators

The mechanisms of moisture absorption by an insulator surface contaminated with different salts is described. A list of some salts depending on their hygroscopicity is given. Measurements of surface conductivity and leakage current on flat insulator models at different relative humidities and with different types of salt were carried out. At natural atmospheric conditions, the flashover voltage of cap and pin insulators subjected to 250/2500 μs switching impulses was evaluated. It is shown that the intensity of moisture absorption on insulator surfaces depends upon the chemical constitution of the pollution. The effect of intense and continuous moisture absorption can cause long-lasting surface discharges at operating voltage or can be a reason for flashovers a short time after the voltage has been switched on to a line