Study of mechanisms leading to failure of insulators under pollution conditions with DC voltages

Higher rate of failure of insulators occur in HVDC systems especially in polluted zones. The main reasons for this are surface erosion, ion migration and voltage distribution. Voltage distribution under clean conditions becomes one of the main causes for failure. Experiments have been carried out for the determination of the voltage distribution under varying ambient in which the relative humidity values varied between 19 to 90%. Puncturing and shattering of insulators are the causes of failures that occur in DC lines especially in polluted zones. Various causes of failure have been put forth when the pin of the insulator is positive. However, for negative voltage applied to the pin of the insulator the reasons have not been found yet. Detailed studies have been analysed. The paper presents the details of the study.