Study on Pollution Performance and Insulation Selection of ±800 kV Long String Insulators

The pollution flashover performance of large tonnage insulators typically used in ±800 kV DC transmission lines were studied in this paper. As V string and double I string would probably be adopted in lines, the influence that structure exerts on pollution flashover voltage has been tested. Test results showed that, for large tonnage insulators, a linear relationship between DC pollution flashover voltage and string length has been presented. The pollution flashover performance of V strings generally coincide with that of I string, and the test results of I string can be directly used to V strings. While the space between paralleled strings has significant influence on pollution flashover performance, and the influencing effect varied with string lengths. Based on the correction of relationship between salt deposit density (SDD) and non-soluble material deposit density (NSDD), methods of external insulation parameter calculation and insulator selection for ±800 kV UHV DC transmission projects were introduced.