对±800 kV直流输电线路上可能用到的几种典型大吨位绝缘子的污闪特性进行了系统的人工污秽试验研究。针对线路中可能用到的V型串及双I串并联结构，通过试验分析了它们对绝缘子串污闪电压的影响。结果表明，大吨位绝缘子的直流污闪电压与串长之间仍存在较好的线性关系，V型绝缘子串的污闪特性与I型串基本一致，可以直接使用I型串的试验结果，但并联绝缘子串间距对绝缘子串污闪特性存在显著影响，且串长不同时，并联绝缘子串间距对其污闪电压的影响效果不同。基于上述试验结果，并考虑了现场等值盐密与试验盐密的校正关系，给出了±800 kV特高压直流输电工程外绝缘参数计算和线路绝缘子选型的方法。

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.