Investigation on natural contamination deposition of insulators on ±500kV DC transmission lines in different environments

China is a country with vast territory, and the environments of the areas where the transmission lines are passing differ greatly. An investigation on natural contamination deposition of insulator in different environments is needed. In this paper, the surface SDD/NSDD of insulators on ±500kV DC transmission lines which located in the Industrial area, agricultural and industrial mixed area and agriculture area are measured. Statistics analysis of the data shows that by select four insulators each from the upper/middle/lower of the string, the result can reflect the contamination of the whole string of insulators; a comparison with the result got before shows that the contamination of the insulators in different environments change differently; the final analysis on the measurement data shows, for the porcelain insulators with RTV sprayed on the surface, the ratio of the SDD/NSDD of the upper and lower surface is between 1:3 to 1:5.5, the SDD and NSDD of the insulators along the string presents a U-shaped distribution.