Natural contamination test results of various insulators under DC voltage in an inland area in China

The authors describe the natural contamination test results of six types of insulators exposed in the southern suburbs of Beijing. The station stands near the eastern terminal of a DC transmission line. It is also located in a smooth terrain, a typical farming area on the North China Plain. The maximum annual equivalent salt deposit density (ESDD) and nonsoluble deposit density (NDD) on insulator surfaces were 0.038-0.057 mg/cm² and 0.144-0.425 mg/cm², respectively, in winter or early spring. The contamination on the surface of a DC energized insulator was 20% more than that of an AC energized one. When contaminants grew markedly, the top surface of the insulators attracted more contaminants than the bottom surface, especially in the case of aerodynamic and outside rib type insulators. There has been a heavy decrease in the contamination degree of insulators after the rainy season