COMPARISON OF NATURAL CONTAMINANTS ACCUMULATED ON SURFACES OF SUSPENSION AND POST INSULATORS WITH DC AND AC STRESS IN NORTHERN CHINA'S INLAND AREAS

The exposure test results of natural contaminants accumulated on the surfaces of cap, pin and post insulators at three testing stations in northern China's inland areas are summarized. The contaminants growth rapidly from the end of autumn to next early spring, and heavy rain in summer can wash away a lot of contaminants from insulator surfaces. Different insulators have different ratios of contamination degree under DC stress to under AC stress: the contamination ratio for cap and pin insulator is 2 and that for post insulator is 3. But the contamination ratio of DC stress to AC stress is less than 2 in good vegetation areas. Influence of two ratios of NDD to ESDD and ESDD on top surface to that on bottom surface, the chemical compositions of soluble salts and the sizes of contaminant particles must be regarded in the outdoor insulation design.