Natural pollution accumulation characteristics of overhead transmission line insulator strings of Zhejiang electric power grid

The characteristics of pollution accumulation on naturally polluted insulators are fundamental for drawing pollutant distribution maps for power systems. Hence, taking some insulator strings on Zhejiang overhead transmission lines as samples, we investigated the natural pollution accumulation of insulators. Using statistical methods, we obtained and analyzed the ratio of top pollution level to bottom pollution level in aspects of equivalent salt deposition density (ESDD), non-soluble deposition density (NSDD), and the ratio between the two, which were denoted by KESDD, KNSDD and KNSDD/ESDD, respectively. Besides, we also analyzed the chemical compositions of the contamination under typical pollution resources. The results show that, for insulators of different structures, their top and bottom surfaces have quite different unevenness of pollution accumulation. For a naturally polluted insulator, the average value of ratio of KNSDD/ESDD is 4.66, while on a whole piece of insulator, the distribution of average KNSDD/ESDD varies in a tendency approximately consistent with that of the piece's bottom surface. In the contamination under study, Ca2+ is the main component of cations and SO42- is the main component of anions. For a piece of insulator, the proportion of different ions on its top surface is different from that of its bottom surface. It is recommended that these features of pollution deposit should be adequately considered in outdoor insulation designing and operation maintenance.