Investigation on the application status of composite insulators and disc insulators in existing ac uhv line projects in China

and analyzing the configuration principles and applicable scope of insulator strings in low altitude regions.Relying on the research results and practical experience of the Sichuan Chongqing AC UHV Project under construction

it is believed that the structural height of composite insulators in high altitude areas is controlled by the switching overvoltage gap

and the insulation coordination method is to match the tower head with the dry arcing distance after stringing.Based on the results of the pollution outer insulation test conducted by CEPRI

the recommended structural height and minimum creepage distance of composite insulators in high-altitude areas are obtained.Analyzing the altitude correction formula for the number of insulator pieces and pollution withstand voltage in existing standard specifications

the results show that the correction method in GB 50665—2011 has not undergone altitude iteration

and the correction coefficient for the number of insulator pieces is a fixed value.The correction coefficient for the number of insulator pieces obtained by the correction method in DL/T 368—2010 increases with the increase of the characteristic index of air pressure influence and altitude.Recent scientific research findings from ongoing AC UHV projects indicate that the correction coefficient for the number of three-umbrella insulator units is positively correlated with altitude

whereas for bell-type insulators it exhibits an abnormal sharp increase at altitudes of 2 000 m～3 000 m.At the same altitude

the correction coefficient is higher for class c pollution severity than for class d

and higher for bell-type insulators than for three-umbrella insulators.