An, RI and TVI from single unit flashover of HVDC suspension insulator strings

This paper presents the results of a study on the unusual discharge activities on dc insulators. The phenomenon, designated as "single unit flashover", completely bridges one or two insulators in a long string, and generates very high AN, RI and TVI. Since this is caused by the extreme voltage concentration on the units resulting from the thermal phenomenon on the insulator surface determined by the rate of wetting and drying, the tests were made in natural humidity conditions at the Shiobara laboratory, which has been converted to a ± 500 kV dc laboratory. This poses a serious problem for dc HV transmission design.