Insulation Coordination for ±800kV UHVDC Converter Stations

This paper describes the configuration and protection scheme of arresters for the ±800kV DC converter station,design principle of insulation coordination,insulation margin(including the insulation margin of converter transformer bushings).The following suggestions are presented based on the analysis:(1) The insulation margin of lightning and switching impulse for the thyristor valve is advised to lower to 10%,and neither the ratio of SIWL/LIWL(0.83) nor the insulation class adjacent to higher level will be applied to the oil-immersed equipment in the DC side of UHV DC conversion station.(2) Referring to the insulation margin between the inner insulation of converter transformer and insulation of bushings,a 1.15 times withstand voltage level of winding is advised for the DC withstand test with the partial discharge measurement and the polarity reversal test with the partial discharge measurement of 800kV converter transformer bushings.In addition,the test voltage level of lightning and switching impulse is 5% more than the winding insulation level instead of 10% adopted previously.(3) The parameters and characteristics of arrester,the protection and insulation level of equipment are also discussed preliminarily in the paper,moreover,the detail data are presented as the reference of further study.