Pollution flashover performance of full-scale ±800 kV converter station post insulators at high altitude area

On the background of the peculiar technology problems with the external insulation of UHV dc equipment in China, caused by high altitude and heavy pollution, this paper presents the pollution flashover performance of full-scale ±800 kV converter station post insulators at actual high altitude area. The tests were carried out according to the solid layer method, and the 50% withstand voltage (U_50%) was determined by the up-and-down method. The artificial contamination test results indicated that the shed configuration and the rod diameter had a significant influence on the flashover voltages. Shed parameters of one big and one small alternating shed composite post insulator which had superior dc pollution flashover performance had been recommended. The relationship between U_50% and insulation height was approximately linear at actual high altitude area for post insulators. It was found that partial discharges occurred at the top section firstly and partial arcs easily appeared at the parts nearby the connecting fittings during the flashover process. And arc floating phenomenon was significantly serious in actual high altitude area. Furthermore, comparison was made between the U_50% values of composite post insulators in fog and in rain. The U_50% values in fog of composite post insulators were generally higher than that in rain. Thus, the outdoor insulation design of composite post insulators should primarily consider the U50% value in fog. This work thus provides useful reference for the design, operation and maintenance of UHV dc converter stations outdoor insulators in China.