Experimental studies on minimum air clearance and critical radius for the stress shielding of A5000 series ±1100 kV UHVDC converter valve

±1100 kV is the highest UHVDC voltage level in the world. ±1100 kV HVDC converter valve is a core equipment, and therefore determining the minimum indoor air clearance for its external insulation is significant. In this paper, according to switching impulse withstand level (SIWL) of ±1100 kV HVDC converter valve, minimum air clearance required for a ±1100 kV HVDC converter valve installation were calculated. In order to improve the SIWL and shorten the minimum air clearance, the stress shield assembly of A5000 series ±1100 kV HVDC converter valve installation was designed by using the previous studies of Ball-plate electrodes critical radius. In the end, a C-EPRI A5000 type ±1100 kV UHVDC converter valve was used to carry out switching impulse tests at the SGCC UHVDC test base in Beijing. The results shows that the new design of the stress shield assembly can effectively shorten air clearance.