Analyzing and understanding the surface potential distribution and charge accumulation characteristics of the UHV converter transformer valve-side bushing

as a critical component in DC transmission systems

under steady DC voltage is essential for ensuring its reliable operation. This paper focuses on an ±800 kV converter transformer valve-side bushing. The bulk conductivity of resin-impregnated paper samples

which were extracted from an actual bushing

was measured in the directions of being both parallel and perpendicular to the paper plane. An equivalent scaled-down bushing was designed and manufactured by the producer. A surface potential measurement platform and a corresponding simulation model for the scaled bushing were established. The study found that the simulation results with anisotropic bulk conductivity settings better matched the measured surface potentials. Furthermore

a fully coupled electro-thermal-fluid steady-state simulation model of the actual ±800 kV bushing was developed. Comparative simulations were conducted with isotropic and anisotropic bulk conductivity assumptions

respectively. The research reveals that

under both conductivity models

a significant amount of positive charge accumulates on the outer surface of the bushing’s epoxy core. However

on the gas gap surface near the shielding electrode

a small amount of negative charge accumulates under the isotropic assumption

whereas a substantial amount of negative charge accumulates under the anisotropic assumption. The stable accumulation of negative charge on the gas gap surface in the anisotropic case leads to a significant potential drop at the bushing’s end

resulting in increased electric field strength within the SF₆ gas gap and enhanced tangential field strength along the gap surface. This condition may raise the risk of surface flashover along the bushing’s gas gap interface.