Different Charge Accumulation Characteristics on Spacer Upper and Lower Surfaces: Impact of Thermal Convection

In this study, an electric-thermal-fluid coupling simulation model of the spacer in 500-kV dc gas-insulated transmission line (GIL) is established to investigate the surface charge accumulation behavior under thermal convection. The variation of the load currents is used to generate different temperature gradients. Results show that homopolar and bipolar charges accumulate on spacer upper and lower surfaces, respectively, which are dominated by bulk conduction. The lower surface has a higher temperature and a faster charge accumulation rate under the thermal convection. Increased temperature gradients lead to an increase in bulk conductivity and bulk current, therefore accelerating surface charge accumulation. Compared with the case without thermal convection, the upper surface shows lower saturation values under the thermal convection, while the lower surface shows higher saturation values. This study could contribute to the optimization of dc GIL.