Modeling of Surface Trapping Effect on Charge Accumulation Pattern at Gas-Solid Interface in DC GIL

In this article, the impact of solid-side electron traps on surface charge accumulation behaviors at a -500-kV basin-type direct-current gas-insulated line (dc GIL) insulator is studied by numerical calculation. A 3-D simulation model in consideration of the physical processes of generation, amalgamation, and dispersion of charge carriers within insulating gases of dc GIL is proposed, with gas-side charge injection dominates the surface charge accumulation process. Surface trapping effect is modeled by assigning surface traps along the gas-solid interface following Gaussian distribution. Research findings reveal that during energization, surface charge accumulation is initially in the form of "uniform charge halo pattern," then evolved to "initial charge speckle pattern," and eventually presented as the "steady-state charge speckle pattern." Furthermore, the discrete charge speckle displays two modes of accumulation with different dominant factors, i.e., one governed by surface currents and the other by gas-side charges. The first mode arises from the synergistic interactions between neighboring charge speckle regions with different polarities, whereas the second originates from the establishment of localized high-density charges. The latter fosters the development of charges with opposite polarity on bilateral surfaces, concurrently impeding the accumulation of nearby charges with identical polarities that are centered on them. Both modes of charge speckle coexist and collectively influence the charge accumulation behaviors. By successful modeling surface charge transport behaviors with inhomogeneous surface conductivity distribution under the trapping effect, a novel theoretical mechanism for the formation of charge speckles is proposed in this study through a process-oriented perspective.