Competitive Effect of Charge Injection on Surface Charge Accumulation of the DC GIL Insulator: A Numerical Study

In this article, a 3-D numerical model of surface charge accumulations on a basin-type direct-current gas-insulated line (dc GIL) insulator is proposed. Simulation shows that when the volume conductivity is <inline-formula> <tex-math notation="LaTeX">$6\times 10^{-{17}}$ </tex-math></inline-formula> S/m, current densities on the gas and solid sides of the insulator interface range from <inline-formula> <tex-math notation="LaTeX">$\sim 10^{-{9}}$ </tex-math></inline-formula> to <inline-formula> <tex-math notation="LaTeX">$\sim 10^{-{8}}$ </tex-math></inline-formula> A/<inline-formula> <tex-math notation="LaTeX">$\text{m}^{{2}}$ </tex-math></inline-formula> and <inline-formula> <tex-math notation="LaTeX">$\sim 10^{-{11}}$ </tex-math></inline-formula> to <inline-formula> <tex-math notation="LaTeX">$\sim 10^{-{9}}$ </tex-math></inline-formula> A/<inline-formula> <tex-math notation="LaTeX">$\text{m}^{{2}}$ </tex-math></inline-formula>, respectively. Surface charge accumulation is dominated by gas-side conduction and its process is divided into three stages, i.e., stage I with the development of uniform charge halo patterns, stage II with the saturation of charge halos while discrete charge speckles appear, and finally, stage III with the saturation of charge speckles. When the volume conductivity increases to <inline-formula> <tex-math notation="LaTeX">$6\times 10^{-{15}}$ </tex-math></inline-formula> S/m, current densities on both gas and solid sides vary in the order of <inline-formula> <tex-math notation="LaTeX">$\sim 10^{-{9}}$ </tex-math></inline-formula> A/<inline-formula> <tex-math notation="LaTeX">$\text{m}^{{2}}$ </tex-math></inline-formula>. In addition, the surface charge accumulation process is dominated by the competition between gas-side and solid-side conductions, which is similar to that under low volume conductivity, but the time to saturation for charge halos is approximately two times higher. When the volume conductivity increases to <inline-formula> <tex-math notation="LaTeX">$8\,\,\times 10^{-{14}}$ </tex-math></inline-formula> S/m, current densities on gas and solid sides range from <inline-formula> <tex-math notation="LaTeX">$\sim 10^{-{9}}$ </tex-math></inline-formula> to <inline-formula> <tex-math notation="LaTeX">$\sim 10^{-{7}}$ </tex-math></inline-formula> A/<inline-formula> <tex-math notation="LaTeX">$\text{m}^{{2}}$ </tex-math></inline-formula> and <inline-formula> <tex-math notation="LaTeX">$\sim 10^{-{7}}$ </tex-math></inline-formula> to <inline-formula> <tex-math notation="LaTeX">$\sim 10^{-{4}}$ </tex-math></inline-formula> A/<inline-formula> <tex-math notation="LaTeX">$\text{m}^{{2}}$ </tex-math></inline-formula>, respectively, with surface charge accumulation process being dominated by solid-side conduction. In this mode, only charge halos appear, and the charging progress is divided into two stages, i.e., stage I with the continuous accumulation of charge halos and stage II with the polarity reversal of charge halos on the convex surface. These phenomena indicate that the polarity reversal phenomena are caused by the bilateral surface charge coupling (BSCC) effect, i.e., the charge accumulation on the convex surface is distorted by that on the concave surface. In this simulation, the formations of discrete charge speckles in the simulation are closely related to the uneven accumulation rates of surface charges on the bilateral surfaces caused by the basin-like structure of the insulator.