固–气界面电荷消散特性及其动力学过程

Charge Dissipation Characteristics and Kinetics on the Gas-solid Interface

直流电场下气体绝缘设备中固体绝缘介质表面电荷的积聚会导致固–气界面的局部电场畸变,从而降低系统的绝缘水平。研究固–气界面电荷的消散特性可为高压直流气体绝缘装置的研发提供重要的理论基础。利用针–板电极向绝缘材料表面注入电荷,在不同条件下进行固–气界面电荷消散实验。采用静电探头法测量试样表面的电位分布,并通过反演计算得到电荷密度分布。结果表明:处在气体氛围中的环氧树脂材料,其表面电荷主要是通过与气体中离子中和消散,消散过程与气体中电场的分布有关。处在开放空间中的试样,表面电荷密度越大的地方电场越集中,因而迁移至此的异号带电粒子更多,表面电荷消散也更快,最后在试样表面会逐渐形成"火山口"形的电荷分布。基于固–气界面电荷消散的三种途径,构建了固–气界面电荷消散的动力学模型,分别考察了通过体电导消散、面电导消散,以及与气体中离子中和消散3种不同消散机理主导下的固–气界面电荷消散特性。研究发现,对于体积电导率小于10?15S/m的材料,表面电荷主要通过与气体中离子中和消散;对于体积电导率大于10?14S/m的材料,表面电荷主要通过体电导消散,各处消散速率基本一致;未经特殊处理的绝缘材料,表面电导率较小,对表面电荷消散的作用有限。

Charge accumulation on a solid insulator under dc field will lead to the local field distortion along the gas-solid interface and decrease the insulation level of the system. To study the surface charge dissipation characteristics will provide an important basis for the development of HVDC gas-insulated equipment. In this paper, the needle-to-plate electrode was used to inject charges onto the surface of insulating material, and the charge dissipation was studied under different conditions. The electrostatic probe method was used to measure the potential distribution on the sample surface, from which charge density distribution was obtained by the inversion calculation. Results show that surface charge on an epoxy resin insulator in the gas is mainly dissipated by neutralization with gas ions, and the process is related to the electric field distribution in the gas. For the charged sample in a free volume, electric field is more concentrated where the surface charge density is the maximum.As a result, more hetero-charges migrate to this area, leading to faster charge decay. Finally, a crater-shaped charge distribution forms. Based on the three ways for the surface charge decay,i.e. bulk conduction, surface conduction, and neutralization with gas ions, a kinetic model was built and the charge dissipation characteristics through the three mechanisms were studied separately. It reveals that surface charge of materials with bulk conductivity less than 10^-15 S/m is mainly dissipated by neutralization with gas ions;for bulk conductivity larger than 10^-14 S/m, surface charges are mainly dissipated through bulk conduction with almost the same dissipation rate on the surface;an insulating material without special treatment has a small surface conductivity, which has limited effect on charge decay.