基于动态离子流场的直流GIL绝缘子表面电荷积聚机理研究

For lack of perfect physical model and especially the ion flow model in gas, current mechanisms of surface charge accumulation on a insulator of the gas insulated transmission line (GIL) under direct-current (DC) voltage are limited by their inability to give more specific information than lab confusing and inconclusive diagnostic testing results. Therefore, the mechanisms of surface charge accumulation on a insulator of the GIL under dc voltage that take into account the interpretation and partial discharge issues will be stuided in this research. Firstly, the time derivative model of current density caused by gas conduction and current density in the insulator volume are studied, and then the time derivative model of the surface charge density on the insulator surface has been studied. Secondly, an improved technique of ion flow field model of GIL under dc voltage is presented. The mathematic basis of ion flow field model technique which is applied for the accumulation method assessment of the surface charge caused by corona discharge which may occur in gas has been studied from theory analysis combing with the constructed time derivative model, and then steady state distribution and transient state distribution of surface charge caused by natural radiation and corona discharge are stuided by numerical simulation analysis. Eventually, electrometer based measurement system is developed, and the results of simulation have been verified by measurements of the surface charge density distribution in a fixed point on surface and along the surface of the insulator samples. The assessment stategies for mechanism of surface charge accumulation are gived to aid in providing a theoretical basis for how to suppress the surface charges. Moreover, according to above-mentioned theory, simulation and experiment, mixed gas of SF6 and N2 which may replace SF6 as a kind of enviromental pretection gas has been studied, and the optimum mixture ratio is presented from the view of surface charge accumulation.

现有的直流GIL绝缘子表面电荷积聚机理受不完善的物理模型影响，缺乏有效的评估基础，特别是气体侧放电离子流模型研究的欠缺，使得评估结果会有较大的不确定性。本课题对直流GIL绝缘子表面电荷积聚机理进行研究，首先针对GIL和绝缘子物理模型，研究气体电导电流密度和体积电导电流密度时变暂态模型，以及相应的绝缘子表面电荷密度暂态模型；其次，提出直流GIL的离子流场模型改进技术，基于上述暂态模型从理论上研究该技术应用于气体侧电晕放电离子源时表面电荷积聚途径的数学基础，并仿真分析自然辐射和电晕放电两种离子源时表面电荷的稳态和暂态分布特性；最后，研制基于静电探头法的表面电荷测量分析系统，提出相应的模型科学性验证方法和试验验证，给出表面电荷积聚机理的评估策略，为有效的解决措施提供理论依据；而且，基于上述理论以及仿真实验方法，研究SF6/N2混合气体对表面电荷分布的影响，提出最优混合比的环境友好气体。

本项目对直流GIL绝缘子表面电荷积聚机理进行研究，基于气体侧离子产生、复合、迁移和扩散等微观过程，建立了自然辐射电离和电晕放电等典型离子源时的离子流场改进数学模型，系统化地研究了固体侧介电弛豫、陷阱、温度场以及气体侧导体微放电等对表面电荷积累和消散的影响机理，分别提出了上述各影响因素的数学模型和分析方法，从这些因素本身、相互作用以及对表面电荷积累和消散过程的作用角度提出了表面电荷积累和消散的电流密度和电荷分布稳态和暂态数学模型，并提出了表面电荷积聚动态变化分析的理论和研究方法，实现了直流GIL绝缘子表面电荷类型、数量、暂态时间、主导机制以及动态分布等关键信息的揭示，有助于正确评估表面电荷积聚对绝缘强度下降（绝缘表面闪络）的真实影响，为合理有效的电荷调控方法提供全新的解决思路和技术手段。