基于内源式EIT的接地网成像基础方法与技术研究

According to safety regulations, grounding grid need to be periodically tested to ensure the safe operation of the power system. With the grounding grid number increasing rapidly of substations and wind farms, and the aggravated environmental pollution, grounding grid detection task and renovation cost increase rapidly. If ground grid drawings of old substation have lost, it will result in the great difficulties of branch impedance detection. To solve the existent problems of grounding grid branch impedance detection method at present, the project will research the grounding grid branch impedance detection method based on endogenous type EIT. Firstly, the grounding grid mathematical model of endogenous type EIT (including governing equation and degenerate boundary conditions) will be researched. For ill-posed source of grounding grid EIT inverse problem, refinement solving methods are studies, including the high-contrast discontinuous medium and the large differences of medium size influence on the accuracy of the solution. Then the branch fault imaging technology and the partition diagnostic imaging method based on EIT are researched. So grounding grid topology detection method and the partition measurement method are obtained. Finally, the experiment is conducted to verify and improve the feasibility of the method by using the alternating 16-channel grounding grid impedance measuring device. Achievements of the project can be used to study corrosion monitoring and state assessment of grounding grid. So the project has important theoretical significance and construction value.Basis preliminary studies of the applicant show that: EIT method can effectively identify differences between large electrical resistivity objects.

根据规程，接地网需要定期进行检测确保电力系统运行安全。随着变电站及风电场接地网数目快速增加和土壤污染的日益严重，接地网检测任务与改造成本快速增加。老旧变电站接地网图纸丢失导致支路阻抗检测难度非常大。针对目前接地网支路阻抗检测存在的问题，本项目拟研究基于内源式EIT的接地网支路故障检测方法，首先研究接地网内源式EIT问题的数学模型（包括控制方程与退化边界条件），针对其逆问题的病态性，研究其精细化求解方法，包括高对比度不连续介质、介质尺寸差异大等问题对解的准确性的影响。进而研究基于电阻抗成像原理的接地网支路故障成像技术和接地网的分区成像诊断方法，得出基于EIT的接地网拓扑检测方法和分块测量方法，最后结合交流16通道接地网阻抗测量装置完成对算法的验证与改进。项目的成果可用于接地网腐蚀检测与性能评估，有着重要的理论意义与工程价值。申请人前期研究基础表明：EIT方法可以有效识别电阻率差异大的物体。

在本项目的资金资助和内容指导下，按期完成了任务书要求内容和相应的研究工作。项目开发了内源式EIT的成像系统与多阶微分法的阻抗拓扑重构系统，实现了内源式EIT的成像方法，并开展了现场应用。项目的主要创新性成果包括：.1）实现了接地网内源式EIT的数学物理模型，提出了针对无限域EIT的人工边界施加方法；通过改进Tikhonov中的单位正则化矩阵，提出一种自诊断的正则化方法，降低了逆问题的病态性。2）实现了基于多阶磁场微分法的接地网拓扑重构方法，解决了EIT对接地网拓扑未知场域无法成像的问题。3）提出了土壤分离与分区成像方法，解决了实际接地网中接地网场域电阻率和物理尺寸对比度很大的问题，提高了成像效率和成像分辨率。4）开发了接地网数字化管理系统，实现了接地网腐蚀诊断的数据长期跟踪和管理，为接地网状态评估和寿命预测提供了依据。5）开展了接地网内源式EIT成像系统的现场测试与应用，根据测试结果提出了下一步推广应用的改进方案。