Abstract:This paper takes the event of a mother differential protection malfunction at a 500kV substation as the research object, and systematically explores the mechanism of protection malfunction caused by two-point grounding through on-site inspection, reproduction experiments, and theoretical analysis. Through the analysis and experimental verification of the equivalent model of the grounding grid, the paper further quantifies the size of the induced current caused by two-point grounding and its influence range on the protection action. Based on the research conclusions, the paper proposes improvement suggestions for the secondary circuit design and standardized operation procedures, providing theoretical support and practical guidance for the operation and maintenance of the power grid.