Abstract: This paper analyzes the causes of the main transformer tripping event induced by insulation damage on the 10 kV side equipment due to water leakage in a substation building, and proposes corresponding treatment measures and preventive recommendations. The incident was caused by insulation aging and roof leakage, which triggered zero-sequence protection, overcurrent protection, and differential protection of the main transformer, ultimately leading to tripping. Detailed discussions are presented on insulation damage, protective actions, external environmental factors, and human factors, highlighting the importance of equipment maintenance, protection system calibration, and environmental monitoring and management. Through on-site emergency response, equipment repair and replacement, and system adjustment and optimization, detailed follow-up monitoring and preventive measures were developed, along with corresponding operation and maintenance recommendations, to ensure the safe and stable operation of the power grid.