Partial discharge of a 500 kV power transformer seriously exceed under 680 kV in routine ACSD test. After the accident

phased oil sampling analysis is taken to the transformer

the diagnostic tests are carried out after check wiring and test equipment. The oil sample test and analysis results indicated the fault of transformer is internal fault. Subsequently

the high-voltage head hanging core examination reveals the outermost insulation and regulated lead insulation wood screws and other parts have traces of discharge. Through the discharge site and the surrounding electric field simulation analysis

clear the discharge path

combined with experimental phenomena

determines that the failure is caused by a design flaw of the transformer and low dielectric strength of the insulation member caused. The corresponding maintenance treatment program is proposed. The accident analysis and processing programs can provide proposals for improving the follow-up of power transformer design and production process.