Abstract:Measuring DC resistance of winding is an important item in transformer test. For large transformers directly connected to GIS terminals, By measuring the DC resistance of the transformer winding, it is possible to check whether the conduction circuit connected with the transformer has any defects such as poor contact, poor welding and coil failure. Because of the need to dismantle the connection between the transformer outlet and GIS when measuring the DC resistance of the high voltage winding, the workload and the risk are large, so in the routine annual preventive test, the high voltage end GIS knife sluice is pulled apart when measuring the DC resistance of the high voltage side winding of the transformer, the ground knife sluice is closed, the external grounding connection is disconnected, then measured the DC resistance of winding between the leading-out end of the ground knife sluice and neutral point.In the process of winding DC resistance measurement for high voltage side of a 500kV #4B transformer,found the fracture of the axis pin of operation mechanism for the 500kV GIS earting swith event ,This paper described the discovery process, inspection, defect analysis, processing, and put forward the corresponding suggestions for the subsequent GIS operation and maintenance