Evaluation of the lifetime of power transformers based on decrease in the strength of insulators supporting the winding

On power transformer in distribution substation, It is said that the life of power transformer is determined by the deterioration of the insulation paper. It is well known that the magnitude of the electromagnetic mechanical force applied to the winding depends on the structure of the windings and iron core. In this paper, to verify the failure behaviour of transformers due to deterioration, we conducted short-circuit tests on core-type disc-winding transformers with an average DP of 200 to 450, which is the life level of insulation paper. The results revealed that transformer failures caused by damage to the insulation paper do not occur, but instead there are transformers that fail due to electromagnetic mechanical forces acting in the axial directio n of the transformer windings (external thrust). Examples of the solid insulating material used in the transformer include structur al materials supporting the winding other than winding insulating paper. The author obtained the thermal deterioration characteristics of the mechanical strength of the insulator supporting the winding by heating it at low temperatures in insulating oil. As a result, it was clarified that one of the causes of failure due to the electromechanical force (external thrust) was a decrease in the strength of the insulator supporting the winding.