Analysis for the abnormal growth of bushing dielectric loss in a 500KV transformer

In the preventive test of a imported 500kV transformer, defects are found in the neutral bushing and mid-voltage side bushing that the dielectric loss grows abnormally. The defective bushings are analysis with the method of dielectric loss comparison, high voltage dielectric loss test, frequency domain dielectric spectrum analysis. And the analysis result shows, the abnormal growth is caused by the defect that the capacitor core is not fully dried. The moisture permeates gradually and increases the power loss. Discovery of this defect lowers the risk of internal insulation breakdown caused by the large power loss and high temperature. Provide a new idea for defect judgment, and avoid long time power failure caused by malfunction of the bushing. It provides reference for the same bushing malfunction in the future.