Study on Failure Mechanism of Oil Paper Insulation Under Partial Discharge of Interlayer Bubble

Partial discharge (PD) induced by bubble will reduce the insulation performance, lead to insulation failure and seriously affect the safe operation of power transformer. Studying the influence of PD in internal bubble on oil paper insulation and understanding the insulation failure mechanism can provide guidance for engineering practice. In this paper, a bubble PD defect model is designed to obtain the mechanism of PD degrading insulation. The inception and breakdown voltage of PD decrease seriously with the increase of bubble area and height. Combined with the surface state of breakdown paper observed by electron microscope, it is concluded that PD can induce the breakdown of oil paper insulation. Then, through the comparative analysis of bubble area and PD parameters, a positive feedback model for insulation degradation is obtained, representing that bubble defects will deteriorate rapidly in exponential form under the effect of PD. Finally, combined with the electron microscope and energy spectrum analysis, the deterioration process of insulating paper is divided into four stages, obtaining the micro deterioration and failure mechanism of insulating paper. This study contributes to understanding the mechanism of insulation failure by bubble, as well as provides a reference for risk assessment of transformers.