Influence of Interfacial Contact Morphology on High Frequency Breakdown Strength and Partial Discharge Characteristics of Epoxy-Polyimide

The air cavities at the interface are an important cause of partial discharge (PD) in SST composite insulation. Therefore, it is of great practical significance to study the partial discharge and breakdown characteristics of composite insulation air cavities under high frequency electric stress. In this article, the interface breakdown strength and partial discharge characteristics under different interface contact morphologies were studied by building a high frequency discharge test system. Experimental results of interface discharge show that breakdown voltage is significantly affected by surface roughness and contact pressure. When the surface roughness increases from 1.23 μm to 4.39 μm, the interface breakdown voltage of the air gap defect at # 2000 mesh decreases from 19.34 kV to 12.91 kV. Under different contact pressures, the variation of breakdown voltage of air cavities with surface roughness is basically consistent. The results of PD characteristics show that, increasing the surface roughness will reduce the partial discharge inception voltage of the air cavities, and the partial discharge amplitude and discharge times will increase with the surface roughness. Combining the effects of secondary electron emission yields (SEEY), resistivity and surface roughness on charge dissipation process, the formation mechanism of interface discharge induced by air cavities under high frequency stress is revealed. This work can provide a theoretical reference for the study of the effect of air cavities on composite insulation characteristics under high frequency stress.