Failure modes of insulating pressboard subjected to high electric fields and durations: Evidence of partial discharge and changes at the microscopic scale

Abstract

The deterioration of insulation pressboard under needle-plate discharge was tested, and the degradation stage was divided according to observed experimental phenomena. Based on the improved Top-hat watershed image segmentation method, the white marks area of the pressboard were tested. Fibres with different discharge states were extracted from SEM images. The fibre width was calculated, and the porosity of the surface of the insulation pressboard at different degradation stages was calculated. Simultaneously, the 3D reconstruction technique was used to observe the 3D morphology of fibres at different discharge stages. The study found that with the deepening of the discharge process, the discharge of the pressboard increased, and the white marks of the pressboard continued to expand from point to surface. In addition, the diameter of the fibre of the insulating pressboard decreased obviously with the increase of the pressing time, and the fibre diameter was 89.6% after the breakdown. Moreover, the electrical stress had a great effect on the expansion of the interlayer pores of the pressboard; the cross-section porosity of the insulating pressboard gradually increased with the deepening of the discharge process, and after breakdown, the interlayer porosity reached 12.5%.