Understanding the Crystalline Region Damage Mechanism of XLPE in Water Tree Propagation by Erosion Method

This study investigates the damage characteristics and mechanism of the crystalline regions of cross-linked polyethylene (XLPE) in water tree propagation. XLPE cable samples are subjected to an accelerated water tree aging at a voltage of 7.5 kV/400 Hz for 240, 480 and 720 hours. After the water tree aging, the crystalline structural changes of the water tree samples are observed by X-ray diffraction (XRD). In addition, the water tree samples are eroded and the morphologies of the crystalline regions in water tree regions are observed by a scanning electron microscope (SEM). The XRD results show that the crystallinities of the aged samples decrease with aging, especially after 240 hours. The SEM results show that after 240 hours of aging, slip lines and dislocation steps emerge on the fracture surfaces. After 480 hours, microcracks with sizes of several micrometers are observed in the directions of the crystal faces. After 720 hours, conical dislocation pits appear in the samples and there are microvoids at the bottoms of the pits. Based on the XRD and SEM results, it is concluded that the crystalline regions of XLPE are damaged in the water tree aging. At last, the initiation process of the dislocations and the damage characteristics of the crystalline regions in the water tree propagation are discussed.