Trap Characteristic and Potential Trap Model of Water Trees in XLPE

Water trees were generally considered to develop in amorphous regions of Cross-linked Polyethylene (XLPE) material, however the present work proved that the growth of water trees might cause the damage in the amorphous regions as well as the crystalline ones in XLPE. Meanwhile, the trap and physical characteristics of water trees in XLPE samples were discussed in the present work. XLPE samples with a thickness of 5 mm were made by the hot-pressing method, and the samples were aged by the water-needle method with the voltage of 6 kV/5 kHz. After aging for 600 hours, the cultivated water trees with the average branch length of 159.88 μm were observed in the anatomical sections of the samples. In order to study the density and crystallinity, the Raman Spectroscopy (RS) was used to analyze the XLPE sample with/without the water trees. The average density and crystallinity of new samples, the regions without/with water trees of Aged samples were 0.9145 g/cm 3 and 40.12%, 0.9095 g/cm 3 and 36.67%, 0.8999 g/cm 3 and 30.04%, respectively. Meanwhile, the Thermal Stimulus Depolarization Current (TSDC) test was employed to analyze the trap level of samples. And the trap level of the new samples and samples without/with water trees 0.6458 eV, 0.6812 eV and 0.8715 eV, respectively. The densities and crystallinity of regions with water trees were lower than that of the non-defective regions, which indicated that the growth of water tree defects might cause the destruction of both the amorphous and the crystalline region, thus the trap level of the water tree samples increases.