Space Charge and Conduction Characteristics of XLPE with Different Ageing

Cable crosslinked polyethylene (XLPE) insulation will accumulate space charge under high voltage DC condition, which will cause the electric field distribution to deviate from the expected value and even cause insulation breakdown. The spatial charge distribution contains information and characteristics about charge transport in the insulation, while the leakage current contains information about charge injection and extraction behavior occurring across the electrode/dielectric interface. In this paper, the correlation properties of the space charge and current of XLPE material with the aging state of the insulation is obtained by simultaneously measuring those on the insulated sections of aged and unaged DC cables. It shows that the space charge accumulation in the voltage application process increases with the prolonging of aging time, and the average charge density becomes more significant with the aging time. The time required for the holes injected by the upper electrode to reach the charge region of the lower electrode is greatly shortened with the aging degree, indicating that the internal carrier increases with the deepening of the aging degree of the sample. At the same time, there are more defects and faster migration. The difference of mobility in depolarization stage indicates that aging brings more deep traps, and the ratio of deep and shallow traps has some increase.