Effect of Thermal Aging on DC Conductivity of NANO-CB/XLPE Insulating Composites

The modification of crosslinked polyethylene by nano-carbon black is a possible way to develop the insulating materials of HVDC cables. The thermal aging performance of nano-CB/XLPE composite materials is critical to the long term operation reliability of HVDC cables. The electric field distribution of HVDC cable depends on the conductivity which is a nonlinear function of the electric field and temperature. Therefore, the influence of different aging time on conductivity of nano-CB/XLPE composites is investigated in this paper. Fourier transform infrared spectroscopy(FTIR) was used to characterize the aging degree of composite materials. Scanning electron microscopy(SEM) and differential scanning calorimetry(DSC) were used to explore the microstructure changes during aging. Experimental results show that the aging process of nano-CB/XLPE composites can be divided into two stages with aging time. At the initial stage of aging, the carbonyl index of composites increases slowly and conductivity decreases with the aging time, and the activation energy and electric field dependence coefficient are larger. At the later stage of aging, the carbonyl index of the composites increases rapidly and the crystallinity decreases, and the activation energy and the electric field dependence coefficient decrease with aging time.