Effect of Thermal Aging on the Cable Insulation Properties of AC Distribution XLPE Cables Under DC Operation

In order to study the effect of thermal aging on the insulation properties of the AC distribution cross-linked polyethylene (XLPE) cable under DC operation, a sample of 10 kV AC XLPE cable that has been in operation for two years is subjected to an accelerated thermal aging test at 135 ℃ in this paper. Through the DC conductivity, space charge measurement, surface potential decay, and DC breakdown tests, combined with the calculation of carrier mobility, activation energy, and trap parameters, the DC insulation properties of AC distribution XLPE cables before and after aging are studied. The results show that, as the aging time increases, the DC conductivity and carrier mobility of the AC XLPE cable insulation sample decrease first and then rise. After long-term aging, the space charge accumulation electric field threshold and activation energy of the samples decrease significantly. As the test temperature increases, the DC conductivity of the sample increases and the electric field threshold decreases. Meanwhile, the accumulated space charge changes from hetero-charge accumulation to homo-charge accumulation with the increase of aging time. The number of deep traps and the DC breakdown strength both increase first and then decrease. Analyses show that short-term thermal aging is beneficial to improve the DC insulation properties of AC distribution XLPE cables. © 2021, High Voltage Engineering Editorial Department of CEPRI. All right reserved.