Considering Moisture Intrusion Evolution Law of Insulation Performance of High-Voltage AC XLPE Cables

The outer sheaths of cables can be damaged by factors, such as mechanical stress, chemical corrosion, and aging, leading to moisture intrusion. This seriously threatens cable insulation performance and may even induce discharge accidents. Based on the corrugated aluminum sheath structure of the cables and moisture diffusion mechanism, the moisture intrusion (moisture absorption) process can be divided into three stages: water-blocking tape adsorption, air-gap wetting, and main insulation diffusion. First, through experimental tests, key electrical parameters such as capacitance, dielectric constant, and dielectric loss of 66 kV cables and XLPE main insulation samples in different moisture absorption stages were obtained. Furthermore, using finite element simulation, theoretical analysis and verification of the parameter variation characteristics of the cable were conducted by adjusting the moisture content and varying the moisture-affected positions. The results show that the electrical parameters of the cable body change most significantly in the third stage of moisture absorption: when the moisture absorption degree increases by 0.01%, the cable body capacitance increases by 1.2% and the insulation resistance decreases by 3.7%; for the XLPE insulation samples, when the moisture absorption degree increases by 0.25%, the relative dielectric constant increases by 0.7%, the conductivity increases by 1.4%, and the dielectric loss increases by a factor of 1.6 times at lower frequencies. In addition, the changes in the main insulation parameters were only related to the moisture content and were not affected by moisture distribution.