Research on Condition Assessment Methods of In-Service 110kV and 220kV XLPE Cables

XLPE cables have been operational for decades within urban transmission and distribution networks. Influenced by various stresses in the underground environment, the insulation performance of these cables has significantly deteriorated, resulting in increased accidents. Therefore, it is necessary to assess the condition of operating high-voltage XLPE cables. This study focuses on 13 high-voltage XLPE cables with different operating periods. Fourier transform infrared spectroscopy, differential scanning calorimetry, X-ray diffraction, broadband dielectric spectroscopy, AC breakdown test, and tensile test were used to analyze the changes in electrical characteristics, physicochemical properties, and mechanical performance of the cables. Additionally, the dependency of each performance parameter on the aging state was evaluated. Finally, parameters such as melting temperature, elongation at break, relative permittivity, breakdown field strength, and Gibbs free energy were selected as input variables to establish a cable condition assessment method based on fuzzy diagnosis. The accuracy of this method was confirmed through case studies.