The Decisive Influence of Insulation Material Characteristics and Thermomechanical Properties on the Long-Term Service Life of Medium and High Voltage Cables

The insulation material characteristics of medium and high voltage cables are the core factor determining their long-term service life. Cross-linked polyethylene (XLPE) has become the mainstream insulation material for medium and high voltage cables due to its excellent comprehensive performance. XLPE is produced by chemically or physically cross-linking polyethylene molecular chains to form a three-dimensional network structure, significantly improving the material's heat resistance and mechanical strength. XLPE can operate at temperatures up to 90 degrees Celsius and has a short-circuit allowable temperature of up to 250 degrees Celsius, far exceeding that of ordinary polyethylene. This characteristic allows XLPE-insulated cables to withstand larger load currents and provides better resistance to thermal aging. XLPE also has low dielectric loss, high electrical strength, and stable insulation performance under high voltage for long-term operation, making it an ideal material for manufacturing medium and high voltage cables.

The thermomechanical properties of medium and high voltage cables have a significant impact on the cable's structural stability and operational reliability. During operation, the conductor and insulation layer experience thermal expansion and contraction due to changes in load current. If the difference in the thermal expansion coefficients of the materials is too large, stress concentration may occur at the interface, leading to insulation layer cracking or shielding layer detachment. Cross-linked polyethylene (XLPE) has a low coefficient of thermal expansion, resulting in good compatibility with conductors and shielding materials, which is beneficial for maintaining long-term structural stability. The cable insulation layer also possesses a certain degree of elasticity, absorbing dimensional changes caused by thermal cycling and reducing internal stress. The metal sheath or armor layer provides mechanical protection while also limiting thermal expansion, enhancing the overall stability of the cable.

The long-term service life of medium- and high-voltage cables is also affected by the anti-aging properties of the insulation material. Under the combined influence of electric fields, thermal fields, and environmental factors, insulation materials undergo a slow aging process, gradually declining in electrical and mechanical properties. XLPE has excellent resistance to thermal oxidation and water treeing, ensuring a service life of over thirty years under appropriate operating conditions. To improve anti-aging performance, antioxidants and anti-water treeing agents are added to the insulation material to inhibit the aging process. For special applications, ethylene propylene rubber (EPR) or polyvinyl chloride (PVC) insulation materials can be selected to meet specific requirements such as oil resistance and corrosion resistance. Through comprehensive optimization of the insulation material characteristics and thermomechanical properties, medium- and high-voltage cables can maintain stable electrical performance and mechanical integrity during long-term operation, providing reliable protection for the power grid.