The aging resistance of the insulation layer in a composite shielding insulation sleeve is influenced by multiple factors, and its aging mechanism involves a complex interaction of electrical, thermal, mechanical, environmental, and intrinsic material properties.
Electric field effects are one of the key factors inducing insulation aging. During long-term operation, the insulation layer must withstand the impact of system voltage and overvoltage. Areas with concentrated electric fields (such as conductor corners and air gap defects) are prone to partial discharge. Charged particles generated by this discharge collide with the insulation material, leading to molecular chain breakage, chemical bond disruption, and the formation of dendritic discharge channels. This electro-aging process gradually erodes the insulation layer, reducing its breakdown resistance. Furthermore, lightning overvoltages or operational overvoltages can directly break down the insulation, causing irreversible damage.
Temperature has a dual effect on insulation aging. On the one hand, high temperatures accelerate the thermal decomposition reactions of the insulation material, such as oxidation and polymer chain breakage, leading to material hardening, embrittlement, and decreased mechanical strength. On the other hand, increased temperature reduces insulation resistance, increases dielectric loss, and creates a thermo-electric coupling aging effect. For example, in high-temperature environments, the heat generated by partial discharge is difficult to dissipate, further exacerbating material degradation. Studies show that for every 10°C increase in temperature, the insulation lifespan may be halved, but the thermal aging rate varies among different materials.
Mechanical stress is a significant factor affecting the durability of insulation layers. During installation, operation, or short-circuit faults, the insulation layer may be subjected to mechanical loads such as tension, bending, and vibration. Long-term mechanical stress can lead to microcracks, delamination, or interface debonding in the insulation layer, providing pathways for moisture and gas intrusion and accelerating the composite aging process. For example, vibration may weaken the bond strength between the insulation layer and the conductor or shielding layer, creating localized weak points.
Ambient humidity has a significant impact on insulation performance. Moisture intrusion into the insulation layer reduces its volume resistivity, increases dielectric loss, and may even induce electrical dendrites. In high-humidity environments, a conductive water film may form on the insulation surface, leading to surface discharge or a decrease in flashover voltage. Furthermore, moisture reacts with chemical components in the insulation material (such as plasticizers and fillers) to potentially generate acidic substances, further corroding the insulation structure. For composite shielding insulation sleeves used outdoors, rain, snow, and condensation significantly exacerbate humidity-related aging.
Chemical corrosion is a potential factor leading to insulation degradation. The insulation layer may come into contact with oxygen, ozone, nitrogen oxides in the air, or corrosive media such as acidic gases and salt spray in industrial environments. These substances can react chemically with the insulating material, damaging its molecular structure and causing it to become brittle, discolored, or lose elasticity. For example, ozone attacks the double bonds in rubber-based insulation materials, initiating a chain oxidation reaction that significantly reduces its mechanical properties.
The intrinsic properties of the material and the manufacturing process play a decisive role in the aging resistance of the insulation layer. Different matrix materials (such as silicone rubber, epoxy resin, and polytetrafluoroethylene) exhibit significant differences in heat resistance, weather resistance, and chemical resistance. The type and dispersion uniformity of fillers, crosslinking density, and impurity content, among other process parameters, also affect the density and stability of the insulation layer. For example, nanofillers can improve the corona resistance of insulation materials, while manufacturing defects (such as pores and cracks) can become the starting point for aging.
The aging resistance of the composite shielding insulation sleeve is the result of the combined effects of electrical, thermal, mechanical, environmental, and material properties. To extend its service life, comprehensive measures are needed from multiple dimensions, including material selection, structural design, manufacturing process optimization, and operating environment control. For example, using a silicone rubber matrix with better weather resistance, optimizing the electric field distribution to reduce partial discharge, and enhancing the interfacial bonding strength between the insulation layer and the shielding layer.
