As a core component in electrical systems, the composite shielding insulation sleeve provides mechanical support, electromagnetic shielding, and electrical insulation. Its mechanical strength and stability are directly related to the long-term operational safety of the equipment. To ensure the composite shielding insulation sleeve withstands long-term damage under complex operating conditions, a multi-dimensional reliability assurance system must be established, encompassing material selection, structural design, manufacturing processes, and environmental adaptability.
The mechanical strength of the composite shielding insulation sleeve primarily depends on the optimal material balance. The inner mechanical support structure typically utilizes an epoxy resin and glass fiber composite material, with the glass fiber content precisely controlled within the 60%-70% range. A low fiber content results in insufficient tensile strength, while a high content can lead to poor resin penetration and localized stress concentrations. The outer insulation layer is often made of polymer materials such as silicone rubber or cross-linked polyethylene. These materials require high elastic modulus and tear resistance. For example, the elongation at break of silicone rubber must exceed 300% to effectively absorb mechanical shock. Furthermore, the conductor shield and insulation shield layers utilize semiconductor materials, whose thermal expansion coefficients must closely match those of the insulation layer to prevent delamination due to temperature cycling.
In terms of structural design, the composite shielding insulation sleeve utilizes a multi-layered synergistic mechanism to enhance overall mechanical strength. The inner epoxy fiberglass tube provides rigid support, the middle insulation layer achieves electrical isolation, and the outer shielding layer provides both electromagnetic and mechanical protection. For example, in the design of a composite bushing for a 500kV circuit breaker, increasing the curvature radius of the shield and adjusting the dielectric constant gradient reduces the maximum field strength under lightning overvoltage by 37%, thereby reducing damage to the structure caused by electromechanical stress. Furthermore, the optimized shed structure significantly improves bending resistance. Increasing the shed spacing and shed extension optimizes the electric field distribution, while also preventing surface discharge in rainy and snowy weather and avoiding material degradation caused by localized overheating.
Precision control in the manufacturing process is critical to ensuring mechanical strength. Epoxy resin casting requires a vacuum degassing process to eliminate air gaps within the material and prevent insulation breakdown caused by localized discharge. During the glass fiber winding process, the tension control system must control fiber tension fluctuations within ±5% to ensure uniform fiber distribution. Plasma activation technology is used for interface treatment, increasing the bond strength between epoxy resin and silicone rubber to over 2.5 MPa, effectively preventing interlayer separation. For prefabricated composite shielded insulated tubular busbar bushings, a three-layer co-extrusion process achieves integrated molding of the conductor shielding layer, insulation layer, and insulation shielding layer, maintaining wall thickness uniformity within ±0.1 mm and eliminating stress concentration caused by thickness variations.
Environmental adaptability design requires specialized optimization for different operating conditions. In high-altitude areas, the use of UV-resistant silicone rubber and an increased dry arc distance to 1.3 times that of conventional designs provide resistance to the combined effects of strong UV rays and low air pressure. For humid environments, the longitudinal wrapping of aluminum-plastic composite tape, achieved through hot or cold bonding, provides radial water resistance, preventing hydrolysis caused by moisture intrusion. In high-temperature environments, a polyimide material with a temperature resistance rating of 200°C, combined with a ceramic silicone rubber coating, ensures the bushing maintains structural integrity during short-circuit faults.
A full lifecycle management system is required to maintain mechanical strength during long-term use. Regular ultrasonic partial discharge testing and X-ray tomography can promptly detect internal air gaps and cracks. Casings in operation for more than 15 years require dielectric loss tangent (tanδ) testing. A tanδ value exceeding 0.5% indicates irreversible material degradation and requires immediate replacement. Furthermore, a mechanical stress monitoring system has been established, using fiber grating sensors to collect real-time bending strain data. When the strain exceeds 80% of the material's allowable stress, an early warning is triggered, effectively preventing fractures caused by mechanical overload.
