Views: 0 Author: Site Editor Publish Time: 2026-10-06 Origin: Site
Composite insulators with silicone rubber (SIR) housings have become the dominant choice for high-voltage transmission lines worldwide, valued for their lightweight construction, superior hydrophobicity, and excellent pollution flashover resistance. However, prolonged outdoor exposure to UV radiation, electrical stress, temperature cycling, and acidic precipitation inevitably triggers material degradation. A typical manifestation is surface chalking accompanied by micro-crack networks, often observable after 5 to 15 years of service. The degraded surface layer can reach thicknesses of up to 250 μm, with hydrolytic degradation of siloxane chains reducing molecular weight and causing loss of flexibility. This article examines practical field repair approaches—RTV silicone coating restoration and structural shed patching with interface sealing enhancement—that offer cost-effective alternatives to complete insulator replacement.
Before any intervention, a systematic assessment is essential. Aged SIR sheds exhibit a characteristic three-layer structure when examined under optical microscopy: an opaque white chalking layer (0.3–0.5 mm), a translucent transition layer, and an unaffected core layer. The aging process develops “outside-in,” so the thickness of the chalking layer serves as a reliable indicator of degradation severity. In-service insulators can be classified into three categories: those with no evident aging, those where aging is reparable, and those beyond repair. If cracking is confined to the chalking and transition layers, field repair is feasible. However, cracks extending into the core or exposing the fiber-reinforced epoxy rod generally mandate replacement.
For superficial cracking without significant material loss, the application of room-temperature-vulcanizing (RTV) silicone coating represents the most practical field solution. RTV coatings, typically one-part condensation-curable materials, restore surface hydrophobicity and provide a protective barrier against further environmental degradation. The repair procedure begins with mechanical grinding using handheld rotary tools to remove the chalking layer, followed by compressed air cleaning to eliminate particulate debris. Pulsed laser ablation has emerged as a promising alternative that selectively removes the aged layer without damaging the underlying substrate while simultaneously enhancing hydrophobicity.
The RTV coating should be applied uniformly at a thickness of 0.2–0.5 mm per pass, with a minimum total thickness of 0.4 mm recommended for effective protection. Studies have demonstrated that this approach effectively improves the degraded surface condition of silicone rubber housings, with hydrophobicity restored to HC1 classification after treatment.
For deeper cracks or erosion defects exceeding 1 mm in depth, a more structural approach is required. Specialized quick-repair adhesives formulated from methyl vinyl silicone rubber (with vinyl content of 0.04–0.20%), modified fumed silica, vinyl silicone oil, composite silane coupling agents, hydroxyl silicone oil, activated aluminum hydroxide powder, and peroxide vulcanizing agents have been developed. These formulations are engineered to cross-link with the substrate surface and, after vulcanization, exhibit physical, chemical, and electrical properties essentially matching those of the original shed material.
The field repair procedure involves several critical steps. First, the damaged contact surfaces are sloped to form single or multiple inclined planes, increasing the contact area with the repair adhesive and providing structural support. The surfaces are then roughened to create a pitted texture that promotes mechanical interlocking. The adhesive is applied to fill the defect, shaped to match the original shed contour, and cured under controlled heating. This heating step activates cross-linking between the original material and the repair adhesive, enabling both sides of the interface to undergo vulcanization and significantly enhancing the overall strength of the repaired shed.
The long-term reliability of any field repair depends critically on the quality of the interface between the repair material and the original SIR substrate. Weak macroscopic interfaces between the FRP epoxy core and the silicone rubber housing represent a known vulnerability. Research indicates that interfaces formed through cured bonding exhibit better long-term stability compared to glued ones, making cured bonding the more suitable method for repairing damaged insulator sheds under field conditions.
Several strategies enhance interface sealing performance. The application of an adhesive primer layer prior to repair material application significantly improves bonding strength. Without primer, bonding between epoxy and silicone rubber is substantially reduced. Silane coupling agents incorporated into the repair adhesive formulation further promote chemical bonding at the interface by forming covalent bridges between the silicone rubber substrate and the repair compound.
For end-fitting sealing, where the connection between the insulator body and metal flange is vulnerable to moisture ingress, a comprehensive sealing approach has been developed. This method involves cleaning the damaged sealing structure, applying annular adhesive strips to define the treatment zone, and then brushing RTV silicone rubber over the sheath and flange surfaces to form an integrated sealing structure. After curing, the temporary adhesive strips are removed and the sealing structure is trimmed to specification.
Field repair of aging composite insulators through RTV silicone coating and structural shed patching with interface sealing enhancement offers a technically sound and economically viable alternative to complete replacement. The success of these interventions depends on three pillars: accurate assessment of aging extent, proper surface preparation, and robust interface bonding. As utilities worldwide face increasing populations of aging composite insulators, these field repair technologies will play an increasingly important role in extending service life and maintaining transmission reliability.
