How do insulators improve the creepage distance and arc resistance of dry-type transformers?
Publish Time: 2025-10-29
In power systems, dry-type transformers are widely used in high-rise buildings, subways, hospitals, data centers, industrial plants, and other locations with extremely high safety requirements due to their advantages such as fire resistance, explosion protection, oil-free operation, and maintenance-free operation. As one of their core insulation structures, corrugated column insulators not only provide mechanical support and electrical isolation but also play a crucial role in improving the overall insulation performance of the equipment. Especially in complex operating environments with high voltage, high humidity, and high pollution, the design of the insulators directly determines the insulation reliability of the transformer. Creepage distance and arc resistance are two core indicators for measuring its insulation capability, and corrugated column insulators effectively improve these two key performance characteristics through their unique structure and material technology.1. Creepage Distance: The "Path Extension" Effect of Corrugated StructuresCreepage distance refers to the shortest path length along the surface of the insulating material between two conductive components. In humid, dusty, or polluted environments, a conductive film may form on the surface, leading to surface discharge or even flashover. Therefore, sufficient creepage distance is a prerequisite for preventing surface breakdown. Traditional flat-plate insulators have short surface paths, making them prone to surface discharge. Dry-type transformers, however, use corrugated cylindrical insulators, which significantly extend the path of surface discharge by designing multiple annular or spiral raised corrugations on the cylindrical surface. This "folded" structure forces the arc to zigzag along the crests and troughs, increasing the actual creepage distance by 2-3 times compared to a straight line. Simultaneously, the corrugated structure effectively blocks the continuous deposition of contaminants, forming "anti-contamination ridges," and in rainy or foggy weather, it acts as a "skirt effect," interrupting the continuity of the water film, further enhancing flashover resistance.2. Arc Resistance: Dual Protection of Materials and StructureArc resistance refers to the ability of insulating materials to resist carbonization, cracking, and the formation of conductive paths under the high temperature of an electric arc. Dry-type transformers may generate arcs during overvoltage, operational shocks, or partial discharges. If the insulators have poor arc resistance, they are prone to carbonization, forming conductive paths and leading to permanent breakdown. Corrugated insulators are typically molded using an epoxy resin system via vacuum casting. Epoxy resin possesses excellent dielectric strength, a high glass transition temperature, and outstanding arc resistance. Under the high temperature of an electric arc, high-quality epoxy resin forms a dense carbonized layer, rather than a loose, conductive carbon black, effectively preventing the arc from penetrating deep into the material. Furthermore, the corrugated structure itself increases the difficulty of arc propagation along the surface, prolonging the arc extinction time and improving overall arc resistance.3. Electric Field Optimization: Suppressing Partial DischargeThe geometry of the corrugated insulator helps to homogenize the electric field distribution. Between the high-voltage and low-voltage windings, the electric field tends to concentrate at sharp corners or edges, triggering partial discharge. The smooth transition design of the corrugations avoids abrupt changes in the electric field, reducing areas of high local field strength. Simultaneously, the air gaps between the corrugations form a multi-layered dielectric structure with the insulator, playing a role in electric field regulation and further suppressing partial discharge. Before leaving the factory, corrugated insulators must undergo partial discharge testing to ensure insulation stability during long-term operation.4. Mechanical Strength and Thermal StabilityCorrugated columns not only provide insulation but also withstand the weight of the windings, short-circuit electrodynamic forces, and thermal expansion and contraction stresses. Epoxy resin, when combined with reinforcing materials, offers high strength and a low coefficient of thermal expansion, ensuring resistance to deformation and cracking within a wide temperature range of -40°C to +130°C. Structural integrity is essential for maintaining creepage distances and arc resistance.5. Environmental and Fire Protection AdvantagesEpoxy resin corrugated column insulators feature a fully solid-state structure and contain no oil, eliminating fire hazards. Even under extreme fault conditions, they will not support combustion, meeting the stringent fire safety requirements of modern buildings.Corrugated column insulators for dry-type transformers utilize a comprehensive design featuring increased corrugation distance, arc-resistant materials, and field-balancing structures, significantly improving creepage distances and arc resistance. They not only provide an electrical isolation barrier but also serve as the "insulating backbone" that ensures safe, reliable, and long-life operation of the transformer. In today's increasingly intelligent and high-density power systems, these insulators, which integrate structural innovation and materials technology, are continuously driving the development of dry-type transformers towards higher voltage levels, harsher environments, and longer lifespans.
