Dry-type transformers are widely used in power systems due to their high strength, flame retardancy, and moisture resistance. Among their components, the copper foil winding structure, through the synergistic effect of material properties, process optimization, and structural design, significantly improves short-circuit withstand capability, providing crucial assurance for the stable operation of dry-type transformers under extreme conditions.
The core advantage of copper foil windings lies in their balance between mechanical strength and conductivity. Compared to traditional wire-wound windings, copper foil is wound in a wide, thin strip form, resulting in a larger conductor cross-sectional area and more uniform thickness, effectively reducing current density and electromagnetic forces generated during short circuits. Simultaneously, the high yield strength of copper foil allows it to withstand radial compressive stress and axial tensile stress during short-circuit impacts, preventing winding deformation or breakage. Furthermore, the larger interlayer contact area of copper foil windings reduces contact resistance, lowers the risk of localized overheating, and further enhances mechanical stability.
The epoxy resin casting process is a key step in improving short-circuit withstand capability. Epoxy resin is cast into the copper foil windings under vacuum, and air bubbles are eliminated through a negative pressure environment, ensuring that the resin fully penetrates the conductor gaps to form a dense, high-strength fiberglass structure. This structure not only tightly bonds the copper foil to the insulating material but also enhances the overall shear resistance through the reinforcement of the fiberglass mesh. During a short circuit, the synergistic effect of the resin and copper foil effectively disperses electromagnetic forces, preventing winding displacement or loosening, thus maintaining structural integrity.
The structural design at the winding ends is crucial for controlling local stress. The copper foil winding uses an integral rigid paper tube as an internal support and features a large pressure ring at the end, using a rigid structure to limit axial displacement of the winding. Simultaneously, a stress control ring is added at the high-voltage winding end, utilizing its dielectric constant gradient distribution characteristics to disperse the electric field from the tip to the entire insulation layer, reducing local field strength peaks and preventing insulation breakdown caused by electric field concentration. Furthermore, the winding ends employ a rounded transition design, eliminating stress concentration caused by right-angle structures and further improving short-circuit impact resistance.
Optimization of the pads and support structure is a core measure to reduce winding deformation. Traditional pads are prone to winding shrinkage during short circuits due to insufficient support, while the copper foil winding uses high-strength molded pads, with fiberglass reinforcement to enhance compressive and shear resistance. The spacers are evenly distributed along the circumference and fit tightly against the winding end face, increasing the contact area and friction, effectively limiting rotational force during short circuits. Simultaneously, an elastic positioning device is installed between the spacers and the clamps to buffer short-circuit impacts and prevent structural damage from hard collisions.
The winding ampere-turn balance design reduces electromagnetic force by lowering leakage flux. The copper foil winding employs a segmented, layered winding process, precisely controlling the number of turns and current distribution in each layer to achieve the best possible balance in ampere-turns. This design reduces the leakage magnetic field strength, thereby lowering the electrodynamic force generated by the combined effect of leakage flux and short-circuit current during a short circuit. Furthermore, the balance design optimizes the electric field distribution, avoiding localized insulation overload and further enhancing short-circuit withstand capability.
The longitudinal ventilation ducts balance heat dissipation and structural strength. Ventilation gaps are reserved between layers of the copper foil winding, reducing operating temperature rise through air convection and minimizing insulation aging caused by thermal expansion. At the same time, the ventilation duct design does not weaken the winding's mechanical structure; instead, its rational layout enhances overall rigidity. During a short circuit, the ventilation structure helps disperse electromagnetic forces, preventing damage to the windings due to localized stress concentration.
The copper foil winding structure, through multi-dimensional innovations in material properties, casting process, end design, support optimization, ampere-turn balance, and ventilation design, constructs a high-strength short-circuit resistant system. Its core logic lies in dispersing short-circuit stress through structural optimization and enhancing mechanical stability through material synergy, thereby ensuring reliable transformer operation under extreme conditions. This design not only extends the service life of dry-type transformers but also reduces operation and maintenance costs, providing crucial protection for the safe and stable operation of power systems.
