High Purity Copper Foil for Transformer Windings
2026-10-29
In the manufacturing of foil-wound transformers, the purity level of the copper foil directly determines the winding's electrical conductivity, temperature-rise characteristics, and long-term operational lifespan. Standard industrial-grade copper foils often contain impurities that limit electrical conductivity and structural stability, failing to meet the design requirements for high-efficiency transformers. Haomei Aluminum offers high-purity copper foil specifically engineered for transformer windings. By utilizing C11000 electrolytic tough-pitch copper and strictly controlling purity from the initial smelting stage, we provide global transformer manufacturers with a conductive material solution that ensures low energy loss and high consistency.
The performance advantages of this high-purity copper foil are rooted in rigorous compositional control. Produced from high-purity copper cathodes—processed through vertical continuous casting and multi-pass cold rolling—the material maintains a total copper-plus-silver content of at least 99.90%. Oxygen content is precisely regulated between 0.02% and 0.04%, while the combined concentration of harmful impurities—such as bismuth, antimony, arsenic, and lead—is kept below 0.03%. Impurity atoms act as electron-scattering centers within the copper crystal lattice; even an increase in impurities by as little as 0.01% (one part in 10,000) can lead to a measurable decline in electrical conductivity. Through precise control of chemical composition, the finished transformer copper foil achieves a stable electrical conductivity of 100%–101% IACS, with a room-temperature resistivity as low as approximately 0.0172 Ω·mm²/m—significantly outperforming standard industrial-grade copper foil. Based on extensive industry experience, the gain in electrical conductivity resulting from higher purity can reduce transformer load losses by 2%–3%; over an operational lifespan of 20 years or more, the cumulative energy savings far outweigh the initial cost difference of the material.
In terms of mechanical properties and process compatibility, the high-purity copper foil undergoes bright annealing in a protective atmosphere to achieve a stable, fully soft (O-temper) state. The Vickers hardness is controlled within the range of HV55–HV65, with a deviation of no more than HV5 across the entire width, and an elongation at break of ≥35%. This uniform softness ensures smooth bending and fitting on high-speed foil-winding production lines, with minimal springback. Once wound, the layers fit tightly together, enabling a winding fill factor of over 90%. The complete elimination of internal residual stress also prevents stress release and winding displacement during long-term thermal cycling, thereby reducing the risk of mid-term operational failures. For the wide-strip windings used in large-capacity transformers, consistent performance across the entire width is critical; the uniform purity of this copper foil ensures stable and consistent forming characteristics throughout the entire coil.
High-precision standards are also applied to dimensions and surface quality. Haomei offer thicknesses ranging from 0.05 mm to 2.0 mm, with slitting widths customizable to specific winding designs. Thickness tolerances are strictly controlled based on the gauge—achieving precision as fine as ±0.005 mm for thinner foils—while edge straightness is maintained at ≤1 mm/m. The surface of transformer copper foil undergoes rigorous multi-stage cleaning to ensure it is free from rolling oil residues, oxidation spots, and roller marks or scratches. Furthermore, the edges can be precision-rounded to remove burrs and sharp corners, which helps suppress inter-layer partial discharge and increases the partial discharge inception voltage (PDIV) of the windings. The clean surface condition ensures excellent compatibility with insulating paper, epoxy resin, and transformer oil, without inducing any degradation of the insulating media.
Haomei Aluminum's high-purity copper foil complies with international standards such as ASTM B152. Each coil is supplied with comprehensive material certification and performance test reports. We offer customized, large-coil-weight options to minimize the number of joints in windings, and provide vacuum-sealed, moisture-proof packaging suitable for long-distance ocean transport. Haomei copper foil products are widely used in dry-type transformers, oil-immersed transformers, step-up transformers for photovoltaic and wind power generation, and high-frequency reactors. We provide tailored material selection advice based on your specific voltage class and energy efficiency requirements. Please contact us for detailed specifications, pricing, and customized solutions.