Copper Strip For Oil-Immersed Transformer

2026-09-10

In high-voltage power transmission and distribution backbone networks and large-capacity substations, oil-immersed transformers play a pivotal role in voltage conversion, thanks to their excellent heat dissipation and insulation reliability. Unlike dry-type transformers that operate with air insulation, the windings here remain submerged in high-temperature insulating oil for extended periods. This environment presents multiple challenges—including oil compatibility, electrochemical corrosion, and long-term thermal aging—placing specific demands on the purity, microstructural stability, and surface quality of the conductive substrate. Haomei Aluminum leverages its deep expertise in electrical copper processing to produce copper strip for oil-immersed transformer conditions. These copper strips are engineered—from material composition to processing details—to be fully compatible with the oil-immersed environment, providing stable winding material support for large-capacity power transformers.

High purity and low impurity precipitation are the core material requirements for copper strips used in oil-immersed transformers. Standard industrial copper strips often contain higher levels of impurities; during long-term operation at oil temperatures of 80–105°C, impurities at grain boundaries tend to leach into the insulating oil. This process reduces the oil's dielectric strength, increases its acid value, accelerates oil aging, and shortens maintenance intervals. Haomei Aluminum’s copper strips for oil-immersed transformers utilize C11000 electrolytic tough-pitch copper, featuring a combined copper and silver content of at least 99.90%. The material undergoes strict control of harmful impurities such as bismuth, arsenic, and lead, with oxygen content stabilized below 0.02% to minimize leachable impurities at the source. The finished product maintains a stable conductivity of 100%–101% IACS, ensuring low load losses under high-current conditions and excellent control over winding temperature rise, thereby meeting the low-loss design requirements of large-capacity transformers. To address the specific requirements of winding oil-immersed transformer coils—which involve wide strips, thick cross-sections, and high-tension winding—this product utilizes a continuous bright annealing process in a protective atmosphere. This ensures complete recrystallization and the total elimination of residual stress, resulting in a stable "O-temper" (fully annealed) state. The Vickers hardness is controlled within the HV55–HV65 range, with a hardness deviation across the full width of no more than HV5 and an elongation at break of ≥35%. Uniform mechanical properties ensure consistent stress distribution during high-tension winding, resulting in tight inter-turn contact without gaps and a high winding fill factor. Furthermore, the absence of internal residual stress prevents winding displacement and insulation deformation caused by stress release during long-term operation. Based on my years of industry experience, many mid-term winding failures in main grid transformers can be traced back to uneven copper strip annealing and the slow release of residual stress.

Surface and edge quality are critical to the long-term stability of oil-immersed systems. The transformer copper strip edges undergo precision rounding to remove slitting burrs and sharp corners; this inhibits partial discharge between winding layers and prevents electrochemical corrosion from initiating at sharp edges. The surfaces undergo multiple cleaning stages to ensure they are free of rolling oil residues and oxidation stains, offering excellent compatibility with both mineral and synthetic insulating oils without inducing oil degradation or sludge formation. Available in thicknesses ranging from 0.2 mm to 3.0 mm with customizable widths, the product maintains a thickness tolerance within ±0.005 mm, meeting the precision winding requirements for various high-capacity coils.

Haomei Aluminum offers customized supply with large coil weights, minimizing the number of intermediate winding joints, reducing the risk of welding defects and joint losses, and facilitating the continuous production of long windings. Each coil comes with comprehensive material certification and performance test reports compliant with ASTM international standards, ensuring seamless integration into global transformer manufacturing supply chains. As global power grids undergo expansion and upgrading, large-capacity oil-immersed transformers are evolving toward higher voltage ratings and extended service lives. Consequently, copper strips for oil-immersed transformers—optimized for specific applications—are no longer mere adaptations of general-purpose copper materials; rather, they are products deeply customized based on operational conditions and serve as critical foundational materials for ensuring the long-term, stable operation of power systems.