Choosing the right aluminum strip for transformer windings requires a balance between conductivity, mechanical strength, and cost-effectiveness. For most transformer applications, 1050 or 1060 aluminum strips are reliable choices due to their good conductivity and ease of handling.
Material Grade
The purity of aluminum is the single most important factor determining its conductivity. For electrical applications, you must use 1xxx series pure aluminum with an aluminum content of at least 99.5%. Common alloys are 1050, 1060, 1070, and 1350
| Alloy | Aluminum Purity (≥) | Conductivity (% IACS) | Best Suited For |
| 1050 | 99.50% | ~61.0% IACS | Cost-sensitive, general-purpose distribution transformers |
| 1060 | 99.60% | 61.0% - 61.5% IACS | General-purpose, medium-voltage (e.g., 35kV class) dry-type transformers |
| 1070 | 99.70% | ≥ 62.7% IACS | High-performance applications, reactors, or where maximum efficiency is required |
| 1350 | 99.50%+ | ≥ 62% IACS | High-conductivity applications, especially in large power transformers |
For most applications, the 1060 alloy strikes the best balance between performance and cost. All aluminum used for transformer windings must be supplied in a fully annealed "O" temper (soft temper); this is crucial because it ensures flexibility during the winding process, preventing cracking and ensuring that the aluminum tightly fits the transformer core.
Surface and Edge Quality
The quality of the strip surface and edges is critical to ensuring the long-term reliability of the equipment, as any defects could lead to insulation failure or even short-circuit faults.
- Surface Quality: The surface of the strip must achieve a mirror-like finish (Ra ≤ 0.8μm), with no scratches, oil stains, or oxidation spots. This high level of smoothness ensures even and strong adhesion of the insulation layer.
- Edge Condition: Sharp edges pose a potential hazard. High-quality strips typically feature rounded (chamfered) edges, completely eliminating burrs and sharp corners that could puncture the inter-layer insulation—this is especially critical in foil winding applications.
- Burr Height: A key quality control indicator. For high-quality strips, the burr height must be strictly controlled, typically requiring ≤ 0.01mm, further minimizing the risk of insulation layer damage.
The aluminum surface should be free from defects such as scratches or corrosion, as these could affect the winding or conductivity. A smooth, oxide-free surface is the preferred choice for transformer applications.
Form Factor: Round vs. Rectangular Wire
Although aluminum strips (including rectangular conductors or foil conductors) are considered the best choice for many designs, round wire remains a viable alternative worth considering.
- Round Wire: The manufacturing process is relatively simple and suitable for various applications. However, this structure leaves "gaps" between turns, reducing the winding filling factor. Additionally, due to uneven heat distribution, it may cause "hotspot" effects.
- Rectangular Flat Wire/Foil: This is the preferred option for high-performance, high-current windings. Thanks to its geometry, the conductors can be arranged more compactly, achieving a higher filling factor. Compared to round wire, this solution utilizes space more efficiently and offers superior heat dissipation and stronger short-circuit resistance.
Cost
The specifications of aluminum strips (such as thickness, width, alloy composition, etc.) also affect the final cost. Choosing the appropriate aluminum alloy (such as 1050, 1060, or 1350) not only meets the electrical performance requirements but also achieves optimal economic efficiency within the budget.
When selecting the appropriate aluminum strip for transformers, balancing cost and performance is essential. Aluminum, with its low cost and lightweight properties, is the preferred choice for many transformer applications, especially in most standard transformer designs. By selecting the right material and specifications for the aluminum, it is possible to ensure the transformer’s performance while maintaining cost-effectiveness.