Among transformer winding materials, aluminum foil and copper foil are more common types. The two have differences in electrical properties, mechanical properties, cost, etc., and are suitable for different application scenarios. Among them, aluminum foil is more common, mainly due to its comprehensive advantages in cost, weight, and large-scale application scenarios.
The following is a detailed introduction to these two materials:
- Aluminum foil winding
- Material properties
– Conductive properties:
The electrical conductivity of aluminum is about 60% of that of copper. Therefore, under the same conductivity, the cross-sectional area of aluminum foil needs to be larger than that of copper foil.
– Density:
The density of aluminum is about 2.7g/cm³, which is much lower than 8.9g/cm³ of copper. It is lighter and suitable for weight-sensitive scenarios (such as mobile devices and transformers in the aerospace field).
– Corrosion resistance:
A dense aluminum oxide film is easily formed on the surface of aluminum, which can effectively resist atmospheric corrosion and has certain advantages in humid or corrosive environments.
– Cost:
The price of aluminum is usually lower than that of copper, which can reduce the raw material cost of transformers, especially in large-scale production.
- Application scenarios
– High-voltage transformers:
In the field of high-voltage power transmission, transformers are large in size and have relatively low weight requirements, so the cost advantage of transformer aluminum foil is more prominent.
– Energy-saving transformers:
In some energy-saving designs, by optimizing the structure of aluminum foil windings (such as increasing the cross-sectional area), performance requirements can be met while reducing costs.
– Scenarios with low heat dissipation requirements:
Although the thermal conductivity of aluminum is lower than that of copper (about 50% of copper), it can still be used normally in transformers with good heat dissipation conditions or low power.
- Advantages and disadvantages analysis
– Advantages: low cost, light weight, and good corrosion resistance.
– Disadvantages: poor conductivity, large winding resistance, which may lead to increased heat generation; relatively low mechanical strength, and under high-frequency or high-current conditions, the skin effect (the phenomenon of current concentration on the surface of the conductor) is more obvious, affecting efficiency.
- Copper foil windings
- Material properties
– Conductive properties:
Copper has a high conductivity of about 5.96×10⁷ S/m. Under the same current, the copper foil winding has a smaller resistance, low energy loss, and higher efficiency.
– Mechanical strength:
Copper has excellent mechanical properties, good toughness and ductility, and is suitable for processing into thin foils. In high-frequency transformers, the loss caused by the skin effect is smaller than that of aluminum foil.
– Thermal conductivity:
The thermal conductivity of copper is about 401 W/(m・K), and it has strong heat dissipation capacity. It can quickly conduct the heat generated by the winding, which is suitable for high-power and high-heat transformers.
– Reliability:
Copper has stable chemical properties, is not easy to oxidize, and has high connection reliability, especially in transformers that operate for a long time, the performance is more stable.
- Application scenarios
– High-frequency transformers:
Such as transformers in switching power supplies and electronic equipment, the skin effect loss of copper foil is lower at high frequencies, and it can maintain efficient operation.
– High-power transformers:
Such as industrial high-current transformers, power transformers, etc., the low resistance and high thermal conductivity of copper foil can reduce energy loss and avoid overheating.
– Miniaturized transformers:
Copper foil can be processed into thinner specifications (such as micron level), which is suitable for micro transformers with strict requirements on volume and weight (such as mobile phone chargers, precision instruments).
- Advantages and Disadvantages Analysis
– Advantages: good conductivity, low resistance, high efficiency, fast heat dissipation, high mechanical strength, and strong reliability.
– Disadvantages: high cost (copper price is usually 3-5 times that of aluminum), heavy weight, and limited application in cost-sensitive scenarios.
- Comparison table of aluminum foil and copper foil
| Comparison | Aluminum foil winding | Copper foil winding |
| Conductivity | About 60% of copper, with high resistance | High conductivity, low resistance |
| Cost | Low resistance, suitable for large-scale low-cost applications | High, suitable for high-performance scenarios |
| Weight | Low density, light weight | High density, heavy weight |
| Mechanical strength | Relatively low, good ductility | High mechanical strength, good toughness |
| Heat dissipation | Thermal conductivity is about 50% of copper, with average heat dissipation | High thermal conductivity, strong heat dissipation capacity |
| Corrosion resistance | Easy to form an oxide film on the surface, good corrosion resistance | Stable chemical properties, good corrosion resistance |
| High frequency performance | More obvious skin effect, greater loss | Low skin effect loss, suitable for high frequency |
| Application scenarios | High-voltage transformers, energy-saving equipment, weight-sensitive scenes | High-frequency transformers, high-power equipment, miniaturized equipment |
- The reason why aluminum foil is more used as transformer windings is:
– Low cost of raw materials
The price of aluminum is lower than that of copper (about 1/3-1/2 of the price of copper), and the reserves of aluminum in the earth’s crust are abundant (accounting for 8.23% of the mass of the earth’s crust, copper is only 0.005%), suitable for large-scale industrial production.
– Low processing cost
Although the ductility of aluminum is slightly inferior to that of copper, its density is small (2.7g/cm³ vs 8.9g/cm³). For the same volume of winding material, aluminum foil is lighter, and the energy consumption and cost during transportation and processing (such as winding and welding) are lower.
– The first choice for lightweight needs
The low density of aluminum makes it extremely advantageous in weight-sensitive scenarios.
– Balance of heat dissipation performance
Although the thermal conductivity of aluminum (237 W/(m・K)) is lower than that of copper (401 W/(m・K)), aluminum foil can make up for the deficiency by increasing the cross-sectional area or optimizing the heat dissipation structure, and the heat dissipation demand can be met in scenarios with low power density.
– Protection of natural oxide film
A dense aluminum oxide (Al₂O₃) film is easily formed on the surface of aluminum, which can resist corrosion in the atmosphere and humid environment, and no additional anti-rust treatment is required. It is suitable for outdoor, high humidity or mildly corrosive scenarios (such as transformers in coastal areas). Although copper is corrosion-resistant, long-term exposure to humid air may generate verdigris (basic copper carbonate), which affects contact reliability.
– High temperature resistance and stability
The melting point of aluminum is 660℃, and that of copper is 1083℃. The operating temperature of transformer windings is usually controlled below 105℃ (Class A insulation). The thermal stability of aluminum foil is sufficient to meet the requirements, and the thermal expansion coefficient of aluminum (23×10⁻⁶/℃) is not much different from that of copper (17×10⁻⁶/℃), so the winding structure will not fail due to thermal expansion and contraction.
Aluminum foil has become a common material for transformer windings. In scenarios where resistance loss and high-frequency performance are not required, aluminum foil meets the core needs of large-scale industrial applications with lower cost, lighter weight, and sufficient corrosion resistance.
