9.How does the tensile strength of aluminum foils compare to copper in transformer applications?

In transformer applications, aluminum foils generally have a lower tensile strength compared to copper, which affects their mechanical durability and performance. Here’s a comparison of the two in this context:

Tensile Strength:

Copper: Copper has a high tensile strength, typically around 210-250 MPa for soft-annealed copper, and up to 500 MPa when work-hardened. This high strength makes copper less susceptible to tearing or breaking, which is beneficial in transformer windings where physical durability under mechanical stress is crucial.

Aluminum: Aluminum has a lower tensile strength, around 90-150 MPa for annealed aluminum, and up to 200 MPa in work-hardened forms. This lower strength means that aluminum foils can be more vulnerable to deformation, particularly under high current and thermal loads that transformers can experience.

Wire Size and Current Carrying Capacity:

To carry an equivalent amount of current, aluminum wire requires approximately 1.6 times the cross-sectional area of copper wire. This means that aluminum wound coils are larger than equivalent copper coils. For applications requiring very tight dimensions, copper coils are often preferred due to their smaller size and higher current carrying capacity per unit area

Connection and Corrosion:

Copper is less susceptible to corrosion compared to aluminum, especially in saltwater applications. Aluminum is more prone to rapid attacks by halide ions, such as chloride, which can be prevalent in certain environments. Copper's resistance to corrosion can be an advantage in environments where the transformer may be exposed to corrosive elements.

Economic Considerations:

Despite its lower tensile strength and larger size requirement, aluminum is often less costly than copper. A pound of aluminum has about twice the current carrying capacity of copper but costs significantly less. This can make aluminum a more economical choice for certain applications, despite the need for larger wire sizes.

Although aluminum has lower tensile strength, it is lighter and less expensive than copper. This makes it attractive for larger transformers where cost and weight are significant factors.

Manufacturability:

Smaller transformers, generally 5kVA and under, are typically wound with copper to avoid breaking or damaging the wire during the winding process due to the brittleness of thin aluminum wire. Copper's higher tensile strength makes it more flexible and resistant to damage during manufacturing, which can be particularly important in the production of smaller transformers.

Lifetime Ratings:

Both aluminum and copper transformers use similar insulation systems and have similar temperature rises, leading to similar lifetime ratings. This indicates that, despite differences in tensile strength, the long-term performance and durability of transformers wound with either material can be comparable.

Implications for Transformer Design:

Because of copper’s higher tensile strength, copper windings can be made thinner and still withstand mechanical stresses, allowing for more compact transformer designs.

Aluminum’s lower strength may require thicker windings or additional support to handle the same mechanical loads, potentially increasing the size and weight of transformers.