Dry type transformers typically feature either copper or aluminum windings, also known as coils. Transformer windings refer to the coils within the transformer that draw and distribute power inside the unit. There are typically two windings in a dry type transformer — one that draws power from the source and another that transfers that power to the load. Both copper and aluminum windings perform the same function.

For some applications, one type is preferable over the other. The option you choose depends on the specific needs of your facility and your unique requirements. 


Differences Between Copper and Aluminum Windings
While most low and medium voltage dry type transformers rely on aluminum windings for energy transfer, many engineers and plant operators prefer copper windings for specific applications. Here are some of the primary differences between the two types:

Initial Costs
At the outset, aluminum windings are generally less expensive than copper windings because the material itself is relatively cheap to produce. Moreover, aluminum’s price has proven to remain stable over long periods — translating to cheaper windings.

Copper’s initial costs have historically been more volatile than those of aluminum. Still, even though copper windings tend to be slightly more expensive, many experts believe this type offers more long-term benefits than its aluminum counterpart.

Operating Costs
Aluminum windings usually take up a larger cross-sectional area of dry type transformers than copper options. The more expansive design of the aluminum windings produces a lower current density, resulting in a lower rate of heat loss and saving more energy when compared to older-model copper wound transformers.

Copper windings usually feature tighter coils that can also be optimized for lower current density. In modern designs, thanks to advancements that allow for reduced copper winding heat loss, copper windings often outrank aluminum windings in their long-term operational cost-effectiveness.

Reliability
While both copper and aluminum windings provide the same general functions for low and medium voltage transformers, copper outranks aluminum when it comes to reliability. Aluminum has only 62% of the electrical conductivity of copper, making copper a much more effective conductor.

Proper insulation can ensure that the energy loss factors for each type stay equivalent. Heat loss also depends on the size of the windings — and aluminum can easily be sized to compensate for this issue. Nevertheless, copper does generally provide more long-term reliability due to its physical strength and resistance to deformation.

Operating Life
If copper and aluminum windings are properly installed and cared for, their operating lives should be nearly equal. One drawback of aluminum is that it’s typically more difficult to install than copper, which sometimes results in preventable operational issues.

Although modern design improvements have let transformer experts navigate the technical problems associated with aluminum, copper is typically a superior option for protection against fault current stresses and overall longevity.

Aluminum wiring is lighter in weight and lower in cost than copper. However, since it is usually incorporated into bigger and, consequently, heavier transformers, the overall benefits of these qualities are minimal. Additionally, its few advantages are often outbalanced by its many disadvantages.

The electrical conductivity and thermal conductivity of aluminum are less than copper. These qualities make the aluminum windings less efficient, which can lead to higher operating costs, and more prone to high hot spot temperatures, which can lead to shorter operating lives.
Transformers wound with aluminum produce more noise during operation than those wound with copper, which can lead to worse working conditions for system operators.

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