In transformers, windings are coils inside the unit that distributes and draw power. A dry-type transformer typically consists of two windings – one for drawing power directly from the source and one for transferring it to the load. A dry transformer’s windings, or coils, are typically made from either aluminium or copper. Copper winding and aluminium winding are both used for the same purpose.

Reliability
Typically, copper and aluminium windings provide the same functions for low and medium-voltage transformers. However, when it comes to reliability, copper tends to dominate over aluminium because aluminium has only 62% of copper’s electrical conductivity, making it a much more effective conductor of electricity.

However, proper insulation can also help ensure that both types’ energy loss factors remain equal. The size of the windings also impacts heat loss, and aluminium can easily be sized to accommodate this. Even so, physical strength and resistance to deformation make copper a more long-term reliable material.

Operating Lifespan
The operational lifespan for transformers with adequately cared for and installed copper or aluminium windings is generally equal. The only downside for aluminium is that it is usually more challenging to install than copper, which could sometimes lead to minor operational issues. Even though modern design improvements have made aluminium more resilient to fault current stresses, copper is generally a more durable option. 

Initial costs
Since aluminium windings are usually cheaper to produce than copper windings, they generally cost less to buy. Furthermore, aluminium’s price has been stable over the last few decades, resulting in cheaper windings.

The initial cost of copper has generally been more volatile than aluminium. It is still widely believed, however, that copper windings offer more extended benefits than aluminium windings, regardless of their higher cost.

Operating costs
Copper windings typically cover a smaller cross-sectional area than aluminium windings in dry-type transformers. Comparatively to older copper wound transformers, more expansive aluminium windings result in lower current densities, leading to a lower rate of heat loss.Copper windings often outperform aluminium windings regarding long-term operational cost-effectiveness in modern designs due to improvements that reduce copper winding heat loss. The coils in copper windings are usually tighter and can also be optimised to operate at lower current densities.

Conclusion
Although both copper and aluminium windings are commonly used, copper tends to be the industry standard for dry-type transformer applications.

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