Since the time when copper was cheaper than aluminium, copper conductors were used for the spools of the winding for power transformers. However, since the rise in copper prices, it became necessary to look for ways to replace copper with other metals, in particular aluminium. 

So in 1 – 1V category transformers, aluminium was successful in replacing copper as a material for winding. In 1 – 111 category, aluminium occupied 85%, practically the entire market niche. In turn transformers of V – V11 category continue to use copper windings for the time being, a decision justified by the advantages of copper conductors. 

However, in order to correctly assess the benefits of copper and aluminium conductors, we must look at the key properties of these metals; weight, conductivity, and price.  

What do we see? Copper conductors are 3.3 times heavier than aluminium ones. Considering the high price of copper, copper conductors are 6 times more expensive than their aluminium counterparts. Furthermore, the price difference between copper and aluminium means that aluminium conductors are often larger in size, which leads to reduced loss of current at a lower cost than if a copper conductor is used. 

The singular advantage copper has over aluminium is that it involves less overall equipment. A copper coil transformer can be smaller than a transformer with aluminium winding. However, this argument has long been disputed; for industrial companies, minimising equipment is not an end in itself. 

In this way, replacing copper with aluminium in power transformers V – VII is simply a question of time. 

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