AEMT - Association of Electrical and Mechanical Trades

26 July 2022
Transformer Windings: Copper Versus Aluminium
Transformer specialist, Bowers Electricals, compares the properties of aluminium and copper when used in transformer windings, outlining the advantages each option can offer.

In the construction of a transformer, there are two main parts: the transformer core and the transformer windings. The function of the transformer is to convert the voltage level of electrical power. Accordingly, one winding is connected at the high voltage side, and the other winding is connected at a low voltage side. Therefore, it is also classified as high voltage (HV) winding and low voltage (LV) winding.


Transformers have at least two winding types – primary windings and secondary windings. There are a lot of variations as to how many windings you can have and their function, but for this example, we are keeping it simple.

The primary winding is the winding of a transformer that is connected to and receives energy from an external source. The secondary winding is the winding of a transformer that delivers the transformed energy – the changed voltage – to the load.

Copper or aluminium conductors can be used to make transformer windings. Aluminium is lighter than copper but has 50% lesser conductivity than copper. It is also cheaper than copper. On the other hand, copper has excellent mechanical strength and twice the conductivity of aluminium.


Initially, all transformers were built with copper windings, as it was easily accessible and priced right. During WWII, the use of aluminium in transformers increased as the industry experienced a shortage of copper which was in high demand by the military.

Due to this demand, copper prices skyrocketed, and aluminium became more popular for windings; in turn, previous technological problems were overcome, and these aluminium transformers became more reliable.

Choosing between aluminium and copper windings for your transformer comes down to personal preference. But there are advantages to both materials.



• Copper is stronger than aluminium.

• Current capacity is double that of aluminium.

• Compact form (small dimension) compared to aluminium.

• Reduced physical expansion.



• Low and stable market price.

• Lower weight compared to copper winding.

• Excellent malleability during the winding process.

• Very suitable for distribution transformers and small power transformers.


Since both aluminium and copper transformers use the same insulation systems and have similar temperature rises, they have similar lifetime ratings.

Most distribution transformer manufacturers are now using aluminium windings, as opposed to the traditional copper windings. Aluminium wound low voltage transformers will probably continue to gain increased acceptance because of their significant cost advantage over copper

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