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Copper or aluminium windings: which distribution transformer to buy

Chinese factories build oil-immersed distribution transformers with either copper or aluminium windings. Aluminium units are usually 30–50% cheaper, which is why price lists differ so much for the same kVA. Here is what you give up and what you do not.

What stays the same

Both can be designed to the same kVA, voltage, vector group and loss class. A well-made aluminium transformer meets the same routine tests and works reliably for decades; aluminium windings are common in many utility networks.

What changes

• Size and weight: aluminium conducts less well, so the conductor is larger. The tank is usually somewhat bigger.
• Losses: at the same size, aluminium has higher load losses. A designer can match the losses of a copper unit by using more material, which narrows the price gap.
• Joints: aluminium needs proper copper-aluminium transition at the terminals. Ask how the bushings are connected.
• Short-circuit strength: copper windings are mechanically stronger. For sites with high fault levels, copper is the safer choice.

When to choose which

• Copper: industrial loads, mines, data centres, high fault levels, or where a tender or utility specifies copper.
• Aluminium: cost-driven distribution, rural networks, projects where the specification allows it.

Compare like with like

When you compare quotations, check the winding material, the loss figures (no-load and load losses) and the efficiency class. A cheaper aluminium offer is not comparable with a copper one unless the losses are stated. Our price list shows copper and aluminium separately.