EU policy initiatives in the slipstream of the Green Deal promote a systematic approach to material efficiency and recyclability in product design. In this respect, medium-power electrical transformers are an interesting case on which to focus.
The Copper Alliance conducted an in-depth survey of the current state of transformer recycling, revealing a sharp contrast between liquid-filled and dry type units.
Liquid-filled medium-power transformers have a high degree of circularity at end-of-life, with about three quarters of the material compatible with an entirely circular process. This potential is fully exploited thanks to the fact that only certified companies are allowed to handle liquid-filled transformer recycling, which is a positive legacy of the PCB crisis.
- About 70% of the mineral oil is recycled for re-use, and the remaining 30% is re-used as a second-grade oil in other applications. Natural esters, now increasingly used as an insulating liquid, could in principle be recovered in the same way as mineral oil, but the market, equipment, and technical standards to govern this process are still lacking.
- Close to 100% of aluminium from windings is recycled in second-life products, for which 98% purity is adequate. The existence of different alloys on the market and impurities in the scrap are a barrier to first-grade aluminium recycling.
- The degree of circularity of a liquid-filled transformer can be enhanced by using copper for the high voltage winding. The vast majority of copper winding shreds are recycled at the highest purity level (99.9%). The copper can be melted down and used again for electrical applications, including transformer windings, without further purification. Copper windings also increase the end-of-life value of the unit, enhancing the business case for recycling and re-use.
- Magnetic steel from the transformer core, as well as structural steel parts, are almost 100% recovered.
Dry type transformers follow a totally different recycling route and demonstrate how a lack of separability in the conception of a device can lead to a problematic end-of-life process. Their coils are overmoulded with an epoxy or quartz resin that is hard to separate from the metal conductors. The separation process is not economically viable in the EU because it is time and energy consuming, and only results in low purity metal scrap. The coils are sold with other electromechanical scrap for export outside the EU, where a lower-paid workforce separates the resin from the aluminium coils in semi-automated processes.