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Although the European regulation is promulgated in terms of maximum watts of core and coil losses (at 100% loading), it is possible to estimate the percentage efficiency of minimally compliant units by assuming 50% loading and adjusting the coil losses accordingly (varying by the square of the current). The figure below presents the minimum European requirements for Tier 1 (2015) and Tier 2 (2021) for three-phase liquid-filled distribution transformers at 50% loading, 50Hz operation. Also plotted on this same graph are the five Tier levels from the SEAD study, published by CLASP. The European Tier 1 is approximately equal to SEAD Tier 2, and the European Tier 2 is between SEAD Tier 3 and 4, with units between about 200 and 900 kVA being at Tier 4.
Europe has less ambition at the 25kVA rating, with a notable drop in efficiency for both Tiers relative to the SEAD levels. SEAD was developed as an approximation of all the regulatory and energy-efficiency programmes on distribution transformers around the world. For more information about the SEAD levels, please visit this webpage: the SEAD study. To review the European regulation on Transformers, visit this webpage: EU No 548/2014.