The impact of eco-design on transformer temperatures in MV/LV substations

Thermally, the main function of the prefabricated substation enclosure is to manage the ambient temperature by controlling the heat generated by the equipment inside. In the past, the transformer was responsible for most of the energy losses. But this is no longer entirely true: transformer losses have been significantly reduced in 2015 and 2021 under the guidance of the Eco-design Directive. Today, a 630 kVA A0-10%Ak distribution transformer has no more losses at rated power than a 10-year-old 400 kVA C0Ck one. Less loss means less heat in the substation and therefore lower temperatures. This undoubtedly has a positive effect on the ageing of equipment. However, although desirable and positive, the effect of transformer eco-design is not without side effects on equipment installed in a confined environment such as the substation. This publication proposes a simple graphical representation to highlight and quantify these effects.