Review of distribution transformer energy efficiency metric

Distribution transformers play an important role in achieving the ambitious energy efficiency targets set by many countries in the world. Distribution transformers are of high value in terms of energy efficiency because of the number of installed units in each country. In this context, energy efficiency metrics have been introduced, such as efficiency at 50 % load, maximum no-load and load losses, maximum combined losses, etc. Typically, the selection of energy-efficient distribution transformer is a two-step process: a) transformers must comply with the minimum power efficiency levels (typically at 50 % load), b) selection of that transformer whose losses are economically optimal over the lifetime of the transformer. In this article, a review of the present energy performance metrics, especially the efficiency at 50 % load is presented, paying particular attention to the Australian and New Zealand market. Alternative metrics such as no-load and load loss values and peak efficiency index are investigated