Efficiency standards for low voltage substation transformers

At present, there are no specific standards to distinguish "premium efficiency" transformers from "standard efficiency" transformers. The National Electrical Manufacturers Association (NEMA) has promulgated performance and test requirements for low voltage designs that can be listed as NEMA Class I, and for such units efficiencies are somewhat higher than those which appear in the literature as standard designs. The US Department of Energy, acting as required by the Energy Policy Act of 1992, is analyzing potential mandatory efficiency standards for a range of product classes that include the 500-2500 kVA dry and liquid-type low voltage transformers that are normally used in industrial substations. This paper explores the practical economic effects of transformer selection over a range of efficiency levels at and above the NEMA Class I levels.