Harmonics-transformer derating

Abstract

Power transformers supplying nonsinusoidal load current often need to be derated. The ANSI/IEEE C57.110-1986 standard provides a method by which derating may be performed. However, derating only provides an estimate of remaining transformer capacity, since subsequent load may significantly change the relative harmonic current values. The contribution of this paper is to provide a clear guide that can be used in applying the standard. This paper is not meant to replace the standard but to supplement it by providing correct examples and simplified equations.<>