Design proposition of transformers used for feeding nonlinear loads — A practical approach based on temperature measurement

The objective of this paper is to present a procedure, experimentally developed, for dimensioning transformers submitted to nonlinear loads conditions. The method is based on the record of the heating curve of the electrical equipment. First of all, the increase of losses in transformers is obtained for several situations of current distortion in transformer windings. Moreover, the increase of losses is divided into two parts: the first corresponding to the increase of the true rms current for the same active power of an equivalent linear load; and the second corresponding to the increase of additional losses in the windings due to skin effect. The results, for each situation of harmonic distortion, are used to obtain the transformer design which, finally, is compared with the transformer design obtained through the theoretical procedure based on IEEE Std C57.110-1998.