The effects of linear and non-linear loads on three-phase transformers supplied from different sources

Abstract

In this study a new approach for the calculation of harmonic transformer parameters by making use of equivalent circuit model of one phase transformers is put forth. With this aim in mind, a three-phase core type transformer from 4 kVA, 400/230 V, 50 Hz, Yy0 connection group was used. To supply transformers voltage sources with sinusoidal and non-sinusoidal wave shapes were used. The transformers supplied on these sources were connected two different loads: one linear and one non-linear. The interactions of these transformers, under different load and supplies, with harmonics were measured simultaneously with two harmonic analyzing devices connected to primer and secondary and the measurements up to the 15th harmonics were assessed and equivalent circuit components were calculated for each harmonic component separately. From the values measured and calculated, copper losses of primer and secondary circuits of three-phase transformers, iron losses and the efficiency of the transformer was calculated harmonically. Measurement and calculations were made separately for two different supplying and two different loads and results were compared. Besides, for each condition, total harmonic distortion (THD) of voltage and current and K factors were calculated, their effects on transformers performance were revealed. Key words: Harmonics, linear loads, non-linear load, transformer loses, equivalent circuit, k-factor.