Index Terms- DC injection, transformer saturation NOMENCLATURE

Abstract- A high enough DC component in the current on the secondary side of a transformer causes distortion of the primary side current. Prediction of such distortion relies on the availability of magnetization curves that extend deep enough into saturation. A simple test, carried out at rated voltage, is proposed which allows the magnetization curve to be deduced from measured data. In addition, a systematic procedure has been developed to evaluate the primary current distortion in both single and three phase transformers. Comparison between theoretical predictions and practical measurements are made with reasonable agreement between the two