Relating a distribution transformer´s connection topology and the influence of inductive disparity to the observed frequency response

This paper uses generic three phase models to illustrate how the frequency response analysis (FRA) data of distribution transformers with different vector group numbers will be effected by inductive disparity. The inductive disparity of a three phase transformer is a well documented property due to variation in the observed core reluctance of transformer windings on different phases. At low frequency this will result in a subtle inductance inequality between the centre and outer limb windings of the transformer core. Understanding the influence of this disparity is important when analysing the frequency response of the transformer. Frequency response analysis data taken from different terminals on the same transformer will display significant variation at low frequencies due to the effects of this inductive disparity. Effects include differences in the self resonant frequency and levels of attenuation. This research facilitates a more comprehensive understanding of the observed responses.