Interpretation of Transformer FRA Responses— Part I: Influence of Winding Structure

Frequency-response analysis (FRA) has been accepted as one of the most sensitive tools to detect mechanical faults of power transformers. Correct interpretation of FRA responses is crucial when assessing the integrity of a transformer. Transformer FRA responses have distinctive frequency regions which are predominated by core, windings, and measuring setup. This paper addresses one of the major factors that affect the FRA responses: the winding structure itself. In terms of the structures of single winding, they can be categorized into windings with either high- or low-series capacitance in proportion to the shunt capacitance. Correspondingly, the FRA responses of windings of high series capacitance exhibit the increasing trend of magnitude, while windings of low series capacitance display a steady magnitude trend with the features of resonances and quasi-antiresonances or antiresonances. For a winding made of two concentric winding coils, the pattern of alternating resonances and antiresonances would be exhibited on its FRA response.