Transformer Winding Modelling to Study the Effect of Inter-disk Faults on Frequency Response Signature

Transformer units are one of the most significant equipment in power network and are integrated in all sectors of the grid. It is highly important to maintain a reliable operation of the transformer unit through timely diagnosis and inspection works. Frequency Response Analysis (FRA) is considered as quite efficient, non-destructive and well-standardized techniques for evaluation of mechanical conditions of the transformer. In this study, one of the most frequent fault type - inter-disk short circuit is emulated and its effect on FRA test results is analyzed. In order to realize this task, both practical and software FRA measurements are conducted on a transformer winding. Software modelling is based on a fabricated winding and a physical model is developed from the geometric and electrical properties of the winding. FRA results have showed identical anti-resonance frequencies and magnitudes for software simulated and practical measurements of frequency response. Furthermore, effect of internal short-circuit was investigated, resulting in magnitude decrease and anti-resonance shift according to amount of disks shorted. Developed software model of the winding can prospectively be used for online FRA application and further analysis of winding internal faults.