Modeling power transformers to support the interpretation of frequency-response analysis

A power transformer will yield a frequency response which is unique to its mechanical geometry and electrical properties. Changes in the frequency response of a transformer can be potential indicators of winding deformation, as well as other structural and electrical problems. A diagnostic tool which leverages this knowledge in order to detect such changes is Frequency Response Analysis (or FRA). To date, FRA has been used to identify changes in a transformer’s frequency response but with limited insight into the underlying cause of the change. However there is now a growing research interest in specifically identifying the structural change in a transformer directly from its FRA signature. The aim of this paper is to support FRA interpretation through the development of wideband three phase transformer models which are based on three types of FRA test. The resulting models can be used as a flexible test bed for parameter sensitivity analysis, leading to greater insight into the effects geometric change can have on transformer FRA. The paper will demonstrate the applicability of this modelling approach by simultaneously fitting each model to the corresponding FRA data sets without a priori knowledge of the transformer’s internal dimensions, and then quantitatively assessing the accuracy of key model parameters.