Interpretation of FRA Results through Low Frequency Transformer Modelling

Currently there is no standard FRA interpretation methods and not all the FRA practitioners are capable to model transformer windings using equivalent circuits. A low-frequency transformer model of a three-limb core-type 1000 MVA 400/275/13 kV auto-transformer is established to analyze the effects of transformer electric parameters on the FRA plots. The equivalent electrical circuit of the magnetic core is derived based on the Principle of Duality. Air-core inductance and winding capacitances are included in the model. FRA simulation results are validated by measurement results, the suitability of transformer model is discussed and the dominant factors in different frequency regions are concluded through sensitivity studies.