Transformer Frequency Response Analysis With the Grouped Indices Method in End-to-End and Capacitive Inter-Winding Measurement Configurations

The paper presents a method for assessing the frequency response results of transformers. The frequency response analysis (FRA) method is widely used in the industrial testing of the mechanical condition of transformers, however, there are still some problems with interpreting the test results. The measurements are usually taken only in an end-to-end open measurement configuration, according to the IEC standard. The literature indicates many numerical indices that are used for the assessment of FRA curves. It is not possible to use all of them, especially as they may give different results. The objective of the presented research was to analyze the behavior of 14 of the most popular indices in the medium-frequency range under the influence of deformations. The experiments allowed them to be divided into four groups, based on similar behavior under data recorded in conditions of deformations introduced into windings. All research is performed for two measurement configurations: end-to-end open and capacitive inter-winding. The division into groups is also tested with data recorded on transformers from industry. The proposed grouped indices method needs only four indices for FRA data assessment, while their behavior covers all 14 analyzed formulas.