Experience with frequency response analysis (FRA) for the mechanical condition assessment of transformer windings

Measurement of the frequency response is now commonly used in the industry to assess the mechanical condition of transformer windings. The analysis of the results, the so-called Frequency Response Analysis (FRA), is based on comparison with a reference measurement which is either a previous measurement on the same unit, a measurement on an identical transformer or a measurement on another phase of a three-phase transformer. To ensure a good quality of the frequency response measurement, it is essential to follow the recommended practices reported in the recently published CIGRÉ and IEEE guides, and in the IEC standard. This paper presents case studies on the application of the method to detect mechanical displacement and some of the influencing parameters that can affect the interpretation of the results.