Using the complex values of the frequency response to improve power transformer diagnostics

Frequency response analysis (FRA) is a well-known technique for detecting the mechanical defects inside a power transformer. There are different methods to interpret the FRA results, and one of them is using the numerical indices. Majority of the indices proposed in the literature use only the magnitude response of the FRA results. This paper, by contrast, proposes new methods to also include the phase response in the interpretation of the FRA results. The data recorded from an experimental setup are used to prove the functionality of the methods. The experimental analysis shows that including the phase response in the analysis makes the results more sensitive to mechanical changes. Furthermore, it sometimes improves the linearity of the indices versus the extents of mechanical deformations. Although further studies are needed to settle the new method, this paper shows the early functionality and the potential of the phase information to improve the diagnostics of power transformers.