Frequency Response Analysis for Power Transformer Diagnostics

Frequency Response Analysis is a leading non-destructive diagnostic method employed to assess the mechanical integrity and electrical continuity of power transformer windings. By injecting a swept or impulse excitation across a broad frequency spectrum and measuring the resulting output, the technique generates a signature transfer function that serves as a diagnostic fingerprint. Deviations from a reference signature can reveal winding deformation, inter-turn faults, core displacement or clamping loss. The method is especially valued for its sensitivity to subtle structural changes, enabling early detection of transport damage, short-circuit stresses and ageing effects. Measurements are typically divided into low-, mid- and high-frequency regions, each reflecting different physical phenomena within the transformer. Despite standardised procedures under international guidelines, interpretation of the resulting spectra remains a challenge and often relies on expert judgement or advanced numerical indicators. Recent advances in modelling and data-driven analysis are addressing these challenges by linking equivalent circuit parameters to spectral features and by automating signature comparison. The global adoption of Frequency Response Analysis supports improved asset management, prolongation of transformer service life and enhanced grid reliability by facilitating targeted maintenance and reducing unplanned outages.

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Frequency Response Analysis for Power Transformer Diagnostics publication trend

The graph below shows the total number of articles in frequency response analysis for power transformer diagnostics across all publications each year (not limited to Nature Index journals).

Technical terms

Frequency Response Analysis (FRA): A diagnostic technique measuring the ratio of output to input voltage over a range of frequencies to detect structural changes in transformer windings.

Sweep Frequency Response Analysis (SFRA): A variation of FRA using a continuous or stepped frequency sweep to derive the transformer’s transfer function signature.

Winding deformation: Mechanical displacement or distortion of transformer windings caused by short-circuits, transport or ageing, affecting the frequency response signature.

Transfer function: The frequency-dependent representation of a transformer’s electrical response, used as a fingerprint for comparison.

Correlation coefficient: A statistical metric quantifying similarity between measured and reference FRA signatures across defined frequency bands.

References

1. A Review of Frequency Response Analysis Methods for Power Transformer Diagnostics. Energies (2016).
2. Comparison of Impulse Wave and Sweep Frequency Response Analysis Methods for Diagnosis of Transformer Winding Faults. Energies (2017).
3. Using Lumped Element Equivalent Network Model to Derive Analytical Equations for Interpretation of Transformer Frequency Responses. IEEE Access (2020).
4. Machine learning for power transformer SFRA based fault detection. International Journal of Electrical Power & Energy Systems (2024).
5. Understanding the Influence of Power Transformer Faults on the Frequency Response Signature Using Simulation Analysis and Statistical Indicators. IEEE Access (2021).
6. Intelligent Classifiers in Distinguishing Transformer Faults Using Frequency Response Analysis. IEEE Access (2021).