What Is a Frequency Response Analysis (FRA) Test?

Published 27 Aug 2026Updated 27 Aug 20266 min readAdvancedTesting

Quick answer — Sweep frequency response analysis (SFRA) measures the transformer winding impedance (or transfer function) over a wide frequency band and compares the response to a baseline or to factory data. Changes in the response indicate deformation, displacement or core movement from short-circuit or transport forces. It is a sensitive diagnostic for mechanical integrity.

Contents

What it measures
Why it is used
Interpreting

What is a frequency response analysis (FRA) test on a transformer?

What it measures

The test applies a swept voltage and records the response of the winding network, which depends on the capacitance and inductance — hence the geometry — of the windings. A healthy unit has a characteristic, repeatable response.

Why it is used

It detects winding deformation (axial/radial), displaced conductors, core and clamping problems and loose connections, which are hard to see with conventional tests.

Interpreting

Compare the trace against the reference (factory or previous). Deviations, typically at specific resonant frequencies, localise the change and help decide whether the deviation is significant.

References & standards

IEEE C57.149 (FRA guide)
IEC 60076-1

Book series Academy

Related manufacturers

Prolec GE (GE Vernova) · Prolec GE Waukesha · Hitachi Energy USA · Siemens Energy · Eaton · Virginia Transformer Corp

Related components

Protection, monitoring & diagnostics Conductors & core steel

Technical content is prepared from engineering references, standards frameworks, manufacturer documentation and industry sources. Contractual or compliance decisions should refer to current official standards. TransformerPath Technical Editorial.

Source transformers for this application

Submit an RFQ or browse manufacturers and components.

Submit an RFQ Get Verified