Sweep Frequency Response Analysis (SFRA) is an electrical testing method which identifies changes to the internal workings of a transformer. The transformer is an electrical filter that has a specific response to each independent input frequency. The test equipment is used to apply a test voltage to a transformer over a range of frequencies.
The output of the transformer is then monitored in relation to its corresponding input frequency. The results, when graphed, make up a signature response, much like a unique fingerprint. The initial SFRA test will then become a baseline for comparison when future tests are performed. When these signatures do not match the baseline signature, something has changed internal to the transformer and merits further investigation.