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.
A transformer that has been damaged may continue to operate for a period of time. However, when there are physical changes internal to the transformer that are variances from the intended design, they can quickly translate into an electrical emergency with significant impacts to the electrical system.
Other testing techniques, common to transformer testing, focus on attributes of the transformer that may not be as sensitive to some of the physical impacts of transportation, movement due to through faults, or other environmental impacts. A thorough investigation of a transformer can involve a fairly invasive review of the transformer and it's components. Fortunately, SFRA testing provides information about internal changes to the transformer without having to go through a process of de-tanking the transformer, making it a more convenient way to observe the health of our electrical assets.
Related electrical test equipment available for rent from Protec:
Editor’s Note: This post was originally published on April, 2011 and has been updated freshness, accuracy and comprehensiveness.