When transformers experience physical impacts or sudden changes in the electrical system that cause movement of the physical components, it is helpful to know if these events have had permanent impacts on the internal geometry of the transformer. This can be particularly difficult in liquid filled transformers without going through the time and very costly expense of de-tanking the transformer. However, the application of Sweep Frequency Response Analysis, allows for a highly sensitive measurement to physical changes of the internal workings of the transformer without having to without having to visually inspect the inner workings of the transformer.
If permanent changes are detected as a result of performing SFRA testing, then it may be necessary to pursue a more intrusive evaluation. However, the ability to make these determinations in a less costly and intrusive manner can help to avoid putting equipment into service that is not fit for duty. Additionally, it may help to avoid unnecessary and more intrusive measures of investigation.
The transformer itself can be viewed as an electrical filter which has a characteristic response to specific signal frequencies. The initial plot of characteristic response signature over a range of frequencies becomes an identifying fingerprint by which future tests are compared. When future tests signatures deviate from the initial characteristic frequency response, then it can be indicative of physical changes such as winding deformations, changes to the spacing between components or other types of physical damage.
A great tester on the market today is the Doble M5400 Sweep Frequency Response Analyzer. This analyzer has a frequency response of 10 Hertz to 25 MegaHertz. It also features a easy setup and automated testing for quick and convenient diagnostics.
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Editor’s Note: This post was originally published April, 2012 and has been updated freshness, accuracy and comprehensiveness.