This month’s Featured Technical Paper is from the Proceedings of the 2020 International Conference of Doble Clients. The paper is titled: SFRA Test on Stator – Experiences and Development of Guidelines.


Sweep frequency response analysis (SFRA) is a well-known technique for the diagnosis of power transformer windings, and test standards have been developed by different standard organization such as IEEE, IEC and CIGRE. Additionally, the test method has been used successfully on other apparatuses such as harmonic filters [1] and rotors [2]. However, on stator windings, the results have been mixed, because many factors can influence the results. Stator windings are more complex, typically have multiple parallel circuits, numerous coil slots, different bus ring configurations and multiple ways to perform the tests. This paper will address the latter by examining different test protocols used in the past fifteen years as well as the test results. It will then propose an application guideline for the test procedures and data analysis. Examination of the past field test experiences are included for stators in different conditions: new, aged with bypassed coil, and failed units from two types of generators (Cylindrical Rotor and Salient Pole Rotor, typically high and low RPM respectively).

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