Investigations on sensitivity of FRA method in diagnosis of interturn faults in transformer winding

This paper presents sensitivity of Frequency Response Analysis (FRA) method applied to detection of interturn faults. Frequency response has been carried out on a special Reduced Scale Traction Transformer (RSTT). The RSTT has the wound iron core and eight coils arranged in the “core” type of construction. Many papers have been published on FRA techniques for detection of shorted turns but still there are some issues that need to be addressed. The simulated faults presented in the paper include different values of shorting resistance and different localization of short-circuited turns. From the measurements performed on the transformer without faults, it can be concluded that handmade coils with the same type of construction differ significantly in frequency response. It is also concluded that FRA magnitude spectrum is sensitive to short-circuit, but for some ranges of shorting resistance only. FRA magnitude spectrum also changes with respect to localization of short-circuited turns. The frequency response showed shift in waveforms in case of some resonant frequencies.