Frequency response analysis (FRA) for diagnosis of power transformers

Power transformer is one of the most important equipments in a high voltage electric power system. In order to maintain the quality of system operation it is necessary to keep the transformer in good condition. This needs appropriate maintenance based on reliable diagnostics. this paper reports experimental results on the application of frequency response analysis (FRA) for the diagnosis of power transformers. The FRA measurement was done using Omicron with sweep frequency of 10 Hz - 10 MHz applied to 3 phase transformer of 100 kVA, 6000 V/220 V under normal as well as faulty conditions. Based on the FRA curves, equivalent circuits which consist of R, L and C were calculated at low, medium and high frequency. Experimental results showed that short circuit greatly affected the low frequency components while axial displacement of coils on slightly affected the medium frequency components. Buckling and short circuit altogether significantly affected the low and medium frequency components. From these results some mechanically-related faults in the transformer initially can be diagnosed using the FRA method.