Failure analysis of power transformer based on transformer turn ratio test and SFRA

A power transformer is one of the most key components of energy transmission and distribution in an electric power system. Inter-turn disturbances or short circuit faults may occur because of insulation degradation between one or more successive turns of the windings. If the fault is not detected early, it may spread to the nearest winding turn and causes permanent damage to the winding. Therefore, it is necessary to detect inter-turn faults to prevent catastrophic failure of the transformer. In this study, failure analysis of a transformer that approaching the catastrophic stage is conducted using sweep frequency response analysis (SFRA) and transformer turns ratio (TTR) testing methods. Correlation between SFRA & TTR tests is analyzed. TTR test before rewinding is > 0.5%, while after rewinding is < 0.5%. 400 VAC voltage is applied, and the output voltage is measured. SFRA and TTR results show that there is a linear correlation for all phases. It can be concluded in this study that the TTR test can be used to detect transformer failure