Phase B winding is suspected to have a problem. Frequency response measurement of transformer windings in the frequency range between 20Hz and 2MHz with injecting 5.66V across each winding is performed for this transformer. Tests are conducted on windings individually. Figure 2 demonstrates FRA test results for HV side. Software package incorporated into measuring instrument utilized in this study considered this amount of difference between frequency response measured on phase B and fingerprint as deformation.