Detection of Axial Displacement of Transformer Winding by Frequency Response Analysis without Past Measured Reference Data

Frequency response analysis is applied to diagnosis of a power transformer that experiences a ground fault due to a lightning strike. Because no past measured reference data are available for comparison, the measured data are compared between three phases. The diagnosis procedure focuses on resonances that show bipolar signatures in the transfer functions of inductive inter-winding measurements because these resonances are sensitive to axial displacements. The resonances of the transfer function of the W phase are found to disagree with those of the other phases. Therefore, it is proposed that the W phase winding is displaced axially. The transformer is dismantled and a tilt in the low-voltage winding of the W phase, which is a type of axial displacement, is found. This result indicates that frequency response analysis is applicable to detection of axial displacement, even when no past measured reference data are available.