Toward reliable interpretation of power transformer sweep frequency impedance signatures: experimental analysis

Power transformers play a significant role in maintaining the reliability of electrical power transmission and distribution networks. The probability that a transformer will fail increases with the aging of its insulation system [1]. Core deformation and winding movement may be caused by severe electromagnetic forces generated during short circuit faults [2]-[5]. Although a transformer may still work normally with minor axial or radial winding deformations, accumulating effects of these deformations may lead to sudden catastrophic failure of a transformer [6]. According to an international CIGRE survey conducted on power transformers covering the period 1996 to 2010, 19.4% of transformer failures during this period were attributed to windings- related problems [7]. It is therefore essential to assess the mechanical integrity of transformers which have been exposed to severe short circuit faults or lightning, or relocated, and take appropriate remedial action.