Power Auto-transformer Mechanical Faults Diagnosis ‎Using Finite Element based FRA

Frequency response analysis (FRA) is a sensitive method established for testing the mechanical integrity of transformers. However, interpretation of FRA signature still needs expert opinions and there is no FRA interpretation code generally accepted. Various mechanical faults with different extents on power transformers are required to aid FRA interpretation. To address this challenge, in this paper a high definition 3D FEM model of a three-phase, three-winding, 125-MVA power auto-transformer was constructed using finite element method and verified by experimental FRA measurements. Various radial deformations and axial displacements were formed using FEM model and the extracted parameters of the winding detailed model were used to obtain power transformer frequency responses. The commonly used appropriate statistical indices in FRA diagnosis were utilized for interpreting FRA results. The study showed that the frequency range between 1-100 kHz is mainly affected by the mechanical faults and the 1st resonance of the double-peak feature of the auto-transformer FRA remains unchanged during winding radial deformation and axial displacement.