Application of numerical techniques to FRA data for diagnosing integrity of transformer windings

The paper presents the investigations carried out on a transformer for various simulated faults to obtain FRA data and study the applicability of various numerical techniques. The numerical parameters Viz., Min-Max ratio (MM), Mean Square Error (MSE), Maximum Absolute Difference (MABS), Absolute Sum of Logarithmic Error (ASLE), Standard Deviation (SD) and Correlation Coefficient (CC) computed in three different frequency bands are presented to aid the interpretation of SFRA data. Frequency responses among identical phases of the sister units and different phases of a healthy three phase transformer were used to obtain the proposed representative numerical parameters for comparison. Deviation of the numerical parameters from the proposed representative parameters for different types of simulated faults is analyzed to diagnose the condition of the transformer. The analysis of the deviations in the parameters suggests the possibility of using the numerical approach to diagnose the transformer winding displacements and deformations. Interpretations of the results presented also indicate the possibility of discriminating the faulty winding using numerical parameter, computed from reference base data, symmetry of the windings, sister units and type of winding approach, and comparing them with the proposed representative numerical parameters presented in the paper.