Assessment of Winding Deformation in Power Transformer Using SFRA and Numerical Techniques

Abstract

In Modern power system the Power transformer is one of the most costly equipment installed in power system. Power transformers are designed to withstand a variety of stresses and mechanical forces during their service life. Abnormal forces generated during short-circuit event (occurring near to a transformer) is the main reason behind the deformation of winding and core. Hence, special care to be taken during installation of a new power transformer in an electrical substation. Studies Shows several winding deformations, which includes tilting and bending of conductors and inter-disc fault. These three faults are examined in terms of their severity of damage and location of the fault. Statistical analysis is applied to determine the overall condition of the winding. In order to contribute to diagnose these faults sweep frequency response analysis (SFRA) is a powerful and highly sensitive diagnostic method of measurement on several common winding deformations including winding deformations and displacements, shorted turns and open windings, loosened or broken clamping structures, core connection problems, partial winding collapse, faulty core grounding, core movements and hoop buckling and explores a new potential diagnostic scheme of FRA Moreover, because FRA relies on graphical analysis, it needs an expert person to analyze the results as so far, there is no standard code for FRA interpretation worldwide. To provide such a reference curve, some manufacturers now carry out SFRA tests on all new transformers before they are dispatched to site. But FRA results are graphical in nature and require trained experts to interpret test results. The work reported discusses numerical-criteria based evaluation techniques. Persons not familiar with interpreting the FRA results can apply the evaluation criteria. The various criteria help in deriving proper conclusions. By evaluating Correlation Coefficient (CC),Standard Deviation (SD) and Absolute Sum of Logarithmic Error(ASLE),Comparative Standard Deviation (CSD),Absolute Difference (AD), Min Max Ration (MM), Mean Square Error (MSE) it is possible to discriminate between defective and non-defective windings vi easily. Among these numerical techniques CCC, SD and ASLE are more effective way of finding deformation in windings.