A Novel Methodology for Detecting and Quantifying Transformer Winding Deformation Using Frequency Response Analysis

A transformer has windings and its structural integrity depends on several factors such as system short circuits,mechanical shocks during transporting,reduction of pressure of winding clamping etc.A transformer can experience severe electromagnetic forces on its winding structure during short circuits. These electromagnetic stresses can lead to winding deformation in both the radial and axial directions.Obviously it will lead to transformer failure. Historicallythe winding deformation and movement in transformer winding is detected by the measurement of leakage inductance. However immediate radial deformation results in a significant change in the leakage inductance. But axial deformation has less change in leakage inductance. Thus leakage inductance measurement method has less sensitivity.Another method was introduce in 1978 based on the frequency response analysis(FRA). In FRA testing method a signal is injected in to one terminal at the same time the response at the other terminal is measured. The commonly used methods for signal injection are swept frequency method(SFRA) and Impulse method(IFRA). This topic proposes a methodology for locating and quan[1]tifying winding deformation in transformers.It is based on the fitting of a Gray Box transformer model to FRA measurements. Here the FRA measurements were recorded both before and after the fault. The refined variations in the key parameters of the model can be then used to quantify winding deformation with in power transformers.