Estimating The Effect of Axial Displacement on Equivalent Circuit Parameters of Transformer Winding Using Finite Element Method

Abstract

Among the different condition monitoring and diagnostic techniques for evaluating mechanical damages in power transformers, Swept Frequency Response Analysis (SFRA) is the most widely used and sensitive tool. Any mechanical fault caused due to short circuit forces or during transportation of transformer causes considerable changes in the equivalent circuit parameters of the winding, which results in detectable changes in the frequency response trace. This trace is then compared with that of a healthy winding for detecting and quantifying the extend of mechanical damage. For interpreting the exact changes for diagnostic purposes, the FRA trace deviation needs to be acknowledged precisely. The winding is modeled as a mutually coupled N section ladder network consisting of inductance and capacitance. These parameters are evaluated initially for a healthy winding and then for axially displaced winding using the Finite Element Method. The changes on the equivalent circuit are then quantified for a wide range of single and multiple axial displacements. The ramification of single and multiple axial displacements on the frequency response signature is also discussed here.