Detection And Diagnosis Of Deformation Of Winding In Transformer Using SFRA

Power transformers are the most expensive and critical component of our power system.Its failure would be a costly event.Winding deformation is caused mainly due to short circuit events,other reasons may be ageing of insulation,and mechanical stresses developed due to transportation.Although,deformation may not result in immediate failure,however the dielectric strength of the winding is greatly reduced.And a further untoward short circuit faults may result in complete rupture of insulation which will result in complete damage of the winding.To prevent permanent damage of the transformers,a routine diagnosis is necessary for detection of winding deformation.Among all the diagnostic approaches,sweep frequency response analysis(SFRA)is a powerful and highly sensitive diagnostic method.In this work,for the purpose of analysis of deformation on the transformer winding,a benchmark winding is considered which has already been validated for experimental studies.It is found from the comparison of 10 and 20 section models on the basis of accuracy,number of resonant frequencies required,and transfer function computation and complexity that the optimal model is the 10 section model.The winding is modeled using finite element method(FEM)based software and parameters such as capacitance and inductance are calculated for 10 section healthy coil.Using these parameter values,SFRA plots are obtained which are a set of reference for deformation analysis.The winding is modeled as radially and axially deformed coils using FEM software.The parameters change with deformation in the winding.The deformation is carried at five consecutive sections,and affected parameters are calculated for the same.The main purpose of doing so is to find the location of deformation corresponding to a similar deformation in an actual transformer.The main advantage of the FEM modeling is we can deform the sections as desired unlike in an actual case and obtain the fingerprint graphs from the modified parameter values.The SFRA plots are obtained for the deformations at five sections for axial and radial deformations.A comparison is carried between the SFRA plots for deformed cases with the reference set.The deviations observed are in resonant frequencies,peak current magnitude and bandwidth.From the observations,the type and location of deformation can be found corresponding to a similar deformation in an actual transformer.The percentage of deviation in resonant frequencies both in radial and axial deformation is not so significant as it oscillates between 0.2%to approx.2%for all the five sections radially deformed.The percentage of deviation is little higher for peak input current with a maximum of around 13%.However,the bandwidth has a greater deviation and hence more sensitive towards change in the physical configuration of the transformer winding.The percentage of deviation in peak input current for axial deformation shows a greater deviation than bandwidth from 3rd order onwards,unlike radial deformation.