Simulation And Experimental Study On Deformation Detection Of Power Transformer Winding Based On Sweep Frequency Impedance Method

With the continuous and rapid growth of the national economy,the amount of electricity used by society is increasing day by day.This places higher and higher demands on the reliability of the power system.How to ensure the stability and reliability of power systems and power equipment has always been a research hotspot in the power industry.Power transformer is one of the most important equipments in the power system.Its operational reliability is high and its cost is expensive.Insulation aging,inrush current and other internal and external factors make the power transformer windings vulnerable to damage,causing transformer failure.The frequency response method can detect the winding state without disintegrating the transformer,which is the most widely used method for domestic and foreign power industry practitioners.However,this method still has misjudgment when evaluating the state of the winding,and it is not sensitive enough to slight deformation.Under this background,it is of great significance to study new detection methods and how to make more accurate judgments on winding deformation,which is of great significance for advancing China's strong power system construction.Based on the principle of frequency sweep impedance method,the sensitivity of this method to transformer winding deformation detection is discussed.The capacitance,inductance and resistance parameters of transformer winding are calculated by analytical algorithm,and the total parameter circuit model of transformer winding is set up.Based on the model,the connection simulation and measurement study the health and reason of the winding.The characteristics of the sweep frequency impedance spectrum in the case of barrier are taken as the main body,the characteristic parameters of the sweep frequency impedance spectrum are extracted and the validity of the characteristic parameters in detecting the transformer winding deformation is demonstrated.The main conclusions of this thesis are as follows:(1)Equivalent circuit modeling and simulation of single-phase model transformers are combined with analytical calculation methods.Theoretical analysis proves that the swept impedance method has higher sensitivity in detecting winding deformation.The variations of the equivalent circuit parameters during the radial deformation,axial displacement,axial bending and interlayer short-circuit faults of the windings are analyzed.The results show that the radial deflection mainly affects the equivalent inductance and the inter-layer capacitance of the windings.The axial displacement fault has a great influence on the mutual inductance parameters of the winding and the capacitance between the high and low voltage windings;the axial bending fault is mainly reflected in the change of the interlayer capacitance;the short circuit fault has the greatest influence on the winding and will cause a large change in the inductance.(2)The axial displacement fault of the winding is simulated on the single-phase transformer,and the axial bending,the radial deformation and the short circuit fault are simulated on the three-phase transformer.The deformation windings of different positions and different faults are set up respectively,and the sweep frequency impedance curve is tested.It is found that the amplitude-to-deformation mainly affects the sweep impedance curve in the middle and high frequency bands,and the change direction of the resonant frequency is opposite in the middle frequency band and the high frequency band;the axial deformation mainly affects the frequency sweep impedance curve in the high frequency band.The fault has a great influence on the frequency sweep impedance spectrum in the whole frequency band.(3)Analyzed the basic characteristics of the frequency sweep impedance spectrum,and propose the characteristic parameters of the impedance spectrum of the winding with the extreme value of the impedance amplitude,phase-to-zero point,70° phase characteristic frequency point,and statistically compare the amplitude direction.Various characteristic parameters of deformation,axial deformation,and short-circuit faults show that the phase-to-zero point and the 70° phase characteristic frequency point have high sensitivity,and combined extreme point frequency variation and correlation coefficient,the type of fault on the winding can be effectively identified.