Calculation Of Compound Coupling Of Power Transformer Considering The Influence Of GIC

With the massive input of high-voltage DC transmission network in the construction of power systems,transformers,as the main components of connecting and regulating AC and DC transmission systems,are susceptible to harmonic losses caused by DC system signals and regional latitude and longitude during operation,resulting in local overheating,which in turn leads to insulation damage and reduced life span.The rise of harmonic content also leads to the occurrence of paramagnetic vibration and vibration displacement of the internal structural components of the transformer.Therefore,this thesis combines theoretical analysis and finite element simulation calculations to conduct in-depth investigation and comprehensive analysis on four aspects of transformer excitation characteristics under the influence of Geomagnetically Induced Current(GIC),harmonic loss calculation,magneto-thermal structure analysis and bias vibration calculation,whose main research contents are as follows.(1)Considering the effect of GIC on the transformer excitation current,a saturation angle calculation method is introduced based on the core half-saturation curve to analytically calculate the amplitude variation and harmonic components of the magnetization current under the influence of GIC,and to analyze the variation relationship between the DC current and the excitation current for different values.At the same time,by introducing Unified Magnetic Equivalent Circuit(UMEC)to simulate the magnetization characteristics of the core,the time domain transient analysis of the transformer under GIC conditions is realized based on the finite element analysis,and the Fourier analysis of the excitation current is used to derive the spectral characteristics,harmonic components and the relationship between the saturation angle and the excitation current of the transformer,which provides a theoretical basis for the accurate calculation of the magnetic density distribution and harmonic It provides a theoretical analysis basis for the accurate calculation of magnetic density distribution and harmonic losses of transformers under the influence of GIC.(2)Under the influence of different GICs,the transformer leakage increases,and the leakage leads to the increase of transformer loss which is prone to local overheating.In order to accurately analyze the loss change of transformer under the influence of GIC,this thesis is based on the calculation method of transient analysis combined with finite element.Firstly,we build a DC bias analysis model of the transformer considering the effect of GIC based on PSCAD,and obtain the loss calculation coefficients of the transformer under the influence of different DC bias electromagnetic transient analysis.The loss distribution of the transformer under the influence of different GIC can be studied.(3)Based on the loss coupling coefficient correction,the loss analysis of different structural parts of the transformer is accurately obtained,and the three-dimensional finite element thermal analysis model of the transformer is built by magnetic thermal coupling.Using the loss values calculated in the electric-magnetic circuit coupling model as the heat source input,while considering the transformer oil on heat dissipation influence factors,the simulation obtains the temperature rise of each structural member of the transformer under different GIC conditions each structural member temperature rise distribution and change law.(4)The increase of transformer leakage will lead to the increase of magnetostriction of transformer core,which causes the increase of transformer vibration.In this thesis,based on the magnetic-structural coupling calculation model,we propose the paramagnetic vibration analysis method of power transformer,that is,based on the transient analysis of finite element method to extract the electromagnetic force of core-structural parts and oil tank of transformer under different DC influence,extract the electromagnetic force for FFT transformation and map to structural force field as excitation.The FFT transformation is applied to the structural force field as the excitation,and the vibration displacement distribution under different DC bias magnetism is studied and compared.Finally,based on the numerical calculation of "magnetic-structural" coupling,the maximum deformation of the internal structure of the transformer under different GIC is studied to provide a basis for the analysis of safe operation of the transformer.