Stress And Strain Analysis Of High Temperature Superconducting Energy Storage Coil

With the development of the society,people have higher and higher requirements for the power quality.High-temperature superconducting energy storage system can effectively balance the load fluctuations in power systems,and maintain the voltage and frequency stability.Superconducting magnet is the most important thing of superconducting energy storage systems,so it is necessary to analyze the magnet mechanical stability.High-temperature superconducting energy storage coil is subject to two different kinds of stresses during operation.One is the electromagnetic stress generated by the ampere force of the superconducting coil,and the other is the thermal stress generated by the temperature rise caused by the AC loss of the superconducting coil during charging and discharging process.In this study,analyzing the stress and strain of superconducting coils is from two aspects:electromagnetic stress and thermal stress.The traditional method of calculating AC loss is used to solve 2D model of superconducting tape,and it is difficult to calculate the 3D superconducting model due to poor convergence and long calculation time.In this study I propose a fast AC loss calculation method based on iterative conductivity.In this method the relationship between the conductivity and the electric field strength E is used to describe the highly nonlinear E-J constitutive relation of superconductors,and the relationship between magnetic field and critical current is also considered.This method can accurately describe the electromagnetic behavior of the superconductor and quickly solve the AC loss of superconducting coil.In this thesis I firstly analyze the electromagnetic stress-strain distribution of four stacked superconducting tape,the results show that the electromagnetic stress and strain distribution of the superconducting tape is not uniform,and the maximum stress is 3.95×104 Pa.After impregnating the epoxy resin,the maximum stress of stacked superconducting tape is 2.16×104 Pa.Combined with the stress value and the stress distribution of stacked superconducting tape,it can be seen that the impregnated epoxy resin can effectively reduce the electromagnetic stress on the superconducting tape.Secondly I analyze the stress-strain distribution of the superconducting energy storage coil under two fixed constraints,the results show that the superconducting energy storage coil has a certain deformation under the electromagnetic stress,and the deformation causes the stretching of superconducting coil.However,the stress and strain in both cases does not exceed the critical value of the superconducting tape.In this thesis I build a three-dimensional superconducting coil finite element model to analyze the thermal stress-strain distribution of superconducting coil with AC loss as the heat source.The AC loss distribution of the superconducting coil is calculated by the electromagnetic analysis.The results show that the AC loss of the superconducting coil has periodicity,and the period is half of current,and the maximum AC loss density is 5.97×105 W/m3.Then I combined with solid heat transfer theory and thermal expansion theory to analyze the thermal stress strain of superconducting coil.The results show that the maximum thermal stress of the superconducting coil is 1.08×104 Pa.The maximum total displacement of the superconducting coil is 8.2×10-7 under the consideration of thermal expansion only.By analyzing the thermal stress and strain distribution of the superconducting coil,it can be concluded that the distribution of the superconducting coil is not uniform,and the heat is concentrated in some area.If the heat transfer is not in time,it may cause gap between the superconducting coil and the epoxy resin insulation layer.In this thesis I wrap a superconducting double cake coil to analyze the effect on the impregnated with epoxy resin.After analyzing the influence of the impregnation curing process on the critical current of superconducting tape,the optimal impregnation curing process is obtained.Superconducting coil using vacuum impregnation method,and measuring the critical current of the superconducting coil before and after impregnation curing process.The result shows that the critical current of the superconducting coil is reduced by 3.2%.