Design And Research On Hybrid High Temperature Superconducting Fault Non-inductive Current Limiter Unit

With the rapid development of Global Network power grid,high temperature superconducting fault current limiter(HTS FCL)with advantages of self-triggered,high current limiting ability and low operation loss is an effective device to solve the problem of short circuit fault in the power girds,which can consequently provide an effective guarantee for the power transmission quality and stability of power system.As a quench type fault current limiter,hybrid HTSCL has been widely highlighted by HTSCL designers due to its sensitivity,economy and safety.It is a great of significance to research the superconducting current limiter unit(SCLU),the core component of HTS FCL,to figure out the transient resistance characteristics under the condition of the line fault and the electromagnetic properties under the non-fault state.To reduce the effect on the impedance of the grid and AC loss,the SCLU is designed as the non-inductive type.In this work,the principle of inductance calculation for the non-inductive SCLU is introduced,and the inductance of the traditional non-inductive SCLU is calculated and compared with the non-inductive SCLU based on the finite element simulation software COMSOL.A new structure of the non-inductive SCLU is proposed,and thus the key design parameters are determined according to the magnitude of the inductance and the insulativityIn order to ensure the low AC loss and high stability of the new SCLU,the AC loss is studied in this work.The basic principle of AC loss in a superconducting strip is introduced,and a simple classification of the AC loss is shown.The theoretical calculation of AC loss is studied.The 2D and 3D simulation model has been established to research the AC loss under different transport current with the power frequency of 50 Hz.The results are also compared with those of no non-inductive SCLU.According to the design parameters of the new SCLU unit in the normal state,the transient resistance characteristics of the short circuit fault are analyzed.In this work,a numerical model for the dependence of transient resistance of resistive SCLU on its transport current and the temperature is built by analyzing the electrical and thermal properties of the YBCO superconductor.In order to investigate the law of the current limiting ability of SFCL with carrying fault current in the power grid,the software PSCAD/EMTDC and MATLAB have been combined to simulate this behavior.PSCAD/EMTDC is used for line modeling and the simulation of short circuit fault operation and MATLAB is used to build the superconducting equivalent mathematic model.According to the analysis of numerical transient simulation,current-limiting ratio in HTSFCL,resistance variation characteristic in SCLU and temperature variation characteristic in SCLU are obtained under the condition of single-phase short circuit fault and three-phase short circuit fault,respectively.Finally,the properties consistent with the design and simulation of the new non-inductive SCLU are verified by the measurement.Firstly,the transient resistance characteristics of the superconducting strip are verified,and thus the transient change of the current limiting resistance is measured by the impact test.Secondly,based on the critical current test platform,a feasibility verification experiment on the design of a new type of SCLU is carried out.The AC loss test platform of the SCLU is finally built,and the test results with the compensation coil method are compared with the simulation results as well.