Three Dimensional Simulation And Experimental Study On Thermal Stability Of A Quasi-isotropic Strand

Superconductors are widely used in the fields of high temperature,low field and low temperature,high field because of their zero resistance and complete diamagnetism.With the development and progress of the second generation of high temperature superconductors,the application of high temperature superconductors in the electric power industry has a bright prospect.During the two sessions in 2021,"peak carbon dioxide emissions,carbon neutralization" was written into the government work report for the first time.Superconducting power technology,with its advantages of extremely low loss in power transmission,perfectly meets the requirements of energy-saving emission reduction of this action plan.However,for a long time,the application of high temperature superconductor in power system has faced a key problem:quench of high temperature superconductor.The investigation on the minimum quench energy(MQE)and quench propagation velocity(QPV)of high temperature superconductors is of great significance to the quench detection and protection of high temperature superconductors when faults occur in power systems.In this dissertation,many quench models for quasi-isotropic high temperature superconducting strand are established to study the thermal stability of the strand,and they are proved by experiments.Firstly,in this dissertation,by establishing a three-dimensional electrothermal quench model based on superconducting shunt theory for quasi-isotropic high temperature superconducting strand,and considering the anisotropy of thermal conductivity of superconducting tapes,the quench and quench recovery process of Q-IS are showed.What's more,the changes of current density and temperature are also showed.Secondly,considering that the self-field of the strand may affect its thermal stability,a three-dimensional electromagnetic thermal quench model based on H method is established to study the thermal stability of strands under self-field,including the calculation of minimum quench energy and quench propagation velocity.The changes of current density,magnetic induction and temperature in the quench process are shown.The results show that MQE and axial QPV of strands are consistent with the operating current.This model can be used to study the thermal stability of HTS conductors in external field.Then,considering that the contact thermal resistance of the internal interface of the HTS strand affect the heat flow conduction,and then affect the quench behavior,this dissertation qualitatively and quantitatively analyzes the influence of the interfacial contact thermal resistance of the HTS strand on its thermal stability.It is found that there is temperature gradient in the cross-section of the strand when we consider the existence of contact thermal resistance.The contact thermal resistance increase the maximum temperature of hot spot,MQE and QPV of the strand.The influence of contact thermal resistance among superconducting tapes on the thermal stability of strand is far less than that of contact thermal resistance between copper sheath and aluminum filler.Finally,a quasi-isotropic superconducting strand is fabricated.The magnetic field generator is used to provide external thermal disturbance on the middle of the strand.The MQE and QPV under different operating currents are measured and compared with the simulation results.It is found that they are consistent in the range of the allowable error,which verifies the rationality of the quench model.