Experimental And Numerical Studies Of Quench Behavior Of High Temperature Superconducting Composite Tapes Trigged By A Heat

High-temperature superconducting materials are widely used in the fields of energy,electrical engineering,medical treatment and traffic because of their good current performance and thermal stability.It has been successfully applied in superconducting structures such as high/low temperature superconducting magnets and fault current limiters.In the future,it is expected to be applied to a new generation of large magnetic constrained Tokmark apparatus.In these huge installations,the stability and safety of superconducting materials and structures in complex environments such as low temperature,high currents,and high magnetic fields are fundamental and key issues in their applications.Quench is a typical phenomenon of electromagnetic instability of superconductors,accompanied by the evolution and interaction of temperature,mechanical,and electromagnetic behavior.In practical applications,such as superconducting coil winding,cooling,a pre-stress or pre-strain state is inevitably generated.Therefore,the multi-field performance of superconducting materials and structures under pre-strain,especially during a quench process,is performed in this study.The multiple behaviors and influences among different fields are of great significance.In this thesis,experimental and numerical simulations of the quench stability of high-temperature superconducting tapes in pre-strain state,including the occurrence and propagation of quenching,and the effect of pre-strain on the thermal behavior,were carried out.Firstly,to conduct a quench test on pre-strained HTS composite tapes,a mechanical-electric loading and testing platform was established in which the quench is triggered by a hot-spot.Various pre-strains can be applied and the real-time measuring and monitoring the voltage,strain,and temperature during a quench process were performed.Secondly,based on the established test platform,the experimental study on the quench behavior of YBCO high-temperature superconducting composite tapes with different pre-strains triggered by hot-spot was carried out.The mechanical-thermal behaviors of the superconducting tape during the process of quench and propagation were investigated experimentally.The voltage and strain response signals were compared and analyzed.Furthermore,the influence of pre-strain on the behavior of critical current degradation caused by quench was also analyzed.Finally,in order to analyze comprehensively the thermo-elastic behavior during the quench process of the high-temperature superconducting composite tapes,a quench analysis model based on one-dimensional superconducting tape using finite element method was developed for the quench process,the temperature evolution and the thermo-elastic behavior in the tapes of the two types of HTS composite tapes with pre-strains.The numerical simulations were compared to experimental observations for explaining some experimental phenomenon.As a pre-strain exists,the superconducting tapes undergo a strain reduction before the quench occurs,and then the strain changes abruptly when the quench propagation arrives.The effect of pre-strain shows a promotion on quench of superconducting tapes and an enhancement of the speed of quench propagation.