Structural Optimization And Safe Operation Analysis Of High-Critical-Current Superconducting Magnet

In the new-type power system with new energy as the main body,the high proportion of clean renewable energy consumption will bring more and more high demand for energy storage and dynamic energy regulation.Compared with conventional battery energy storage,superconducting magnetic energy storage technology has very high power density and very fast dynamic response speed,which is expected to solve the millisecond-level power quality problem of sensitive power loads.Superconducting magnet is the core part of superconducting magnetic energy storage system.Its safety and stability directly affect the reliability and practicability of the whole system.Once the magnet current exceeds the upper limit of its working current,namely,the critical current,the superconducting material inside the magnet will lose the superconductivity phenomenon,resulting in serious heat accumulation,and then cause a sharp temperature rise of the magnet,a large amount of volatilization of the refrigeration medium of the cryogenic container,resulting in a series of safety accidents.Aiming at the safety operation of superconducting magnets,on the one hand,based on the essential safety theory,the structure of the magnets is optimized from the application of superconducting technology,and the safety performance of the magnets is improved by increasing the critical current capacity.On the other hand,combined with accident tree analysis and trajectory crossing theory,the cause of loss of superconducting magnet accident was analyzed and safety evaluation was carried out from the system level.The main research contents and innovations of this paper are as follows:(1)Based on COMSOL multi-physical field coupling analysis platform,a twodimensional axisymmetric model of superconducting magnet is established,the variation rules of minimum critical current,vertical flux density,inductance capacity and energy storage capacity are analyzed,and the structural optimization process of gap type and step type superconducting magnet is clarified.The critical current lifting method of superconducting magnet is preliminarily formed.In the case study of the stepped superconducting magnet,the critical current of the optimized superconducting magnet increases by 26.9%,and the amount of superconducting material is reduced by 39.4%.In the case study of the gap superconducting magnet,the critical current and energy storage capacity of the optimized superconducting magnet are increased by 23.1% and 39.2%respectively.(2)A small capacity superconducting magnet was wound based on the optimization scheme of gap superconducting magnet,and the inductance and critical current parameters of the magnet were tested and verified experimentally.The experimental results show that the inductance of the optimized magnet reaches 10.1m H and the critical current rises to 112.5A,which is about 5% deviation from the simulation results.Based on the superconducting magnet system,a small capacity superconducting energy storage experimental circuit was built,which verified the feasibility of superconducting energy storage to maintain dc power load safely,reliably and with high quality.At the same time,based on the semiconductor switch short circuit fault experiment and based on the PLECS software magnet overcurrent simulation,quantitative analysis of the superconducting magnet system security risks and loss of superconducting energy loss law.(3)Taking the superconducting magnet loss accident as the top event,55 kinds of basic events leading to loss of superconducting magnet accident are analyzed in detail,and the superconducting magnet loss accident tree is established based on this,and the basic event combination leading to the minimum loss of superconducting magnet and the basic event with the maximum structural importance are identified.Based on the theory of trajectory crossing,12 kinds of failure cases are analyzed from the aspects of "things" and "human" in the operation of superconducting magnet system,combined with the actual safety accidents of the magnet system.Finally,from the superconducting magnet,cooling system,control system and human factors,these four aspects put forward has certain engineering application value of the "things" + "human" of accident prevention and control measures,designed to fundamentally improve the safety of the superconducting magnet operation stability,minimize the probability of safety accidents and hazards.To sum up,this paper organically integrates relevant theories and evaluation methods of electrical engineering and safety engineering in the study of superconducting magnet system,which is an interdisciplinary exploration in applied superconductivity,cryogenic refrigeration,power electronics,accident prevention,emergency management and other fields.This article carried out the theoretical analysis and experimental verifications from two aspects of technology and management to the superconducting magnet quenching accidents,initially formed some feasible technology and management plans to strengthen the safety of superconducting magnet,and finally put forward the "things" + "human" based accident prevention and control measures,with aims to provide a certain theory basis and technical reference for the safety early warning and emergency disposal of superconducting magnet systems.