Research On Properties Of Quasi-isotropic Strand Fabricated By 2G Coated Conductors

Because of high critical temperature,high critical magnetic field,remarkable critical current(Ic)density as well as excellent mechanical properties,ReBCO coated conductors(CC)or second generation(2G)CC show great potential for use in power transmission cables,store energy equipment,fault current limiters,magnets and so on.As the technology of superconducting material and manufacturing technique are enhancing day by day,ReBCO CCs can be already produced commercially by one kilometer length up to now.Since a single CC has limited current ability and anisotropic mechanical and critical current characteristics,the conductor or strand fabricated by multi-CCs is essential to acquire high current capacity.Owing to quasi-isotropic critical current and outstanding engineering current density,quasi-isotropic strand(QI-S)fabricated by ReBCO CCs are promising for applications in case of electric devices operating at high temperature and low magnetic field environments or in other case of magnets operating at low temperature and high magnetic fields.Direct current(DC)performance,Alternating current(AC)losses,electromechanical behaviors and quench behaviors of quasi-isotropic strand(QI-S)fabricated by ReBCO CCs are studied in this thesis.The specific contents are researched as follows:DC properties of QI-S operating at 77 K are studied as well as the factors affecting current distribution among CCs such as strand inductance,inter-CC resistance and the soldering method of current lead,according to which a QI-S with minimum current transfer length and evenly current distribution among CCs can be designed.To accurately predict Ic of QI-S,a self-consistent model for calculating Ic is proposed and verified by the corresponding measurements at 77 K,which will be a powerful tool for design and optimizing QI-S.Based on H-formulation of Maxwell's equations,a model for calculating AC losses of QI-S is built and verified by measuring AC losses of QI-S sample with the help of pick-up coil method setup at 77 K.This model can be a new tool for estimating and optimizing AC losses of QI-S.After calculation made by the model and experimental measurements,dependences of AC losses of QI-S on background magnetic field magnitude,frequency and orientation are acquired.Effects of twisting among CCs and inter-CC resistances on components of AC losses are investigated.The whole results can be as the basic for design the cooling system of QI-S equipment.By means of analytical calculation,three dimension(3D)structure simulation by ANSYS software and experimental measurements,electro-mechanical behaviors of QI-S under twisting,bending,transverse compression and axial tension loads are investigated and critical mechanical parameters under those mechanical loads are determined,which is very helpful for the application.During the tension tests,a new strain measuring method by using fiber bragg grating(FBG)sensor is tried,which effectively and accurately acquires the strain variations of QI-S in liquid nitrogen bath through calibrating the measuring results of extensometer,so FBG sensor can be a new method for monitoring the structure status of QI-S.3D electro-thermal model established by Comsol Multiphysics is taken to study the quench behaviors of QI-S at 4.2 K temperature both in liquid helium and adiabatic conditions.Minimum quench energy(MQE)and quench propagation velocity(QPV)of QI-S when carrying different operation currents are studied as well as their relation with the inter-CC thermal and electrical resistances.The results can be the reference for safe operation and protection of fusion coils make by QI-S.According to the studied results,50 kA CICC and 60 kA Rutherford cable for making fusion magnet coils are designed by using round QI-S as the basic element in the last chapter.Equations of strain calculation during the manufacture and bending process are derived and critical twisting pitch and bending radius of CICC and Rutherford cable are determined.In the end,current sharing temperature(Tcs)and AC losses of CICC and Rutherford cable operating at 4.2 K 12 T environment are also analyzed.