Investigations Of Electromagnetic And Mechanical Behavior Of High-temperature Superconducting Cables

Compared to conventional conductors,superconductors have advantages such as small size,high current density and low loss.They have broad applications in fields such as nuclear magnetic resonance(NMR),maglev train,electric power transmission and storage.Additionally,the discovery of superconducting materials offers a potential solution to the energy crisis.Magnet systems made from superconductors can generate high magnetic fields,confining high-speed and high-temperature plasma within controlled thermonuclear fusion reactors,enabling the continuous production of new clean energy.High-temperature superconducting cables are typically constructed using either round wires or flat tapes.By employing multi-level or multi-layer winding techniques,superconducting round wires or tapes can form a compact and uniform cable,thereby enhancing its current-carrying capacity and reducing the AC losses within the conductor.However,the critical current density of high-temperature superconducting materials is sensitive to strain.Strain induced during production,cooling,and operation may lead to the degradation of the current-carrying capacity of superconducting cables.This directly poses a threat to the functionality and safety of superconducting devices during operation.Therefore,the investigations of the electromagnetic characteristics and mechanical behavior of high-temperature superconducting cables,as well as analyzing current density,magnetic field,stress and strain distribution under multiple fields,is important to optimize cable structures and enhance performance.The main research contents of this paper are as follows:Firstly,the electromagnetic model is established for Bi2212 superconducting round wire.Due to the extremely small diameter of superconducting filaments in the wire,the calculation speed is improved while ensuring the accuracy of the results by optimizing the initial model and assembling dispersed superconducting filaments into superconducting bundles.Using the optimized model,the distribution of magnetic field and current density in the superconducting coil,as well as the AC losses generated by the superconductor and substrate are investigated.Furthermore,an electromagnetic model of CORC cables,which are made from high-temperature superconducting tapes,is established using the T-A formulation.The relationship between AC losses and the helical angle of the CORC cables is studied.The accuracy of the electromagnetic model is validated by comparing the AC losses obtained from experimental testing and numerical predictions.Next,the mechanical behavior of multi-stage cables wound with superconducting wires is analyzed under axial tension and uniform temperature variation.The line contact model and elliptical contact model are established based on the contact between the wires and cables,and the contact deformation is calculated using the Hertz contact pressure distribution model.Considering the effects of Poisson’s ratio,temperature,and contact,the mechanical characteristics of the strand and cable under combined axial tension and uniform temperature variation are derived based on the elastic thin rod theory.Due to the coupling relationship between the local mechanical response of strand and radial deformation,the iterative method is employed to reduce the errors between the resultant forces and moments and the finite element results.Furthermore,the influence of the change in helical angle on the axial force and helical radius of the cable is investigated.Then,the two-dimensional axisymmetric electromagnetic and mechanical models for multi-layer CORC cables are established to study the electromagnetic and mechanical behavior of CORC cables wound by multiple layers of high-temperature superconducting tapes.The electromagnetic model is utilized to analyze the current density,magnetic field,and AC losses generated in the cable under three different current loading methods: free,uniform,and intra-layer uniform.The impact of magnetic field and air gaps within the cable on AC losses and current carrying capacity is investigated.Furthermore,the distribution of electromagnetic forces generated by the CORC cable considering with or without of shielding current is analyzed.The stress and strain distributions under the influence of electromagnetic forces are also investigated.The impact of gap size between CORC cables and the thickness of the outer copper layer on stress and strain are evaluated.Finally,the electric-magnetic-mechanical coupled model of the CORC cable is established to investigate the influence of structural deformations on critical current density and electromagnetic field distribution.Initially,the mechanical model is utilized to calculate the stress and strain generated in the CORC cable during the winding and cooling processes.Subsequently,strain and structural deformations are introduced into the electromagnetic analysis to study their effects on the critical current density of the superconducting tapes while considering the action of electromagnetic forces.Based on the sequence of CORC winding,cooling,and electromagnetic loading,the strain and critical current density of the CORC cable under multiple fields are determined,and the distribution patterns of strain under different external field conditions are explored.Furthermore,through the analysis of electromagnetic and mechanical behavior of CICC conductors wound with CORC cables under multi-physics field,the electromechanical characteristics of the CORC cables at different locations within the CICC conductor is obtained.