Research On Magnetization Loss And Dynamic Resistance Characteristics Of High Temperature Superconducting Coils

REBCO high-temperature superconducting(HTS)coated conductors have become the preferred wire choice for HTS electromagnetic applications due to its high current carrying capacity and advanced mechanical properties.In these potential applications such as HTS synchronous motors,HTS flux pumps,HTS persistent current switches,REBCO coated conductors and coils generate AC loss including dynamic resistance loss and magnetization loss when carrying DC currents in an AC magnetic field environment.The existence of AC loss seriously restricts the stability,reliability and cost of HTS electromagnetic equipment.In addition,dynamic resistance is a key technical indicator for HTS flux pumps and HTS persistent current switches,directly affecting the amplitudes of AC loss.Therefore,it is of great significance to study the magnetization loss and dynamic resistance characteristics of REBCO coated conductors and coils at theoretical and engineering-guided levels to reveal the underlaying loss mechanisms and to underpin relevant engineering applications.Based on experimental measurements and numerical calculations,the magnetization loss and dynamic resistance characteristics of REBCO coated conductors and coils are studied in this doctoral thesis.The following contents are included in this doctoral thesis:(1)An experimental method of AC susceptibility and magnetization loss for long HTS superconducting wire is proposed.Based on the dimensions of a rectangular pickup coil,a one-dimensional numerical analysis model of AC susceptibility is established using Brandt method and E-J power law,which reveals the experimental requirements of the rectangular pickup coil’s width and height.Finally,a comprehensive test platform for AC susceptibility and magnetization loss is designed and built.(2)Considering the asymmetric critical current characteristics of REBCO coated conductors,the field-angle-dependence and temperature dependence of the magnetization loss in REBCO coated conductors is experimentally investigated;Based on the effective magnetic field,a quantitative criteria is defined when using the analytical model of the magnetization loss.Based on the experimental data and finite element simulation model,the intrinsic correlation between the asymmetric critical current characteristics and the magnetization loss is revealed and the influence of operating temperature on the correlation is also investigated.(3)A systematic experimental measurement on magnetization loss component and dynamic resistance loss component is carried out for commercial-available REBCO coated conductors under the sinusoidal AC magnetic field with the DC currents.And the temperature dependence and frequency dependence for the dynamic resistance and two loss components are explored;the mechanism of AC loss is also revealed via visualized electromagnetic parameters from the finite element simulation model.(4)The dynamic resistance characteristics of REBCO coated conductors are studied under the conditions of an AC magnetic field superimposed with a DC bias magnetic field;The influence of the DC bias magnetic field’s amplitudes,DC current amplitudes,AC magnetic field’s waveforms,amplitudes and frequency is analyzed;The concept of dynamic threshold magnetic field is proposed based on the dynamic resistance theory and the dynamic voltage response,providing theoretical and engineering references.(5)Experimental investigation on the magnetization loss and dynamic resistance characteristics of REBCO superconducting coils is conducted.Firstly,the field-angle dependence and temperature dependence of a REBCO double pancake coil is experimentally investigated under the AC magnetic field environment only.Then the dynamic resistance and loss components of REBCO double pancake coils and double racetrack coils are studied under the combined the AC magnetic field with DC currents.The influence of AC magnetic field’s amplitude and frequency,DC current’s amplitude,operating temperature and coil geometry on dynamic resistance and loss components are analyzed,revealing the general loss characteristics of REBCO superconducting coils.