Electromagnetic-Thermal Analysis Method Of High Temperature Superconducting Magnets

The electromagnetic and thermal stabilities of superconducting magnets have direct effects on the operation feature of the electromagnetic system such as the power system with superconducting facilities. Since the electromagnetic feature of high temperature superconductors(HTS) are highly depend on the temperature, the current density and the magnetic field vector, it is extremely complex to analyze the stability of HTS magnets as the current wave, the magnetic field distribution, heat losses and the cooling condition should be taken into consideration. This paper has investigated the calculating method of AC loss which is the base of the electro-thermal analysis, the relationship between inductance variation and physical factors influencing the critical current, besides, methods to reduce the heat sources of HTS magnets have been investigated including the optimizing method of current leads and reducing the joint resistance of HTS tapes.(1) In terms of AC loss calculation, a numerical model based on different tape features has been established. Then, this model has been applied to calculating the AC loss in a HTS double pancake coil in different currents. What is more, the direct couple of electromagnetic field and the temperature field have been realized by the finite element method. This model is able to analyze the temperature distribution continuously with different cooling conditions, laying the foundation for assessing the dynamic thermal stability of HTS magnets.(2) The related technics to increase the electro-thermal stability have been studied. First, a method to reduce the AC loss by applying flux diverters in a HTS superconducting magnetic energy storage magnet has been presented considering the magnetization features of the flux diverters. Second, based on the optimizing design, a composite current lead operating in 250 A has been fabricated. Third, a splicing machine has been developed to fabricate the low resistance HTS tapes joints repeatedly and reliably. Finally, essential features of the no-insulation coil has been studied which has proved that the thermal stability of HTS magnets can be improved by this magnet configuration.(3) The inductance variation of HTS magnets has been investigated by applying the electro-thermal direct coupling model, considering the magnetic penetration in different temperatures and directing transport currents. The result is of great value in the inductance designing on HTS energy storage magnets.