Study on Thermal and Electromagnetic Properties of Superconducting Wires for AC Use

交流用CuNi矩阵超导导线。由于CuNi的高电阻率和低的热导率，与铜的性质相比，应用并不完全稳定，正常的转变很容易受到各种干扰的影响。因此，这种线材在淬火过程中的热行为和电磁行为明显不同于传统的铜稳定复合材料。为了研究这些性质，我们考虑了导线横截面径向的温度梯度和法向前沿的电流重分布的影响。测量了不同冷却条件下NbTi/CuNi复合丝的纵向正常区传播速度，并与三维有限元分析结果进行了比较，其中考虑了电流的再分布，横向电导对复合材料中电流分布的影响。分析型…更多的结果与实验吻合较好。而在AC。利用超导电性，还需要了解超导变压器短路电流、超导限流器电流变化、多股电缆失超过程中电流再分布等传输电流突变时的热行为和电磁行为。测量了NbTi/CuNi超导线材的失超电流与外加直流电流的关系。磁场，在10A/S到100kA/S范围内的电流扫描速度和初始电流，这是电流变化之前的输运电流。实验数据与有限元分析结果进行了比较，同时考虑了金属丝横截面径向的磁场扩散和热扩散。根据这些结果，讨论了多股超导电缆中正常区传播的机制、失超电流的退化以及这些现象对具有明显高正常区传播速度的异常失超过程的影响。较少

Superconducting wires with a CuNi matrix for a.c. applications are not fully stabilized and normal transition is easily induced by various disturbances because the CuNi matrix has a high electrical resistivity and a very low thermal conductivity comparing with the properties of copper. Therefore, the thermal and the electromagnetic behavior of such wires during quench is apparently different from that of conventional copper-stabilized composites. To investigate these properties, we consider the effects of temperature gradient in radial direction of wire cross-section and the redistribution of currents at normal front. We measured longitudinal normal-zone propagation velocities of NbTi/CuNi composites wires which have different cooling condition and compared them with analytical results by the three-dimensional finite element method taking into account the redistribution of currents; influence of the transverse electrical conductance on the current sharing in a composite. The analytical … More results agree well with experiments. And in a.c. use of superconductivity we also need to know the thermal and electromagnetic behaviors during such abrupt increase of transport currents as short-circuit current in superconducting transformers, current changing in super-conducting current limiters and current redistribution during quench process in multi-strand cables. We measured the quench current of NbTi/CuNi superconducting wires as a function of a external d.c. magnetic field, the current sweep rate in the range of 10A/s to 100KA/s and the initial current, which is a transport current just before current changing. Experimental data is compared with analytical results by the finite element method taking the magnetic and the thermal diffusion in radial direction of wire cross-section into account. From these results, the mechanism of normal-zone propagation, the quench current degradation and influence of these phenomena on the abnormal quench process with apparent high normal-zone propagation velocity in multi-strand superconducting cables were discussed. Less