Abstract In this work we evaluate the performance of various electrical conductors, both normal-state and superconducting, at cryogenic temperatures with an eye towards motor, generator, and power transmission applications for use in all-electric and more-electric aircraft. In addition to MgB2 and YBCO superconductors, we consider high purity Cu and Al as well as carbon-nanotube (CNT) yarn. We analyze the normal-state conductors for current carrying capacity at room temperature as well as LN2 (77 K) and liquid hydrogen temperatures (20 K), where appropriate. To parameterize these materials for aerospace applications we have explored various options for defining current capacity metrics for these conductors at cryogenic temperatures. Paralleling definitions for ambient environment conductors, we first define electrical current capacity in terms of a limiting temperature rise for (i) windings directly immersed in a pool-boiling cryogen environment, and (ii) the case of thermal conduction though an epoxy winding. While neither metric is fully satisfactory, their implications are important. These results are then compared to a current capacity criterion developed in terms of a specified loss generation limit, which turns out to be a more meaningful approach. The results for these normal-state conductors operating at cryogenic temperatures are then compared to superconducting MgB2 and YBCO. After this, we consider two cases for overall system-level benefit in terms of power density, one for the case where the size of the cryogenic cooling apparatus is included, and a second case where the cooling is “free” (e.g., when liquid hydrogen is already onboard). We find total system weight reductions for the cryocooled case only for the superconducting options. If time varying magnetic fields are present, superconductor filament size must be kept small; an expression for limiting filament size is developed. For the case of “free” cooling, higher current levels are possible leading to reductions in winding size up to 16X using cryogenic normal-state conductors and values of 100-200 X for superconducting options. The waste heat load is also substantially reduced because the total size of the winding is strongly reduced. This may significantly reduce the thermal management burden, a difficult problem for electric propulsion aircraft. We conclude that both superconductors and normal-state cryogenic conductors can increase power density in a case when liquid cryogen is “free”, but only superconductors can lead to total system power density increases when heat cannot be rejected to the fuel.

中文翻译：

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航空航天低温电机、发电机和传输电缆用电导体的性能指标

摘要 在这项工作中，我们评估了各种电导体（常态和超导）在低温下的性能，着眼于全电动和多电动飞机中使用的电机、发电机和电力传输应用。除了 MgB2 和 YBCO 超导体外，我们还考虑了高纯度 Cu 和 Al 以及碳纳米管 (CNT) 纱线。我们分析了常态导体在室温以及 LN2 (77 K) 和液氢温度 (20 K) 下的载流能力，在适当的情况下。为了为航空航天应用参数化这些材料，我们探索了各种选项来定义这些导体在低温下的电流容量指标。周围环境导体的并行定义，我们首先根据 (i) 绕组直接浸入池沸腾的冷冻剂环境中的限制温升和 (ii) 通过环氧树脂绕组进行热传导的情况来定义电流容量。虽然这两个指标都不能完全令人满意，但它们的含义很重要。然后将这些结果与根据指定损失产生限制制定的当前容量标准进行比较，结果证明这是一种更有意义的方法。然后将这些在低温下运行的常态导体的结果与超导 MgB2 和 YBCO 进行比较。在此之后，我们考虑在功率密度方面的整体系统级优势的两种情况，一种是包括低温冷却设备的尺寸的情况，另一种是“免费”冷却的情况（例如，当液态氢已经在船上时）。我们发现，仅针对超导选项，低温冷却情况下的总系统重量减少了。如果存在随时间变化的磁场，则超导体丝的尺寸必须保持较小；开发了限制长丝尺寸的表达式。对于“自由”冷却的情况，使用低温常态导体和100-200 倍的超导选项，更高的电流水平可能导致绕组尺寸减少多达 16 倍。由于绕组的总尺寸大大减小，因此废热负荷也大大减少。这可以显着减轻热管理负担，这是电力推进飞机的难题。