一、引言超导材料可以无阻地承载一个大电流,这一重要的特性只存在于直流电中,许多实用的超导材料在工频下的交流损耗已接近于铜了。所以,现阶段在强电领域内,超导电技术的应用还多限于直流。但是,在许多重要的技术领域内,超导技术希望能运行在交流模式下,如电机、变压器、输电线、高能加速器等。在这些领域超导技术能否获得应用并显示出优越性,在很大程度上取决于能否将交流损耗降低到许用的程度。交流损耗尽管在一般情况下并非很大,但考虑到 I. INTRODUCTION Superconducting materials can carry a large current unimpeded. This important characteristic exists only in direct current. Many practical superconducting materials have similar AC loss under power frequency. Therefore, at this stage in the field of strong electricity, the application of superconducting technology is mostly limited to DC. However, in many important technical fields, superconducting technology is expected to be able to operate in AC mode, such as motors, transformers, power lines, high-energy accelerators and the like. The availability of superconducting technology in these areas and their demonstrated superiority depend to a large extent on the ability to reduce AC losses to a permissible level. AC loss Although not generally large, but considered