长距离超导直流输电的低温制冷流程和沿长度方向的制冷站配置研究

Superconducting DC transmission is one of the most competitive technologies for large-scale power transmission in the near future based on superconductor's zero resistance and high current density. Although superconducting DC transmission technology has made rapid progress in recent years, there are still a number of basic scientific and technological problems to be solved, refrigeration is the one among them. Thus, reaerarch on the refrigeration flowsheet and cryogenic station configuration for long-distance superconducting DC power transmission is of great scientific and practical value. The goal is to provide a reseanable refrigeration mode and cryogenic station configuration principle and its optimization method on a thermodynamic basis, so as to provide theoretical guidance for superconducting DC transmission planning and design. Main research activities are on: (1) the coaxial two-way DC power cable structure and configuration for the superconducting DC power cable and the investigation and verification on its electromagnetic properties; (2) the flow model of the coolant and its cooling method for superconducting DC power transmission based on the DC power cable structure; (3) the spatial distribution, process optimization and configuration manner of the refrigeration station are proposed, based on heat loss analysis and flow dynamics calculation.

超导直流输电具有低损耗、大容量、绿色环保等特点，是未来大规模电力输送最具竞争力的技术选择之一。尽管近些年来超导直流输电技术取得长足发展，但对长距离应用仍有一系列基础科学技术问题亟待解决，低温及其制冷问题就是其中之一。本项目开展长距离超导直流输电的低温制冷及其配置问题，具有重大创新性和应用价值，其目标是系统性地提出超导直流输电的低温制冷流程及其热力学依据，进而提出面向长距离应用的低温制冷站设置依据及其优化原则，为超导直流输电工程的规划设计和技术发展提供理论指导。项目的实施，依托具有雄厚基础的超导和低温技术研究机构和科研团队，将：①提出同轴双向直流传输模式的超导直流电缆构型，并对其电磁特性进行深入研究和验证；②基于超导电缆构型，通过热力学建模和仿真分析，提出超导直流输电的制冷工质流动模型及其冷却方式；③通过系统热损耗分析和流体动力学计算，提出低温制冷站的空间分布、流程优化及其配置方式。

课题以面向长距离应用高温超导直流输电电缆为基本前提，分析并计算了超导直流电缆系统的热损耗，提出了长距离应用下电缆热损耗分析的特殊考虑，确定了将各种损耗归结为内部损耗和外部损耗的抽象方法；从传热学和流体力学的角度建立了两液氮通道构型的超导直流电缆的制冷系统的物理模型，该物理模型将所有制冷流程概括统一为同一个方程，具有普遍性意义。以所建的物理模型为基础，采用解析法解出了单端逆流制冷方式、双端逆流制冷方式和顺流制冷方式等三种制冷方式下的温度分布。该解析解指明了制冷系统的温度分布的依赖关系，是分析制冷系统特性钥匙。提出了使用最大制冷长度作为评价标准，以温度分布解析解为基础研究冷流程的温度分布特性和参数依赖关系的方法。参数相互关系是低温制冷站配置的直接参考依据。最后，以一套长距离超导直流电缆参数为基准，将长距离应用的低温制冷站配置归纳为两类问题，初步提出了面向长距离应用的高温超导直流电缆的低温制冷站的配置原则和方法，并以提出的方法和原则为依据做了案例研究分析。