RESEARCH AND DEVELOPMENT OF SUPERCONDUCTORS WITH LARGE CURRENT CAPACITY FOR SUPERCONDUCTING TRANSFORMERS INSTALLED IN UNDERGROUND SUBSTATIONS

我们首先对之前设计制造的500kVA液氮冷却氧化物超导变压器的试验结果进行分析，然后提炼出开发更大容量超导变压器所需要的研究课题。根据研究结果，我们以实现大电流容量、高耐压水平的氧化物超导变压器绕组为目标，进行了以下基础研究；(1)银护双系超导导线的电磁特性研究；(2)由氧化物超导股构成的大电流容量转置并联导线的最佳构型研究；(3)液氮温度下超导并联导线的稳定性研究。(4)评价饱和和过冷液氮在超导绕组变为正常状态时的气泡形成条件；(5)进一步研究过冷液氮的绝缘强度和适用的绝缘结构；(6)设计和试验模拟电力系统超导变压器绕组实际情况的氧化物超导模型线圈。进一步研究了氧化物超导变压器在电网中的实际应用。在此基础上，全力支持液氮冷却1000kVA-22kV/6.9kV氧化物超导变压器研制项目，并成功生产。我们首先在日本进行了超导变压器的现场试验。在试验中，我们观察并评估了超导并联导体的电磁性能，以及超导变压器绕组暴露在电网实际条件下的过冷液氮的绝缘强度和冷却性能。因此我们对本研究得到的结果进行了验证。少

We first analyzed the test results of a 500kVA liquid-nitrogen cooled oxide superconducting transformer, which we previously designed and built, and then extracted the research subjects necessary for the development of superconducting transformers with larger capacity. According to the results, we made the following basic research with the aim of the realization of oxide superconducting transformer windings with large current capacity and high voltage withstand level ; (1)investigation of electromagnetic properties of silver-sheathed Bi-system superconducting wires, (2)study on the optimum configuration of transposed parallel conductors with large current capacity, which are composed of oxide superconducting strands, (3)study on the stability of superconducting parallel conductors at liquid-nitrogen temperature, (4)evaluation of the condition of the bubble formation in saturated and sub-cooled liquid nitrogen in the case where superconducting windings are changed into normal state, (5) … More study on the insulation strength of subcooled liquid nitrogen and the applicable insulation structure, and (6)design and test of oxide superconducting model coils which simulate the actual condition of superconducting transformer windings in the electric power system. Furthermore we studied the practical use of oxide superconducting transformers in the electric power grid. On the basis on the obtained results, we entirely supported the development project of a 1000kVA-22kV/6.9kV oxide superconducting transformer cooled by liquid nitrogen and produced it successfully. We performed the field-test of the superconducting transformer first in Japan. In the test, we observed and evaluated the electromagnetic properties of superconducting parallel conductors, and the insulation strength and cooling properties of sub-cooled liquid nitrogen in the case that the superconducting transformer windings was exposed to the actual condition in electric power grid. Therefore we verified the obtained results in this study. Less