Development of Design Method of Electrical Insulation and Improvement Method of withstand Strength in HTC Superconducting Power Apparatus

近年来，高温超导（HTS）导线技术的发展引起了人们对高温超导电力设备发展的兴趣。为了确保将高温超导电力设备引入现有电力系统的可行性，必须从设备开发的早期开始就将电气绝缘的可靠性纳入设计。本研究的主要目的是建立考虑到淬火现象的高温超导电力设备的电气绝缘策略，淬火现象不仅会在绝缘介质中形成气泡，而且会在线圈层上产生高电压降。为此，本研究项目分为三个部分：(1)模拟裸线圈电极的电击穿机理和特性研究；(2)模拟高温超导线圈淬火条件下的气泡行为研究；(3)空穴放电研究。研究结果对电气绝缘策略提出了以下建议。由于高温超导线圈在淬火状态下，冷却通道中会出现气锁现象，因此，如果淬火不可避免，且需要高可靠的电绝缘，则应确定所需的绝缘空间为淬火导体温度下的氮气。绝缘材料在低温条件下比在常规电力设备工作温度下具有更好的长时间V-t特性。但是，在含谐波的电压应力作用下，固体绝缘子所含空隙内的局部放电，应被认为是绝缘材料退化的重要因素之一。此外，在固体绝缘子的任何部分的温度变化应抑制在低于5K/min。避免热应力产生疯狂裂纹。

Recent advancements in High Tc Superconducting (HTS) wire technology have stimulated increasing interest in the past few years in the development of high Tc superconducting power apparatus. To ensure the feasibility of the introduction of HTS power apparatus into present electric power systems, the reliability of the electrical insulation must be incorporated in the design from the early beginning of the development of the apparatus. The aim of the present study is essentially to establish the electrical insulation policy of HTS power apparatus taking into account of the quenching phenomena which will not only cause bubble formation in insulation medium but also create a high voltage drop across the coil layer. For this purposes, this research project was divided into three parts : (1) Studies on electrical breakdown mechansm and characteristics with modeled bare coil electrodes, (2) Studies on bubble behavior under quenching condition with a modeled HTS coil and (3) Void discharge studies.The results suggests the following about the electrical insulation policy. Since the vapor locking can appear in the cooling channel of HTS superconducting coil at quenching state, the required insulation space should be determined as the insulation medium being nitrogen gas at temperature of quenched conductor if the quenching is unavoidable and high reliable electrical insulation is required. Instulation material under cryogenic conditions has better long time V-t characteristics than under operating temperatures of conventional electric power apparatus. However, partial discharge in voids included in solid insulator under voltage stresses with harmonics, should be considered to be one of the important degradation factors of insulation material. Moreover, the temperature change at any portion in solid insulator should be suppressed lower than 5K/min. to avoid the formation of crazy crack by the heat stress.