Mechanisms of dielectric breakdown of ljquid coolants under quench condition and estimation of withstand voltage

淬火条件下液体冷却剂的介电击穿机理及耐压估算

基本信息

批准号：
08455136
负责人：
HARA Masanori
金额：
$ 4.8万
依托单位：
KYUSHU UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
1996
资助国家：
日本
起止时间：
1996 至 1997
项目状态：
已结题

项目摘要

In this study, establishment of electrical insulation technique and development of insulation trust of a superconducting magnet were aimed at. Boiling phenomena of liquid nitrogen and helium used for coolant of the magnet under high electric field was investigated. Moreover, mechanism of breakdown of those liquid coolant and characteristics of withstand voltage were discussed. Obtained results were summarized as follows.1.Electrical insulation design of pool-boiling He-cooled superconducting coilsInsulation design procedure was proposed and applied to a small SMES.It was found that the main parameters determining insulation space were delay time of quench protection switch, initial coil current, coil inductance, and conductor geometry and size.2.Bubble behavior in liquid coolant under quench conditionBubble behavior under high electric fields was studied theoretically and experimentally. The results showed that bubble motion was influenced mainly by an electrical gradient force acting on it. Then it is very important to pay attention to a setting of the gasp length in order to get a passage of the coolant under quench condition.3.Breakdown characteristics of LNi and LHe including a superfluid condition were investigated statistically.It was shown that the statistical characteristic of breakdown were well fitted to Weibull distribution based on weak-link theory and area effect was dominant rather than volume effect for size effect of electrodes to the breakdown characteristics.

本研究的目的是建立电绝缘技术并发展超导磁体的绝缘可靠性。研究了强电场下磁体冷却剂液氮、液氦的沸腾现象。此外，还讨论了这些液体冷却剂的击穿机理和耐压特性。所得结果概括如下： 1.池沸腾氦冷超导线圈的电气绝缘设计提出了绝缘设计流程，并将其应用于小型SMES。发现决定绝缘空间的主要参数是失超保护开关的延迟时间、初始线圈电流、线圈电感以及导体的几何形状和尺寸。2.淬火条件下液体冷却剂中的气泡行为从理论上和实验上研究了高电场下的气泡行为。结果表明，气泡运动主要受到作用在其上的电梯度力的影响。那么为了在淬火条件下获得冷却剂的通道，注意气体长度的设置是非常重要的。3.对包括超流体条件在内的LNi和LHe的击穿特性进行了统计研究。击穿特性很好地符合基于弱连接理论的威布尔分布，并且电极尺寸效应对击穿特性的影响以面积效应而非体积效应为主。