Investigation of the voltage life of mica-alumina composite insulation at high temperatures

Experiments and investigations were carried out on the voltage life of a bar-coil model with a nickel-plated copper conductor covered with mica-alumina composite insulation at a temperature range of 550–850 °C. Diffusion of copper into the insulation layer was observed on the specimens aged for a long period. Insulation with mica paper gave faster diffusion speed and shorter voltage life than insulation with mica flake. The diffusion speed became higher with an increase in temperature. The ac current gradually increased with aging time and increased rapidly just before breakdown. There was the relationship I = aEⁿ (a, n: constants) between ac current I and applied stress E, and n was approximately equal to 1 in the region where thermal unbalance did not occur. Arrhenius's law held in the relationship between ac current and aging time. Therefore, the breakdown mechanism might be that the effective insulation thickness decreased due to copper diffusion into the insulation layer and the ac current increased gradually until thermal breakdown in the last stage. If copper diffuses into the insulation layer, even with no voltage application, the aging time required to decrease the breakdown voltage to a certain level (the voltage life) obeys Arrhenius's law. If the voltage life is dominated by diffusion into the insulation layer, the activation energy for voltage life in the aging test becomes twice that for diffusion, both with and without voltage application. © 1999 Scripta Technica, Electr Eng Jpn, 129(4): 24–31, 1999     

Dielectric properties of mica-alumina combined insulation at high temperatures

Development of sodium-immersed-type Electromagnetic Pumps (EMP) is expected to improve reliability, safety, maintainability, and construction cost of the Fast Breeder Reactor (FBR) compared with the conventional mechanical pumps. To realize the EMP, establishment of a high-temperature-resistant electrical insulating system is indispensable. A mica-alumina combination is selected for the insulating system at temperatures higher than 500°C. Using this insulating system, an aging pretest was performed. The aging condition was to apply 1.5-kV ac voltage in the nitrogen atmosphere at 550°C for 4000 hours. The dielectric properties before and after the aging were measured to understand the tendency of temporal change in the aging. In this result, the dielectric performance after aging was improved compared with the initial performance. The curious phenomenon was clarified to be caused by a decrease of organic component in the insulation, which remained due to incomplete burning. Also, the possibility of thermal runaway was considered to be higher as a dielectric breakdown mechanism.     

干涉成象光谱仪动镜运动误差分析(Ⅱ)——角反射体或猫眼镜横移容限分析

本文分析了干涉成象光谱仪动镜采用角反射体或猫眼镜时，运动过程中横向移动量对干涉条纹调制度的影响，导出了对横移量的限制条件。     

测量磁单极子通量的天然白云母的裂变径迹年龄测定

当自然界中的磁单极子穿过地壳时,磁单极子—原子核结合体在云母中形成径迹。选用新疆白云母作为探测器,测得云母的裂变径迹年龄为(129±8)×10~6a,可以认为白云母的裂变径迹年龄即为它记录磁单极子—原子核结合体径迹年龄的近似值。     

Dielectric response of humid phlogopite

The dielectric response of phlogopite mica has been measured for frequency lying between 10 mHz and 10 kHz with humidity as a parameter. The measured complex capacitance shows a low frequency dispersion (LFD) at high humidities. A weak loss peak is also present at high frequencies and low humidity levels. Work carried out at former Chelsea College, London University, London.     

织物组织结构对吸湿快干机织物性能的影响

以质量比50/50的云母纤维/竹浆纤维混纺纱为原料,设计开发了具有吸湿快干功能的平纹组织、小提花组织和透孔组织3种单层机织物,对这3种组织织物的基本性能和热、湿舒适性能进行了测试,分析了织物组织结构对机织物吸湿快干性能的影响。测试结果得出:这3种织物均具有吸湿快干的性能,其中透孔组织为吸湿快干性能最佳的织物组织。     

一种高效、简便原子力显微镜液体中原位实验方法

原子力显微镜从1986年发明以来,由于其在显微成像术中的独特优势,受到愈来愈多的来自各个学科领域研究人员的高度注视。目前所报道的有关原子力显微镜原位动态观察的方法在实际操作中需要较高的技巧性。本文介绍一种原子力显微镜的原位成像方法,能够做到在液体中高效、简便观察生物样品。     

基于横观各向同性模型的片岩隧洞稳定性研究

以四川大渡河丹巴水电站引水隧洞为研究对象,结合三轴试验和自主研发的空间多角度片理抗拉强度测试技术,对不同片理夹角下石英云母片岩的力学参数进行测定,得出石英云母片岩的弹性模量、c和φ与围压之间的关系,并分别给出干燥和饱和条件下各力学参数围压敏感性排序。通过表征各向异性的参数k_1、k_2,对不同片理夹角下石英云母片岩的各向异性与围压的关系进行评价,并进一步指出不同高度岩样抗拉强度随片理角度的变化规律。采用横观各向同性本构模型,通过设定材料主轴空间方位,可模拟片理空间任意角度展布的岩体。针对大区域模型存在的不足,提出一种主应力构造精细应力场的新方法,避免了大模型的应力边界效应,可方便快捷对局部区域进行精细应力构造。根据片理走向及不同倾角选定15个不同片理空间展布模型进行计算分析,分别得出应力、位移、塑性区随片理角度的变化规律,并指出不同片理展布条件下的最不利工况。     

无机填料对功能弹性体吸声性能的影响

基于调节聚氨酯/环氧树脂(PUR/EP)弹性体基材声阻抗,增加材料对声能弛豫吸收和传播路径、加大声波损耗的目的,在基材中加入空心玻璃微珠和云母两种无机材料,并通过改变无机材料的添加量和梯度结构设计对其水声吸声性能展开了研究。研究结果表明:无机填料云母和空心微珠的加入均能有效改善PUR/EP基材的吸声性能。空心微珠量越多,吸声效果越佳。云母添加量的影响规律为5%含量时平均吸声系数高,而高云母含量则只能对基材的低频吸声性能的提高贡献较大。这两种无机填料的梯度分层复合材料的吸声性能要优于非梯度材料(总含量10%)。