极不均匀场中振荡型雷电冲击电压下变压器油击穿特性研究

针对目前振荡型冲击电压和标准冲击电压的等效性研究尚不成熟的问题,采用100、300、400kHz的正极性振荡型雷电冲击电压(OLI)和标准雷电冲击电压(SLI)进行对比,以间距为5mm的针尖和球体作为电极,研究了极不均匀场中变压器油在振荡型雷电冲击电压下的击穿特性,记录了这3种频率的振荡型雷电冲击电压和标准雷电冲击电压的击穿波形,统计并分析了不同雷电冲击电压下的伏秒特性、起始击穿电压和最大击穿时延。结果表明:振荡型冲击电压下的变压器油击穿后会产生一定的振荡,需串接电阻抑制;标准雷电冲击电压的变压器油击穿点主要分布在波峰处,而振荡型雷电冲击电压的击穿点在每个振荡周期的峰值处都有分布;振荡型冲击电压的起始击穿电压随频率升高而上升,最大击穿时延随频率的升高而缩短,但比标准雷电冲击电压长。该研究为现场对变压器进行振荡型冲击耐压试验奠定了基础。     

负极性振荡雷电冲击电压下SF_6尖板模型局部放电特性

为了深入研究尖板模型振荡雷电冲击电压下局部放电特性,首先搭建了振荡冲击电压发生器,产生符合IEC 60060-3标准的振荡型雷电冲击电压,基于特高频法和脉冲电流法,建立了冲击电压下局部放电测量系统,进而构建了SF6尖板模型,对负极性振荡雷电冲击电压下局部放电进行了测量,对比了特高频法和脉冲电流法测量局部放电的灵敏度,分析了放电时延、放电幅值、放电数目和放电相位随外施电压的变化规律。结果表明:特高频法测量灵敏度更高,适合在气体绝缘组合电器(GIS)现场冲击耐压试验中使用;局部放电集中在外施电压各波峰附近;随着外施电压的升高,放电时延和放电起始相位急剧减小,放电结束相位则稍有增大;各周期放电幅值和数目随波峰电压的升高而线性增加。进一步分析表明,在负极性振荡雷电冲击电压下,局部放电的产生和发展可用金属电极表面发射、负离子场致碰撞脱附和电晕稳定化作用进行很好的阐释。研究成果有助于GIS现场冲击耐压试验中局部放电的检测与分析。     

SF_6气体中绝缘子沿面放电的发光特性

利用光电倍增管及高速摄影机 ,对SF6气体中绝缘子沿面预放电及放电通道形成过程中的发光进行了检测 ,得出快速振荡冲击 (FOI)比雷电冲击 (LI)更容易使绝缘子沿面的SF6气体产生电离与复合 ,从而造成快速振荡冲击电压下 ,极不均匀场中绝缘子沿面放电电压的降低 .试验结果还证实 ,雷电冲击下绝缘子沿面放电遵循先驱机理 ,而快速振荡冲击下放电遵循先驱与高频联合机理 .     

SF6气体中绝缘子沿面放电的发光特性

利用光电倍增管及高速摄影机,对ＳＦ６气中绝缘子沿面预放电子及放电通道形成过程中的发光进行了检测,得出快速振荡冲击（ＦＯＩ）比雷电击（ＬＩ）更容易使绝缘子沿面的ＳＦ６气体产电离与复合,从而造成快速振荡冲电压下,极不均匀场中绝缘子沿面放电电压的降低,试验结果还证实。雷电冲击下绝缘子沿面放电遵循先驱机理,而快速振荡冲击下放电遵循先驱与高频联合机理。     

丙烷喷射火焰中电极形状对间隙击穿特性的影响

高压输电导线作为输电系统的核心部分,一旦发生火灾将可能造成严重的后果。目前针对电极形状对输电线路间隙击穿的定性定量研究较少。该文利用30 kV·A/50 kV高压工频放电系统、丙烷喷射模拟火源以及棒/板2种不同形状电极,从击穿电压、击穿极性特征、击穿电弧特征3个方面研究了火焰条件下电极形状对间隙击穿特性的影响。研究发现,火焰条件下间隙距离小于8.0 cm时击穿波形具有“两期两点”特征,即击穿前“放电诱导期”、临界击穿时“间隙击穿点”、击穿产生电弧后“电弧导通期”、电弧阶段性消失时“击穿消失点”。通过设置不同间隙距离,测量不同电极组合的平均击穿电压和平均击穿场强,发现随间隙距离增大,棒-棒和棒(阴)-板(阳)电极击穿电压值增加速率分别为最低和最高。相较于空气间隙击穿,火焰条件下由于存在火焰流场和热浮力,间隙击穿具有更明显的极性特征,不同电极形状会影响正负周期形成导电通道的概率。击穿方向为正周期时,棒(阴)-板(阳)电极组合击穿概率最大,击穿方向为负周期时,棒(阳)-板(阴)电极组合击穿概率最大。研究结果表明：击穿电弧演变过程可分为导通阶段、燃烧阶段和熄灭阶段,火焰条件下电弧体积明显增大,...     

直流电压下两相体放电路径预测（英文）

通过实验研究了两相体放电路径的预测问题,结果表明:放电路径中选择空气或两相体由被畸变的电场决定,而电场的畸变受两相体颗粒粒径大小的影响。为了解释实验现象,利用传统的流注理论和概论统计理论,以泊松方程求解的空间场强为流注发展的判据,并假设流注发展的击穿时间满足Weibull分布,将两相体空间电场畸变后电场值的变化决定流注的发展方向,建立了正极性的放电路径选择的物理模型。将直流电压下两相体放电路径发展问题的目标函数(即最短路径)与连续性Hopfield神经网络的能量函数相对应,将经过的节点顺序(局部电场值的影响大小)与网络的神经元状态相对应,此时对应的节点发展顺序就是待求的最佳路线。仿真和实验结果比较显示,基于该模型两相体直流放电路径选择概率分布的计算结果与实验所得规律一致。     

正棒—板短间隙雷电冲击放电电压的海拔修正

多功能人工气候室内模拟高海拔地区的气压，按照IEC对棒－板间隙试验方法的要求对200mm、300mm和450mm3种正棒－板短空气间隙雷电冲击放电特性进行了系统的试验研究。根据理论分析，提出了由于气压是大气3个基本参数即温度、空气相对密度和绝对湿度的综合反映，因此可以作为表征大气条件对空气间隙击穿电压影响的特征量；根据试验结果，提出了高海拔地区的短空气间隙雷电冲击击穿电压的是相对气压的幂函数，且其特征指数小于1，并因此得出海拔每升高1km，其击穿电压下降8.7%。     

六氟化硫与空气的混合气体的冲击击穿特性

本文报告了在六氟化硫与空气混合气体(SF_6/Dry Air)同轴电极系统中内电极固定导电微粒时,施加不同波形的冲击电压(250/2500μs操作冲击电压,1.5/50μs雷电冲击电压,1.5/2500μs短波前长波尾冲击电压)下的电晕稳定——击穿特性.实验结果表明,冲击电晕稳定与击穿电压决定于SF_6含量及波前时间,几乎与波尾时间无关.     

介质击穿模型参数对雷电先导放电数值模拟的影响

为研究介质击穿模型参数的选取对雷电先导放电数值模拟结果的影响,以雷云荷电模型和WZ模型为基础,模拟计算了三维先导放电通道在50 m空间分辨率下的分形维数和先导临近对地面电场峰值的增强程度.统计分析结果表明:分形维数随着概率指数和电场击穿阈值的增大而减小,但随着通道内电场的增大先减小而后基本趋于稳定,且概率指数对分形维数的影响程度最为剧烈,电场击穿阈值次之,通道内电场的影响相对最弱;地面电场峰值的增强程度随着通道内电场和电场击穿阈值的增大而减小,但随着概率指数的增大先减小而后基本趋于稳定,且通道内电场对地面电场峰值增强程度的影响最为剧烈,概率指数次之,电场击穿阈值的影响相对最弱.     

低气压对棒-板间隙工频放电特性影响研究

为研究低气压对棒-板间隙工频放电特性影响,利用低气压放电试验平台对1~20 kPa气压范围内200~500 mm棒-板间隙工频放电进行了试验研究,分析了工频50%击穿电压U_(50%)与气压P及间隙距离d的关系;以及气压对放电通道外形的影响。研究结果表明:在1~20 kPa气压范围内不同间隙距离下U_(50%)-P曲线均有饱和趋势,开始出现饱和趋势的拐点随间隙距离增大向低气压方向移动且拐点处击穿电压U_(50%)和间隙距离与气压乘积Pd之间存在函数关系。随气压升高放电通道由低亮度"间断状"逐渐收细、变亮为高亮度"连续状",曲折现象逐渐显著。研究成果为进一步开展低气压下长间隙放电研究提供参考。     

Markedness and its Interpretation in Language Use

Language markedness is a common phenomenon in languages, and is reflected from hearing, vision and sense, i.e. the variation in the three aspects such as phonology, morphology and semantics. This paper focuses on the interpretation of markedness in language use following the three perspectives, i.e. pragmatic interpretation, psychological interpretation and cognitive interpretation, with an aim to define the function of markedness.     

Features of Women's language

Language is a means of verbal communication. People use language to communicate with each other. In the society, no two speakers are exactly alike in the way of speaking. Some differences are due to age, gender, statue and personality. Above all, gender is one of the obvious reasons. The writer of this paper tries to describe the features of women＇s language from these perspectives： pronunciation, intonation, diction, subjects, grammar and discourse. From the discussion of the features of women＇s language, more attention should be paid to language use in social context. What＇s more, the linguistic phenomena in a speaking community can be understood more thoroughly.     

An Analysis of Catherine＇s Character——Wuthering Heights

Wuthering Heights, Emily Bronte＇s only novel, was published in December of 1847 under the pseudonym Ellis Bell. The book did not gain immediate success, but it is now thought one of the finest novels in the English language. Catherine is the key character of this masterpiece, because everybody and everything center on her though she had a short life. We can understand this masterpiece better if we know Catherine well.     

Lower Paleozoic oil relationships within Williston Basin, Canada

The Williston Basin is a significant petroleum province, containing oil production zones that include the Middle Cambrian to Lower Ordovician, Upper Ordovician, Middle Devonian, Upper Devonian and Mississippian and within the Jurassic and Cretaceous. The oils of the Williston Basin exhibit a wide range of geochemical characteristics defined as "oil families", although the geochemical signature of the Cambrian Deadwood Formation and Lower Ordovician Winnipeg reservoired oils does not match any "oil family". Despite their close stratigraphic proximity, it is evident that the oils of the Lower Palaeozoic within the Williston Basin are distinct. This suggests the presence of a new "oil family" within the Williston Basin. Diagnostic geochemical signatures occur in the gasoline range chromatograms, within saturate fraction gas chromatograms and biomarker fingerprints. However, some of the established criteria and cross-plots that are currently used to segregate oils into distinct genetic families within the basin do not always meet with success, particularly when applied to the Lower Palaeozoic oils of the Deadwood and Winnipeg Formation.     

低渗透非均质砂岩油藏启动压力梯度研究

理论推导与室内实验相结合,建立了低渗透非均质砂岩油藏启动压力梯度确定方法。首先借助油藏流场与电场相似的原理,推导了非均质砂岩油藏启动压力梯度计算公式。其次基于稳定流实验方法,建立了非均质砂岩油藏启动压力梯度测试方法。结果表明:低渗透非均质砂岩油藏的启动压力梯度确定遵循两个等效原则。平面非均质油藏的启动压力梯度等于各级渗透率段的启动压力梯度关于长度的加权平均;纵向非均质油藏的启动压力梯度等于各渗透率层的启动压力梯度关于渗透率与渗流面积乘积的加权平均。研究成果可用于有效指导低渗透非均质砂岩油藏的合理井距确定,促进该类油藏的高效开发。     

On Tragic Consciousness In The Works By Ernest Hemingway

As an American modern novelist who were famous in the literary world, Hemingway was not a person who always followed the trend but a sharp observer. At the same time, he was a tragedy maestro, he paid great attention on existence, fate and end-result. The dramatis personae's tragedy of his works was an extreme limit by all means tragedy on the meaning of fearless challenge that failed. The beauty of tragedy was not produced on the destruction of life, but now this kind of value was in the impact activity. They performed for the reader about the tragedy on challenging for the limit and the death.     

Achieving Unusual States of Matter Under High Pressure

正The periodicity of the elements and the non-reactivity of the inner-shell electrons are two related principles of chemistry,rooted in the atomic shell structure.Within compounds,Group I elements,for example,invariably assume the+1 oxidation state,and their chemical properties differ completely from those of the p-block elements.These general rules govern our understanding of chemical structures and reactions.Using first principles calcula-     

Exchange-Correlation and Electronic Excitation Energies from Pairing Matrix Fluctuations

We have developed an adiabatic connection to formulate the ground-state exchange-correlation energy in terms of pairing matrix linear fluctuations.This formulation of the exchange-correlation energy opens a new channel for density functional approximations based on the many-body perturbation theory.We illustrate the potential of such approaches with an approximation based on the particle-particle Random Phase Approximation(pp-RPA).This re-     

Density Functional Theory for the Response of Periodic Systems to Electric Fields Based on the Vector Potential Approach

正The electronic and nuclear(structural/vibrational)response of 1D-3D nanoscale systems to electric fields gives rise to a host of optical,mechanical,spectral,etc.properties that are of high theoretical and applied interest.Due to the computational difficulty of treating such large systems it is convenient to model them as infinite and periodic(at least,in first approximation).The fundamental theoretical/computational problem in doing so is that     

Call for Papers

<正>"The Journal of Shanghai Normal University:Mathematics"is published by Shanghai Normal University as regular issues of The Journal of Shanghai Normal University each year from 2014 in English.The editors-in-chief of the issues are professors Yuhao Cong and Maoan Han.The Journal of Shanghai Normal University was started in 1958 with