变压器强油风冷二次控制回路的改造

探讨了变压器强迫油循环风冷却装置工作原理和变压器冷却器二次回路控制原理,在此基础上提出改造主变压器强油风冷二次控制回路的方案。     

变压器强油风冷冷却器控制系统启停回路改造

该文通过对以礼河发电厂设备整治改造五年规划中对主变压器冷却器的现场改造调试经验,通过统计对比传统设计变压器强油风冷冷却器控制系统变压器的多年运行温度.注重在设备改造中,既能满足变压嚣的技术要求和现场安全要求,又要达到科学合理、技术先进、安全可靠,降耗节能,提高变压器运行效率为目的.提出了变压器强油风冷冷却器控制系统启停回路改造思路,并进行了实施,取得了较好的效果,以供同行参考借鉴.     

强迫油循环风冷变压器冷却器控制回路的改进

强迫油循环风冷变压器由于冷却面较小,不允许不带冷却器运行,当出现冷却器全停时,为了防止运行中产生的热量无法散出,损坏变压器的绝缘,将延时启动跳闸回路,跳开变压器各侧开关,使变压器退出运行。在实际运行中,传统冷却器控制回路存在着冷却器全停而无法启动跳闸回路的情况。针对这一情况,对强迫油循环风冷控制回路进行分析,并提出解决方案。     

可编程控制器在大型变压器冷却系统中的应用

大型变压器是电力系统安全运行的基本保证。用可编程控制器(以下简称PLC)对原有的变压器强油空气冷却器继电—接触器控制进行改造,无论是在控制精度和可靠性方面均有较大提高,另外发挥PLC通讯功能,将变压器的运行纳入电力系统的“三遥”子系统,可为其建立一可靠的通讯控制平台,为无人值守系统打下基础。     

基于EDA技术的继电控制回路设计

指出了机电设备常见电气继电控制在使用中的不足，阐述了在继电控制回路的开发设计中运用EDA技术的可行性，介绍了用VHDL语言设计单片控制系统的方法，给出了电机周期性正反转运行的VHDL设计程序和仿真波形图．仿真结果证明了这种设计方法的正确性．这种设计理念对传统电气继电控制的设计是一种挑战．     

模糊神经网络PID在变压器风冷控制系统中的应用

针对现有的大、中型变压器风冷控制系统中存在的问题,设计了一种基于模糊神经网络PID技术的变频调节风冷控制系统,通过模糊神经网络控制优化PID的控制参数,精确控制变频器的输出频率,使变压器的发热量与散热量实时平衡,以达到节能运行的目的。     

干式变压器温度控制系统运行故障的分析处理

随着干式变压器应用领域的不断扩大,对干式变压器的运行状态和监控提出了更高的要求。结合供电系统运行实际,依据干式变压器风冷系统和温度控制系统的工作原理,对风冷系统和温度控制系统在运行中发生的故障进行了分析处理,以保证干式变压器安全稳定运行。     

非电量继电保护装置常见问题和处理

电力变压器是电力系统中使用相当普遍和十分重要的电气设备。变压器内部进入空气．严重渗漏油、环境温度骤降使变压器油位下降，各种原因非内部故障油流涌动，二次回路短路，运行人员误碰探针等都会引起瓦斯保护动作。如果变压器发生故障．将给供电的可靠性和系统的正常运行带来严重的后果。为了保证变压器的安全运行，防止故障扩大，按照变压器可能发生的故障，装设灵敏、快速、可靠且选择性好的保护装置是十分必要的。     

基于EDA技术的继电控制回路的设计

指出了机电设备常见电气继电控制在使用中的不足,阐述了在继电控制回路的开发设计中运用EDA技术的可行性,介绍了用VHDL语言设计单片控制系统的方法,给出了电机周期性正反转运行的VHDL设计程序和仿真波形图.仿真结果证明了这种设计方法的正确性.这种设计理念对传统电气继电控制的设计是一种挑战.     

变压器油泵对冷却系统的影响

东北电网使用的变压器油泵主要是由长春第二电机厂生产的,它是一种特制的油内电动机型离心泵,电动机的定子和转子浸在油中,使油系统构成密封循环系统,通过法兰接到冷却器和变压器的管路中,运行在电力系统中的大型变压器的冷却系统大都采用强油循环风冷结构,这种结构是由风冷却器、潜油泵、油流继电器等通过连接管路和蝶阀与变压器本体相连而构成.     

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.     

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     

Journal of Donghua University ( English Edition) Contents of Volume 31

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Brief Introduction to “Journal of Jilin University( Science Edition) ”

<正>"Journal of Jilin University(Science Edition)"is a comprehensive academic journal in the fields of science sponsored by Jilin University and administrated by the Ministry of Education of the Peoples Republic of China.The journal started publication in 1955.The original name at starting publication was"Journal of Natural Science of Northeast People University",which was changed into"Acta Scientiarum Naturalium Universitatis Jilinensis"in 1958 owing to the name change of the university.The present journal name has