架空输电线路地线多点取能的功率分布特性

架空输电线路地线多点取能可以为线路的全面监测提供电源保证,同时还可以有效避免传统供电方式的弊端。地线取能可行与否的关键之一在于取能功率是否足够,有必要分析各取能点的功率分布情况。文中针对典型架空输电线路,结合理论分析与EMTP-ATP程序的仿真计算对地线多点取能时各取能点的功率分布特性进行了分析计算。结果表明,距离单点接地处最远的取能负载的功率随与前面负载的距离的增加而增加,但增幅逐渐降低并趋于稳定;而前面的负载则随该距离的增加而减小,但降幅逐渐降低并趋于稳定。同时,取能负载阻抗减小时,最后一个负载电流的变化幅度增大,而前面负载的变化幅度则减小。此外,距离单点接地处较远的取能负载功率大于较近处的负载功率。但是,取能负载位于单点接地处两侧时彼此互不影响。     

大型同步发电机参数在线辨识原理

提出一种测取大型同步电机参数的在线辨识方法。阐述和推导了参数辨识原理及辨识模型。首次提出运动方程和外部等效线路方程的辨识模型。在发电机带负载运行时,对励磁系统施加阶跃干扰,量测电机电压、电流及功角的暂态响应。采用简化大扰动数学模型,一次辨识出同步电机电磁参数和运动方程参数,以及等效无穷大电网电压Ｕｃ和等效线路阻抗Ｘｃ。该方法多次应用于我国大型火电站和水电站,先后对１００ＭＷ和２００ＭＷ汽轮发电机和７５ＭＷ水轮发电机进行了在线参数辨识。用辨识参数计算出的电机动态响应与实测结果有很好的一致性。     

基于压电变压器的高压能源变换器负载频率特性

为研究压电变换器在高电压低电流能源变换中充电的负载频率特性,利用集总参数压电变压器等效电路模型分析了压电变压器的负载频率特性,说明工作频率随负载的增大逐渐增大,最终达到饱和.以KHMPT3206压电变压器为实验对象,在负载小于50 kΩ时,理论分析与实验结果相吻合,大于50 kΩ时相对误差逐渐增加,最大相对误差为2.5%.验证了等效集总参数电路模型建立的正确性,即负载的变化影响等效串联电容的大小,从而引起压电变压器工作频率发生变化.     

基于自适应限流电流互感器取能电源设计方法

针对输电线路电流大小大范围波动导致在线取能装置能量溢出的问题,通过在电流互感器直流侧增添泄能电路,利用泄能电路的电流值对取能负载进行限流。首先在分析电流互感器取能原理的基础上建立取能负载模型,推导出负载电压与电流互感器母线电流的关系。通过引入开关电路,由脉冲信号与电流比较器结合产生的信号控制晶体管的导通与关断,从而解决电流过大时能量溢出的问题,给出了稳压电路的实现形式,建立整个装置的等效模型。同时建造试验平台,证明了该方法能够在母线电流变换的条件下达到自动调节取能负载电压的效果,从而有效地改善取能装置在大输入电流下的能量溢出状况,可见所提方法的可行性。     

处理面积对AZ31B镁合金微弧氧化负载特性的影响

为了明确处理过程中试样面积对微弧氧化负载特性及膜层性能的影响,采用单极性脉冲电源模式,对4个具有不同面积的AZ31B镁合金试样进行微弧氧化处理.处理中采用LCR测试仪采集负载的等效电阻和等效电容值,用示波器记录负载的电压、电流波形,并用MATLAB对负载电压波形进行拟合,以研究试样面积对微弧氧化处理过程中负载特性的影响.结果表明:随着处理电压的升高,所有的负载等效电容都持续减小,等效电阻都持续增大,负载的放电时间常数不断增大,等效电阻的增大说明膜层厚度随处理电压的增高而不断增长.此外,随着处理面积的增大,相同电压下负载的等效电阻不断减小,负载电容不断增大,负载的放电时间常数不断减小,说明随着面积的增大,膜层的增长变慢,而且面积越大的试样,负载波形更接近于方波,因此对单极性脉冲的实用性越好.     

地线干扰与抑制对策

地线造成电磁干扰的主要原因是地线存在阻抗,当电流流过地线时,会在地线上产生电压,在这个电压的驱动下,会产生地线环路电流,形成地环路干扰。当两个电路共用一段地线时,会形成公共阻抗耦合。解决地环路干扰的方法有切断地环路,增加地环路的阻抗,使用平衡电路等;解决公共阻抗耦合的方法是减小公共地线部分的阻抗,或采用并联单点接地,彻底消除公共阻抗。     

基于小波变换的电池阻抗测量及分析

对电池的负载电流和响应电压信号进行小波变换,提出不需要从外部对电池进行特定激励,而是直接利用电池电路开关瞬间的放电电流和电压信号,运用小波变换的方法直接得到电池的阻抗信息的思路。在此基础上,对比分析了基于小波变换得到的电池交流阻抗谱和基于电化学工作站所测量的电化学阻抗谱。通过改变温度和电池荷电状态,研究了两种方法所测量阻抗的异同,并对差异来源进行了分析,为车用锂离子电池阻抗信息的在线测量提供了基础。     

不平衡大电流线路电参数的计算方法

应用电磁场理论和电路理论,分析了不平衡大电流线路的电压电流关系·由物理结构计算出等效参数·利用等效参数和受控电源,提出一种简便的等效电路,用来比较方便地计算电参数·在允许的架设空间内,对传输线的尺寸和相对位置进行优化,为设计和改造大电流线路提供比较准确的计算方法     

特快波前下金属氧化物电阻片伏安特性试验研究

设计搭建了模拟特快速瞬态过电压发生器,并确定了相关的电压、电流测量方法,选定具有代表性的超高压避雷器使用的金属氧化物电阻片(MOV)作为研究对象,试验研究了MOV在电流波头时间为80~150ns的特快波前冲击电流下的伏安特性、电流陡度的影响关系及阻抗特性。在特快波前冲击电流作用下,MOV伏安特性试验结果表明:随着电流波头时间的减小,MOV的电压峰值升高,MOV电压峰值远大于同电流标准雷电波下的电压峰值,特快波前电流冲击波下MOV残压上升约9%~16%;MOV的电压峰值随着电流峰值的增大而增大,而且电流波头时间越短,同一电流值下的电压峰值越高,在特快波前冲击电流波头时间由150ns变化至80ns时,MOV电压峰值上升约为10%~20%;在试验研究的电流波头时间范围和电流峰值范围内,电压峰值出现的时间明显超前于电流峰值出现的时间,呈现感性阻抗特征。     

浅谈频率对变压器运行性能的影响

频率是交流电的一个重要参数,对电气产品的稳定运行起着重要的作用。本文重点阐述了频率的改变对变压器空载电流、阻抗电压、空载损耗、负载损耗等方面的影响。     

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.     

Characterization of Ordovician carbonate reservoirs, southeastern Saskatchewan, Canada

The discovery of the prolific Ordovician Red River reservoirs in 1995 in southeastern Saskatchewan was the catalyst for extensive exploration activity which resulted in the discovery of more than 15 new Red River pools. The best yields of Red River production to date have been from dolomite reservoirs. Understanding the processes of dolomitization is, therefore, crucial for the prediction of the connectivity, spatial distribution and heterogeneity of dolomite reservoirs.The Red River reservoirs in the Midale area consist of 3～4 thin dolomitized zones, with a total thickness of about 20 m, which occur at the top of the Yeoman Formation. Two types of replacement dolomite were recognized in the Red River reservoir: dolomitized burrow infills and dolomitized host matrix. The spatial distribution of dolomite suggests that burrowing organisms played an important role in facilitating the fluid flow in the backfilled sediments. This resulted in penecontemporaneous dolomitization of burrow infills by normal seawater. The dolomite in the host matrix is interpreted as having occurred at shallow burial by evaporitic seawater during precipitation of Lake Almar anhydrite that immediately overlies the Yeoman Formation. However, the low δ18O values of dolomited burrow infills (-5.9‰～ -7.8‰, PDB) and matrix dolomites (-6.6‰～ -8.1‰, avg. -7.4‰ PDB) compared to the estimated values for the late Ordovician marine dolomite could be attributed to modification and alteration of dolomite at higher temperatures during deeper burial, which could also be responsible for its 87Sr/86Sr ratios (0.7084～0.7088) that are higher than suggested for the late Ordovician seawaters (0.7078～0.7080). The trace amounts of saddle dolomite cement in the Red River carbonates are probably related to "cannibalization" of earlier replacement dolomite during the chemical compaction.     

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.     

A computer generator for randomly layered structures

AcomputergeneratorforrandomlylayeredstructuresYUJia shun1,2,HEZhen hua2(1.TheInstituteofGeologicalandNuclearSciences,NewZealand;2.StateKeyLaboratoryofOilandGasReservoirGeologyandExploitation,ChengduUniversityofTechnology,China)Abstract:Analgorithmisintrod…     

An Index mechanism for multi-scale view in spatial databases

There are numerous geometric objects stored in the spatial databases. An importance function in a spatial database is that users can browse the geometric objects as a map efficiently. Thus the spatial database should display the geometric objects users concern about swiftly onto the display window. This process includes two operations:retrieve data from database and then draw them onto screen. Accordingly, to improve the efficiency, we should try to reduce time of both retrieving object and displaying them. The former can be achieved with the aid of spatial index such as R-tree, the latter require to simplify the objects. Simplification means that objects are shown with sufficient but not with unnecessary detail which depend on the scale of browse. So the major problem is how to retrieve data at different detail level efficiently. This paper introduces the implementation of a multi-scale index in the spatial database SISP (Spatial Information Shared Platform) which is generalized from R-tree. The difference between the generalization and the R-tree lies on two facets: One is that every node and geometric object in the generalization is assigned with a importance value which denote the importance of them, and every vertex in the objects are assigned with a importance value,too. The importance value can be use to decide which data should be retrieve from disk in a query. The other difference is that geometric objects in the generalization are divided into one or more sub-blocks, and vertexes are total ordered by their importance value. With the help of the generalized R-tree, one can easily retrieve data at different detail levels.Some experiments are performed on real-life data to evaluate the performance of solutions that separately use normal spatial index and multi-scale spatial index. The results show that the solution using multi-scale index in SISP is satisfying.     

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     

On the Thermodynamic Limit for Responses to Static Electromagnetic Fields

For molecular systems,the quantum-mechanical treatment of their responses to static electromagnetic fields usually employs a scalar-potential treatment of the electric field and a vector-potential treatment of the magnetic field.Although the potential for each field separately is associated with the choice of an(unphysical)origin,the precise choice of the origin for the electrostatic field has little consequences for the results.This is different for the