AN ACCURATE METHOD OF FAULT ANALYSIS FOR RESPONSE OF FAULTY DISTANT TRANSMISSION LINE

本文应用分布参数故障传输线复频域布参数节点导纳方程和另一种数值拉普拉斯反变换方法，对故障传输线首末端电压响应进行了分析，基于matlab的分析结果显示，与应用pade有理函数近似的拉普拉斯反变换方法相比较，该方法更易于分析，结果更准确。     

SIMULATION OF EMERGENCY CONTROL MEASURES AND THEIR EFFECTS ON PROBABILISTIC ASSESSMENT OF TRANSIENT STABILITY

Multiple emergency control measures (ECMs) such as fast valve control (FV), generator shedding (GS), under frequency load shedding (UFLS), under voltage load shedding (UVLS) and interior control measures of DC system etc are simulated, and the effects of ECMs on the risk indices of probabilistic transient stability of hybrid AC/DC power systems are discussed in detail. The statistical results of the modified EPRI 36bus system are investigated and compared. It is shown that different ECMs may have positive or negative effects on the transient stability under different conditions or parameters. And it also shows the necessity of optimizing and coordinating among ECMs.     

A NEW METHOD FOR THE SYNTHETIC DETERMINATION OF THE LOSSES OF THREE–PHASE INDUCTION MOTORS

ABSTRACT

A new method for the synthetic determination of the losses of three–phase induction motors by means of direct tests is described. The tests are carried out with a reduced supply voltage and a reduced braking torque: subsequent calculations to refer the results to rated values are then applied.

Using this procedure, a considerable extension of the power range over which direct methods can be employed becomes possible, whilst avoiding the use of correspondingly more powerful braking devices.

A few experimental tests confirm the validity of the proposed method. Moreover, the potentialities of the method are discussed; then a few error analysis considerations are developed; finally, some possible thermal referring procedures are proposed.     

DETERMINATION OF HEAT STATE OF NORMAL LOAD INDUCTION MOTORS BY A NO–LOAD TEST RUN

ABSTRACT

Determining the nominal thermal conditions of Induction Motors (IM) experimentally requires the appropriate equipment for loading the motor, expending the electrical energy and an enormous amount of time, The difficulties of these tests increase with the size of the motors and when it is necessary to perform the tests at the place of installation. This paper discusses the heating process of induction motors in a no–load test run under normal and over–voltage conditions. The method of prediction and recounting the results of a no–load test of IM on a full load run is proposed. The theoretical research of heat processes into IM is based on its thermal circuit and its electrical equivalent. Some of the parameters of the equivalent circuit were determined from the experiment. The influence of the technological uncertainties of manufacturing IM on their thermal parameters is also discussed.     

JOURNAL OF CHANGSHA UNIVERSITY OF ELECTRIC POWER(NATURAL SCIENCE) 2002 VOL.17 General Contents

(Sum 56—59)Matllema缅cs and Computer Science0n the cs—images of locally compact metric spaces …………………………………………Li Zhaowen(1.1Vector model for the computation of individual human resource……………Peng Yuan Peng Zhaohui(1.3A neural network model structure based on spline………………………………………Yuan Xiaohong(1.7Application research of elliptic curve cryptography in TLS protocol……………Xu Liang Xiao Ruliang(1.1 0Programming language with graphic means——LabVIEW…     

COMPARISON OF CASCADE MULTI LEVEL MEDIUM VOLTAGE CONVERTERS

Mediumvoltage adjustablefrequencydrive (AFD) systems for the save of electrical energy have been developed during recent years. There are various converter configurations, but the detail control methods are rarely in publications. This paper describes two novel control strategies for mediumvoltage AFD systems, and analyzes output waveforms and their spectrums.     

IDENTIFICATION OF A COMPOSITE LOAD MODEL WITH APPLICATIONS

Composite induction motor load models have been long studied in power systems. However, the identifiability problem of the load model, i.e. whether the parameters could be identified with the measured data, has not been studied. It is found in this paper that the 3rd order composite induction motor load model is structural unidentifiable with presteady and dynamic response, but identifiable with adding poststeady. Both theoretical analysis and case studies approve the conclusions. Then a genetic algorithm is applied for estimating the parameters of the load model. Practical applications are reported.     

ADVANCES IN THE MODEL OF CYLINDRICAL ALKALINE CELLS

IntroductionCylindricalalkalinecellsaremanufacturedinvari－oussizesandforawiderangeofapplications．Inordertomeetenergyandpowerrequirementsindifferentdevices，itisimportanttoknowtheperformancecharacteristicsofdifferentdesignspriortomanufacturing．However，thedesign－of－experimentapproachforallcellsizescanbeverytime－consumingandcostly．Mathematicalmodelingbasedonrealisticphysical，chemicalandgeometricalparametersisthereforeaveryusefultoolincelldesignandevaluation．Nearlyallbatteriesuseporouse…     

DAMPING OF TORSIONAL OSCILLATIONS–A COORDINATED APPROACH

ABSTRACT

Damping of torsional oscillations using coordinated control through power system stabilizer (PSS) and thyristor controlled reactor(TCR) is presented in this paper. The PSS has modal speed deviations as its feedback signal. The reactive power control is achieved through thyristor controlled reactor (TCR) at the machine terminals. Generator speed deviation is used as auxiliary signal and terminal voltage feedback signal as main control signal for TCR. The following control strategies have been analysed :

a PSS with modal speed control

b PSS with modal speeds plus TCR with terminal voltage control

c PSS with modal speeds plus TCR with complete controls (voltage feed back signal and generator speed deviation signal)

The main objective of this paper is to discuss the modelling aspects and analyse different control strategies for damping torsional oscillations in series compensated ac transmission system. The control parameters like gains and time constants have been obtained by performing repeated eigenvalue analysis. IEEE First Benchmark Model is considered for illustration.     

FRACTAL CHARACTERIZATION OF LIQUID DISPERSION IN TRICKLE BED REACTOR

Dispersion is very important to the design of trickle bed reactor for both chemical and biochemical processes. The degree of dispersion often influences reactor performance and scaleup. The traditional method for modeling dispersion processes in trickle bed reactors is based on the     

IDENTIFICATION OF TRANSFORMER INRUSH CURRENT USING MORPHOLOGICAL SIGNAL DECOMPOSITION

Based on Mathematical Morphology (MM), this paper presents a new method for discrimination between internal fault and magnetising inrush conditions for power transformer protection. The proposed algorithm is to decompose the signal with a class of morphologically simple function, known as Blum functions, to allow the unique feature associated with the inrush current waveform to be preserved, while suppressing other irrelevant features. The proposed scheme has been applied to simulated signals generated by PSCAD/EMTDC. The results confirm that features extracted by the MM filtering have a distinctive property, on which simple identification criteria can be applied for detecting an inrush current from internal fault conditions.     

FAST EXTRACTION OF POWER FREQUENCY COMPONENT USING WAVELET TRANSFORM

Power frequency based protection schemes are widely used for their maturity and high reliability. However, for the exponent decaying component, fast and accurate extraction of power frequency component in system fault remains a challenge for such protection employment. The paper proposed a new algorithm to extract power frequency component based on wavelets and sinuous model based algorithm commonly. Using the new algorithm, accurate amplitude and phase of power frequency component can be achieved at approximately 3/4 period after fault. Extensive simulations have verified the algorithm, which yields satisfactory outcome.     

THE COMMON LAWS OF MASS TRANSFER PROCESSES IN CHEMICAL ENGINEERING

ＴＨＥＣＯＭＭＯＮＬＡＷＳＯＦＭＡＳＳＴＲＡＮＳＦＥＲＰＲＯＣＥＳＳＥＳＩＮＣＨＥＭＩＣＡＬＥＮＧＩＮＥＥＲＩＮＧＺｈｏｎｇＤｕｎａｎ（ＳｃｉｅｎｃｅＤｅｐａｒｔｍｅｎｔⅡ）Ａｂｓｔｒａｃｔ：Ｉｎｔｈｅｖａｒｉｏｕｓｍａｓｓｔｒａｎｓｆｅｒｐｒｏｃｅ...     

OBJECT ORIENTED MODEL TRANSFORMATION OF LINES IN WHOLE TRANSIENT SIMULATION

For building models of transmission lines to simulate whole transient, this paper coordinates the travelling wave model, the lumped parameter model and the quasisteady state model by dynamic characteristics of lines and makes use of OOP to build the selfadaptive model of lines. This model describes whole transient of lines and has characters of high precision, less time complexity and reliable transformation criterion. It can be used in studies of overvoltage, shortcircuits, interactions between AC/DC systems and transient stability.     

基于语料库的中国英语专业学生使用OF的研究

本研究在CLEC语料库基础上对中国大学英语专业学生书面语中使用OF的情况进行了调查研究。与本族语学生相比，中国大学英语专业学生书面语中使用OF时有显著差异。本研究旨在发现中国大学英语专业学生英语写作中存在的问题，对改进我国英语写作教学有重要的启示意义。     

DESIGN AND IMPLEMENTATION OF A NEW GENERATION DISTRIBUTED EMS PLATFORM

Based on an open architecture model of distributed real time system, a new generation platform of EMS is designed and implemented . Server side components are developed in Linux system, including event bus, data access bus, and some SCADA/EMS applications. Client side components include maintenance and operation control subsystems. Based on Web Java technology, maintenance subsystem is to be accessed anywhere. While operation control subsystem is implemented into Java application to obtain good responsibility and reliability. In particular, the platform can run on multi vendor heterogeneous computers, and be easy to integrate the clients of EMS/DMS/DMIS into one workstation. Bench mark testing shows that the new platform could satisfy the requirements of EMS.     

XLPE和OF电缆国内外发展近况及选型之我见

随着上海市城市电网的进一步改造 ,电缆作为城市的输、配、供电方式已成为供电部门的首选 ,但在选用充油电缆 (OF)还是交联聚乙烯电缆(XLPE)的问题上 ,供电部门尚要综合比较考虑。1　国内外 XLPE电缆与 OF电缆的应用情况1 .1　日本日本电网中 XLPE电缆 OF电缆的应用情况见表 1。表 1　日本 XLPE与 OF电缆 (单芯 )首次应用时间电压系级 /k V XLPE OF661973年 192 8年15 41980年 195 8年2 75 1981年 195 9年5 0 0 1988年 (短距离 ) 1972年　　表 2为日本两大电缆公司生产的 XLPE和OF电缆长度统计。表 2　日本两公司生产 XLPE…     

LIWER ESTIMATES FOR A GENERALIZED SUMS OF LEBESGUE FUNCTION TYPE

1IntroductionI,etX:={x,,*,k=l,2,..',n,n=1,2,..-}beandtriangularmatrixofnodeswith(1)(X,=X,,O=)-1<.T,,,<.Tn,C-'..r.,,<1(=X,,;) 1=X'. 1),n=1,2,-..Putingarethecorrcspondlngfundan1cntalpolynon1ialsoftheI,agranginterpoilation,isthelebesguefunction,andforanyfixednonnegat1veintegersandtiscalledthesumofI,ebesguefuncti0ntype.Tostateourresultweneedtointroducesomeothernotation-Foreachn,n=1,2,';define1相似文献   

学校德育中“5＜2“现象的成因及策略探讨 AN ANALYSIS OF CAUSE AND EXPLORATION OF MEASURE ABOUT “5

学校德育的"5＜2"是一种比较普遍存在的现象.本文试图从产生这种现象的根源入手,以期为这一问题的解决提供一种思路.