۱Application of Black–box Modeling of Circuit Breakers to Determine the Most Critical Short Line Fault Conditions
نویسنده(ها): ، ،
اطلاعات انتشار: بیست و یکمین کنفرانس بین المللی برق، سال
تعداد صفحات: ۶
Because of increased steepness of the Transient Recovery Voltage, interruption of short–line faults is the most severe task for almost all high voltage circuit breakers. On the other hand, to determine the black box models of the circuit breakers, the voltage and current measurements during high current interruption tests are normally used. In this paper, different black–box models for circuit breakers are used to study short–line fault (SLF). Parameters of different black–box models are estimated based on the measurements. The implemented models are used to simulate the faults occurring near the circuit breaker terminals (short line faults). The critical length of the line is determined. The results indicate that the interrupting capability of the circuit breaker is enhanced when the shunt capacitor at the line side is increased. As a concrete case, a part of the
Tehran electricity network is considered; the evaluations indicate that the circuit breakers utilized in the considered network can clear all possible faults.<\div>

۲The Future Short–Circuit Current Level And Control of Central China Electric Power System
نویسنده(ها): ، ، ،
اطلاعات انتشار: نهمین کنفرانس بین المللی برق، سال
تعداد صفحات: ۱۲
This paper, considering long and medium term planning of Central China Power Network (CCPN), calculated and analyzed the shortcircuit
current level and its variation trend in future CCPN particularly for the construction of the Three Gorges Hydroelectric Power Station (TGHPS). According to the experience of construction and operation of international large power systems, It put forward the measures and methods of short–circuit current–limitation in the 220–500KV network, studied the effect of operation modes and inter –connection of TGHPS on short–circuit currents (SCC) of power networks and suggested the solving methods.<\div>

۳Intelligent Short–term Load Forecasting of an Urban Area
نویسنده(ها): ،
اطلاعات انتشار: هفدهمین کنفرانس بین المللی برق، سال
تعداد صفحات: ۶
This paper presents the application of an Artificial neural Network (ANN) for short–term load forecasting (STLF) of an urban area in Japan (Tokyo Metropolitan Area). The basic reason for STLF is to predict the loads of next 24 hours ahead. This will allow a utility to match its generation capabilities to the expected demand. Although, there are several methods to determine such forecasting, however a neural network is selected in this paper. The reason is because the ANN can correspond to the problems, which have highly nonlinearity among their inputs and outputs. The ANN mode can forecast next 24 hours loads (one day) in advance. Presentl y, one of the most popular, effective, and easy to learn three–layer back– propagation (BP) models is introduced. 15 to 25 input neurons are chosen based on their impacts on the output loads. They are. actual load, temperature, wind speed and direction There is one neuron in output layer which is corresponded to an hour load of next day. Training and testing of STLF are carried out based on historical data collected for two years (calendar year 1996 and 1997). On the basis of each day's load characteristics, three ANNs are designed for STLF. Also, three types of simulations for STLF have been discussed.<\div>

۴Short Term Wind Speed Forecast Using Optimized Neural Networks
نویسنده(ها): ،
اطلاعات انتشار: همایش ملی سوخت، انرژی و محیط زیست، سال
تعداد صفحات: ۱۲
The paper investigate a real–world application, the short–term wind speed forecasting in a wind farm using parametric recurrent neural networks as forecast model. To deal with the complexity of the process and to improve the performance of the model, a special on–line learning algorithm is employed for training the parametric recurrent networks, based on the windowing method. Using an improved activation function (AF) and a parameter, p, one is able to get the optimize size of the needed network. This is possible by training the shape of AF. After finishing the training by checking the value of the p, it is possible to reduce and optimize the size of the network to find out the minimum size of the network. Finally, simulation results for the numerical method and parametric neural networks are shown.<\div>

نویسنده(ها): ، ،
اطلاعات انتشار: ششمین کنفرانس بین‌المللی مسائل فنی و فیزیکی در مهندسی قدرت، سال
تعداد صفحات: ۵
The use of distributed generation (DG) within distribution systems has increased in the last two decades, due to institutional requirements and technical advances. The short–circuit capacity of existing distribution networks is often close to their design level, leaving little margin for the interconnection of DG resources. In general all forms of DG contribute to fault levels. The connection of DG can raise the fault level on existing equipment, due to the fault contribution from the DG itself, to values beyond the capacity of existing switchgear. Faults occurring in power networks normally result in a large short–circuit current flow in the system, which may exceed the rating circuit breakers and damage system equipments. The aim of this paper is to use the latest edition of the IEC Standard 60909 for calculating the maximum fault level in the proposed test case, and make a comparison between the IEC60909 and the results obtained from the software in an IEEE 34 node MV test feeder.<\div>

۶A neuro–fuzzy network model for interval time series forecasting in exchange rate markets
نویسنده(ها): ،
اطلاعات انتشار: هفتمین کنفرانس بین المللی مهندسی صنایع، سال
تعداد صفحات: ۱۰
Applying quantitative models for forecasting in financial markets and assisting investment decision making has become more indispensable in business practices than ever before. In recent years, various time series models are proposed to financial markets forecasting. In each case, the accuracy of time series forecasting models is fundamental to make decision and hence the research for improving the effectiveness of forecasting models have been curried on. Many researchers have compared different time series models to distinguish more efficient once in financial markets<\div>

۷Issues on short– and long–term stability of historical and modern man–made cavities in the Cappadocia Region of Turkey
نویسنده(ها): ،
اطلاعات انتشار: نهمین همایش ملی تونل، سال
تعداد صفحات: ۱۲
Underground space has long been used through the history for the purposes of human accomodation, religious ceremony, defense, food storage etc.by humankind. There are a number of man–made underground rock structures in different areas all over the world. Today the interest to utilization of underground space is still continuing. The Cappadocia Region of Turkey is one of the seven sites in Turkey included in the World Heritage List in 1985. In this area, there exist significant historical underground settlements such as rock cut dwellings, cities, churches, and semi–underground cliff settlements, and modern man–made cavities used for multi–purposes. Easy carving and thermal isolation properties of the Cappadocian soft tuffs have been the main reasons for the extensive multi–purpose underground use in the region from past to present. In addition to historical and archeological characteristics of the rock structures in the Cappadocia, their short– and long–term behaviors are also important data source in terms of underground rock engineering. The paper attempts to point out some issues including short– and long–term geomechanical properties of the Cappadocian tuffs, in which underground openings are carved, a critical overview on rock mechanical aspects, particularly their stability and implications in rock engineering using some typical structures selected from the region, and possible measures of protection and mitigation based on the authors’ collaborative studies with their colleagues both from Japan and Turkey.<\div>

۸Operational Analysis and Designing Impedance Network of Current–Type Z–Source Inverters
نویسنده(ها): ،
اطلاعات انتشار: بیستمین کنفرانس مهندسی برق ایران، سال
تعداد صفحات: ۶
This paper presents an analytic method of designing the impedance network of the ZSCI. In the available works on impedance ZSI network, mathematical complexityequations have been used for obtaining values of the impedance network, this paper provides guidelines in approximate sizing ofthe impedance network components by means of linearization techniques. Computer Simulation results verity the accuracy of the design method<\div>

۹Data analysis and discussion on the predictability of wind speed with short–term forecasting of Rostamabad city wind speed
اطلاعات انتشار: دومین کنفرانس بین المللی سالانه انرژی پاک، سال
تعداد صفحات: ۷
Wind energy has been well recognized as renewable resource in electricity generation. Programs in many countries are that by 2020 about 20 percent of theelectricity production from renewable energy that are considered part of the clean energy will be provided. In this paper, Data analysis and investigate thepredictability of wind speed with short–term forecasting of wind speed in Rostamabad in northern Iran from 2002 to 2004. The data is analyzed and forecasted bysingular spectral analysis (SSA) method and is investigated predictability with δ–ε method. SSA decomposes a time series into its principal componentsi.e. its trend and oscillation components, which are then used for time series forecasting effectively. The 10–minute intervals average wind speed data used to demonstrate the effectiveness of the proposed approach. It is found that the prediction errors can be decreasedand the method has a good ability in characterizing and prediction of the desired time series<\div>

۱۰Activities study of PET’s radioisotope Productions with plasma focus devices
نویسنده(ها): ،
اطلاعات انتشار: هفدهمین کنفرانس مهندسی پزشکی ایران، سال
تعداد صفحات: ۴
In recent years, the request for radioisotopes has been increasing steadily. Experiments in the past five years have demonstrated production of Short–Lived radioisotopes (SLRs) with a plasma focus devices. Radioisotope activity only a few microcuries have been obtained from single discharges in small scale plasma focus machines and at high pulse repetition rate in large and high energy plasma focus devices and these devices will be used to breed Short–Lived radioisotopes (SLRs) for positron emission medical examination such as PET.<\div>

۱۱Short Term Load Forecasting Using Artificial Neural Network And Imperialist Competitive Algorithm
اطلاعات انتشار: همایش ملی مهندسی برق و توسعه پایدار با محوریت دستاوردهای نوین در مهندسی برق، سال
تعداد صفحات: ۷
In last two decades, statistical methods have been usual techniques for short–term load forecasting. But today, much research has been carried out on the application of Artificial Neural Network techniques to Short–Term Load–Forecasting (STLF) problem. In this paper, The time of STLF is reduced by identifying of effective parameters in STLF by using of imperialist competitive algorithm.<\div>

۱۲Analysis of UV–Vis absorption spectrum for the evaluation of structural chemistry of LAST glass containing Fe3+ ions
اطلاعات انتشار: سومین همایش ملی فن آوری های نوین شیمی و مهندسی شیمی، سال
تعداد صفحات: ۵
Structural chemistry of Fe3+ doped LAST glass has been analyzed using the UV–Vis absorptionspectra. Optical parameters like absorption and extinction coefficients, direct and indirect opticalband gaps, Fermi energy level as same as Urbach energy of samples were calculated using theirabsorption spectra. It was revealed that Fe3+ ions have network forming role in the glass structureby increasing the Bridging Oxygen’s (BOs) in the matrix.<\div>

۱۳The Impact of Teaching Vocabulary–Acquisition Strategies on Reading Comprehension of EFL Third Grade High School Students
اطلاعات انتشار: اولین همایش ملی زبان انگلیسی، ادبیات و ترجمه در آموزش و پرورش، سال
تعداد صفحات: ۹
This research was an attempt to study the effect of two strategies of guessing meaning fromthe context and the use of affixes on the reading comprehension of a group of EFL thirdgrade high school students. For this purpose, 90 intermediate students studying English inShahed high school in Farsan, Shahrekord, Iran were chosen to participate in this study. Theparticipants were randomly divided into three equal groups, each containing thirty students.The first experimental group received instruction based on guessing meaning from thecontext, while students learnt the affix instruction in the second experimental group. At theend of the treatment, a multiple–choice posttest of reading comprehension was administeredto compare vocabulary achievement among the groups. Analysis of the results of the posttestrevealed a positive effect for guessing meaning from the context method, resulting in therejection of the first null hypothesis. Comparison of the results of immediate posttest anddelayed posttest of the groups further helped to reject the second null hypothesis, since theresults showed that the participants who used guessing the meaning from the context methodcould store and retain vocabulary items in their long–term memory better than those who usedanother method.<\div>

۱۴Checking Effects of short–term financing on the efficiency of the companies listed in Tehran Stock Exchange
نویسنده(ها): ،
اطلاعات انتشار: کنفرانس بین المللی مدیریت و علوم انسانی، سال
تعداد صفحات: ۸
There is no doubt that to study this, 05 of the companies listed in Tehran Stock Exchange was selected as the target population. Based on statistical methods, thus, indicate that the average rate of return on equity financing methods, there is no significant relationship. Keywords: stock returns – short–term financing – securities – short–term loans – Advances sale the new investments necessary for growth and competitiveness in today's world. Finance the various financing these investments is usually done by means of which each has its own characteristics. managers in investment project special attention should be output to the rate and the cost of the project have financial investment companies in therefore always two indexes are much attention: 1–expenditure financial security 2–output rate shares. This study sought to connection between financial cost and output rate shares in companies has been accepted in Tehran stock exchange to study. To study this, 05 of the companies listed in Tehran Stock Exchange was selected as the target population. Based on statistical methods, thus, indicate that the average rate of return on equity financing methods, there is no significant relationship.<\div>

۱۵بررسی رابطۀ حافظۀ کوتاه مدت و میزان آگاهی واج شناختی یا وضوح گفتاری خواندن در دانش آموزان ناشنوا
اطلاعات انتشار: تابستان ،چهاردهم- شماره ۵۲، سال
تعداد صفحات: ۱۲
Objective: This study investigated the relationship between short–term memory and phonological awareness with speech intelligibility of reading in deaf students. Methods: Eighty–two deaf and hearing students from special and regular primary schools were selected. Wechsler intelligence digits span subtest was presented in visual and also verbal mode for measuring short term memory، Persian Phonological Awareness Test was used to measure phonological awareness. Speech intelligibility of reading was assessed by Speech Intelligibility Rating Scale. Results: Findings indicated that short term memory span and phonological awareness in deaf children is lower than their hearing peers. Also، the relation between short–term memory span and phonological awareness and speech intelligibility was significant. Conclusions: Deaf students are poorer in short term memory and phonological awareness than hearing peers، in addition there is a significant relation between short–term memory and phonological awareness with speech intelligibility، so the role of intervention programs should be emphasized to improve these skills.

۱۶Set–up and location of the fault current limiter (fcl) in power systems by fuzzy HFL sorting algorithm and optimization pso HIGA
اطلاعات انتشار: چهارمین کنفرانس بین المللی پژوهش های نوین در علوم مهندسی و تکنولوژی، سال
تعداد صفحات: ۱۷
As the number of new power plants and the scale of transmission systems sustainably grow, the probability of exceeding the short circuit rating of circuit breakers (CBs) increases, a fact which leads the system's security and stability to a big issue. Fault Current Limiter (FCL), as one of the solutions to current surge attenuation, attracts a lot of attention from utilities. To make the best use of FCL, the placements must be optimally determined along with the most suitable FCL parameters settings. This paper proposes a method combining Hierarchical Fuzzy Logic System (HFLS) method for pre–sorting the feasible solutions and Hashing–Integrated Generic Algorithm (HIGA) as an optimization tool to find the best solution in the reduced search space. To verify the proposed approach as an effective means for placement of the FCLs, the proposed method is implemented through Mat lab and Dig SILENT and tested in a practical power system. The numerical results show that the proposed method may achieve a better solution in less time with fewer placements of FCLs, thus reducing the cost, while maintaining comparable system security.<\div>

۱۷Negative Sequence Impedance Measurement for Islanding Detection In Presence of Distributed Generation
اطلاعات انتشار: دومین کنفرانس بین المللی و سومین همایش ملی کاربرد فناوری های نوین در علوم مهندسی، سال
تعداد صفحات: ۷
Distributed generation (DG), similar to other generators require electrical protection against system short–circuit and unusual conditions. Adding DG to the electric power distribution systems, can reduce the reliability, protection, system stability and power quality to consumers. The challenges associated with DG, protecttion against the unscheduled islanding, is an important issue. It is essential that the islands are immediately detected and the DG is disconnected from the distribution network or taking it under control. According to distribution utility Standards, the island must be detected in less than 2 seconds. In this paper a new method for detecting active synchronous type generator island DG, based on negative sequence impedance measurement is introduced. A negative sequence impedance islanding detection (NSIID) method is an improvement in the impedance measurement techniques for the detection of an island due to the negligible non detection zone and specifically large threshold window. Finally The algorithm for implementing this network protecting approach will be presented. In this paper, simulations have been done in Digsilent and results have been analyzed.<\div>

۱۸The structure of module contractible Banach algebras
اطلاعات انتشار: International Journal Of Nonlinear Analysis And Applications، اول،شماره۱، ۲۰۱۰، سال
تعداد صفحات: ۶
In this paper we study the module contractibility of Banach algebras and characterize them in terms the concepts splitting and admissibility of short exact sequences. Also we investigate module contractibility of Banach algebras with the concept of the module diagonal.

۱۹Application of an Improved Neural Network Using Cuckoo Search Algorithm in Short–Term Electricity Price Forecasting under Competitive Power Markets  (Text in Persian)
اطلاعات انتشار: Journal of Operation and Automation in Power Engineering، اول،شماره۲، ۲۰۱۳، سال
تعداد صفحات: ۱۱
Accurate and effective electricity price forecasting is critical to market participants in order to make an appropriate risk management in competitive electricity markets. Market participants rely on price forecasts to decide on their bidding strategies، allocate assets and plan facility investments. However، due to its time variant behavior and non–linear and non–stationary nature، electricity price is a complex signal. This paper presents a model for short–term price forecasting according to similar days and historical price data. The main idea of this article is to present an intelligent model to forecast market clearing price using a multilayer perceptron neural network، based on structural and weights optimization. Compared to conventional neural networks، this hybrid model has high accuracy and is capable of converging to optimal minimum. The results of this forecasting method for Market Clearing Price (MCP) of Iranian and Nord Pool Electricity Markets، as well as Locational Marginal Price (LMP) forecasting in PJM electricity market، verify the effectiveness of the proposed approach in short–term price forecasting.

۲۰A Context–Sensitive Dynamic Role–Based Access Control Model for Pervasive Computing Environments
نویسنده(ها): ،
اطلاعات انتشار: International Journal of Information Security، دوم،شماره۱، Jan ۲۰۱۰، سال
تعداد صفحات: ۲۰
Resources and services are accessible in pervasive computing environments from anywhere and at anytime. Also, due to ever–changing nature of such environments, the identity of users is unknown. However, users must be able to access the required resources based on their contexts. These and other similar complexities necessitate dynamic and context–aware access control models for such environments. In other words, an efficient access control model for pervasive computing environments should be aware of context information. Changes in context information imply some changes in the users' authorities. Accordingly, an access control model for a pervasive computing environment should control all accesses of unknown users to the resources based upon the participating context information, i.e., contexts of the users, resources and the environment. In this paper, a new context–aware access control model is proposed for pervasive computing environments. Contexts are classified into long–term contexts (which do not change during a session) and short–term contexts (which their steady–state period is less than an average time of a session). The model assigns roles to a user dynamically at the beginning of their sessions considering the long–term contexts. However, during a session the active permission set of the assigned roles are determined based on the short–term context conditions. Formal specification of the proposed model as well as the proposed architecture are presented in this paper. Furthermore, by presenting a real case study, it is shown that the model is applicable, decidable, and dynamic. Expressiveness and complexity of the model is also evaluated.

۲۱The role of 1–hexene comonomer content in thermal behavior of medium density polyethylene (MDPE) synthesized using Phillips catalyst
اطلاعات انتشار: Polyolefins Journal، اول،شماره۲، Autumn ۲۰۱۴، سال
تعداد صفحات: ۱۳
In this work, the role of comonomer content of 1–hexene–medium density polyethylene (MDPE) copolymer, synthesized using Phillips catalyst, on thermal behavior parameters such as: crystallization, melting temperature and thermal degradation was investigated in detail. The copolymer was fractionated to homogenous short–chain branching (SCB) fractions by "preparative temperature rising elution fractionation" (P–TREF) method and then it was subjected to thermal analyses. A broad chemical composition distribution (CCD) in terms ofSCB content and molecular weight (Mw) was observed by P–TREF and gel permeation chromatography (GPC), respectively. Based on P–TREF results, a parabolic relationship between methylene sequence length (MSL) and elution temperature (ET) was presented. Differential scanning calorimetry (DSC) showed distinct, well–defined melting peaks over a 22 °C temperature range for SCB contents of about 3–12 (br\1000 C). The variations in physical characteristics such as melting temperature (Tm), crystallinity (Xc), crystallization temperature (Tc) and lamellae thickness (Lc) against SCB content were correlated. Thermogravimetric analysis (TGA) suggested linear relationships between the temperature at maximum degradation rate (Tmax) as well as the degradation initiationtemperature (T5%) versus SCB content. Moreover, the TGA curves exhibited distinct differences at both initiation and propagation stages of thermal degradation at dissimilar comonomer contents.
نمایش نتایج ۱ تا ۲۱ از میان ۲۱ نتیجه

ارتباط با ما

لینک‌های مفید