Delta-Bar-Delta and directed random search algorithms to study capacitor banks switching overvoltages

This paper introduces an approach to analyse transient overvoltages during capacitor banks switching based on artificial neural networks (ANN). Three learning algorithms, delta-bar-delta (DBD), extended delta-bar-delta (EDBD) and directed random search (DRS) were used to train the ANNs. The ANN training is based on equivalent parameters of the network and therefore, a trained ANN is applicable to every studied system. The developed ANN is trained with extensive simulated results and tested for typical cases. The new algorithms are presented and demonstrated for a partial 39-bus New England test system. The simulated results show the proposed technique can accurately estimate the peak values of switching overvoltages

Extended Delta-Bar-Delta Algorithm Application to Evaluate Transmission Lines Overvoltages

In this paper an intelligent approach is introduced to study switching overvolatges during transmission lines energization. In most countries, the main step in the process of power system restoration, following a complete/partial blackout, is energization of primary restorative transmission lines. An artificial neural network (ANN) has been used to evaluate the overvoltages due to transmission lines energization. Three learning algorithms, delta-bar-delta (DBD), extended delta-bar-delta (EDBD) and directed random search (DRS), were used to train the ANNs. Proposed ANN is trained with equivalent circuit parameters of the network as input parameters; therefore developed ANNs have proper generalization capability. The simulated results for 39-bus New England test system, show that the proposed technique can estimate the peak values and duration of switching overvoltages with acceptable accuracy and EDBD algorithm presents best performance

RATERS’ FATIGUE AND THEIR COMMENTS DURING SCORING WRITING ESSAYS: A CASE OF IRANIAN EFL LEARNERS

Rating accuracy in writing among EFL learners is crucial in determining their English proficiency. Despite the importance of its accuracy, little is known about various factors may affect the accuracy of rating writing essays. This study examines how raters’ comments on EFL writing tasks change as a result of fatigue. To this end, four raters were selected and each given 28 essays to score and comment on. Six general types of raters’ comments (i.e., those on grammar, choice of words, organization, punctuation, dictation, and capitalization) were into focus in this study. Overall, results suggested that fatigue affects raters’ frequency of comments on grammar, choice of words, and organization, and that raters’ comments on punctuation, dictation, and capitalization do not seem to change significantly due to the effect of fatigue. Furthermore, this study revealed that the most and least frequent comments in 112 scored essays were those on grammar and dictation, respectively

Application of the ant colony search algorithm to reactive power pricing in an open electricity market

a b s t r a c t Reactive power management is essential to transfer real energy and support power system security. Developing an accurate and feasible method for reactive power pricing is important in the electricity market. In conventional optimal power flow models the production cost of reactive power was ignored. In this paper, the production cost of reactive power and investment cost of capacitor banks were included into the objective function of the OPF problem. Then, using ant colony search algorithm, the optimal problem was solved. Marginal price theory was used for calculation of the cost of active and reactive power at each bus in competitive electric markets. Application of the proposed method on IEEE 14-bus system confirms its validity and effectiveness. Results from several case studies show clearly the effects of various factors on reactive power price

Developing Iranian EAP Students’ Writing Skill through Explicit Instruction of Lexical Bundles

This study sought to investigate the effect of explicit instruction of lexical bundles (LBs) on the development of Iranian EAP students’ writing quality and receptive and productive knowledge of LBs. Assigned to two experimental and control groups, the eighty participants took pre- and post-tests of writing tasks and the receptive knowledge test. Afterwards, the obtained scores were subjected to a series of Analyses of Covariance (ANCOVAs) and paired samples t-tests. Results of the within-group and between-group analyses indicated that explicit instruction of LBs enhanced the participants’ productive and receptive knowledge of LBs and also improved the overall quality of their written productions. Possible explanations are provided and the implications of the findings for the applicability of LBs instruction are discussed

Tuning the analog and digital performance of Germanene nanoribbon field effect transistors with engineering the width and geometry of source, channel and drain region in the ballistic regime

In this paper, with taking advantage of electrical properties of a germanene nanoribbon, we propose a germanene nanoribbon field effect transistor (GeNR-FET). Here by tuning the width and geometry of the germanene nanoribbon in the source, drain and channel regions, we investigate theoretically the transistor characteristics, analog and digital performances of these several different GeNR-FETs at room temperature. Our simulations are obtained usingdensity functional theory (DFT) combined withnon-equilibrium Green’s function (NEGF) method. The simulation results show that for digital applications, by tuning the width of the germanene nanoribbon a GeNR-FET with a finite band gap in the channel region and small band gap in the source and drain regions showsa better Ion/Ioff ratio in transfer characteristics. However, for the analog applications, if the band gap of the channel region has small value and the band gap of the source and drain regionshave a finite value, the output characteristic shows a higher peak to valley (PVR) ratio which is an important figure of merit in analog applications. Also from the output characteristics, we find that the T-shape channel shows more desirable (PVR) compared with otherdevices and it reaches to 17.28 in this case

Optimal adaptive protection of smart grids using high-set relays and smart selection of relay tripping characteristics considering different network configurations and operation modes

Much attention has been paid to optimizing smart grids (SGs) and microgrids (MGs) protection schemes. The SGs' operation in different operating modes (especially grid-connected and islanded conditions) and various system configurations (such as the outage of each of the distribution generations) adversely influence the protection system. The adaptive protection schemes using different setting groups are suitable and reliable solutions to achieve a fast protective system. However, the literature shows a research gap in developing optimized adaptive protection schemes, focusing on constraint reduction, besides the optimal selection of time-current characteristics for direction overcurrent relays (DOCRs) and high-set relays (HSRs). This research aims to fill such a research gap. The power system analyses, such as power flow and short circuit studies, are done in DIgSILENT, and the genetic algorithm (GA) is used to find the optimum solutions. Test results of the IEEE 38-bus distribution system illustrate the advantages of this study compared to existing ones. The comparative test results emphasize that 31.78% and 21.62% decrement in time of the protective scheme in different topologies for the distribution networks of the IEEE 38-bus and IEEE 14-bus test systems could be achievable by simultaneously optimizing relay characteristics and HSRs compared to existing approaches.Much attention has been paid to optimizing smart grids (SGs) and microgrids (MGs) protection schemes. The SGs' operation in different operating modes (especially grid-connected and islanded conditions) and various system configurations (such as the outage of each of the distribution generations) adversely influence the protection system. The adaptive protection schemes using different setting groups are suitable and reliable solutions to achieve a fast protective system. However, the literature shows a research gap in developing optimized adaptive protection schemes, focusing on constraint reduction, besides the optimal selection of time-current characteristics for direction overcurrent relays (DOCRs) and high-set relays (HSRs). This research aims to fill such a research gap. The power system analyses, such as power flow and short circuit studies, are done in DIgSILENT, and the genetic algorithm (GA) is used to find the optimum solutions. Test results of the IEEE 38-bus distribution system illustrate the advantages of this study compared to existing ones. The comparative test results emphasize that 31.78% and 21.62% decrement in time of the protective scheme in different topologies for the distribution networks of the IEEE 38-bus and IEEE 14-bus test systems could be achievable by simultaneously optimizing relay characteristics and HSRs compared to existing approaches

NOUVELLE APPROCHES POUR LA RESTAURATION D'UN RESEAU ELECTRIQUE APRES UN INCIDENT GENERALISE

The problem of restoring power Systems after a complète or partial blackout is as old as the power industry itself. In récent years, due to économie compétition and deregulation, power Systems are operated closer and closer to their limits. At the same time, power Systems hâve increased in size and complexity. Both factors increase the risk of major power outages. After a blackout, power needs to be restored as quickly and reliably as possible, and consequently, detailed restoration plans are necessary. This thesis concentrâtes on the initial stages of restoration where four major problem areas are identified. A method to détermine optimal units start-up séquence during power plants re-start up is presented. The system frequency behavior after the energization of loads is assessed using a novel approach. An approach to standing phase angle réduction is explained. The occurrence of overvoltages is assessed in the frequency domain. Sensitivity analysis is used in order to find the most efficient network change that can be applied to limit overvoltages. In case time-domain simulations need to be carried out, a method based on Short-Time Fourier Transform helps to limit the overall calculation time. Ail the proposed approaches are validated using time-domain simulations based on IEEE test Systems data. Also a blockset in MATLAB/SIMULINK environment has been developed for long term dynamics simulation to study frequency and voltage responses due to load and génération mismatches for analysis power system restoration scénarios.Le problème de reprise de service des réseaux électriques à la suite d'un incident partiel ou généralisé est un problème bien connu depuis très longtemps. Cependant, ces dernières années, à cause de la concurrence économique et de la dérégulation, les réseaux électriques sont appelés à fonctionner de plus en plus près de leurs limites. Parallèlement à cela, les réseaux électriques sont devenus de plus en plus complexes et leurs dimensions ne cessent de croître, ce qui a augmenté le risque de pannes généralisés. La maîtrise de la reprise de service revêt alors une importance nouvelle. La reprise de service d'un réseau, après un incident quelconque, doit être à la fois rapide et fiable. Une telle opération exige la disponibilité de plans détaillés. Cette thèse porte plus particulièrement sur la phase initiale de la reprise de service d'un réseau électrique, phase pendant laquelle quatre problèmes sont identifiés. Afin de pouvoir apporter des solutions à ces problèmes, quatre approches ont été développées tout au long de ce travail: La première consiste à déterminer la séquence optimale de la mise en marche des groupes pendant la reprise de service des centrales électriques. L'évaluation du comportement fréquentiel du système lors de la ré-alimentation des charges fait l'objet de la deuxième approche. Dans la troisième approche, nous expliquerons comment réduire l'angle de la phase stationnaire. La quatrième permet l'estimation et le contrôle des surtensions harmoniques pendant le renvoi de la tension ver les transformateurs. Ainsi, un blockset dans l'outil de simulation MATLAB/SIMULINK a été développé pour la simulation dynamique à long terme afin de pouvoir étudier la réponse fréquentielle du système, à la suite d'un déséquilibre entre la charge et la production lors d'un scénario de reprise de service