Security constrained reactive power dispatch in electrical power systems

With the increased loading and exploitation of the power transmission system and also due to improved optimised operation, the problem of voltage stability and voltage collapse attracts more and more attention . A voltage collapse can take place in systems or subsystems and can appear quite abruptly. Continuous monitoring of the system state is therefore required. The cause of the 1977 New York black out has been proved to be the reactive power problem. The 1987 Tokyo black out was believed to be due to reactive power shortage and to a voltage collapse at summer peak load. These facts have strongly indicated that reactive power planning and dispatching play an important role in the security of modern power systems. A proper compensation of system voltage profiles will enhance the system securities in the operation and will reduce system losses. In this thesis, some aspects of reactive power dispatch and voltage control problem have been investigated. The research has focused on the following three issues: Firstly, the steady-state stability problem has been tackled where, a voltage collapse proximity indicator based on the optimal impedance solution of a two bus system has been generalised to an actual system and the performance of this indicator has been investigated over the whole range (stable and unstable region) to see how useful this indicator can be for an operator at any operating point. Then we went further to implement a linear reactive power dispatch algorithm in which this indicator was used for the first time to attempt to prevent a voltage collapse in the system. Secondly, a new efficient technique for N-1 security has been incorporated aiming at either maximising the reactive power reserve margin for the generators or minimising active power losses during normal as well as outage conditions (single line outage) .The reactive power redistribution after an outage is based on the S-E graph adopted by Phadke and Spong[72].Thirdly, the dispatch (N-1 security excluded) has been incorporated on line in the O.C.E.P.S. control package to improve the quality of the service and system security by optimally controlling the generator voltages (potentially the reactive control system is able to control transformers, switchable capacitors and reactors). A new function called load voltage control (similar to the load frequency control function) has been introduced to allow smooth variation of the reactive control signals towards their targets

Power transmission planning using heuristic optimisation techniques: Deterministic crowding genetic algorithms and Ant colony search methods

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.The goal of transmission planning in electric power systems is a robust network which is economical, reliable, and in harmony with its environment taking into account the inherent uncertainties. For reasons of practicality, transmission planners have normally taken an incremental approach and tended to evaluate a relatively small number of expansion alternatives over a relatively short time horizon. In this thesis, two new planning methodologies namely the Deterministic Crowding Genetic Algorithm and the Ant Colony System are applied to solve the long term transmission planning problem. Both optimisation techniques consider a 'green field' approach, and are not constrained by the existing network design. They both identify the optimal transmission network over an extended time horizon based only on the expected pattern of electricity demand and generation sources. Two computer codes have been developed. An initial comparative investigation of the application of Ant Colony Optimisation and a Genetic Algorithm to an artificial test problem has been undertaken. It was found that both approaches were comparable for the artificial test problem.EPRSC and National Grid Company pl

An assessment of the respective contributions of flow-rate and concentration variations to mass discharge variations at the outlets of two combined catchments during rain events

International audienceThis paper presents a method for assessing the respective contributions of the variations of flow-rate and concentration of any pollution parameter to the variations of the mass discharge of the same parameter. This method uses a specially designed decomposition of variance, which gives a priority to the information provided by flow-rates, either directly, or through the correlation between flow-rates and concentrations. To demonstrate the potential interest of this method, data monitored on two catchments in the city of Paris (France) are processed according this method, with turbidity being used as a surrogate for suspended solids concentration. Results show that volumes provide a fairly good evaluation of masses at the scale of whole events. Inside any particular event, concentrations are major contributors to the variations of mass discharge, despite the correlations between flow rate and concentration which may be observed for many rain events

Évaluation de la contribution des dépôts aux flux de matières en suspension par temps de pluie dans les réseaux d'assainissement unitaires

Trois sources de polluants de temps de pluie ont été déterminées à l'exutoire des réseaux d'assainissement unitaires : les eaux usées, les eaux de ruissellement et le stock de dépôt contenu dans le réseau. Plusieurs études ont évalué la contribution de ces trois sources au moyen d'un bilan de masses à partir de quelques événements pluvieux (Krejci et al., 1987; Chebbo, 1992; Gromaire et al., 2001; Soonthornnonda and Christensen, 2008; Gasperi et al., 2010). Les résultats obtenus mettent en évidence le rôle important des dépôts comme une source significative de MES, voire majeure, lors des épisodes pluvieux. Ces contributions ont été évaluées pour des réseaux d'assainissement surdimensionnés pour les écoulements de temps sec, de faible pente, présentant des zones connues d'accumulation de dépôts (grossiers) (Ahyerre et al., 2001; GROMAIRE et al., 2006). Par ailleurs la quantification précise des différentes entrées (eaux usées, eaux de ruissellement) et de leur variabilité a souvent été abordée de manière simplifiée. En effet, ces études ont été menées sur un nombre restreint d'événements pluvieux en les comparant à quelques journées de temps sec, sur la base d'échantillons prélevés in situ à des intervalles de temps de plusieurs minutes voire plusieurs dizaines de minutes. Ces évaluations soulèvent certaines questions concernant l'importance de l'effet des incertitudes dans le calcul et nécessitent pourtant une bonne description des entrées incluant leur variabilité. Dans le cadre du réseau d'observatoires français SOERE " URBIS " ont été constituées des bases de données de mesure en continu de la turbidité cumulant plusieurs centaines d'événements pluvieux et autant de journées sèches pour deux sites de caractéristiques différentes : Clichy à Paris et Ecully à Lyon. Ces mesures, converties en concentration en matières en suspension (MES) par des relations MES-Turbidité et couplées avec un modèle de concentrations moyennes événementielles des eaux de ruissellement, ont permis d'évaluer la contribution des dépôts aux masses événementielles des MES observées à l'exutoire de deux bassins versants de caractéristiques très différentes. La contribution des trois sources aux flux de MES à l'échelle de l'événement a été évaluée par une approche de bilan de masse entre l'entrée (eaux usées et eaux de ruissellement) et la sortie (exutoire) du réseau de chaque bassin versant a été réalisée. La méthode proposée permet de prendre en compte toutes les sources d'incertitudes et de variabilité des entrées et de la sortie. Les bilans réalisés sur des bases de données représentatives (88 événements pluvieux à Clichy et 200 événements à Ecully) consolident les résultats similaires suggérés par d'autres études : la masse en MES transitée à l'exutoire pendant un événement pluvieux ne correspond pas à la somme des masses en provenance des eaux usées et des eaux de ruissellement, cette dernière composante étant minoritaire. La contribution des dépôts dans le réseau se situe entre 20 et 80% de la masse de MES observés à l'exutoire en temps de pluie. La robustesse de cette estimation a été établie par une étude de sensibilité aux incertitudes et aux hypothèses affectant le bilan. Ces résultats confirment et affinent les évaluations obtenues précédemment (Gasperi et al., 2010) sur le réseau d'assainissement parisien. De plus, à l'échelle d'un événement pluvieux le dépôt mobilisé ne représente qu'une faible épaisseur si on rapporte la masse érodée concernée à une surface de collecteur immergée par temps sec : de l'ordre de 1 à 3 mm le long de l'ensemble du collecteur du Clichy. Ils montrent aussi que cette contribution n'est pas spécifique au réseau parisien de faible pente et surdimensionné mais aussi elle est importante dans un réseau d'assainissement comme celui d'Ecully qui a une pente de 2.7% contre 0,14% pour le réseau de Clichy et il ne présente pas aussi de zones connues d'accumulation de sédiments

Dynamics of pollutant discharge in combined sewer systems during rain events: chance or determinism?

International audienceA large database of continuous flow and turbidity measurements cumulating data on hundreds of rain events and dry weather days from two sites in Paris (called Quais and Clichy) and one in Lyon (called Ecully) is presented. This database is used to characterize and compare the behaviour of the three sites at the inter-events scale. The analysis is probed through three various variables: total volumes and total suspended solids (TSS) masses and concentrations during both wet and dry weather periods in addition to the contributions of diverse-origin sources to event flow volume and TSS load values. The results obtained confirm the previous findings regarding the spatial consistency of TSS fluxes and concentrations between both sites in Paris having similar land uses. Moreover, masses and concentrations are proven to be correlated between Parisian sites in a way that implies the possibility of some deterministic processes being reproducible from one catchment to another for a particular rain event. The results also demonstrate the importance of the contribution of wastewater and sewer deposits to the total events' loads and show that such contributions are not specific to Paris sewer networks

A Study of Medium Access Control Protocols for Wireless Body Area Networks

The seamless integration of low-power, miniaturised, invasive/non-invasive lightweight sensor nodes have contributed to the development of a proactive and unobtrusive Wireless Body Area Network (WBAN). A WBAN provides long-term health monitoring of a patient without any constraint on his/her normal dailylife activities. This monitoring requires low-power operation of invasive/non-invasive sensor nodes. In other words, a power-efficient Medium Access Control (MAC) protocol is required to satisfy the stringent WBAN requirements including low-power consumption. In this paper, we first outline the WBAN requirements that are important for the design of a low-power MAC protocol. Then we study low-power MAC protocols proposed/investigated for WBAN with emphasis on their strengths and weaknesses. We also review different power-efficient mechanisms for WBAN. In addition, useful suggestions are given to help the MAC designers to develop a low-power MAC protocol that will satisfy the stringent WBAN requirements.Comment: 13 pages, 8 figures, 7 table

Hydrocarbons and heavy metals in the different sewer deposits in the ‘Le Marais’ catchment (Paris, France): stocks, distributions and origins

International audienceThe knowledge of the pollution stored in combined sewers is of prime importance in terms of management of wet weather flow pollution since sewer deposits play a significant role as source of pollution in combined sewer overflows. This work, which focused on the hydrocarbon (aliphatic and aromatic hydrocarbons) and metallic (Fe, Zn, Pb, Cu and Cd) pollution fixed to the different kinds of sewer deposits (gross bed sediment wGBSx, organic layer wOLx and biofilm), was performed in order to provide a complete overview of the contaminant storage in the ‘Le Marais’ combined sewer (Central Paris, France).Firstly , our results have shown that, for all kinds of pollutants, a major part was stored in the GBS (87 to 98%), a lesser part in the OL (2 to 13%) and an insignificant part in the biofilm (< 1%). These results demonstrated that the potential contribution of biofilm to wet weather pollution was negligible compared to the OL one. Secondly, the investigation of hydrocarbon fingerprints in each deposit has provided relevant information about contamination origins: (1) aliphatic hydrocarbon distributions were indicative of petroleum input in the GBS and reflected a mixture of biogenic and petroleum inputs in the OL and biofilm, (2) aromatic hydrocarbon distributions suggested an important pyrolytic contamination in all the deposits.Finally , the study of pollutant fingerprints in the different deposits and in the suspended solids going through the collector has shown that: (1) the suspended solids were the major component of OL and biofilm while urban runoff seemed to be the main transport mechanism introducing pollutants in the GBS and (2) the residence times in sewer of OL and biofilm were quite short compared to those for GBS.

IMPACT DES MATÉRIAUX DE TOITURES SUR LA CONTAMINATION MÉTALLIQUE DES EAUX DE RUISSELLEMENT URBAINES

13 p. (version initiale du 24 mai 2006, mise en forme)National audienceDepuis les années 1990, plusieurs travaux de recherche ont montré que les eaux de ruissellement de toitures ont des teneurs élevées en éléments traces métalliques. Les résultats d'échantillonnages d'eaux de ruissellement menés à Paris révèlent que les niveaux de métaux dans les eaux de ruissellement de toitures sont très supérieurs à ceux des eaux de ruissellement de chaussées ou de cours. Dans ce contexte urbain précis, cet apport métallique a pu être imputé à la corrosion des matériaux métalliques utilisés pour la couverture des toits et l'évacuation des eaux pluviales. Cependant, les connaissances sur les différents éléments de toiture et matériaux incriminés dans cette corrosion, leur taux de relargage, leur fréquence d'utilisation restent à ce jour très limitées. Ces connaissances sont pourtant des éléments clés pour le développement de stratégies de réduction à la source des flux polluants, telles que préconisées par la directive européenne cadre sur l'eau (Directive 2000/60 CE). Cet article résume les résultats des études menées à Paris sur les eaux de ruissellement de toiture et présente la stratégie générale et expérimentale du projet de recherche « TOITEAU », qui a débuté en octobre 2005

Evaluation of roofing materials emissions at the city scale: Statistical approach for computing roofing area distribution

International audienceRoofing materials are considered as a major source of urban runoff contamination. Today, in the context of the European Water Directive (2000/60 CE), an accurate evaluation of contaminant flows from roofs is thus required at the city scale, and therefore the development of assessment tools is needed. However, at the city scale, the important diversity of roofing materials represents a difficult task. In fact, the most restrictive step when estimating contaminant flows for large-scale territories is the estimation of the roofing materials surfaces area, for which no direct data exists. This paper aims to describe the proposal statistical approach for computing roofing materials area distribution. This method is based on two steps. The first one is the sampling theory which aims to define the required size of the selected sample which represents the proportion R (%) from any total urban area surface. The second step is based on applying the estimation theory. In fact, after determining the proportion R (%), we estimate the unknown distribution of roofing materials in an urban area by performing a sample representing R (%) from the total urban area surface. The reliability of the methodology has been proved for tow different urban areas with known roofing materials distribution. Results obtained showed that a sample representing R=4% of the zone area should be randomly generated