• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 11
  • 6
  • 5
  • 3
  • 3
  • 2
  • 2
  • 1
  • 1
  • Tagged with
  • 39
  • 39
  • 9
  • 6
  • 6
  • 6
  • 5
  • 5
  • 5
  • 5
  • 4
  • 4
  • 4
  • 4
  • 4
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Voltage breakdown in polluted insulators

Ahmed, Ibrahim Saad M. January 1989 (has links)
No description available.
2

Galloping of overhead transmission lines

Koutselos, Lakis Thrassyvoulos January 1989 (has links)
This Thesis describes a technique for collecting, moulding and testing naturally occurring ice accretions. Faithful reproductions of the ice shapes were cast in silicone rubber from which wind tunnel models were made. They were tested using a specifically designed wind tunnel rig which measured the aerodynamic lift, drag and pitching moment of the models. From the aerodynamic data the gradients of lift, drag and pitching moment of each ice shape were calculated. The aerodynamic data were consequently used in a two-dimensional two degree of freedom theoretical aerodynamic model which included aerodynamic lift, drag, moment, ice eccentricity, conductor wake effects and the mechanical properties of the conductor. Wind tunnel tests were carried out on a specifically designed wind tunnel dynamic rig. Instabilities of the coupled vertical/torsional galloping were established. Regions of instability were also predicted using a two-dimensional theoretical conductor model. The initial theoretical analysis formed the basis upon which a more sophisticated three-dimensional finite element aeroelastic model was developed. The effects of ice and wind on the natural frequencies and the stability of the conductor were investigated. The use of galloping control devices, the pendulum detuners was also examined. Results showed that the pendulums had a stabilising effect in controlling the vertical/torsional frequency ratio of twin bundles. The vibration characteristics and the stability of quad bundles were investigated using finite elements. In this case, the pendulums shifted the torsional frequencies of the bundle to higher values close to the corresponding vertical frequencies, thus enhancing coupling and having an adverse effect on stability. Finally, limitations in the performance of the pendulum detuners were predicted.
3

Investigation of broadband over power line channel capacity of shipboard power system cables for ship communications networks

Akinnikawe, Ayorinde 15 May 2009 (has links)
Broadband over Power Line (BPL) technology has garnered significant attention lately due to recent advancements in solid state technologies and channel coding schemes. The successful application of BPL technology for in-home automation and networking has led to suggestions of applying BPL in other systems including ships. The application of BPL technology using the Shipboard Power System (SPS) as a potential communications network for ship automation systems has been proposed, to achieve recent U.S. Navy ship management concepts geared toward reducing ship manning while improving operational efficiency. This thesis presents an analytical model developed to examine the channel response characteristics and estimated throughput capacity of SPS cables. The work used a multiconductor transmission line theory based approach to model the channel response of SPS distribution lines and estimated the channel throughput capacity using a “water-filling” communication technique. This work found that BPL using the SPS holds a strong potential for use as a communications network for ship communication systems.
4

Investigation of broadband over power line channel capacity of shipboard power system cables for ship communications networks

Akinnikawe, Ayorinde 15 May 2009 (has links)
Broadband over Power Line (BPL) technology has garnered significant attention lately due to recent advancements in solid state technologies and channel coding schemes. The successful application of BPL technology for in-home automation and networking has led to suggestions of applying BPL in other systems including ships. The application of BPL technology using the Shipboard Power System (SPS) as a potential communications network for ship automation systems has been proposed, to achieve recent U.S. Navy ship management concepts geared toward reducing ship manning while improving operational efficiency. This thesis presents an analytical model developed to examine the channel response characteristics and estimated throughput capacity of SPS cables. The work used a multiconductor transmission line theory based approach to model the channel response of SPS distribution lines and estimated the channel throughput capacity using a “water-filling” communication technique. This work found that BPL using the SPS holds a strong potential for use as a communications network for ship communication systems.
5

Power system arcing fault location based on VHF radiowave propagation

Bartlett, E. J. January 2000 (has links)
No description available.
6

Αξιολόγηση των παραμέτρων που επηρεάζουν την απόδοση των BPLC συστημάτων στα ηλεκτρικά δίκτυα / Evaluation of the factors that affect the performance of the BPLC systems at electric networks

Μπακλαγής, Δημοσθένης- Σωτήριος 28 September 2010 (has links)
Στην εργασία αυτή αρχικά θα αναφερθούν οι τρόποι παροχής ευρυζωνικών υπηρεσιών και θα αναλυθεί το δίκτυο BPL, καθώς και τα οφέλη που μπορεί να έχουν χρήστες και επιχειρήσεις από το δίκτυο αυτό. Επίσης θα δειχθεί η αρχιτεκτονική ενός δικτύου BPL και οι απαραίτητες συσκευές ώστε το υπάρχων ηλεκτρικό δίκτυο να παρέχει ευρυζωνικές υπηρεσίες. Στη συνέχεια θα παρουσιαστούν στατιστικά στοιχεία για την παγκόσμια πρόσβαση σε τηλεπικοινωνιακές υπηρεσίες και ηλεκτρισμό και θα προταθεί μια προοπτική επέκτασης της τεχνολογίας BPL στις αναπτυσσόμενες χώρες. Στο επόμενο κεφάλαιο παρουσιάζονται οι παράμετροι που επηρεάζουν την απόδοση των BPL δικτύων Μέσης, Χαμηλής Τάσης και εσωτερικού. Διαπιστώνεται ότι η αύξηση των κλάδων ανάμεσα σε πομπό και δέκτη προκαλεί σημαντική μείωση στην απόδοση, επίσης το επίπεδο της διαμόρφωσης επηρεάζει σημαντικά τη χωρητικότητα των καναλιών. Στη συνέχεια συγκρίνονται τα ασύρματα με τα ενσύρματα οικιακά δίκτυα, αναφέρονται τα διαθέσιμα πρωτόκολλα στην ενσύρματη και ασύρματη δικτύωση και παρατίθεται μία συγκριτική δοκιμή ανάμεσα σε BPL προσαρμογείς διαφόρων κατασκευαστών. Τέλος χρησιμοποιήθηκε ένα ζευγάρι προσαρμογέων της Belkin βασισμένων στο πρόσφατο πρωτόκολλο Homeplug AV για την δημιουργία ενός οικιακού δικτύου BPL ανάμεσα σε δύο υπολογιστές. Κάνοντας χρήση του προγράμματος Jperf μετρήθηκε το διαθέσιμο εύρος ζώνης για το δίκτυο μας με τα πρωτόκολλα TCP και UDP, επίσης διευκρινίστηκαν οι παράγοντες εκείνοι που μπορεί να μειώσουν το εύρος ζώνης. Πιο συγκεκριμένα διαπιστώθηκε μείωση της απόδοσης με αύξηση των κλάδων ανάμεσα στους προσαρμογείς. Ταυτόχρονα διαπιστώθηκε ότι η χρήση πολύπριζου με φίλτρα προστασίας προκαλεί σημαντική πτώση μέχρι και μηδενισμό του διαθέσιμου εύρους ζώνης και πρέπει να αποφεύγεται. Παράλληλα, έγινε σύγκριση του πρωτοκόλλου Homeplug AV με το παλαιότερο Homeplug 1.0 καθώς και με το πρωτόκολλο ασύρματης δικτύωσης IEEE 802.11.g, και διαπιστώθηκε η εξέλιξη που υπάρχει στα πρωτόκολλα μεταφοράς δεδομένων μέσω των ηλεκτρικών καλωδιώσεων. Με την διεξαγωγή πειραμάτων στον χώρο του εργαστηρίου Υψηλών τάσεων, διαπιστώθηκε ότι το δίκτυο μας δεν επηρεάζεται από κρουστικό θόρυβο. Τέλος, διαπιστώσαμε ότι η σύνδεση και αποσύνδεση φορτίου επηρεάζει σημαντικά το εύρος ζώνης όταν παρεμβάλλονται πολλοί κλάδοι. / The way of providing broadband services and the analysis of Broadband over Power Lines (BPL) networks will be initially presented in this thesis˙ Plus the benefits that can be assessed by the users and companies alike. The architecture of a typical bpl network will be presented and the necessary devices to use power lines for broadband communications. Following statistics for the global access to telecommunication services and electricity will be presented plus the prospect of extending the BPL technology is introduced, for the developed countries. In the next chapter parameters that affect outputs’ performance for Low, Medium Voltage as well as indoor BPL networks are referred. It is realized that the increase of branch between transmitter and receiver causes important reduction in the capacity, also the level of modulation influences considerably the capacity of channels. Afterwards, wireless and the wired home networks are compared, the available protocols in the wired and wireless networking are reported and a comparative trial between bpl adaptors by various constructors are mentioned. Finally a pair of Belkin bpl adaptors based on recent Homeplug AV was used for the creation of one home network between two computers. Using the Jperf we measured the available bandwidth for our network with TCP and UDP protocols, we also clarified those factors that can degrade the bandwidth. We also mentioned reduction of bandwidth icreasing the number of branches between the adaptors. It was also realized that the use of surge protector causes important reduction to bandwidth and it should be avoided. We also compared the Homeplug AV protocol with the older Homeplug 1.0 and with the IEEE 802.11.g protocol. Finally , after experiments in the laboratory of High voltages, it was realized that our adaptors are not influenced by impulse noise.
7

Contribuições metodológicas à implementação da tecnologia PLC/BPL. / Methodological contributions to PLC/BPL implementations.

Oliveira, Otávio Luís de 30 June 2010 (has links)
Este trabalho tem como objetivo fornecer contribuições metodológicas à implementação da tecnologia PLC/BPL em seus diversos ambientes reais de instalação. São apresentados os aspectos básicos envolvidos, princípio de operação, as topologias das redes PLC, vantagens e desvantagens e exemplos de aplicação. Além disso, são apresentadas as contribuições deste trabalho, as quais visam estabelecer procedimentos no desenvolvimento dos projetos de redes de comunicação que utilizam a tecnologia PLC, assim como procedimentos de instalação nos diversos ambientes reais e os procedimentos para o comissionamento das redes implantadas. São destacados os aspectos relacionados às redes comerciais, as quais possuem inúmeros requisitos de desempenho, manutenção preventiva e/ou corretiva, além dos aspectos financeiros dos projetos e os pontos importantes para atendimento da legislação atualmente em vigor. Finalmente, para cada procedimento apresentado, o mesmo é contextualizado através da apresentação de um caso prático associado. / This work aims to provide methodological contributions to PLC/BPL implementations in their several real installation environments. It is presented the basic aspects of the technology as well as the operation principle, the networks topologies, the advantages and the disadvantages and application examples. Furthermore, it is presented the contributions of this work, which goal is to establish procedures related to projects developments of PLC communication networks, some procedures related to the installation process in their real environments and the procedures for commissioning a deployed network. It is emphasized the commercial networks aspects, which demand several performance requirements, the preventive and/or corrective maintenance, as well as the financial aspects and the main topics to comply with the current regulation. Finally, every presented procedure is exemplified with a real case in order to demonstrate its practical functionality.
8

Contribuições metodológicas à implementação da tecnologia PLC/BPL. / Methodological contributions to PLC/BPL implementations.

Otávio Luís de Oliveira 30 June 2010 (has links)
Este trabalho tem como objetivo fornecer contribuições metodológicas à implementação da tecnologia PLC/BPL em seus diversos ambientes reais de instalação. São apresentados os aspectos básicos envolvidos, princípio de operação, as topologias das redes PLC, vantagens e desvantagens e exemplos de aplicação. Além disso, são apresentadas as contribuições deste trabalho, as quais visam estabelecer procedimentos no desenvolvimento dos projetos de redes de comunicação que utilizam a tecnologia PLC, assim como procedimentos de instalação nos diversos ambientes reais e os procedimentos para o comissionamento das redes implantadas. São destacados os aspectos relacionados às redes comerciais, as quais possuem inúmeros requisitos de desempenho, manutenção preventiva e/ou corretiva, além dos aspectos financeiros dos projetos e os pontos importantes para atendimento da legislação atualmente em vigor. Finalmente, para cada procedimento apresentado, o mesmo é contextualizado através da apresentação de um caso prático associado. / This work aims to provide methodological contributions to PLC/BPL implementations in their several real installation environments. It is presented the basic aspects of the technology as well as the operation principle, the networks topologies, the advantages and the disadvantages and application examples. Furthermore, it is presented the contributions of this work, which goal is to establish procedures related to projects developments of PLC communication networks, some procedures related to the installation process in their real environments and the procedures for commissioning a deployed network. It is emphasized the commercial networks aspects, which demand several performance requirements, the preventive and/or corrective maintenance, as well as the financial aspects and the main topics to comply with the current regulation. Finally, every presented procedure is exemplified with a real case in order to demonstrate its practical functionality.
9

Uso do espaço e dieta do Bugio-Ruivo ALOUATTA GUARIBA CLAMITANS (PRIMATES: ATELIDAE) em uma área urbanizada no Bairro Lami, Porto Alegre, Rio Grande do Sul, Brasil

Corrêa, Fabiana Müller January 2015 (has links)
Entre janeiro e dezembro de 2014 um grupo de bugios foi acompanhado a fim de determinar o seu deslocamento e dieta, relacionando com a disponibilidade de recursos alimentares, em uma matriz alterada no bairro Lami, extremo sul da capital. Estes dados foram obtidos durante seis dias por mês, através do método de amostragem de todas as ocorrências e varredura instantânea, este último somente para dieta com 5 minutos de observação e 10 de descanso. As distâncias percorridas pelo grupo foram medidas e plotadas em um mapa, onde foi sobreposto um sistema de quadrados (25m x 25m). Adicionalmente foi feito um estudo fenológico, registrando as seguintes fenofases: folha nova, folha madura, fruto novo, fruto maduro e flor. O tamanho total da área de vida foi estimado em 4,9 ha e em média, a distância percorrida diariamente foi de 446 metros. Foi observada a utilização de diferentes elementos que compõem a matriz, como os fios da rede elétrica, que contribuíram em 23% no deslocamento. Os bugios incorporaram a dieta 30 espécies arbóreas, na qual oito são exóticas (20,8%), com destaque para Ficus cestrifolia (34,8%) e Morus nigra (9,7%). Houve um maior consumo de frutos (56,2%), seguido por folhas (39,8%) e flores (4%), onde foi observado uma alta correlação entre o consumo destes itens e a disponibilidade temporal dos recursos. De modo geral, os bugios mostraram certa habilidade em se deslocar em uma matriz alterada, utilizando os fios da rede elétrica para deslocamento quando ausência de árvores, para acessar os recursos. E mesmo estando inseridos em uma região fragmentada pela urbanização, esta área ainda oferece condições básicas à sua sobrevivência, com a disponibilidade de recursos de alta qualidade nutricional durante todo o ano. Porém, o crescente corte de árvores e a ocorrência de acidentes com estes primatas coloca em risco a existência das populações de bugios na região e reforça a necessidade de mitigação dos impactos causados pela urbanização. O conhecimento dos padrões de uso do espaço e preferências alimentares de Alouatta guariba clamitans em uma paisagem antropizada poderá fornecer subsídios para diminuir os efeitos da presença humana e evitar os acidentes com bugios, como choque na rede elétrica, atropelamentos e ataque por cães, no município de Porto Alegre, RS. / Knowledge of space use patterns and food preferences of Alouatta guariba clamitans in an anthropic landscape may provide subsidies to reduce the human presence effects and avoid accidents with red howler monkeys, as shock in the power grid, road kill and dog atacks in the municipality of Porto Alegre, RS. Thus, between january and december 2014 a red howler monkey group was followed aiming to determine its displacement and diet, relating to the availability of food resources in a modified landscape matrix in the Lami neighborhood, southernmost of the capital. These data were obtained during six days monthly, by all occurrences and scan sampling method, these latter only for diet by 5 minutes of observation with 10 minutes gap between samples. The distances covered by the group were measured and plotted on a map, which was overlaid a square system (25m x 25m). In addition was carried out a phenological study, recording the following phenophases: new leaf, mature leaf, new fruit, ripe fruit and flower. The red howler monkey group home range was estimated at 4.9 ha and the average distance daily traveled was 446 meters. It was observed the use of different elements that compose the matrix by the red howler monkey group, as the wires from the power supply, which contributed with 23% of the movements. The group entered the diet of 30 tree species, in which eight are exotic (20.8%), especially Ficus cestrifolia (34.8%) and Morus nigra (9.7%). There was higher consumption of fruits (56.2%), followed by leaves (39.8%) and flowers (4%), which was observed a high correlation between the consumption of these items and the temporal availability of the resources. Overall, howler monkeys showed some ability to move in a modified matrix, and even when inserted in a region fragmented by urbanization, this area still offers basic conditions for their survival, with the availability of high quality nutritional resources throughout the year. However, the increasing lumbering and accidents with these primates endanger the existence of populations of red howler monkeys in the region and strengthens the need to mitigate the urbanization impacts.
10

Apports méthodologiques à l'étude des interactions des oiseaux avec le réseau de transport d'électricité en France / Methodological contributions to the study of bird interactions with the electricity transmission network in France

Borner, Leyli 24 March 2016 (has links)
La plupart des activités humaines, industrielles ou domestiques, requièrent aujourd’hui l’utilisation d’énergie électrique. Les choix faits pour la production de cette électricité ont nécessité le développement de réseaux de transport d’électricité. En raison de sa densité de câbles, ce réseau induit une fragmentation de l’habitat des animaux volants et principalement des oiseaux. Au-delà des électrocutions au niveau des pylônes, cette fragmentation peut causer la mort d’individus par collision avec les câbles (Bevanger, 1998; Jenkins et al., 2010) et également le dérangement des espèces ou des modifications de leur comportement (Deng and Frederick, 2001; Prinsen et al., 2011; Shimada, 2001). Un grand nombre de facteurs influençant les collisions sont aujourd’hui identifiés (Janss, 2000; Martin and Shaw, 2010). Cependant, la quantification de la mortalité par collision reste complexe en raison de l’hétérogénéité des méthodes utilisées et de l’existence de biais à la quantification (Bech et al., 2012; Ponce et al., 2010). Cette thèse se concentre sur une approche méthodologique de l’étude des interactions des oiseaux avec le réseau de lignes électriques haute-tension (HT) et très-haute-tension (THT) en France métropolitaine. Le premier volet de la thèse concerne la localisation et la hiérarchisation de zones à risque d’interaction pour les oiseaux sur l’ensemble du réseau. Dans ce but, des données de configuration des lignes électriques, de présence (atlas) et de déplacement (couloirs de migration) d’espèces d’oiseaux vulnérables aux lignes électriques sont combinées. Le deuxième volet de la thèse consiste à mettre au point des méthodes qui pourraient permettre de quantifier à l’échelle nationale la mortalité des oiseaux par collision avec les lignes électriques HT-THT. La méthodologie proposée se base sur l’estimation des biais à la quantification, réalisée au cours de la thèse, que sont la détection des cadavres d’oiseaux par les observateurs et la persistance des cadavres sous les lignes électriques. Le troisième et dernier volet de la thèse concerne les modifications de comportement des oiseaux en réponse à la fragmentation de l’espace aérien. Afin de caractériser les mouvements des oiseaux à l’approche des lignes électriques, nous avons adapté une méthodologie d’analyse proposée récemment pour étudier les stratégies d’évitement des oiseaux à différentes échelles spatiales. L’objectif de cette analyse est d’identifier les comportements de vol qui pourraient résulter en une collision avec les câbles. Des données de suivis par télémétrie en trois dimensions (données GPS 3D) de Vautour fauve (Gyps fulvus) sont utilisées dans cette étude comportementale. Ce travail de recherche a permis de proposer un cadre méthodologique pour l’étude des interactions entre oiseaux et lignes électriques et de mettre en évidence l’importance des biais de quantification associés à la recherche de cadavres d’oiseaux sous les lignes. Il a établi pour la première fois une hiérarchisation du risque d’interaction des oiseaux avec les lignes électriques sur l’ensemble du réseau de transport d’électricité français. Les facteurs qui influencent l’utilisation de l’espace à proximité des lignes électriques par les vautours fauves dans les Causses ont également été mis en évidence. / Nowadays, most human activities, be they industrial or domestic, involve the use of electricity. Electricity production choices have required the development of electricity transmission networks. The density of this network has fragmented the habitats of flying animals, birds mainly. Further to the electrocution at power poles, this fragmentation can also cause the death of birds colliding with power lines (Bevanger, 1998; Jenkins et al., 2010) and also the disturbance of species or changes in their behaviour (Deng and Frederick, 2001; Prinsen et al., 2011; Shimada, 2001). Many factors have been identified that influence collision (Janss, 2000; Martin and Shaw, 2010). However, bird mortality by collision is difficult to quantify because of the heterogeneity of methods used and also of the existence of quantification biases (Bech et al., 2012; Ponce et al., 2010). This work is centered on a methodological analysis of the interactions between birds and the High-Voltage(HV) and the Very-High-Voltage (VHV) power grid in Metropolitan France. The First Part discusses the localisation and proposes a hierarchy of the risk areas for birds all along the power network. To this purpose we combine data on the configuration of the power network with data on the presence (breeding atlas), and the movements (migration corridors) of bird species that are vulnerable to power lines. In the Second Part, we developed methods for the quantification, at the national level, of bird mortality that result from the collision with HV and VHV power lines. The methodology proposed builds on the estimation achieved during this thesis of the quantification biases through bird carcass detection by observers and the persistence of these carcasses below power lines. The third and last part of this thesis is about bird behaviour change as a response to airspace fragmentation. We characterised the behaviour of birds when they come close to power lines, by adapting a methodology that analyses bird movements. This methodology was recently proposed for the study of bird avoidance at different spatial scales. The aim of our analysis was to identify flight behavior that potentially results in a collision with power lines. Griffon vultures (Gyps fulvus) data collected with three dimensional telemetry (3D GPS data) were used in this behavioural study. This research corpus brings forward a methodological framework for the study of the interaction between birds and power lines and highlights the magnitude of quantification biases associated to the search for bird remains below power lines. For the first time a hierarchy of interactions risks between birds and power lines is established across the entire electricity transmission network in France. Factors that influence Griffon vultures spatial use in the vicinity of power lines in the French Causses were identified.

Page generated in 0.0705 seconds