De nombreux projets visant à réduire l’impact environnemental global des avions sont lancés au niveau européen. L’un des moteurs étudié pour les avions moyens et longs courriers est le moteur Ultra High Bypass Ratio (UHBR) : un moteur simple corps, double flux, à flux externe fortement augmenté. Le moteur UHBR doit être équipé d’un réducteur épicycloïdal, qui est un composant jamais utilisé dans un turboréacteur jusqu’à présent. L’optimisation d’un réducteur épicycloïdal a conduit à l’utilisation de paliers hydrodynamiques pour supporter les pignons satellites du porte-satellites.Pour une telle application, le palier hydrodynamique subit une déformation très élevée due aux charges de l’engrènement sur le pignon satellite et à l’effet centrifuge engendré par la rotation du porte-satellites. La géométrie optimisée des composants du palier varie avec le comportement thermique et mécanique des pièces, nécessitant la prise en compte d’une modélisation thermoélastohydrodynamique (TEHD).Afin de modéliser précisément ces phénomènes, un modèle conservatif dans la zone inactive en régime TEHD a été développé et validé à l’aide des résultats d’essais de la littérature et des bancs d’essais de Safran Transmission Systems. Les résultats obtenus montrent un double champ de pression dans le palier hydrodynamique du réducteur épicycloïdal, engendré par la forte déformation élastique du pignon agissant ainsi de façon significative sur le comportement dynamique du palier. De plus, l’influence de l’effet centrifuge sur l’huile dans le palier a été également examinée. / Several projects aimed at reducing the overall environmental impact of aircrafts are launched at European level. One of the engines studied for medium and long-haul aircraft is the Ultra High Bypass Ratio (UHBR) engine: a single-body, dual-flow gas turbine, with a greatly increased external flow rate. The UHBR engine must be equipped with an epicyclic reduction gearbox, which is a component never used before in a turbofan engine. The optimization of an epicyclic gearbox has resulted to the use of hydrodynamic bearings for supporting the satellite gears on the planet carrier.The hydrodynamic bearing of such application undergoes high deformations due to the gear contact loads on the satellite gear and to the centrifugal effect generated by the rotation of the planet carrier. The optimized geometry of the bearing components is influenced by the thermal and mechanical behavior of the bearing components, which requires a thermoelastohydrodynamic (TEHD) modeling taking into account the real film thickness under operation.In order to precisely simulate these phenomena, a conservative modeling in the inactive zone, under a TEHD regime has been developed and validated by comparing the predictions to the test results of the literature and of the test benches of Safran Transmission Systems. The results obtained show a double pressure field in the hydrodynamic bearing of the epicyclic reduction gearbox, due to the strongly deformed film thickness, which greatly affect the dynamic behavior of the bearing. In addition, the influence of the centrifugal force on the oil pressure in the oil film was also examined.

This thesis is devoted to the development of new models for a recently-implemented FACTS (flexible alternating current transmission system) device, the unified power flow controller (UPFC), and the control coordination of power systems with FACTS devices in steady-state operating mode. The key objectives of the research reported in the thesis are, through online control coordination based on the models of power systems having FACTS devices, those of maximising the network operational benefit and restoring system static security following a disturbance or contingency. Based on the novel concept of interpreting the updated voltage solutions at each iteration in the Newton-Raphson (NR) power-flow analysis as dynamic variables, the thesis first develops a procedure for representing the unified power flow controllers (UPFCs) in the steady-state evaluation. Both the shunt converter and series converter control systems of a UPFC are modeled in their dynamical form with the discrete time variable replaced by the NR iterative step in the power-flow analysis. The key advantage of the model developed is that of facilitating the process of UPFC constraint resolution during the NR solution sequence. Any relative priority in control functions pre-set in the UPFC controllers is automatically represented in the power-flow formulation. Although the developed UPFC model based on the dynamic simulation of series and shunt converter controllers is flexible and general, the number of NR iterations required for convergence can be large. Therefore, the model is suitable mainly for power system planning and design studies. For online control coordination, the thesis develops the second UPFC model based on nodal voltages. The model retains all of the flexibility and generality of the dynamic simulation-based approach while the number of iterations required for solution convergence is independent of the UPFC controller dynamic responses. Drawing on the constrained optimisation based on Newton’s method together with the new UPFC model expressed in terms of nodal voltages, a systematic and general method for determining optimal reference inputs to UPFCs in steady-state operation is developed. The method is directly applicable to UPFCs operation with a high-level line optimisation control (LOC) for maximising the network operational benefit. By using a new continuation technique with adaptive parameter, the algorithm for solving the constrained optimisation problem extends substantially the region of convergence achieved with the conventional Newton’s method. Having established the foundation provided by the comprehensive models developed for representing power systems with FACTS devices including the UPFC, the research, in the second part, focuses on real-time control coordination of power system controllers, with the main purpose of restoring power system static security following a disturbance or contingency. At present, as the cost of phasor measurement units (PMUs) and wide-area communication network is on the decrease, the research proposes and develops a new secondary voltage control where voltages at all of the load nodes are directly controlled, using measured voltages.

In the recent years, there has been a trend to run metallic pipelines carrying petroleum products and high voltage AC power lines parallel to each other in a relatively narrow strip of land. The case of electromagnetic interference between high voltage transmission lines and metallic pipelines has been a topic of major concern since the early 60’s. The main reasons for that are: • The ever increasing cost of right-of-ways, suitable for power lines and pipelines, along with recent environmental regulations, aiming to protect nature and wildlife, has forced various utilities to share common corridors for both high voltage power lines and pipelines. Therefore, situations where a pipeline is laid at close distance from a transmission line for several kilometers have become very frequent. • The rapid increase in energy consumption, which has led to the adoption of higher load and short circuit current levels, thus making the problem more acute. Due to this sharing of the right-of-way, overhead AC power line field may induce voltages on the metallic pipelines running in close vicinity leading to serious adverse effects. This electromagnetic interference is present both during normal operating conditions as well as during faults. The coupling of the field with the pipeline takes place either through the capacitive path or through the inductive or conductive paths. In the present work, the induced voltages due to capacitive and inductive coupling on metallic pipelines running in close vicinity of high voltage power transmission lines have been computed.The conductor surface field gradients calculated for the various phaseconfigurations have been presented in the thesis. Also the electric fields under transmission lines, for both single circuit and double circuit (various phase arrangements) have been analysed. Based on the above results, an optimum configuration giving the lowest field under the power line as well as the lowest conductor surface gradient has been arrived at and for this configuration induced voltage on the pipeline has been computed using the Charge Simulation Method (CSM). For comparison, induced voltages on the pipeline have been computed for the various other phase configurations also. A very interesting result is that the induced voltage on the pipeline becomes almost negligible at a critical lateral distance from the center of the powerline and beyond which the induced voltage again increases.This critical distance depends on the conductor configuration. Hence it is suggested that the pipeline be located close to the critical distance so that the induced voltage would be close to zero. For calculating the induced voltage due to the inductive coupling, electromotive force (EMF),induced along the pipeline due to the magnetic field created by the transmission line has been calculated. The potential difference between the pipeline and the earth, due to the above induced EMFs, is then calculated. As the zones of influence are generally formed by parallelism, approaches, crossings as well as removals, the computation involves subdividing the zone into several sections corresponding to these zones. The calculation of voltages is carried out at both the ends of the sections. Each section is represented by an equivalent π electrical network, which is influenced by the induced EMF. The induced EMF is calculated during faulted conditions as well as during steady state conditions. Inductive coupling calculations have been carried out for the following cases: •Perfect parallelism between powerline and pipeline. •zone of influences formed by parallelism, approaches, crossings and removals. It has been observed that when the pipeline is approaching the HV transmission line at an angle, then running parallel for certain distance and finally deviating away, the induced voltage is maximum at the point of approach or removal of the pipeline from the transmission line corridor.The induced voltage is almost negligible near to the midpoint of the zone of influence. The profile of the induced voltage also depend on whether the pipeline is grounded or left open circuited at the extremities of the zone of influence. Effect of earth resistivity and anti-corrosive coatings on induced voltage has also been studied. For mitigating the induced voltage on the pipeline,numerous low resistive earthings have been suggested. Results show that significant reduction in induced voltage can be achieved as the number of earth points is increased.

The Eskom Transmission Network experiences an exceptionally high number of line faults, the cause of which, may not be correctly identified. This thesis analyses a number of all the possible factors responsible for causing these faults. The objective is to assign probable causes of these faults and that the correct preventative or corrective measures may be planned. The percentage of unexplained line faults is estimated to be 35 % of the total system faults. It is important for the Transmission Group of Eskom to minimise the number of faults. Major efforts to minimise identified faults such as bird streamers, veld fires, sugar cane fIfes, lightning and a hypothesised light pollution, light wetting mechanism has been undertaken by the transmission grid authority. This thesis presents an analysis of the statistical data of the unknown faults (unknown faults is defined as lines that trip due to a reason which could not be identified) that has been undertaken. This analysis takes into account a number of categories of causes of line faults. The period, for which the performance of the lines was analysed for was the years inclusive of 1993 to 1997. The investigation has focused on the identification of the under-performing lines of the main Transmission Network. The identified poorly performing lines have been compared with each other from the perspective ofthe following variables: • Region • Voltage (System Voltage) • Climatic Data Line faults - Time ofDay analysis • Line Faults - Time of Year analysis. The analysis indicates that the majority of unexplained flashovers occur between 22 :00 and 07:00 the following morning (Britten et al, 1999). Almost all of the under performing lines in South Africa fall in the sub-tropical/humid climatic area. All the lines studied are insulated with standard glass disc insulators. The analysis indicated that most of the unexplained line faults occur during the months when the seasons change, e.g. from autumn to winter. The analysis further indicates that most unexplained line faults occurred during the months of April to May and August to September. Of note is that during the period of this investigation bird guarding was performed on some lines. Installing bird guards may reduce those line faults that are caused by bird streamers. However, the bird pollution (deposited on glass disc insulators) that is not washed off at the same time as the bird guard installation may cause the line to trip due to the combination of the pollution and wetting resulting in a pollution type flashover. This is a possible cause of some unexplained line faults that occur from April to May. Bird streamers are also identified as the most probable cause of the unexplained faults which occur during the late evening periods (22:00 - 00:00). Pollution (with wetting) during the early morning periods may result in faults for the period 00:00 to 02:00. Line faults in the early morning periods (04:00 - 7:00) could be due to bird streamers or pollution and wetting, depending on the time of year in which the faults occurs. / Thesis (M.Sc.)-University of Natal, Durban, 2003.

The management of parallel and series resonance conditions is important for ensuring that harmonic levels are managed on utility networks, and that shunt compensators are able to operate without constraints for various network conditions (states). For these and similar problems, harmonic impedance assessment of the ac network is required for the design of ac filter or shunt capacitor bank installations. This is particularly important for large installations connected to HV or EHV systems, because resonances at these voltage levels tend to be highly un-damped resulting in potentially damaging voltage and current amplification. The objective of this dissertation was to develop and demonstrate a design methodology which makes use of network impedance assessment methods to provide robust harmonic integration of large shunt compensators into a transmission and HVDC systems. The design methodology has two aspects. The first part considers network modeling, evaluation of different models and simulation of harmonic impedance. In the second part, methods of analyzing and assessing the simulated harmonic impedance are developed. A detailed step-by-step approach was taken in the development of the design methodology. The methodology was documented as a guideline and accompanied by the development of an Excel tool that can be used to assess the simulated harmonic impedance. The Excel tool permits a systematic assessment of the simulated network impedance where shunt compensators are integrated into transmission systems. The tool also ensures that the design of transmission and HVDC ac shunt compensation is optimally robust in terms of harmonic resonances. The theoretical and computational review has been tested and demonstrated on the existing Eskom Transmission system through several case studies. The results have shown the merits of the design methodology. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2013.

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Thesis submitted in fulfilment of the requirements for the degree Master of Technology: Electrical Engineering in the Faculty of Engineering at the Cape Peninsula University of Technology 2014 / The IEC 61850 standard, “Communication networks and systems in substations” was promulgated to accommodate the need for a common communication platform within substations for devices from different vendors. The IEC 61850 standard proposes a substation automation architecture that is Ethernet-based, with a “station-bus” for protection devices within the substation and a “process bus” where raw data from the voltage and current transformers are published onto the data network using a device known as a Merging Unit. To date, most of the standardization efforts were focused at the station bus level where event-triggered messages are exchanged between the substation automation devices, commonly referred to as Intelligent Electronic Devices (IEDs). These messages are known as Generic Object Oriented Substation Event messages. Equipment from vendors to accommodate the “process bus” paradigm, however is still limited at present. The Centre for Substation Automation and Energy Management Systems was established within the Electrical Engineering Department at the Cape Peninsula University of Technology with one of its objectives being the development of equipment either for simulation or real-time purposes in compliance with the IEC 61850 standard. In order to fulfil this long-term objective of the Centre, an in-depth understanding of the IEC 61850 standard is required. This document details the efforts at acquiring the requisite knowledge base in support of the educational objectives of the Centre and the research project implements a simulation of a merging unit which is compliant with the functional behavior as stipulated by the standard. This limited functional implementation (i.e. non-real-time) of the merging unit, is achieved through the development of a virtualized data acquisition node capable of synthetic generation of waveforms, encoding of the data and publishing the data in a format compliant with the IEC 61850-9-2 sampled value message structure. This functional behavior of the virtual sensor node which was implemented has been validated against the behavior of a commercial device and the sampled value message structure is validated against the standard. The temporal behavior of the proposed device is commented upon. This research project forms the basis for future real-time implementation of a merging unit.

CNPq;CAPES / Neste trabalho é investigado o uso de codificação analógica conjunta fonte-canal em uma rede de sensores sem fio onde a fonte de informação é alimentada pelo destino por meio de transmissões de rádio frequência. É assumido que o destino não possui restrições energéticas. Logo após coletar energia do destino, a fonte transmite sua informação utilizando a energia recebida. As fases de transferência de energia e de transmissão de informação são multiplexadas no tempo. Como uma fração do intervalo de transmissão é utilizado para transferência de energia, as amostras da fonte são armazenadas e comprimidas utilizando tanto códigos analógicos paramétricos quanto não paramétricos com compressão de dimensão (ou largura de banda) N:K para transmiti-las utilizando a fração do intervalo restante. São analisados tanto esquemas com largura de banda casadas e não casadas entre fonte e canal. Além disso, é investigado também o parâmetro de compartilhamento de tempo ótimo o qual otimiza o desempenho da transmissão analógica. Por fim, é demonstrado que os esquemas analógicos propostos podem superar um sistema digital em termos de relação sinal-distorção. / We investigate the use of discrete-time analog joint source channel coding (JSCC) in a wireless sensor network (WSN) where the source of information is wirelessly powered by the destination, which does not have energy constraints. Right after harvesting energy from the destination, the source transmits its information using the energy harvested. Wireless energy transfer and information transmission are multiplexed via a time-switching protocol. As a fraction of the time slot is spent for energy transfer, the source samples are saved and compressed using either parametric or non-parametric N:K dimension compression analog JSCC to transmit the information in the remaining fraction of the time slot. We analyze both matched and unmatched source and channel bandwidths. Moreover, we investigate the time-sharing parameter that optimizes the analog system performance and show that the proposed analog scheme can outperform a fully digital system.

CNPq;CAPES / Neste trabalho é investigado o uso de codificação analógica conjunta fonte-canal em uma rede de sensores sem fio onde a fonte de informação é alimentada pelo destino por meio de transmissões de rádio frequência. É assumido que o destino não possui restrições energéticas. Logo após coletar energia do destino, a fonte transmite sua informação utilizando a energia recebida. As fases de transferência de energia e de transmissão de informação são multiplexadas no tempo. Como uma fração do intervalo de transmissão é utilizado para transferência de energia, as amostras da fonte são armazenadas e comprimidas utilizando tanto códigos analógicos paramétricos quanto não paramétricos com compressão de dimensão (ou largura de banda) N:K para transmiti-las utilizando a fração do intervalo restante. São analisados tanto esquemas com largura de banda casadas e não casadas entre fonte e canal. Além disso, é investigado também o parâmetro de compartilhamento de tempo ótimo o qual otimiza o desempenho da transmissão analógica. Por fim, é demonstrado que os esquemas analógicos propostos podem superar um sistema digital em termos de relação sinal-distorção. / We investigate the use of discrete-time analog joint source channel coding (JSCC) in a wireless sensor network (WSN) where the source of information is wirelessly powered by the destination, which does not have energy constraints. Right after harvesting energy from the destination, the source transmits its information using the energy harvested. Wireless energy transfer and information transmission are multiplexed via a time-switching protocol. As a fraction of the time slot is spent for energy transfer, the source samples are saved and compressed using either parametric or non-parametric N:K dimension compression analog JSCC to transmit the information in the remaining fraction of the time slot. We analyze both matched and unmatched source and channel bandwidths. Moreover, we investigate the time-sharing parameter that optimizes the analog system performance and show that the proposed analog scheme can outperform a fully digital system.

The power sector of a country is highly relevant for its competitiveness and social development. In Peru, this sector has passed through many changes before having its current configuration, which has negative and positive aspects.In the present versus, two different perspectives come face to face as the debate about key and current topics starts. The discussion is about questions such as the “oversupply” of power generation, the creation of additional charges to the power transmission  service, or the frontiers of the regulated market. / El sector eléctrico de un país es de suma importancia para su competitividad y desarrollo social. En el Perú, este sector ha pasado por varios cambios hasta tener su configuración actual, que tiene aspectos tanto positivos como negativos.En el presente versus, dos diferentes perspectivas se encuentran y se abre paso al debate acerca de temas clave y de actualidad, tales como: la “sobreoferta” de generación eléctrica, la creación de cargos adicionales a la transmisión, o los límites del mercado regulado.