Made available in DSpace on 2014-10-09T12:34:11Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:06:49Z (GMT). No. of bitstreams: 0 / Neste trabalho analisou-se de forma técnica e econômica, diferentes unidades de geração elétrica. São elas: célula a combustível movida a hidrogênio, geração eólica, geração solar, geração hídrica, grupo moto gerador à diesel. Utiliza-se do software HOMER para simular o funcionamento das unidades geradoras. Ainda discute-se o tema energético, levanta-se os parâmetros de entrada, analisa-se as variáveis de sensibilidade e discute-se os resultados obtidos. / Dissertação (Mestrado) / IPEN/D / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Recent decades have witnessed a significant increment in power contribution from wind generators. This increment in penetration requires power engineers to tackle multi-fold challenges concerning operational and stability aspects. There exists a significant attention among the researchers in analyzing the impact of wind generation on various system aspects. This thesis focuses on steady state voltage stability aspects with penetration of Variable speed wind generators. Traditionally, ancillary services are supplied by large conventional generators. However, with the huge penetration of wind generators as a result of the growing interest in satisfying energy requirements, and considering the benefits that they can bring along to the electrical system and to the environment, it appears reasonable to assume that ancillary services could also be provided by wind generators in an economical and efficient way. Certain types of wind generators can support reactive power for the Power Market. Fixed and Semi-Variable speed wind turbine generators were predominantly employed during the early installations of wind generators. These units require reactive power support from the grid and are usually equipped with capacitor banks to provide the necessary reactive power. Further, STATic synchronous COMpensator (STATCOM) and Static Var Compensator (SVC) with various configurations were proposed to enhance the system operations under normal and disturbed conditions. On the other hand, Variable speed wind turbine generators provide flexibility in control and hence are becoming increasingly popular. Popular among this class of wind turbine generating units are Doubly Fed Induction Generator(DFIG) and induction/synchronous Generator with Front End Converter(GFEC). Contrary to Fixed and Semi-Variable speed wind machines, Variable speed wind turbine generators are capable of providing reactive power to the grid. The converter and control schemes associated with these machines permits controlling the active and reactive power output to desired level. It is possible to control the reactive power output of these machines independently of the active power. Researchers in the past have investigated the impact of reactive power output of variable speed wind machines on system stability. In literature, approaches are proposed to utilize the flexibility in reactive power generation of DFIG to reduce system losses, improve reliability in static and dynamic system operation. Approaches in literature investigate the impact on voltage stability of system by considering the flexibility of reactive power output of wind machine in isolation. However, significant improvement in static voltage stability, voltage profile, system power losses etc. can be attained if the Reactive Power output of Variable Speed wind machines can be properly coordinated with other reactive power controllers. The prime objective of the thesis is to propose algorithms to coordinate the reactive power output of Variable Speed Wind Generators with other reactive power controllers for Enhancement in voltage stability margin, system losses and voltage profiles.

Submitted in fulfilment of the requirements for M.Tech.: Electrical Engineering, Durban University of Technology, 2017. / Industrial plants are excellent sources of waste heat and provide many opportunities for energy harvesting using thermo-electric principles. A thermoelectric generator (TEG) is utilized in this study for harvesting expended heat from various sources. The main challenge associated with this type of technology lies in the creation of a sufficient thermal gradient between the hot side and the cold side of the TEG device. This is necessary for the module to generate an appreciable quantity of electrical energy. The performance of the TEG generator is tested using different configurations, different heat sources and different cooling methods. Heat sources included electrically driven devices, gas, biomass and gel fuel. Expended heat from different sites within an industrial environment was also chosen for operating the TEG device. The power produced by the generator is sufficient to operate low power LED lights, a DC radio receiver and a cellular phone charger. / M

This thesis investigates the phenomenon of subsynchronous resonance (SSR) in meshed series compensated AC/DC systems in the presence of operational uncertainties. The main contribution of this research is the novel application of risk assessment methods to SSR studies. In terms of network topology, future electric power transmission networks alongside the current power networks are expected to be meshed, and consequently, exposed to relative low risk of subsynchronous resonance. However, power systems are increasingly operated closer to stability limits in order to enhance efficiency and economics of their use. These stressed operating conditions may contribute to the deterioration in the system reliability. Uncertainty associated with the loads will also further diversify in the future due to new type of devices connected to the network whilst the integration of stochastic renewable generation sources will add another layer of uncertainty to system operation. There is a growing necessity to explore the challenges created by the increased uncertainty in generation and loads, and quantify risk to keep a balance between avoiding potentially catastrophic systems failures and mitigating for extremely rare event. This research work introduces risk assessment in subsynchronous resonance studies. Two indices are developed to quantify the severity of dynamic instability and transient torque amplification. Using these indices generators in the network can be ranked based on potential exposure to SSR. Following the development of indices, a methodology is proposed to evaluate the risk of SSR. The developed methodology takes into account the severity of SSR problem and probabilities of different contingencies and different operating conditions of a turbine generator. A robust investigation, into the effect of uncertainties on both aspects of SSR with symmetrical and asymmetrical compensation schemes, is also performed. The results of the analysis reveal that a critically compensated system in normal meshed network configuration may become dynamically unstable with as low as ±5% uncertainty in mechanical parameters. The critical compensation level with asymmetrical compensation in normal network configuration and each contingency becomes higher. It is also shown that the risk level assessed with the developed methodology does not change under the influence of ±5% uncertainties in the mechanical parameters. After establishing, that risk, based approach provides a better picture of all credible scenarios and risk of SSR in compensated power network, a methodology based on risk evaluation of SSR for selecting an optimal combination of TCSCs and fixed series capacitors for compensation of transmission lines is presented. This proposed methodology maximizes the use of fixed capacitors whilst maintaining the risk of SSR within an acceptable level in all credible contingencies and operating conditions.

Ce travail a pour objectif d'évaluer l'impact de la nanostructuration de résines d'imprégnation, destinées aux isolations statoriques d'alternateur de puissance, sur leurs propriétés électriques et thermiques. La première étape concerne l'étude de résines d'imprégnation aux propriétés physiques supérieures à celles des résines actuellement utilisées. La seconde étape concerne la détermination des caractéristiques de prototypes industriels développés par les sociétés Von Roll et Alstom ; ces prototypes sont composés d'un substrat « ruban » (composé de papier micacé et de tissu de verre) imprégné d'une résine innovante. Les améliorations apportées par les modifications des résines et des rubans permettent d'obtenir, dans le meilleur des cas, des augmentations respectives pouvant aller jusqu'à 14 % pour la rigidité diélectrique, 30 % pour la diffusivité thermique et 100 % pour l'endurance en tension. Une diminution de 33% des niveaux de charges d'espace accumulées est aussi observable. Les résultats obtenus lors de ce travail de thèse montrent qu'il est possible, dans certains cas, d'améliorer les propriétés électriques et/ou thermiques des isolations en modifiant les résines de référence par l'ajout de particules submicroniques de nitrure de bore (BN) et/ou de nanoparticules de dioxyde de silicium (SiO2). Cependant, il est également montré que ces propriétés peuvent être fortement influencées par le processus de fabrication, notamment par les paramètres de polymérisation. / This work aims to access the impact of nanostructuring over the impregnation resin, developed for the electrical insulation of alternator stator bars, on their electrical and thermal properties. The first step of this study concerns the analysis of impregnation resins with improved physical properties with respect to the usual resins. The second part concerns the characterization of prototypes which are manufactured by Alstom and Von Roll companies; these prototypes are composed by a tape (mica paper and glass fabric) impregnated with the innovative resin.In the best case, the modifications of the resins and the prototypes led to respective improvements up to 14 % for the dielectric strength, 30 % for the thermal diffusivity and 100 % for the voltage endurance. A decrease up to 33 % of the space charge levels can be also observed.The results obtained show that it is possible, in some cases, to improve the electrical and the thermal properties of the insulation by modifying the impregnation resin and the prototypes, with the addition of boron nitride (BN) submicron particles and/or silicon dioxide (SiO2) nanoparticles. However, it is shown that these properties can be highly influenced by the manufacture process of the resin and the prototypes, in particular by the curing parameters.

Les crises énergétiques et environnementales nous obligent à chercher les sources d’énergies renouvelables, qui contribuent à la fois à réduire l’effet de serre et la consommation des sources traditionnelles d’énergie fossile. Récemment, un nouveau système, le nano-générateur triboélectrique (TENG), se convertit l’énergie mécanique en énergie électrique en combinant l’effet de la triboélectronique et de l’induction électrostatique. TENG montre comme un outil alternatif et prometteur pour la récupération des énergie s renouvelables. Pour réaliser des matériaux plus performants, la plupart des recherches s’appuie sur le choix des différents types des céramiques ou charges conductrices, de taux de charge et de nouvelle structure, l’effet de l’interface entre charge, ainsi que la taille des charges, matrice a été très peu étudié. Donc, l’objectif de cette thèse consiste à étudier les effets de taille des charges, de l’interface entre charge-matrice et de la polarisation sur les performances électriques du TENG et les nano-générateurs du type piézo/tribohybride (P-TENG). Tout d’abord, un TENG fonctionnant sous la mode de contact-séparation avec la motion de l’accélération/décélération a été utilisé dans notre expérimentation et les équations progressives du type du second ordre polynomial ont été choisi pour l’ajustement des courbes. Différents paramètres cinétiques comme distance entre deux électrodes, fréquence de déplacement, pression de contact et temp du repos du TENG basés sur les conditions expérimentales ont été étudiés dans le chapitre 2 afin de comprendre leur contributions sur les performances des sorties électriques. Deuxièmement, deux différentes tailles (BT-70, BT-500) des nanoparticules de BaTiO3 sont considérées et utilisées pour préparer des composites di électriques BaTiO3/PDMS et BaTiO3-MWCNT/PDMS dans le chapitre 3. Les propriétés di électriques de tous ces composites ont été caractérisées et le déplacement électrique entre les particules et le polymère a été analysé théoriquement. En plus, l’effet synergique de MWCNT, de nitrure de bore (BN) et de noir de carbone (CB) avec BaTiO3 dans BaTiO3-70-MWCNT (CB, BN) / PDMS ont été comparés. Tous ces films composites fabriqués précédemment sont ensuite utilisés dans l’assemblage des dispositifs TENG dans le chapitre 4. Les performances électriques ont été mesurées pour étudier l’influence de l’interface charge-matrice et l’effet synergique des particules MWCNT (CB, BN) pour les dispositifs TENG. Les résultats de la différence potentielle surfacique induite par les effets synergiques des BaTiO3/MWCNT ont été confirmé avec les simulations COMSOL Multiphysics. En outre, dans le chapitre 5 les films composites contenant des particules de BaTiO3 sont polarisés pour étudier les effets piézoélectriques et triboélectriques couplés pour P-TENG. Les effets des différents paramètres de polarisation, tels que la direction de polarisation, la température, le ratio massique du BaTiO3, le champ électrique et la taille des BaTiO3 sur les performances de P-TENG ont été discutées. Enfin, les conclusions générales sont présentées et certains ou quelques perspectives sont proposées pour le futur. / The increasing energy crisis and environmental pollution stimulate the development of renewable energies, which contribute to reducing the greenhouse effect and the consumption of traditional fossil fuels. As a new type of renewable energy harvesting system, triboelectric nanogenerator (TENG) converts mechanical energy to electrical energy by coupling the effect of triboelectrification and electrostatic induction. TENG has been proved to be an alternative and promising approach to harvest renewable energy in recent years. For the dielectric material candidates, more attention has been paid to choosing different types of ceramic or conductive fillers, filler loading and surface structure design, rather than considering the filler-matrix interface effect. Thus, it is desired to clarify the effect of filler size and fillermatrix interface on the performance of compositebased TENGs. This work aims to research the influence of filler size, filler-matrix interface, and polarization on the output performance of TENG and piezo/tribo-hybrid nanogenerator (P-TENG). Firstly, the contact-separation mode TENG with acceleration/deceleration motion is utilized in our experiments. The piecewise second-order polynomial fitting is chosen for the motion process curve fitting. Various kinematic parameters including gap distance, motion frequency, contact pressure, and pause time of TENG are studied theoretically based on the experiment conditions in chapter 2, to understand their contributions to the electrical output performance. Secondly, in chapter 3, BaTiO3 nanoparticles with two different sizes (BT-70, BT-500) are considered and utilized to prepare BaTiO3/PDMS and BaTiO3-MWCNT/PDMS dielectric composites. The dielectric properties of all composites are characterized, and the electric displacement between particle and polymer are theoretically analyzed. Moreover, the synergistic effect of MWCNT, boron nitride (BN) and carbon black (CB) with BaTiO3 in BaTiO3-70-MWCNT(CB, BN)/PDMS are compared. Then, all composite films fabricated were further utilized to assemble TENG devices in chapter 4. The output voltage, current, and charges densities of TENGs are evaluated to investigate the influence of fillermatrix interface and synergistic effect of MWCNT (CB, BN) particles on the output performance of TENG devices. COMSOL Multiphysics simulation are performed to further confirm the surface potential difference introduced by the synergistic effects of BaTiO3/MWCNTs. Furthermore, the composite films with BaTiO3 particles are polarized to further explore the interaction of piezoelectric and triboelectric effects for P-TENG in chapter 5. Influences of different polarization parameters, such as polarization direction, poling temperature, BaTiO3 mass ratio, poling electric field and BaTiO3 sizes, on the output performance of the PTENG have been discussed. Finally, general conclusions are presented and perspectives are proposed for the future work.

Wind power generation has gained a large share in the renewable energy market over the past few years. This study investigates the impact of large scale penetration of permanent magnet synchronous generator (PMSG) based wind turbines on power quality of the grid. PMSGs are attractive due to the absence of a gearbox in the drive-train, which results in lower maintenance costs and higher reliability. Moreover, the advancements in power electronics have facilitated PMSGs to generate optimal power at varying wind speed conditions. This is achieved through the use of maximum power point tracking algorithms. The drawbacks of PMSG-based wind energy systems are that they inject harmonics into the network and cause flicker as well as other power quality issues. Despite these disadvantages, the grid code requires that PMSGs stay connected to the grid even under grid disturbances. This is because the reactive power control capability of PMSG-based wind energy systems can actually assist with voltage support. It will be shown in this study that disconnecting large scale PMSGs based wind turbines during grid disturbances has a detrimental effect on transient stability of the grid. This study will show that PMSG-based wind energy systems improve transient stability and assist in voltage support through reactive power control. Moreover, the impacts of large scale PMSG based wind turbines on power quality of the grid can be reduced by various means, which are also addressed in the study.

The proposed hybrid system generates AC power by combining solar and wind energy converted by a doubly-fed induction generator (DFIG). The DFIG, driven by a wind turbine, needs rotor excitation so the stator can supply a load or the grid. In a variable-speed wind energy system, the stator voltage and its frequency vary with wind speed, and in order to keep them constant, variable-voltage and variable-frequency rotor excitation is to be provided. A power conversion unit supplies the rotor, drawing power either from AC mains or from a PV panel depending on their availability. It consists of a multilevel inverter which gives lower harmonic distortion in the stator voltage. Maximum power point tracking techniques have been implemented for both wind and solar power. The complete hybrid renewable energy system is implemented in a PSIM-Simulink interface and the wind energy conversion portion is realized in hardware using dSPACE controller board.

Skakeling met diffusie-transistors by höe kollektorspannings word ontleed. Die gebied waar vermenigvuldiging verkry word en skakelsnelheid aansienlik verhoog word, is ondersoek met behulp van 'n relaksasie-ossillator. Lawineskakeling soos veral benut in pulsgenerators, is hier ter sake. Met behulp van 'n ladingsmodel is dit moontlik om uitdrukkings vir stygtyd, piekstroom en daaltyd in terme van transistorparameters te kry. Hierdie waardes is getoets met 2N414-transistors. Die invloed van eksterne komponente en toevoer word beskou. ENGLISH : Switching with transistors (diffusion flow type) in the high voltage region is analysed. The high Switching speed in this multiplication region is investigated by means of a relaxation oscillator. Avalanche mode switching as is relevant here, is mostly used in pulse generators. Expressions for rise time, peak current and fall time are obtained by means of a charge control model in terms of transistor parameters. 2N414 transistors were used to verify the theory experimentally. The influence of external components and supplies are also considered. / Dissertation (MEng)--University of Pretoria, 1969. / Electrical, Electronic and Computer Engineering / unrestricted

Thesis: B.S., Massachusetts Institute of Technology, Department of Mechanical Engineering, 1980 / Includes bibliographical references. / by Christopher P. Hamkins. / B.S. / B.S. Massachusetts Institute of Technology, Department of Mechanical Engineering