Polymers are widely used as insulating materials in high voltage power apparatus because of their excellent electrical insulating properties and good thermomechanical behavior. However, under high electrical stress, polymeric materials can get deteriorated which can eventually lead to the failure of the insulation and thereby the power apparatus. Electrical treeing is one such phenomena whereby dendritic paths progressively grow from a region of high electrical stress and branch into conducting channels in a solid dielectric. The propagation of electrical trees is of particular interest for the power industry as it is one of the major causes of failure of high voltage insulation especially in high voltage cables, cast resin transformers as well as rotating machines. To improve the life time of the electrical insulation systems there is a need to improve the electrical treeing resistance of the insulating material for high voltage application. With the development of nanotechnology, polymer nanocomposites containing nano sized particles have drawn much attention as these materials are found to exhibit unique combinations of physical, mechanical and thermal properties that are advantageous as compared to the traditional polymers or their composites. Literature reveals that significant progress has been made with respect to the mechanical, optical, electronic and photonic properties of these functional materials. Some efforts have also been directed towards the study of dielectric/electrical insulation properties of these new types of materials. Considering the above facts, the present research work focuses on utilizing these new opportunities which have been opened up by the advent of nanocomposites to develop tree resistant insulating materials for high voltage power applications. Electrical treeing is a common failure mechanism in most of the polymeric insulation systems and hence electrical treeing studies have been carried out on two types of polymers (viz. polyethylene used in high voltage cable and epoxy used in rotating machines and resin cast transformers) along with three different types of nano-fillers, viz. Al2O3, SiO2 and MgO and with different filler loadings (0.1, 1, 3, 5 wt%). Furthermore, considering the fact that electrical treeing is a discharge phenomenon, the partial discharge characteristics during electrical tree growth in polymer nanocomposites was studied. As morphological changes in the polymer influence the electrical tree growth, the influence of nano-particle induced morphological changes on the electrical treeing has also been studied. Above all, an attempt has also been made to characterize and analyze the interaction dynamics at the interface regions in the polymer nanocomposite and the influence of these interface regions on the tree growth phenomena in polymer nanocomposites. A laboratory based nanocomposite processing method has been successfully designed and adopted to prepare the samples for treeing studies. Treeing experimental results show that there is a significant improvement in tree initiation time as well as tree inception voltage with nano-filler loading in polymer nanocomposites. It is observed that even with the addition of a small amount (0.1 and 1 % by weight) of nano-particles to epoxy results in the improvement of electrical treeing resistance as compared to the unfilled epoxy. In fact, different tree growth patterns were observed for the unfilled epoxy and epoxy nanocomposites. Surprisingly, even though there is not much improvement in tree inception time, a saturation tendency in tree growth with time was observed at higher filler loadings. To understand the influence of nano-particles on electrical treeing, the interaction dynamics in the epoxy nanocomposites were studied and it was shown that the nature of the bonding at the interface play an important role on the electrical tree growth in epoxy nanocomposites. The results of electrical treeing experiments in polyethylene nanocomposites obtained in this study also reveal some interesting findings. An improved performance of polyethylene against electrical treeing with the inclusion of nano-fillers is observed. It is observed that there is a significant improvement in the tree inception voltage even with low nano-filler loadings in polyethylene. Other interesting results such as change in tree growth pattern from branch to bush as well as slower tree growth with increase in filler loading were also observed. Another peculiar observation is that tree inception voltage increased with increase in filler loading upto a certain filler loadings (3 % by weight) and then decreased in its value at high filler loading. The morphology of polyethylene nanocomposites was studied and a good correlation between morphological changes and treeing results was observed. Effect of cross-linking on electrical treeing has also been studied and a better performance of cross-linking of nano-filled polyethylene samples as compared to the polyethylene samples without cross-linking was observed. The partial discharge (PD) activity during electrical tree growth was monitored and different PD characteristics for unfilled and nano-filled polyethylene samples were observed. Interestingly, a decrease in PD magnitude as well as the number of PD pulses with electrical tree growth in polyethylene nanocomposites was observed. It is known that PD activity depends on the tree channel conductivity, charge trapping and gas pressure inside the tree channel. The ingress of nano-particles into the tree channel influences the above known phenomena and affects the PD activity during electrical tree growth. The observed decrease in PD magnitude with increase in filler loading leads to the slow propagation of electrical trees in polyethylene nanocomposites. In summary, it can be concluded that polymer nanocomposites performed better against electrical treeing as compared to the unfilled and the conventional micron sized filled polymer composites. Even with low filler loading an improved electrical treeing resistance was observed in polymer nanocomposites. An optimum filler loading and a suitable filler to inhibit electrical treeing in the polymers studied are proposed. This work also establishes the fact that the characteristics of the interface region and the induced morphological changes have a strong influence on the electrical treeing behaviors of nanocomposites. These encouraging results showed that epoxy and polyethylene nanocomposites can be used as tree resistant insulating materials for high voltage applications. These results also contribute to widen the scope of applications of polymer nanocomposites in electrical power sector as well as development of multifunctional insulation systems.

Orientador: Jose Antonio Siqueira Dias / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação / Made available in DSpace on 2018-08-07T11:11:31Z (GMT). No. of bitstreams: 1 Leite_RogerioLara_D.pdf: 18262113 bytes, checksum: 8c49a719bdf98e92810c4c7275e7da78 (MD5) Previous issue date: 2006 / Resumo: Os sensores a fibra óptica são especialmente indicados para operarem em ambientes eletricamente ruidosos, uma vez que são imunes aos efeitos da interferência eletromagnética (EMI) encontrados nestes ambientes. Tal característica faz com que os sensores ópticos sejam altamente vantajosos para as aplicações nos sistemas de sensoreamento utilizados pelas empresas de energia elétrica. Este trabalho apresenta o desenvolvimento de um protótipo de baixo custo de um sensor óptico de alta tensão com alta confiabilidade, que pode ser usado para monitorar o estado ou limiares de tensão em uma rede elétrica. Uma técnica de detecção do sinal através do sensoreamento com grades de Bragg é apresentada, fabricada e avaliada. Os resultados mostram que a técnica de detecção empregada, onde a amplitude ac do sinal da luz refletido é medida em um fotodiodo, mostra-se adequada para a aplicação em sensores de alta tensão. As medidas realizadas em um protótipo de sensor de alta tensão com fibra óptica com grade de Bragg indicam que o esquema de detecção desenvolvido é promissor, e pode ser usado para medir outros sinais dinâmicos que respondam a um esforço de pequena amplitude aplicado à fibra óptica. O protótipo desenvolvido permitiu a detecção de tensões variando na faixa de 143 V -60kY. É também apresentada uma nova técnica para estabilizar termicamente grades de Bragg com a temperatura, utilizando o sinal uma fibra extra, casada com a fibra do sensor, que através de um circuito de realimentação atua no elemento aquecedor/resfriador do laser semicondutor(thenno electrical cooler), para fazer com que o comprimento de onda do laser siga as variações da sintonia da grade de Bragg sensora, causadas por variações da temperatura. Esta técnica inovadora poderá ser utilizada para a compensação térmica de outros tipos de sensores com grade de Bragg, permitindo a fabricação de sensores de baixo custo e grande simplicidade de implementação / Abstract: Fiber optics sensors are specially indicated to operate in noisy electrical environments because they are immune to the effects of electromagnetic interference (EM!) found in these environrnents. Such characteristic makes these sensors highly advantageous to the applications in the measurement systems used by electrical energy companies. This work presents the development of a prototype of a high-voltage and a low cost optical sensor which is used to monitor the state or voltage threshold with a high reliability. A technique for the detection of fiber Bragg grating sensors signals was developed, presented and tested. The experimental results showed that the developed detection technique, where the ac amplitude of the signal result from the light reflection is measured with a photodiode is adequate for high voltage sensing applications. The prototype of the high voltage fiber Bragg sensor was tested and the measured results indicate that the technique can be used to detect any other dynarnic measurand which induces a small strain amplitude when applied to the fiber Bragg grating. The developed prototype detected voltages in the range from 143 V to 60 kV. It is also presented a new technique for obtaining temperature independent fiber Bragg gratings, using a feedback circuit which uses the signal detected from a matched fiber and generates a signal which actuates on the thermo electrical cooler of the semiconductor laser, modifying the laser' s output wavelength, in orer to accurate track the Bragg wavelength shifts caused by temperature variations. This novel technique can be used for the fabrication of simple and low-cost temperature compensated fiber Bragg grating sensors / Doutorado / Eletrônica, Microeletrônica e Optoeletrônica / Doutor em Engenharia Elétrica

Malgré les récentes avancées technologiques, les combustions thermiques des véhicules génèrent toujours trop de gaz polluants et les systèmes purement catalytiques ne parviennent pas à les traiter efficacement pour toutes les phases de fonctionnement des moteurs. Les oxydes d’azote font partie des gaz polluants les plus préoccupants, pour lesquels il est urgent de trouver une solution. Ce travail est dédié à la mise en œuvre d’une de ces solutions par l’utilisation des plasmas non-thermiques. La maîtrise et la compréhension des décharges dans les gaz permettent de générer des plasmas non-thermiques, où seuls les électrons sont portés à haute température. Les traitements par plasmas non-thermiques ne provoquent pas d’échauffement significatif du gaz, mais produisent néanmoins des modifications moléculaires importantes. Sous l’influence de champs électriques intenses, et selon la composition initiale des gaz, les oxydes d’azote sont oxydés ou réduits. Afin de modifier favorablement la réactivité des gaz, différentes configurations géométriques de réacteurs ont été optimisées et réalisées. L’optimisation de chaque géométrie est basée sur des calculs en champ électrostatique, pour lesquels l’amplitude de la tension appliquée est inférieure à 20 kV. Certains réacteurs sont pourvus d’une barrière diélectrique, dont la disposition, les dimensions et la nature du matériau sont variables. Un banc expérimental spécifique a été réalisé pour évaluer les performances des réacteurs sur le traitement des oxydes d’azote. différentes sources de tension ont été testées. L’analyse des décharges s’appuie sur la mesure des tensions et des courants. Les expériences ont montré que pour une géométrie fil-cylindre, associée à une source de tension AC moyenne fréquence appropriée, la réduction des oxydes d’azote dans du diazote est proche de 80 %. / Despite recent technological advances, thermal combustion in vehicles still generates a large amount of polluting gases that pure catalytic systems are unable to treat efficiently during the various phases of motor function. Nitrogen oxides are among the more problematic of the polluting gases, and a solution for their removal is critical. This work is aimed at the implementation of a solution using non-thermal plasma. The control and understanding of electrical discharges in gas enables to generate non-thermal plasmas, where only the electrons are raised to a high temperature. A non-thermal plasma treatment does not significantly heat the gas, but it still triggers important molecular changes. Under the influence of intense electric fields and depending on the initial gas composition, nitrogen oxides are either oxidized or reduced. In order to increase the gas reactivity, different geometric configurations of the reactors have been optimized and implemented. The optimization of each configuration is based on calculations of the electrostatic field, for which the amplitude of applied voltage was kept lower than 20 kV. Some of the reactors were constructed with dielectric barriers with varying arrangements, sizes, and materials. To evaluate reactor treatment efficiency of nitrogen oxides, a specialized experimental bench was constructed. Different voltage sources were tested, and the discharge was analyzed via voltage and current measurements. The experiments showed that 80 % of the nitrogen oxides in nitrogen could be reduced usinga wire-cylinder configuration with a suitable intermediate frequency AC voltage source.

Le système de transport d’électricité doit évoluer pour satisfaire les besoins du marché de l’électricité et de l’insertion de la production renouvelable. Les systèmes de transport dits HVDC se développent. Les interfaces d’électroniques de puissance vont jouer un rôle majeur et doivent faire preuve d’une extrême fiabilité, d’une grande efficacité et rester économiquement abordables.La technologie MMC (Convertisseur Modulaire Multi-niveaux) connaît un essor par rapport à des technologies classiques, comme le convertisseur trois-niveaux. Sa topologie étant complexe, deux niveaux de contrôle peuvent être définis. Le premier niveau porte sur le contrôle des interrupteurs pour équilibrer les tensions des sous-modules. Le second niveau contrôle les courants, la puissance et l’énergie dans le système.Cette thèse est axée sur ce deuxième niveau de contrôle. Une approche hiérarchisée et formelle, basée sur l’inversion du modèle pour le contrôle de l’énergie du MMC est présentée. Pour ce contrôle, différentes méthodes ont été proposées et comparées. Cela implique de développer une modélisation, mettre en place un contrôle. Différents modèles et contrôles ont été développés.Le MMC est généralement intégré dans une liaison HVDC où deux stations AC/DC ont un contrôle différent. Un soin particulier doit être apporté à la station dédiée au contrôle de la tension. En effet, la gestion de l’énergie dans le MCC est un point critique pour la stabilité de la tension.Enfin, les différents types de contrôle évoqués ont été étudiés dans le cas d’une liaison HVDC. Il a été montré que les échanges entre le bus DC et les MMC jouent un rôle important pour la régulation de la tension du bus DC / In future, the capability of the electric power transmission continues to grow due to renewable energy production and the needs of electrical market. Consequently, many HVDC transmission systems are developed. Definitely the power electronic interfaces will play a key role to provide high reliability, good efficiency and cost effectiveness for this AC/DC conversion.Recently, the Modular Multilevel Converter (MMC) has taken the advantage over the more classical converter as three-level VSC. Since MMC topology is complex, two different control levels may be distinguished: the control of the switches mainly orientated on the balance of hundreds of voltage on the elementary submodules, the higher level control whose aim is to control the currents, power and energy in the system.This thesis is oriented mainly on the latter. It discusses a hierarchical and formal approach for the MMC to control the energy in all the storage elements. At first it is shown that an energy control is required mandatory. Secondly, it supposes to develop an energetic model which is inverted to design the energy control. Then different solutions of control have been developed and discussed.In the majority of applications, MMC is integrated in an HVDC point to point link where the two AC/DC substations have different roles. A specific attention has to be paid on the station which controls the voltage since the way to manage the energy in the MMC has a critical role in the DC voltage stability.Finally, all these types of control have been tested and discussed on an HVDC. It is shown that the exchange between the DC bus and the MMC placed on both sides play a key role in the DC bus voltage regulation.

Ce travail porte sur l’amélioration quantitative et qualitative du procédé de fabrication d’extraits de marc de raisin riches en composés phénoliques. Les effets de technologies alternatives de traitement de la biomasse végétale sur l’amélioration des rendements d’extraction ont été étudiés à l’échelle laboratoire. Leurs impacts sur la qualité biochimique des extraits obtenus ont été évalués via la caractérisation analytique des composés phénoliques.Une étude comparative de différentes technologies alternatives de pré-traitement en milieux aqueux (décharges électriques haute tension (DEHT), champs électriques pulsés (CEP) et ultrasons (US)), d’un marc de raisin issu d’un procédé de vinification en rouge, en amont de la diffusion, a permis d’approfondir la compréhension des phénomènes induits et de leurs effets sur l’amélioration de l’extractabilité des composés. Nous avons montré que le choix du procédé à mettre en oeuvre était relatif au type de composés phénoliques ciblés : la localisation tissulaire de ces composés est apparue comme un facteur-clé pour optimiser leur extraction. La technologie de pré-traitement par CEP, induisant un endommagement localisé des structures végétales, s’est avérée particulièrement intéressante pour extraire sélectivement les anthocyanes situés au niveau des couches de cellules supérieures de l’hypoderme de la pellicule de raisin. Nous avons, par la suite, montré que le pré-traitement par CEP, en milieu sec (sans ajout de solvant) et à intensité de champ électrique modérée, était plus efficace pour la récupération sélective des anthocyanes et moins énergivore qu’un traitement CEP de forte intensité d’une suspension aqueuse de marc. Pour ce faire, nous avons mis en place une nouvelle configuration de cellule qui nous a permis d’étudier la faisabilité d’un pré-traitement en milieu sec, sans ajout de liquide conducteur, et d’optimiser les paramètres opératoires (masse volumique, intensité du champ électrique, énergie spécifique) influençant la récupération subséquente, lors de la diffusion, des composés phénoliques. Afin d’intégrer notre démarche expérimentale dans une approche systémique de type « bioraffinerie », l’accent a été mis sur le traitement du marc réhydraté à posteriori de la diffusion. L’intensification du pressage de ce marc par chauffage ohmique (CO) permet d’améliorer les rendements globaux d’extraction tout en assurant un premier niveau de déshydratation de cette biomasse.Un bilan technico-économique montre que l’application successive des électro-technologies (pré-traitement par CEP en milieu sec et pressage assisté par CO à posteriori de la diffusion) permet une amélioration des rendements massiques d’extraction de l’ordre de 30 % comparativement au procédé classique. Ce gain matière compense l’augmentation du coût de production (+ 2.7 % comparativement au procédé classique) et résulte une diminution du coût de production de l’extrait (7.3 €/kg vs 9.4 €/kg pour le procédé classique). / This work aims at studying the effect of alternative technologies for the processing of winery byproducts on the improvement of extraction yields at laboratory scale. Their impacts on the biochemical quality of the extracts obtained from grape pomace were evaluated by the characterization of the extracted compounds. A comparative study on the effects of different alternative pre-treatment (pulsed electric field (PEF), high voltage electric discharges (HVED) and ultrasounds (US)) of aqueous suspensions of red grape pomace, prior to the extraction step, was realized with the specific objective of understanding the induced phenomena. The electroporation induced by PEF may allow the specific recovery of anthocyanins that are located in the upper cell layers of the hypodermis by facilitating the solvent penetration to particular skin tissues of grape. The location of targeted compounds with respect to tissue structures seems to be a key issue to optimize their extraction. As a consequence, we subsequently examined the feasibility of a PEF pre-treatment of relatively low humidity grape pomace for the enhancement of bioactive compounds extraction. We demonstrated that a relatively dry pomace (RH ≈ 55 %) can be effectively treated by PEF after optimal densification using a suitable configuration of the PEF cell. The PEF pre-treatment of a densified fermented grape pomace, at moderate electric field strengths, requires less output current and lower specific energy and is also more efficient for the selective recovery of anthocyanins than Hi-PEF pre-treatment of an aqueous suspension of grape pomace. We finally focused on the treatment of rehydrated grape pomace following the diffusion step. The enhancement of pressing of the grape pomace by ohmic heating allowed the recovery of two fractions: a solid fibrous residue partly dehydrated which could be further valorized as an agro-material or in feeding, and an extract, particularly rich in bioactive components.The technical-economic assessment shows that the successive application of electro-technologies (pre-treatment of grape pomace in dry environment by PEF followed by a pressing step assisted by ohmic heating) lead to an improvement of extraction yields of about 30 % compared to the conventional method. This mass improvement offset the increased production costs (+ 2.7 % compared to the conventional process) by reducing the total production costs of the extract (7.3 €/kg vs 9.4 €/kg for the conventional process).

In theoretical part of diploma thesis are written basic information about cost calculation, types and methods of cost calculation especially in building industry. Practical part identifies cost types in company MARTEL Slovakia and cost-distribution sheet for the most frequent company order - high voltage disconnector.

The beginning of this thesis contains an overview of properties of the insulators, and description of insulators that were used for in depth research of surface breakdown in vacuum. Furthermore, this work focuses on mechanisms of an electric breakdown initiation at the interface of the solid insulator and surrounding low pressure gas. Multiple methods for measurements of dielectric strength are examined. The experimental part describes the measurements performed in the vacuum chamber. The results of these measurements are then analysed. In conclusion, used insulators are compared and suggestions for further work are given.

ABSTRACT This thesis is concerned with a technical modification of design of the electrical power systems for Modřice and its surroundings. The thesis describes a basic theoretical distribution of the electricity network and the distribution network itself. Following chapters are devoted to the development and construction of the HV networks and to the methods and ways of calculating the steady operation of the network. These methods are then used in the computational programs that are presented in the next chapter of this paper. The aim of the practical part of the thesis is to first determine the current state of the network in the given location. Furthermore, several modifications are proposed according to the requirements for increasing the power consumption or connecting the new supply places. The proposed modifications are further assessed for the different operating conditions. The result is a network that is functional, operational and reliable. The whole analysis is carried out in the PAS DAISY Off-line V4 Bizon computing program.

This dissertation thesis describes a phenomenon called electroporation. It is about its theoretical aspects as well as about modeling of processes in the tissue during electroporation. Further, it describes the technical design of two developed unique experimental generators of DC and AC pulses for electroporation purposes. It also includes a description of experiments which were done using discussed generators.

In it´s first part, this presented master´s thesis focuses on the problematics of actions taking place in dielectric materials and phenomenons on the surface of real insulators placed in electric field. This research is followed by selection and rating of appropriate ceramic materials for the actual design of the metal – ceramic assembly. The greatest emphasis is given to design of the optimal configuration of the insulator and electrode, which is supported by simulations from the software that implements finite element method. Eventually, the high voltage tests of the assembly used for measuring leakage currents are performed.