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The author's aim is to investigate ZnO varistors with high voltage to 1000V/mm and good resistance to electrical degradation, which could be applied to the UHV transmission systems and reduce ZnO varistor element amounts in surge arresters. The conduction processes in ZnO varistors is clarified. By adjusting additive type and amounts in ZnO the electrical properties of ZnO varistors can be controlled. Based on this recipe, Y, Cr, Ni, B, Si oxides were added in this study. These oxides can be divided into two categories, the Y doping group and the Si doping group. / 博士(工学) / Doctor of Philosophy in Engineering / 同志社大学 / Doshisha University

Advancements in power semiconductor and power converter technology have enabled new low-voltage (LV) and medium-voltage (MV) direct current (DC) distribution systems for a variety of applications. Power electronics converters and DC circuit breakers (DCCBs) are the key components of a DC system and are hence the focus of this work. The combination of growing power density requirements and higher voltages can result in enhanced electric field (E-field) intensities, leaving the system vulnerable to partial discharges (PDs). The manifestation of such PD events gradually degrades the insulation system of the equipment, reducing its lifetime and ultimately leading to total insulation failure. Therefore, inception E-field based insulation design guidelines are developed to help achieve zero-PD operation of power electronics systems with considerations for internal as well as external (surface) E-field distribution. Additionally, surface E-field mitigation methods are experimentally investigated using representative PCB coupons to provide suitable solutions for low air pressure applications. Consequently, E-field management methods consisting of geometry-based techniques are proposed for PCB-based systems to mitigate E-field magnitudes in areas of the system that are prone to peak stresses (e.g. surface interconnections and triple junctions, conductor discontinuities, critical airgaps etc.). Successful design examples are provided including that of a 16 kV rated PCB-based DC bus and a 540 V, 100 kW aircraft generator rectifier unit operating at up to 50,000 ft cruising altitudes. DC circuit breaker (DCCB) technology, though crucial to ensure the safety of DC systems, is still in the early stages of development. As protection devices, their reliable operation is paramount and the selection and sizing of their components are not trivial. In this regard, comprehensive design guidelines are developed for the DC solid-state circuit breaker (SSCB) to ensure that its functional requirements can be met. System analyses and modeling are performed to understand the interactions between the various components, i.e. solid-state device, metal oxide varistor (MOV), and their impact on the breaker operation. A 2.5 kV, 400 A SSCB prototype is designed and verified with experimental results to validate the design approach. Traditional MOV based voltage clamping circuits (VCC) used in solid-state circuit breakers (SSCBs) impose a high interruption voltage on the main solid-state device. The voltage burden arises from the material properties of the MOV which fixes its clamping voltage at a value more than twice its maximum continuous dc voltage rating. A novel and reliable VCC termed as the electronic MOV (eMOV) is proposed to decouple the peak clamping voltage of the MOV from the nominal dc voltage of the system aiming to improve the voltage suppression index (V SI = Vpk/Vdc) of the VCC, thereby reducing the peak system voltage and allowing easier insulation design. By virtue of the proposed circuit, a lower voltage rated device can be used for the main switch enabling higher system efficiency and power density. In all, this work aims to address insulation system design for power electronics converters and systems, ultimately to eliminate PD under specified working voltage conditions for improved electrical safety and insulation lifetime. The implications of high-density integration, unsuitable ambient conditions and higher system voltages are considered to develop a suitable design and assessment methodology for practicing engineers. Techniques to mitigate/ manage E-Field inside and outside (surface) solid dielectric are proposed to attain the above goal. Additionally, design guidelines are formulated for DC SSCBs which are essential to the safety of DC distribution systems and an enhanced VCC is proposed for the same to limit its clamping voltage for easier insulation design. / Doctor of Philosophy / The recent advancements in power conversion technology have promoted the development and use of DC distribution networks for a variety of applications (e.g. electric ships, aircrafts, electric vehicle charging stations etc.). The insulation system of typical power electronics equipment consists of multiple solid insulating media (e.g. PCB dielectric, potting material, conformal coat etc.) separated by air gaps in the assembly. The combination of higher operating voltages, power density targets and unfavorable ambient conditions (e.g. low air pressure) can pose a risk to the insulation system of the equipment, if not addressed. The electric field (E-Field) stresses at certain vulnerable areas can exceed breakdown values of the corresponding media, initiating localized electrical discharge events also called as partial discharges (PD). Internal discharges generally occur in the vicinity of material defects, conductor discontinuities or sharp geometric features, while surface discharges may occur along exposed conductor metallizations on insulator surfaces (at the interface of multiple media) or critical air gaps in the assembly. PD events, while not posing any imminent threat, can degrade the surrounding area over time to reduce the operating life of the system and in some cases may cause catastrophic failures. Therefore, irrespective of location, such PD events must be eliminated to improve the overall system lifetime and reliability. Therefore, the main focus of this work is to develop insulation design guidelines and methodologies to achieve zero-PD operation of power converters and DC circuit breakers (DCCBs), both of which are key components of DC systems. A generalized design guideline is proposed to help with the insulation design of power electronics systems. Design techniques are developed to reduce E-field magnitude at critical areas to avoid over-designing the insulation system. Successful converter-level design examples are provided to validate the proposed approaches. DCCB technology is still in the early stages of development. As a protection device, its reliable operation is paramount and the selection and sizing of its components are not trivial. Therefore, in addition to the above insulation design methodology, comprehensive design guidelines are developed for the solid-state device and voltage clamping circuit (VCC) of the DC solid-state circuit breaker (SSCB), to ensure that its functional requirements can be met. Additionally, a novel VCC is proposed for the same to limit its fault interruption voltage for easier insulation design. Both SSCB and VCC prototypes are built and successfully demonstrated in a fault current breaking application. Overall, this dissertation provides a reference for the design and assessment of next generation power electronics converters and DC circuit breakers, to address, specifically, the challenges to their insulation systems.

[pt] Apesar de seus muitos benefícios, uma das poucas desvantagens da tecnologia do semicondutor é a vulnerabilidade dos dispositivos de estado sólido à temperatura, sobretensões e sobre correntes. Mesmo os pulsos de tensão de energia muito baixos, podem produzir interferências e danos, às vezes com conseqüências de grande envergadura. Assim, enquanto a eletrônica é utilizada em mais e mais aplicações, a temperatura, a proteção contra sobretensão e a supressão de transientes transformam-se em fatores de suma importância para o desenvolvimento de um projeto. Os varistores provaram ser excelentes dispositivos protetores por causa da sua flexibilidade da aplicação e elevada confiabilidade. Os varistores do óxido do zinco (ZnO) são dispositivos eletrônicos de última geração, desenvolvidos para promover a proteção de circuitos elétricos contra a sobretensão, causada pelas descargas elétricas atmosféricas, tensões induzidas e manobras elétricas, e ideal para limitar a corrente de pico, bem como para absorver energia. O objetivo deste trabalho é propor uma metodologia para avaliação metrológica de varistores de óxido de zinco de média tensão, visando garantir o atendimento dos requisitos metrológicos para a proteção de circuitos elétricos, eletrônicos e de telecomunicações contra a sobretensão e supressão de transientes elétricos. Propõe-se ainda determinar a incerteza de medição dos parâmetros temperatura, tensão, corrente e resistência ôhmica de amostras comerciais de varistores de óxido de zinco. / [en] Despite its many benefits, one of the few disadvantages of semiconductor technology is the vulnerability of solid state devices to undesired increase in temperature, voltage and current . Even low voltage pulses can produce interference and damages with several consequences. Thus, as electronics are used in more and more applications, temperature, protection against surge and transient suppression are becoming factors of decisive importance in projects. Varistors have proven to be excellent protective devices due to their flexibility in applications and heightened trustworthiness. The zinc oxide varistors (ZnO) are state of the art electronic devices of last generation, developed to promote the protection of electric circuits against overvoltage, caused by atmospheric electric discharges, induced voltages and electric maneuvers, and suited to limit peak current, as well as absorbing energy. The purpose of this work is to propose a methodology for experimental characterization of zinc oxide varistors of average voltage, with the purpose of guarantee the attendance of the metrological requirements for protection of electric, electronic and telecommunication circuits against transient surges and suppression of electric transients. Uncertainty of measurement of the parameters temperature, voltage, current and ohmic resistance on commercial samples of zinc oxide varistors are also determined.

Solution chemistry is a versatile and powerful tool in the synthesis of designed, complex nano-level high-tech materials. Normally, the technique is considered too expensive for large-scale production of complex multi-component ceramic materials. This thesis describes the expansion of the useful area of solution processing to multi-component bulk materials such as ZnO-based high-field varistors and WC–Co cutting tools, by developing novel techniques for solution-based coating of conventionally prepared metal and ceramic powders. The chemistry and microstructure development in the preparation of coatings, and the sintering of the coated powders to compacts, were studied in detail by SEM-EDS, TEM-EDS, XRD, IR-spectroscopy, dilatometry, TGA and DSC chemical analysis. ZnO powder with a ca 20 nm thick, homogeneous oxide coat of Bi–Sb–Ni–Co–Mn–Cr–Al oxide was prepared. After sintering to dense varistor bodies, much improved microstructures with much reduced ZnO-grain sizes were obtained. This shows that the oxides added as liquid sintering aid and grain-growth inhibitor become much more active when added homogeneously as a skin on the ZnO powder. After sintering of cobalt-coated WC, much improved micro-structures were obtained with a much more narrow WC grain-size distribution than that obtained from starting powders mixed by a conventional milling route. Coated powders also obviate the need for the extensive milling of WC and Co powders used in conventional mixing. The novel solution route was also applied to preparation of porous sponges and thin films on metal, glass and Al2O3 of sub 20 nm sized Co- or Ni-particles.

<p>Solution chemistry is a versatile and powerful tool in the synthesis of designed, complex nano-level high-tech materials. Normally, the technique is considered too expensive for large-scale production of complex multi-component ceramic materials. This thesis describes the expansion of the useful area of solution processing to multi-component bulk materials such as ZnO-based high-field varistors and WC–Co cutting tools, by developing novel techniques for solution-based coating of conventionally prepared metal and ceramic powders. The chemistry and microstructure development in the preparation of coatings, and the sintering of the coated powders to compacts, were studied in detail by SEM-EDS, TEM-EDS, XRD, IR-spectroscopy, dilatometry, TGA and DSC chemical analysis. </p><p>ZnO powder with a ca 20 nm thick, homogeneous oxide coat of Bi–Sb–Ni–Co–Mn–Cr–Al oxide was prepared. After sintering to dense varistor bodies, much improved microstructures with much reduced ZnO-grain sizes were obtained. This shows that the oxides added as liquid sintering aid and grain-growth inhibitor become much more active when added homogeneously as a skin on the ZnO powder.</p><p>After sintering of cobalt-coated WC, much improved micro-structures were obtained with a much more narrow WC grain-size distribution than that obtained from starting powders mixed by a conventional milling route. Coated powders also obviate the need for the extensive milling of WC and Co powders used in conventional mixing.</p><p>The novel solution route was also applied to preparation of porous sponges and thin films on metal, glass and Al₂O₃ of sub 20 nm sized Co- or Ni-particles. </p>

Orientador: Mario Cilense / Banca: Carlos de Oliveira Paiva Santos / Banca: Paulo Roberto Bueno / Banca: Edson Roberto Leite / Banca: Dulcina Maria Pinatti Ferreira de Souza / Resumo: Estudos preliminares foram realizados em cerâmicas com propriedades varistoras, à base, SnO2-TiO2-Co2O3, com adições de Nb2O5, Ta2O5, Cr2O3 e Al2O3, preparados por meio de misturas de óxidos em moinho de alta energia, sinterizados em forno tubular na temperatura de 1250ºC durante 90 min em atmosfera de oxigênio, argônio e ambiente. Foram caracterizados quanto à densidade e propriedades elétricas.Terminada essa etapa, o sistema escolhido foi aquele que melhor se adaptou ao propósito do estudo desse trabalho. O sistema escolhido, SnO2-0,75TiO2-0,1Co2O3-0,05Nb2O5 mol %, foi preparado nas mesmas condições que na fase preliminar, sinterizados em atmosfera ambiente, tratados termicamente a 900ºC durante 60 min em atmosfera de oxigênio, e a pressão reduzida (10- 2torr). Em seqüência, essas amostras foram caracterizadas quanto as suas propriedades elétricas (medida tensão-corrente, espectroscopia de impedância e microscopia de força eletrostática) e microestruturais (difração de raios x, microscopia eletrônica de varredura, analise de EDX, analise de EDS, microscopia eletrônica de transmissão e espectroscopia de fotoelétrons induzida por raios x). A medida da altura da barreira foi obtida por meio da técnica de microscopia de força eletrostática através de uma modelagem matemática. / Abstract: In the present thesis it was studied nonohmic electronic ceramics based on SnO2.TiO2.Co2O3 ternary systems doped with Nb2O5, Ta2O5, Cr2O3 and Al2O3. These systems were prepared using traditional ball milling oxide mixture process. The sintering was conducted using tubular furnace at 1250 ºC for 90 min in different atmospheres: oxygen, argon and ambient atmosphere. Structural, density and electrical properties were investigated in all of the systems. The system presenting superior electrical properties was chosen to be studied concerning relationship between microstructural features and electrical properties. Therefore, SnO2-0.75TiO2-0.1Co2O3-0.05Nb2O5 % mol composition was thermal treated at 900 ºC for 60 min at oxygen-rich and oxygen-poor (10-2torr) atmospheres. After this step, the system was characterized by using different electrical, structural and microstructural techniques (current-voltage, impedance spectroscopy and electronic force image, X-ray diffraction, scanning electronic microscopy (SEM) and energy dispersive x-ray (EDX), energy dispersive spectroscopy (EDS) and transmission electron microscopy (TEM). The potential barrier was mathematical modeled according to electrostatic force images. The mathematical treatment is based on a matrix systems applied to each potential difference existing in the sample. From the solution of the matrix system it is possible to obtain the barrier height as a function of the applied potential. / Doutor

Orientador: Leinig Antonio Perazolli / Resumo: Neste trabalho foi estudado cerâmicas densas a base de SnO2, utilizando técnicas de Difração de Raios X (DRX), Microscopia Eletrônica de Varredura (MEV) e Transmissão (MET), área de superfície pelo método B.E.T., Análise Térmica, Dilatometria e Caracterização Elétrica, com o objetivo de entender seu comportamento elétrico, para possível utilização como varistor. O primeiro passo foi estudar algumas características do SnO2 dopado com diferentes concentrações de ZnO, tais como densidade, tamanho de grão, limite de solução sólida, formação de precipitados e a concentração ideal de ZnO a ser adicionado ao SnO2 para produção de cerâmicas densas. Em seguida passou-se a estudar o sistema SnO2- ZnO-WO3, obtendo para o novo sistema os mesmos parâmetros estudados no sistema SnO2- ZnO, e também as posições dos dopantes na rede cristalina do SnO2 e as características elétricas do sistema SnO2-ZnO-WO3 para utilização como varistor. E por último pesquisou-se, dando-se ênfase aos estudos de caracterização elétrica, o sistema SnO2-ZnO-WO3 acrescido de novos dopantes, a fim de se obter um varistor de baixa tensão. Obteve-se varistores de média e alta tensão de boa qualidade, com α>50, Er≅1.300 a 19.000V/cm e If=0,08mA/cm2 e varistores de baixa tensão com pequeno comportamento varistor, apresentando α=4,6, Er≅400V/cm e If≅0,4mA/cm2. / Abstract: In this work it was studied dense ceramic of the SnO2 based, using techniques of XRay Diffraction (XRD), Scanning Electronic Microscopy (SEM) and Transmission (TEM), surface area for the B.E.T. method, Thermal Analysis, Dilatometry and Electric Characterization, with the objective of understanding your electric behavior, for possible use as varistor. The first step was to study some characteristics of SnO2 doped with different concentrations of ZnO, such as density, grain size, limit of solid solution, precipitate formation and the ideal concentration of ZnO to be added at the SnO2 to product dense ceramics. Soon after that we started the study the system SnO2-ZnO-WO3 obtaining for the new system the same parameters studied in the system SnO2-ZnO, and also the positions of the dopings in the crystalline net of SnO2 and the electric characteristics of the system SnO2- ZnO-WO3 for use as varistor. And the last thing it has researched, giving emphasis to the studies of electric characterization, the system SnO2-ZnO-WO3 added of new dopings, trying to obtain a low tension varistor. We obtained medium and high tension varistors of good quality, with α>50, Er≅1,300 to 19,000V/cm and If=0.08mA/cm2 and low tension varistors of bad quality, presenting α=4.6, Er≅400V/cm and If ≅0.4mA/cm2. / Mestre

Made available in DSpace on 2017-07-21T20:42:35Z (GMT). No. of bitstreams: 1 JulianeCiorcero.pdf: 6092625 bytes, checksum: d6ae5b000ef3bf54c409ce74be787173 (MD5) Previous issue date: 2011-12-19 / Conselho Nacional de Desenvolvimento Científico e Tecnológico / This work studied systematically the substitution of Nb2O5 by Sb2O3 in composition of a ternary varistor system and study of calcination of binary and multi-component systems and their relationship microstructure-electric property. In part I of the work, study of substitution of Nb2O5 by Sb2O3, the compositions were prepared by conventional ceramic processing and dried by "spray-dryer" Pellets were produced at 25 MPa and sintering was produced at 1350ºC/ 2h.Increasing the concentration of Sb2O3, the nonlinear behavior of ceramics was reduced, accompanied by the reduction of the breakdown electric field and increased leakage current. With increasing concentration of 0.05% Sb2O3 to 0.5% (mol%), the samples were more porous, suggesting that higher concentrations of Sb2O3 decreases the rate of sintering. This decrease was linked to the increased concentration of tin vacancies that leads to nondensifying processes. In part II, was studied the influence of calcination (700oC, 1000oC and 1200oC) of binary and multi-component systems. The compositions were prepared by the conventional method, with the addition of the calcination process. The samples were comformed at 75 MPa and sintered at 1300oC for systems calcined at 1200oC and 1300oC, and at 1350oC for systems calcined at 700oC and 1000oC. Some studied systems have showed cassiterite phase associated to the SnO phase. With the addition of dopants, there was an increase in density of the systems, and the increase in temperature of sintering also led to a slight increase in density. The addition of chromium to systems calcined at 700oC and 1000oC led to a decrease in the breakdown electric field, with the exception of the systems 99.5% +0.5% Sb2O3 + 0.5% Co3O4 e 99.5% +0.5% Sb2O3 + 0.5% Co3O4 (excess) + 0.05% Cr2O3 (excess), where there was a decrease of breakdown electric field with the addition of chromium, and this can be explained because of their densities. All samples calcined at 1200oC regardless of the composition, showed very similar microstructure, high porosity and small grain size. The sample that presented the best varistor behavior with the lower leakage current was the FCC25% (75% of varistor formulation, 99,4%SnO2. 0,5%Co3O4. 0,05%Nb2O5. 0,05%Cr2O3 and 25% of conductive formulation, 99,0%SnO2. 0,5%Co3O4. 0,5%Sb2O3). / Neste trabalho estudou-se sistematicamente a substituição do Nb2O5 por Sb2O3 na composição de um sistema varistor ternário e estudo da calcinação de sistemas binários e multicomponentes e sua relação microestruturapropriedade elétricas. Na Parte I do trabalho, estudo da substituição do Nb2O5 por Sb2O3, as composições foram preparadas via processamento cerâmico convencional e secadas via “spray-dryer”. A conformação foi realizada a 25 MPa e a sinterização foi realizada a 1350C por 2 horas. Com o aumento da concentração de Sb2O3 o comportamento não linear da cerâmica foi reduzido, acompanhado da redução do campo elétrico de ruptura e aumento da corrente de fuga. Com o aumenta da concentração de Sb2O3 de 0,05% para 0,5% em mol, as amostras apresentaram-se mais porosas, sugerindo que concentrações mais elevadas de Sb2O3 diminuem a taxa de sinterização. Esta diminuição foi associada ao aumento da concentração de vacâncias de estanho que conduz a processos não densificantes. Na parte II, estudou-se a influência da calcinação (700oC, 1000oC e 1200oC) de sistemas binários e multicomponentes. As composições foram preparadas pelo método convencional, com a adição do processo de calcinação. As amostras foram conformadas a 75 MPa e sinterizados a 1300oC para os sistemas calcinados a 1200OC e 1300OC e 1350OC por 2 horas para os sistemas calcinados a 700OC e 1000OC. Alguns sistemas estudados apresentaram a fase cassiterita associada a fase SnO. Com a adição de dopantes ocorreu um aumento na densidade dos sistemas e o aumento da temperatura de sinterização também levou a um leve aumento na densidade. A adição de cromo aos sistemas calcinados a 700OC e 1000OC levou a uma diminuição do campo elétrico de ruptura, com exceção dos sistemas, 9,5%+0,5%Sb2O3 + 0,5% Co3O4 e 99,5%+0,5%Sb2O3 + 0,5% Co3O4 (excesso) + 0,05% Cr2O3 (excesso), onde ocorreu a diminuição do campo elétrico de ruptura com a adição de cromo, podendo isto ser explicado através de suas densidades. Todas as amostras calcinadas a 1200oC, independentemente da composição, apresentaram microestrutura muito semelhantes, apresentaram alta porosidade e pequeno tamanho de grão. A amostra que apresentou o melhor comportamento varistor, com menor corrente de fuga foi a FCC25% (75% da formulação varistora, 99,4%SnO2.0,5%Co3O4. 0,05%Nb2O5.0,05%Cr2O3 e 25% da formulação condutora, 99,0%SnO2. 0,5%Co3O4. 0,5%Sb2O3).

In order to meet the high demand for power transmission capacity, some power companies have installed series capacitors on power transmission lines. This allows the impedance of the line to be lowered, thus yielding increased transmission capability. The series capacitor makes sense because it's simple and could be installed for 15 to 30% of the cost of installing a new line, and it can provide the benefits of increased system stability, reduced system losses, and better voltage regulation.1 Protective distance relays, which make use of impedance measurements in order to determine the presence and location of faults, are "fooled" by installed series capacitance on the line when the presence or absence of the capacitor in the fault circuit is not known a priori. This is because the capacitance cancels or compensates some of the inductance of the line and therefore the relay may perceive a fault to be in its first zone when the fault is actually in the second or third zone of protection. Similarly, first zone faults can be perceived to be reverse faults! Clearly this can cause some costly operating errors. The general approach of interest is a method leading to the determination of the values of series L and C of the line at the time of the fault. This is done by analyzing the synchronous and subsynchronous content of the V and I signals seperately which provides adequate information to compute the series L and C of the line. / Master of Science