Orientador: Walmir de Freitas Filho / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação / Made available in DSpace on 2018-08-16T21:04:55Z (GMT). No. of bitstreams: 1 Ricciardi_TiagoRodarte_M.pdf: 3291776 bytes, checksum: c647c3c5eaa394835294087b10e89863 (MD5) Previous issue date: 2010 / Resumo: O uso de geradores conectados via inversores em redes de distribuição de energia elétrica tem aumentado consideravelmente nos últimos anos em razão dos avanços obtidos nas tecnologias de células a combustível e fotovoltaicas bem como de microturbinas e turbinas eólicas. Nesse contexto, a utilização de sistemas de proteção antiilhamento no ponto de conexão do gerador com a rede elétrica é uma das exigências previstas nos principais guias técnicos empregados pelas concessionárias. Ilhamento ocorre quando uma parte da rede de distribuição torna-se eletricamente isolada da fonte de energia principal (subestação), mas continua a ser energizada por geradores distribuídos conectados no subsistema isolado. No caso particular dos geradores conectados via inversores, os principais dispositivos utilizados comercialmente para fornecer proteção antiilhamento são baseados no conceito de realimentação positiva, cuja idéia básica é empregar um dos parâmetros que definem a tensão terminal do gerador como sinal de realimentação positiva no seu sistema controle. Caso o gerador esteja conectado ao sistema de distribuição, a realimentação positiva não consegue, a priori, desestabilizar o gerador. Por outro lado, caso o gerador torne-se ilhado, a realimentação positiva fará com que o gerador se torne instável e, por conseguinte, a situação de ilhamento pode ser rapidamente detectada por relés de sub/sobre tensão e/ou sub/sob freqüência. Visto que tal esquema de proteção esforça-se para desestabilizar o gerador independentemente da ocorrência ou não de ilhamentos, é fundamental desenvolver ferramentas para analisar a estabilidade de redes com múltiplos geradores equipados com proteção antiilhamento via realimentação positiva. O objetivo desta dissertação de mestrado foi desenvolver uma série de modelos linearizados no espaço de estados para representar os principais dispositivos de proteção antiilhamento existentes comercialmente a fim de investigar a estabilidade frente a pequenas perturbações de sistemas de distribuição de energia elétrica com múltiplos geradores conectados via inversores utilizando-se análise modal / Abstract: The usage of inverter-based generators connected directly to electric Power distribution systems has considerably increased in recent years due to the technological advances of fuel and photovoltaic cells as well as microturbines and wind turbines. In this context, the usage of anti-islanding protection devices at the interconnection point is required by the main technical guides utilized by the utilities. Islanding occurs when a portion of the distribution system becomes electrically isolated from the remainder of the power system, yet continues to be energized by distributed generators. In the case of inverter-based generators, the main devices commercially employed to supply anti-islanding protection are based on the positive feedback concept. These methods use the deviations of voltage frequency and/or magnitude from normal values as positive feedback signals into the control system to influence the operation of inverterbased distributed generators. If the generator is connected to a strong utility system, in priori, the destabilizing force of the positive feedback has a negligible impact and the generator can operate without difficulties. On the other hand, when the generator is islanded, the positive feedback can destabilize the generator easily. Such distinctively different generator behaviors facilitate the detection of islanding conditions by using under/over voltage and frequency relays. Since the positive feedback scheme is a destabilizing force, the impact of this scheme on the stability of system with multiples inverter-based generators is of concern. If the positive feedback gain is too high, the generator may become unstable even if it is connected to the main supply system. Thus, the objective of this master thesis is to develop several small-signal models to investigate the stability of distribution network with multiple inverter-based generators with positive feedback anti-islanding protection by using modal analysis / Mestrado / Energia Eletrica / Mestre em Engenharia Elétrica

Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico / A espÃcie Aspergillus niger AN 400 foi inoculada em reatores em batelada com o objetivo de remover corante vermelho do congo de meio sintÃtico e estudar a eficiÃncia do tratamento na presenÃa e ausÃncia de glicose e o efeito da imobilizaÃÃo da biomassa sobre a otimizaÃÃo do processo. Foram utilizados 84 reatores, confeccionados em vidro e vedados com tampa rosqueÃvel, e com volume Ãtil de 1,5 L, sendo o ar fornecido por mini-compressores de ar. O experimento abrangeu perÃodo de 25 dias e os reatores foram agrupados de acordo com sua respectiva funÃÃo em: 14 reatores de controle sem meio suporte; 14 reatores de controle com meio suporte; 14 reatores com biomassa fÃngica dispersa; 14 reatores com biomassa fÃngica dispersa e adiÃÃo de 1 g/L de glicose; 14 reatores com biomassa imobilizada e 14 reatores com biomassa imobilizada e adiÃÃo de 1 g/L de glicose. Os resultados obtidos mostraram que a maior eficiÃncia de remoÃÃo do corante ocorreu nos reatores contendo biomassa imobilizada, com meio com glicose (87%) e meio sem glicose (85%). A glicose, na concentraÃÃo utilizada, nÃo influenciou na eficiÃncia do processo. A remoÃÃo de matÃria orgÃnica, em termos de DQO, nÃo acompanhou a remoÃÃo do corante, o que foi atribuÃdo à provÃvel presenÃa de subprodutos da degradaÃÃo do corante e compostos excretados no meio pelos microrganismos. A imobilizaÃÃo da biomassa nas espumas de poliuretano foi determinante para a eficiÃncia do processo, uma vez que os fungos estavam estabelecidos na forma de biofilme, representando um mecanismo contra o efeito tÃxico do poluente. / The species Aspergillus niger AN 400 has been inoculated in batch in order to remove Congo Red dye from the synthetic environment and study the treatment efficiency in the presence and absence of glucose and the biomass immobilization effect on the process optimization. It has been applied 84 reactors, produced and held in a screw top container of glass, which had a useful capacity of 1,5 L, whilst the air was supplied by small compressors. The experiment lasted a period of 25 days and the reactors without support medium; 14 control reactors with dispersed fungal biomass on which was added glucose (1 g/L); 14 reactors with immobilized fungal biomass and 14 reactors with immobilized fungal biomass on which was added glucose (1 g/L). The results obtained demonstrated that the greatest efficiency in removing the dye occurred in the reactors containing immobilized biomass in a environment with glucose concentration (87%) or not (85%). The glucose considering the utilized concentration has not performed any influence on the process efficiency. The organic matter removal which was assigned to the likely presence of by products originated by the dye and compounds expelled in the environment by microorganisms. The immobilization of the biomass in the polyurethane foams was determinant to the process efficiency as fungus was in a biofilm shape, representing a mechanism against the toxic effect of the pollutant.

O interesse em escoamento bifásico líquido-líquido aumentou recentemente, em especial devido às grandes perdas de energia envolvidas no transporte de petróleo, onde comumente uma mistura bifásica óleo-água é deslocada ao longo de grandes distancias. Embora este tipo de escoamento seja comum na indústria, não existem tantos trabalhos na literatura quanto os relacionados ao escoamento gás-líquido. Alguns estudos sobre escoamentos óleo-água reportam uma redução de atrito em dispersões e emulsões em regime turbulento sem adição de qualquer tipo de substancia química, mas a física por trás do fenômeno ainda não é bem compreendida. Neste trabalho, foi estudado o padrão de escoamento disperso óleo-água em tubulação horizontal, visando a obtenção de novos dados experimentais e um melhor entendimento do fenômeno de redução de atrito. Uma série de parâmetros considerados importantes para a caracterização do escoamento foi investigada: queda de pressão, fração volumétrica e sub-padrões de escoamento disperso. Apresentam-se dados de distribuição das fases e fração volumétrica in situ, obtidos através de um moderno sensor intrusivo, do tipo wire-mesh, baseado em medidas de capacitância (permissividade). Câmera de alta velocidade e técnica das válvulas de fechamento rápido foram utilizadas para validar os sinais do sensor. Um modelo prospectivo simplificado foi desenvolvido como uma tentativa de explicar a ocorrência do fenômeno de redução de atrito no padrão disperso óleo-água estudado. O modelo sugere que a presença de uma fina película de água rente a parede hidrofílica/oleofóbica do tubo poderia explicar a diminuição no gradiente de pressão bifásico observada. / The interest in two-phase liquid-liquid flow has increased recently mainly due to the petroleum industry where oil and water are often produced and transported together for long distances and the significant frictional pressure gradient involved. Liquid-liquid flows are present in a wide range of industrial processes; however, they have not been studied as intensively as gas-liquid flows. Drag reduction phenomenon in oil-water flows without the addition of any drag reduction agent has been detected in previous works, but the physics behind the phenomenon is yet not well understood. The aim of the research was to study the dispersed oil-water flow pattern in a horizontal pipe in order to better understand the phenomenon and the obtaining of new experimental data of oil-water dispersed flows. Important issues related to oil-water pipe flow were investigated: pressure drop, volume fraction and flow patterns. Phase distribution and holdup data were obtained by a new wire-mesh sensor based on capacitance (permittivity) measurements. A high-speed video camera and the Quick-Closing-Valves technique were used to compare and validate the signals of the wire-mesh sensor. A simplified mathematical model was proposed to explain the drag reduction phenomenon in the oil-water dispersed flow studied. The model suggests that the presence of a thin water film between the homogenously dispersed flow and the pipe wall could explain the observed decreases of the two-phase pressure gradient.

Submitted by Renata Lopes (renatasil82@gmail.com) on 2017-04-19T19:08:59Z No. of bitstreams: 1 filipecaixeiromattos.pdf: 2641141 bytes, checksum: 014bbdead0d71ad1d9852cb7403b3439 (MD5) / Approved for entry into archive by Adriana Oliveira (adriana.oliveira@ufjf.edu.br) on 2017-04-20T12:46:42Z (GMT) No. of bitstreams: 1 filipecaixeiromattos.pdf: 2641141 bytes, checksum: 014bbdead0d71ad1d9852cb7403b3439 (MD5) / Made available in DSpace on 2017-04-20T12:46:42Z (GMT). No. of bitstreams: 1 filipecaixeiromattos.pdf: 2641141 bytes, checksum: 014bbdead0d71ad1d9852cb7403b3439 (MD5) Previous issue date: 2011-09-02 / Esta dissertação apresenta uma contribuição ao estudo de um inversor de tensão monofásico (VSI – Voltage Source Inverter), com saída em corrente, aplicado ao processamento de energia em sistemas solares fotovoltaicos (PV) monofásicos conectados à rede elétrica de distribuição. Através do controle por corrente média, é possível em um único estágio de processamento de energia rastrear o ponto de máxima potência do arranjo fotovoltaico e injetar na rede elétrica uma corrente com baixa distorção harmônica total (THD) e em fase com a tensão da rede CA. Para implementação do controle do sistema é utilizado o circuito integrado UC3854, da Texas Instruments, componente analógico de baixo custo e com funções típicas de correção de fator de potência de fontes de alimentação. Equações de análise e projeto, resultados de simulação e informações experimentais, obtidas de um protótipo de 720W, são incluídos neste material. / This dissertation presents a contribution to the study of a single-phase voltage inverter (VSI – Voltage Source Inverter), with current output, applied to the processing of photovoltaic (PV) solar power connected to single-phase electric distribution network. By controlling the average current, it is possible, in a single stage of power processing, to track the maximum power point of PV array and inject into the grid a current with low total harmonic distortion (THD) and in phase with the AC mains voltage. To implement the control system it is used a low cost Texas Instruments' analog integrated circuit UC3854, which includes a power factor correction typical function. Equations concerning analysis and design steps, simulation results and experimental data obtained from a 720W prototype are included in this document.

Global Software Development (GSD) is an emerging trend in today's software world in which teams are geographically dispersed, either in close proximity or globally. GSD provides certain advantages to development companies like low development cost, access to cheap and skilled labour etc. This type of development is noted as a more risky and challenging as compared to projects developed with teams under same roof. Inherently the nature of GSD projects are cooperative in which many software developers work on a common project, share information and coordinate activities. Coordination is a fundamental part of software development. GSD comprises different types of development systems i.e. insourcing, outsourcing, nearshoring, or farshoring, whatever the types of development systems selected by a company there exist the challenges to coordination. Therefore the knowledge of potential challenges, associated threats to coordination and practices to mitigate them plays a vital role for running a successful global project.

Dans ce travail, des écoulements liquide-liquide dispersés homogènes (c'est-à-dire sans gradient de concentration) ont été étudiés dans une conduite horizontale de 7.5m de long et de 50mm de diamètre interne. Les expériences ont été réalisées dans une large gamme de paramètres opératoires (vitesses de mélange comprises entre 0.28 et 1.2m/s et concentration volumique en phase dispersée, f, de 0.08 à 0.7). Le facteur de frottement de ces écoulements a été mesuré et modélisé en régime turbulent, intermédiaire et laminaire. Ces différents régimes ainsi que l’effet de la concentration en phase dispersée ont été identifiés à partir des mesures locales de vitesse par une technique de vélocimétrie par image de particules (PIV). Lorsque f=0.56, les dispersions se comportent comme des fluides newtoniens auxquels le concept de viscosité effective peut s’appliquer. Le modèle de viscosité de Krieger et Dougherty (1959) décrit l’ensemble des émulsions formées. Le facteur de frottement mesuré suit les lois de frottement classiques en régime laminaire et turbulent (Hagen-Poiseuille et Blasius respectivement) en fonction du nombre de Reynolds basé sur les propriétés de mélange des émulsions (densité et viscosité). Toutefois, la concentration en phase dispersée induit un retard à l’apparition de la turbulence. En milieu très concentré (f=0.7), la dispersion a un comportement rhéofluidifiant et suit la loi d’Ostwald avec un exposant, n=0.5. Tous ces écoulements ont été étudiés, en détail, par l’analyse locale des vitesses. / Homogeneous dispersed flows have been investigated in a horizontal pipe (7.5m long and 50mm internal diameter) in a wide range of flow parameters (mixture velocity from 0.28 to 1.2m/s and concentration, f, up to 0.7). In this work, the wall friction of this emulsion has been measured and modeled in turbulent, intermediate and laminar regime. The different flow regime and the effect of dispersed phase volume fraction have been determined from the velocity profiles measured by PIV measurements in a refractive index matched medium. When f=0.56, emulsion behaves as newtonian fluid. It was shown that the concept of effective viscosity is relevant to scale the wall friction of the emulsion flow. The effective viscosity follows the classical trend of low inertia suspension of hard spheres (Krieger & Dougherty 1959). The friction factor is described by the classical single phase laws in turbulent and laminar regime (Hagen-Poiseuille and Blasius respectively) as a function of Reynolds number based on mixture properties (density and viscosity). Compared to single phase flow, the transition to turbulence is delayed as dispersed phase fraction is increased. For higher dispersed phase fraction (f=0.7), emulsion behaves as a shear-thinning fluid. Emulsion follows the Ostwald law with an exponent equal to 0.5. All these homogeneous dispersed flow have been studied in details.

Continuous processing in the pharmaceutical and fine chemical industries, particularly in micro/milli-scale reactors, has been a topic of interest in literature in recent years due to the advantages offered over batch reactions. One such advantage is the enhanced transport properties of operating at smaller scales, although the quantification of the transport phenomena is not straightforward when wall and entrance effects cannot be neglected. In the first study presented, various micro-mixer geometries and scales were considered to increase the mixing efficiency in liquid-liquid systems of diverse interfacial tensions for fast reactions. The conditions were varied over different flow regimes; including slug flow, parallel flow, and drop flow. A mass-transfer-limited test reaction was used to evaluate the overall volumetric mass transfer coefficients (Korga) as a function of the average rate of energy dissipation (ε) for each mixer design. The onset of drop flow occurred at a lower ε for the LL-Triangle mixer when compared with the Sickle or LL-Rhombus mixers for low interfacial-tension systems (i.e., n-butanol-water). In the drop flow regime for energy dissipation rates of around 20 to 500 W/kg, Korga values ranged from approximatively 0.14 to 0.35 s-1 and 0.004 to 0.015 s-1 for the relatively low and high interfacial-tension (i.e., toluene-water) systems, respectively. The second investigation explored the heat transfer properties of a FlowPlate® system by Ehrfeld Mikrotechnik BTS. First, in a non-reactive system with rectangular serpentine channels (d_h<1mm, 400<Re<2000), a Gnielinski-type model was fit to the internal Nusselt number. Using a silver-based thermal paste between the reactor and heat transfer fluid plates proved to reduce the external resistance to heat transfer by ~70%, yielding overall heat transfer coefficients of ~2200 [W/(m^2 K)]. Secondly, a Grignard reaction was highlighted as a test reaction to compare different reactors’ localized heat transfer characteristics (i.e., hotspot formation) with various micro-mixer geometries, materials, injection ports, and channel scales. Lastly, a case study of four reactions utilized the fourth Damköhler number to determine a maximum channel diameter that would remove sufficient heat to avoid hotspot formation. Each of these studies provides insight to aid in the proper selection of a reactor for a given set of physical properties and reaction kinetics/enthalpies.

This project deals with calculation parts of complex permittivity varnish samples which is filled by nanoparticles of metal oxides. Opening of this project deals with theory of dielectric and effects in dielectric, theory of compounds and expressions in composite systems. Following topic is theory of nanoparticles and nanotechnologies and summarize adjusted results about this branch of knowledge. In practical part of work is include method which was use to make varnish samples filled by nanoparticles, prepare to measurement methods and whole results of measurement. In the end of work is analysis influence of filler particles each filler types to dielectric material and results verified mixture mathematical expressions.

This work deals with the deployment of distributed power sources into the electric power grid. The nature of these sources causes that the massive integration may experience problems with power quality in the local context, and also overall reliability of supply in the range of interconnected power systems may be endangered. Work is focused on local voltage quality problems with special emphasis on analysis and design of tools (e.g. reactive power compensation units of power plants or dynamic voltage control by transformers 110/22kV) for voltage control in power distribution systems. These tools should be used as a part of uniform concept of voltage control. The proposed concept is involved.

Although the Task Team on leadership and development (DoE, 1996) has introduced the notion of shared (collaborative) leadership as embodied among others in school management teams, considerable doubt remains about its practical implementation (DoE, 1996). It seems that there may be widespread failure to implement the idea of collaborative (shared) leadership (DoE, 1996). The problem this research explores is whether, in the opinion of school management team members, the traditional approach to leadership has changed (DoE, 1996). According to Grant (2006 in Grant&Singh, 2009), despite an enabling democratic policy framework the leadership at many South African schools seems to remain firmly entrenched within the formal, hierarchical management structure. During the period of colonialism and apartheid in South Africa government legislation perpetuated a society of inequality based on race, class and gender (Grant 2006 in Grant & Singh, 2009). To control and maintain this inequality, government policies promoted centralised, authoritarian control of education at all levels within the system (Grant 2006 in Grant&Singh, 2009). Today, within a democratic South Africa, the South African Schools Act (1996), the Government Gazette of the Norms and Standards for Educators (2000) and the Task Team Report on Education Management Development (DoE, 1996) challenge schools to review their management policies, which have traditionally been top-down, and create a whole new approach to managing schools where management is seen as an activity in which all members of education engage and should not be seen as the task of a few (DoE, 1996:27). According to Moloi (2002 in Grant&Singh, 2009), although our education policies call for new ways of managing schools, many remain unresponsive and retain their rigid structures because educators are unable to make a shift away from patriarchal ways of thinking. It is against this backdrop that I explore whether leadership has indeed shifted to become more participatory and inclusive. One form of leadership that would reflect this shift is termed collaborative leadership (Grant&Singh, 2009). This form of leadership is based on the premise that leadership should be shared throughout an organisation such as a school (Grant&Singh, 2009). This alternate form of leadership allows for the emergence of teachers as one of the multiple sources of guidance and direction (Grant&Singh, 2009). According to Grant and Singh (2009), collaborative leadership offers a radical departure from the traditional understanding of leadership because it deconstructs the notion of leadership in relation to position in the school. It constructs leadership as a process which involves working with all stakeholders in a collegial and creative way to seek out the untapped leadership potential of people and develop this potential in a supportive environment for the betterment of the school (Grant&Singh, 2009). The general aim of this research is to investigate school management teams’ understanding of the implementation of collaborative leadership in primary schools in Gauteng District 4 in Pretoria. In this research I discuss important issues relating to collaborative leadership. My findings reveal that schools management teams indeed understand and implement collaborative leadership in their schools but also that collaborative leadership is much more than just working together as a team. My argument is that there must be a radical reconceptualisation of the concept of collaborative leadership as well as an attempt to move towards more dispersed and democratic forms of it. / Dissertation (MEd)--University of Pretoria, 2012. / Education Management and Policy Studies / unrestricted