Submitted by Johnny Rodrigues (johnnyrodrigues@ufcg.edu.br) on 2018-03-15T16:40:52Z No. of bitstreams: 1 ALDREANY PEREIRA DO NASCIMENTO - DISSERTAÇÃO PPGEQ 2016..pdf: 4384493 bytes, checksum: 8cf20c9f79749f12b562389c82ec5d3f (MD5) / Made available in DSpace on 2018-03-15T16:40:52Z (GMT). No. of bitstreams: 1 ALDREANY PEREIRA DO NASCIMENTO - DISSERTAÇÃO PPGEQ 2016..pdf: 4384493 bytes, checksum: 8cf20c9f79749f12b562389c82ec5d3f (MD5) Previous issue date: 2016-10-30 / Capes / A crise do petróleo juntamente com a grande necessidade de novas fontes de energias sustentáveis leva ao desenvolvimento de tecnologias mais limpas e eficientes. Neste contexto, as células a combustível aparecem como uma das soluções promissoras para a geração de energia elétrica, tendo como produto da reação, basicamente água e calor. Este trabalho de dissertação consiste na caracterização de uma célula a combustível PEM (Polymer Electrolyte Membrane) alimentada com hidrogênio e ar para a conversão de energia elétrica da energia química contida no gás hidrogênio. A célula a combustível utilizada é de potência nominal de 1 kW, constituída por 72 células ligadas em série com um sistema de controle próprio. A caracterização é feita através da utilização de uma carga resistiva configurável com base num microcontrolador. A partir dos parâmetros registrados (corrente e tensão), a curva de polarização, a densidade de corrente e a eficiência foram calculadas com base nos sistemas de curto circuito ligado e desligado (SCU: ON e SCU: OFF, respectivamente). Os resultados mostram uma potência máxima de saída de aproximadamente 623 W (37,09 V, 16,78 A), e uma densidade de corrente de 209,75 mA/cm2, com uma eficiência operacional em torno de 42 %, com o sistema de SCU: OFF. Para o sistema SCU: ON a potência máxima de saída é em torno de 664 W (39,10 V, 17,81 A) com densidade de corrente de 222,62 mA/cm2 e uma eficiência operacional de 44 %. O sistema de carga variável mostrou-se satisfatório para testar a célula, com um desvio entre a potência nominal e a real inferior a 20 %. Os relativamente baixos valores de eficiência do sistema (<20 %) são explicados pelo tempo de vida da célula. / The use of new sustainable energy sources is dependent on the development of clearer and more efficient technologies. Therefore, the fuel cells appear like a promising solution for the electrical energy generation, since that the reaction products are water and heat. This work plans to characterize a polymer electrolyte membrane fuel cell, feeding with hydrogen and air. The tested 1 kW nominal power fuel cell is constituted by 72 cells connected in serial. The characterization is made using a variable resistive charge system. It comprises 64 resistors (20 W) together with blowers for cooling. From the electrical parameters (voltage and current), the polarization curve, the current density and the efficiency of the fuel cell were calculated, with the short-circuit system on and off (SCU: ON and SCU: OFF). A maximum output power of 623 W (37.09 V and 16.78 A), with a current density of approx. 209.75 mA/cm2 and an efficiency around 42 % are obtained when the SCU is OFF. With the SCU: ON, the values are 664 W (39.10 V and 17.81 A), 222.62 mA/cm2 and 44 %, respectively. The results show that the resistive charge system is appropriate to test this kind of fuel cell. The low global efficiency values (< 20 %) can be explained by the fuel cell age.

As escolas de ensino mÃdio brasileiras suscitam questionamentos quanto ao perfil do processo e ensino e da aprendizagem de ciÃncias, destacando-se na presente investigaÃÃo certos cenÃrios limitantes, concernentes aos discentes deste nÃvel de escolaridade. Tais questionamentos tÃm propiciado discussÃes nÃo sà dentro das escolas, mas tambÃm dentro de outros ambientes acadÃmicos e no prÃprio MinistÃrio da EducaÃÃo, que atravÃs de suas Diretrizes Curriculares Nacionais incentiva o redirecionamento da prÃtica pedagÃgica dos professores de fÃsica, no sentido de melhorar o perfil do aprendizado dos alunos. Uma proposta que vem ganhando espaÃo à a aprendizagem mediada pelo computador. Se pedagogicamente utilizado baseado em princÃpios teÃricos, metodolÃgicos e prÃticos (ALMEIDA; VALENTE),o computador pode se constituir numa ferramenta estratÃgica para propiciar uma maior interatividade entre o aprendiz e o saber, bem como favorecer o desenvolvimento de competÃncias, que propiciem o discente construir autonomamente seu conhecimento, enquanto que o professor migra do papel de dono do conhecimento para o de mediador. Nestes termos, focando-se a constante dificuldade apresentada na aprendizagem dos conteÃdos de fÃsica por arte dos alunos da Escola de Ensino MÃdio Padre Rodolfo Ferreira da Cunha, situada no municÃpio de Trairi-CE, a presente DissertaÃÃo busca pesquisar como a inserÃÃo do computador como ferramenta pedagÃgica pode auxiliar o desenvolvimento da aprendizagem significativa e fÃsica dos alunos do 3 ano. O objetivo à investigar como a prÃtica pedagÃgica, desenvolvida com o auxÃlio de recursos de simulaÃÃo computacional, mais especificamente os simuladores do Physics Education Technology (PhET), e fundamentada na Teoria da Aprendizagem Significativa de David Ausubel, pode proporcionar a inter-relaÃÃo e ressignificaÃÃo de leis e conceitos de eletricidade, atravÃs do desenvolvimento de prÃticas, envolvendo a simulaÃÃo de circuitos de resistores elÃtricos (RIBEIRO, VALENTE). Para se perar esse objetivo, metodologicamente se optou por realizar uma pesquisa qualitativa, do tipo pesquisa-aÃÃo. Nesse processo, foram aplicados questionÃrios para se proceder a identificaÃÃo os conhecimentos prÃvios dos educandos quanto aos conteÃdos bÃsicos de eletricidade e circuitos de resistores. Foram realizadas minioficinas para que os alunos aprendessem a utilizar peracional e pedagogicamente o PhET nas atividades discentes. Em seguida, foram realizadas oito oficinas para estudo colaborativo dos conteÃdos de eletricidade. Estas oficinas foram desenvolvidas atravÃs de atividades prÃticas e preenchimento de roteiros de atividades de forma colaborativa. A anÃlise dos resultados da pesquisa de campo revelou indÃcios preliminares que as atividades de simulaÃÃo de circuitos de resistores, desenvolvidas pelos alunos, permitiram ressignificaÃÃo e inter-relaÃÃo entre leis e conceitos bÃsicos de eletricidade, mostrando assim como potencialmente significativas, em virtude do leque de possibilidades de interaÃÃes colaborativas e situaÃÃes de aprendizagem que elas poderiam possibilitar junto aos alunos. AlÃm disso, a utilizaÃÃo dos simuladores despertou o interesse dos alunos em participar e realizar as atividades. Observou-se que, diante de certas dificuldades apresentadas pelos alunos, a utilizaÃÃo de simuladores se mostrou como um recurso promissor para auxiliar o desenvolvimento da aprendizagem de fÃsica na escola. / Brazilianâs schools of average education raise questionings about the profile of the sciences education and learning process, being distinguished in the present investigation certain limiting scenes, concerning the learning process of this level of education. Such questionings have propitiated quarrels not only inside of the schools, but also inside of other academic environments and in the proper Ministry of the Education, that through its National Curricular Lines of direction stimulates the practical redirection of Physics professors in pedagogical line, to improve the profile of the pupilâs learning. The proposal that comes gaining space is the learning mediated from the computer. If pedagogically used based in theoretical, methodology and practical principles (ALMEIDA; VALENTE), the computer can consist in a strategical tool to propitiate a bigger interactivity between the apprentice and knowledge, as well as favoring the development of abilities, that propitiate the learning to construct its knowledge independently, whereas the professor migrates of the role of knowledge ownerâs for the mediator. In these terms, focusing itself it constant difficulty presented in the learni ng of the Physics contents, on the part of the pupils from average education school Padre Rodolfo Ferreira da Cunha, situated in the city of Trairi-CE, this study has the objective to search as the insertion of the computer as pedagogical tool, can assist the development of significant learning of physics for 3 year pupils. The objective is to investigate how the pedagogical practice, developed with the help of computer simulation resources, more specifically the simulators of the Physics Education Technology (PhET), and based on the Theory of the Significant Learning of David Ausubel, can provide interrelation and redefinition of laws and concepts of electricity, through the development of practical, involving the simulation of circuits of electrical resistor (RIBEIRO, VALENTE). To operate this objectively methodologically it was opted to carrying through a qualitative research, of the type research-action. In this process, questionnaires had been applied to proceed the identification of previous knowledge of the pupils, on how much to the basic contents of electricity and circuits of electrical resistors. Mini -workshops, so that the pupils learned to use operational and the PhET pedagogically in the learning activities had been carried through. After that, eight workshops had been carried through for collaborative study of the electricity contents. These workshops had been developed through practical activities and fulfilling activities collaborative form. The analysis of the field research results raised preliminary indications that the activities of circuits simulation of electrical resistor, developed for the pupils, had allowed the redefinition and interrelation between laws and basic concepts of electricity, revealing as well as potentially significant, in virtue of the variety of possibilities of collaborative interactions and learning situations that they could possible make,with the pupils. Moreover, the uses of simulators awaken the interest of the pupils to participate and to carry through the activities. It was observed that, in spite of certain difficulties presented for the pupils, the use of simulators showed itself as a promising resource to assist the development of the learning of physics in school.

The most widespread system of an earthing neutral point of a supply transformer in a MV network is an earthing through an arc-suppression coil. In this case of a resonant-earthed power system a fault current is compensated by the suppression coil and only residual current flows through a fault point. A value of the residual current is much smaller then a value of an original capacitive current of the network and is not dependent on the fault location. According to that reasons it is really complicated to fast and accurately determine the fault point location. Since nowadays used methods for the ground fault location inside wide distribution networks have a lot of disadvantages, the thesis is focused on a proposal of a new method for the ground fault location especially inside of a compensated network. The main reasons for a consecutive installation of power quality meters into distribution transformer substations are a power quality monitoring and a global evolution of an electrical network onto the “SmartGrids”. In case that all results from the meters are properly synchronized and centralized, new possibilities of control or of an evaluation of a network are enabled. This doctoral thesis proposes the possibility for the ground fault detection with an aid of synchronized records recorded on the low-voltage side of the distribution transformers 22/0.4 kV into the network equipped with automatics for short-time increasing of an active part of a faulty current. The described method uses a voltage drop evoked by connecting of the auxiliary resistor for location of the faulty section. The proposed method is tested with help of numerical model which presents a part of the distribution network Series of simulation are executed and correct function and force function of the method is reviewed. Finally the thesis describes real experiment and also a confrontation between simulation and real measuring, and also possibilities of method usage are commented.

My thesis is focused on realization of three inrush current limitors samples. This limiters will be used in ABB´s metal-clad, air-insulated switchgears for medium voltage distribution. On the basis of the results there is chosen the sample with optimal properties suitable for practice in the conclusion.

In this masters's thesis is closely studied questins of current (power) side channel. It deals with attack upon this type of side channels and methods, which can this channel analyse. Also two methods of measurements, which make possible successfully attack, are presented here. Below the work describes progress, which was used for analyse current side channel of chip PIC16F84A. This chip, which was plugged in the circuit in agreement with diagram introduced here, processes step by step variety of programs implementing always other operation, which matches concrete used instruction. In corresponding chapters are introduced resulting values and graphs, which was obtained by measurement.

This project deals with comparing types and properties of commercial produced incubators for exotic birds. It searches the best solution from these area. In this project are compars individual components and their choice for realization in this project. Then in this project is solution of regulation temperature and humidity in engineered mechanism and discovered parameters of specifically space. Then is developed solution of thermostat and hydrosatat for this prototype. Temperature is changed by Peltier module, who is involved in correct system. Humidity is regulated by resistor humidifier. Complex system is managed by microcontroler. System communicates with PC via USB interface and Ethernet. Solution of this project is maked functional prototyp.

This master’s thesis deals with the design and manufacture of device for testing and verification of functionality of atmospheric resistors produced by IMI CCI Czech Republic. An atmospheric resistor, also called disk stack, is a stack of disks through which the medium flows and the system of labyrinths in disk stack causing a pressure reduction of medium. This thesis describe design of the mechanical parts of stand for atmospheric resistors, choice pneumatic circuit’s components, data acquisition hardware for measuring flow, inlet and outlet pressure, and temperature. The software was created in LabVIEW programming environment. In the end of this paper was done measurement in order to test functionality of test stand and software.

The doctoral thesis is aimed at research of application possibilities of low-temperature co-fired ceramics, especially its non-conventional usage. It deals with particular topics ensue from electronic chips package design. The thesis also touches optoelectronic sensor application of this ceramics.

Overcrowding during indoor events can be risky, in-case of any kind of a hazard such as fire.This solution address this by providing real-time crowd detection solution using Force-SensingResistor (FSR) sensors, referred sensor (IR) and microcontrollers. The solution needs to offer accurate data in real-time to the event managers including number of people and entrancerate to help when and if the event areas will be overcrowded, thereby enhancing event safetyand decision-making. This thesis indicate that the system offers essential real-time data forevent safety with an accuracy of 87.25%. These data will assists event managers in makinginformed decisions to avoid the risks of overcrowding. This thesis evaluates the effectivenessof our system in comparison to other systems, discussing what we’ve learned, suggest possibleimprovements, and talk about whether our system could be useful in real-world indoor events.

Reactive power is critical to reliable operation of the modern AC power system. There is a plethora of motor-loads, transformers, and power-electronic loads connected to the power grid, which consume reactive power for normal operation. Transmission lines also consume reactive power when they are loaded above their surge impedance loading (SIL). Reactive power can exact opportunity cost due to reduced capacity of the lines to carry real power, which in turn lowers revenue. Most transmission owners (TOs) levy large penalties against load serving entities (LSEs), industrial facilities, and other end-use customers, who consume more than their allotted amount, as measured by their power factor. These penalties are to incentivize their customers to meet their reactive power needs locally as well as to recuperate the TOs' financial losses. Harmonic pollution is another factor that prevents the optimal operation of the grid and the connected loads. Harmonics are attributable to proliferation of the diode-rectifier- or thyristor-rectifier-interfaced loads such as variable speed ac drives and power supplies in server farms, electric arc furnaces, and other non-linear loads, which are widely employed by the industrial sector. With wider adoption of harmonic-rich loads by the consumer sector as well, such as HDTVs and compact fluorescent lamps (CFLs), greater level of triplen harmonics associated with single-phase loads are also increasingly seen on the distribution grid. The increasing penetration of renewable resources and electrification of light-duty vehicles are expected to further aggravate the stresses and congestion on the utility grid. Reactive power compensation is necessary for supporting the AC grid and maintaining a healthy voltage stability margin. Compensation can also enhance the utilization of system capacity, lower system losses, provide fault ride-through, and enable a quick fault recovery. Existing VAR and harmonic compensation technologies are either too expensive or inadequate to meet the dynamic needs of the modern and the future power system. This dissertation presents a novel class of Dynamic VAR and Harmonic Compensators (DVHCs) for supplying or absorbing reactive power and providing harmonic filtering, where the compensation is in shunt with the line and the load. The underlying concept is based on augmenting a static or passive component like a capacitor or an inductor with a direct AC converter and imbuing the passive component with dynamic properties. The direct AC converter can be configured as a buck, a boost, or a buck-boost. A `fail-normal' switch is an integral part of the DVHCs that bypasses the converter when it fails, preserving the original functionality and the reliability of the passive component. The DVHCs are modular and scalable such that they can be employed in applications ranging from residential and industrial with voltages less than 480 V, to power distribution level with voltages as high as 35 kV. The Dynamic Inductor (D-IND) and the Dynamic Capacitor (D-CAP) are subclasses of the DVHCs. As the applications for supplying leading VARs are more prevalent, the primary focus of this work is on the buck, the boost, and the buck-boost configurations of the D-CAP. To understand the characteristics and operation of the DVHCs, this work has developed time-domain models for analyzing the transient and dynamic behavior; frequency-domain models for understanding the harmonic interactions and the steady-state relationships between switch duty and current harmonics; and small-signal models for studying the dynamics of the converter due to various perturbations. The small-signal models also enable extraction of transfer functions in designing controllers and assessing stability margins. Control architectures and techniques are presented for effectively controlling the D-CAP when commutating the semiconductor devices with both high and low switching frequencies. In modularly scaling the DVHCs to higher voltages, three medium-voltage topologies are discussed. They are based on series-connecting fractionally-rated devices, AC flying capacitors, and series cascading multiple two-level cells. These implementations allow direct connect to the medium-voltage grid, thereby obviating the use of transformers, and subsequently reducing the losses, cost, complexity, and footprint. A novel AC snubber concept is proposed to provide safe commutation of the AC switches, fault tolerance by managing the energy trapped in parasitics and filters, and to enable dynamic and static voltage sharing when integrated around the series-connected devices. Design equations for selecting and rating the devices and components in the buck, the boost, and the buck-boost configurations of the D-CAP are presented. Three sets of example designs, with one at low-voltage and two at medium-voltage, are discussed to demonstrate the typical size and ratings of the various components under realistic operating conditions. Measurements and the related discussions of a 40 kVA buck D-CAP prototype built to validate the effectiveness of the proposed concepts are presented.