Comparação do desempenho de duas bombas acopladas diretamente a geradores fotovoltaicos

No Brasil, assim como em outros países que recebem abundantes quantidades de radiação solar durante todo o ano, há um grande potencial para os sistemas que usam a tecnologia fotovoltaica para promover o bombeamento de água. Entretanto, a escolha dos conjuntos de motores e bombas mais adequados para cada situação passa pela análise do desempenho dos sistemas de bombeamento. Portanto, devem ser analisadas tanto as melhores configurações de geradores fotovoltaicos destinados a operar os conjuntos formados pelos motores e bombas, quanto às eficiências das bombas e da conversão fotovoltaica. Nesse trabalho são apresentadas medidas e comparações do desempenho de dois sistemas de bombeamento diretamente acoplados a geradores fotovoltaicos. Para tanto, foi construída uma bancada destinada a realizar uma série de experimentos. Um dos sistemas usou uma bomba centrífuga acoplada a um gerador fotovoltaico formado por três módulos fotovoltaicos. O outro, utilizou uma bomba volumétrica de diafragma acoplada a um único módulo fotovoltaico. Os experimentos foram conduzidos em duas etapas distintas. A primeira foi feita com os motores acoplados a uma fonte de potência em corrente contínua e serviu para a determinação das curvas de desempenho de cada uma das bombas, das curvas dos sistemas, assim como das curvas de corrente (I) e de tensão (V) de cada um dos motores que acionavam as bombas. A segunda foi realizada com os sistemas acoplados diretamente aos geradores fotovoltaicos. A determinação da configuração dos geradores fotovoltaicos destinados a acionar os diferentes sistemas de bombeamento em análise nesse trabalho foi feita por meio da sobreposição das curvas de corrente e tensão dos motores e dos módulos fotovoltaicos. A parte experimental, estando os sistemas acoplados aos geradores, constou de medidas realizadas em intervalos de tempo de cinco segundos, para cada bomba e em várias alturas, das seguintes variáveis: temperatura ambiente, irradiância, temperatura dos módulos, corrente e tensão do motor, rotação do motor, temperatura da água, diferencial de pressão entre entrada e saída da bomba e vazão. As diversas alturas foram simuladas por meio da abertura e/ou fechamento de uma válvula de controle de vazão colocada na extremidade tubulação de descarga, operada manualmente. Os procedimentos adotados nessa dissertação permitiram caracterizar os sistemas de bombeamento propostos, assim como determinar quais os arranjos mais adequados para operar cada sistema. Verificou-se que o melhor arranjo para operar o conjunto motor e bomba centrífuga foi aquele formado por três módulos fotovoltaicos ligados em paralelo, enquanto que a melhor opção para operar o conjunto motor e bomba de diafragma foi com somente um módulo fotovoltaico. De posse dos dados medidos foi possível determinar as eficiências: instantâneas, máximas instantâneas e diárias da conversão fotovoltaica assim como dos conjuntos motores e bombas, em diferentes alturas. Relativamente à conversão fotovoltaica, verificou-se que o conjunto motor e bomba centrífuga operou com eficiência instantânea máxima de 5,74% e eficiência diária de 4,70%, enquanto que o conjunto motor e bomba volumétrica de diafragma operou com eficiência instantânea máxima de 7,66% e eficiência diária de 5,82%. Relativamente à eficiência dos conjuntos motores e bombas, verificou-se que o conjunto motor e bomba centrífuga operou com eficiência instantânea máxima de 19,19% e eficiência diária de 16,79%, enquanto que o conjunto motor e bomba volumétrica de diafragma operou com eficiência instantânea máxima de 38,88% e eficiência diária de 34,30%. Verificou-se ainda que a altura foi determinante na eficiência do conjunto motor e bomba centrífuga e pouco influenciou na eficiência do conjunto motor e bomba de diafragma. Além dessas, outras considerações sobre o comportamento dos sistemas de bombeamento ao longo de um dia também foram ser registrados, tais como: limiares de irradiância para início e final de vazão, correntes de pico ou de arranque dos motores e correntes de início de vazão ou escoamento.

On the efficiency of the Argentinean electricity wholesale market

This paper discusses two key aspects regarding the efficiency of the Argentinean Electricity Market. Using hourly data on prices, marginal costs, and operational status of generators, it will be argued that, unlike the former British and Californian electricity spot markets, this market is not subject to the conventional forms of exercise of market power by generators. We then use Chao's (1983) model of optimal configuation of electricity supply to evaluate the social desirability of the change in the supply pattern of the Argentinean electricity industry, which took place throughout the last ten years.

Credibilidade e função de reação do Banco Central do Brasil

Recentemente as expectativas de inflação de mais longo prazo passaram a ficar desancoradas da meta. A fim de testar a perda de credibilidade no compromisso do Banco Central do Brasil de trazer a inflação para o centro da meta, inicialmente, recriamos indicadores de credibilidade para essa instituição e encontramos que esses índices estão em patamares relativamente baixos em termos históricos. Em seguida, calculamos a função de reação do Banco Central utilizando uma Regra de Taylor em janelas moveis de cinco anos no período 2005-2014 como uma tentativa de justificar essa queda da credibilidade nos últimos anos. Os resultados apontaram uma mudança mais acentuada na função de reação do Banco Central do Brasil a partir de 2013, em que a variável hiato do produto ganhou maior importância e o desvio da inflação em relação à meta perdeu significância. Essa mudança pode ter sido um dos principais geradores para a queda recente de credibilidade.

On invariant Rings of Sylow subgroups of finite classical groups

In this thesis we study the invariant rings for the Sylow p-subgroups of the nite classical groups. We have successfully constructed presentations for the invariant rings for the Sylow p-subgroups of the unitary groups GU(3; Fq2) and GU(4; Fq2 ), the symplectic group Sp(4; Fq) and the orthogonal group O+(4; Fq) with q odd. In all cases, we obtained a minimal generating set which is also a SAGBI basis. Moreover, we computed the relations among the generators and showed that the invariant ring for these groups are a complete intersection. This shows that, even though the invariant rings of the Sylow p-subgroups of the general linear group are polynomial, the same is not true for Sylow p-subgroups of general classical groups. We also constructed the generators for the invariant elds for the Sylow p-subgroups of GU(n; Fq2 ), Sp(2n; Fq), O+(2n; Fq), O-(2n + 2; Fq) and O(2n + 1; Fq), for every n and q. This is an important step in order to obtain the generators and relations for the invariant rings of all these groups.

Estudo comparativo de pás para aerogeradores de grande porte fabricadas em materiais compósitos reforçadas com fibra de carbono ou fibra de vidro

The research and development of wind turbine blades are essential to keep pace with worldwide growth in the renewable energy sector. Although currently blades are typically produced using glass fiber reinforced composite materials, the tendency for larger size blades, particularly for offshore applications, has increased the interest on carbon fiber reinforced composites because of the potential for increased stiffness and weight reduction. In this study a model of blade designed for large generators (5 MW) was studied on a small scale. A numerical simulation was performed to determine the aerodynamic loading using a Computational Fluid Dynamics (CFD) software. Two blades were then designed and manufactured using epoxy matrix composites: one reinforced with glass fibers and the other with carbon fibers. For the structural calculations, maximum stress failure criterion was adopted. The blades were manufactured by Vacuum Assisted Resin Transfer Molding (VARTM), typical for this type of component. A weight comparison of the two blades was performed and the weight of the carbon fiber blade was approximately 45% of the weight of the fiberglass reinforced blade. Static bending tests were carried out on the blades for various percentages of the design load and deflections measurements were compared with the values obtained from finite element simulations. A good agreement was observed between the measured and calculated deflections. In summary, the results of this study confirm that the low density combined with high mechanical properties of carbon fibers are particularly attractive for the production of large size wind turbine blades

Protótipo de um microgerador termoelétrico de estado sólido: cogeração a gás

The thermoelectric energy conversion can be performed directly on generators without moving parts, using the principle of SEEBECK effect, obtained in junctions of drivers' thermocouples and most recently in semiconductor junctions type p-n which have increased efficiency of conversion. When termogenerators are exposed to the temperature difference (thermal gradient) eletromotriz a force is generated inducing the appearance of an electric current in the circuit. Thus, it is possible to convert the heat of combustion of a gas through a burner in power, being a thermoelectric generator. The development of infrared burners, using porous ceramic plate, is possible to improve the efficiency of heating, and reduce harmful emissions such as CO, CO2, NOx, etc.. In recent years the meliorate of thermoelectric modules semiconductor (TEG's) has stimulated the development of devices generating and recovery of thermal irreversibility of thermal machines and processes, improving energy efficiency and exergy these systems, especially processes that enable the cogeneration of energy. This work is based on the construction and evaluation of a prototype in a pilot scale, for energy generation to specific applications. The unit uses a fuel gas (LPG) as a primary energy source. The prototype consists of a porous plate burner infrared, an adapter to the module generator, a set of semiconductor modules purchased from Hi-Z Inc. and a heat exchanger to be used as cold source. The prototype was mounted on a test bench, using a system of acquisition of temperature, a system of application of load and instrumentation to assess its functioning and performance. The prototype had an efficiency of chemical conversion of 0.31% for electrical and heat recovery for cogeneration of about 33.2%, resulting in an overall efficiency of 33.51%. The efficiency of energy exergy next shows that the use of primary energy to useful fuel was satisfactory, although the proposed mechanism has also has a low performance due to underuse of the area heated by the small number of modules, as well as a thermal gradient below the ideal informed by the manufacturer, and other factors. The test methodology adopted proved to be suitable for evaluating the prototype

Avaliação de HPA e BTEX no solo e água subterrânea, em postos de revenda de combustíveis: estudo de caso na cidade de Natal -RN

The retail fuel stations are partially or potentially polluters and generators of environmental accidents, potentially causing contamination of underground and surface water bodies, soil and air. Leaks in fuel retail stations´ underground storage systems are often detected in Brazil and around the world. Monoaromatic hydrocarbons, BTEX (benzene, toluene, ethylbenzene and xylenes) and polycyclic aromatic hydrocarbons (PAHs) are an indication of the presence of contamination due to its high toxicity. This paper presents a case study of contamination in a Fuel Retail Station by petroleum derivative products in the city of Natal. For identification and quantification of the hydrocarbons, EPA analytical methods were used. The values of benzene quantified by EPA method 8021b CG-PID/FID, ranged from 1.164 to 4.503 mg.Kg-1 in soil samples, and from 12.10 to 27,639 μg.L-1 in underground water samples. Among the PAHs, naphthalene and anthracene showed the most significant results in soil samples, 0.420 to 15.46 mg.Kg-1 and 0.110 to 0,970 mg.Kg-1, respectively. In underground water samples, the results for Naphthalene varied between 0.759 and 614.7 μg.L-1. PAHs were quantified by EPA Method 8270 for GCMS. All of the results for the chemical analysis were compared with the values for the CONAMA 420/2009 resolution. The results for benzene (27,639 μg.L-1) showed levels highly above the recommended by the CONAMA 420 resolution, wherein the maximum permissible for underground water is 5 μg.L-1. This is a worrying factor, since underground water makes up 70% of the city of Natal´s water supply

Diagnóstico Socioambiental da disposição final dos resíduos sólidos no distrito de Guajiru São Gonçalo do Amarante/RN, ressaltando a situação socioeconômica dos catadores

One of the concerns of this century is with the handling and the final destination of urban solid waste (RSU), where depending on the form as they will be made use, they can cause diverse problems, they are of ambient or social order, being able to generate the loss of the quality of life and illnesses to the population, of direct or indirect form. The objective of the present work was to diagnosis the environmental partner situation of the Final Destination of the urban solid residues in the District of Guajiru, city of São Gonçalo do Amarante/RN, standing out the partner-economic situation of the scavengers. The research was carried through in the period of March of 2008 the October of 2009, with a methodology developed through analyzes them of documents made available for the state ambient agency, the Air base of Christmas and managing agencies of the city. For collection of the date, it was used directly application of the questionnaire with 20 existing scavengers in points of destination of residues, evaluation of the old place of final destination through the use of the spread sheet of the IQR (Index of Quality of the Residues), developed for the CETESB, identification of the matter dump and photographic register. For effect of treatment of the data, a descriptive analysis with regard to the answers of the interviewed scavengers was carried through. The acquired date, Scale had been according to tabulated and analyzed in Excel 2003, where they had been generated graphical to observe the behavior of the data. The results show that of the twenty interviewed scavengers, 35% possess age between 20 and 30 years; 75% possess incomplete basic education; 60% inhabit in houses of waal or huts (cardboard or wood); 55% do not make use of system of water supply and system of sanitary exhaustion; with regard to income monthly for scavengers, 35% had presented income between R$ 200,00 and R$300,00 and 20% possess income above of R$ 500,00 for possessing another source of income; 80% of the interviewed ones, use some type of equipment of individual protection; In the year of 2009, confirming what it was informed by the State agency of Environment, during the field visit, we evidence that the city of Is Gonçalo do Amarante, currently, destines its residues in Sanitary landfill of São Region Metropolitan of Natal in the District of Massaranduba in the city of Ceará-Mirim, after some interventions of the State Public prosecution service. However, in the district of Guajiru some diggings still exist that today are used as final destination of RCD' s (Residues of Construction and Demolition) of the cities of Natal and São Gonçalo do Amarante, as well as private dumps that are used by scavengers that deviate the final destination (Sanitary landfill) of the residues of the great generators (supermarkets, shopping Center and hotels), with presence of urubus, generating a new ambient problem for the city and the aeroportuária security. Ahead of this scene, the study it suggests viable alternatives for the elimination of the private dumps and for the social situation of the escavengers, aiming at to improve its quality of life and 10 to minimize the ambient impacts caused by the inadequate destination of the solid waste in the community of Guajiru, São Gonçalo do Amarante/RN, being able to contribute so that the public managers carry through action in the handling and the control of the final destination of the urban solid waste

Comparação entre modelos equivalentes de aerogeradores síncronos utilizando o programa ATP

At present, the electricity generation through wind energy has an importance growing in the world, with the existence of very large plans for future wind power installation worldwide. Thus, the increasing the electricity generation through wind power requires, more and more, analysis of studies of interaction between wind parks and electric power systems. This paper has as purposes to implement equivalent models for synchronous wind generators to represent a wind park in ATP program and to check behavior of the models through simulations. Simulations with applications of faults were achieved to evaluate the behavior of voltages of system for each equivalent model, through comparisons between the results of models proposed, to verify if the differences obtained allows the adoption of the simplest model

Uma proposta de regulador nebuloso para geradores eólicos de indução

This work presents a proposal for a voltage and frequency control system for a wind power induction generator. It has been developed na experimental structure composes basically by a three phase induction machine, a three phase capacitor and a reactive static Power compensator controlled by histeresys. lt has been developed control algorithms using conventional methods (Pl control) and linguistic methods (using concepts of logic and fuzzy control), to compare their performances in the variable speed generator system. The control loop was projected using the ADJDA PCL 818 model board into a Pentium 200 MHz compu ter. The induction generator mathematical model was studied throught Park transformation. It has been realized simulations in the Pspice@ software, to verify the system characteristics in transient and steady-state situations. The real time control program was developed in C language, possibilish verify the algorithm performance in the 2,2kW didatic experimental system

Identificação remota de sistemas operacionais utilizando análise de processos aleatórios e redes neurais artificiais

A new method to perform TCP/IP fingerprinting is proposed. TCP/IP fingerprinting is the process of identify a remote machine through a TCP/IP based computer network. This method has many applications related to network security. Both intrusion and defence procedures may use this process to achieve their objectives. There are many known methods that perform this process in favorable conditions. However, nowadays there are many adversities that reduce the identification performance. This work aims the creation of a new OS fingerprinting tool that bypass these actual problems. The proposed method is based on the use of attractors reconstruction and neural networks to characterize and classify pseudo-random numbers generators

Regulador automático de tensão robusto utilizando técnicas de controle adaptativo

The stability of synchronous generators connected to power grid has been the object of study and research for years. The interest in this matter is justified by the fact that much of the electricity produced worldwide is obtained with the use of synchronous generators. In this respect, studies have been proposed using conventional and unconventional control techniques such as fuzzy logic, neural networks, and adaptive controllers to increase the stabilitymargin of the systemduring sudden failures and transient disturbances. Thismaster thesis presents a robust unconventional control strategy for maintaining the stability of power systems and regulation of output voltage of synchronous generators connected to the grid. The proposed control strategy comprises the integration of a sliding surface with a linear controller. This control structure is designed to prevent the power system losing synchronism after a sudden failure and regulation of the terminal voltage of the generator after the fault. The feasibility of the proposed control strategy was experimentally tested in a salient pole synchronous generator of 5 kVA in a laboratory structure

Efeitos do treino em esteira na marcha com dupla tarefa de indivíduos com doença de Parkinson: ensaio clínico controlado randomizado

Background: The gait automaticity loss difficults realization of concurrent activities - Dual Task (DT). In these situations, individuals with Parkinson`s disease (PD) show a significant reduction in gait velocity and stride length, as strides variability and asymmetry increased, factors predisposing to falls. However, recent studies have shown that training involving DT may cause subsequent improvements in gait variables with DT in individuals with PD. The treadmill use was adopted by this study, by promoting greater regularity in step and enhance training. Objective:To investigate immediate effects of gait training associated with cognitive tasks on gait in individuals with PD. Methods: Twenty-two volunteers were randomly divided into two groups: control group (n = 11), who performed gait training on a treadmill for 20 minutes, and the experimental group (n = 11), who performed treadmill gait training for 20 minutes associated with cognitive tasks of verbal fluency, memory, and spatial planning. Participants were evaluated in phase on of antiparkinsonian medication as the demographic, clinical and anthropometric (identification form), cognitive status (Montreal Cognitive Assessment - MoCA), executive function (Frontal Assessment Battery), level of physical disability (Hoehn and Yahr Modified), motor and functional status (Unified Rating Scale for Parkinson`s Disease - UPDRS), and kinematics (Qualisys Motion Capture System). Results: There were not differences between groups, but both showed improvement after the intervention. The control group had an increase in velocity (p = 0.008), stride length (p = 0.04), step length (p = 0.02) and decreased double support time(p = 0.03). The experimental group showed an increase in speed (p = 0.002), stride length (p = 0.008), step length (p = 0.02) and cadence (p = 0.01), as well as a decrease in the width stride (p = 0.001) and total support time (p = 0.02). As the angular variables, the experimental group had a significant increase in the initial contact angle of ankle (p = 0.01). Conclusion: The gait training combined with cognitive activities didn`t provide significant improvements in gait variables with DT, but this study was the first to demonstrate that gait training on treadmill as simple task minimized the negative interference of DT in PD

Optimization analysis of dual-purpose systems

This paper aims to analyze dual-purpose systems focusing the total cost optimization; a superstructure is proposed to present cogeneration systems and desalination technologies alternatives for the synthesis process. The superstructure consists of excluding components, gas turbines or conventional steam generators with excluding alternatives of supplying fuel for each combustion system. Also, backpressure or condensing/extraction steam turbine for supplying process steam could be selected. Finally one desalination unit chosen between electrically-driven or steam-driven reverse osmosis. multi-effect and multistage flash should be included. The analysis herein performed is based on energy and mass conservation equations, as well as the technological limiting equation of equipment. The results for ten different commercial gas turbines revealed that electrically-driven reverse osmosis was always chosen together with both natural gas and gasified biomass gas turbines. (C) 2009 Elsevier B.V. All rights reserved.

A new method for real time computation of power quality indices based on instantaneous space phasors

One of the important issues about using renewable energy is the integration of dispersed generation in the distribution networks. Previous experience has shown that the integration of dispersed generation can improve voltage profile in the network, decrease loss, etc. but can create safety and technical problems as well. This work report the application of the instantaneous space phasors and the instantaneous complex power in observing performances of the distribution networks with dispersed generators in steady state. New IEEE apparent power definition, the so-called Buchholz-Goodhue effective apparent power, as well as new proposed power quality (oscillation) index in the three-phase distribution systems with unbalanced loads and dispersed generators, are applied. Results obtained from several case studies using IEEE 34 nodes test network are presented and discussed. (C) 2006 Elsevier B.V. All rights reserved.