Esta dissertação realiza uma análise comparativa de sobretensões transitórias que ocorrem durante o chaveamento de disjuntores a vácuo. Estas sobretensões podem ocasionar a falha da isolação dos equipamentos conectados aos disjuntores, conforme vários relatos da literatura. Esse fenômeno está associado às características intrínsecas dos disjuntores a vácuo, na formação do arco elétrico em seu interior e de sua interrupção, na sua capacidade de recuperação da rigidez dielétrica, na sua capacidade de interromper correntes de alta frequência, além de características do circuito protegido. Devido à natureza complexa e aleatória das sobretensões transitórias, observou-se a necessidade do desenvolvimento de ferramentas para reprodução dos fenômenos associados às características operacionais dos disjuntores a vácuo. Esse trabalho busca preencher tal lacuna, desenvolvendo um modelo que contempla o comportamento do disjuntor a vácuo tanto para a manobra de abertura quanto para de fechamento, de modo a colaborar com o entendimento dos fenômenos e no cálculo das sobretensões no domínio do tempo. O algoritmo desenvolvido foi implementado no programa Alternative Transient Program (ATP) por meio da linguagem Models. A partir da preparação desse modelo e da escolha de um experimento de referência, foi possível analisar o comportamento do modelo proposto do disjuntor e dos modelos dos principais componentes elétricos dos programas de cálculo de transitórios elétricos, como transformadores e cabos, cujos méritos e deficiências são discutidos ao longo do trabalho. A pesquisa foi orientada em buscar resultados que pudessem ser mais representativos para validação do modelo de disjuntor ao se alterar os modelos dos demais componentes elétricos do circuito, sendo o ajuste dos parâmetros dos disjuntores a vácuo realizados de forma a obter os resultados mais próximos da referência. Por fim, foram simuladas condições onde os fenômenos de sobretensão se agravam e soluções que podem ser incorporadas ao circuito para redução das sobretensões e das frequências dos transitórios. / The current dissertation project performs a comparative analysis of the transient overvoltages generated during the switching of vacuum circuit breakers. The overvoltage phenomenon for these cases can lead to the insulation failure of the equipment connected to the circuit-breakers, according to several reports in the literature. This phenomenon is associated to intrinsic characteristics of the vacuum circuit-breakers, as the formation of the electric arc in their interior and its interruption, their dielectric strength recovery, in their capacity to interrupt high frequency currents interruption, beyond characteristics from the circuit. Due to the complex and random nature of the transient overvoltage, the necessity of developing tools to reproduce such phenomenon associated to the operational features of the vacuum circuit-breaker arose. This dissertation seeks filling this gap, by developing a model that contemplates the vacuum circuitbreaker behavior for both opening and closing switching, in order to collaborate with the understanding of such phenomenon and in the calculations of overvoltages in the time domain. The developed algorithm was implemented in the software Alternative Transient Program (ATP) by means of the programming language Models. From the preparation of this model and from the choice of a reference experiment, it was possible to analyze the behavior of the proposed model and of the models from the main electrical components present in software to calculate electrical transients, e.g. transformers and cables, which merits and deficiencies are discussed along the dissertation. The research was oriented in searching for results that could be more representative to the validation of the circuit-breaker model when changing the models of the remaining electrical components of the circuit, being the parameters adjustment of the vacuum circuit-breakers performed in order to achieve the results closer to the reference. Finally, conditions to aggravate the transitory and the incorporation of solution to reduce the overvoltage and frequencies of the transients were also simulated.

The dissertation studies the nonlinear resonance problems of power systems. Generally speaking, ferroresonance has usually occurred in low-voltage distribution system, especially for potential transformers. Due to the considerable increase of power consumption, the power system is more complex than before. Besides, a number of under-ground cables are used, and transformers¡¦ loss reduce due to improvement of core iron material. These factors could probably result in ferroresnance occurring in extra-high-voltage power system. The dissertation proposed three-phase representation method to analyze unbalance and non-linear system. This method employ magnetically coupled electrical circuit techniques and the original voltage equations can be used without the need for any transformations, which improves significantly computation accuracy. Consequently, it is quite suitable for power system design and incident investigation. Since the traditional d-q-0 model is not well suited for the study of unbalanced faults and requires further transformation, the analytical solution becomes rather complicated and the solutions are still inaccurate. At last we simulated the ferroresonant overvoltages occurring at a nuclear power station in Taiwan in order to investigate the causes and afford mitigation. The simulation results were enough to prove accuracy and practicability of this method.

Any switching action or lightning stroke on a transmission system causes excessive of voltage, which are propagated through the equipment. The withstand capability of the electrical equipment to these overvoltages is dependent on the rate of rise, peak value and the duration of these overvoltages and are especially critical to information technology (IT) equipment. Whenever there is a probability of these overvoltages appearing across the electrical equipment, they should be limited to a safe value by the application surge arresters of the metal oxide type. However, surge arresters are expensive, an optimal location for these should be found so as to minimise the number of surge arresters used.

The purpose of this bachelor thesis is to assess whether it is possible to create a simplified model that estimates the hosting capacity of a low-voltage grid. The Simplified model is compared with a more elaborate model created by the Built Environment Energy Systems Group (BEESG) at Uppsala University. The Simplified model takes three easily obtainable variables into account. The model created by BEESG allows us to observe both the amount of photovoltaic (PV) power that is installed as well as the voltages in each bus in a grid. The hosting capacity is found by gradually increasing the amount of PV power installed in a low-voltage grid until overvoltage is reached. Simulations with BEESG’s model are done for a week in July when the PV generation has its peak and the load is generally low. The Simplified model is created using linear regression with the calculated values from the BEESG’s model as a reference. The report shows that the Simplified model will give an estimation of the low-voltage grid’s hosting capacity that is comparable to the value calculated with BEESG’s model. The results show that it is rarely the low-voltage grid that restricts the installation of PV facilities and that a high self-consumption is advantageous regarding to the grids hosting capacity.

Made available in DSpace on 2014-06-11T19:24:47Z (GMT). No. of bitstreams: 0 Previous issue date: 2004-12-03Bitstream added on 2014-06-13T18:52:41Z : No. of bitstreams: 1 thomazella_r_me_bauru_prot.pdf: 788309 bytes, checksum: a630d7e9326542247d07d560a3da2dd5 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / O presente trabalho visa o desenvolvimento de uma ferramenta computacional confiável na análise e estimação dos níveis de tensões induzidas em linhas de distribuição. Neste contexto, utilizam-se ferramentas computacionais consolidadas, como o ATP (Alternative Transients Program), que combinado a um software desenvolvido em Visual Basic, permitem quantificar e avaliar o nível de sobretensões nas linhas de distribuição. Por meio de modificações nas técnicas clássicas de modelagem das descargas atmosféricas, foi possível a construção de um software em Visual Basic capaz de quantificar os valores das tensões induzidas em linhas de distribuição finitas. A avaliação dos níveis de sobretensões induzidas nas mesmas foi implementada pela associação deste software a um programa de simulação (ATP), a fim de se obter resultados fidedignos deste transitório. Tais resultados foram utilizados para se avaliar o desempenho das... / The present work aims at the development of a trustworthy computacional tool in the analysis and estimate of the levels of induced overvoltage in distribution network. In this context, consolidated computacional tools are used, as ATP (Alternative Transients Program), that combined with a software developed in Visual Basic (beginner's all-purpose symbolic instruction code), they allow to quantify and to evaluate the level of overvoltage in the distribution network. By the means of modifications in the classic techniques of modeling of the atmospheric discharges, the construction of a software in Visual Basic was possible to quantify the values of the induced overvoltage in a finite... (Complete abstract click electronic access below)

There is great concern by the power systems utilities related to disturbances that generate induced overvoltages in the power network, as they reach the consumer sensitive equipment, causing damage and losses. In consequence of this framework, the power systems utilities get large financial losses every year due to indemnity for damage to such equipments. Among the disturbances that lead to induced overvoltages are lightning. Thus, in this work it was developed the study and analysis of the lightning´s effect on loads allocated on average (11kV/15kV) and low voltage (below 600V) under the influence caused by the resistance of grounding. For modeling and simulation of the system under analysis, the program for transient study ATP (Alternative Transient Program) was used. To develop the study, it was designed a system comprising of an 88kV transmission line, a substation, a distribution line of 13.8 kV and loads representing residential consumers. It was also analyzed the use of surge suppressor in the low voltage distribution transformers as a way to mitigate the induced overvoltages that reach consumers. / Existe uma grande preocupação por parte das concessionárias de energia relacionada aos distúrbios que geram sobretensões induzidas na rede elétrica, pois estas atingem os equipamentos sensíveis dos consumidores, causando danos e perdas. Em conseqüência deste quadro, as concessionárias contraem grandes prejuízos financeiros todos os anos devido ao ressarcimento por danos a tais equipamentos. Dentre os distúrbios causadores de sobretensões induzidas destacam-se as descargas atmosféricas. Sendo assim, neste trabalho foi desenvolvido o estudo e análise do efeito de descargas atmosféricas em cargas alocadas em média (11kV/15kV) e baixa tensão (abaixo de 600V) relacionada a influência causada pela resistência de aterramento. Para a modelagem e simulações do sistema sob análise utilizou-se o programa para estudo de transitórios ATP (Alternative Transient Program). Para a realização do estudo modelou-se um sistema composto de uma linha de transmissão de 88kV, uma subestação, uma linha de distribuição de 13,8kV e cargas que representam os consumidores residenciais. É analisada também a utilização de supressores de surto na baixa tensão dos transformadores de distribuição como forma de atenuar as sobretensões induzidas que atingem os consumidores. / Mestre em Ciências

Orientadores: Gilberto de Martino Jannuzzi, Luiz Carlos Pereira da Silva / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-16T17:50:00Z (GMT). No. of bitstreams: 1 MoyaChaves_FranciscoDavid_D.pdf: 2595862 bytes, checksum: b7384c05596f9dc99d6f2e42bbbe231c (MD5) Previous issue date: 2009 / Resumo: Com a finalidade de constituir os princípios para um futuro marco regulatório no Brasil, que contemple a participação da geração distribuída para o fornecimento de serviços ancilares, este trabalho apresenta uma análise desenvolvida em três grandes áreas assim: técnica, econômica e regulatória. Como objetivo específico do projeto, realiza-se uma analise da utilização da GD para o fornecimento de reservas de potência ativa e suporte de reativos. Para atingir os objetivos dessa pesquisa, o trabalho e realizado em três seções complementares. A primeira parte á uma análise técnica, feita mediante a simulação de sistemas elétricos em regime permanente utilizando a analise de fluxos de carga. Apresentam-se algumas das vantagens e limitações técnicas no uso da GD no fornecimento de potencia ativa e reativa. Apresenta-se também, o estudo sobre o fornecimento de reservas operativas com GD, propondo-se uma metodologia para estabelecer o nível máximo de GD que pode ser instalado sem causar impactos negativos sobre a rede. Apresenta-se o desempenho da GD e seus impactos em situações de entrega de reservas operativas, simulando casos diante de possíveis desligamentos de geradores centralizados. Listam-se diversas tecnologias que podem ser utilizadas em aplicações de GD fornecendo serviços ancilares. A segunda seção é uma análise econômica, na qual, e apresentado o despacho adequado de geradores centralizados e descentralizados, realizada mediante a simulação de cenários de sistemas elétricos com fluxos de carga ótimos. Também e feita uma quantificação da contribuição da GD no fornecimento de suporte de reativos. A análise regulatória lista os aspectos a serem considerados num marco regulatório que permita o fornecimento de serviços ancilares através da GD para o futuro mercado de eletricidade no Brasil. Este trabalho, conseqüentemente, conceitua a GD; especifica suas aplicações; evidencia as suas vantagens; lista os segmentos potencialmente geradores e os principais agentes operantes da GD; aponta as tecnologias ora disponíveis e aquelas em processo de desenvolvimento; mostra, generalizadamente, os aspectos legais e institucionais vigentes que influenciam a GD; detalha as principais barreiras a sua inserção como uma alternativa complementar, no fornecimento de servicos ancilares tão necessários nos sistemas elétricos / Abstract: In order to set the principles for a future regulatory framework in Brazil which involves the participation of distributed generation (DG) to provide ancillary services; this work presents an analysis developed in three broad areas, technical, economic and regulatory. A specific objective of the project is to make an analysis of the use of the DG for the supply of active power reserves and reactive support. To achieve the objectives of this research it is necessary to develop three additional sections. The first part is a technical analysis done through the simulation of electrical systems on a permanent regime that uses the analysis of power flows. There are some advantages and technical limitations in the use of DG for the supply of active and reactive power. This part also presents the study on the provision of operating reserves with DG, and proposes a methodology to establish the level of DG, which can be installed without causing negative impacts on the network. In addition to this, this section shows the performance of DG and its impact in case of delivery of operating reserves, simulating some cases before possible disconnections of centralized generators. Finally, it lists different technologies that can be used in applications of DG provided with ancillary services. The second section is an economic analysis which is presented in the appropriate order that centralized and decentralized generators are made by the simulation of scenarios in electrical systems with optimal power flows. It is a quantification of the contribution of DG in the provision of reactive support. The analysis lists the regulatory aspects to be considered in a regulatory framework that enables the provision of ancillary services through the DG for the future market of electricity in Brazil. This work, therefore, conceptualizes a DG; specifies its applications highlighting their advantages, listing segments and potentially generating the key players involved in DG; outlines the technologies now available and those in the development process; shows generally, the legal and institutional force affecting DG; details the key barriers to their inclusion as an additional alternative in the provision of ancillary services as needed in the electrical systems / Doutorado / Engenharia Mecanica / Doutor em Planejamento de Sistemas Energéticos

The grid-connected photo-voltaic (PV) system is one of the most promising renewable energy solutions which offers many benefits to both the end user and the utility network and thus it has gained the popularity over the last few decades. However, due to the very nature of its invariability and weather dependencies, the large scale integration of this type of distributed generation has created challenges for the network operator while maintaining the quality of the power supply and also for reliable and safe operations of the grids. In this study, the behavioral impact of large scale PV system integration which are both steady and dynamic in nature was studied.  An aggregate PV model suited to study the impacts was built using MATLAB/Simulink.  The integration impacts of PV power to existing grids were studied with focus on the low voltage residential distribution grids of Mälarenergi Elnät AB (10/0.4 kV). The steady state impacts were related to voltage profile, network loss. It was found that the PV generation at the load end undisputedly improves the voltage profile of the grid especially for the load buses which are situated at farther end of the grid. Further, with regard to the overvoltage issue, which is generally a concern during the low load demand period it was concluded that, at a 50% PV penetration level, the voltage level for the load buses is within the limit of 103% as prescribed by the regulator excepting for few load buses. The voltage level for load buses which deviate from the regulatory requirement are located at distance of 1200 meter or further away from the substation. The dynamic impact studied were for voltage unbalancing in the grid, which was found to have greater impact at the load buses which is located farther compared to a bus located nearer to the substation. With respect to impact study related to introduction of harmonics to the grid due to PV system integration, it was found that amount of harmonic content which was measured as total harmonic distortion (THD) multiplies with integration of more number of PV system. For a 50 % penetration level of PV, the introduced harmonics into the representative network is very minimal. Also, it was observed from the simulation study that THD content are be less when the grid operates at low load condition with high solar irradiance compared to lower irradiance and high load condition.

No description available.

This thesis is oriented to a specific section of energetics concerned with detection and registration of time responses of fast overvoltages in high-voltage power networks. The first part of this text is information about measuring frequency response characteristics of CR-divider and calculation of typical signal distortion caused by transfer function of this divider. The design of anti-aliasing filter is also included. The second part of this thesis is oriented to selecting key features of a measuring instrument specialized for detecting and recording fast events in electrical power networks. A selection of optimal type of processor and also a choice of communication interfaces is included there as well. The last chapter prepares mathematical procedures for classification of typical fast events in electrical power network using artificial neural networks.