The Eskom Transmission Network experiences an exceptionally high number of line faults, the cause of which, may not be correctly identified. This thesis analyses a number of all the possible factors responsible for causing these faults. The objective is to assign probable causes of these faults and that the correct preventative or corrective measures may be planned. The percentage of unexplained line faults is estimated to be 35 % of the total system faults. It is important for the Transmission Group of Eskom to minimise the number of faults. Major efforts to minimise identified faults such as bird streamers, veld fires, sugar cane fIfes, lightning and a hypothesised light pollution, light wetting mechanism has been undertaken by the transmission grid authority. This thesis presents an analysis of the statistical data of the unknown faults (unknown faults is defined as lines that trip due to a reason which could not be identified) that has been undertaken. This analysis takes into account a number of categories of causes of line faults. The period, for which the performance of the lines was analysed for was the years inclusive of 1993 to 1997. The investigation has focused on the identification of the under-performing lines of the main Transmission Network. The identified poorly performing lines have been compared with each other from the perspective ofthe following variables: • Region • Voltage (System Voltage) • Climatic Data Line faults - Time ofDay analysis • Line Faults - Time of Year analysis. The analysis indicates that the majority of unexplained flashovers occur between 22 :00 and 07:00 the following morning (Britten et al, 1999). Almost all of the under performing lines in South Africa fall in the sub-tropical/humid climatic area. All the lines studied are insulated with standard glass disc insulators. The analysis indicated that most of the unexplained line faults occur during the months when the seasons change, e.g. from autumn to winter. The analysis further indicates that most unexplained line faults occurred during the months of April to May and August to September. Of note is that during the period of this investigation bird guarding was performed on some lines. Installing bird guards may reduce those line faults that are caused by bird streamers. However, the bird pollution (deposited on glass disc insulators) that is not washed off at the same time as the bird guard installation may cause the line to trip due to the combination of the pollution and wetting resulting in a pollution type flashover. This is a possible cause of some unexplained line faults that occur from April to May. Bird streamers are also identified as the most probable cause of the unexplained faults which occur during the late evening periods (22:00 - 00:00). Pollution (with wetting) during the early morning periods may result in faults for the period 00:00 to 02:00. Line faults in the early morning periods (04:00 - 7:00) could be due to bird streamers or pollution and wetting, depending on the time of year in which the faults occurs. / Thesis (M.Sc.)-University of Natal, Durban, 2003.

Thesis (MEng)-- Stellenbosch University, 2013. / ENGLISH ABSTRACT: The deployment of Unmanned Aerial Vehicles (UAV) for power line inspection requires the definition of safe-fly zones. Transient Over-Voltages (TOVs) on the Overhead Transmission Lines (OHTLs) put the UAV at risk if it encroaches on these zones. In order to determine the safe-fly zones of a UAV in the vicinity of OHTLs, realistic full-scale experimental tests are done. Non-linearity in breakdown effects renders small-scale testing and computational work inaccurate. Experimental work is used to describe the close-up approach distances for worst-case scenarios. Testing cannot provide a full solution due to the limitation of the equipment available. Further tests must therefore be done at a specialised facility. Experiments are run in two phases, namely non-linear and linear tests in the High Voltage (HV) laboratory. The non-linear tests are done to derive Minimum Approach Distances (MAD). The linear experiments are used to calibrate FEKO, the simulation tool, to the measurement environment. Once correlation between the linear test data and the simulated data is found, confidence is derived in both the simulation model and the test setup. The simulations can then be used to determine a geometric factor as an input into F. Rizk’s prediction equations. The Rizk equations are used to describe the safe-fly zones alongside OHTLs as an addition to the non-linear experimental work. Along with the standard’s suggestions, the Rizk predictions are formulated in such a way that line-specific solutions can be determined. The suggested clearance values are provided in terms of per unit values, which can be selected in accordance with historical line data. Power line sparking is investigated to better understand the line radiation phenomenon. This understanding could assist in the line inspection process, as well as in the layout of power lines near radio quiet areas. Knowledge of OHTL radiation patterns can aid in the location of corona and sparking sources in the inspection process. Aerial sparking measurements are taken using a UAV carrying a spectrum analyser. Measured sparking levels are used to verify a Computational Electromagnetic (CEM) model. The CEM model can then be used to further investigate OHTL radiation characteristics. / AFRIKAANSE OPSOMMING: Die aanwending van Onbemande Vliegtuie (UAVs) vir kraglyn inspeksies, vereis die definiëring van veilige vlieg sones. Oorspannings (TOVs) op oorhoofse kraglyne (OHTLs) kan hierdie vliegtuie in gevaar stel as hulle die grense van hierdie sones oorskry. Om die veilige vlieg sones van 'n UAV in die omgewing van OHTLs te bepaal, is realistiese volskaalse toetse gedoen. Die nie-lineariteit in afbreek effekte lewer onakkurate kleinskaal toetse en rekenaar werk. Eksperimentele werk word gebruik om die benaderde afstande vir die ergste geval te beskryf. Hierdie werk kan nie 'n volledige oplossing gee nie as gevolg van ‘n beperking op huidige toerusting. Dit beteken dat verdere toetse, by ‘n meer gespesialiseerde fasiliteit, gedoen moet word. Eksperimente is uitgevoer in twee fases: nie-lineêre en lineêre toetse in die Hoogspannings (HV) laboratorium. Die nie-lineêre toetse word gedoen om die kleinste-benaderde-afstand (MAD) af te lei en die lineêre eksperimente word gebruik om FEKO (‘n numeriese elektromagnetika simulasie program) met die metings omgewing te kalibreer. Sodra daar ‘n korrelasie tussen die lineêre data en die gesimuleerde data is, kan daar aangeneem word dat die simulasie model en die toets-opstelling betroubaar is. Die simulasies kan dan gebruik word om 'n meetkundige faktor te bepaal as 'n bydrae tot F. Rizk se voorspellings vergelykings. Die Rizk vergelykings word gebruik om die veilige vlieg sones langs die OHTLs te beskryf. Dit kan dus gebruik word as ‘n toevoeging tot die nie-lineêre eksperimentele werk. Saam met die normale meet standaard voorstellings, is die Rizk voorspellings geformuleer sodat dit die lyn spesifieke oplossings kan bepaal. Die voorgestelde verklarings waardes word in per eenheid waardes beskryf, wat dan gekies kan word met ooreenstemmende historiese lyn data. Kraglyn-vonke word ondersoek om die lyn-bestraling verskynsel beter te verstaan. Hierdie begrip kan in die lyn inspeksie proses en in die uitleg van kraglyne naby radiostilte-areas help. Kennis van OHTL bestralings patrone kan help met die identifisering van corona en vonk-bronne tydens die inspeksie proses. 'n UAV met 'n aangehegte spektrum analiseerder is gebruik om die lug-vonkende metings te neem. Vonk vlakke wat gemeet is word dan gebruik om 'n Numeriese Elektromagnetiese (CEM) model te bevestig. Die CEM model kan dan gebruik word om OHTL bestralings eienskappe verder te ondersoek.

Thesis (MA)--Stellenbosch University, 2004. / ENGLISH ABSTRACT: This study addresses the problem of Blue Crane (Anthropoides paradiseus) collisions with power lines in the Overberg region, home to approximately 50% of South Africa's national bird's global population. The low visibility of power lines against the landscape is considered to be the major cause of collisions. These claim at least 20 birds annually, which is a considerable loss to a vulnerable species. For this study, expert knowledge of the Blue Cranes' biology, general behaviour and use of its habitat were compiled. These were then translated into rules that were integrated into a Geographic Information System (GIS) to establish a predictive model, which attempts to identify and quantify risk power lines that Blue Cranes are most likely to collide with. The criteria that were considered included landscape proximity of power lines to water bodies arid congregation sites, land cover, power lines orientation in relation to predominant wind directions (North Westerly and South Easterly) and visibility of the power lines against the landscape. The power lines were ranked as highest, high, medium, low and no risk. It is recommended that this classification be used to prioritize the proactive marking of power lines with bird flappers in order to reduce collisions. The results show that 27% of the power lines in the study area pose the highest risk and should therefore be marked immediately. The power lines classified as high (1%), medium (28%) and low risk (21 %) should be marked over short, medium and long term, respectively .. The study demonstrated the potential of GIS in the conservation of Blue Crane. The GIS model developed in this study can be applied in areas of similar habitat such as the Swartland or with some modifications in a slightly different habitat such as the Karoo. It is envisaged that the results of this study will be of great value to the ESKOM (South African Electricity Commission) and Endangered Wildlife Trust (EWT) Partnership and conservation authorities in the effort to save the Blue Crane. / AFRIKAANSE OPSOMMING: Hierdie studie het die probleem van botsings deur Bloukraanvoëls met kraglyne in die Overberg-omgewing van die Wes-Kaap ondersoek. Die Overberg-omgewing huisves ongeveer 50% van Suid Afrikaanse nasionale voël se wêreldbevolking van Bloukraanvoëls, en aangesien kraglyne normaalweg nie maklik sigbaar is teen die landskapsagtergrond nie, verhoog dit, tesame met die biologiese eienskappe van Bloukraanvoëls, die waarskynlikheid dat die voëls met kraglyne sal bots. Hierdie botsings met kraglyne eis minstens 20 Bloukraanvoëls per jaar, wat 'n aansienlike en beduidende aantal vir 'n kritiese bedreigde spesie is. Die studie het gepoog om spesialiskennis oor Bloukraanvoël-biologie, algemene gedrag en habitatgebruik, om te sit in 'n stel reëls, wat in 'n Geografiese Inligtingstelsel (GIS) geïntegreer is om 'n voorspellingsmodel te bou. Hierdie voorspellingsmodel is aangewend om kraglyne wat 'n hoë risiko vir Bloukraanvoëls inhou, te identifiseer en die waarskynlikheid vir botsings te kwantifiseer. Die model aanvaar dat die volgende omgewingsfaktore in die Overberg-omgewing verband hou met die waarskynlikheid van botsings, naamlik: die nabyheid van kraglyne aan waterliggame of gebiede waar voëls saamtrek, die voorkoms van natuurlike veld, die heersende windrigtings (Noordwes en Noordoos) en lae sigbaarheid van kraglyne teen die donker landskapsagtergrond. Die geïdentifiseerde kraglyne is as eerste-, tweede, derde. en vierderangse prioriteit geprioritiseer om as riglyn te dien vir die proaktiewe aanbring van flappers (wat dit ten doel het om voëlbotsings te verminder) deur ESKOM. Die studie het bevind dat 27% van die kraglyne in die Overberg-omgewing eersterang prioriteite is, en dat hierdie kraglyne onmiddellik gemerk sal moet word. Die tweederang prioriteit kraglyne (1%) saloor die mediumtermyn gemerk word, terwyl die derderangse prioriteit kraglyne (28%) oor die langtermyn gemerk sal word. Die vierde prioriteit kraglyne (21 %) kon oor die langertermyn gemerk word. Die studie het die omvang van die probleem, sowel as die rol van GIS in die bewaring van die Bloukraanvoëls beklemtoon. Die GIS-model wat in die studie ontwikkel en gebruik is, kan in soortgelyke gebiede soos die Swartland, of in ietwat verskillende omgewings soos die Karoo getoets word, met die doelom die habitatvoorkeure van Bloukraanvoëls beter te verstaan en navorsers te help om 'n beter begrip van die model te ontwikkel en sodoende die resultate te verbeter. Dit word voorsien dat hierdie studie en verslag baie belangrik sal wees vir die ESKOM-EWT Vennootskap en ander betrokke bewaringsorganisasies in 'n poging om Bloukraanvoël-bewaring aan te help.

The purpose of this work was investigate and measure the possibility to exist multipath caused by the corona noise generated in high voltage electric lines recepting GNSS signals. Experiments were realized with a 69 kV tension electric line localized in Santa Maria/RS. A serie was located with eleven transversal points to the longitudinal ranging of the transmission line. In this points, the eletromagnetic field was estimated using an equipment to measure the electromagnetic field EM-8000 model. Valuations was realized about the interferences on positioning by the absolut method, using a GNSS receiver with C/A code Garmin GPS II Plus model and the positioning by the relative method with the GNSS receiver L1/L2 Topcon Hiper model. To estimate the interference in the points was necessary to obtain the geodesic coordinates of this points without multipath possibilities caused of corona noise. For this was implanted a squared topographical polygonal where the support points were located far from the transmission lines, free of the electromagnetic field influence. Calculating the variances among the coordinates was necessary transform the geodesic coordinates obtained at GNSS receivers to the Local Topographic System, to make the systems compatible, using the rotation and translation model. Calculating was possible conclude that to the raising method and the geodesic equipment used in this experiment, in a 69 kV transmission line, the found discrepancies were in the standard deviation of 17,10 mm admitted to equipment GNSS receiver L1/L2 and 15 mm to GNSS receiver C/A code, in a 95% confidence level. So it was not evidenced interferences in the electromagnetic field at GNSS signal reception. / O propósito deste trabalho foi investigar e mensurar a possibilidade de haver multicaminhamento pelo efeito corona gerado em linhas elétricas de alta tensão na recepção de sinais GNSS. Foram realizados experimentos em uma rede elétrica com tensão de 69 kV localizado no município de Santa Maria/RS. Foi implantada uma série de onze pontos transversais ao alinhamento longitudinal da linha de transmissão. Nestes pontos realizou-se uma avaliação do campo eletromagnético gerado utilizando um equipamento medidor de campo eletromagnético modelo EM- 8000. Foram realizadas avaliações da interferência no posicionamento pelo método absoluto utilizando o receptor GNSS de código C/A Garmin modelo GPS II Plus e o posicionamento pelo método relativo com o receptor GNSS portadora L1/L2 Topcon modelo Hiper. Para avaliar a interferência dos pontos foi necessário obter as coordenadas geodésicas desses pontos sem possibilidades de multicaminhamento pelo efeito corona. Para isto implantou-se uma poligonal topográfica enquadrada em que os marcos de apoio localizavam-se distantes a linha de transmissão sem a influência do campo eletromagnético. Ao realizar o cálculo das discrepâncias entre as coordenadas foi necessário realizar a transformação das coordenadas geodésicas obtidas pelos receptores GNSS para o Sistema Topográfico Local para a compatibilização dos sistemas, sendo utilizado o modelo das rotações e translações. Realizando os cálculos concluiu-se que para os métodos de levantamento e os equipamentos geodésicos utilizados neste experimento, em uma linha de transmissão de 69 kV, as discrepâncias constatadas ficaram dentro do desviospadrões de 17,10 mm admitido ao equipamento receptor GNSS portadora L1/L2 e 15 m ao receptor GNSS código C/A, a nível de confiança de 95%. Assim não se constatou interferências do campo eletromagnético na recepção dos sinais GNSS.

Orientadores: André Franceshi de Angelis, José Geraldo Pena de Andrade / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Tecnologia / Made available in DSpace on 2018-08-24T15:13:51Z (GMT). No. of bitstreams: 1 Paiva_WilliamRobertode_M.pdf: 3222455 bytes, checksum: 4ba3e5407135ec1d8483e94ec4c11749 (MD5) Previous issue date: 2014 / Resumo: Neste trabalho, propõe-se a avaliação de quatro métodos que possam melhorar a resiliência de redes de alta tensão através da adição de linhas de transmissão, utilizando-se a Teoria das Redes Complexas. Criou-se um modelo da rede brasileira de geração e transmissão de energia elétrica em forma de grafo para testar os métodos. O primeiro deles consiste em ligar pares de vértices que possuam menor grau em toda a rede. O segundo liga os vértices de menor betweenness. O terceiro efetua ligações entre pares de vértices de menor grau que estejam ligados aos vértices de maior carga em toda a rede. O último, faz ligações entre os dois vértices de betweenness mediano. Todos os métodos foram testados com e sem o auxílio do procedimento "min-cut", capaz de identificar as arestas que, ao serem removidas, dividem a rede em duas sub-redes, permitindo assim efetuar ligações que reduzam o risco dessa divisão. Além dos testes no modelo da rede brasileira, utilizaram-se também 1000 redes Scale-Free e 1000 aleatórias para verificar o aumento de eficiência trazidos. Todos os métodos foram capazes de aumentar a eficiência, tanto no modelo da rede real quanto nos modelos artificiais. A estratégia de ligar os vértices de betweenness mediano com auxílio do min-cut trouxe o maior aumento. A resiliência da rede, diante de falhas planejadas e falhas aleatórias, foi aumentada em poucos casos, porém, em nenhum houve redução da mesma. Conclui-se que as estratégias propostas podem ser utilizadas para melhorar a eficiência de redes de alta tensão, mantendo ou aumentando sua resiliência, bem como podem ser usadas para trazer os mesmos atributos para redes complexas em geral / Abstract: In this work we purpose to assess four methods to improve high-voltage networks resilience against failures and attacks, using the Complex Network Theory to do it. To test these methods, we created a network model in graph format, based on the Brazilian generation and transmission electrical network. The first of these methods consist in to link pairs of nodes which have the lowest degree in the network. The second creates a link betweenn the lowest betweenness nodes. The third method is to link the two lowest degree nodes which are linked to the highest load nodes. The last one creates a link betweenn the two nodes which has the median betweenness. All methods were tested with and without the use of the "min-cut" procedure. This procedure finds the lowest number of necessary links that, when removed, divide the network in two sub-networks. It allows us to identify these links and reduce the risk of this partitioning the network by adding new links. We also test the strategies in 1000 artificial Scale-Free networks and 1000 artificial Random networks to validate those methods. All strategies were able to increase efficiency, in the real and artificial networks models. The strategy which links the median betweenness nodes using the "min-cut" procedure brought the best results. The network resilience against planned and random failures was increased in in few cases, but no decreases was registered. We conclude that our strategies can be used to improve high-voltage network efficiency, keeping or improving its resilience, as they can be used to bring the same attribute to any type of complex networks / Mestrado / Tecnologia e Inovação / Mestre em Tecnologia

Orientadores: José Pissolato Filho, Eduardo Coelho Marques da Costa / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação / Made available in DSpace on 2018-08-25T04:23:41Z (GMT). No. of bitstreams: 1 Monteiro_JoseHumbertoAraujo_D.pdf: 2599049 bytes, checksum: 247f68cef0523b44c3d1e9c69dc48119 (MD5) Previous issue date: 2014 / Resumo: Este trabalho apresenta o desenvolvimento de um modelo de linha de transmissão trifásica utilizando uma nova implementação do efeito pelicular, além do estudo da resposta transitória obtida a partir do referido modelo quando surtos de manobra são simulados. A metodologia tradicionalmente utilizada para o cálculo da impedância interna de cabos sólidos cilíndricos faz uso das funções de Bessel, o que a torna complexa. A metodologia descrita por Gatous é tão precisa quanto a metodologia que utiliza as funções de Bessel e possui a vantagem de ser mais simples, visto que a solução final é um somatório cuja precisão depende da frequência estudada. O modelo desenvolvido neste trabalho emprega a metodologia de Gatous em uma linha de transmissão trifásica, cujos modos de propagação independentes são obtidos a partir da aplicação da matriz de Clarke. Para validar a metodologia de Gatous, foram calculadas a resistência e a indutância interna de cabos com raios variados em uma ampla faixa de frequências. Os resultados foram comparados aos obtidos a partir da metodologia tradicional. A metodologia de Gatous reproduziu com precisão a variação da impedância interna com a frequência. Para avaliar o funcionamento do modelo de linha de transmissão trifásico no domínio do tempo, um caso base foi estabelecido. Uma linha de transmissão trifásica de 69kV, circuito simples, foi submetida a chaveamentos de carga em duas situações distintas: chaveamento sendo executado no ponto de cruzamento com o zero da tensão e; chaveamento no ponto de 90° da tensão. Os transitórios de tensão e corrente foram obtidos a partir do modelo elaborado e comparados com os resultantes do software de análise de transitórios ATP. Os resultados alcançados reproduzem com fidelidade o comportamento transiente descrito pelo software supracitado / Abstract: This paper presents the development of a three-phase transmission line model using a new skin effect calculation and its transient response when some switching surges are applied to it. The methodology commonly used to calculate the internal impedance of solid conductors with cylindrical cross sectional area employs Bessel functions, which makes it a hard task to accomplish. Gatous, in his doctoral work, presented a new method to calculate skin effect impedance as accurate as Bessel¿s methodology with advantage of simplicity, whereas that final solution is an algebraic sum whose precision depends of frequency studied. The transmission line model developed in this work utilizes Gatous¿s method for skin effect impedance calculation in a three-phase transmission line, whose independent modes of propagation are obtained from the application of Clarke's matrix. In order to validate the mentioned methodology, internal resistances and inductances of cables with different size radii were calculated for a wide range of frequencies. The results were compared with those obtained through the traditional method, reproducing correctly the variation of the internal impedance with frequency. A base case was established to evaluate the operation of the three-phase transmission line in the time-domain model. A 69kV three-phase transmission line, single circuit, was subjected to switching load in two distinct situations: switching at zero crossing voltage and switching at voltage peak. Voltage and current transients were obtained from the developed model and compared with those derived from transient analysis software ATP. The results faithfully reproduced the transient behavior described by the above software / Doutorado / Energia Eletrica / Doutor em Engenharia Elétrica

Orientadores: José Pissolato Filho, Pierre Kaufmann / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação / Made available in DSpace on 2018-08-23T01:41:59Z (GMT). No. of bitstreams: 1 Duro_MagdaAparecidaSalgueiro_D.pdf: 3861523 bytes, checksum: f5896319d2a3653a7903f977210f3ac1 (MD5) Previous issue date: 2013 / Resumo: A atual dependência da sociedade aos diversos sistemas tecnológicos em funcionamento na Terra traz uma constante preocupação pela sua vulnerabilidade a fatores menos conhecidos. As possíveis falhas no fornecimento de energia elétrica podem ocasionar transtornos de grande impacto às comunidades podendo acarretar perdas financeiras expressivas. Diversos fatores podem ocasionar falhas nas linhas de transmissão, entre eles, os fatores climáticos. Nesse contexto, são pouco conhecidas as influências qualitativas de distintos fatores, destacando-se os efeitos do denominado clima espacial. Há indicações que o clima espacial influencia a alta atmosfera terrestre, com repercussão no clima bem como em sistemas de engenharia em operação na Terra. As redes de transmissão de alta tensão representam um grande circuito elétrico pouco acima do solo sujeito a uma série de sobrecargas temporárias de vários tipos, algumas das quais podem levar a falhas. Algumas destas falhas podem estar relacionadas ao ambiente geofísico. Neste trabalho foi analisada uma base de dados sem precedentes de falhas em linhas de transmissão por um longo período (nove anos) numa grande malha localizada no Estado de São Paulo (sudeste do Brasil). O período estudado (1998-2006) compreende uma significativa fração do ciclo de atividade solar 23. A concessionária responsável (ISA.CTEEP) pela operação das linhas estudadas classifica as falhas em noventa e cinco tipos distintos de causas possíveis, sendo que a maior parte está relacionada às descargas atmosféricas. Este estudo está relacionado aos desligamentos devido às descargas atmosféricas, em duas redes de alta voltagem da companhia, de 138 kV e de 440 kV. No período estudado, estes desligamentos correspondem a 1.957 (42,80%) num total de 4.572 para a linha de 138 kV e de 170 (22,28%) sobre 763 para a linha de 440 kV. Equivale a menos de um a cada dez mil do número total de descargas atmosféricas ocorridas na mesma área, o que demonstra alta resiliência das redes de potência em relação aos raios. Durante a época das chuvas, há uma maior concentração de desligamentos. Para todo o período estudado houve redução de 67% e 77% no número de desligamentos devido às descargas atmosféricas, para as linhas de 138 kV e 440 kV, respectivamente, havendo uma boa correspondência com a redução do número de manchas solares. Nenhuma correlação foi encontrada em relação às atividades geomagnéticas caracterizadas pelo índice planetário (Kp) e pelas grandes tempestades (Dst) tanto em longos quanto em curtos prazos. Uma explicação sugerida associa a diminuição da atividade solar ao aumento da condutividade na atmosfera causada pelo maior fluxo de raios cósmicos. Consequentemente poderá ocorrer uma redução do limiar de voltagem necessário para produzir descargas atmosféricas para provocar desligamentos nas redes de alta voltagem. O circuito elétrico global descrito pelo acoplamento ionosfera-terra (a eletrosfera) exerce um papel importante para explicar a redução dos desligamentos. Com o aumento da condutividade atmosférica as descargas são menos potentes, resultando em menor número de desligamentos com o decréscimo do ciclo solar / Abstract: The current society dependence on the operating technological systems on the Earth brings a permanent concern for their vulnerability to not well known factors. Possible failures in electricity supply can cause inconveniences with large impact to the communities, which may cause significant financial losses. Different factors can cause failures in the transmission networks, including, climate factors. In this context, the influences of various qualitative factors, especially the effects of space weather are not well known. There are indications that space weather affects the upper atmosphere, with repercussions on the climate as well as in engineering systems in operation on Earth. High-voltage transmission networks represent large electrical circuits just above the ground which are subjected to a number of transient overcharges of various kinds, some of which may lead to failures. Some failures might be related to anomalies of the geophysical environment. In the present study we analyze a database consisting in a one unprecedented long series of transmission grid failures (nine years) on high-voltage networks located in São Paulo state (southeastern Brazil). The studied period (1998-2006) includes an important fraction of the solar activity cycle 23. The company responsible by the power grid operator (ISA.CTEEP) classifies causes in ninety-five distinct failure classes to explain the transmission grid shut downs. Most of the failures were attributed to atmospheric discharges. We have studied the failures attributed to atmospheric discharge, in the two power grids of the company, 138 kV and 440 kV. The failures attributed to atmospheric discharge correspond to 1.957 (42.80%) for a total 4.572 at 138 kV and to 170 (22.8%) out of 763 at 440 kV. They correspond to less than one ten thousandth of the actual number of atmospheric discharges recorded in the same area, demonstrating the grid's high resilience to breakdowns due to lightning. A clear concentration of failures in the region's thunderstorm season has been found. A significant 67% and 77% reduction in the number of failure rates has been found for the 138 and 440 kV grids, respectively, for the period studied, in good correspondence with the decay in the sunspot numbers. No obvious correlation was found between power failures and geomagnetic activity, represented by (Kp) the planetary index or major geomagnetic storms (Dst) in the period, either on short or on long time scales. One suggested explanation associates the decrease in solar activity to the increased conductivity in the atmosphere caused by increase cosmic ray flux. Consequently there may be a reduction in the threshold voltage necessary to produce discharge atmospheric to cause failures in high-voltage grids. The global electric circuit described by the ionosphere-ground coupling (the electrosphere), plays an important role in explaining the reduction the failures. With increase in conductivity atmospheric discharges are less potent, resulting in fewer failures with the decreasing solar cycle / Doutorado / Energia Eletrica / Doutor em Engenharia Elétrica

No description available.

Electric power systems are among the most complex man made systems on the world. Most of the time, they operate under quasi-steady state. With the ever increasing load demand and the advent of the deregulated power market recently, the power systems are pushed more often to operate close to their design limits and with more uncertainty of the system operating mode. With the increasing complexity and more interconnected systems, power systems are operating closer to their performance limits. As a result, maintaining system security and facilitating efficient system operation have been challenging tasks. Transmission systems are considered the most vital components in power systems connecting both generating/substation and consumer areas with several interconnected networks. In the past, they were owned by regulated, vertically integrated utility companies. They have been designed and operated so that conditions in close proximity to security boundaries are not frequently encountered. However, in the new open access environment, operating conditions tend to be much closer to security boundaries, as transmission use is increasing in sudden and unpredictable directions. Transmission unbundling, coupled with other regulatory requirements, has made new transmission facility construction more difficult. Unfortunately these transmission lines are frequently subjected to a wide variety of faults. Thus, providing proper protective functions for them is essential. Generally the protection of Extra High Voltage (EHV) and Ultra High Voltage (UHV) transmission lines are carried out by the use of distance relays in view of the fact that they provide fast fault clearance and system coordination. Transmission line relaying involves detection, classification and location of transmission line faults. Fast detections of faults enable quick isolation of the faulty line from service and hence, protecting it from the harmful effects of fault. Classification of faults means identification of the type of fault and faulted line section, and this information is required for finding the fault location and assessing the extent of repair work to be carried out. Accurate fault location is necessary for facilitating quick repair and restoration of the line, to improve the reliability and availability of the power supply. Generally, the protection system using conventional distance relaying algorithm involves three zones. The first zone (Z1) of the relay is set to detect faults on 80%90% of the protected line without any intentional time delay. The second zone (Z2) is set to protect the remainder of the line plus an adequate margin. Second zone relays are time delayed for 1530 cycles to coordinate with relays at remote bus. The settings of the third zone (Z3) ideally will cover the protected line, plus all of the longest line leaving the remote station. Z3 of a distance relay is used to provide the remote backup protection in case of the failure of the primary protection. Since Z3 covers an adjacent line, a large infeed (outfeed) from the remote terminal causes the relay to underreach (overreach). Thus, a very large load at the remote terminal may cause distance relays to mal-operate. Settings for conventional distance relays are selected to avoid overreach/underreach operation under the worst case scenarios. Studies of significant power system disturbances reported by North American Electric Reliability Council (NERC) indicate that protective relays are involved, one way or another, in 75% of the major disturbances and the most troublesome ones are backup protection relays. With their limited view of the interconnected network based on their locally measured inputs, conventional backup protection relays generally take actions to protect a localized region of the network without considering the impact on the whole network. Relay mal-operations or unintended operations due to overload, power swing, and relay hidden failure are the main factors contributing to the blackouts. Most of the problems are associated with relays tripping too many healthy lines. Since a relay makes the decision automatically to remove a component from the system according to its internal mechanism, the relay mal-operation or unintended operation can make an effective influence on the system stability. Approaches to reduce the relay misbehavior need to be identified. Real time monitoring tools to assess the relay misbehavior are needed, providing the system operator, the accurate information about unfolding events. Existing transmission line protection scheme still has drawbacks. Advanced fault analysis mechanism to enhance the system dependability and security simultaneously is desirable. Relay settings play a significant role in major blackouts. So correct settings should be calculated and coordinated by suitable studies. Attempts are to be made to employ highly accurate AI techniques in protective system implementation. The research work focussed on developing knowledge based intelligent tools for the improving the transmission system security. A process to obtain knowledgebase using SVMs for ready post-fault diagnosis purpose is developed. SVMs are used as Intelligent tool for identifying the faulted line that is emanating from a substation and finding the distance from the substation. The approach uses phasor values of the line voltages and currents after the fault has been detected. The approach is particularly important for post-fault diagnosis of any mal-operation of relays following a disturbance in the neighboring line connected to the same substation. This may help in improving the fault monitoring/diagnosis process and coordination of the protective relays, thus assuring secure operation of the power systems. The approach based on SVMs, exploits the first part of this goal. For comparison, a classifier and regression tools based on the RBFNNs was also investigated. The RBFNNs and SVM networks are introduced and considered as an appropriate tool for pattern recognition problems. Results on a practical 24Bus equivalent EHV transmission system of Indian Southern region and on IEEE39 bus New England system are presented to illustrate the proposed method. In a large connected power network, the number of generators are more in number and their set patterns number will be large. As the line flows are sensitive to generator set patterns, it is difficult to consider all the combinations of generators while simulating the training and testing patterns as input to SVMs. To simulate the training and testing patterns corresponding to possible changes in line flows to meet the load in the present deregulated environment, line flow sensitive generators set to be identified/merit-listed. In this regard, to identify the most sensitive generators for a particular line of interest, a method from the literature is adopted and developed a software program based on the graph theory concepts. Case studies on generator contributions towards loads and transmission lines are illustrated on an equivalent 33bus system, a part of Indian Northern grid with major part of Uttar Pradesh and also with an equivalent 246bus system of practical Indian Southern grid. A distance relay coordination approach is proposed using detailed simulation studies, taking into account various operating conditions and fault resistances. Support Vector Machines as a pattern classifier is used for obtaining distance relay coordination. The scheme uses the apparent impedance values observed during fault as inputs. SVMs are used to build the underlying concept between reach of different zones and the impedance trajectory during fault. An improved performance with the use of SVMs, keeping the reach when faced with different fault conditions as well as line flow changes are illustrated with an equivalent 246bus system of practical Indian Southern grid and also with an equivalent 265bus system of practical Indian Western grid. A strategy of Supportive System is described to aid the conventional protection philosophy in combating situations where protection systems are mal-operated and/or information is missing and provide selective and secure coordination. Highly accurate identification/discrimination of zones plays a key role in effective implementation of the region-wide supportive system. This typically requires a multiclass SVM classifier to effectively analyze/build the underlying concept between reach of different zones and the apparent impedance trajectory during fault. Different multiclass methods are compared for their performance with respect to accuracy, number of iterations, number of support vectors, training and testing time. The performance analysis of these methods is presented on three data sets belonging to the training and testing patterns of three supportive systems for a region, part of a network, which is an equivalent 265bus system of practical Indian Western grid.

Over the last several decades, electricity consumption and generation have continually grown. Investment in the Transmission and Distribution (T&D) infrastructure has been minimal and it has become increasingly difficult and expensive to permit and build new power lines. At the same time, a growing increase in the penetration of renewable energy resources is causing an unprecedented level of dynamics on the grid. Consequently, the power grid is congested and under stress. To compound the situation, the utilities do not possess detailed information on the status and operating margins on their assets in order to use them optimally. The task of monitoring asset status and optimizing asset utilization for the electric power industry seems particularly challenging, given millions of assets and hundreds of thousands of miles of power lines distributed geographically over millions of square miles. The lack of situational awareness compromises system reliability, and raises the possibility of power outages and even cascading blackouts. To address this problem, a conceptual Power Line Sensor Network (PLSN) is proposed in this research. The main objective of this research is to develop a distributed PLSN to provide continuous on-line monitoring of the geographically dispersed power grid by using hundreds of thousands of low-cost, autonomous, smart, and communication-enabled Power Line Sensor (PLS) modules thus to improve the utilization and reliability of the existing power system. The proposed PLSN specifically targets the use of passive sensing techniques, focusing on monitoring the real-time dynamic capacity of a specific span of a power line under present weather conditions by using computational intelligence technologies. An ancillary function is to detect the presence of incipient failures along overhead power lines via monitoring and characterizing the electromagnetic fields around overhead conductors. This research integrates detailed modeling of the power lines and the physical manifestations of the parameters being sensed, with pattern recognition technologies. Key issues of this research also include design of a prototype PLS module with integrated sensing, power and communication functions, and validation of the Wireless Sensor Network (WSN) technology integrated to this proposed PLSN.