Resumo: Com a necessidade de atender com qualidade a crescente demanda por energia eletrica, com poucas interrupcoes e com níıveis de tensao satisfatorios, e tendo em vista as restricoes ambientais existentes, que dificultam a implantacao de novos recursos aos sistemas de transmissao, como linhas, usinas, subestacoes, etc., as empresas de transmissao tem buscado otimizar os recursos existentes, operando os sistemas com menos folga o que, em alguns casos, pode ocasionar pequenas sobrecargas nas linhas. Nas estruturas atuais de operacao, acoes corretivas usualmente aplicadas ao alıvio dos sistemas de transmissao, como alteracoes nos nıveis de geracao e corte de cargas, fazem parte das atribuicoes do operador do sistema e estao fora do escopo de acao das empresas transmissoras que podem, contudo, alterar as condicoes de operacao de seus dispositivos, como transformadores, compensadores, etc. Neste trabalho e apresentada uma proposta para o alıvio de pequenas sobrecargas em redes de transmissao com base no controle do fluxo reativo das linhas. As acoes corretivas sao determinadas com base na linearizacao dos parametros do sistema em torno de seu ponto de operacao inicial, solucionando-se um problema de programacao linear (PL) cuja funcao objetivo a ser minimizada e o produto entre o custo dos servicos de suporte de reativos prestados pelos dispositivos e o desvio do sistema de seu ponto de operacao inicial. Haja vista a grande quantidade de dispositivos instalados no sistema que podem fornecer servicos de suporte de reativos e que problemas relativos a potencia reativa sao solucionados localmente, e possıvel reduzir a quantidade de dispositivos "candidatos" a realizacao das acoes corretivas e, consequentemente, o numero de variaveis e restricoes no PL a ser solucionado... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The growing demand for electric power associated with the environmental limitations imposed to the expansion of power systems hamper the installation of new facilities, such as transmission lines, substations and power plants, and leads the transmission companies to optimize the existing resources. In consequence, transmission systems operate closer to their boundaries and small overloads may surge. In the deregulated operating environment, the standard overload relief procedures, based on generation redispatch and load shedding, are in charge of the system operator and cannot be performed by the transmission companies, which can, otherwise, modify the control parameters of the transmission system devices, such as transformers, shunt compensators, etc. An overload relief procedure based on reactive power control applicable to small disturbances is presented in this paper. The corrective actions are determined by linearizing the system parameters around the initial operating point and solving a linear problem (LP), that minimizes the product between the total cost of the reactive power support provided by the devices and the deviation of the system from its initial operating point. Considering that reactive sources are spread over the whole system and the solution for reactive power problems can be found locally, the set of devices to be applied for the corrective actions can be reduced and, consequently, the number of variables and constraints to be added to the LP problem. To accomplish that, linear sensitivity factors which relate the reactive flow variation in the overloaded line to the devices' control parameters are applied and the "n" most effective devices to mitigate the overloads can be determined. In many market structures reactive power support is a mandatory service and, in some cases, it is not remunerated. However, despite the low cost of production of reactive power... (Complete abstract click electronic access below) / Orientador: Antonio Padilha Feltrin / Coorientador: Javier Contreras Sanz / Banca: Percival Bueno Araújo / Banca: Dilson Amancio Alves / Banca: Eduardo Nobuhiro Asada / Banca: Madson Cortes de Almeida / Doutor

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.

Abstract The goal of this research is to advance the state of the art in bulk power system reliability assessment. Bulk power system reliability assessment is an important procedure at both power system planning and operating stages to assure reliable and acceptable electricity service to customers. With the increase in the complexity of modern power systems and advances in the power industry toward restructuring, the system models and algorithms of traditional reliability assessment techniques are becoming obsolete as they suffer from nonrealistic system models and slow convergence (even non-convergence) when multi-level contingencies are considered and the system is overstressed. To allow more rigor in system modeling and higher computational efficiency in reliability evaluation procedures, this research proposes an analytically-based security-constrained adequacy evaluation (SCAE) methodology that performs bulk power system reliability assessment. The SCAE methodology adopts a single-phase quadratized power flow (SPQPF) model as a basis and encompasses three main steps: (1) critical contingency selection, (2) effects analysis, and (3) reliability index computations. In the critical contingency selection, an improved contingency selection method is developed using a wind-chime contingency enumeration scheme and a performance index approach based on the system state linearization technique, which can rank critical contingencies with high accuracy and efficiency. In the effects analysis for selected critical contingencies, a non-divergent optimal quadratized power flow (NDOQPF) algorithm is developed to (1) incorporate major system operating practices, security constraints, and remedial actions in a constrained optimization problem and (2) guarantee convergence and provide a solution under all conditions. This algorithm is also capable of efficiently solving the ISO/RTO operational mode in deregulated power systems. Based on the results of the effects analysis, reliability indices that provide a quantitative indication of the system reliability level are computed. In addition, this research extends the proposed SCAE framework to include the effects of protection system hidden failures on bulk power system reliability. The overall SCAE methodology is implemented and applied to IEEE reliability test systems, and evaluation results demonstrate the expected features of proposed advanced techniques. Finally, the contributions of this research are summarized and recommendations for future research are proposed.

Electric power distribution network is an important part of electrical power systems for delivering electricity to consumers. Electric power utilities worldwide are increasingly adopting the computer aided monitoring, control and management of electric power distribution systems to provide better services to the electrical consumers. Therefore, research and development activities worldwide are being carried out to automate the electric power distribution system. The power distribution system consists of a three-phase source supplying power through single-, two-, or three-phase distribution lines, switches, and transformers to a set of buses with a given load demand. In addition, unlike transmission systems, single-, two-, and three-phase sections exist in the network and single-, two-, and three-phase loads exist in the distribution networks. Further, most distribution systems are overhead systems, which are susceptible to faults caused by a variety of situations such as adverse weather conditions, equipment failure, traffic accidents, etc. When a fault occurs on a distribution line, it is very important for the utility to identify the fault location as quickly as possible for improving the service reliability. Hence, one of the crucial blocks in the operation of distribution system is that of fault detection and it’s location. The achievement of this objective depends on the success of the distribution automation system. The distribution automation system should be implemented quickly and accurately in order to isolate those affected branches from the healthy parts and to take alternative measures to restore normal power supply. Fault location in the distribution system is a difficult task due to its high complexity and difficulty caused by unique characteristics of the distribution system. These unique characteristics are discussed in the present work. In recent years, some techniques have been discussed for the location of faults, particularly in radial distribution systems. These methods use various algorithmic approaches, where the fault location is iteratively calculated by updating the fault current. Heuristic and Expert System approaches for locating fault in distribution system are also proposed which uses more measurements. Measurements are assumed to be available at the sending end of the faulty line segment, which are not true in reality as the measurements are only available at the substation and at limited nodes of the distribution networks through the use of remote terminal units. The emerging techniques of Artificial Intelligence (AI) can be a solution to this problem. Among the various AI based techniques like Expert systems, Fuzzy Set and ANN systems, the ANN approach for fault location is found to be encouraging. In this thesis, an ANN approaches with limited measurements are used to locate fault in long distribution networks with laterals. Initially the distribution system modeling (using actual a-b-c phase representation) for three-, two-, and single-phase laterals, three-, two-, and single- phase loads are described. Also an efficient three-phase load flow and short circuit analysis with loads are described which is used to simulate all types of fault conditions on distribution systems. In this work, function approximation (FA) is the main technique used and the classification techniques take a major supportive role to the FA problem. Fault location in distribution systems is explained as a FA problem, which is difficult to solve due to the various practical constraints particular to distribution systems. Incorporating classification techniques reduce this FA problem to simpler ones. The function that is approximated is the relation between the three-phase voltage and current measurements at the substation and at selected number of buses (inputs), and the line impedance of the fault points from the substation (outputs). This function is approximated by feed forward neural network (FFNN). Similarly for solving the classification problems such as fault type classification and source short circuit level classification, Radial Basis Probabilistic Neural Network (RBPNN) has been employed. The work presented in this thesis is the combinational use of FFNN and RBPNN for estimating the fault location. Levenberg Marquardt learning method, which is robust and fast, is used for training FFNN. A typical unbalanced 11-node test system, an IEEE 34 nodes test system and a practical 69- bus long distribution systems with different configurations are considered for the study. The results show that the proposed approaches of fault location gives accurate results in terms of estimated fault location. Practical situations in distribution systems such as unbalanced loading, three-, two-, and single- phase laterals, limited measurements available, all types of faults, a wide range of varying source short circuit levels, varying loading conditions, long feeders with multiple laterals and different network configurations are considered for the study. The result shows the feasibility of applying the proposed method in practical distribution system fault diagnosis.

This research investigates how to draw energy from a distant emanating and alternating (i.e., AC) magnetic source and deliver it to a battery (i.e., DC). The objective is to develop, design, simulate, build, test, and evaluate a CMOS charger integrated circuit (IC) that wirelessly charges the battery of a microsystem. A fundamental challenge here is that a tiny receiver coil only produces mV's of AC voltage, which is difficult to convert into DC form. Although LC-boosted diode-bridge rectifiers in the literature today extract energy from similar AC sources, they can do so only when AC voltages are higher than what miniaturized coils can produce, unless tuned off-chip capacitors are available, which counters the aim of integration. Therefore, rather than rectify the AC voltage, this research proposes to rectify the current that the AC voltage induces in the coil. This way, the system can still draw power from voltages that fall below the inherent threshold limit of diode-bridge rectifiers. Still, output power is low because, with these low currents, small coils can only extract a diminutive fraction of the magnetic energy available, which is why investing battery energy is also part of this research. Ultimately, the significance of increasing the power that miniaturized platforms can output is higher integration and functionality of micro-devices, like wireless microsensors and biomedical implants.

La calidad de energía eléctrica incluye la calidad del suministro y la calidad de la atención al cliente. La calidad del suministro a su vez se considera que la conforman dos partes, la forma de onda y la continuidad. En esta tesis se aborda la continuidad del suministro a través de la localización de faltas. Este problema se encuentra relativamente resuelto en los sistemas de transmisión, donde por las características homogéneas de la línea, la medición en ambos terminales y la disponibilidad de diversos equipos, se puede localizar el sitio de falta con una precisión relativamente alta. En sistemas de distribución, sin embargo, la localización de faltas es un problema complejo y aún no resuelto. La complejidad es debida principalmente a la presencia de conductores no homogéneos, cargas intermedias, derivaciones laterales y desbalances en el sistema y la carga. Además, normalmente, en estos sistemas sólo se cuenta con medidas en la subestación, y un modelo simplificado del circuito. Los principales esfuerzos en la localización han estado orientados al desarrollo de métodos que utilicen el fundamental de la tensión y de la corriente en la subestación, para estimar la reactancia hasta la falta. Como la obtención de la reactancia permite cuantificar la distancia al sitio de falta a partir del uso del modelo, el Método se considera Basado en el Modelo (MBM). Sin embargo, algunas de sus desventajas están asociadas a la necesidad de un buen modelo del sistema y a la posibilidad de localizar varios sitios donde puede haber ocurrido la falta, esto es, se puede presentar múltiple estimación del sitio de falta.Como aporte, en esta tesis se presenta un análisis y prueba comparativa entre varios de los MBM frecuentemente referenciados. Adicionalmente se complementa la solución con métodos que utilizan otro tipo de información, como la obtenida de las bases históricas de faltas con registros de tensión y corriente medidos en la subestación (no se limita solamente al fundamental). Como herramienta de extracción de información de estos registros, se utilizan y prueban dos técnicas de clasificación (LAMDA y SVM). Éstas relacionan las características obtenidas de la señal, con la zona bajo falta y se denominan en este documento como Métodos de Clasificación Basados en el Conocimiento (MCBC). La información que usan los MCBC se obtiene de los registros de tensión y de corriente medidos en la subestación de distribución, antes, durante y después de la falta. Los registros se procesan para obtener los siguientes descriptores: a) la magnitud de la variación de tensión ( dV ), b) la variación de la magnitud de corriente ( dI ), c) la variación de la potencia ( dS ), d) la reactancia de falta ( Xf ), e) la frecuencia del transitorio ( f ), y f) el valor propio máximo de la matriz de correlación de corrientes (Sv), cada uno de los cuales ha sido seleccionado por facilitar la localización de la falta. A partir de estos descriptores, se proponen diferentes conjuntos de entrenamiento y validación de los MCBC, y mediante una metodología que muestra la posibilidad de hallar relaciones entre estos conjuntos y las zonas en las cuales se presenta la falta, se seleccionan los de mejor comportamiento.Los resultados de aplicación, demuestran que con la combinación de los MCBC con los MBM, se puede reducir el problema de la múltiple estimación del sitio de falta. El MCBC determina la zona de falta, mientras que el MBM encuentra la distancia desde el punto de medida hasta la falta, la integración en un esquema híbrido toma las mejores características de cada método. En este documento, lo que se conoce como híbrido es la combinación de los MBM y los MCBC, de una forma complementaria. Finalmente y para comprobar los aportes de esta tesis, se propone y prueba un esquema de integración híbrida para localización de faltas en dos sistemas de distribución diferentes. Tanto los métodos que usan los parámetros del sistema y se fundamentan en la estimación de la impedancia (MBM), como aquellos que usan como información los descriptores y se fundamentan en técnicas de clasificación (MCBC), muestran su validez para resolver el problema de localización de faltas. Ambas metodologías propuestas tienen ventajas y desventajas, pero según la teoría de integración de métodos presentada, se alcanza una alta complementariedad, que permite la formulación de híbridos que mejoran los resultados, reduciendo o evitando el problema de la múltiple estimación de la falta. / Power quality includes the supply and customer support quality. The supply quality considers two aspects, the wave shape and continuity. In this thesis the fault location problem, topic related with supply continuity is considered. Fault location is a relatively solved problem in power transmission systems, due to the homogeneous characteristics of the power line, measurements in both terminals and also the availability equipment such as fault locators normally included in distance relays. However, in power distribution systems the fault location is a complex problem which remains unsolved. The complexity is mainly because the presence of laterals, load taps, non homogeneous conductors, unbalances in the system and load. In addition, these power systems only have measurements at the substation and a simplified model of the power network. The main efforts to solve this problem have been oriented to the development of impedance based methods. Because of the reactance estimation makes possible the estimation of the distance to the faulted node by using the circuit model, those methods are considered as Model Based Methods (MBM). However the main drawbacks are related to the requirement of a good system model and to the possibility of multiple estimation of the location of the fault due to the three-shape of such networks. As a result, in this thesis an analysis and a comparative test between several MBM frequently cited is presented. In addition, the solution of the fault location is complemented by using methods which use more than the rms values of current and voltage obtained from fault databases. As tool to relate this information with the fault location, two classification techniques are used and tested (LAMDA and SVM). These relate the voltage and current characteristics to the faulted zone and are denoted in this document as Classification Methods Based on the Knowledge (CMBK).The information used by CMBK is obtained from current and voltage fault registers measured at the distribution substation, before, during and after the fault. These registers are pre-processed to obtain the following characteristics or descriptors: a) The magnitude of the voltage variation between the steady states of fault and pre-fault ( dV ), b) the magnitude of the current variation between the steady states of fault and pre-fault ( dI ), c) the magnitude of the apparent power variation between the steady states of fault and pre-fault ( dS ), d) the magnitude of the reactance as seen from the substation ( Xf ), e) the frequency of the transient caused by the fault ( f ), and f) the maximum eigenvalue of the correlation matrix of the currents ( Sv ). By using these descriptors, several training and validation sets were used with CMBK and by means of a proposed methodology it is shown how to relate these sets with the faulted zone and also to select those which offer the best performances.The application results demonstrate how by combining the MBM with the CMBK it is possible to reduce the multiple estimation of the fault location. The CMBK is used to determine the faulted zone while the MBM finds the distance from the measurement point to the faulted node. Thus the integration in a hybrid approach uses the best characteristics of each method. In this document, the term hybrid is used to describe the complementary combination of MBM and CMBK. Finally and aimed to compare the thesis results, an integration hybrid scheme to fault location is proposed and tested in two different power distribution systems. Both, methods which use the system parameters and are based on the impedance estimation (MBM), and those which use the information represented by the signal descriptors and are based in classification techniques (CMBK) have shown the capability to solve the problem of fault location. The two proposed methodologies have advantages and drawbacks, but according to the integration theory presented, high complementarity has been reached. This makes possible the development of a hybrid approach used to avoid or reduces the multiple estimation of the fault location.

Made available in DSpace on 2014-06-11T19:30:50Z (GMT). No. of bitstreams: 0 Previous issue date: 2011-02-25Bitstream added on 2014-06-13T19:19:30Z : No. of bitstreams: 1 hoji_es_dr_ilha.pdf: 852924 bytes, checksum: 9b1bcf1d76e563dd1037dc628a5c3e2e (MD5) / Fundação de Ensino Pesquisa e Extensão de Ilha Solteira (FEPISA) / PROPG - Programa de Pós-Graduação / Com a necessidade de atender com qualidade a crescente demanda por energia eletrica, com poucas interrupcoes e com níıveis de tensao satisfatorios, e tendo em vista as restricoes ambientais existentes, que dificultam a implantacao de novos recursos aos sistemas de transmissao, como linhas, usinas, subestacoes, etc., as empresas de transmissao tem buscado otimizar os recursos existentes, operando os sistemas com menos folga o que, em alguns casos, pode ocasionar pequenas sobrecargas nas linhas. Nas estruturas atuais de operacao, acoes corretivas usualmente aplicadas ao alıvio dos sistemas de transmissao, como alteracoes nos nıveis de geracao e corte de cargas, fazem parte das atribuicoes do operador do sistema e estao fora do escopo de acao das empresas transmissoras que podem, contudo, alterar as condicoes de operacao de seus dispositivos, como transformadores, compensadores, etc. Neste trabalho e apresentada uma proposta para o alıvio de pequenas sobrecargas em redes de transmissao com base no controle do fluxo reativo das linhas. As acoes corretivas sao determinadas com base na linearizacao dos parametros do sistema em torno de seu ponto de operacao inicial, solucionando-se um problema de programacao linear (PL) cuja funcao objetivo a ser minimizada e o produto entre o custo dos servicos de suporte de reativos prestados pelos dispositivos e o desvio do sistema de seu ponto de operacao inicial. Haja vista a grande quantidade de dispositivos instalados no sistema que podem fornecer servicos de suporte de reativos e que problemas relativos a potencia reativa sao solucionados localmente, e possıvel reduzir a quantidade de dispositivos “candidatos” a realizacao das acoes corretivas e, consequentemente, o numero de variaveis e restricoes no PL a ser solucionado... / The growing demand for electric power associated with the environmental limitations imposed to the expansion of power systems hamper the installation of new facilities, such as transmission lines, substations and power plants, and leads the transmission companies to optimize the existing resources. In consequence, transmission systems operate closer to their boundaries and small overloads may surge. In the deregulated operating environment, the standard overload relief procedures, based on generation redispatch and load shedding, are in charge of the system operator and cannot be performed by the transmission companies, which can, otherwise, modify the control parameters of the transmission system devices, such as transformers, shunt compensators, etc. An overload relief procedure based on reactive power control applicable to small disturbances is presented in this paper. The corrective actions are determined by linearizing the system parameters around the initial operating point and solving a linear problem (LP), that minimizes the product between the total cost of the reactive power support provided by the devices and the deviation of the system from its initial operating point. Considering that reactive sources are spread over the whole system and the solution for reactive power problems can be found locally, the set of devices to be applied for the corrective actions can be reduced and, consequently, the number of variables and constraints to be added to the LP problem. To accomplish that, linear sensitivity factors which relate the reactive flow variation in the overloaded line to the devices’ control parameters are applied and the “n” most effective devices to mitigate the overloads can be determined. In many market structures reactive power support is a mandatory service and, in some cases, it is not remunerated. However, despite the low cost of production of reactive power... (Complete abstract click electronic access below)

This dissertation deals with the challenge of power utility in South Africa which is on proactive detection of fallen power line conductors and real time sagging measurement together with slipping of such conductors. Various methods which are currently used for sag detection were characterized and evaluated to the aim of the research. A mathematical reconstruction done to estimate the lowest point of the conductor in a span is presented. Practical simulations and application of radio frequency identification (RFID) for sag detection is attempted through matlab software. RFID radar system is then analyzed in different modes and found to give precision measurement for sag in real time as opposed to global positioning system (GPS) if one dimension of the tag assumed fixed on the power line. Lastly errors detected on the measurements are corrected using a trainable artificial neural network. A conclusion is made by making recommendations in the advancement of the research. / Electrical Engineering / M. Tech. (Electrical Engineering)

A construção de linhas de transmissão são obras de grande impacto ambiental e requerem grandes investimentos financeiros. Este projeto de pesquisa, visa por meio de ensaios de laboratório, conceber uma ferramenta sistêmica para o aperfeiçoamento do método de determinação da fluência em cabos condutores de energia e OPGW (Optical Ground Wire), que tem sido utilizada no Brasil durante os últimos 30 anos, e analisar os efeitos na construção das linhas aéreas de transmissão. Visa também, proporcionar ganhos de confiabilidade ao sistema de transmissão de energia elétrica, pois o projeto, a construção, a operação e a manutenção de linhas de transmissão dependem de parâmetros de desempenho mecânico dos condutores. Conclui–se que a metodologia de ensaio proposta proporciona resultados finais mais confiáveis quando comparado com o atual procedimento normatizado, utilizado no Brasil, e sua utilização em projetos de linhas aéreas de transmissão de energia podem reduzir custos de construção, aumentar a ampacidade das linhas já existentes, bem como, diminuir os riscos ao a que pessoas estão sujeitas quando expostas a campos elétricos e eletromagnéticos gerados por linhas de transmissão. / Overhead Transmission Line construction projects have a great environmental impact and require a large financial investment. This research aims, through laboratory tests, to improve the method of determining the creep of power cables and OPGW (Optical Ground Wire) that has been utilized in Brazil for the last thirty years, as well as analyze the effects on the construction of overhead transmission lines. It will provide greater reliability to the overhead transmission line system, since the design, construction, operation and maintenance of transmission lines depend on the mechanical performance of the conductors. In conclusion, the proposed methodology provides more reliable final results compared to the current standardized procedure and its use in overhead transmission line projects could reduce construction costs, increase the ampacity, as well as reduce the risks to which people are subject when exposed to electric and electromagnetic fields generated by power lines.

Thesis (MTech (Quality)--Cape Peninsula University of Technology, 2009 / There is a South African Government initiative to use State-owned Enterprises (SOE’s) to roll out a programme for the development and stimulation of local small businesses in South Africa. The state has requested SOE’s to set targets on a voluntary basis to increase trade with small businesses, with the purpose of developing small enterprises to eventually enhance skills transfer, training and employment. However, when large customers such as Eskom Nuclear Generation require ISO certification as a prerequisite for a supplier to provide goods and/or services to them, most small businesses are unable to comply. The requirement of ISO9000 compliance inhibits the ability of most small businesses to compete with their larger counterparts. Small businesses constitute as much as 90% of most world economies. They have many advantages to offer customers, such as a high level of flexibility, innovation and responsiveness to customer needs. These attributes can introduce healthy competition to the supply chain. Small businesses, by their very nature experience more risks, such as a higher vulnerability to volatile market forces and skills loss. In addition, they are generally less specialised. They are under continuous competitive pressure, and are generally not able to provide assurance of a sustainable product over a longer period. Although there is an imperative to develop and use small suppliers, they introduce higher risk to the supply chain. The primary research objective of this dissertation is to develop a robust model to identify risks inherent to small businesses, and to propose measures to mitigate such risks. A classification of problems with small suppliers that have occurred at Koeberg Nuclear Power Station over a period of 3 years (from June 2005 to May 2008), will form the basis of the research methodology. The anticipated findings of the research include the following. _ Several common critical issues of failure will be identified in the internal processes of small suppliers, with variations between types of suppliers, which will indicate which elements within the context of ISO9000 can be applied to address shortcoming in the suppliers’ processes. _ A matrix will be compiled from this by which the customer can identify the type of supplier, the types of risks inherent to that supplier, and which elements of ISO9000 the customer should insist upon to be adopted into an elementary quality management system of that small supplier. This should be executed as part of a larger supplier development programme.