The fast clearing of faults is essential for preventing equipment damage and preserving the stability of the power transmission systems with smaller operating margins. This thesis examined the application of fault generated transients for fast detection and isolation of faults in a transmission system. The basis of the transient based protection scheme developed and implemented in this thesis is the fault current directions identified by a set of relays located at different nodes of the system. The direction of the fault currents relative to a relay location is determined by comparing the signs of the wavelet coefficients of the currents measured in all branches connected to the node. The faulted segment can be identified by combining the fault directions identified at different locations in the system. In order to facilitate this, each relay is linked with the relays located at the adjacent nodes through a telecommunication network. In order to prevent possible malfunctioning of relays due to transients originating from non-fault related events, a transient recognition system to supervise the relays is proposed. The applicability of different classification methods to develop a reliable transient recognition system was examined. A Hidden Markov Model classifier that utilizes the energies associated with the wavelet coefficients of the measured currents as input features was selected as the most suitable solution. Performance of the protection scheme was evaluated using a high voltage transmission system simulated in PSCAD/EMTDC simulation software. The custom models required to simulate the complete protection scheme were implemented in PSCAD/EMTDC. The effects of various factors such as fault impedance, signal noise, fault inception angle and current transformer saturation were investigated. The performance of the protection scheme was also tested with the field recorded signals. Hardware prototypes of the fault direction identification scheme and the transient classification system were implemented and tested under different practical scenarios using input signals generated with a real-time waveform playback instrument. The test results presented in this thesis successfully demonstrate the potential of using transient signals embedded in currents for detection, localization and recognition of faults in transmission networks in a fast and reliable manner.

The fast clearing of faults is essential for preventing equipment damage and preserving the stability of the power transmission systems with smaller operating margins. This thesis examined the application of fault generated transients for fast detection and isolation of faults in a transmission system. The basis of the transient based protection scheme developed and implemented in this thesis is the fault current directions identified by a set of relays located at different nodes of the system. The direction of the fault currents relative to a relay location is determined by comparing the signs of the wavelet coefficients of the currents measured in all branches connected to the node. The faulted segment can be identified by combining the fault directions identified at different locations in the system. In order to facilitate this, each relay is linked with the relays located at the adjacent nodes through a telecommunication network. In order to prevent possible malfunctioning of relays due to transients originating from non-fault related events, a transient recognition system to supervise the relays is proposed. The applicability of different classification methods to develop a reliable transient recognition system was examined. A Hidden Markov Model classifier that utilizes the energies associated with the wavelet coefficients of the measured currents as input features was selected as the most suitable solution. Performance of the protection scheme was evaluated using a high voltage transmission system simulated in PSCAD/EMTDC simulation software. The custom models required to simulate the complete protection scheme were implemented in PSCAD/EMTDC. The effects of various factors such as fault impedance, signal noise, fault inception angle and current transformer saturation were investigated. The performance of the protection scheme was also tested with the field recorded signals. Hardware prototypes of the fault direction identification scheme and the transient classification system were implemented and tested under different practical scenarios using input signals generated with a real-time waveform playback instrument. The test results presented in this thesis successfully demonstrate the potential of using transient signals embedded in currents for detection, localization and recognition of faults in transmission networks in a fast and reliable manner.

abstract: This dissertation presents a new hybrid fault current limiter (FCL) topology that is primarily intended to protect single-phase power equipment. It can however be extended to protect three phase systems but would need three devices to protect each individual phase. In comparison against the existing fault current limiter technology, the salient fea-tures of the proposed topology are: a) provides variable impedance that provides a 50% reduction in prospective fault current; b) near instantaneous response time which is with-in the first half cycle (1-4 ms); c) the use of semiconductor switches as the commutating switch which produces reduced leakage current, reduced losses, improved reliability, and a faster switch time (ns-µs); d) zero losses in steady-state operation; e) use of a Neodym-ium (NdFeB) permanent magnet as the limiting impedance which reduces size, cost, weight, eliminates DC biasing and cooling costs; f) use of Pulse Width Modulation (PWM) to control the magnitude of the fault current to a user's desired level. g) experi-mental test system is developed and tested to prove the concepts of the proposed FCL. This dissertation presents the proposed topology and its working principle backed up with numerical verifications, simulation results, and hardware implementation results. Conclu-sions and future work are also presented. / Dissertation/Thesis / Ph.D. Electrical Engineering 2013

As the world strives towards finding alternative sources of power generation, photovoltaic generation has become an increasingly prevalent alternative energy source on power systems world-wide. This paper studies the effects that incorporating photovoltaic generation has on the existing power systems and their power system protection schemes. Along with the addition of this emerging alternative energy source comes the volatility of PV power generation as cloud-cover produces erratic variations in solar irradiance and PV power production. Such variations in PV power may lead to unfavorable operating conditions and power system failures. The issues addressed in this paper include a study of inverter harmonic levels for variations in DC voltage and power, and a study of power system protection failures caused by cloud-induced PV power variations. Such issues are addressed so as to provide a better understanding of the effects that cloud-induced PV power generation variability has on power systems and its protection schemes.

Wide-area disturbances are power outages occurring over large geographical regions that dramatically affect the power system reliability, causing interruptions of the electric supply to residential, commercial, and industrial users. Historically, wide-area disturbances have greatly affected societies. Virginia Tech directed a research project related to the causes of the major disturbances in electric power systems. Research results showed that the role of the power system's protection schemes in the wide-area disturbances is critical. Incorrect operations of power system's protection schemes have contributed to a spread of the disturbances. This research defined hidden failures of protection schemes and showed that these kinds of failures have contributed in the degradation of 70-80 percent of the wide-area disturbances. During a wide-area disturbance analysis, it was found that hidden failures in protection schemes caused the disconnection of power system elements in an incorrect and undesirable manner contributing to the disturbance degradation. This dissertation presents a methodology to assess and rank the effects of unwanted disconnections caused by hidden failures based on Regions of Vulnerability and index of severity in the protection schemes. The developed methodology for the evaluation of the Region of Vulnerability found that the indicator that most accurately reflects the relationship of the Region of Vulnerability with the single line diagram is kilometers. For the representation of the Region of Vulnerability in the power system, we found segments in the transmission line in which the occurrence of faults do make the relay to operate, producing the unwanted disconnection caused by hidden failure. The results in the test system show that the infeed currents restrain the Region of Vulnerability from spreading along power system elements. Finally the methodology to compute the index of severity is developed. The index of severity has the objective of ranking the protection schemes, considers the dynamics of the protection schemes, and evaluates the overall disturbance consequence under the static and dynamic perspectives. / Ph. D.

Este trabalho apresenta novas explorações do uso de sistemas agentes aplicados à proteção de sistemas elétricos de potência (SEP). Os sistemas agentes são definidos como softwares capazes de interagir com seu ambiente. Todos estudos apresentados focam o uso de agentes dentro de um SEP, através de uma rede privada de comunicação (intranet) baseada na tecnologia da internet. O objetivo final deste trabalho é o desenvolvimento de agentes que possam ser examinados em situações reais. Para facilitar esta tarefa, uma plataforma computacional foi desenvolvida denominada como EPOCHS (Electric Power and Communication Synchronizing Simulator). A principal função desta plataforma é permitir a integração dos agentes a um ambiente que combine simuladores que ofereçam informações sobre um SEP, assim como dados sobre uma rede intranet. Dentro deste contexto, um método para proteção primária e de retaguarda foi desenvolvido e testado dentro da plataforma EPOCHS. Os agentes desenvolvidos apresentaram resultados melhores que as técnicas tradicionais. Resultados ilustrando o desempenho e viabilidade deste sistema de proteção baseado em agentes são apresentados. / This work presents new explorations into the use of agent technology applied to the protection of power systems. We broadly define an agent to be an autonomous piece of software capable of interacting with its environment. Our investigation centers on the use of agents within an electric power grid using a private communication network, termed a utility intranet, based on internet technology. Our goal is to create practical agents that can be examined in realistic situations. To facilitate this aim, a new platform has been developed, EPOCHS, which allows agents to operate in an environmental that combines proven electric power electromagnetic and electromechanical transient simulators with a popular network communication simulation engine. We developed primary and a backup protection system using agent technology and evaluated this system within the EPOCHS environment. The agent-based system studied improved on traditional methods. Results illustrating the performance and viability of agent-based protection system are presented.

O objetivo do desenvolvimento deste trabalho é tecer uma análise da viabilidade técnica - econômica da modernização do sistema de Proteção da Distribuição, comparando a utilização dos relés digitais aos quais foram incorporadas novas funções, em relação aos relés eletromecânicos e estáticos. As informações apresentadas nesse trabalho mostram que os relés digitais oferecem uma significante economia quanto ao custo de aquisição e implantação, no desenvolvimento dos projetos de aplicação e na manutenção destes equipamentos após instalados em campo. Os relés eletromecânicos tem sido largamente utilizados nos esquemas de proteção de consumidores industriais e residencias de grande porte e nos sistemas de proteção das companhias de eletricidade. Devido a quantidade de peças móveis e freqüentes re-ajustes que estes tipos de equipamentos necessitam, os mesmos demandam muitas horas dispendidas pelo pessoal de calibração e manutenção das empresas de eletricidade. A realização de Estudos de Proteção, com a parametrização destes relés muitas vezes torna-se inviável, sob o ponto de vista de sensibilidade e da coordenação das proteções, devido ao fato de que estes equipamentos possuem ajustes limitados tanto de valores de corrente de partida como na seleção de curvas tempo x corrente utilizadas para temporização das proteções, no caso de relés eletromecânicos de sobrecorrente. Durante os últimos anos, com o advento da evolução da indústria, da micro eletrônica e do desenvolvimento de softwares, os relés digitais veêm substituíndo os relés eletromecânicos e estáticos, tanto em instalações novas como também nas remodelações das instalações mais antigas, nos sistemas elétricos de proteção industrial e de empresas de eletricidade. Realizou-se uma análise quanto ao histórico dos relés de proteção, mostrando o seu desenvolvimento desde os relés mais antigos, tipos eletromecânicos, após os relés estáticos, que foram a evolução dos anteriores e finalmente estudando os relés digitais. Os relés digitais oferecem muitas vantagens se comparados com os relés eletromecânicos e estáticos, as quais serão abordandos em items específicos da revisão de literatura neste trabalho. O trabalho é finalizado com uma análise de casos, onde foram computados e analisados casos, como índices de fornecimento, custos de instalação de relés digitais em substituição à relés e sistemas eletromecânicos e estáticos, utilizados convencionalmente para a proteção em alimentadores de Subestações da Copel - Companhia Paranaense de Energia, com o objetivo de coletar-se e analisar-se, ao longo de 12 meses as reais vantagens e desvantagens da utilização destes equipamentos nos sistemas elétricos de proteção dos circuitos de distribuição de energia. / The purpose of this study is to carry out a technical and economic feasibility assessment of the updating of the Distribution Protection system, comparing the use of digital relays, to which new functions have been integrated, with electromechanical and static relays. Information hereby presented shows that digital relays are significantly cost-effective in terms of acquisition and implementation for developing application projects and in maintaining that equipment after it has been set up in the field. Electromechanical relays have been largely used in protection schemes for large-scale industrial and residential consumers, as well as in security schemes for power plant companies. Because of the large number of moving parts and frequent readjustments required by that type of equipment, many manhours must be put in by calibration and maintenance staff employed by power plant companies. Carrying out a Protection Study that establishes parameters for those relays is often unfeasible given the sensitivity and coordination of the protections, in that the equipment in question has limited adjustments, both in terms of pick-up currents values and of the selection of time curve vs. current used in the protection timer, in the case of overcurrent electromechanical relays. During the last years, with the rise of industrial evolution, microelectronics and software development, digital relays are replacing electromechanical and static relays in electrical security systems used by industrial and power plant company protection, both in new facilities and in refurbished facilities. A study was carried out on the history of protection relays showing how they developed from the older, electromechanical type after the static relays, which evolved form the former, and was concluded with the study of digital relay models. Digital relays provide significant advantages compared to electromechanical and static relays, which will be covered under specific revision items of the references provided herein. The study is concluded by assessing case studies that were accounted for and assessed, such as supply rates, installation costs of digital relays to replace electromechanical and static systems used traditionally to provide protection for COPEL´s (Power Company of the State of Paraná) Substations. The purpose was to collect and analyze, over a 12-month period, the actual advantages and disadvantages of using that type of equipment in electrical systems that provide circuit protection for power distribution.

The increasing volume of renewable and intermittent generation that is being connected to power systems means that system operators need more advanced dynamic control tools to manage the increase in congestion and the resulting pressure on system constraints. The introduction of synchronised measurement technology provides the wide area real-time measurements that are essential to develop and implement adaptive online solutions for current network issues. The objective of the research presented in this thesis is to design intelligent system integrity protection schemes (SIPS) that protect transmission lines and power transformers from thermal overloading. An intelligent protection scheme should be able to identify the fault severity, predict the post disturbance trend of system states, continue monitoring specific vulnerable system variables and propose an accurate solution that is tailored to the actual system conditions and the specific contingencies that have occurred. The intent of this research is to contribute to the development of adaptive protective schemes that are enabled by modern synchronized measurement technologies for future power systems. The research presented in this thesis focuses on the creation of novel Operational Tripping Schemes (OTSs) that explicitly satisfy both the functionality and economical requirements by integrating an improved assessment of thermal behaviour of the monitored assets. Novel OTSs are proposed for both transmission lines and transformers and they can be considered to be intelligent, adaptive and efficient SIPS for the thermal protection of system assets. A novel functional block is proposed that be included within the OTS and that uses optimization theory to determine the lowest cost solution to overheating in the time available. Furthermore, case studies have been conducted to verify the performance of each novel OTS using simulations of a full GB system model.

O objetivo do desenvolvimento deste trabalho é tecer uma análise da viabilidade técnica - econômica da modernização do sistema de Proteção da Distribuição, comparando a utilização dos relés digitais aos quais foram incorporadas novas funções, em relação aos relés eletromecânicos e estáticos. As informações apresentadas nesse trabalho mostram que os relés digitais oferecem uma significante economia quanto ao custo de aquisição e implantação, no desenvolvimento dos projetos de aplicação e na manutenção destes equipamentos após instalados em campo. Os relés eletromecânicos tem sido largamente utilizados nos esquemas de proteção de consumidores industriais e residencias de grande porte e nos sistemas de proteção das companhias de eletricidade. Devido a quantidade de peças móveis e freqüentes re-ajustes que estes tipos de equipamentos necessitam, os mesmos demandam muitas horas dispendidas pelo pessoal de calibração e manutenção das empresas de eletricidade. A realização de Estudos de Proteção, com a parametrização destes relés muitas vezes torna-se inviável, sob o ponto de vista de sensibilidade e da coordenação das proteções, devido ao fato de que estes equipamentos possuem ajustes limitados tanto de valores de corrente de partida como na seleção de curvas tempo x corrente utilizadas para temporização das proteções, no caso de relés eletromecânicos de sobrecorrente. Durante os últimos anos, com o advento da evolução da indústria, da micro eletrônica e do desenvolvimento de softwares, os relés digitais veêm substituíndo os relés eletromecânicos e estáticos, tanto em instalações novas como também nas remodelações das instalações mais antigas, nos sistemas elétricos de proteção industrial e de empresas de eletricidade. Realizou-se uma análise quanto ao histórico dos relés de proteção, mostrando o seu desenvolvimento desde os relés mais antigos, tipos eletromecânicos, após os relés estáticos, que foram a evolução dos anteriores e finalmente estudando os relés digitais. Os relés digitais oferecem muitas vantagens se comparados com os relés eletromecânicos e estáticos, as quais serão abordandos em items específicos da revisão de literatura neste trabalho. O trabalho é finalizado com uma análise de casos, onde foram computados e analisados casos, como índices de fornecimento, custos de instalação de relés digitais em substituição à relés e sistemas eletromecânicos e estáticos, utilizados convencionalmente para a proteção em alimentadores de Subestações da Copel - Companhia Paranaense de Energia, com o objetivo de coletar-se e analisar-se, ao longo de 12 meses as reais vantagens e desvantagens da utilização destes equipamentos nos sistemas elétricos de proteção dos circuitos de distribuição de energia. / The purpose of this study is to carry out a technical and economic feasibility assessment of the updating of the Distribution Protection system, comparing the use of digital relays, to which new functions have been integrated, with electromechanical and static relays. Information hereby presented shows that digital relays are significantly cost-effective in terms of acquisition and implementation for developing application projects and in maintaining that equipment after it has been set up in the field. Electromechanical relays have been largely used in protection schemes for large-scale industrial and residential consumers, as well as in security schemes for power plant companies. Because of the large number of moving parts and frequent readjustments required by that type of equipment, many manhours must be put in by calibration and maintenance staff employed by power plant companies. Carrying out a Protection Study that establishes parameters for those relays is often unfeasible given the sensitivity and coordination of the protections, in that the equipment in question has limited adjustments, both in terms of pick-up currents values and of the selection of time curve vs. current used in the protection timer, in the case of overcurrent electromechanical relays. During the last years, with the rise of industrial evolution, microelectronics and software development, digital relays are replacing electromechanical and static relays in electrical security systems used by industrial and power plant company protection, both in new facilities and in refurbished facilities. A study was carried out on the history of protection relays showing how they developed from the older, electromechanical type after the static relays, which evolved form the former, and was concluded with the study of digital relay models. Digital relays provide significant advantages compared to electromechanical and static relays, which will be covered under specific revision items of the references provided herein. The study is concluded by assessing case studies that were accounted for and assessed, such as supply rates, installation costs of digital relays to replace electromechanical and static systems used traditionally to provide protection for COPEL´s (Power Company of the State of Paraná) Substations. The purpose was to collect and analyze, over a 12-month period, the actual advantages and disadvantages of using that type of equipment in electrical systems that provide circuit protection for power distribution.

Protection of both the wind plant and the interconnecting transmission system during short-circuit faults is imperative for maintaining system structural integrity and reliability. The circuit breakers and protective relays used to protect the power system during such events are designed based upon calculations of the current that will flow in the circuit during the fault. Sequence-network models of various power-system components, such as synchronous generators, transformers, transmission lines, etc., are often used to perform these calculations. However, there are no such models widely accepted for certain types of wind-turbine generators used in modern wind plants. The problem with developing sequence-network models of wind plants is that several different wind-turbine generator designs exist; yet, each exhibit very different short-circuit behavior. Therefore, a “one size fits all” approach is not appropriate for modeling wind plants, as has been the case for conventional power plants based on synchronous-generator technology. Further, many of the newer wind-turbine designs contain proprietary controls that affect the short-circuit behavior, and wind-turbine manufacturers are often not willing to disclose these controls. Thus, protection engineers do not have a standard or other well-established model for calculating short-circuit currents in power systems with wind plants. Therefore, the research described in this dissertation involves the development of such models for calculating short-circuit currents from wind-turbine generators. The focus of this dissertation is on the four existing wind-turbine generator designs (identified as Types 1 – 4). Only AC-transmission-interconnected wind-turbine generators are considered in this dissertation. The primary objective of this research is the development of sequence-network models, which are frequency-domain analysis tools, for each wind-turbine generator design. The time-domain behavior of each wind-turbine generator is thoroughly analyzed through transient simulations, experimental tests on scaled wind-turbine generator test beds, and solutions to the system dynamic equations. These time-domain analyses are used to support the development of the sequence-network models.