Maintenance costs in deregulated power systems play an important role. This mainly includes direct costs associated with material and labor costs; and indirect costs associated with spare parts inventory, shipment, test equipment cost, indirect labor, and opportunity costs. The cost function is used as the sole or main component of the objective function in maintenance scheduling and planning activities. The cost has been modeled in literature with several representations for centralized power systems. With deregulation of power industries in many countries the costs representation to be used within the maintenance model in the decentralized power systems has become an important research question. This paper presents modeling of different components of maintenance costs that can be used within the main objective function of the maintenance scheduling and planning problem for the deregulated environment.

The internal voltage angle of a generator is an important parameter that indicates the stability, both transient and steady-state, of the generator. This paper proposes a method of measuring and synchronizing the internal angle using a microprocessor and an optical encoder installed on the shaft of a generator. With a synchronized angle measurement, accurate stability studies and wide-area controls can be implemented. The experimental setup for measuring the rotor angle of a generator is explained in this work. A wide-area power system stabilizer implementing the synchronized angle measurement is then investigated using a four machine, two-area system. A synchronized remote feedback rotor angle signal is included in a traditional stabilizer design. It is shown that this remote signal helps increase the stability of the system while also having the benefit of being able to be predicted accurately. This capability makes bad data detection and communication delay compensation possible. / Master of Science

This dissertation is a systematic study of artificial neural networks (ANN) applications in power system restoration (PSR). PSR is based on available generation and load to be restored analysis. A literature review showed that the conventional PSR methods, i.e. the pre-established guidelines, the expert systems method, the mathematical programming method and the petri-net method have limitations such as the necessary time to obtain the PSR plan. ANN may help to solve this problem presenting a reliable PSR plan in a smaller time. Based on actual and past experiences, a PSR engine based on ANN was proposed and developed. Data from the Iowa 162 bus power system was used in the implementation of the technique. Reactive and real power balance, fault location, phase angles across breakers and intentional islanding were taken into account in the implementation of the technique. Constraints in PSR as thermal limits of transmission lines (TL), stability issues, number of TL used in the restoration plan and lockout breakers were used to create feasible PSR plans. To compare the time necessary to achieve the PSR plan with another technique a PSR method based on a breadth-search algorithm was implemented. This algorithm was also used to create training and validation patterns for the ANN used in the scheme. An algorithm to determine the switching sequence of the breakers was also implemented. In order to determine the switching sequence of the breakers the algorithm takes into account the most priority loads and the final system configuration generated by the ANN. The PSR technique implemented is composed by several pairs of ANN, each one assigned to an individual island of the system. The restoration of the system is done in parallel in each island. After each island is restored the tie lines are closed. The results encountered shows that ANN based schemes can be used in PSR helping the operators restore the system under the stressful conditions following a blackout. / Ph. D.

Small satellites and CubeSats have established themselves within the aerospace community because of their low cost and high return on investment. Many CubeSats are developed in a short time frame and often leverage commercial off the shelf components for quick turnaround missions. With regard to the Electrical Power System, commercially available products typically use a centralized architecture. However, a centralized architecture is not reusable, since missions that require additional solar arrays or batteries would necessitate a redesign of the power system. With the range of CubeSat sizes and mission goals, it is obvious that a one-size-fits-all solution is not appropriate. This thesis details a reusable and scalable power system architecture applicable to a variety of missions. Reusability is achieved by using common building blocks or "modules," where the same modules can be used between missions. Scalability is achieved by not limiting the number of modules that can be connected together—more modules can be added as needed. In this system, solar arrays and battery units connect directly to a common bus, supplying an unregulated voltage to each subsystem. These subsystems then regulate the bus voltage to their individual needs. The power system also features direct energy transfer and solar-only operation.

The objective of this research is to present a comprehensive framework for harnessing the flexibility of power systems in the presence of unforeseen events, such as those associated with component outages or renewable energy variability. Increased penetration of variable resources in the power grid, mainly in the form of wind and solar plants, has resulted in variable power flow patterns, increased thermal unit cycling and higher reserve capacity requirements. Furthermore, the variability of renewable energy output has increased the system’s ramping requirements and threatens the system’s voltage control capabilities. However, new sources of flexibility and network control are emerging to address these problems. Specifically, energy storage systems, demand side management, distributed energy resources and flexible transmission operation can participate by providing ramping services and/or voltage control, as well as by alleviating transmission congestion. This research focuses on contributing to modeling and optimization approaches for scheduling the operation of these sources of flexibility in a certain look-ahead horizon, ensuring a state of the art level of modeling accuracy, with full inclusion of voltage control considerations which do not exist in current DC-OPF modeling approaches. Also, by including reactive power flows, the network congestion model proposed is above par compared to the current state-of-the-art for look-ahead dispatch literature. Nevertheless, the model is further expanded by including a thermal model for transmission lines, which allows for the implementation of dynamic line ratings in look-ahead economic dispatch. The benefits from these augmented modeling capabilities are documented and compared with current operating practices. Once an AC-OPF look-ahead optimization problem has been established, and the corresponding components have been modeled, further contributions are made in the area of remedial action schemes. The developed formulations allow for the identification of appropriate corrective actions that will restore feasibility in infeasible cases. Finally, a combination of contingency filtering and contingency analysis approaches is developed, to allow for fast identification and analysis of critical outages in the transmission system. The filtering approach is based on a basic Taylor expansion of network power flow equations as well as a new formulation of margin indices that directly quantify the proximity to constraint violation in the post-outage system state. The analysis approach is based on low-rank modifications of the Jacobian matrix of network equations, to produce good estimates of post-outage operating states and map the effect on the system’s operating constraints. Compared to current state of the art, advances are made both in the speed and the accuracy of the analysis, since the proposed filtering and analysis methods are fully unbalanced. The need for unbalanced security analysis is discussed and justified. Through the contributions made in this research, a roadmap to increase flexibility in power system operations is developed. Namely, an enhanced modeling capability allows for integration of additional sources of flexibility and voltage control and a highly accurate security analysis and remedial actions formulation allows for improved response to unforeseen critical outages and rapid generation changes.

Faculty of Engineering & Built Environment, School of Electrical & Infomation Engineering, MSC Dissertation / The South African electrical utility,ESKOM, is one of the largest in the world with 40 GW capacity, worth R 965 billion, and an annual income of R 33 billion. The people responsible for the voltage control of the ESKOM transmission grid are highly skilled voltage controllers. An investigation was conducted to identify what constitutes their expertise. This is a ultidisciplinary research project that incorporates the fields of Power System Engineering, Industrial and Cognitive Psychology and Neuro-Linguistic Programming. Observations of the voltage controllers at work were carried out followed by in-depth interviews in order to identify, their Mental Control Strategies, Power System Visualization techniques, and Mental Models. Expert and novice voltage controllers were included in the research as well as one in-house Man Machine Interface (MMI) developer. Some of the main findings are: ·The sophisticated mental strategies that allow controllers to simplify the overabundance of data presented to them. ·The subconsciously created vivid mental imagery that they use to make fast intuitive decisions. Having obtained the above information, MMI design and human controller training can be optimised.

Um dos problemas mais graves e preocupantes que ocorrem em redes de distribuição é a falta de alta impedância proveniente do rompimento e conseqüente queda do condutor primário. Devido ao seu alto grau de periculosidade, é fundamental que tal fenômeno seja exaustivamente analisado e pesquisado. Com a evolução da tecnologia digital, os programas de simulação computacional se tornaram grandes aliados nas pesquisas em proteção de sistemas elétricos. A partir do estudo de modelos já desenvolvidos e testados de faltas de alta impedância em redes de distribuição, o presente trabalho realiza uma análise deste tipo de falta e discute a implementação de um modelo de fácil configuração e adaptável a diferentes cenários. Mais do que isso, este trabalho se propõe a desenvolver uma interface computacional propícia para viabilizar este tipo de estudo em redes de distribuição, dada a necessidade de se obter uma ferramenta que possibilite a automatização do processo de simulação deste fenômeno. Com o resultado deste trabalho será possível testar e validar esquemas de proteção contra faltas de alta impedância ocasionadas por rompimento e queda de condutor primário em redes de distribuição, bem como auxiliar no desenvolvimento e implementação de novos algoritmos de detecção deste tipo de falta. / The high impedance fault caused by the broken and fallen conductor is one of the most hazardous and worrying problems that occur in distribution network. Due to its high harmful level it is necessary to analyze and research such phenomenon exhaustingly. The evolution of digital technology allowed the development of computing simulation software that became a great ally to the research of electrical systems protective devices. Based on the study of already developed and tested high impedance fault models the present work revisits this type of fault and discuss the implementation of an easy configureable model that is adaptable to different scenarios. Beyond this, the present work also proposes to develop a proper computing interface in order to make the study of such faults at distribution network viable once it is necessary to have a tool that allows the automation of high impedance fault simulating process. The results of thiswork will allowto test and validate protective schemes against high impedance faults caused by the breakdown and fall of primary conductors at distribution network systems, as well as they will be helpful when developing and implementing new algorithms for detection of such kind of fault.

Significant penetration of distributed generation (DG) and the increasing automation level available for distribution networks have opened an option of splitting a network into subsystems and operating each as an "autonomous island". This is particularly important when a major contingency occurs. However, there are issues and challenges that must be addressed before islanded operation becomes viable, among which, ensuring seamless switching of a distribution subsystem from grid-connected to islanded mode is critically important. Unless the subsystem is a predesigned microgrid, it is highly possible that the subsystem load demand will exceed the generation capacity of island DGs. Therefore, an appropriate load shedding scheme must be implemented to ensure the islanded subsystem is power balanced. In this thesis, a switching control strategy is designed to deliver seamless islanding switching. This strategy comprises a multiple-DG coordination method and a single-step load shedding scheme. Mathematical studies and time-domain simulations that investigate the transients observed during the islanding switching process are both conducted, and together, they are used to address the transient stability issues of an islanded subsystem. This thesis focuses on a distribution subsystem consisting of a mix of synchronous and inverter-based DGs and a combination of static and dynamic loads. DG modelling and control is first introduced, and based on that, various types of method to achieve multiple-DG coordination, including an innovative multiple-master strategy, are investigated. The widely accepted master-slave strategy is used to coordinate DGs when the subsystem is islanded. The strategy demands a single dispatchable and controllable DG, such as a synchronous generator, to be the master, whilst requires the others, such as intermittent renewable-based DGs, to be the slaves. Dynamic load modelling is another critical part of this thesis. The transient stability of dynamic loads after major disturbances is investigated and then used to design the stability-oriented load shedding priority. The single-step load shedding scheme calculates the load shedding amount based on the power flow at the point of common coupling (PCC) and the spinning reserve available in the island. This scheme is activated by the tripping event of the PCC circuit breaker between the grid and the island, and then priorities the load to be shed according to the priority predetermined from the stability perspective. Mathematical analysis is first conducted on a simple subsystem to investigate the impact of DG settings on the islanding transients. A full-scale subsystem is also simulated in PSCAD/EMTDC and used to verify the effectiveness of the switching control strategy. In time-domain simulations, the subsystem is islanded following either a routine switching event or a permanent grid fault. Various factors that may affect the transient performance are analysed, such as the severity of the fault, the DG penetration level, the fault clearance time and the switching control delay. This thesis concludes that based on the proposed switching control strategy, the concept of seamless switching from grid-connected to islanded operation is technically viable.

Um dos problemas mais graves e preocupantes que ocorrem em redes de distribuição é a falta de alta impedância proveniente do rompimento e conseqüente queda do condutor primário. Devido ao seu alto grau de periculosidade, é fundamental que tal fenômeno seja exaustivamente analisado e pesquisado. Com a evolução da tecnologia digital, os programas de simulação computacional se tornaram grandes aliados nas pesquisas em proteção de sistemas elétricos. A partir do estudo de modelos já desenvolvidos e testados de faltas de alta impedância em redes de distribuição, o presente trabalho realiza uma análise deste tipo de falta e discute a implementação de um modelo de fácil configuração e adaptável a diferentes cenários. Mais do que isso, este trabalho se propõe a desenvolver uma interface computacional propícia para viabilizar este tipo de estudo em redes de distribuição, dada a necessidade de se obter uma ferramenta que possibilite a automatização do processo de simulação deste fenômeno. Com o resultado deste trabalho será possível testar e validar esquemas de proteção contra faltas de alta impedância ocasionadas por rompimento e queda de condutor primário em redes de distribuição, bem como auxiliar no desenvolvimento e implementação de novos algoritmos de detecção deste tipo de falta. / The high impedance fault caused by the broken and fallen conductor is one of the most hazardous and worrying problems that occur in distribution network. Due to its high harmful level it is necessary to analyze and research such phenomenon exhaustingly. The evolution of digital technology allowed the development of computing simulation software that became a great ally to the research of electrical systems protective devices. Based on the study of already developed and tested high impedance fault models the present work revisits this type of fault and discuss the implementation of an easy configureable model that is adaptable to different scenarios. Beyond this, the present work also proposes to develop a proper computing interface in order to make the study of such faults at distribution network viable once it is necessary to have a tool that allows the automation of high impedance fault simulating process. The results of thiswork will allowto test and validate protective schemes against high impedance faults caused by the breakdown and fall of primary conductors at distribution network systems, as well as they will be helpful when developing and implementing new algorithms for detection of such kind of fault.

The strain on modern electrical power systems has led to an ever-increasing utilization of new information and communication technologies (ICT) to improve their efficiency and reliability. Wide area monitoring and control (WAMC) systems offer many opportunities to improve the real-time situational awareness in the power system. These systems are essen-tially SCADA systems but with continuous streaming of measurement data from the power system. The quality of WAMC systems and the applications running on top of them are heavily, but not exclusively, dependent on the underlying non-functional quality of the ICT systems. From an ICT perspective, the real-time nature of WAMC systems makes them susceptible to variations in the quality of the supporting ICT systems. The non-functional qualities studied as part of this research are performance, interoperability and cyber security. To analyze the performance of WAMC ICT systems, WAMC applications were identified, and their requirements were elicited. Furthermore, simulation models capturing typical utility communication infrastructure architectures were implemented. The simulation studies were carried out to identify and characterize the latency in these systems and its impact on data quality in terms of the data loss. While performance is a major and desirable quality, other non-functional qualities such as interoperability and cyber security have a significant impact on the usefulness of the sys-tem. To analyze these non-functional qualities, an enterprise architecture (EA) based framework for the modeling and analysis of interoperability and cyber security, specialized for WAMC systems, is proposed. The framework also captures the impact of cyber security on the interoperability of WAMC systems. Finally, a prototype WAMC system was imple-mented to allow the validation of the proposed EA based framework. The prototype is based on existing and adopted open-source frameworks and libraries. The research described in this thesis makes several contributions. The work is a systematic approach for the analysis of the non-functional quality of WAMC ICT systems as a basis for establishing the suitability of ICT system architectures to support WAMC applications. This analysis is accomplished by first analyzing the impact of communication architectures for WAMC systems on the latency. Second, the impact of these latencies on the data quali-ty, specifically data currency (end to end delay of the phasor measurements) and data in-completeness (i.e., the percentage of phasor measurements lost in the communication), is analyzed. The research also provides a framework for interoperability and cyber security analysis based on a probabilistic Monte Carlo enterprise architecture method. Additionally, the framework captures the possible impact of cyber security on the interoperability of WAMC data flows. A final result of the research is a test bed where WAMC applications can be deployed and ICT architectures tested in a controlled but realistic environment. / <p>QC 20130218</p>