The role of electric power systems has grown steadily in both scope and importance over time making electricity increasingly recognized as a key to social and economic progress in many developing countries. In a sense, reliable power systems constitute the foundation of all prospering societies. The constant expansion in electric power systems, along with increased energy demand, requires that power systems become more and more complex. Such complexity results in much uncertainty which demands comprehensive reliability and security assessment to ensure reliable energy supply. Power industries in many countries are facing these challenges and are trying to increase the computational capability to handle the ever-increasing data and analytical needs of operations and planning. Moreover, the deregulated electricity markets have been in operation in a number of countries since the 1990s. During the deregulation process, vertically integrated power utilities have been reformed into competitive markets, with initial goals to improve market efficiency, minimize production costs and reduce the electricity price. Given the benefits that have been achieved by deregulation, several new challenges are also observed in the market. Due to fundamental changes to the electric power industry, traditional management and analysis methods cannot deal with these new challenges. Deterministic reliability assessment criteria still exists but it doesn’t satisfy the probabilistic nature of power systems. In the deterministic approach the worst case analysis results in excess operating costs. On the other hand, probabilistic methods are now widely accepted. The analytical method uses a mathematical formula for reliability evaluation and generates results more quickly but it needs accurate and a lot of assumptions and is not suitable for large and complex systems. Simulation based techniques take care of much uncertainty and simulates the random behavior of the system. However, it requires much computing power, memory and other computing resources. Power engineers have to run thousands of times domain simulations to determine the stability for a set of credible disturbances before dispatching. For example, security analysis is associated with the steady state and dynamic response of the power system to various disturbances. It is highly desirable to have real time security assessment, especially in the market environment. Therefore, novel analysis methods are required for power systems reliability and security in the deregulated environment, which can provide comprehensive results, and high performance computing (HPC) power in order to carry out such analysis within a limited time. Further, with the deregulation in power industry, operation control has been distributed among many organizations. The power grid is a complex network involving a range of energy resources including nuclear, fossil and renewable energy resources with many operational levels and layers including control centers, power plants and transmission and distribution systems. The energy resources are managed by different organizations in the electricity market and all these participants (including producers, consumers and operators) can affect the operational state of the power grid at any time. Moreover, adequacy analysis is an important task in power system planning and can be regarded as collaborative tasks, which demands the collaboration among the electricity market participants for reliable energy supply. Grid computing is gaining attention from power engineering experts as an ideal solution to the computational difficulties being faced by the power industry. Grid computing infrastructure involves the integrated and collaborative use of computers, networks, databases and scientific instruments owned and managed by multiple organizations. Grid computing technology offers potentially feasible support to the design and development of grid computing based infrastructure for power system reliability and security analysis. It can help in building infrastructure, which can provide a high performance computing and collaborative environment, and offer an optimal solution between cast and efficiency. While power system analysis is a vast topic, only a limited amount of research has been initiated in several places to investigate the applications of grid computing in power systems. This thesis will investigate probabilistic based reliability and security analysis of complex power systems in order to develop new techniques for providing comprehensive result with enormous efficiency. A review of existing techniques was conducted to determine the computational needs in the area of power systems. The main objective of this research is to propose and develop a general framework of computing grid and special grid services for probabilistic power system reliability and security assessment in the electricity market. As a result of this research, grid computing based techniques are proposed for power systems probabilistic load flow analysis, probabilistic small signal analysis, probabilistic transient stability analysis, and probabilistic contingencies analysis. Moreover, a grid computing based system is designed and developed for the monitoring and control of distributed generation systems. As a part of this research, a detailed review is presented about the possible applications of this technology in other aspects of power systems. It is proposed that these grid based techniques will provide comprehensive results that will lead to great efficiency, and ultimately enhance the existing computing capabilities of power companies in a cost-effective manner. At a part of this research, a small scale computing grid is developed which will consist of grid services for probabilistic reliability and security assessment techniques. A significant outcome of this research will be the improved performance, accuracy, and security of data sharing and collaboration. More importantly grid based computing will improve the capability of power system analysis in a deregulated environment where complex and large amounts of data would otherwise be impossible to analyze without huge investments in computing facilities.

The role of electric power systems has grown steadily in both scope and importance over time making electricity increasingly recognized as a key to social and economic progress in many developing countries. In a sense, reliable power systems constitute the foundation of all prospering societies. The constant expansion in electric power systems, along with increased energy demand, requires that power systems become more and more complex. Such complexity results in much uncertainty which demands comprehensive reliability and security assessment to ensure reliable energy supply. Power industries in many countries are facing these challenges and are trying to increase the computational capability to handle the ever-increasing data and analytical needs of operations and planning. Moreover, the deregulated electricity markets have been in operation in a number of countries since the 1990s. During the deregulation process, vertically integrated power utilities have been reformed into competitive markets, with initial goals to improve market efficiency, minimize production costs and reduce the electricity price. Given the benefits that have been achieved by deregulation, several new challenges are also observed in the market. Due to fundamental changes to the electric power industry, traditional management and analysis methods cannot deal with these new challenges. Deterministic reliability assessment criteria still exists but it doesn’t satisfy the probabilistic nature of power systems. In the deterministic approach the worst case analysis results in excess operating costs. On the other hand, probabilistic methods are now widely accepted. The analytical method uses a mathematical formula for reliability evaluation and generates results more quickly but it needs accurate and a lot of assumptions and is not suitable for large and complex systems. Simulation based techniques take care of much uncertainty and simulates the random behavior of the system. However, it requires much computing power, memory and other computing resources. Power engineers have to run thousands of times domain simulations to determine the stability for a set of credible disturbances before dispatching. For example, security analysis is associated with the steady state and dynamic response of the power system to various disturbances. It is highly desirable to have real time security assessment, especially in the market environment. Therefore, novel analysis methods are required for power systems reliability and security in the deregulated environment, which can provide comprehensive results, and high performance computing (HPC) power in order to carry out such analysis within a limited time. Further, with the deregulation in power industry, operation control has been distributed among many organizations. The power grid is a complex network involving a range of energy resources including nuclear, fossil and renewable energy resources with many operational levels and layers including control centers, power plants and transmission and distribution systems. The energy resources are managed by different organizations in the electricity market and all these participants (including producers, consumers and operators) can affect the operational state of the power grid at any time. Moreover, adequacy analysis is an important task in power system planning and can be regarded as collaborative tasks, which demands the collaboration among the electricity market participants for reliable energy supply. Grid computing is gaining attention from power engineering experts as an ideal solution to the computational difficulties being faced by the power industry. Grid computing infrastructure involves the integrated and collaborative use of computers, networks, databases and scientific instruments owned and managed by multiple organizations. Grid computing technology offers potentially feasible support to the design and development of grid computing based infrastructure for power system reliability and security analysis. It can help in building infrastructure, which can provide a high performance computing and collaborative environment, and offer an optimal solution between cast and efficiency. While power system analysis is a vast topic, only a limited amount of research has been initiated in several places to investigate the applications of grid computing in power systems. This thesis will investigate probabilistic based reliability and security analysis of complex power systems in order to develop new techniques for providing comprehensive result with enormous efficiency. A review of existing techniques was conducted to determine the computational needs in the area of power systems. The main objective of this research is to propose and develop a general framework of computing grid and special grid services for probabilistic power system reliability and security assessment in the electricity market. As a result of this research, grid computing based techniques are proposed for power systems probabilistic load flow analysis, probabilistic small signal analysis, probabilistic transient stability analysis, and probabilistic contingencies analysis. Moreover, a grid computing based system is designed and developed for the monitoring and control of distributed generation systems. As a part of this research, a detailed review is presented about the possible applications of this technology in other aspects of power systems. It is proposed that these grid based techniques will provide comprehensive results that will lead to great efficiency, and ultimately enhance the existing computing capabilities of power companies in a cost-effective manner. At a part of this research, a small scale computing grid is developed which will consist of grid services for probabilistic reliability and security assessment techniques. A significant outcome of this research will be the improved performance, accuracy, and security of data sharing and collaboration. More importantly grid based computing will improve the capability of power system analysis in a deregulated environment where complex and large amounts of data would otherwise be impossible to analyze without huge investments in computing facilities.

Thesis (MEng)--University of Stellenbosch, 2000. / ENGLISH ABSTRACT: Recent advances in semiconductor device development pushed a large number of network devices onto the market. These devices can solve network problems more effectively and economically than ever before. Network planners need tools to analyse and implement such devices to help solve the largest network problem in South Africa: voltage regulation. Rural networks experience the majority of voltage-regulation problems in South Africa. The networks are long sub-transmission and reticulation networks and are modelled by two generic networks, namely a radial network and a two-source ring network. The equations describing voltage regulation for the generic networks are developed and implemented in PSAT, a software analysis tool. The voltage regulation for two case studies that represent the two generic networks are analysed. Four generic network devices are defined and various control methods for these devices are developed to solve the network problem. The aim of PSAT is to help the network planner to quickly evaluate a number of possible solutions and to choose the best solution for further studies. This is demonstrated with the aid of the case studies. PSAT provides a sturdy platform on which future developments, such as stability analyses, can be built. However, PSAT can already function as a stand-alone analysis tool to solve voltage regulation as a network problem. / AFRIKAANSE OPSOMMING: Onlangse vooruitgang in halfgeleier ontwikkeling het 'n groot aantal netwerktoestelle op die mark geplaas. Hierdie toestelle kan netwerk probleme doeltreffender en meer ekonomies oplos as ooit vantevore. 'n Behoefte aan 'n pakket wat netwerkbeplanners in staat stelom die netwerktoestelle te analiseer, is geïdentifiseer. So 'n pakket sal hulle help om die vernaamste netwerkprobleem in Suid-Afrika, nl. spanningsregulasie, op te los. Die oorgrote meerderheid spanningsregulasie probleme word op die platteland ondervind. Plattelandse netwerke word gekenmerk deur lang sub-transmissie en retikulasie netwerke. Hierdie netwerke word met behulp van twee generiese netwerke gemodelleer. 'n Radiale netwerk en 'n dubbelbron ringnetwerk word aangewend om enige plattelandse netwerk te analiseer. Vergelykings is vir spanningsanalise ontwikkel en in PSAT, 'n analitiese sagteware pakket, geïmplementeer. Twee gevallestudies is gedoen om die twee netwerke afsonderlik voor te stel en die vergelykings van PSAT te evalueer. Alle netwerktoestelle is in een van vier generiese kategorieë geklassifiseer. Modelle is vir elk van die kategorieë ontwikkel vtr spanningsregulasie analise. Die doel van PSAT is om die netwerk beplanner te help om vinnig en effektief soveel moontlik opsies te ondersoek as oplossings vir 'n spesifieke netwerk probleem. PSAT is reeds 'n alleenstaande pakket wat in die toekoms uitgebrei sal word om na die analise van stabilitietsprobleme te kyk.

More and more system operators are interested in calculating transfer capability in real-time using real-time power flow models generated from the Energy Management System (EMS). However, compared to off-line study models, EMS models usually cover only a limited portion of the interconnected system. In most situations, it is not practical to extend the EMS model to capture the impact of the external systems and therefore using an equivalent network becomes necessary. The development of equivalent circuits to represent external areas was a topic discussed over the last 50 years. Almost all of these methods require impedance information about the external area to develop the equivalent circuit. Unfortunately utilities do not have the external impedance information in the real-time. Therefore, normal industry practice is to use off-line studies to develop an equivalent circuit and use that circuit in the real-time operation without any validation. This can result in errors in the security assessment. Therefore, power industry need a method to develop or validate an equivalent circuit based on the available real-time information. This thesis work is focussed on meeting that industry need. The work on this thesis presents two new methods that can be used to generate an equivalent circuit based on the boundary conditions. This method involves calculating equivalent impedance between two areas based on the boundary stations voltages, voltage angles and power leaving the boundary stations into external areas. This thesis uses power system simulation between two areas to change the system condition to obtain different boundary bus voltages, voltage angles and power injections to generate necessary data. Regression analysis and least square method is then used to generate the equivalent circuit using these data. It is expected that system changes will provide necessary information in the real-time to generate the equivalent circuit. The proposed methodology is validated with modified three area 300 bus system as well as using Manitoba Hydro’s system. Contingency analysis, transfer level calcula-tion and PV curves analysis is used to validate the proposed method. Simulation results show that the proposed method produces adequate accuracy in comparison with detailed off-line system models. The main advantage of the proposed method as compared to other existing meth-ods such as Ward and REI is that the proposed method does not require external imped-ance information to generate the equivalent circuit. The ability to generate reasonably good equivalent circuit only using available boundary information will help utilities to generate or validate the equivalent circuit based on the current system conditions, which will intern help improve the accuracy of the security assessment / February 2017

Submitted by isabela.moljf@hotmail.com (isabela.moljf@hotmail.com) on 2017-03-02T12:45:01Z No. of bitstreams: 1 arleilucasdesouzarosa.pdf: 827143 bytes, checksum: 9b9df97bf2f2804c9287dcee04958895 (MD5) / Approved for entry into archive by Adriana Oliveira (adriana.oliveira@ufjf.edu.br) on 2017-03-06T19:38:30Z (GMT) No. of bitstreams: 1 arleilucasdesouzarosa.pdf: 827143 bytes, checksum: 9b9df97bf2f2804c9287dcee04958895 (MD5) / Made available in DSpace on 2017-03-06T19:38:30Z (GMT). No. of bitstreams: 1 arleilucasdesouzarosa.pdf: 827143 bytes, checksum: 9b9df97bf2f2804c9287dcee04958895 (MD5) Previous issue date: 2009-05-27 / CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Durante décadas, problemas relacionados à estabilidade de tensão ou, segurança de tensão, têm despertada a atenção crescente de pesquisadores do setor elétrico. O crescimento da economia e o aumento do consumo de energia elétrica, aliados à falta de investimentos nos setores de geração e transmissão, têm levado o sistema elétrico de potência a operar muito próximo de seus limites. Desta forma, a habilidade do sistema em manter um nível operacional satisfatório, após a ocorrência de alguma contingência, pode ficar comprometida. Este trabalho avalia a segurança de tensão através de um método simples, eficiente e rápido computacionalmente, além de propor ações de reforço para melhorar a margem de carregamento do sistema elétrico. A análise da rede é função dos caminhos de transmissão de potência ativa e um modelo matemático muito simples é utilizado. Quanto às ações de reforço, a análise de sensibilidade fornece as barras mais adequadas ao redespacho de potência ativa e reativa. Um processo iterativo é estabelecido com o intuito de recomendar ações de controle e fornecer condições de segurança de tensão menos severas. Os resultados apresentados para um sistema real de 34 barras demonstram a eficácia da metodologia desenvolvida. / Voltage stability or voltage security analysis has motivated an expressive attention of power systems researchers. The economy growth and the increased electric energy consumption, allied to the lack of investments in generation and transmission areas, have led electrical power systems to operate very close to their limits. Therefore, they cannot be able to operate in a secure way after some contingencies. In this work, a simple and fast method evaluates voltage security and proposes conditions to improve the loading margin. System analysis is carried out in terms of active power transmission path. Sensitivity analysis provides the most adequate buses to active and reactive power redispatch. A sequential iterative methodology to reinforce system conditions is presented. The results for a real 34-bus system demonstrate the efficiency of proposed methodology.

The demand for electrical power is growing due to factors such as population growth, urbanisation, and the transition from fossil fuels to renewable energy sources. To be able to keep up with the changes in electricity demand, the Swedish power grid must connect more renewable power generation, but also  increase its transmission capacity. Traditionally, power grids are expanded to increase the transmission capacity which requires a lot of time and investments. In order not to hinder the electrification of society, it is important to adequately estimate the current transmission capacity and plan the expansions accordingly. In the past, the generation of electrical power was primarily based on dispatchable energy sources, and the planning of new connections to the grid was assessed according to the stable and controllable nature of the electricity supply. However, renewable sources like solar and wind power are affected by weather variations. Therefore, the traditional methods of planning the power grid are no longer sufficient. Instead, there is a need to develop and implement new methods that account for the variable nature of renewable energy sources, and also the possible complementarity between different renewable power sources. This can possibly allow more connection of renewable power generation to the grid, without the need of expanding it. The aim of this thesis is to investigate two different methods for analysing how much renewable power generation that can be connected to the power grid, so-called hosting capacity methods. The first method is a deterministic method which is traditionally used in power system analyses since it is a fast, simple and conservative method. This method does neither consider the intermittent nature of solar and wind power, nor any complementarity. The second method is a time series method which considers the complementarity and intermittency of solar and wind power but requires much data. The methods are compared in regards to assessed hosting capacities, risks and reliability of results. The study is performed on a regional grid case in the middle of Sweden. Solar and wind power plants with different capacities are modeled at ten buses in the power grid. The power grid is analysed in PSS/E with loading of lines and voltage levels determining the assessed hosting capacities. A correlation map presenting the temporal correlations of solar and wind power over the grid case area is also created in order to evaluate the complementarity in the area and its possible effects on the assessed hosting capacities.  The results show that the time series method is more reliable than the deterministic method. This is due to the difficulties in identifying accurate worst case hours that are used for the deterministic method. The time series method is also preferred as it considers complementarity between solar and wind power. However, the correlation map argues that the grid case area has weakly positive correlations, meaning low complementarity between solar and wind power. This suggests that the differences in hosting capacity between the two methods are more likely dependent on the temporal variations in existing load and power generation. The differences in assessed hosting capacity between the ten buses in the power grid are probably not due to the local complementarity either, but rather the structural differences of the grid in terms of components, local loads and existing power generation.

The main objectives of this research are (a) to develop advanced simulation methods for voltage-recovery phenomena using improved, realistic system models and accurate solution techniques and (b) to develop methods for the mitigation of problems related to slow voltage recovery. Therefore, this work concentrates on the areas of voltage-recovery analysis in electric power systems, dynamic load modeling with emphasis on induction-motor models, dynamic simulation with emphasis on the numerical integration methods, and optimal allocation and operation of static and dynamic VAr resources. In the first part of this work, a general framework for power-system analysis is presented the main characteristics of which are (a) the utilization of full three-phase models and (b) the use of a "quadratized" mathematical formulation, which models the system under study as a set of mathematical equations of order no more than two. The modeling approach is essentially the same for steady-state, quasi-steady-state, and dynamic analysis. Furthermore, a new approach for time-domain transient simulation of electric power systems and dynamical systems, in general, is introduced in this research. The new methodology has been named quadratic integration method. The method is based on a numerical integration scheme that assumes that the system states vary quadraticaly within an integration time step. Accurate modeling and simulation of voltage-recovery phenomena allows the development of mitigation methodologies via the optimal allocation and operation of static and dynamic VAr resources over the planning horizon. This problem is solved with successive dynamic programming techniques with the following two innovations: (a) the states at each stage (candidate solutions) are obtained with static and dynamic (trajectory) sensitivity analysis and (b) each candidate solution is evaluated by considering the optimal operation of installed static and dynamic VAr sources utilizing concepts from the theory of applied optimal control and trajectory optimization.

This study selects several new advanced topics in power systems, and verifies their usefulness using the simulation. In the study on ratio of the equivalent reactance and resistance of the bulk power systems, the simulation results give us the more correct value of X/R of the bulk power system, which can explain why the active power compensation is also important in voltage flicker mitigation. In the application study of the Energy Storage System(ESS) to the wind power, the new model implementation of the ESS connected to the wind power is proposed, and the control effect of ESS to the intermittency of the wind power is verified. Also this study conducts the intensive simulations for clarifying the behavior of the wide-area power system frequency as well as the possibility of the on-line instability detection. In our POWER IT Laboratory, since 2003, the U.S. national frequency monitoring network (FNET) has been being continuously operated to monitor the wide-area power system frequency in the U.S. Using the measured frequency data, the event of the power system is triggered, and its location and scale are estimated. This study also looks for the possibility of using the simulation technologies to contribute the applications of FNET, finds similarity of the event detection orders between the frequency measurements and the simulations in the U.S. Eastern power grid, and develops the new methodology for estimating the event location based on the simulated N-1 contingencies using the frequency measurement. It has been pointed out that the simulation results can not represent the actual response of the power systems due to the inevitable limit of modeling power systems and different operating conditions of the systems at every second. However, in the circumstances that we need to test such an important infrastructure supplying the electric energy without taking any risk of it, the software based simulation will be the best solution to verify the new technologies in power system engineering and, for doing this, new models and better application of the simulation should be proposed. Conducting extensive simulation studies, this dissertation verified that the actual X/R ratio of the bulk power systems is much lower than what has been known as its typical value, showed the effectiveness of the ESS control to mitigate the intermittence of the wind power from the perspective of the power grid using the newly proposed simulation model of ESS connected to the wind power, and found many characteristics of the wide-area frequency wave propagation. Also the possibility of using the simulated responses of the power system for replacing the measured data could be confirmed and this is very promising to the future application of the simulation to the on-line analysis of the power systems based on the FNET measurements. / Ph. D.