The global mean surface temperature rise was observed in the past century and proved the warming of the earth climate system. Global warming is believed to continue into the next decades due to unprecedented increases in greenhouse gas emissions. As a consequence of global warming, extreme weather scenarios are also expected to occur more frequently. In such a context, it is of vital importance to assess the impacts of climate change on the operational performance of power systems. This thesis investigates the impacts of climate change on the operational performance of power systems. The future climate is simulated based on emission scenarios and is then used as an input to the thermal models of power system components to assess their ratings and ageing, and further the reliability of the system. This research contributes to a number of areas in power system research. In the literature review, the risks that climate change may cause to power systems are identified. The models used for the simulation of future climate are firstly introduced. The weather variables that can be simulated from the models include air temperature, solar radiation, wind speed and direction, soil moisture and soil temperature. Among the models, the one for soil temperature is originally developed in this thesis. Following this, the component thermal models of overhead line, cable and transformer, from different standards are compared and selected. After that, the sensitivity of component ratings to individual weather variables is investigated, as a preliminary study for the later research in this thesis. Then, the impacts of climate change on component ratings (including both static and dynamic rating) are comprehensively and probabilistically assessed. The assessment results indicate the reduction of component ratings due to climate change. The impacts of climate change on system reliability is further examined on the IEEE Reliability Test System. Results demonstrate and quantify the reduction of both component ratings and system reliability, and prove that the dynamic rating can be used to mitigate the reduction. Finally, the preliminary exploration of transformer ageing is carried out and shows an increased ageing rate due to air temperature rises.

As human society develops, there is an increasing demand for electricity. However, the reserves of fossil fuels on earth are limited and may run out in the foreseeable future. Therefore, the possibility of replacing traditional fossil fuels with renewable energy sources is widely being investigated to resolve the world-faced energy shortage and environmental problems. The first method is to utilize more renewable energy such as wind and solar power and increase the percentage of distributed generation. Another method is to popularize electric vehicles due to their environmental-friendly and energy-saving characteristics. However, the integration of distributed generation and electric vehicles may greatly influence the operation and planning of power systems in several ways. This might result in deterioration of power system reliability. Since the society development highly depends on a safe and reliable power grid, it is essential to ensure high reliability of power systems when integrated with renewable energy resources. This master thesis aims to investigate the reliability performance of power distribution systems after integrating distributed generation and electric vehicles. First, the probabilistic model of distributed generation and electric vehicles for various scenarios are simulated. After that, a set of reliability analyses based on a standard reliability test system are carried out, in which a sequential Monte-Carlo simulation method is adopted to estimate average reliability indices. The overall conclusion is that the integration of distributed generation enhances power system reliability performance through supplying power to nearby customers in island mode. For electric vehicles, the proper regulation of charging behavior can help reduce the deterioration of power system reliability to the most extent, and the Vehicle-to-Grid mode can also improve system reliability. Furthermore, the electric bus dynamic charging mode has no additional harm to power system reliability performance than non-dynamic charging and has a promising prospect. / När det mänskliga samhället utvecklas finns det en ökande efterfrågan på el. Reserverna av fossila bränslen på jorden är dock begränsade och kan ta slut inom en överskådlig framtid. Därför undersöks möjligheten att ersätta traditionella fossila bränslen med förnybara energikällor för att lösa den världsomspända energibristen och miljöproblemen. Den första metoden är att använda mer förnybar energi såsom vind- och solenergi och öka andelen distribuerad produktion. En annan metod är att popularisera elfordon på grund av deras miljövänliga och energibesparande egenskaper. Integrationen av distribuerad produktion och elfordon kan dock påverka sätt och planering av kraftsystem i hög grad på flera sätt. Detta kan leda till försämring av elsystemets tillförlitlighet. Eftersom samhällsutvecklingen i hög grad beror på ett säkert och tillförlitligt kraftnät är det viktigt att säkerställa hög tillförlitlighet hos kraftsystem när de är integrerade med förnybara energikällor. Syftet med detta examensarbete är att undersöka tillförlitligheten hos kraftdistributionssystemet efter integrering av distribuerad generation och elfordon. För det första konstrueras den probabilistiska modellen för distribuerad generation och elfordon inklusive olika scenarier. Därefter genomförs en uppsättning tillförlitlighetsanalys baserad på RBTS buss 6-system, där sekventiell Monte-Carlo-simuleringsmetod antas för att uppskatta genomsnittliga återansvarsindex. Den övergripande slutsatsen är att integreringen av distribuerad produktion förbättrar systemets tillförlitlighet genom att leverera kraft till närliggande kunder på öns plats. För elektriska fordon kan korrekt reglering av laddningsbeteendet bidra till att minska försämringen av elsystemets tillförlitlighet i största möjliga utsträckning, och läget Fordon till nät kan även förbättra systemets tillförlitlighet. Dessutom har det elektriska bussens dynamiska laddningsläge ingen ytterligare skada på kraftsystemets tillförlitlighet och har ett lovande perspektiv.

The utilization of renewable energy resources such as wind and solar energy for electric power supply has received considerable attention in recent years due to adverse environmental impacts and fuel cost escalation associated with conventional generation. At the present time, wind and/or solar energy sources are utilized to generate electric power in many applications. Wind and solar energy will become important sources for power generation in the future because of their environmental, social and economic benefits, together with public support and government incentives. <p>The wind and sunlight are, however, unstable and variable energy sources, and behave far differently than conventional sources. Energy storage systems are, therefore, often required to smooth the fluctuating nature of the energy conversion system especially in small isolated applications. The research work presented in this thesis is focused on the development and application of reliability and economic benefits assessment associated with incorporating wind energy, solar energy and energy storage in power generating systems. A probabilistic approach using sequential Monte Carlo simulation was employed in this research and a number of analyses were conducted with regards to the adequacy and economic assessment of generation systems containing wind energy, solar energy and energy storage. The evaluation models and techniques incorporate risk index distributions and different operating strategies associated with diesel generation in small isolated systems. Deterministic and probabilistic techniques are combined in this thesis using a system well-being approach to provide useful adequacy indices for small isolated systems that include renewable energy and energy storage. The concepts presented and examples illustrated in this thesis will help power system planners and utility managers to assess the reliability and economic benefits of utilizing wind energy conversion systems, solar energy conversion systems and energy storage in electric power systems and provide useful input to the managerial decision process.

The reliability of protection systems has emerged as an important topic because protection failures have critical influence on the reliability of power systems. The goal of this research is to develop novel approaches for modeling and analysis of the impact of protection system failures on power system reliability. It is shown that repairable and non-repairable assumptions make a remarkable difference in reliability modeling. A typical all-digital protection system architecture is modeled and numerically analyzed. If an all-digital protection system is indeed repairable but is modeled in a non-repairable manner for analysis, the calculated values of reliability indices could be grossly pessimistic. The smart grid is emerging with the penetration of information-age technologies and the development of the Special Protection System (SPS) will be greatly influenced. A conceptual all-digital SPS architecture is proposed for the future smart grid. Calculation of important reliability indices by the network reduction method and the Markov modeling method is illustrated in detail. Two different Markov models are proposed for reliability evaluation of the 2-out-of-3 voting gates structure in a generation rejection scheme. If the model with consideration of both detectable and undetectable logic gate failures is used as a benchmark, the simple model which only considers detectable failures will significantly overestimate the reliability of the 2-out-of-3 voting gates structure. The two types of protection failures, undesired-tripping mode and fail-to-operate mode are discussed. A complete Markov model for current-carrying components is established and its simplified form is then derived. The simplified model can appropriately describe the overall reliability situation of individual components under the circumstances of complex interactions between components due to protection failures. New concepts of the self-down state and the induced-down state are introduced and utilized to build up the composite unit model. Finally, a two-layer Markov model for power systems with protection failures is proposed. It can quantify the impact of protection failures on power system reliability. Using the developed methodology, we can see that the assumption of perfectly reliable protection can introduce errors in reliability evaluation of power systems.

The utilization of renewable energy resources such as wind and solar energy for electric power supply has received considerable attention in recent years due to adverse environmental impacts and fuel cost escalation associated with conventional generation. At the present time, wind and/or solar energy sources are utilized to generate electric power in many applications. Wind and solar energy will become important sources for power generation in the future because of their environmental, social and economic benefits, together with public support and government incentives. <p>The wind and sunlight are, however, unstable and variable energy sources, and behave far differently than conventional sources. Energy storage systems are, therefore, often required to smooth the fluctuating nature of the energy conversion system especially in small isolated applications. The research work presented in this thesis is focused on the development and application of reliability and economic benefits assessment associated with incorporating wind energy, solar energy and energy storage in power generating systems. A probabilistic approach using sequential Monte Carlo simulation was employed in this research and a number of analyses were conducted with regards to the adequacy and economic assessment of generation systems containing wind energy, solar energy and energy storage. The evaluation models and techniques incorporate risk index distributions and different operating strategies associated with diesel generation in small isolated systems. Deterministic and probabilistic techniques are combined in this thesis using a system well-being approach to provide useful adequacy indices for small isolated systems that include renewable energy and energy storage. The concepts presented and examples illustrated in this thesis will help power system planners and utility managers to assess the reliability and economic benefits of utilizing wind energy conversion systems, solar energy conversion systems and energy storage in electric power systems and provide useful input to the managerial decision process.

As open access market principles are applied to power systems, significant changes are happening in their planning, operation and control. In the emerging marketplace, systems are operating under higher loading conditions as markets focus greater attention to operating costs than stability and security margins. Since operating stability is a basic requirement for any power system, there is need for newer tools to ensure stability and security margins being strictly enforced in the competitive marketplace. This dissertation investigates issues associated with incorporating voltage security into the unbundled operating environment of electricity markets. It includes addressing voltage security in the monitoring, operational and planning horizons of restructured power system. This dissertation presents a new decomposition procedure to estimate voltage security usage by transactions. The procedure follows physical law and uses an index that can be monitored knowing the state of the system. The expression derived is based on composite market coordination models that have both PoolCo and OpCo transactions, in a shared stressed transmission grid. Our procedure is able to equitably distinguish the impacts of individual transactions on voltage stability, at load buses, in a simple and fast manner. This dissertation formulates a new voltage stability constrained optimal power flow (VSCOPF) using a simple voltage security index. In modern planning, composite power system reliability analysis that encompasses both adequacy and security issues is being developed. We have illustrated the applicability of our VSCOPF into composite reliability analysis. This dissertation also delves into the various applications of voltage security index. Increasingly, FACT devices are being used in restructured markets to mitigate a variety of operational problems. Their control effects on voltage security would be demonstrated using our VSCOPF procedure. Further, this dissertation investigates the application of steady state voltage stability index to detect potential dynamic voltage collapse. Finally, this dissertation examines developments in representation, standardization, communication and exchange of power system data. Power system data is the key input to all analytical engines for system operation, monitoring and control. Data exchange and dissemination could impact voltage security evaluation and therefore needs to be critically examined.

Due to growth of wind power, system operators are being challenged by the integration of large wind farms into their electrical power systems. Large scale wind farm integration has adverse effects on the power system due to its variable characteristic. These effects include two main aspects: voltage stability and active line flow. In this thesis, a novel techniques to forecast active line flow and select pilot bus are introduced with wind power integration. First, this thesis introduces a methodology to forecast congestion in the transmission line with high wind penetration. Since most wind resources tend to be located far away form the load center, the active line flow is one of the most significant aspects when wind farm is connected to electrical grid. By providing the information about the line flow which can contribute to transmission line congestion, the system operators would be able to respond such as by requesting wind power or load reduction. The second objective of this thesis is to select the weakest bus, called pilot bus, among all load buses. System reliability, especially voltage stability, can be adversely affected by wind variability. In order to ensure reliable operation of power systems with wind power integration, the index to select the pilot bus is developed, and further prediction of voltage profile at the pilot bus is fulfilled. The objective function to select the pilot bus takes account of the N-1 contingency analysis, loading margin, and reactive power sensitivity. Through on the objective function, the pilot bus is representative of all load buses as well as controllable by reactive power regulation. Predicting the voltage profile at the pilot bus is also useful for system operators to determine wind power output. / text

The objective of the proposed research is to develop a cost-effective power flow controller to improve the utilization and reliability of the existing transmission, sub-transmission, and distribution networks. Over the last two decades, electricity consumption and generation have continually grown at an annual rate of around 2.5%. At the same time, investments in the Transmission and Distribution (T&D) infrastructure have steadily declined. Further, it has become increasingly difficult and expensive to build new power lines. As a result, the aging power-grid has become congested and is under stress, resulting in compromised reliability and higher energy costs. In such an environment it becomes important that existing assets are used effectively to achieve highest efficiency. System reliability is sacrosanct and cannot be compromised. Utility system planners are moving from radial towards networked systems to achieve higher reliability, especially under contingency conditions. While enhancing reliability, this has degraded the controllability of the network, as current flow along individual lines can no longer be controlled. The transfer capacity of the system gets limited by the first line that reaches the thermal capacity, even when majority of the lines are operating at a fraction of their capacity. The utilization of the system gets further degraded as the lines are operated with spare capacity to sustain overloads under contingencies. Market efficiency is also sub-optimal, with congestion on key corridors restricting the low-cost generators to connect to the end users, resulting in higher electricity prices for the consumers. The proposed technology offers the capability to realize a controllable meshed-network, with the ability to utilize static and dynamic capacity of the grid to provide system-wide benefits, including- increased line and system-capacity utilization, increased reliability, improved operation under contingencies, and rapid implementation. It would allow a broadening of the energy market, permitting owners to direct how energy flows on their wires, and making it easier to connect to new sources of generation.

The object of this research is to optimize the overall power system performance using FACTS devices. Particularly, it is intended to improve the reliability, and the performance of the power system considering steady state operating condition as well as the system subjected to small and large disturbances. The methodology proposed to achieve this goal corresponds to an enhanced particle swarm optimizer (Enhanced-PSO) that is proven in this work to have several advantages, in terms of accuracy and computational effort, as compared with other existing methods. Once the performance of the Enhanced PSO is verified, a multi-stage PSO-based optimization framework is proposed for optimizing the power system reliability (N-1 contingency criterion). The algorithm finds optimal settings for present infrastructure (generator outputs, transformers tap ratios and capacitor banks settings) as well as optimal control references for distributed static series compensators (DSSC) and optimal locations, sizes and control settings for static compensator (STATCOM) units. Finally, a two-stage optimization algorithm is proposed to improve the power system performance in steady state conditions and when small and large perturbations are applied to the system. In this case, the algorithm provides optimal control references for DSSC modules, optimal location and sizes for capacitor banks, and optimal location, sizes and control parameters for STATCOM units (internal and external controllers), so that the loadability and the damping of the system are maximized at minimum cost. Simulation results throughout this research show a significant improvement of the power system reliability and performance after the system is optimized.

abstract: The standard optimal power flow (OPF) problem is an economic dispatch (ED) problem combined with transmission constraints, which are based on a static topology. However, topology control (TC) has been proposed in the past as a corrective mechanism to relieve overloads and voltage violations. Even though the benefits of TC are presented by several research works in the past, the computational complexity associated with TC has been a major deterrent to its implementation. The proposed work develops heuristics for TC and investigates its potential to improve the computational time for TC for various applications. The objective is to develop computationally light methods to harness the flexibility of the grid to derive maximum benefits to the system in terms of reliability. One of the goals of this research is to develop a tool that will be capable of providing TC actions in a minimal time-frame, which can be readily adopted by the industry for real-time corrective applications. A DC based heuristic, i.e., a greedy algorithm, is developed and applied to improve the computational time for the TC problem while still maintaining the ability to find quality solutions. In the greedy algorithm, an expression is derived, which indicates the impact on the objective for a marginal change in the state of a transmission line. This expression is used to generate a priority list with potential candidate lines for switching, which may provide huge improvements to the system. The advantage of this method is that it is a fast heuristic as compared to using mixed integer programming (MIP) approach. Alternatively, AC based heuristics are developed for TC problem and tested on actual data from PJM, ERCOT and TVA. AC based N-1 contingency analysis is performed to identify the contingencies that cause network violations. Simple proximity based heuristics are developed and the fast decoupled power flow is solved iteratively to identify the top five TC actions, which provide reduction in violations. Time domain simulations are performed to ensure that the TC actions do not cause system instability. Simulation results show significant reductions in violations in the system by the application of the TC heuristics. / Dissertation/Thesis / Doctoral Dissertation Electrical Engineering 2016