Browsing by Subject "Power System"
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Item An Integrative Approach to Reliability Analysis of an IEC 61850 Digital Substation(2012-11-28) Zhang, Yan 1988-In recent years, reliability evaluation of substation automation systems has received a significant attention from the research community. With the advent of the concept of smart grid, there is a growing trend to integrate more computation and communication technology into power systems. This thesis focuses on the reliability evaluation of modern substation automation systems. Such systems include both physical devices (current carrying) such as lines, circuit breakers, and transformers, as well as cyber devices (Ethernet switches, intelligent electronic devices, and cables) and belong to a broader class of cyber-physical systems. We assume that the substation utilizes IEC 61850 standard, which is a dominant standard for substation automation. Focusing on IEC 61850 standard, we discuss the failure modes and analyze their effects on the system. We utilize reliability block diagrams for analyzing the reliability of substation components (bay units) and then use the state space approach to study the effects at the substation level. Case study is based on an actual IEC 61850 substation automation system, with different network topologies consideration concluded. Our analysis provides a starting point for evaluating the reliability of the substation and the effects of substation failures to the rest of the power system. By using the state space methods, the steady state probability of each failure effects were calculated in different bay units. These probabilities can be further used in the modeling of the composite power system to analyze the loss of load probabilities.Item Analyses of power system vulnerability and total transfer capability(Texas A&M University, 2006-04-12) Yu, XingbinModern power systems are now stepping into the post-restructuring era, in which utility industries as well as ISOs (Independent System Operators) are involved. Attention needs to be paid to the reliability study of power systems by both the utility companies and the ISOs. An uninterrupted and high quality power is required for the sustainable development of a technological society. Power system blackouts generally result from cascading outages. Protection system hidden failures remain dormant when everything is normal and are exposed as a result of other system disturbances. This dissertation provides new methods for power system vulnerability analysis including protection failures. Both adequacy and security aspects are included. The power system vulnerability analysis covers the following issues: 1) Protection system failure analysis and modeling based on protection failure features; 2) New methodology for reliability evaluation to incorporate protection system failure modes; and, 3) Application of variance reduction techniques and evaluation. A new model of current-carrying component paired with its associated protection system has been proposed. The model differentiates two protection failure modes, and it is the foundation of the proposed research. Detailed stochastic features of system contingencies and corresponding responses are considered. Both adequacy and security reliability indices are computed. Moreover, a new reliability index ISV (Integrated System Vulnerability) is introduced to represent the integrated reliability performance with consideration of protection system failures. According to these indices, we can locate the weakest point or link in a power system. The whole analysis procedure is based on a non-sequential Monte Carlo simulation method. In reliability analysis, especially with Monte Carlo simulation, computation time is a function not only of a large number of simulations, but also time-consuming system state evaluation, such as OPF (Optimal Power Flow) and stability assessment. Theoretical and practical analysis is conducted for the application of variance reduction techniques. The dissertation also proposes a comprehensive approach for a TTC (Total Transfer Capability) calculation with consideration of thermal, voltage and transient stability limits. Both steady state and dynamic security assessments are included in the process of obtaining total transfer capability. Particularly, the effect of FACTS (Flexible AC Transmission Systems) devices on TTC is examined. FACTS devices have been shown to have both positive and negative effects on system stability depending on their location. Furthermore, this dissertation proposes a probabilistic method which gives a new framework for analyzing total transfer capability with actual operational conditions.Item Evaluation of power system security and development of transmission pricing method(Texas A&M University, 2004-11-15) Kim, HyungchulThe electric power utility industry is presently undergoing a change towards the deregulated environment. This has resulted in unbundling of generation, transmission and distribution services. The introduction of competition into unbundled electricity services may lead system operation closer to its security boundaries resulting in smaller operating safety margins. The competitive environment is expected to lead to lower price rates for customers and higher efficiency for power suppliers in the long run. Under this deregulated environment, security assessment and pricing of transmission services have become important issues in power systems. This dissertation provides new methods for power system security assessment and transmission pricing. In power system security assessment, the following issues are discussed 1) The description of probabilistic methods for power system security assessment 2) The computation time of simulation methods 3) on-line security assessment for operation. A probabilistic method using Monte-Carlo simulation is proposed for power system security assessment. This method takes into account dynamic and static effects corresponding to contingencies. Two different Kohonen networks, Self-Organizing Maps and Learning Vector Quantization, are employed to speed up the probabilistic method. The combination of Kohonen networks and Monte-Carlo simulation can reduce computation time in comparison with straight Monte-Carlo simulation. A technique for security assessment employing Bayes classifier is also proposed. This method can be useful for system operators to make security decisions during on-line power system operation. This dissertation also suggests an approach for allocating transmission transaction costs based on reliability benefits in transmission services. The proposed method shows the transmission transaction cost of reliability benefits when transmission line capacities are considered. The ratio between allocation by transmission line capacity-use and allocation by reliability benefits is computed using the probability of system failure.Item Fast Detection and Mitigation of Cascading Outages in the Power System(2012-02-14) Pang, ChengzongThis dissertation studies the causes and mechanism of power system cascading outages and proposes the improved interactive scheme between system-wide and local levels of monitoring and control to quickly detect, classify and mitigate the cascading outages in power system. A novel method for evaluating the vulnerability of individual components as well as the whole power system, which is named as weighted vulnerability analysis, is developed. Betweenness centrality is used to measure the importance of each bus and transmission line in the modeled power system network, which is in turn used to determine the weights for the weighted vulnerability index. It features fast reaction time and achieves higher accuracy when dealing with the cascading outage detection, classification and mitigation over the traditional methods. The overload problem due to power flow redistribution after one line tripped is a critical factor contributing to the cascading outages. A parallel corridor searching method is proposed to quickly identify the most vulnerable components after tripping a transmission line. The power system topology model can be simplified into state graph after searching the domains for each generator, the commons for each bus, and links between the commons. The parallel corridor will be determined by searching the links and commons in system topology graph for the given state of power system operation. During stressed operating state, either stable or unstable power swing may have impacts on distance relay judgment and lead to relay misoperation, which will result in the power system lines being tripped and as a consequence power system operating state becoming even more stressful. At the local level, an enhanced fault detection tool during power system swing is developed to reduce the chance of relay misoperation. Comprehensive simulation studies have been implemented by using the IEEE 39-bus and 118-bus test systems. The results are promising because: The results from weighted vulnerability analysis could provide better system situational awareness and accurate information about the disturbance; The results form parallel corridor search method could identify the most vulnerable lines after power re-distribution, which will give operator time to take remedial actions; The results from new travelling wave and wavelet transform based fault detection could reduce the impact of relay misoperation.Item Numerical Simulations of a Wave Energy Conversion Device Used for Oceanographic Buoys(2014-07-24) Lee, YongseokMoored buoy systems are often deployed by oceanographers to gather scientific information on local and global changes in the water column, weather patterns and climate change. The data they gather is first transmitted to satellites or passing oceanographic ships prior to transmission land based research facilities. Most buoy designs are powered by battery systems that provide ballast and some can be recharged by solar panels. At-sea maintenance may include regular battery replacement or repairs to the buoy system due to vandalism, each being expensive propositions. In order to reduce the costs and utilize green energy, this thesis research investigates the use of incorporating a pendulum wave energy conversion (WEC) device as a permanent or semi-permanent power source for some oceanographic buoys having an average power consumption that can vary from 0.1W to 6.0W. The main criteria for selecting a WEC device for this application are operational reliability, sustainability during operational and extreme weather conditions, and minimizing the opportunity for vandalism. A general analytical model was developed and simulations of the motions of the buoy were performed using the numerical code COUPLE, which was originally developed to simulate the coupled response behavior of a deepwater floating hull and the associated mooring/riser/tendon systems. Based upon the motion behavior from the numerical simulation, the electrical power output by the selected WEC device is estimated using an iterative scheme to estimate equivalent damping of a hydraulic Power Take-Off (PTO) system. Several illustrative case studies are presented to verify that the electrical power output rate is in the range of the power demands needed by typical oceanographic buoys. It is concluded that the proposed pendulum WEC device is a feasible solution that can be designed to provide an alternative power system to power oceanographic buoys. The research study provides a way to approach the design and utilization of WEC devices to capture wave energy as a natural power source for a wide range of buoy shapes, sizes and configurations for existing and future buoy designs.Item Power system fault analysis based on intelligent techniques and intelligent electronic device data(Texas A&M University, 2007-09-17) Luo, XuThis dissertation has focused on automated power system fault analysis. New contributions to fault section estimation, protection system performance evaluation and power system/protection system interactive simulation have been achieved. Intelligent techniques including expert systems, fuzzy logic and Petri-nets, as well as data from remote terminal units (RTUs) of supervisory control and data acquisition (SCADA) systems, and digital protective relays have been explored and utilized to fufill the objectives. The task of fault section estimation is difficult when multiple faults, failures of protection devices, and false data are involved. A Fuzzy Reasoning Petri-nets approach has been proposed to tackle the complexities. In this approach, the fuzzy reasoning starting from protection system status data and ending with estimation of faulted power system section is formulated by Petri-nets. The reasoning process is implemented by matrix operations. Data from RTUs of SCADA systems and digital protective relays are used as inputs. Experiential tests have shown that the proposed approach is able to perform accurate fault section estimation under complex scenarios. The evaluation of protection system performance involves issues of data acquisition, prediction of expected operations, identification of unexpected operations and diagnosis of the reasons for unexpected operations. An automated protection system performance evaluation application has been developed to accomplish all the tasks. The application automatically retrieves relay files, processes relay file data, and performs rule-based analysis. Forward chaining reasoning is used for prediction of expected protection operation while backward chaining reasoning is used for diagnosis of unexpected protection operations. Lab tests have shown that the developed application has successfully performed relay performance analysis. The challenge of power system/protection system interactive simulation lies in modeling of sophisticated protection systems and interfacing the protection system model and power system network model seamlessly. An approach which utilizes the "compiled foreign model" mechanism of ATP MODELS language is proposed to model multifunctional digital protective relays in C++ language and seamlessly interface them to the power system network model. The developed simulation environment has been successfully used for the studies of fault section estimation and protection system performance evaluation.Item The detection, prevention and mitigation of cascading outages in the power system(2009-05-15) Song, HongbiaoThis dissertation studies the causes and mechanism of power system cascading outages and develops new methods and new tools to help detect, prevent and mitigate the outages. Three effective solutions: a steady state control scheme, a transient stability control scheme, and an interactive system-wide and local scheme have been proposed using those new methods and tools. A steady state control scheme can help detect and prevent the possible cascading outage at its initial slow steady state progress stage. It uses new methods and new tools to solve the line overload, congestion or bus high/low voltage problems. New methods, such as vulnerability index (VI), margin index (MI), network contribution factor (NCF), topology processing and selected minimum load shedding (SMLS), and new tools, such as transmission network control based on a network contribution factor (NCF) method, generator control based on a generator distribution factor (GDF) method, and load control based on a load distribution factor (LDF) method have been proposed and developed. A transient stability control scheme can help prevent and mitigate the possible cascading outage at its transient progress stage if there is enough time to take action. It uses one Lyapunov direct method, potential energy boundary surface (PEBS) method, and sensitivity analysis of transient energy margin for fast stabilizing control. The results are verified by the accurate time-domain transient stability analysis method. The interactive scheme takes advantage of accurate system-wide and local information and analysis results, uses some techniques from both steady state control and transient stability control, works at both the system-wide level and local substation level, monitors the system all the time, and takes actions when needed to help detect, prevent and mitigate the possible cascading outage. Comprehensive simulation studies have been implemented using the IEEE 14- bus, 24-bus, 39-bus and 118-bus systems and promising results show the ability of the proposed solutions to help detect, prevent and mitigate cascading outages.Item Using graph theory to resolve state estimator issues faced by deregulated power systems(2009-05-15) Lei, JianshengPower industry is undergoing a transition from the traditional regulated environment to the competitive power market. To have a reliable state estimator (SE) in the power market environment, two major challenges are emerging, i.e. to keep SE running reliably even under a contingency and to run SE over a grid with extremely large size. The objective of this dissertation is to use graph theory to address the above two challenges. To keep SE running reliably under a contingency, a novel topological approach is first proposed to identify critical measurements and examine network observability under a contingency. To advance the classical topological observability analysis, a new concept of contingency observability graph (COG) is introduced and it is proven that a power system network maintains its observability under a contingency if and only if its COG satisfies some conditions. As an application of COG, a two-stage heuristic topological approach is further developed based on the new concept of qualified COG (QCOG) to minimize the number of measurements and RTUs under the constraint that the system remains observable under any single contingency. To overcome the disadvantages of existing SE over extremely large networks, a textured distributed state estimator (DSE), which consists of the off-line textured architecture design and the on-line textured computation, is proposed based on COG and a new concept of Bus Credibility Index (BCI). The textured DSE is non-recursive, asynchronous and avoids central controlling node. Numerical tests verify that the performance of the new textured DSE algorithm improves greatly compared with existing DSE algorithms in respect of bad data detection and identification. Furthermore, the software implementation for DSE is formulated as an information integration problem over regional power markets, and is very challenging because of its size and complexity. A new concept of semantic knowledge warehouse (SKW), together with the proposed concepts of semantic reasoning software component (SRSC) and deduction credibility, is developed to implement such an information integration system.