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Magnus, Olofsson. „Undersökning av transient stabilitet i matningssystem för elektrisk tågdrift“. Thesis, KTH, Elkraftteknik, 1989. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-156241.
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Söderström, Sebastian. „Simplified Model For Simulation of Fault Ride Through at Hydropower Units“. Thesis, Uppsala universitet, Institutionen för fysik och astronomi, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-445855.
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As new requirements for grid connected generators were implemented, the requirements for evaluating the Fault Ride Through capabilities of the generators became stricter. When refurbishing a power unit, proof that the power unit meet the requirements must be submitted to the authorities. Performing simulations of the Fault Ride Through of a production unit is an extensive process and requires advanced simulation models and tools. Therefore, the need for a simplified tool for estimating the Fault Ride Through capability arose, which is what the project produced. Also, knowledge of which production module characteristics (such as the generator parameters, transformer and excitation system) have the largest effect on the Fault Ride Through time, would also be beneficial. Through the creation of Simulink simulation models of two hydropower stations and a sensitivity analysis of station parameters, the relative effect of the parameters on the Fault Ride Through time is estimated and implemented into a time independent Fault Ride Through time estimation tool, based on the Equal Area criterion. The purpose of the time-independent Fault Ride Through time estimation tool is to provide an insight into the approximate transient stability of the hydropower station and which parameters affect the performance the most. Simulations show that the transient reactance of the generator, the generator inertia, the transient time constant and the transformer inductance have the largest effect on the Fault Ride Through capability. The results show that a simplified tool cannot estimate the Fault Ride Through as accurately as a time-domain simulation model can.
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Peltonen, Joanna. „Effective Spatial Mapping for Coupled Code Analysis of Thermal–Hydraulics/Neutron–Kinetics of Boiling Water Reactors“. Doctoral thesis, KTH, Kärnkraftsäkerhet, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-122088.
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Analyses of nuclear reactor safety have increasingly required coupling of full three dimensional neutron kinetics (NK) core models with system transient thermal–hydraulics (TH) codes. In order to produce results within a reasonable computing time, the coupled codes use two different spatial description of the reactor core. The TH code uses few, typically 5 to 20 TH channels, which represent the core. The NK code uses explicit one node for each fuel assembly. Therefore, a spatial mapping of a coarse grid TH and a fine grid NK domain is necessary. However, improper mappings may result in loss of valuable information, thus causing inaccurate prediction of safety parameters. The purpose of this thesis is to study the effectiveness of spatial coupling (channel refinement and spatial mapping) and develop recommendations for NK/TH mapping in simulation of safety transients. Additionally, sensitivity of stability (measured by Decay Ratio and Frequency) to the different types of mapping schemes, is analyzed against OECD/NEA Ringhals–1 Stability Benchmark data. The research methodology consists of spatial coupling convergence study, by increasing the number of TH channels and varying mapping approaches, up to and including the reference case. The reference case consists of one-to-one mapping: one TH channel per one fuel assembly. The comparisons of the results are done for steady–state and transient results. In this thesis mapping (spatial coupling) definition is formed and all the existing mapping approaches were gathered, analyzed and presented. Additionally, to increase the efficiency and applicability of spatial mapping convergence, a new mapping methodology has been proposed. The new mapping approach is based on hierarchical clustering method; the method of unsupervised learning that is adopted by many researchers in many different scientific fields, thanks to its flexibility and robustness. The proposed new mapping method turns out to be very successful for spatial coupling problem and can be fully automatized allowing for significant time reduction in mapping convergence study. The steady–state results obtained from three different plant models for all the investigated cases are presented. All models achieved well converged steady–state and local parameters were compared and it was concluded that solid basis for further transient analysis was found. Analyzing the mapping performance, the best predictions for steady–state conditions are the mappings that include the power peaking factor feature alone or with any combination of other features. Additionally it is of value to keep the core symmetry (symmetry feature). The big part of this research is devoted to transient analysis. The selection of transients was done such that it covers a wide range of transients and gathered knowledge may be used for other types of transients. As a representative of a local perturbation, Control Rod Drop Accident was chosen. A specially prepared Feedwater Transient was investigated as a regional perturbation and a Turbine Trip is an example of a global one. In the case of local perturbation, it has been found that a number of TH channels is less important than the type of mapping, so a high number of TH channels does not guarantee improved results. To avoid unnecessary averaging and to obtain the best prediction, hot channel and core zone where accident happens should be always separated from the rest. The best performance is achieved with mapping according power peaking factors, and therefore this one is recommended for such type of perturbation. The regional perturbation has been found to be more challenging than the others. This kind of perturbation is strongly dependent on mapping type that affects the power increase rate, SCRAM time, onset of instability, development of limit cycle, etc. It has been also concluded that a special effort is needed for input model preparation. In contrast to the regional perturbation, the global perturbation is found to be the least demanding transient. Here, the number of TH channels and type of mapping do not have significant impact on average plant behaviour – general plant response is always well recreated. A special effort has also been paid to investigate the core stability performance, in both global and regional mode. It has been found that in case of unstable cores, a low number of TH channels significantly suppresses the instability. For these cases number of TH channels is very important and therefore at least half of the core has to be modeled to have a confidence in predicted DR and FR. In case of regional instability in order to get correct performance of out-of-phase oscillations, it is recommended to use full-scale model. If this is not possible, the mapping which is a mixture of 1st power mode and power peaking factors, should be used. The general conclusions and recommendations are summarized at the end of this thesis. Development of these recommendations was one of the purposes of this investigation and they should be taken into consideration while designing new coupled TH/NK models and choosing mapping strategy for a new transient analysis.QC 20130516
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Karimishad, Amir. „Transient stability-constrained load dispatch, ancillary services allocation and transient stability assessment procedures for secure power system operation“. University of Western Australia. Energy Systems Centre, 2008. http://theses.library.uwa.edu.au/adt-WU2009.0028.
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[Truncated abstract] The present thesis is devoted to the development of new methods for transient stability-constrained optimal power flow, probabilistic transient stability assessment and security-constrained ancillary services allocation. The key objective of the thesis is to develop novel dispatch and assessment methods for power systems operation in the new environment of electricity markets to ensure power systems security, particularly transient stability. A new method for economic dispatch together with nodal price calculations which includes transient stability constraints and, at the same time, optimises the reference inputs to the Flexible AC Transmission System (FACTS) devices for maintaining power systems transient stability and reducing nodal prices is developed. The method draws on the sensitivity analysis of time-domain transient stability simulation results to derive a set of linearised stability constraints expressed in terms of generator active powers and FACTS devices input references. '...' The low computing time requirement of the two-point estimate method allows online applications, and the use of detailed power systems dynamic model for time-domain simulation which offers high accuracy. The two-point estimate method is integrated in a straightforward manner with the existing transient stability analysis tools. The integrated software facility has potential applications in control rooms to assist the system operator in decision making process based on instability risks. The software system when implemented on a cluster of processors also makes it feasible to re-assess online transient stability for any change in system configuration arising from switching control. The method proposed has been tested on a representative power system and validated using the Monte Carlo simulation. In conjunction with the energy market, by which forecasted load demand is met by generator dispatch, ancillary services are required in relation to control for secure system operation and power quality. The final part of the thesis has a focus on the key aspect of allocating these ancillary services, subject to an important constraint that the dispatch of the ancillary services will not impair the system security achieved in the load dispatch. With this focus and requirement, the thesis develops a new dispatch formulation in which the network security constraints are represented in the optimal determination of generator active power schedule and allocation of ancillary services. Contingencies considered include power demand variations at individual load nodes from the values specified for the current dispatch calculation. The required changes in generator active powers to meet the new load demands are represented by additional control variables in the new dispatch formulation which augment those variables in the traditional OPF dispatch calculation. Based on the Lagrange function which includes the extended set of security constraints, the formulation derives the optimality condition to be satisfied by the dispatch solution, together with the marginal prices for individual ancillary service providers and LMPs. The effects of the security constraints are investigated and discussed. Case studies for representative power systems are presented to verify the new dispatch calculation procedure.
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Gonzalez-Torres, Juan Carlos. „Transient stability of high voltage AC-DC electric transmission systems“. Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLS041.
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Les nouvelles politiques adoptées par les autorités nationales ont encouragé pendant les dernières années l'intégration à grande échelle des systèmes d'énergie renouvelable (RES). L'intégration à grande échelle des RES aura inévitablement des conséquences sur le réseau de transport d'électricité tel qu'il est conçu aujourd'hui, car le transport de l'électricité massif sur de longues distances pourrait amener les réseaux de transport à fonctionner près de leurs limites, réduisant ainsi leurs marges de sécurité. Des systèmes de transport d’électricité plus complexes seront donc nécessaires.Dans ce scénario, les systèmes de transmission à Courant Continu Haute Tension (HVDC) constituent la solution la plus intéressante pour le renforcement et l'amélioration des réseaux à Courant Alternatif (AC) existants, non seulement en utilisant des configurations point à point, mais aussi dans des configurations multi-terminales. L'introduction des systèmes HVDC aboutira à terme à un réseau électrique hybride haute tension AC/DC, qui doit être analysé comme un système unique afin de mieux comprendre les interactions entre le réseau AC et le réseau DC.Cette thèse porte sur l'analyse de la stabilité transitoire des systèmes de transmission électrique hybrides AC/DC. Plus particulièrement, deux questions ont été abordées: Quel est l'impact d'un défaut du réseau DC sur la stabilité transitoire du réseau AC? Comment est-il possible de se servir des systèmes de transmission DC en tant qu'actionneurs afin d'améliorer la stabilité transitoire AC ?Dans la première partie de ce travail, les modèles mathématiques du réseau hybride AC/DC sont décrits ainsi que les outils nécessaires à l'analyse du système en tenant compte de sa nature non linéaire. Ensuite, une analyse approfondie de la stabilité transitoire du réseau électrique dans le cas particulier d'un court-circuit dans le réseau DC et l'exécution des stratégies de protection correspondantes sont effectuées. En complément, des indicateurs de stabilité et des outils pour dimensionner les futurs réseaux de la MTDC afin de respecter les contraintes des stratégies de protection existantes sont proposés.La deuxième partie de la thèse porte sur les propositions de commande pour la modulation des références de puissance des systèmes de transmission HVDC dans le but d'améliorer la stabilité transitoire du système AC connecté à ce réseau DC. Tout d'abord, nous axons notre étude sur le contrôle non linéaire des liaisons HVDC point à point dans des liaisons hybrides AC/DC. La compensation rapide des perturbations de puissance, l'injection de puissance d'amortissement et l'injection de puissance de synchronisation sont identifiées comme des mécanismes par lesquels les systèmes HVDC peuvent améliorer les marges de stabilité des réseaux AC.Enfin, une stratégie de contrôle pour l'amélioration de la stabilité transitoire par injection de puissance active dans par un réseau MTDC est proposée. Grâce à la communication entre les stations, la commande décentralisée proposée injecte la puissance d'amortissement et de synchronisation entre chaque paire de convertisseurs en utilisant uniquement des mesures au niveau des convertisseurs. L'implémentation proposée permet d'utiliser au maximum la capacité disponible des convertisseurs en gérant les limites de puissance d'une manière décentraliséeThe new policy frameworks adopted by national authorities has encouraged the large scale-integration of Renewable Energy Systems (RES) into bulk power systems. The large-scale integration of RES will have consequences on the electricity transmission system as it is conceived today, since the transmission of bulk power over long distances could lead the existing transmission systems to work close to their limits, thus decreasing their dynamic security margins. Therefore more complex transmissions systems are needed.Under this scenario, HVDC transmission systems raise as the most attractive solution for the reinforcement and improvement of existing AC networks, not only using point-to-point configurations, but also in a Multi-Terminal configuration. The introduction of HVDC transmission systems will eventually result in a hybrid high voltage AC/DC power system, which requires to be analyzed as a unique system in order to understand the interactions between the AC network and the DC grid.This thesis addresses the transient stability analysis of hybrid AC/DC electric transmission systems. More in particular, two questions sought to be investigated: What is the impact of a DC contingency on AC transient stability? How can we take advantage of the of DC transmission systems as control inputs in order to enhance AC transient stability?In the first part of this work, the mathematical models of the hybrid AC/DC grid are described as well as the necessary tools for the analysis of the system taking into account its nonlinear nature. Then, a thorough analysis of transient stability of the power system in the particular case of a DC fault and the execution of the corresponding protection strategies is done. As a complement, stability indicators and tools for sizing future MTDC grids in order to respect the constraints of existing protection strategies are proposed.The second part of the thesis addresses the control proposals for the modulation of power references of the HVDC transmission systems with the purpose of transient stability enhancement of the surrounding AC system. Firstly, we focus our study in the nonlinear control of point-to-point HVDC links in hybrid corridors. Fast power compensation, injection of damping power and injection of synchronizing power are identified as the mechanisms through which HVDC systems can improve stability margins.Finally, a control strategy for transient stability enhancement via active power injections of an MTDC grid is proposed. Using communication between the stations, the proposed decentralized control injects damping and synchronizing power between each pair of converters using only measurements at the converters level. The proposed implementation allows to fully use the available headroom of the converters by dealing with power limits in a decentralized way
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Couturier, Nicolas. „Transient Stability During Asymmetrical Faults“. Thesis, KTH, Elektroteknisk teori och konstruktion, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-160521.
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This research project has been conducted at RTE in order to study the transient stability after asymmetrical faults. When three-phase short-circuits occur in a network, almost all the electrical power is lost on the relevant line(s). Among all short-circuit types, it is the most drastic event and the issue has to be solved very quickly. But oddly, it is also the easiest problem to solve mathematically speaking. This comes from the fact that the system stays balanced, and equations can be simplified. However with line-to-ground faults this is no longer the case, and transient stability analysis becomes tricky. Until now, unbalanced situations have not been studied much. Since this kind of trouble is less serious than losing all three phases, every protection devices on the network have been sized to counter three-phase faults in time and avoid severe consequences. They will then also work for onephase problems. Despite this, there is a desire from RTE to understand – physically and mathematically – what happens when one-phase faults occur, and it is the mission behind this master thesis. First, a mathematical theoretical model was derived to examine a network’s stability without running any simulation. Then, once simulation software programs were taken in hand, several tests were run on a very simplified network, and compared with the theory developed previously. Finally, these experiments were carried out on a much larger scale. It is important to understand that, except for the theoretical model, all the results and conclusions in this document come from simulations. Even if a lot of tests and models led to them, these conclusions must be handled with care. The goal of this work was also to have a better understanding of unbalanced systems, of the Fortescue representation and thus, understand more clearly the parameters required by simulation tools like Eurostag© for future studies.Detta forskningsprojekt genomfördes hos RTE för att undersöka transientstabilitet efterosymmetriska fel. När trefasiga kortslutningar inträffar i en nätverk försvinner nästan all kraft i derelevanta ledningarna. Bland alla kortslutningstyper är detta den mest drastiska händelsen och måstelösas väldigt snabbt. Konstigt nog är det det lättaste problemet att lösa matematiskt. Detta på grundav faktumet att systemet förblir balanserat och ekvationer kan förenklas. Hursomhelst vid enfasigajordfel är detta inte längre fallet och transientstabilitetsanalys blir plötsligt svårt att räkna på. Fram tills nu har inte lösningar på obalanserade situationer studerats mycket. Eftersom denna typ avproblem är mindre allvarliga än att förlora alla tre faser, så har enheter på nätverket utformats för attmotverka trefas--‐fel snabbt och undvika allvarliga konsekvenser. Enheterna kommer då också fungeraför enfasproblem. Trots detta så finns det en önskan från RTE att förstå –fysiskt och matematiskt –vad som händer närett enfasproblem uppstår, det är det som är målet med mitt examensarbete. Först framtogs enmatematisk teoretisk modell för att examinera nätverkets stabilitet utan att köra någon simulation. Sedan med hjälp av mjukvarusimulatorer så utfördes flertalet test med den tidigare utveckladeteorin. I slutändan utfördes experimenten i en mycket större skala. Det är viktigt att förstå att, utom den teoretiska modellen, kommer alla resultat i denna rapportenfrån simuleringar. Även om flera tester och modeller ledde fram till dem, ska dessa slutsatserhanteras varsamt. Målet med detta arbete var att få bättre förståelse för obalanserade system, representationen med symmetriska komponenter och därmed, få en klarare förståelse för parametrarna som krävs avsimuleringssverktyg så som Eurostag© för framtida studier.
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Kwasnicki, Wieslaw T. „High Speed Transient Stability, multiprocessing solutions“. Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape17/PQDD_0024/NQ32881.pdf.
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Farantatos, Evangelos. „A predictive out-of-step protection scheme based on PMU enabled distributed dynamic state estimation“. Diss., Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/45863.
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Recent widespread blackouts have indicated the need for more efficient and accurate power system monitoring, control and protection tools. Power system state estimation, which is the major tool that is used nowadays for providing the real-time model of the system, has significant biases resulting mainly from the complexity and geographic spread and separation of an electric power system. Synchrophasor technology is a promising technology that has numerous advantages compared to conventional metering devices. PMUs provide synchronized measurements, where synchronization is achieved via a GPS clock which provides the synchronizing signal with accuracy of 1 μsec. As a result, the computed phasors have a common reference (UTC time) and can be used in local computations, thus distributing the state estimation process. The first part of the work presents a PMU enabled dynamic state estimator (DSE) that can capture with high fidelity the dynamics of the system and extract in real time the dynamic model of the system. The described DSE is performed in a decentralized way, on the substation level based on local measurements which are globally valid. The substation based DSE uses data from relays, PMUs, meters, FDRs etc in the substation only, thus avoiding all issues associated with transmission of data and associated time latencies. This approach enables very fast DSE update rate which can go up to more than 60 executions per second.
The distributed state estimation architecture that synchrophasor technology enables, along with the fast sampling rate and the accuracy of the measurements that PMUs provide, enable the computation of the real-time dynamic model of the system and the development of numerous power system applications for more efficient control and protection of the system. In the second part of the work, a transient stability monitoring scheme is presented that utilizes the information given by the dynamic state estimation and enables real-time monitoring of the transient swings of the system and characterizes the stability of the system in real time. In particular, the real-time dynamic model of the system, as given by the DSE, is utilized to evaluate the system's energy function based on Lyapunov's direct method and extract stability properties from the energy function. The two major components of the scheme are a) the calculation of the center of oscillations of the system and b) the derivation of an equivalent, reduced sized model which is used for the calculation of the potential and kinetic energy of the system based on which the stability of the system is determined. Finally, as an application of the transient stability monitoring scheme, an energy based out-of-step protection scheme is proposed. The energy of the generator is continuously monitored and if it exceeds a predefined threshold then instability is asserted and a trip signal can be sent to the generator. The major advantage of the scheme is that the out-of-step condition is predicted before its occurrence and therefore relays can act much faster than today's technology. The scheme is compared to presently available state of the art out-of-step protection schemes in order to verify its superiority.
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Niday, Thomas A. „Stability and transient effects in ultraviolet filaments“. Diss., The University of Arizona, 2004. http://hdl.handle.net/10150/280637.
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Short, high intensity laser pulses induce nonlinear optical effects in the atmosphere that have the potential to make them propagate for long distances. Applications for long distance propagation of short pulses include active spectral remote sensing and laser lightning control. Much of the work in this field has been done with infrared pulses; however, it has been proposed that ultraviolet pulses have the advantage that longer pulse lengths can be used, thereby delivering more energy. Long pulse lengths lead to a simplified instantaneous model for the plasma response, which has been shown by Schwarz and Diels to admit steady state or oscillatory solutions corresponding to beam propagation. We have verified this model and have adjusted it to achieve closer agreement with numerical results. In this work we investigate the effects of transient behavior, and the stability of these solutions. Analysis of the modulational instability is done from the plane wave level to a full three dimensional model of the propagation. It is shown that both the transient behavior arising from the finite pulse length, and the modulational instability cause pulses to fragment over lengths on the scale of meters. We present results showing the growth of unstable modes in various propagation regimes. We discuss the pertinent length scales for ultraviolet pulses, as well as the impact of the instability and transient effects on theory and experiment. The results imply that continuous-wave models are very limited when used to predict dynamical properties of pulse propagation.
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Hiskens, Ian A. „Energy functions, transient stability and voltage behaviour /“. Online version, 1990. http://bibpurl.oclc.org/web/30417.
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Musaazi, M. K. „Generator transient stability improvement by optimal aim strategies“. Thesis, Imperial College London, 1985. http://hdl.handle.net/10044/1/37795.
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Oztop, Celal. „Beforehand Obtaining A Safety Operation Condition By Using Daily Load Curves In Transient Stability And Graphical Software For Transient Stability Applications“. Master's thesis, METU, 2005. http://etd.lib.metu.edu.tr/upload/2/12606457/index.pdf.
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ABSTRACT
In this thesis, relationship between two most important transient stability indices, critical clearing time and generator rotor angle is examined for one machine-infinite bus system and then extended to the multimachine case and is observed to be linear.
By using the linear relationship between critical clearing time and generator rotor angle and utilizing the daily load curve, a new preventive method is proposed. The aim of this method is to make all critical clearing times longer than the relay and circuit breaker combination operation time. In the proposed method, desired critical clearing times are obtained by using on line system data and daily load curves. Then desired values are adjusted by generators output rescheduling and terminals voltage control
Visual computer language is used for graphical and numerical solutions. Comprehension of one machine infinite bus system and multimachine system transient stability become easier.
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Arioua, Leyla. „Commande des liaisons en courant continu dans un contexte réseau“. Thesis, Cachan, Ecole normale supérieure, 2014. http://www.theses.fr/2014DENS0029/document.
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Cette thèse porte sur les convertisseurs des liaisons à courant continu (HVDC- High Voltage Direct Current). Une nouvelle méthodologie de synthèse des régulateurs des convertisseurs basée sur un modèle de commande a été développée. Ce dernier prend en considération non seulement les deux convertisseurs de la liaison HVDC mais aussi l'ensemble des principaux éléments impactant la stabilité transitoire du système électrique dans lequel la liaison est insérée. Une commande robuste coordonnée est proposée pour, à la fois, répondre au cahier des charges de la liaison et améliorer la stabilité de la zone AC voisine à la liaison. La coordination de la synthèse de régulateurs pour les convertisseurs se fait à deux niveaux : le premier concerne les deux stations de conversion d'une même liaison HVDC et un second consistant en la coordination de plusieurs liaisons HVDC. De plus, seules les mesures disponibles localement (i.e., au niveau des stations de conversion) sont utilisées. Ce nouveau cadre de commande est une alternative à la commande vectorielle classique. L'approche a été validée à la fois sur des benchmarks académiques et en grande taille sur des cas concrets de renforcement du réseau de transport européenThis thesis focuses on the control of converters of high voltage direct current (HVDC) links. A new methodology of synthesis of the controllers of the HVDC converters based on a control model has been developed. The latter takes into consideration not only the two converters of HVDC link but all the main dynamics affecting the transient stability of the power system in which the link is inserted. In order to improve the stability of the AC zone neighboring the HVDC link, in addition to the local objectives like power and voltage control, a coordinated robust control is proposed. The coordination of the synthesis controllers for converters is done at two levels: the first one is the coordination of the two stations of an HVDC link the second is consisting on the coordination of several HVDC links. In addition, only measures available locally (i.e., at the converter stations) are used. This new control frame is an alternative to the conventional vector control. The approach was validated on both academic benchmark and a large-scale dynamic model of the whole European power system
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Gromotovič, Ivan. „Modelování a simulace elektromechanických přechodných jevů v elektrizační soustavě“. Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2020. http://www.nusl.cz/ntk/nusl-413126.
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This work deals with the issue of evaluating transient stability in the simulation program PSCAD. Factors affecting transient stability were analyzed on a single-machine SMIB model. The results of this analysis confirmed the theoretical assumption that for more accurate results of the analysis of transient stability, it is necessary to consider the mentioned factors. A short circuit was simulated on the IEEE9 test model and subsequently the load angles of the generators were monitored using various methods. The method of reference of the largest generator in the system proved to be a more suitable method for the assessment of relative load angles from the results of the analysis.
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Sleep, Matthew David. „Analysis of Transient Seepage Through Levees“. Diss., Virginia Tech, 2011. http://hdl.handle.net/10919/40356.
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Levees are a significant part of the United States flood protection infrastructure.
It is estimated that over 100,000 miles of levees exist in the United States. Most
of these levees were designed many years ago to protect farmland and rural
areas. As growth continues in the United States, many of these levees are now
protecting homes and other important structures. The American Society of Civil
Engineers gave the levees in the United States a grade of D- in 2009. To bring
flood protection up to modern standards there requires adequate methods of
evaluating levees with respect to seepage, erosion, piping and slope instability.
Transient seepage analyses provide an effective method of evaluating seepage
through levees and its potentially destabilizing effects.
Floods against levees usually last for days or weeks. In response to a flood,
pore pressures within the levee will change from negative (suction) to positive as
the phreatic surface progresses through the levee. These changes can be
calculated by finite element transient seepage analyses. In order for the
transient seepage analysis to be valid, appropriate soil properties and initial
conditions must be used. The research investigation described here provides
simple and practical methods for estimating the initial conditions and soil
properties required for transient seepage analyses, and illustrates their use
through a number of examples.Ph. D.
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Jiriwibhakorn, Somchat. „Transient stability assessment of power systems using neural networks“. Thesis, Imperial College London, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.249489.
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Anderson, Sharon Lee. „Reduced order power system models for transient stability studies“. Thesis, This resource online, 1993. http://scholar.lib.vt.edu/theses/available/etd-09052009-040743/.
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MORAES, ADELIO JOSE DE. „CONTRIBUITIONS TO THE LOAD MODELLING FOR TRANSIENT STABILITY STUDIES“. PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 1992. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=8361@1.
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UNIVERSIDADE FEDERAL DE UBERLÂNDIAEste trabalho, relacionado com a área de modelagem de cargas para estudos de estabilidade transitória de sistemas elétricos, tem por objetivo discutir a adequação dos modelos clássicos normalmente utilizados, bem como o aprimoramento e desenvolvimento de representações para cargas com características específicas. Inicialmente, são enfocados os aspectos das representações clássicas de cargas e, através de desenvolvimentos teóricos e estudos computacionais, ressaltadas as adequações destas estratégias ao contexto atual. Reconhecendo algumas limitações quanto às técnicas para a obtenção dos parâmetros de motores de indução, apresenta- se procedimentos sistematizados para o tratamento destes componentes de carga. Tendo em vista a busca da melhoria de modelos e respostas aos questionamentos a respeito da relevância da inclusão dos efeitos da variação da freqüência sobre as cargas e parâmetros da rede, o trabalho prossegue com investigações nesta direção. Objetivando a análise do desempenho dos modelos simplificados de cargas através de funções algébricas, são discutidas as propostas atuais e verificadas suas adequações aos estudos de estabilidade. Finalmente, considerando a importância atual das cargas conversoras estáticas, são desenvolvidos modelos apropriados e realizados os estudos necessários à incorporação de unidades retificadoras em programas de estabilidade.
This work, involved with the load modeling for electrical system transiente stability analysis, aim to discuss the classical load models normally used, and to develop and improve representations of specific types of loads. Initially, aspects concerned with classical load representations are dealt with aiming to evaluate, through theoretical and computational analyses, the current employment of such models. Knowing that the techiques to obtain induction motor parameters are still deficient, this work presents some systematic procedures for the treatment of such loads. Additionally, it continues seeking improvements in electrical system component models and answers to the questions about the need for inclusion of the frequency variation effects on loads and network parameters. Moreover, it takes into account the tendencies of using simplified load models represented by algebraic expressions. Some recent proposals in this area are discussed and tested with a view to acess the perfomance of the models in stability studies. Finally, considering the present importance of static load converters, it is developed the related models and presented the necessary studies to include rectifier units in stability programs.
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WENG, CHIYUAN. „Transient Stability Analysis of Power Systems with Energy Storage“. Case Western Reserve University School of Graduate Studies / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=case1348453228.
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Zhang, Yi. „Adaptive remedial action schemes for transient instability“. Online access for everyone, 2007. http://www.dissertations.wsu.edu/Dissertations/Fall2007/y_zhang_112707.pdf.
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Mihirig, Ali Mohamed. „Transient stability analysis of multimachine power systems by catastrophe theory“. Thesis, University of British Columbia, 1987. http://hdl.handle.net/2429/29022.
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Transient stability analysis is an important part of power system planning and operation. For large power systems, such analysis is very demanding in computation time. On-line transient stability assessment will be necessary for secure and reliable operation of power systems in the near future because systems are operated close to their maximum limits.
In the last two decades, a vast amount of research work has been done in the area of fast transient stability assessment by direct methods. The major difficulties associated with direct methods are the limitations in the power system model, determination of transient stability regions and adaptation to changes in operating conditions. In this thesis catastrophe theory is used to determine the transient stability regions. Taylor series expansion is used to find the energy balance equation in terms of clearing time and system transient parameters. The energy function is then put in the form of a catastrophe manifold from which the bifurcation set is extracted. The bifurcation set represents the transient stability region in terms of the power system transient parameters bounded by the transient stability limits. The transient stability regions determined are valid for any changes in loading conditions and fault location. The transient stability problem is dealt with in the two dimensions of transient stability limits and critical clearing times. Transient stability limits are given by the bifurcation set and the critical clearing times are calculated from the catastrophe manifold equation. The method achieves a breakthrough in the modelling problem because the effects of exciter response, flux decay and systems damping can all be included in the transient stability analysis. Numerical examples of one-machine infinite-bus and multi-machine power systems show very good agreement with the time solution in the practical range of first swing stability analysis. The method presented fulfills all requirements for on-line assessment of transient stability of power systems.Applied Science, Faculty of
Electrical and Computer Engineering, Department of
Graduate
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Parsons, Antony Cozart. „Automatic location of transient power quality disturbances /“. Digital version accessible at:, 1999. http://wwwlib.umi.com/cr/utexas/main.
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Seethapathi, Nidhi Seethapathi. „Transients, Variability, Stability and Energy in Human Locomotion“. The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1534590933898397.
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Al, Marhoon Hussain Hassan. „A Practical Method for Power Systems Transient Stability and Security“. ScholarWorks@UNO, 2011. http://scholarworks.uno.edu/td/114.
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Stability analysis methods may be categorized by two major stability analysis methods: small-signal stability and transient stability analyses. Transient stability methods are further categorized into two major categories: numerical methods based on numerical integration, and direct methods. The purpose of this thesis is to study and investigate transient stability analysis using a combination of step-by-step and direct methods using Equal Area Criterion. The proposed method is extended for transient stability analysis of multi machine power systems. The proposed method calculates the potential and kinetic energies for all machines in a power system and then compares the largest group of kinetic energies to the smallest groups of potential energies. A decision based on the comparison can be made to determine stability of the power system. The proposed method is used to simulate the IEEE 39 Bus system to verify its effectiveness by comparison to the results obtained by pure numerical methods.
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Zhou, Bowen. „The impact of electric vehicles on power system transient stability“. Thesis, Queen's University Belfast, 2016. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.709884.
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The penetration of the electric vehicle (EV) has increased rapidly in recent years mainly as a consequence of advances in both transportation and electricity sectors and in response to global pressure to reduce carbon emissions and limit fossil fuel consumption. Large-scale EV integration in power systems has modified the nature of the traditional electric load such that it should be controllable. Moreover, uncertain power sources and demand pose challenges in electricity transmission grid, leading to significant impact on power system security and stability. Therefore, it is timely that a comprehensive study of the impacts of large-scale EVs integration on power system stability is published. This thesis introduces EV development and typical global research and examines stochastic and intermittent issues which have parameterised in time, location, and magnitude. The work initially develops a flexible EV charging and discharging capacity forecasting model, which is suitable for different kinds of optimisation objects. Based on the proposed model, the main body of this work examines steady-state and transient stability analysis. In steady-state analysis, EV station siting and sizing and steady-state stability are considered. In transient stability analysis, an AC/DC converter-based EV station model has been proposed. EV connections and typical faults are discussed. Critical clearing time (CCT) and transient stability margin are used to assess transient stability by time-domain simulation. Two further topics, using local battery energy storage to meet local demand and application of an EV module for power system dispatch have been proposed as complementary applications for distribution networks and transmission grids.
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Zadehkhost, Sajjad. „Efficient algorithms to expedite transient stability analysis of power systems“. Thesis, University of British Columbia, 2015. http://hdl.handle.net/2429/52816.
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With rapid increase in complexity of modern power systems, there is a strong need for better computational tools to ensure the reliable operation of electrical grids. These tools need to be accurate, computationally efficient, and capable of using advanced measurement devices. In this context, transient stability assessment (TSA) is an important study that determines system’s dynamic security margins following a major disturbance. The TSA consists of a set of differential-algebraic equations (DAEs), which are typically solved using time-domain simulation (TDS) approach. While being very accurate, the TDS requires significant computational resources when applied to practical power systems. This problem becomes more significant in transient stability monitoring (TSM), wherein the computational performance of the TDS is typically the bottleneck. This research is to investigate available challenges in the TSM applications and develop new algorithms to help realizing a practical monitoring tool for transient stability studies. The thesis focuses on three research thrusts: i) dynamic reduction of power system to reduce problem size; ii) advanced computation approaches to expedite the TDS method; iii) integration of PMU measurements into the TSM. Initially, a new adaptive aggregation algorithm for dynamic reduction is proposed, wherein parameters of generators and structure of transmission network are considered to aggregate coherent generators and create a reduced-order system. Also, a new criterion is defined to monitor validity of the constructed reduced system. It is shown that the proposed technique is more accurate than traditional aggregation methods. To expedite the TDS approach, this thesis presents two new integration techniques, which are called Multi-Decomposition Approach (MDA) and Successive Linearization and Integration Technique (SLIT). In these methods, the nonlinear DAEs are decomposed into a series of linear subsystems, which participate in approximating actual solution. It is demonstrated that sequential and parallel versions of the MDA and SLIT are faster than state-of-the-art integration techniques. Finally, a dynamic state estimator based on Extended Kalman Filter is developed to convert the PMU measurements into a set of state variables suitable for transient stability studies. Computer studies show that the proposed framework provides accurate results in highly disturbed power systems with fairly low PMU sampling rates.Applied Science, Faculty of
Electrical and Computer Engineering, Department of
Graduate
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Rudraraju, Seetharama raju. „SMALL SIGNAL AND TRANSIENT STABILITY ANALYSIS OF MVDC SHIPBOARD POWER SYSTEM“. MSSTATE, 2009. http://sun.library.msstate.edu/ETD-db/theses/available/etd-11052009-170217/.
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Recent developments in high power rated Voltage Source Converters (VSCs) have resulted in their successful application in Multi-Terminal HVDC (MTDC) transmission systems and also have potential in the Medium Voltage DC (MVDC) distribution systems. This work presents the findings of stability studies carried out on a zonal MVDC architecture for the shipboard power distribution system. The stability study is confined to rotor angle stability of the power system, i.e. the transient and small signal stability analysis. The MTDC ring structure similar to MVDC shipboard power system was implemented in MATLAB/Simulink to look at the transient behavior of the MVDC system. Small signal stability analysis has been carried out with the help of Power System Toolbox (PST) for both MVAC as well as MVDC architectures. Later, Participation Analysis has been carried out to address the small signal instability in the case of MVAC architecture and methods for enhancement were also presented.
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SILVA, KARLA GUEDES CARNEIRO DA. „POWER SYSTEM TRANSIENT STABILITY ASSESSMENT USING THE EXTENDED EQUAL AREA CRITERION“. PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 1996. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=8752@1.
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CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOEste trabalho analisa o desempenho do Critério das Áreas Iguais Estendido na avaliação da estabilidade transitória de sistemas de potência. O Critério das Áreas Iguais Estendido consiste em representar o sistema multimáquina por um sistema equivalente de duas máquinas, que é, em seguida, reduzido a um sistema máquina-barra infinita, no qual é aplicado o conhecido critério das áreas iguais. A evolução no tempo do sistema máquina-barra infinita resultante é aproximada por uma série de Taylor truncada. As medidas de estabilidade calculadas, através de expressões algébricas simples, são o tempo crítico de eliminação de falta e a margem de segurança. A análise da estabilidade é feita, portanto, sem procedimentos de tentativa e erro. Os resultados são comparados com os obtidos utilizando um programa convencional de estabilidade transitória.
This work evaluates the performance of the Extended Equal area Criterion for power system transient stability assessment. The Extended Equal Area Criterion consists in replacing the multimachine power system by an equivalent two machine system, which is further reduced to a one- machine-infinite-bus system. The well-know Equal Area Criterion is then applied to the latter system. The time evolution of the one-machine-infinite-bus system is approximated by a truncated Taylor s series. The stability measures are computed by simple algebraic expressions and the transient stability margin. These measures are computed by simple algebraic expressions and the stability analysis is performed without any trial and error procedures. The results are compared to those obtained using a conventional transient stability program.
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PESSANHA, JOSE EDUARDO ONODA. „VOLTAGE STABILITY PHENOMENON ANALYSIS: TRANSIENT AND LONG TERM TIME DOMAIN SIMULATION“. PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 1997. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=8941@1.
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CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOEste trabalho analisa o fenômeno da estabilidade de tensão no domínio do tempo incluindo fenômenos rápidos (transitórios) e lentos (longo-termo). As diferentes formas de estabilidade existentes nos sistemas elétricos de potência são definidas e classificadas de acordo com a variável de interesse e com a amplitude do distúrbio. Utilizando-se um simples sistema elétrico de potência, verifica-se através de formulações dinâmicas fatores relevantes ao fenômeno da estabilidade de tensão. Investiga-se a influência de cargas do tipo potência constante e impedância constante sobre a estabilidade de tensão. Compensadores estáticos são incluídos nas análises e verifica-se a existência de regiões de operação onde as ações de controle não apresentam o efeito esperado. Investiga-se através de cenários o efeito adverso de dispositivos de controle com o limitador de sobre- excitação e o transformador de tape variável sobre a estabilidade de tensão. A partir de uma versão do programa de estabilidade transitória TRANSTAB, foram desenvolvidas duas versões do programa computacional VOLTDYN para simular no domínio do tempo o fenômeno da estabilidade de tensão. A primeira versão do programa Utiliza um algoritmo de integração de passo variável usando o método trapezoidal implícito enquanto que a segunda versão utiliza o método de Adams-Bashforth- Moulton. Diversos testes computacionais com as duas versões são realizados comprovando-se a importância desta forma de análise.
This work is concerned with voltage stability analysis in time domain including transient and long-term time frames. Different power system stability forms are defined and classified according to the variable of interest and with the disturbance magnitude. Using a simple power system model, it is shown through dynamics formulations important aspects of the voltage stability phenomenon. Important aspects of load characteristics of constant power type and mixed (constant power/constant impedance) type on voltage stability are investigated. A static compensator model is included in the analysis and it is verified that under specific operation conditions the control actions are not efficient. Scenarios show the adverse effects of long-term control devices such as overexcitation limiters and under load tap changers on voltage stability. One version of the transient stability program TRANSTAB is modified in order to simulate transient and long-term voltage phenomena. The resulting modified computer program is called VOLTDYN. Two versions of the VOLTDYN progran are available. The first version uses a variable step-size algorithm based on the trapezoidal method. The other includes a variable step-size algorithm based on the Adams- Bashforth-Moulton method.
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Al, Marhoon Hussain Hassan. „Adaptive Online Transient Stability Assessment of Power Systems for Operational Purposes“. ScholarWorks@UNO, 2015. http://scholarworks.uno.edu/td/2036.
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Online stability assessment is an important problem that has not been solved completely yet. The purpose of this research is to tackle online transient stability assessment. Currently, most utility companies use step-by-step integration in order to set protective equipment so that they effectively work for critical contingencies. However, there are times an unforeseen contingency may occur which may cause the system to transit and the protective equipment to misoperate and does not isolate the disturbed part of the system. This research introduces a method that automatically determines a group of generators that participate in system separation and hence transient instability. The method consists of four phases: modeling and simulation, critical machines identification, online transient stability assessment, and critical clearing time calculation. In the modeling and simulation phase, the power system is built and the generators’ rotor angles and speeds are captured. In the critical machines identification phase, the average instantaneous rotor accelerating powers, coherency measures, the during-fault rotor angles and speeds characteristics, and the pre- and post-fault rotor angles are used to identify the Severely Disturbed Group (SDG) of machines. The results of this phase are used to calculate the kinetic energy of the SDG and potential energy of another (or possibly the same) group of generators. Utilization and success of the proposed method will be documented using results from the IEEE 39-Bus test system. Each step of each phase will be demonstrated as needed. The proposed method is compared to step-by-step integration and two direct methods. The suitability of the proposed method for operation will be shown in cases where the Y-Bus matrix and rotor angles and speeds are given. The proof of concept of the proposed method was used in simulating the test system and encouraging results of the simulation were published in [1] and [2]. The proof of concept is the foundation of the method proposed in this dissertation to determine transient stability of large-scale power systems.
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Li, Meiyan. „Transient Stability Prediction based on Synchronized Phasor Measurements and Controlled Islanding“. Diss., Virginia Tech, 2013. http://hdl.handle.net/10919/52623.
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Traditional methods for predicting transient stability of power systems such as the direct method, the time domain approach, and the energy function methods do not work well for online transient stability predictions problems. With the advent of Phasor Measurement Units (PMUs) in power systems, it is now possible to monitor the behavior of the system in real time and provide important information for transient stability assessment and enhancement. Techniques such as the rotor oscillation prediction method based on time series have made the prediction of system stability possible for real-time applications. However, methods of this type require more than 300 milliseconds after the start of a transient event to make reliable predictions. The dissertation provides an alternate prediction method for transient stability by taking advantage of the available PMUs data. It predicts transient stability using apparent impedance trajectories obtained from PMUs, decision trees, and FLDSD method. This method enables to find out the strategic locations for PMUs installation in the power system to rapidly predict transient stability. From the simulations performed, it is realized that system stability can be predicted in approximately 200 milliseconds (12 cycles). The main advantage of this method is its simplicity as the PMUs can record the apparent impedance trajectories in real-time without any previous calculations. Moreover, using decision trees built in CART, transient stability prediction becomes straightforward and computationally very fast. The optimum locations for PMUs placement can also be determined using this technique.
After the transient instability prediction by the apparent impedance trajectories, a slow- coherency based intelligent controlled islanding scheme is also developed to restore the stability of system. It enables the generators in the same island to stay in synchronism and the imbalance between the generators and load demand is minimized.Ph. D.
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Emmanuel, Paul. „Investigation into transient stability of a nuclear power plant using DIgSILENT“. Master's thesis, University of Cape Town, 2016. http://hdl.handle.net/11427/20322.
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The current electricity crisis, coupled with the lack of generation, has led to a major focus on continuity of supply. The Western Cape has been severely affected, as it only has a limited number of generation sources, namely Koeberg Nuclear Power Station (base supply) along with other power stations used for peak load running such as Ankerlig, Palmiet, etc. Koeberg Nuclear Power Station is located at the end of a long transmission line with no other base-load generation for 1500km, between the power station and the mass pool of coal-fired generation in Mpumalanga. Koeberg Nuclear Power Station (herein referred to as "Koeberg") plays a significant role in ensuring the stability of the Western Cape's electricity network. Without this power stattion, the network power flow is greatly affected, and is placed under severe strain. Koeberg is the determining factor when the system operators control the Western Cape network. The network is modelled having one of Koeberg's unit offline, using contingency analysis N-1. The one Koeberg unit being the N-1 contingency factored into the transmission network. The network should be able to withstand a disturbance with one Koeberg unit out of service and maintain stability after the disturbance. With the Eskom's decision to increase Koeberg power plant's electrical output power, it became apparent that the impact of this upgrade needed to be assessed. In the past, various hand calculations and assumptions were made before implementation of these types of changes could occur. With the advent of technology, modern computer-based software simulation tools have reduced the time to analyse such changes and aid engineers to quickly assess the impact it would have on various components. A load flow and short circuit studies of the Koeberg internal networks were performed and verified against plant data. The original data was compared to simulated data using a computer-based simulation package. The simulation software package used to validate the results is the DIgSILENT software package. This is one of the standard software packages used by Eskom to validate models on the network. Load flow studies for Koeberg have been completed in the past, but many changes have since been made to the plant. There was thus a requirement to re-calculate the original load flow studies and ensure that all plant and protection settings are within an acceptable criterion. This new study found that there were minor errors in the on-site documentation and that the software is compatible with the plant data.
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Khomari, Moloantoa. „The impact of wind generators on a Powe system's transient stability“. Master's thesis, University of Cape Town, 2009. http://hdl.handle.net/11427/5193.
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This thesis discusses the investigations carried out on the different types of wind generators and how these would affect the transient stability of a hypothetical power network as presented in this report. Focus was on the transient responses of the conventional synchronous generator’s rotor angle and terminal voltage when connected to different types of wind generators. The three different wind generator technologies explored were the squirrel cage induction generator (SCIG), doubly-fed induction generator (DFIG) and the converter driven synchronous generator (CDSG).
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Olulope, Paul Kehinde. „Transient stability assessment of hybrid distributed generation using computational intelligence approaches“. Doctoral thesis, University of Cape Town, 2014. http://hdl.handle.net/11427/9288.
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Includes bibliographical references.Due to increasing integration of new technologies into the grid such as hybrid electric vehicles, distributed generations, power electronic interface circuits, advanced controllers etc., the present power system network is now more complex than in the past. Consequently, the recent rate of blackouts recorded in some parts of the world indicates that the power system is stressed. The real time/online monitoring and prediction of stability limit is needed to prevent future blackouts. In the last decade, Distributed Generators (DGs) among other technologies have received increasing attention. This is because DGs have the capability to meet peak demand, reduce losses, due to proximity to consumers and produce clean energy and thus reduce the production of CO₂. More benefits can be obtained when two or more DGs are combined together to form what is known as Hybrid Distributed Generation (HDG). The challenge with hybrid distributed generation (HDG) powered by intermittent renewable energy sources such as solar PV, wind turbine and small hydro power is that the system is more vulnerable to instabilities compared to single renewable energy source DG. This is because of the intermittent nature of the renewable energy sources and the complex interaction between the DGs and the distribution network. Due to the complexity and the stress level of the present power system network, real time/online monitoring and prediction of stability limits is becoming an essential and important part of present day control centres. Up to now, research on the impact of HDG on the transient stability is very limited. Generally, to perform transient stability assessment, an analytical approach is often used. The analytical approach requires a large volume of data, detailed mathematical equations and the understanding of the dynamics of the system. Due to the unavailability of accurate mathematical equations for most dynamic systems, and given the large volume of data required, the analytical method is inadequate and time consuming. Moreover, it requires long simulation time to assess the stability limits of the system. Therefore, the analytical approach is inadequate to handle real time operation of power system. In order to carry out real time transient stability assessment under an increasing nonlinear and time varying dynamics, fast scalable and dynamic algorithms are required. Transient Stability Assessment Of Hybrid Distributed Generation Using Computational Intelligence Approaches These algorithms must be able to perform advanced monitoring, decision making, forecasting, control and optimization. Computational Intelligence (CI) based algorithm such as neural networks coupled with Wide Area Monitoring System (WAMS) such as Phasor Measurement Unit (PMUs) have been shown to successfully model non-linear dynamics and predict stability limits in real time. To cope with the shortcoming of the analytical approach, a computational intelligence method based on Artificial Neural Networks (ANNs) was developed in this thesis to assess transient stability in real time. Appropriate data related to the hybrid generation (i.e., Solar PV, wind generator, small hydropower) were generated using the analytical approach for the training and testing of the ANN models. In addition, PMUs integrated in Real Time Digital Simulator (RTDS) were used to gather data for the real time training of the ANNs and the prediction of the Critical Clearing Time (CCT).
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Fahmi, Nagi R. „Modelling of induction motors for system faults and transient stability studies“. Thesis, Aston University, 1986. http://publications.aston.ac.uk/8049/.
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The research carried out in this thesis was mainly concerned with the effects of large induction motors and their transient performance in power systems. Computer packages using the three phase co-ordinate frame of reference were developed to simulate the induction motor transient performance. A technique using matrix algebra was developed to allow extension of the three phase co-ordinate method to analyse asymmetrical and symmetrical faults on both sides of the three phase delta-star transformer which is usually required when connecting large induction motors to the supply system. System simulation, applying these two techniques, was used to study the transient stability of a power system. The response of a typical system, loaded with a group of large induction motors, two three-phase delta-star transformers, a synchronous generator and an infinite system was analysed. The computer software developed to study this system has the advantage that different types of fault at different locations can be studied by simple changes in input data. The research also involved investigating the possibility of using different integrating routines such as Runge-Kutta-Gill, RungeKutta-Fehlberg and the Predictor-Corrector methods. The investigation enables the reduction of computation time, which is necessary when solving the induction motor equations expressed in terms of the three phase variables. The outcome of this investigation was utilised in analysing an introductory model (containing only minimal control action) of an isolated system having a significant induction motor load compared to the size of the generator energising the system.
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Roberts, Lewis George Wilson. „Parametric analysis of transient stability in power systems using classical models“. Thesis, University of Bristol, 2016. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.702145.
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This thesis aims to strengthen the bridge between mathematical and practical research into the transient stability of power systems. Literature that exploits the mathematical parallels between models for transient dynamics in power systems and the phenomenon of synchronisation in complex networks is explored. However, it is contended that research at the intersection of complex systems and power system stability can limit its applications to practical issues in power engineering. This thesis focuses on the measurement of transient stability in power systems in terms of a traditional stability metric for short-circuit faults on a power network, the critical clearing time (CCT). The CCT provides an upper bound on the duration of a short circuit on a power network before it is removed - cleared - by the action of protection mechanisms to isolate the faulted circuit such that the system will regain synchrony once the fault is cleared. Approaches that use energetic methods for assessing the transient stability of a power system are extended by developing metrics that can measure stability trends for different scenarios in a power system via the numerical continuation of equilibrium configurations under the variation of system parameters. An analytical CCT (ACCT) approximation is derived from this energetic framework in order to capture trends in stability with respect to a system parameter. The performance of the ACCT is compared to more accurate computations of CCT that use slower numerical simulation techniques. Attention is given to how well the ACCT approximation can capture stability trends under variation of key network design parameters such as load admittance and generator inertia. It is found for a two-machine infinite bus (TMIB) system that load parameter values that can improve stability can be identified using the ACCT. Also, the general dependence of a fault's CCT on the inertia of a generator in a TMIB power system is identifiable using the ACCT. For power systems with stationary generator inertia values, a method to provide a contingency analysis of fault locations is proposed. The method ranks the locations of short-circuit faults by their CCT; the more severe a fault the shorter its CCT. It is found in a TMIB system that the ACCT can identify the general location of severe faults under different inertia scenarios. It is shown that in larger power systems, energetic methods can be used to accurately identify the locations of faults with short CCTs. These results, together with relevant literature are used to suggest possible strategies to monitor transient stability within modern power systems.
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Cvetkovic, Milos. „Power-Electronics-Enabled Transient Stabilization of Power Systems“. Research Showcase @ CMU, 2013. http://repository.cmu.edu/dissertations/344.
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Transient stability of electric energy grids is defined as the ability of the power system to remain in synchronism during large disturbances. If the grid is not equipped with controllers capable of transiently stabilizing system dynamics, large disturbances could cause protection to trigger disconnecting the equipment and leading further to cascading system-wide blackouts. Today’s practice of tuning controllers generally does not guarantee a transiently stable response because it does not use a model for representing system-wide dynamic interactions. To overcome this problem, in this thesis we propose a new systems modeling and control design for provable transient stabilization of power systems against a given set of disturbances. Of particular interest are fast power-electronically-controlled Flexible Alternating Current Transmission System (FACTS) devices which have become a new major option for achieving transient stabilization. The first major contribution of this thesis is a framework for modeling of general interconnected power systems for very fast transient stabilization using FACTS devices. We recognize that a dynamic model for transient stabilization of power systems has to capture fast electromagnetic dynamics of the transmission grid and FACTS, in addition to the commonly-modeled generator dynamics. To meet this need, a nonlinear dynamic model of general interconnected electric power systems is derived using time-varying phasors associated with states of all dynamic components. The second major contribution of this thesis is a two-level approach to modeling and control which exploits the unique network structure and enables preserving only relevant dynamics in the nonlinear system model. This approach is fundamentally based on separating: a) internal dynamics model for ensuring stable local response of components; b) system-level model in terms of interaction variables for ensuring stability of the system when the components are interconnected. The two levels can be controlled separately which minimizes the need for communication between controllers. Both distributed and cooperative ectropy-based controllers are proposed to control the interaction-level of system dynamics. Proof of concept simulations are presented to illustrate and compare the promising performance of the derived controllers. Some of the most advanced FACTS industry installations are modeled and further generalized using our approach.
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Kanchanaharuthai, Adirak. „Small-Signal Stability, Transient Stability and Voltage Regulation Enhancement of Power Systems with Distributed Renewable Energy Resources“. Case Western Reserve University School of Graduate Studies / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=case1321988036.
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Garnaud, Xavier. „Modes, transient dynamics and forced response of circular jets“. Palaiseau, Ecole polytechnique, 2012. https://theses.hal.science/tel-00740133/document.
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La stabilité linéaire des jets axisymétriques est étudiée dans un contexte global, c'est à dire en prenant en compte sans approximation la géométrie et le non-parallélisme de l'écoulement. Afin de caractériser le "mode préféré" du jet observé expérimentalement et numériquement, différentes analyses ont été mises en oeuvre. Une conjecture étant que ces structures à une résonance entre des perturbations extérieures et le mode propre le moins atténué, une analyse modale de l'écoulement a tout d'abord été effectuée. Cette étude a demandé la mise au point d'une méthode numérique spécifique pour pouvoir traiter les écoulements compressibles de manière efficace. Cependant, les résultats ont montré qu'une représentation modale n'est pas adaptée pour décrire la dynamique des écoulements stable dominés par l'advection. Des modèles simplifiés permettant de mieux comprendre les limites de cette approche sont présentés. Cette dynamique peut cependant être caractérisée par le calcul des perturbations optimales et du forçage harmonique optimal. Cette dernière approche reproduit de manière robuste les observations expérimentales concernant la fréquence et la structure spatiale du "mode préféré". La structure de ce paquet d'onde global est interprétée comme provenant de la coopération entre différentes familles de modes locaux. L'analyse présentée dans cette thèse montre que le "mode préféré" du jet ne vient pas de la résonance d'un mode propre, mais qu'il s'agit en fait d'une pseudo-résonanceThe linear stability of axisymmetric jets is studied in a global frame- work, such that the geometry and the non-parallelism of the base flow are fully accounted for. In order to characterize the "preferred mode" of the jet, which is consistently observed in experiments and numerical simulations, different types of analyses are carried out. As a well-known conjecture ascribes the existence of this "preferred mode" to a resonance between external noise and the least-stable eigenmode, a modal study is first performed. This analysis prompted the development of a new numerical method allowing an efficient treatment of compressible flows; however, the results indicate that a modal representation is not well-suited for a description of the dynamics of convection-dominated stable flows. Studies of simplified model problems are presented that underpin this conclusion. Instead, the instability dynamics of such flows are characterized in a consistent manner in terms of optimal initial perturbations and optimal harmonic forcing. The latter approach robustly reproduces experimental observations with regard to the frequency and the spatial structure of the jet "preferred mode". Furthermore, the results allow an interpretation of this global wavepacket structure as a cooperation of different families of local instability modes. The present analysis demonstrates that the "preferred mode" does not arise from resonance with an eigenmode, but rather is to be interpreted as a pseudo-resonance
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Jiang, Hong. „A graphical interface for the BPA load flow and transient stability programs“. Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp05/mq23355.pdf.
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Chapman, Jeffrey W. (Jeffrey Wayne). „Power system control for large-disturbance stability : security, robustness and transient energy“. Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/39393.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1996.Includes bibliographical references (p. 223-228).
by Jeffrey Wayne Chapman.
Ph.D.
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Ferri, Matthew A. (Matthew Anthony). „Current distribution and stability criteria for superconducting cables in transient magnetic fields“. Thesis, Massachusetts Institute of Technology, 1997. http://hdl.handle.net/1721.1/10406.
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Laury, John. „Transient Stability in Low Frequency Railways with Mixed Electronic and Rotational Generation“. Licentiate thesis, Luleå tekniska universitet, Energivetenskap, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-26485.
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Transient stability concerns the ability of a power system to maintain synchronism after a large disturbance. Transient stability plays an important role in guaranteeing operational security and reliability and has been extensively studies for large 50 Hz and 60 Hz transmission systems. However, transient stability of low frequency railway grids has not been properly investigated.As low frequency railway grids operate at another frequency than the public grid, conversion of frequency is needed. This conversion is performed by Rotary Frequency Converters or by Static Frequency Converters. These two types of converters have a different impact on stability. In this thesis, the overall aim is to obtain knowledge on transient stability in low frequency railway grids, with focus on the Swedish synchronous-synchronous railway grid with a mix of Rotary and Static Frequency Converters.The transient stability problem is approached by developing a simplified model of a Static Frequency Converter that can be used for the stability studies in low frequency railways. The Static Frequency Converter is modelled as single phase generator with an equivalent inertia and damping. However as Static Frequency converters cannot handle currents much above their ratings, current limitation is implemented. The current limitation is needed to avoid unnecessary tripping of the converter during fault or other high current situations. With the model developed for a Static Frequency Converter and with a simplified model of a Rotary Frequency Converter, transient stability studies have been performed for several test systems representing the Swedish railway grid.The simulations performed shows the appearance of power oscillations after a large disturbance, between a Static Frequency Converter and a Rotary Frequency Converter when these are operating in parallel. The simulations also showed that the systems studied were stable for realistic values of the fault-clearing time.Godkänd; 2016; 20160510 (johlau); Nedanstående person kommer att hålla licentiatseminarium för avläggande av teknologie licentiatexamen. Namn: John Laury Ämne: Elkraftteknik/Electric Power Engineering Uppsats: Transient Stability in Low Frequency Railways with Mixed Electronic and Rotational Generation Examinator: Professor Math Bollen, Institutionen för teknikvetenskap och matematik, Avdelning: Energiteknik, Luleå tekniska universitet. Diskutant: Docent Thorsten Schütte, STRI AB, Västerås Tid: Fredag 17 juni, 2016 kl 10.00 Plats: Skellefteå, Luleå tekniska universitet
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Parsi-Feraidoonian, Raiomand. „Application of catastrophe theory to transient stability analysis of multimachine power systems“. Thesis, University of British Columbia, 1990. http://hdl.handle.net/2429/29723.
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Transient stability analysis is an important part of power planning and operation. For large power systems, such analysis is very time consuming and expensive. Therefore, an online
transient stability assessment will be required as these large power systems are operated close to their maximum limits. In this thesis swallowtail catastrophe is used to determine the transient stability regions. The bifurcation set represents the transient stability region in terms of power system transient parameters bounded by the transient stability limits. The system modelling is generalized in such, that the analysis could handle either one or any number of critical machines. This generalized model is then tested on a three-machine as well as a seven-machine system. The results of the stability analysis done with the generalized method is compared with the time solution and the results were satisfactory. The transient stability regions determined are valid for any changes in loading conditions and fault location. This method is a good candidate for on-line assessment of transient stability of power systems.Applied Science, Faculty of
Electrical and Computer Engineering, Department of
Graduate
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Krakowski, Vincent. „Intégration du renouvelable et stratégie de déploiement du réseau électrique : réconciliation d'échelles spatio-temporelles dans des exercices prospectifs de long terme“. Thesis, Paris Sciences et Lettres (ComUE), 2016. http://www.theses.fr/2016PSLEM025/document.
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Les systèmes électriques évoluent actuellement vers l'intégration d'une production moins carbonée, éventuellement plus locale. Afin d’explorer les évolutions possibles de ces systèmes sur le long terme, l’exercice prospectif s’appuyant sur des modèles est un outil précieux. Cependant, pour être pertinent, il doit réconcilier des phénomènes spatiaux et temporels à des échelles variées. Ainsi, le fonctionnement du système électrique repose sur un équilibre offre – demande à chaque instant. Afin de corriger les fluctuations de la production ou de la consommation qui surviennent nécessairement, les gestionnaires de réseau mettent en place un certain nombre de régulations dont les durées d’activation sont de l’ordre de quelques secondes à quelques heures. A des échelles de temps encore plus fines le système électrique présente une robustesse interne : le réseau électrique créé un couplage électromagnétique entre les machines synchrones qui leur permet de mutualiser leur inertie respective. Cette inertie, qui constitue une réserve d’énergie cinétique, est instantanément disponible pour faire face aux fluctuations. Pour que les scénarios de long terme proposés ne soient pas en contradiction avec les exigences de robustesse du système électrique, qui permettront son opération, il est nécessaire que l’évaluation de cette robustesse soit intégrée à la modélisation prospective. Dans ce travail, nous proposons un indicateur, calculable au sein des études de prospective, qui évalue la stabilité d’un système électrique, c’est- à-dire son aptitude à revenir au synchronisme suite à une perturbation. Cet indicateur repose sur une description agrégée du réseau de transport et traduit le couplage électromagnétique apporté par le réseau. Associé au modèle bottom-up de la famille MARKAL/TIMES décrivant le système électrique français, cet indicateur de synchronisme et un indicateur quantifiant la réserve cinétique disponible, nous permet d’évaluer les conséquences de la pénétration du renouvelable, notamment sur la robustesse du système électriquePower systems are currently facing several issues in order to evolve and integrate less carbon-heavy, and potentially more local, production. Prospective model-based analysis is a precious tool for exploring the possible long-term developments of these systems and comparing their advantages and disadvantages. However, to ensure relevance, it is important to reconcile the spatial and temporal phenomena that occur at various scales. Power system management depends on constantly maintaining a complex supply- demand balance. Meeting this challenge requires anticipating demand variations and power plant availability, combined with regulation systems to resolve remaining discrepancies. These regulations are activated in from a few seconds up to several hours. On shorter timescales, power systems show inherent robustness: the power grid creates an electromagnetic coupling between synchronous machines allowing them to share their inertia. This inertia, which takes the form of kinetic energy, is instantaneously available to face natural demand or supply fluctuations. To ensure that proposed long-term scenarios are consistent with the robustness requirements of power systems, which enable their management, this robustness must be assessed using prospective modeling. In this work, we propose an indicator, calculable within prospective studies, which assesses power system stability, namely its ability to return to synchronism after a perturbation. This indicator is based on an aggregated description of the transportation power grid and describes the electromagnetic coupling brought by the power grid. When combined with a bottom-up model from the MARKAL/TIMES family describing the French power system, this synchronism indicator, along with another indicator quantifying the available kinetic reserve, enables us to assess the consequences of renewable penetration, especially in terms of power system robustness
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Milliken, Robert Jon. „A capacitor-less low drop-out voltage regulator with fast transient response“. Texas A&M University, 2005. http://hdl.handle.net/1969.1/3275.
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Power management has had an ever increasing role in the present electronic industry.
Battery powered and handheld applications require power management techniques to extend the
life of the battery and consequently the operation life of the device. Most systems incorporate
several voltage regulators which supply various subsystems and provide isolation among such
subsystems. Low dropout (LDO) voltage regulators are generally used to supply low voltage,
low noise analog circuitry. Each LDO regulator demands a large external capacitor, in the range
of a few microfarads, to perform. These external capacitors occupy valuable board space,
increase the IC pin count, and prohibit system-on-chip (SoC) solutions.
The presented research provides a solution to the present bulky external capacitor LDO
voltage regulators with a capacitor-less LDO architecture. The large external capacitor was
completely removed and replaced with a reasonable 100pF internal output capacitor, allowing
for greater power system integration for SoC applications. A new compensation scheme is
presented that provides both a fast transient response and full range ac stability from a 0mA to
50mA load current. A 50mA, 2.8V, capacitor-less LDO voltage regulator was fabricated in a
TSMC 0.35um CMOS technology, consuming only 65uA of ground current with a dropout
voltage of 200mV.
Experimental results show that the proposed capacitor-less LDO voltage regulator exceeds
the current published works in both transient response and ac stability. The architecture is also
less sensitive to process variation and loading conditions. Thus, the presented capacitor-less
LDO voltage regulator is suitable for SoC solutions.
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Bagheri, Shervin. „Stability analysis and control design of spatially developing flows“. Licentiate thesis, KTH, Mechanics, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4769.
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Methods in hydrodynamic stability, systems and control theory are applied to spatially developing flows, where the flow is not required to vary slowly in the streamwise direction. A substantial part of the thesis presents a theoretical framework for the stability analysis, input-output behavior, model reduction and control design for fluid dynamical systems using examples on the linear complex Ginzburg-Landau equation. The framework is then applied to high dimensional systems arising from the discretized Navier–Stokes equations. In particular, global stability analysis of the three-dimensional jet in cross flow and control design of two-dimensional disturbances in the flat-plate boundary layer are performed. Finally, a parametric study of the passive control of two-dimensional disturbances in a flat-plate boundary layer using streamwise streaks is presented.
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Kurt, Burcak. „Impact Of High-level Distributed Generation Penetration On The Transmission System Transient Stability“. Master's thesis, METU, 2009. http://etd.lib.metu.edu.tr/upload/2/12611199/index.pdf.
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This thesis investigates the impact of high-level penetration of distributed generation especially from the renewable energy sources on the transient stability of the transmission system.
Distributed generation is a source of electric power connected to the distribution network or on the consumer side. It is expected that distributed generation grows significantly by the increasing environmental concerns and deregulation in the market. As soon as the increasing penetration level, distributed generation starts to influence the distribution system as well as the transmission system.
To investigate the impact of distributed generation with different penetration levels on the transmission system transient stability, simulation scenarios are created and simulations are run on the basis of these scenarios by the implementation of the different distributed generation technologies to the &ldquoNew England&rdquo
test system. Stability indicators are observed to assess the impact on the transient stability. Results are presented throughout the thesis and the impact of the different distributed generation technologies and the different penetration levels on the transient stability is discussed by comparing the stability indicators.
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Elkington, Katherine. „On the Use of Wind Power for Transient Stability Enhancement of Power Systems“. Thesis, KTH, Elektriska energisystem, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-118931.
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This report deals with the impact of doubly fed induction generators on the stability of a power system. The impact was quantified by means of detailed numerical simulations. The report contains a full description of the simulation, and details of the small signal analysis performed to analyse the system. Before the simulation results are presented, a foundation is laid, explaining the theory required to understand the models used and the calculations performed in the simulation. The derivation of a model of a doubly fed induction generator is presented, along with a description of the model of a synchronous generator. These are used in the simulation and analysis of a multi-machine power system, consisting of both of these types of generators. An explanation of how dynamic simulations of power systems can be performed is also put forward. This is useful, not only for understanding the simulation performed for this report, but as a guide to performing simulations of this type. This is true also for a description of linearisation and small signal analysis contained in this report. The software package MATLAB is used to perform the simulations, and the small signal analysis. Since the method described in this report is very general, it can be used to perform similar power system simulations for other power systems, and with other software. Numerical simulations reveal that the addition of doubly fed generators, such as those in wind parks, to a power system improves the response of the system after small disturbances, but can worsen it after larger disturbances.
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Kiss, Andras Laszlo Andor. „Two investigations of compressor stability : spike stall inception and transient heat transfer effects“. Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/101445.
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Thesis: S.M., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2015.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 139-142).
Two investigations of current problems in the field of compressor stability are presented. The first is of the formation of spike-type rotating stall precursors. Recently, high fidelity computations have attributed pre-cursor formation to a leading-edge separation and consequent shedding of vorticity near the rotor tip due to high incidence. This hypothesis is assessed via experiments in a low-speed compressor and a linear cascade, supported by unsteady computations. Fast-response pressure measurements at the blade tip show spike pre-cursors propagating in the cascade environment at a rate consistent with the low-speed compressor. The cascade design produces high incidence at the mid-span and fast-response velocity measurements show pre-cursor formation away from the tip region. Unsteady computations confirm leading-edge separation and vortex shedding in both the compressor and cascade. A single blade was instrumented with smoke injection at the leading-edge to visualize the separation and the effect of Reynolds number on pre-cursor formation was quantified to facilitate smoke visualization. The resultant visualizations confirm the leading-edge separation and propagation of shed vorticity. The second investigation is of the effects of heat transfer between the compressor structure and gas path during transient operation. A mean line model of an advanced, high pressure ratio compressor is extended to include the effects of heat transfer. Diabatic, transient calculations show a 9.9 point reduction in stall margin from the adiabatic case. 2.5 points are attributed to the effect of heat transfer on blade row deviation and the remainder is attributed to stage rematching. Heat transfer increases loading in the front stages and the stalling pressure ratio is set by front stage stall, suggesting heat transfer effects are greater for compressors with highly loaded front stages. Sensitivity studies of heat flow rate and deviation show a linear dependence of stall margin loss for ratios of heat flow rate to inlet stagnation enthalpy flux much less than unity.
by Andras Laszlo Andor Kiss.
S.M.