Дисертації з теми "Load stability"
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1
Dai, F. "Load modelling for power system stability studies." Thesis, University of Manchester, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.578290.
Повний текст джерела
2
Monnin, Jared P. "Impact of load type on microgrid stability." Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/76821.
Повний текст джерелаАнотація:
Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2012.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
CD-ROM contains PDF of thesis and MDL file.
Both MIT Institute Archives and Barker Library copy: with CD-ROM.
Cataloged from student submitted PDF version of thesis.
Includes bibliographical references.
Microgrids show great promise as a means of integrating distributed generation sources into the public grid distribution system. In order to provide uninterrupted,high quality power to local loads, microgrids must have the ability to operate independently of or in parallel with the local utility. Transitioning between independent operation, also called "islanded" operation, and utility connected operation can induce stability problems in the microgrid, especially when islanding is fault induced. Software simulation suggests that induction motor loads on the microgrid significantly decrease stability during fault induced islanding. To validate the software simulations and to investigate the impact of load type on microgrid stability, we have built a hardware system that simulates the operation of a microgrid.
by Jared P. Monnin.
M.Eng.
3
Vargas, Rios Leon Maximino. "Local voltage stability assessment for variable load characteristics." Thesis, University of British Columbia, 2009. http://hdl.handle.net/2429/21424.
Повний текст джерелаАнотація:
Voltage stability problems originate when a generation-transmission system is not able to supply a load connected remotely from the generation centers. Knowledge of the load characteristics and the load composition are necessary tools for voltage stability assessment (VSA). This thesis presents methods and results to evaluate local voltage stability conditions, considering the actual static load characteristics.
Simulation of a modern load, verified by experimental tests, such as a variable frequency drive feeding an induction motor (IM), shows that the real power characteristic is very similar to the directly-connected motor, while the reactive power characteristic is different. The effect on voltage stability is described.
A small-scale voltage stability test is performed for a single IM under increasing mechanical load, fed by a source and series reactance. A set of slip dependent PV curves, which show variable power factor (PF) behavior, is obtained and compared with the assumption of constant PF loads for VSA.
A comprehensive case study is performed, which presents an experimentally obtained IM load characteristic, resulting in variable PF as expected from the equivalent circuit model. The IM is aggregated by simulation in a bus fed by a Thevenin network, and a numerical method is proposed to compute a local PQV curve that considers the actual load characteristic. It is demonstrated that traditional PV curves for constant PF loads do not describe properly the aggregation of induction motor loads in a bus. A graphical approach of network and load PV characteristic intersections for this variable PF load, confirmed with a time domain simulation, shows that the point of matching impedance, typically assumed as the voltage stability limit, is not the power transmission limit (“nose”), and the latter is not the static voltage stability (loadability) limit.
The methods and results developed in the case study are extended to other motor, heating and lighting types of loads. Their experimental characteristics are later combined by simulation in one distribution bus of a university building to perform static local VSA.
Finally, some implementation ideas for on-line load characteristic estimation and PQV curve computation are described as part of the tools for local VSA.
4
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.
Повний текст джерелаАнотація:
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.
5
MOROTE, CARLOS HUGO SOTO. "STABILITY AND DEFORMATION OF SOIL SLOPES UNDER SEISMIC LOAD." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2006. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=9532@1.
Повний текст джерелаАнотація:
CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOO comportamento sísmico de taludes tem sido um tópico de grande interesse da engenharia geotécnica nos últimos 40 anos. Durante este período, a prática da engenharia nesta área evoluiu do emprego de técnicas elementares para procedimentos numéricos bastante complexos. A abordagem mais simples é a análise pseudo-estática na qual o carregamento do terremoto é simulado por uma aceleração horizontal estática equivalente atuando na massa de solo deslizante, utilizando-se um procedimento de equilíbrio limite (método das fatias), geralmente conservativo. O parâmetro que descreve o comportamento dinâmico do solo é referido como coeficiente sísmico k, e sua seleção depende fortemente da experiência e normas técnicas locais, porque não há maneira simples e segura de se escolher um valor adequado. O segundo procedimento é conhecido como método de Newmark, que envolve o cálculo de uma aceleração de escoamento, definida como a força inercial necessária para o fator de segurança atingir 1 em uma análise pseudo-estática pelo método de equilíbrio limite. O procedimento então usa os registros de aceleração do terremoto de projeto e o integra duplamente no tempo para calcular os deslocamentos permanentes acumulados. O terceiro método é referido como análise de Makdisi- Seed, que procura definir a estabilidade sísmica do talude em termos de deslocamentos aceitáveis em vez de um fator de segurança tradicional através de uma versão modificada do método de Newmark. Esta técnica apresenta uma maneira racional de calcular uma aceleração de escoamento média, necessária para produzir um valor do coeficiente de segurança do talude igual a 1. Gráficos específicos foram também desenvolvidos para estimativa dos deslocamentos permanentes, tendo sido bastante aplicados em aterros rodoviários, barragens e aterros sanitários. Finalmente, o mais sofisticado método para análise de estabilidade sísmica de taludes é conhecido como análise dinâmica, que normalmente incorpora modelos de elementos finitos e relações tensão x deformação complexas numa tentativa de obter melhores representações para o comportamento mecânico de taludes sob cargas cíclicas Os resultados destas análises podem incluir a história no tempo dos deslocamentos e tensões, bem como das freqüências naturais, efeitos de amortecimento, etc. Este trabalho apresenta uma comparação entre os métodos mencionados anteriormente, analisando o comportamento sísmico dos taludes da estrutura de contenção dos resíduos de lixiviação de minério de urânio, na Bahia, e dos taludes do bota-fora sul da mina de cobre Toquepala, situada no Peru.
The seismic stability of slopes has been a topic of considerable interest in geotechnical engineering for the past 40 years. During that period, the state of practice has moved from simples techniques to more complicated numerical procedures. The simplest approach is the pseudo-static analysis in which the earthquake load is simulated by an equivalent static horizontal acceleration acting on the mass of the landslide, according to a generally conservative limit equilibrium analysis. The ground motion parameter used in a pseudo-static analysis is referred to as the seismic coefficient k, and its selection has relied heavily on engineering judgment and local code requirements because there is no simple method for determining an appropriate value. The second main procedure is known as the Newmark displacement analysis which involves the calculation of the yield acceleration, defined as the inertial force required to cause the static factor of safety to reach 1 from the traditional limit equilibrium slope stability analysis. The procedure then uses a design earthquake strong-motion record which is numerically integrated twice for the amplitude of the acceleration above the yield acceleration to calculate the cumulative displacements. These displacements are then evaluated in light of the slope material properties and the requirements of the proposed development. The third method is referred to as the Makdisi-Seed analysis sought to define seismic embankment stability in terms of acceptable deformation instead of conventional factors of safety, using a modified Newmark analysis. Their method presents a rational means to determine yield acceleration, or the average acceleration required to produce a factor of safety of unity. Design curves were developed to estimate the permanent earthquake- induced deformations of embankments, which have since been applied to sanitary landfill and highway embankments. Finally, the most sophisticated method for seismic slope stability calculations is known as the dynamic analysis, which normally incorporates a finite element model and a rather complex stress-strain behavior for geological materials in an attempt to obtain a better representation of the behavior of soils under cyclic loading. The results of the analysis can include a time history of displacements and stresses, as well as natural frequencies, effects of damping, etc. This work presents a comparison of the results obtained by the aforementioned approaches, considering the seismic behavior of the slopes of an uranium lixiviation pad situated in Bahia, Brazil, and the South embankment of the waste landfill of the Toquepala Mine, Peru.
6
Genet, Benjamin. "On monitoring methods and load modeling to improve voltage stability assessment efficiency." Doctoral thesis, Universite Libre de Bruxelles, 2009. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/210258.
Повний текст джерелаАнотація:
Power systems must face new challenges in the current environment. The energy market liberalization and the increase in the loading level make the occurrence of instability phenomena leading to large blackouts more likely. Existing tools must be improved and new tools must be developed to avoid them.The aim of this thesis is the improvement of the voltage stability assessment efficiency. Two orientations are studied: the monitoring methods and the load modeling.
The purpose of the monitoring methods is to evaluate the voltage stability using only measurements and without running simulations.
The first approach considered is local. The parameters of the Thevenin equivalent seen from a load bus are assessed thanks to a stream of local voltage and current measurements. Several issues are investigated using measurements coming from complete time-domain simulations. The applicability of this approach is questioned.
The second approach is global and uses measurements acquired by a Wide-Area Measurement System (WAMS). An original approach with a certain prediction capability is proposed, along with intuitive visualizations that allow to understand the deterioration process leading to the collapse.
The load modeling quality is certainly the weak point of the voltage security assessment tools which run simulations to predict the stability of the power system depending on different evolutions. Appropriate load models with accurate parameters lead to a direct improvement of the prediction precision.
An innovative procedure starting from data of long measurement campaigns is proposed to automatically evaluate the parameters of static and dynamic load models. Real measurements taken in the Belgian power system are used to validate this approach.
Doctorat en Sciences de l'ingénieur
info:eu-repo/semantics/nonPublished
7
Regulski, Pawel Adam. "Estimation of parameters of dynamic load models for voltage stability studies." Thesis, University of Manchester, 2012. https://www.research.manchester.ac.uk/portal/en/theses/estimation-of-parameters-of-dynamic-load-models-for-voltage-stabily-studies(db6176e0-c7df-4ad6-83f7-5772eb9f8421).html.
Повний текст джерелаАнотація:
Current environmental and economic trends have forced grid operators to maximize the utilization of the existing assets, which is causing systems to be operated closer to their stability limits than ever before. This requires, among other things, better knowledge and modelling of the existing power system equipment to increase the accuracy of the assessment of current stability margins.This research investigates the possibility of improving the quality of load modeling. The thesis presents a review of the traditional methods for estimation of load model parameters and proposes to use Improved Particle Swarm Optimization. Different algorithms are tested and compared in terms of accuracy, reliability and CPU requirements using computer simulations and real-data captured in a power system.Estimation of frequency and power components has also been studied in this thesis. A review of the existing methods has been provided and the use of an Unscented Kalman Filter proposed. This nonlinear recursive algorithm has been thoroughly tested and compared against selected traditional techniques in a number of experiments involving computer-generated signals as well as measurements obtained in laboratory conditions.
8
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.
Повний текст джерелаАнотація:
[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.
9
Garmroodi, Doiran Mehdi. "Sensitivity Analysis for Future Grid Stability Studies." Thesis, The University of Sydney, 2016. http://hdl.handle.net/2123/15978.
Повний текст джерелаАнотація:
The increasing penetration of converter-interfaced generators (CIGs) has raised concerns about the stability and security of future grids (FGs). These resources affect power systems dynamics in many ways including reducing system inertia, interacting with existing generators, changing power flow paths, etc. In this thesis, we carry out a sensitivity study to explore the structural impacts from CIGs on the damping and frequency stability of power systems. Initially, we study the impact of the intermittent power from wind turbine generators (WTGs) on the damping of the electromechanical oscillations in power systems. It will be shown that the inability of WTGs to provide synchronizing and damping torque to the system jeopardize the small signal stability of power systems. Stable operation regions, in terms of wind penetration and tie-line power, are derived and the impact of load flexibility on these regions are discussed. Next, we have studied the impact of the inertia distribution on the damping of the inter-area modes in power systems. It is shown that tie-line power has a significant role on the damping of the inter-area modes. Moreover, we show that dynamic voltage control and inertia emulation can be utilized to improve the damping of the system. By developing an oscillatory recovery model for power system loads, we have also studied the impact of load oscillations on the damping of the inter-area modes. It is shown that the load dynamics can have a significant influence on the electromechanical oscillations of power systems. Finally, the frequency support capability of WTGs is investigated and the performance of different techniques in utilizing the kinetic energy of the WTGs to assist the frequency stability of power systems is evaluated. A novel time-variable droop characteristic is proposed to enhance the contribution of WTGs in supporting system frequency.
10
Jadric, Ivan. "Modeling and Control of a Synchronous Generator With Electronic Load." Thesis, Virginia Tech, 1998. http://hdl.handle.net/10919/36549.
Повний текст джерелаАнотація:
Design and analysis of a system consisting of a variable-speed synchronous generator that supplies an active dc load (inverter) through a three-phase diode rectifier requires adequate modeling in both time and frequency domain. In particular, the system's control-loops, responsible for stability and proper impedance matching between generator and load, are difficult to design without an accurate small-signal model. A particularity of the described system is strong non-ideal operation of the diode rectifier, a consequence of the large value of generator's synchronous impedance. This non-ideal behavior influences both steady state and transient performance. This thesis presents a new, average model of the system. The average model accounts, in a detailed manner, for dynamics of generator and load, and for effects of the non-ideal operation of diode rectifier. The model is non-linear, but time continuous, and can be used for large- and small-signal analysis.
The developed model was verified on a 150 kW generator set with inverter output, whose dc-link voltage control-loop design was successfully carried out based on the average model.Master of Science
11
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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Colombari, Luan Filipe dos Santos. "An approach to handle sudden load changes on static voltage stability analysis." Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/18/18154/tde-31032017-091235/.
Повний текст джерелаАнотація:
In the context of static Voltage Stability Assessment (VSA), as the power system load grows, bus voltages tend to drop. This reduction may lead to generator or load disconnections caused by undervoltage protection schemes. These events comprise sudden parametric variations that affect the equilibrium diagram and the Voltage Stability Margin (VSM) of power systems. Practical examples of such sudden load changes are caused by the mandatory disconnection of Distributed Generation (DG) units and Undervoltage Load Shedding (ULS). There are no thorough studies in the literature concerning these load parametric variations and the discontinuities that they cause in power system equilibria. This dissertation describes a predictor/corrector scheme specifically designed to handle these discontinuities, so it is possible to evaluate their effect on the VSM of power systems. This method successively calculates the load discontinuities that exist in the equilibrium locus of the system under analysis. It results in the sequence of sudden load variations that happens and their overall impact on the system. When applied to quantify the effect of DG mandatory disconnections and ULS, the proposed predictor/corrector scheme yielded better results than the traditional Continuation Power Flow (CPFLOW), which experienced convergence problems caused by the discontinuities under analysis. However, due to its design, the applicability of the proposed method should be restricted to power systems that go through several successive sudden load changes. In this sense, it should not be regarded as a replacement for the CPFLOW, but rather as a technique that could award this traditional VSA tool with new features to enhance its performance.No contexto de análise estática de estabilidade de tensão, conforme a carga de um sistema de potência cresce, as tensões nas suas barras tendem a cair. Essa redução pode causar a desconexão de geradores e cargas devido a atuação de proteções de subtensão. Esses eventos representam variações abruptas de demanda que alteram o diagrama de equilíbrio de um sistema e sua Margem de Estabilidade de Tensão (MET). Exemplos práticos dessas variações são causados pelo desligamento mandatório de unidades de Geração Distribuída (GD) e pelo Corte de Carga por Subtensão (CCS). Não há estudos detalhados na literatura que trabalham especificamente com essas variações nos parâmetros da carga, nem com as descontinuidades que elas causam no diagrama de equilíbrio de sistemas de potência. Essa dissertação descreve um procedimento especificamente projetado para lidar com essas descontinuidades, de modo que seja possível avaliar seu efeito na MET de sistemas elétricos. Esse método calcula sucessivamente as descontinuidades de carga que existem no diagrama de equilíbrio do sistema em análise. Ele resulta na sequência de variações súbitas de carga que ocorre e no seu impacto no sistema. Quando o método foi aplicado para quantificar o efeito do desligamento mandatório de GD e do CCS, ele apresentou resultados melhores do que o tradicional Fluxo de Carga Continuado (CPFLOW), o qual sofreu problemas de convergência causados pelas descontinuidades em questão. Entretanto, devido ao seu projeto, o método proposto só deve ser utilizado para sistemas de potência que estão sujeitos a várias sucessivas variações abruptas de carga. Por essa razão, esse método não pode ser considerado um substituto do CPFLOW, mas sim como uma técnica capaz de agregar novas funcionalidades a essa ferramenta tradicional, amentando assim seu horizonte de aplicações.
13
Pozzi, Antonio. "The menisci of the canine stifle: function in load transmission and stability." The Ohio State University, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=osu1400073280.
Повний текст джерела
14
Nguyen, Tan. "Load transfer mechanisms and seismic stability of embankments subjected to basal subsidence." Kyoto University, 2018. http://hdl.handle.net/2433/235077.
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Zähe, Bernd, Peter Anders, and Simon Ströbel. "A new energy saving load adaptive counterbalance valve." Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-200267.
Повний текст джерелаАнотація:
The paper shows standard circuits with load reactive and non load reactive counterbalance valves. A Matlab simulation based on a linear model for the circuit with load reactive counterbalance valves shows what parameters have a significant influence on the stability of the system. The most important parameters of the counterbalance valve that influence the stability are pilot gain and relief gain. The factors describe how pilot pressure and load pressure affect the flow across the counterbalance valve. A new counterbalance valve (patent pending) has the pilot gain and relief gain required for stability only in operating ranges that require the parameters for stability. When the load is not moving or the counterbalance valve is not required for positive (non overrunning) loads, the new valve has a higher pilot ratio, which means that the valve opens further at lower inlet pressures. The new counterbalance valves saves about 30% power compared with a standard counterbalance valve that has the same parameters for stability when it is lowering an overrunning load. The standard counterbalance can be replaced with the new load adaptive valve in the same cavity. The paper shows test results and the design of the valve.
16
Parveen, Tania. "Composite load model decomposition : induction motor contribution." Thesis, Queensland University of Technology, 2009. https://eprints.qut.edu.au/31301/1/Tania_Parveen_Thesis.pdf.
Повний текст джерелаАнотація:
In this thesis, a new technique has been developed for determining the composition of a collection of loads including induction motors. The application would be to provide a representation of the dynamic electrical load of Brisbane so that the ability of the power system to survive a given fault can be predicted. Most of the work on load modelling to date has been on post disturbance analysis, not on continuous on-line models for loads. The post disturbance methods are unsuitable for load modelling where the aim is to determine the control action or a safety margin for a specific disturbance. This thesis is based on on-line load models. Dr. Tania Parveen considers 10 induction motors with different power ratings, inertia and torque damping constants to validate the approach, and their composite models are developed with different percentage contributions for each motor. This thesis also shows how measurements of a composite load respond to normal power system variations and this information can be used to continuously decompose the load continuously and to characterize regarding the load into different sizes and amounts of motor loads.
17
Anastasiadis, John S. "Stability of cylindrical laminates by highter order shear deformable theories." Diss., Georgia Institute of Technology, 1990. http://hdl.handle.net/1853/12376.
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Yang, Robin S. "Shipboard MVDC Voltage Stabilization by Negative Load Energy Storage Compensated Virtual Capacitance." Thesis, Virginia Tech, 2019. http://hdl.handle.net/10919/94129.
Повний текст джерелаАнотація:
Shipboard MVDC power systems need to support pulsed loads, which have destabilizing ef-fects on the MVDC power transmission bus voltage. Despite the reference shipboard MVDC architecture having energy storage to buffer the large power swings of pulsed loads, a large constant power still needs to be delivered to maintain the energy storage state of charge. This recharging constant power itself introduces small signal instability to the MVDC bus voltage. This thesis investigates the advantages of adding a dynamically tuneable virtual capacitor and resistor in parallel to the pulsed load for maintaining small signal stability. The stabi-lizer is implemented in a negative load configuration in the existing reference architecture hardware, where the stabilizer negatively impacts the power quality of the downstream load. To address this, a dual use is added to existing hardware by having the energy storage also cancel out the newly introduced noise. A controller was designed to control a MVDC power converter module for providing these stability services. In addition, the controller manages its internal energy storage and stabilizes its internal DC bus that powers its downstream pulsed load.Future ships will have a special shipboard power grid and power converters to power future electronics. Most of these power converters will have an internal battery device that provides power when the generators do not provide enough power. Generators are very slow to change their power output. Some shipboard electronics may consume very large amounts of power at very quickly changing rates, causing instability to the power system. The batteries can accomodate the instability caused by these electronics. However, the batteries need to be quickly recharged, which is also unstable to the special power grid. This thesis modifies the recharging behavior so that it does not cause this instability. Also, it is preferable that the batteries will only draw power from the power grid in one direction and send power to the power consuming electronics. This setup is called negative load. This setup is preferable, because sending power back to the power grid will require extra hardware. Ships can only carry so much equipment due to constraints in weight or room, so additonal hardware is undesireable. There already exists similar research to provide this stabilizing service, but they are not designed for a shipboard power grid supporting these quick high power electronics. This thesis also makes a controls system that manages the battery and other requirements of the power system.
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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.
Повний текст джерелаАнотація:
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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Vadari, Subramanian V. "An intelligent load shedding approach to enhance the voltage stability of a power system /." Thesis, Connect to this title online; UW restricted, 1991. http://hdl.handle.net/1773/6094.
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Wang, Tianjiao. "Feasibility for spinal muscles creating pure axial compressive load or follower load in the lumbar spine in 3-D postures." Diss., University of Iowa, 2015. https://ir.uiowa.edu/etd/1790.
Повний текст джерелаАнотація:
Previous in-vivo studies showed that compressive force acting on the spine may exceed 2600 N. However, the ligamentous lumbar spine becomes unstable when subjected to compressive loads less than 100 N. It is generally accepted that the ligamentous spine itself is unstable but can be stabilized by muscle forces (MFs) in vivo. Nevertheless, normal spinal muscle contraction patterns remain unknown.
In recent in vitro studies, when the direction of the applied load was controlled along the spinal curvature so that the internal spinal load became perfect compressive follower loads (CFLs) at all lumbar levels, the ligamentous lumbar spine was found to withstand large compressive load (up to 1200 N) without buckling while maintaining its flexibility in neutral or flexed postures. The results of in-vivo animal studies also have shown that shear stress has a more detrimental effect on the rate of disc degeneration compared to compressive stress. These results suggest CFLs in the lumbar spine would be a normal spinal load whereas the transverse (or shear) load abnormal. An initial test of this postulation would be to investigate whether the spinal muscles can create perfect internal CFLs in the lumbar spine in all 3-D postures. In addition, small intrinsic muscles (SIMs) are crucial for better control of the direction of the internal spinal load along the spinal axis was also proposed.
A finite element (FE) model together with an optimization model were used for this study. Both models consist of the trunk, sacrolumbar spine and 244 spinal muscles. Different from other studies, 54 SIMs were also included in the models. The FE model was validated by comparing the ROM of the spine with the literature data. Minimization of the summation of the spinal loads and moments was used as the cost function for the optimization model. The geometrical data obtained from the FE model was used as the input for the optimization model; it was then used to calculate the MFs required for creating the CFLs at all lumbar spine levels. The MFs determined in the optimization model were then imported back to the FE model as input loads to check the stability of the spine under this loading condition. Five different postures were studied: neutral, flexion 40°, extension 5°, lateral bending 30° and axial rotation 10°.
Many optimization solutions for spinal muscle force combinations creating pure CFLs in the lumbar spine were found available in each posture. However, FE analyses showed that only muscle forces and patterns solved at FLPs along the curve in the vicinity of the baseline curve stabilized the lumbar spine. Stability was determined by small displacement of the trunk (less or equal to 5mm) due to small deformation of the lumbar spine. The magnitudes of joint reaction forces (JRFs) predicted from the optimization model were comparable to those reported in the literature. When the SIMs were removed, optimization solutions were still feasible in all five postures, but JRFs and trunk displacement were increased. This suggests the need of SIM inclusion in future spine biomechanics studies and clinically, damages to the SIMs may have a high risk of future spinal problems, such as spinal instability, early disc degeneration, deformity and/or early failure of spinal fixation devices.
The results from this study supported the hypothesis that the perfect CFLs at all lumbar levels could be the normal physiological load under which the lumbar spinal column could support large load without buckling while allowing flexibility. SIMs played an important role in creating CFLs as by including SIMs in the models, the JRFs at all lumbar spine levels were lowered and the stability of the spine was increased.
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Bahadornejad, Momen. "On-line local load measurement based voltage instability prediction." Thesis, Queensland University of Technology, 2005. https://eprints.qut.edu.au/16187/1/Momen_Bahadornejad_Thesis.pdf.
Повний текст джерелаАнотація:
Voltage instability is a major concern in operation of power systems and it is well known that voltage instability and collapse have led to blackout or abnormally low voltages in a significant part of the power system. Consequently, tracking the proximity of the power system to an insecure voltage condition has become an important element of any protection and control scheme.
The expected time until instability is a critical aspect. There are a few energy management systems including voltage stability analysis function in the real-time environment of control centres, these are based on assumptions (such as off-line models of the system loads) that may lead the system to an insecure operation and/or poor utilization of the resources.
Voltage instability is driven by the load dynamics, and investigations have shown that load restoration due to the on-load tap changer (OLTC) action is the main cause of the voltage instability. However, the aggregate loads seen from bulk power delivery transformers are still the most uncertain power system components, due to the uncertainty of the participation of individual loads and shortcomings of the present approaches in the load modeling.
In order to develop and implement a true on-line voltage stability analysis method, the on-line accurate modeling of the higher voltage (supply system) and the lower voltage level (aggregate load) based on the local measurements is required.
In this research, using the changes in the load bus measured voltage and current, novel methods are developed to estimate the supply system equivalent and to identify load parameters. Random changes in the load voltage and current are processed to estimate the supply system Thevenin impedance and the composite load components are identified in a peeling process using the load bus data changes during a large disturbance in the system. The results are then used to anticipate a possible long-term voltage instability caused by the on-load tap changer operation following the disturbance. Work on the standard test system is provided to validate the proposed methods.
The findings in this research are expected to provide a better understanding of the load dynamics role in the voltage stability, and improve the reliability and economy of the system operation by making it possible to decrease uncertainty in security margins and determine accurately the transfer limits.
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Bahadornejad, Momen. "On-line local load measurement based voltage instability prediction." Queensland University of Technology, 2005. http://eprints.qut.edu.au/16187/.
Повний текст джерелаАнотація:
Voltage instability is a major concern in operation of power systems and it is well known that voltage instability and collapse have led to blackout or abnormally low voltages in a significant part of the power system. Consequently, tracking the proximity of the power system to an insecure voltage condition has become an important element of any protection and control scheme. The expected time until instability is a critical aspect. There are a few energy management systems including voltage stability analysis function in the real-time environment of control centres, these are based on assumptions (such as off-line models of the system loads) that may lead the system to an insecure operation and/or poor utilization of the resources. Voltage instability is driven by the load dynamics, and investigations have shown that load restoration due to the on-load tap changer (OLTC) action is the main cause of the voltage instability. However, the aggregate loads seen from bulk power delivery transformers are still the most uncertain power system components, due to the uncertainty of the participation of individual loads and shortcomings of the present approaches in the load modeling. In order to develop and implement a true on-line voltage stability analysis method, the on-line accurate modeling of the higher voltage (supply system) and the lower voltage level (aggregate load) based on the local measurements is required. In this research, using the changes in the load bus measured voltage and current, novel methods are developed to estimate the supply system equivalent and to identify load parameters. Random changes in the load voltage and current are processed to estimate the supply system Thevenin impedance and the composite load components are identified in a peeling process using the load bus data changes during a large disturbance in the system. The results are then used to anticipate a possible long-term voltage instability caused by the on-load tap changer operation following the disturbance. Work on the standard test system is provided to validate the proposed methods. The findings in this research are expected to provide a better understanding of the load dynamics role in the voltage stability, and improve the reliability and economy of the system operation by making it possible to decrease uncertainty in security margins and determine accurately the transfer limits.
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Paparo, Maria Ausilia <1983>. "Evaluation of slope stability under water and seismic load through the Minimum Lithostatic Deviation method." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2014. http://amsdottorato.unibo.it/6602/1/Paparo_Maria_Ausilia_tesi.pdf.
Повний текст джерелаАнотація:
The main objective of this thesis is to obtain a better understanding of the methods to assess the stability of a slope.
We have illustrated the principal variants of the Limit Equilibrium (LE) method found in literature, focalizing our attention on the Minimum Lithostatic Deviation (MLD) method, developed by Prof. Tinti and his collaborators (e.g. Tinti and Manucci, 2006, 2008).
We had two main goals: the first was to test the MLD method on some real cases. We have selected the case of the Vajont landslide with the objective to reconstruct the conditions that caused the destabilization of Mount Toc, and two sites in the Norwegian margin, where failures has not occurred recently, with the aim to evaluate the present stability state and to assess under which conditions they might be mobilized.
The second goal was to study the stability charts by Taylor and by Michalowski, and to use the MLD method to investigate the correctness and adequacy of this engineering tool.
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Paparo, Maria Ausilia <1983>. "Evaluation of slope stability under water and seismic load through the Minimum Lithostatic Deviation method." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2014. http://amsdottorato.unibo.it/6602/.
Повний текст джерелаАнотація:
The main objective of this thesis is to obtain a better understanding of the methods to assess the stability of a slope.
We have illustrated the principal variants of the Limit Equilibrium (LE) method found in literature, focalizing our attention on the Minimum Lithostatic Deviation (MLD) method, developed by Prof. Tinti and his collaborators (e.g. Tinti and Manucci, 2006, 2008).
We had two main goals: the first was to test the MLD method on some real cases. We have selected the case of the Vajont landslide with the objective to reconstruct the conditions that caused the destabilization of Mount Toc, and two sites in the Norwegian margin, where failures has not occurred recently, with the aim to evaluate the present stability state and to assess under which conditions they might be mobilized.
The second goal was to study the stability charts by Taylor and by Michalowski, and to use the MLD method to investigate the correctness and adequacy of this engineering tool.
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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.
Повний текст джерелаАнотація:
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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Lidström, Erica. "Voltage Stability at Hydropower Stations Influenced by close-located Wind Farms." Thesis, Uppsala universitet, Elektricitetslära, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-181017.
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The number of integrated wind farms into the power system is increasing as well as the total installed wind power capacity, which may cause voltage stability concerns. Additionally, there are European Transmission System Operators (TSOs) that do notinvolve wind farms in contributing to the voltage control in any significant extent. In the on-going project by the European Network of Transmission System Operators for Electricity (ENTSO-E), to update the European grid requirements, this will probably be changed. The aim of this Master thesis is to demonstrate the voltage variations in the high voltage grid during different operational conditions. Thereafter, clarify when high voltages may occur at the connection point of the studied wind farm. Furthermore, it is investigated whether the wind farm is able to regulate the voltage in the cases when high voltages occur. The load flow and switching studies are performed with the software tool Power System Simulator for Engineering (PSS/E) version 32.1.1. The grid model represents a part of the Swedish high voltage grid. Since voltage stability often is a local issue, special modelling aspects has been performed at the hydropower generators in the close-located area of the wind farm. The main conclusions of this Master thesis are that high voltages is associated with low load situations, i.e., mostly during summer nights. Furthermore, the studied close-located reactor is not able to keep the voltage within desired level by itself. Finally, it has been shown that the wind farm is technically able to contribute to the voltage stability in the close-located area. But since wind power is an intermittent power source it makes the voltage regulating capacity less reliable compared to hydropower. The results and conclusions given in this Master thesis have also been summarized in a conference paper for The 11th International Workshop on Large-Scale Integration of Wind Power into Power Systems as well as on Transmission Networks for Offshore Wind Power Plants, see Lidström et al [35].
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Sun, Miao. "Use of Material Tailoring to Improve Axial Load Capacity of Elliptical Composite Cylinders." Diss., Virginia Tech, 2006. http://hdl.handle.net/10919/29693.
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This study focuses on the improvement of the axial buckling capacity of elliptical composite cylinders through the use of a circumferentially-varying lamination sequence. The concept of varying the lamination sequence around the circumference is considered as a viable approach for off-setting the disadvantages of having the cylinder radius of curvature vary with circumferential position, the source of the reduced buckling capacity when compared to a circular cylinder with the same circumference. Post-buckling collapse behavior and material failure characteristics are also of interest. Two approaches to implementing a circumferential variation of lamination are examined. For the first approach the lamination sequence is varied in a stepwise fashion around the circumference. Specifically, each quadrant of the cylinder circumference is divided into three equal-length regions denoted as the crown, middle, and side regions. Eight different cylinders designs, whereby each region is constructed of either a quasi-isotropic or an axially-stiff laminate of equal thickness, are studied. Results are compared to the baseline case of an elliptical cylinder constructed entirely of a quasi-isotropic laminate. Since the thickness of the quasi-isotropic and axially-stiff laminates are the same, all cylinders weight the same and thus comparisons are meaningful. Improvements upwards of 18% in axial buckling capacity can be achieved with one particular stepwise design. The second approach considers laminations that vary circumferentially in a continuous fashion to mitigate the effects of the continuously-varying radius of curvature. The methodology for determining how to tailor the lamination sequence circumferentially is based on the analytical predictions of a simple buckling analysis for simply-supported circular cylinders. With this approach, axial buckling load improvements upwards of 30% are realized. Of all the cylinders considered, very few do not exhibit material failure upon collapse in the post-buckled state. Of those that do not, there is little, if any, improvement in bucking capacity. Results for the pre-buckling, buckling, post-buckling, and material failure are obtained from the finite-element code ABAQUS using both static and dynamic analyses. Studies with the code demonstrate that the results obtained are converged.Ph. D.
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Gozzard, Charles. "Optimisation of cementation, bone graft preparation, stability and load transfer in primary and revision hip arthroplasty." Thesis, University of Bristol, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.430174.
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Khumalo, Joseph. "An investigation into the effects of load modeling of transient stability and analysis of voltage collapse." Master's thesis, University of Cape Town, 1992. http://hdl.handle.net/11427/9645.
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Bibliography: leaves 187-193.The aim of this thesis is to investigate the effects of load modeling on transient stability studies and to analyze the phenomenon of voltage collapse. In addition, the different generator models are compared and the effects of voltage dips on induction motor performance are investigated. The modeling of loads dates back to the late forties when network analyzers were still in use. The prohibitive computational requirements resulted in many approximations being made to the load models. In turn, this resulted in the use of simple models which did not provide sufficient information about the dynamic behavior of loads. With the advent of digital computers, more accurate load models could be used in dynamic simulations. Despite this improvement in computational tools, the problem of load modeling for stability studies is still very complex. The load composition changes with the time of the day, the consumer's lifestyle, weather, state of the economy and other factors. The accurate load model would include amongst other things, the effects of the abovementioned factors. Since these factors are unpredictable, accurate load modeling becomes very complex indeed. It is mainly for these reasons that the approximate are still widely in use. Ideally, the response of these approximate models should be compared to the actual loads under similar disturbances. A further concern of the thesis is the study of voltage stability. The voltage stability problem has become a matter of growing concern amongst bulk transmission utilities worldwide over the last decade. For long, the stability of a power system was related exclusively to the synchronous stability of the generators.
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Jeffs, Shaun B. "The Passive Load-Bearing Capacity of the Human Lumbar Spine in the Neutral Standing Posture." BYU ScholarsArchive, 2011. https://scholarsarchive.byu.edu/etd/2638.
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The human lumbar spine has been shown to support compressive loads of 1000 N in standing and walking, and up to many thousands of Newtons in strenuous activities such as lifting. The literature presents a number of biomechanical models that seek to replicate the load-carrying capacity of the spine while adhering to physiological constraints. While many of these models provide invaluable insights into the mechanisms governing spinal stability, there is a nearly universal disregard for the magnitude of the muscle forces required in the neutral standing posture. In compliance with constraints on metabolic cost and muscle fatigue, muscle activations in excess of 5% maximum voluntary contraction (MVC) in the standing posture are physiologically infeasible. The purpose of this thesis was to investigate the hypothesis that the passive structures of the lumbar spine are sufficient to produce static equilibrium under the body weight load in the neutral standing posture. A novel method of applying physiologic loads to the lumbar spine in vitro to determine its passive stability was developed. Five cadaver specimens were tested and a passive equilibrium posture was discovered for each. Further, the parameters defining the equilibrium posture correlate well with the standing posture as reported in the literature. This is an indication that the lumbar spine is inherently capable of remaining erect in the neutral posture with muscle activations below 5% MVC. It is postulated that the iliolumbar ligament and the thoracolumbar fascia, passive components that are not typically incorporated into stability models of the spine, have the potential to provide added passive stabilization to the system. It is recommended that biomechanical models of the spine incorporate this 5% MVC constraint and place greater emphasis on the contributions of passive structures to overall stability.
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Čížek, Ondřej. "Stabilita napětí v NN sítích zatížených měniči s aktivní regulací na konstantní výstup." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2017. http://www.nusl.cz/ntk/nusl-317025.
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This thesis contains a summary of voltage stability issues caused by appliances with constant load output. It also contains models of this appliance and outcomes of simulations done for the purpose of conformation of influence of appliances with constant output on voltage stability.
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Whitlock, Rogers Jr. "Identification of Power System Stability Using Relevant Modes." ScholarWorks@UNO, 2011. http://scholarworks.uno.edu/td/1384.
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The purpose of this investigation is to identify appropriate location of capacitor banks and sources of reactive power by studying power system stability in the vicinity of system equilibrium states. The locations for reactive power sources are determined by identifying those modes of the system that participate most in the system behavior in general and in dictating the final state of the system after experiencing faults or disturbances. To identify the relevant modes of the system that participate most in the system dynamic, we shall make use of modal and participation analysis for different system conditions. We also apply modal and participation analysis to a system in order to identify the components of greatest impact that result in the most efficient system control. The ideas developed in this study are used to analyze and identify weak boundaries of the IEEE 39- Bus system that contribute to the system’s instability.
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Damaraju, Avinash Sharma. "Investigation on the Stability of Noncompact and Slender Concrete Filled Tubes Subjected to Axial Loads." University of Cincinnati / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=ucin151179557053975.
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Suh, Inyoung. "Determining the load composition in commercial buildings based upon harmonic current characteristics /." Digital version accessible at:, 2000. http://wwwlib.umi.com/cr/utexas/main.
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Molloy, Sean J. "Finite Element Analysis of a Pair of Leaning Pressurized Arch-Shells Under Snow and Wind Loads." Thesis, Virginia Tech, 1998. http://hdl.handle.net/10919/36608.
Повний текст джерелаАнотація:
A structure comprised of two arches that lean against each other at the apex is considered. The arches are thin shells with internal pressure. This type of structure with solid arches has been used in bridges, such as the Gateway Arch Bridge in Columbus, Indiana, U.S.A., the Monongahela River Bridge in Pittsburgh, Pennsylvania, U.S.A., and a pedestrian bridge at the Pacific Tower in Paris, France. A series of leaning arches was incorporated in the frame of the Museum of the Moving Image, a temporary structure in London, England, during 1992-1994. Pressurized arch-shells made of a flexible material have been utilized as part of the framework for some transportable tent-like structures.
The behavior of a pair of pressurized leaning arch-shells with various tilt angles, boundary conditions, and loads is investigated numerically. Several types of loads are considered, including uniformly-distributed vertical loads applied over all or half of the structure (representing snow), and wind loads on the structure. The arches are pinned or fixed to the ground. Deflections, vibrations, and stability of the structures are investigated using the finite element method. The effect of the tilt angle on the response is examined, and buckling may occur for some tilt angles under vertical loading. This type of structure has not been used widely, but may be effective for various applications.
Master of Science
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Tamimi, Ala. "Voltage stability limits for weak power systems with high wind penetration." Diss., Kansas State University, 2011. http://hdl.handle.net/2097/13100.
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Doctor of PhilosophyDepartment of Electrical and Computer Engineering
Anil Pahwa
Shelli K. Starrett
Analysis of power system voltage stability has practical value in increasing wind penetration levels. As wind penetration levels increase in power systems, voltage stability challenges arise due to locating wind resources far away from load centers. This dissertation presents several different voltage stability methods for sizing new wind farms. Power system wind penetration levels depend on the available voltage stability margins (VSMs) of the existing power system and system load characteristics. Three new iterative methods have been developed to maximize wind penetration level in weak power systems based on systems’ VSMs. The first two methods use an iterative approach for increasing the size of each wind farm until reaching the collapse point. Wind farms with less negative impact on system VSMs are sized larger than others. A third wind farm sizing method has been developed using modal analysis in conjunction with the traditional voltage stability method (Q-V method). Wind farms are placed at buses in the power system which have the lowest negative impact on voltage instability modes (strong wind injection buses). By placing the wind farms at the strongest wind injection buses, higher amounts of wind power can be injected into the power system. To further increase wind penetration in weak power systems, two additional techniques are introduced and applied to the western Kansas power system. The first technique uses modes of voltage instability to place voltage support equipment like static var compensators at locations in the power system where they provide the needed reactive power support for increasing levels of wind penetration. The second technique uses the fact that wind patterns at a wind farm site may rarely allow the wind farm to produce its maximum capacity during the peak loading hours. Wind farm maximum sizes can be increased above their maximum voltage stable size limit without driving the power system into becoming voltage unstable. Preventing voltage collapse for the additional increases in wind farm sizes is accomplished by disconnecting some wind turbines inside the wind farm during critical times to reduce its power output to a voltage stable level.
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Roth, George J. "Stability Analysis of a Constant Power Load Serviced by a Buck Converter as the Source Impedance Varies." Thesis, Monterey, California. Naval Postgraduate School, 2012. http://hdl.handle.net/10945/17451.
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Approved for public release; distribution is unlimitedAs the NAVY moves forward with plans to become less dependent on fossil fuels and more dependent on hybrid electric drives and all-electric ships, being aware of the stability issues associated with direct current (DC)-DC and DC-alternating current (AC) power converters and understanding how to solve the issues that come with using them, are very important. The negative input impedance that is observed when using a buck converter servicing a constant power load (CPL) is one of the issues that needs to be understood. Understanding the stability issue caused by the negative input impedance and mitigating this instability by varying the input source impedance is the focus of this thesis. Using a Simulink model of an ideal CPL, we determined the expected results. Then, the Simulink results were compared to the analysis of the linearized small signal transfer function to determine how well the results of the two matched. Finally, the hardware model was observed and its results compared to the Simulink model and linearized small signal transfer function. These experiments led to the conclusion that increasing the capacitance or decreasing the inductance reduces the input source impedance and, ultimately, reduces instability in the system.
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Baxant, Radek. "Řešení stability prutových konstrukcí." Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2015. http://www.nusl.cz/ntk/nusl-227507.
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This diploma thesis deals with the subject of slenderness bars’ stability assessment, especially in the steel structures. Before the assessment of bars in the frame constructions, we search for the influence of the computational model’s settings on the final result. The initial geometrical imperfections are examined on the model of Euler’s bar. The influence of the rigidity of girders on the poles’ buckling length is examined on the basic frame construction. The buckling lengths are assessed in the comparison with the figures we got from the statistical tables and the computational software. The influence of construction’s initial tilt and its replacement by the system of outer forces is examined on the frame structure. Three-hinged frame structure with variable cross-section member is designed then and the influence of non-linear calculations on the inner forces is studied. In the complex frame assessment, the influence of the number of parts of variable cross-section member on the bars’ buckling length is examined.
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Hedkvist, Simon. "Throughflow Study on Bleeding for Part Load Compressor Operation." Thesis, Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-75337.
Повний текст джерелаАнотація:
The transition of the European energy grid to renewable energy sources is increasing the demand for back-up capacity with high flexibility. Current fossil fuel plants are continuously being forced into part load operation, where they are limited by pollution regulations that dictate their minimum environmental load, MEL. The power plants need to shut down when they no longer can comply to pollution regulations, but shutting down means that they can't act as quick back-up for the energy grid. Thus the EU project Turbo-Reflex aims to retrofit existing power plants in order to improve MEL by extending it to lower loads and, by doing so, meeting some of the back-up capacity that is needed. One method of improving MEL in a gas turbine power plants is reducing the mass flow from the compressor to the combustor. This study aims to investigate the stability and performance changes in a compressor as a function of intermediate mass extraction through bleeding lines. The study was made using a 2D throughflow model of a 15 stage axial compressor. Three different bleeding lines, positioned along the length of the compressor, were used for flow reduction. A design of experiments was made to get a structured data collection, combining different configurations of bleeding levels through the three lines, with up to 20% flow reduction. The influence of lowering the ambient temperature was also studied. Results detail the aerodynamic influence of intermediate mass extraction. The loading at the last stage increases with flow reduction, as evaluated by the diffusion factor, and stator 15 becomes the highest aerodynamically loaded position in the compressor. The increased loading is significantly dependent on the bleeding configuration, where upstream extraction is advantageous. The compressor power requirement has the same behavior, where extracting upstream has a 10% advantage. However, bleeding reduces efficiency, and in this regard it is better to use a bleed line further downstream. This combines into a trade off between these three parameters that needs to be made by the operator. Lowering the ambient temperature changes the interplay between these parameters. These research's results are part of the TURBO-REFLEX project, which has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No. 764545.
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Zhou, Yang. "Parametric stability analyses for fluid-loaded thin membranes." Licentiate thesis, KTH, Strukturmekanik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-176030.
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Membrane structures are commonly used in many elds. The studies of thesestructures are of increasing interest. The two projects focus on the evaluations ofequilibrium states for uid-pressurized membranes under dierent loading conditions,and the corresponding instability behavior.The rst part of the current work discusses the instability behavior of a thin,planar, circular and initially horizontal membrane subjected to downwards or upwards uid pressure. The membrane structures exhibit large deformations under uid pressure. Various instability behaviors have been observed for dierent loadingparameters. Limit and bifurcation points have been detected for dierent loadingconditions. Dierent loading parameters have been used to interpret the instabilitybehavior. The eects on instability of parameters, the initial states of the membrane,and the chosen mesh have been discussed.The second part of the current work discusses instability behavior of a thin,spherical and closed membrane containing gas and uid placed on a horizontal rigidand non-friction plane. A multi-parametric loading has been described. By addingthe practically relevant controlling equations, the complex equilibrium paths werefollowed using the generalized path following algorithm, and the stability conclusionswere made dierently, according to the considered load parameters and theconstraints. A generalized eigenvalue analysis was used to evaluate the stabilitybehavior including the constraint eects. Fold line evaluations were performed toanalyze the parametric dependence of the instability behavior. A solution surfaceapproach was used to visualize the mechanical response under this multi-parametricsetting.QC 20151029
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Felix, Isbi. "Dynamic analysis of the impact of grid connection of "La Higuera" hydropower plant to the transmission grid." Thesis, KTH, Elektriska energisystem, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-118929.
Повний текст джерелаАнотація:
Studies regarding the development of a new hydropower plant exploiting the water resources offered by the upper Tinguiririca river, located about 150 km south-east of the capital Santiago in Chile, has been done by Pacific Hydro Ltd from Australia and Lahmeyer International from Germany. These studies have resulted in proposals to construct two Hydropower Stations, �La Higuera� and �Confluencia�. Both hydropower stations will have a total installed capacity of 300 MW. When setting up a new hydropower plant, it is important to foresee how the hydropower plant would affect the existing transmission grid in different situations during operation as well as how events in the grid may affect the La Higuera and/or Confluencia hydropower stations. In this report three kind of analysis are highlighted, which are static analysis, large signal stability and rotor angle stability. To perform these analyses a simulation tool named DigSilent is used. DigSilent is used to perform these analyses in a simulated network of the studied transmission system. These two hydropower stations as shown in the results will improve the existing transmission system by enhancing the stability margins in the presence of a fault. When performing the simulation of the existing transmission system with the newly installed hydropower plant we could see that it had a poor damping after a disturbance; this might be due to the large distance between production plants and the existing loads. This phenomenon can be alleviated if a power system stabilizer (PSS) is integrated in the hydropower plant. The final conclusion is that the integration of the two hydropower plants will improve the existing transmission system in Chile.
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Dhasarathy, Deepak. "Estimation of vertical load on a tire from contact patch length and its use in vehicle stability control." Thesis, Virginia Tech, 2010. http://hdl.handle.net/10919/33559.
Повний текст джерелаАнотація:
The vertical load on a moving tire was estimated by using accelerometers attached to the inner liner of a tire. The acceleration signal was processed to obtain the contact patch length created by the tire on the road surface. Then an appropriate equation relating the patch length to the vertical load is used to calculate the load. In order to obtain the needed data, tests were performed on a flat-track test machine at the Goodyear Innovation Center in Akron, Ohio; tests were also conducted on the road using a trailer setup at the Intelligent Transportation Laboratory in Danville, Virginia. During the tests, a number of different loads were applied; the tire-wheel setup was run at different speeds with the tire inflated to two different pressures. Tests were also conducted with a camber applied to the wheel. An algorithm was developed to estimate load using the collected data.
It was then shown how the estimated load could be used in a control algorithm that applies a suitable control input to maintain the yaw stability of a moving vehicle. A two degree of freedom bicycle model was used for developing the control strategy. A linear quadratic regulator (LQR) was designed for the purpose of controlling the yaw rate and maintaining vehicle stability.
Master of Science
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Nord, Thomas. "Voltage Stability in an Electric Propulsion System for Ships." Thesis, KTH, Elektriska energisystem, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-118932.
Повний текст джерелаАнотація:
This Master of Science thesis was written based on the shipbuilder Kockums AB feasibility study regarding the development of an All- Electric Ship for the Swedish Navy. The thesis was aiming at addressing voltage stability issues in a dc system fed by PWM rectifiers operating in parallel when supplying constant power loads. A basic computer model was developed for investigating the influence from various parameters on the system. It was shown that the voltage stability is dependent upon the ability to store energy in large capacitors. It was also shown that a voltage droop must be implemented maintaining load sharing within acceptable limits. Different cases of operation were modelled, faults were discussed, and the principal behaviour of the system during a short-circuit was investigated. It was shown that the short-circuit current is much more limited in this type of system in comparison to an ac system. It was concluded that more research and development regarding the components of the system must be performed.
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Togiti, Santosh. "Comparative Analysis of Load Flow Techniques for Steady State Loading Margin and Voltage Stability Improvement of Power Systems." ScholarWorks@UNO, 2015. http://scholarworks.uno.edu/td/2042.
Повний текст джерелаАнотація:
Installation of reactive compensators is widely used for improving power system voltage stability. Reactive compensation also improves the system loading margin resulting in more stable and reliable operation. The improvements in system performance are highly dependent on the location where the reactive compensation is placed in the system. This paper compares three load flow analysis methods - PV curve analysis, QV sensitivity analysis, and Continuation Load Flow - in identifying system weak buses for placing reactive compensation. The methods are applied to three IEEE test systems, including modified IEEE 14-bus system, IEEE 30-bus system, and IEEE 57-bus system. Locations of reactive compensation and corresponding improvements in loading margin and voltages in each test system obtained by the three methods are compared. The author also analyzes the test systems to locate the optimal placement of reactive compensation that yields the maximum loading margin. The results when compared with brute force placement of reactive compensation show the relationship between effectiveness of the three methods and topology of the test systems.
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Gedda, Emil, and Anders Eriksson. "Practical analysis of the Precision Time Protocol under different types of system load." Thesis, KTH, Skolan för datavetenskap och kommunikation (CSC), 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-208493.
Повний текст джерелаАнотація:
The existence of distributed real-time systems calls for protocols for high accuracy time synchronization between devices. One such protocol, the Precision Time Protocol (PTP) reaches sub microsecond synchronization precision. PTP can be implemented both in hardware and software. This study aimed to analyze how system stress could affect the accuracy and precision of software implemented PTP between two devices. This was done using two Intel Galileo Generation 2 running Linux systems. Software was used to simulate CPU, I/O, network, and OS usage. Data was extracted from software logs and summarized in charts and then analyzed. The results showed that PTP synchronization accuracy and precision does suffer under certain types of system load, most notably under heavy I/O load. However the results might not be applicable to real-world scenario due to limitations in hardware and the synthetic stress tests do not correspond to real-world usage. Further research is required to analyze why and how different types of system load affects PTPs accuracy and precision.Förekomsten av distribuerade realtidssystem kräver protokoll för noggrann tidssynkronisering mellan enheter. Ett sådant protokoll, Precision Time Protocol (PTP), kan uppnå en precision på under mikrosekunden under synkronisering. PTP kan implementeras i både hårdvara och mjukvara. Den här rapporten fokuserar på att analysera hur systembelastning kan påverka precision och noggrannheten hos mjukvaruimplementerad PTP mellan två enheter. Testen utfördes på två stycken Intel Galileo Generation 2 kö- randes Linux. Mjukvara användes sedan för att simulera belastning på olika system såsom CPU, I/O, nätverk och på operativsystemet. Data extraherades ifrån loggar från mjukvaran, vilken sammanfattades i grafer för att sedan analyseras. Resultaten visade att precisionen och noggrannheten hos PTP försämras under vissa typer av systembelastningar, mest märkbart under tung I/O belastning. Resultaten är dock potentiellt inte applicerbara på verklighetscenarion på grund av begränsingar i hårdvaran samt att syntetiska stresstest inte motsvarar normal belastning. Ytterligare forskning krävs för att analysera hur och varför olika typer av systembelastning påverkar PTPs precision och noggrannhet.
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Rocolle, Guillaume. "Simulation and Experimental Verification of the Flooding and Draining Process of the Tidal Energy Converter “Deltastream” during Deployment and Recovery." Thesis, Cranfield University, 2014. http://dspace.lib.cranfield.ac.uk/handle/1826/9206.
Повний текст джерелаАнотація:
Deltastream is an on-going project carried by Tidal Energy Limited since almost
twenty years. It is a tidal energy converter with a triangular shape and one
turbine on each tower. It has gone through many evolutions of design but a first
prototype will be installed in the end of 2014 at Ramsey Sound.
The deployment and recovery operations will be carried out with a single lift
point through a heavy lift frame. Two issues have to be tackled during the
operation: the rate of flooding of the ballasts and the tension on the lift crane
cable. The most favourable sea state must be found in order to minimise the
crane cable tension as well as the best inlets and outlets configuration for the
ballasts system.
In order to tackle those issues, preliminary analytical work was conducted on
the demonstrator to assess the stability during the flooding process. A scaled
model was designed and built in order to be tested in a wave-towing tank.
The results from the tests highlight that the deployment and the recovery
operations are safe for both the barge and Deltastream for the range of wave
conditions tested in the tank. However, the sea state has an important impact
on the proceeding of the operations, especially the period of the waves.
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Khamisi, Ali. "Stability of Tubular Steel Structures : Buckling and Lateral Torsional Buckling." Thesis, Université de Lorraine, 2016. http://www.theses.fr/2016LORR0172.
Повний текст джерелаАнотація:
Ce sujet est d’actualité suite à une évolution rapide des types de conception de structures élancées utilisées dans les installations provisoires. C’est seulement depuis une vingtaine d’années que ces structures sont préfabriquées en cadres multidirectionnels (de sections tubulaires en acier ou en aluminium). Ces structures sont légères et leur stabilité réside seulement dans les raideurs internes au niveau des files de montants et au niveau horizontal par les planchers ainsi que dans les liaisons avec l’ouvrage. Ce travail concerne l’étude des instabilités (flambement-déversement) en tenant compte de différents types d’imperfections. De nouvelles courbes de flambement ainsi que les facteurs d’imperfection associés sont proposés dans cette thèse. Ces courbes sont obtenues en imposant une déformée initiale représentant les défauts géométriques et mécaniques (contraintes résiduelles). Les résultats expérimentaux confrontés avec les prévisions théoriques de l’Eurocode 3 montrent que les valeurs des imperfections figurant dans la littérature sont extrêmement exagérées. Les valeurs préconisées dans ce travail pourraient présenter un certain intérêt pour une modification éventuelle des courbes européennes de flambement pour ce type de structure. En ce qui concerne l’instabilité latérale, une méthodologie originale d’essais en vraie grandeur de poutres à treillis formés d’éléments tubulaires a été également mise au point. Le système de chargement à « roues libres » développé permet de libérer le point d’application de l’effort dès le début de l’instabilité. Cette technique conduit à des mesures plus précises du moment critique de déversementThis subject becomes topical following a rapid evolution of design procedures for slender structures used widely in the temporary installations. Only through the last twenty years that these structures are prefabricated of multidirectional frames (steel or aluminium tubular sections). These structures are lightweight and their stability lies only in the internal stiffness at rows of posts and horizontally by the planking as well as the links with the building. This work concerns the study of instabilities (buckling - lateral torsional buckling) taking into account different types of imperfections. New buckling curves and the associated imperfection factors are proposed in this thesis. These curves are obtained by imposing an initial deformed representing the geometrical and mechanical defects (residual stress). The experimental results were confronted with theoretical predictions of Eurocode 3 which show that the values of the imperfections in the literature are extremely exaggerated. The values advocated in this work could be of interest for a possible adjustment of the European buckling curves for this type of structure. Regarding the lateral instability, an original methodology in real scale tests of trusses consist of tubular elements was also developed. The developed loading system of "free wheels" allows releasing the point of application of the force from the beginning of instability. This technique leads to more accurate measurements of the critical lateral torsional buckling moment
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Hansson, Henrik, and Martin Ludvigsson. "Praktisk Lastnedräkning och Stomstabilitet enligt Eurokoder." Thesis, KTH, Byggvetenskap, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-174067.
Повний текст джерелаАнотація:
Eurokoderna som utgör svenska normer för verifiering av bärförmåga, stadga och beständighet är i en fortgående utvecklingsfas och är ibland svåra och tidsödande att tillämpa i konstruktionsarbetet. Normerna anpassas kontinuerligt efter att frågor debatteras i branschen och det är viktigt att användarna av Eurokoderna håller sig uppdaterade. Svårtolkade begrepp och definitioner tillsammans med en omständig struktur i Eurokoderna skapar merarbete för användarna. Detta examensarbete sammanställer nödvändig information samt undersöker och utvecklar tillhörande begrepp för två ämnen, lastnedräkning och stomstabilitet. Examensarbetet kommer likt en handbok kunna användas i vardagligt konstruktörsarbete för att snabbt hitta rätt i Eurokoderna och bidra till att reda ut oklarheter kring de två berörda ämnena. Beräkningsexempel är upprättade som praktisk vägledning för respektive ämne där Eurokoderna tillämpas och hänvisas till. Examensarbetet är inriktat på handberäkningar. Dessa handberäkningar kan ligga till grund för initiala bedömningar av ett bärverks dimensioner och övergripande stabilitet men även vara ett stöd i beräkningar i bygghandlingsskeden.The Eurocodes, which serve as the Swedish standards for verification of mechanical resistance and stability, are in an ongoing development phase and are sometimes difficult and time consuming to apply in the design process. The standards are continuously adapted to issues debated in the industry and it is important that users of the Eurocodes keep themselves up to date. Indistinct terms and definitions in the Eurocodes create, together with an inconvenient structure, extra work for users. This thesis compiles the necessary information and examines and elaborates terms related to two topics, load distribution and structure stability. Similar to a handbook, this thesis can be used in designer’s everyday work to quickly find the right Eurocodes and help sort out the confusion related to the topics in this thesis. Calculation examples are given as a practical guide where Eurocodes are applied and referred to. The thesis is focused on hand calculations. These hand calculations could act as a base for initial assessments concerning structure dimensions and overall stability as well as a guide during final calculations for construction drawings.
50
Tbaileh, Ahmad Anan. "Robust Non-Matrix Based Power Flow Algorithm for Solving Integrated Transmission and Distribution Systems." Diss., Virginia Tech, 2017. http://hdl.handle.net/10919/89362.
Повний текст джерелаАнотація:
This work presents an alternative approach to power system computations, Graph Trace Analysis (GTA), and applies GTA to the power flow problem. A novel power flow algorithm is presented, where GTA traces are used to implement a modified Gauss-Seidel algorithm coupled with a continuation method. GTA is derived from the Generic Programming Paradigm of computer science. It uses topology iterators to move through components in a model and perform calculations. Two advantages that GTA brings are the separation of system equations from component equations and the ability to distribute calculations across processors. The implementation of KVL and KCL in GTA is described. The GTA based power flow algorithm is shown to solve IEEE standard transmission models, IEEE standard distribution models, and integrated transmission and distribution models (hybrid models) constructed from modifying IEEE standard models. The GTA power flow is shown to solve a set of robustness testing circuits, and solutions are compared with other power flow algorithms. This comparison illustrates convergence characteristics of different power flow algorithms in the presence of voltage stability concerns. It is also demonstrated that the GTA power flow solves integrated transmission and distribution system models. Advantages that GTA power flow bring are the ability to solve realistic, complex circuit models that pose problems to many traditional algorithms; the ability to solve circuits that are operating far from nominal conditions; and the ability to solve transmission and distribution networks together in the same model.PHD