Testing and validation of an algorithm for configuring distribution grid sensor networks

The control of Smart Grids depends on a reliable set of measurement information such that distributed generation and demand can be effectively managed. The cost of procuring and installing sensors at multiple nodes in the grid is prohibitive and choosing the optimum strategy with regards to sensor location, accuracy, number and type is very important. This report describes the testing of a sensor placement algorithm developed to determine measurement strategies for distribution grids. This testing was performed on a laboratory microgrid at the University of Strathclyde. The ability of the algorithm to choose the optimal subset of measurements was tested by comparing the estimated power flow with the measured power flow of a fully instrumented grid. The chosen subset is found to have the close to the lowest overall error and all estimates agree with the rejected measurements within the calculated uncertainties

Operating strategies to preserve the adequacy of power systems circuit breakers

The objective of the proposed research is to quantify the limits of overstressed and aging circuit breakers in terms of probability of failure and to provide guidelines to determine network reconfigurations, generator commitment, and economic dispatch strategies that account for these limits. The proposed temporary power system operating strategies address circuit breaker adequacy issues and allow overstressed breakers to be operated longer and more reliably until they are replaced with adequate equipment. The expansion of electric networks with new power sources (nuclear plants, distributed generation) results in increased short-circuit or fault currents levels. As fault currents increase, they will eventually exceed circuit breaker ratings. Circuit breakers exposed to fault currents in excess of their ratings are said to be overstressed, underrated, or inadequate. Insufficient ratings expose overstressed breakers to increased failure probabilities. Extensive common-mode outages caused by circuit breaker failures reduce the reliability of power systems. To durably avoid outages and system unreliability, overstressed breakers must eventually be replaced. Large-scale replacements of overstressed breakers cannot be completed in a short time because of budgetary limits, capital improvement schedules, and manufacturer-imposed constraints. Meanwhile, to preserve the ability of old and overstressed breakers to safely interrupt faults, short-circuit currents must be kept within the limits imposed by the ratings and the age of these breakers by using the substation reconfiguration and generator commitment strategies described in this study. The immediate benefit of the above-mentioned operating strategies is a reduction of the failure probability of overstressed breakers obtained by avoiding the interruption of currents in excess of breaker ratings. Other benefits include (i) increased network reliability, (ii) restored operating margins with respect to existing equipment, and (iii) prioritized equipment upgrades that enhance the long-term planning of power systems.Ph.D.Committee Chair: Meliopoulos, A. P. Sakis; Committee Member: Divan, Deepakraj M.; Committee Member: Harley, Ronald G.; Committee Member: Johnson, Ellis L.; Committee Member: Taylor, David G

Autonomous state estimation and its application to the autonomous operation of the distribution system with distributed generations

The objective of this thesis is to propose guidelines for advanced operation, control, and protection of the restructured distribution system by designing the architecture and functionality for autonomous operation of the distribution system with DGs. The proposed architecture consists of (1) autonomous state estimation and (2) applications that enable autonomous operation; in particular, three applications are discussed: setting-less component protection, instant-by-instant management, and short-term operational planning. Key elements of the proposed approach have been verified: (1) the proposed autonomous state estimation has been experimentally tested using laboratory test systems and (2) the feasibility of the setting-less component protection has been tested with numerical simulations.Ph.D

Seamless design of energy management systems

The contributions of the research are (a) an infrastructure of data acquisition systems that provides the necessary information for an automated EMS system enabling autonomous distributed state estimation, model validation, simplified protection, and seamless integration of other EMS applications, (b) an object-oriented, interoperable, and unified component model that can be seamlessly integrated with a variety of applications of the EMS, (c) a distributed dynamic state estimator (DDSE) based on the proposed data acquisition system and the object-oriented, interoperable, and unified component model, (d) a physically-based synchronous machine model, which is expressed in terms of the actual self and mutual inductances of the synchronous machine windings as a function of rotor position, for the purpose of synchronous machine parameters identification, and (e) a robust and highly efficient algorithm for the optimal power flow (OPF) problem, one of the most important applications of the EMS, based on the validated states and models of the power system provided by the proposed DDSE.Ph.D

Completely Recursive Least Squares and Its Applications

The matrix-inversion-lemma based recursive least squares (RLS) approach is of a recursive form and free of matrix inversion, and has excellent performance regarding computation and memory in solving the classic least-squares (LS) problem. It is important to generalize RLS for generalized LS (GLS) problem. It is also of value to develop an efficient initialization for any RLS algorithm. In Chapter 2, we develop a unified RLS procedure to solve the unconstrained/linear-equality (LE) constrained GLS. We also show that the LE constraint is in essence a set of special error-free observations and further consider the GLS with implicit LE constraint in observations (ILE-constrained GLS). Chapter 3 treats the RLS initialization-related issues, including rank check, a convenient method to compute the involved matrix inverse/pseudoinverse, and resolution of underdetermined systems. Based on auxiliary-observations, the RLS recursion can start from the first real observation and possible LE constraints are also imposed recursively. The rank of the system is checked implicitly. If the rank is deficient, a set of refined non-redundant observations is determined alternatively. In Chapter 4, base on [Li07], we show that the linear minimum mean square error (LMMSE) estimator, as well as the optimal Kalman filter (KF) considering various correlations, can be calculated from solving an equivalent GLS using the unified RLS. In Chapters 5 & 6, an approach of joint state-and-parameter estimation (JSPE) in power system monitored by synchrophasors is adopted, where the original nonlinear parameter problem is reformulated as two loosely-coupled linear subproblems: state tracking and parameter tracking. Chapter 5 deals with the state tracking which determines the voltages in JSPE, where dynamic behavior of voltages under possible abrupt changes is studied. Chapter 6 focuses on the subproblem of parameter tracking in JSPE, where a new prediction model for parameters with moving means is introduced. Adaptive filters are developed for the above two subproblems, respectively, and both filters are based on the optimal KF accounting for various correlations. Simulations indicate that the proposed approach yields accurate parameter estimates and improves the accuracy of the state estimation, compared with existing methods

Estudo do desempenho de canais de instrumentação para a medição sincronizada de fasores

Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-Graduação em Engenharia Elétrica, Florianópolis, 2014.Sistemas de Medição Fasorial Sincronizada constituem uma ferramenta que permite o monitoramento em tempo real da dinâmica dos sistemas elétricos de potência. Aplicações que fazem uso de sincrofasores podem ser sensíveis aos erros de medição. Desta maneira, as normas aplicáveis à medição fasorial exigem elevados requisitos de exatidão e desempenho por parte dos equipamentos de medição. Entretanto, o erro fasorial total em uma instalação de medição de fasores é consequência não só da unidade de medição, mas de toda a cadeia de instrumentos, denominada Canais de Instrumentação, cuja finalidade é adequar os sinais de tensão e corrente para patamares mensuráveis, e transportar esses sinais até os instrumentos de medição. Neste trabalho é investigada a influência produzida pelos Canais de Instrumentação nos erros de medição, do ponto de vista da tecnologia de medição fasorial sincronizada. Para tanto são discutidos os aspectos de exatidão que abrangem todos os equipamentos que compõem um Canal de Instrumentação típico, incluindo a própria unidade de medição fasorial. É realizada a correlação dos conceitos adotados pelas normas, e proposto um índice de avaliação do erro fasorial global, que incorpora a contribuição de todos os equipamentos. Em seguida é feita a modelagem dos equipamentos do Canal de Instrumentação. Através desta modelagem são realizadas diversas simulações computacionais, com o intuito de verificar a magnitude dos erros fasoriais, presentes em uma instalação de medição fasorial. Estas simulações são realizadas nas condições nominais de operação dos equipamentos, nas condições de testes de regime permanente e regime dinâmico exigidas pela norma de medição fasorial, e durante eventos reais observados no sistema elétrico brasileiro. Os resultados obtidos mostram que as atuais normas aplicadas a CI permitem erros fasoriais muito superiores aos exigidos pela norma de medição fasorial. Além disso, os resultados de simulação mostram que os CI podem provocar erros fasoriais elevados, principalmente quando submetidos a condições onde os parâmetros do sinal de entrada (tensão e corrente) estão fora dos seus valores nominais.Abstract : Synchronized Phasor Measurement Systems represent a useful tool on real time monitoring of power systems dynamics. Applications that use synchrophasors may be sensitive to measurement errors. Thus, the phasor measurement standards require high accuracy levels from measurement equipments. However, the total phasor error on a phasor measurement installation is not caused only by the measurement unit, but by the entire instruments network, called Instrumentation Channel. The Instrumentation Channel function consists in adjusting the voltage and current signals to measurable levels, and transport these signals to the measurement instruments. In this work, the influence of Instrumentation Channels on measurement errors is investigated, from the point of view of synchronized phasor measurement technology. For that purpose, the accuracy aspects that cover all the equipaments which compose a typical Instrumentation Channel are analyzed, including the phasor measurement unit itself. The concepts used by the standards are correlated and then an evaluation index for the global phasor error, that incorporates all equipment contribution, is proposed. After that, the modelling of Instrumentation Channel equipments is developed. Through this modelling, many computational simulations are performed, in order to verify the magnitude of phasor errors, present in a phasor measurement installation. These simulations are performed on nominal operation conditions, on test conditions of steady state and transient required by phasor measurement standard, and during real events observed on the Brazilian Interconnected Power System. The results show that the current standards, applied to Instrumentation Channels, allow phasor errors much higher than those required by the phasor measurement standard. Furthermore, the simulation results show that the instrumentation channels may produce high phasor errors, especially when facing conditions where the parameters of the input signal (voltage and current) are different from their nominal values

Influência dos canais de instrumentação na exatidão da medição fasorial sincronizada

Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-Graduação em Engenharia Elétrica, Florianópolis, 2010Neste trabalho, investiga-se a influência exercida pelos Canais de Instrumentação (CIs) na exatidão da medição fasorial sincronizada. São abordados estudos relacionados aos aspectos de exatidão dos CIs, em regime permanente, e à modelagem de seus elementos: Transformadores de Potencial Capacitivos (TPCs); Transformadores de Corrente (TCs); e cabos de controle. Destaca-se o problema do erro na medição de corrente em condições de baixo carregamento de Linhas de Transmissão (LTs), bem como a influência da carga imposta ao secundário dos TIs Transformadores de Instrumentos) sobre a exatidão de medições fasoriais. Foi também investigada a aplicação de diferentes metodologias para o cálculo do fluxo de potência em LTs, bem como o cálculo de seus parâmetros. Esses estudos são complementados por meio da análise de sensibilidade destes cálculos frente a erros fasoriais. Por fim, são apresentadas análises de desempenho envolvendo o protótipo de SPMS MedFasee Eletrosul, visando à detecção e à compensação de erros fasoriais introduzidos pelos CIs envolvidos. Constata-se a possibilidade de ocorrência de erros significativos de módulo e ângulo nos fasores, dependendo do nível de carregamento da LT e das peculiaridades dos CIs. Tais características foram comprovadas por estudos de sensibilidade aplicados a casos reais.This work investigates the influence of the Instrumentation Channels (ICs) in the synchronized phasor measurement accuracy. Studies are addressed to accuracy of ICs, in steady state, and modeling of its elements: Coupled Capacitive Voltage Transformers (CCVTs) Current Transformers (CTs), and control cables. The problem of error in current measurement under conditions of low loading of Transmission Lines (TL) is highlighted, as well as the importance of the burden on the accuracy of phasor measurements. The application of different methodologies for power flow calculation in TL and its parameters calculation are also investigated. Those studies are complemented by sensitivity analysis of these methodologies against phasor errors. Finally, a performance analysis involving the SPMS MedFasee Eletrosul prototype is presented, focusing on the detection and compensation of errors introduced by the phasor ICs involved. The presence of significant errors in the module and phasor angle is verified, depending on the loading level of the TL and the peculiarities of ICs. These characteristics are confirmed by sensitivity analysis applied to real cases