The aim of this paper is to present the operation and utilization of a digital protective system for power subsystems, which consist of a power generation unit and a transmission line. The specific protective system has been designed and... more
The aim of this paper is to present the operation and utilization of a digital protective system for power subsystems, which consist of a power generation unit and a transmission line. The specific protective system has been designed and developed by the Greek company “PROT.A.S.I.S SA” [1] and is established in the electric energy systems laboratory of the School of Electrical & Computer Engineering at the National Technical University of Athens (NTUA). In particular, the procedures of setting and testing the SEL-587 and SEL-311B digital relays of “Schweitzer Engineering Laboratories, Inc.” company [2] are described. For this purpose, several short-circuit studies were carried-out at different locations of the studied power networks and then the setting parameters were calculated and loaded to the digital relays, using the AcSELerator Quickset® software [2]. In addition, the relays' secondary tests were conducted utilizing the OMICRON CMC 356 device of the “OMICRON electronics GmbH” company [3] and the results are used to verify the proper and prompt response of their protection elements. Finally, the prospect of utilizing this laboratory protective system for research in adaptive protection schemes, for modern distribution networks with high penetration of distributed generation, is discussed.
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ABSTRACT Abstract—This article presents a non-linear programming-based model for the optimal placement of phasor measurement units. The optimal phasor measurement units placement is formulated to minimize the number of phasor measurement... more
ABSTRACT Abstract—This article presents a non-linear programming-based model for the optimal placement of phasor measurement units. The optimal phasor measurement units placement is formulated to minimize the number of phasor measurement units required for full system observability and to maximize the measurement redundancy at all buses in a power system. A sequential quadratic programming algorithm is used for the solution of the proposed model. The existence of power flow and injection measurements, the limited phasor measurement units channel capacity, the lack of communication facilities in substations, and the single phasor measurement units loss are also incorporated into the initial proposed formulation. The non-linear programming model is applied to IEEE 14- and 118-bus test systems in MATLAB. The accuracy and the effectiveness of the proposed method is verified by comparing the simulation results to those obtained by a binary integer programming model also implemented in MATLAB. The comparative study shows that the proposed non-linear programming model yields the same number of phasor measurement units as the binary integer programming model. A remarkable advantage of the non-linear programming against binary integer linear programming is its capability to give more than one optimal solution, each one having the same minimum number of phasor measurement units (same minimum objective value), but at different locations.
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This paper presents a power system state estimation (SE) in a distributed manner. In order to perform a state estimation algorithm we must ensure system's observability by restoring local and global observability. In the proposed... more
This paper presents a power system state estimation (SE) in a distributed manner. In order to perform a state estimation algorithm we must ensure system's observability by restoring local and global observability. In the proposed method, measurements are divided into local and boundary. Each control area performs its own local state estimation using local measurements and exchanges information, concerning boundary states and measurements, with a coordination SE. The coordinator computes the overall system state vector and decides whether the SE algorithm converges or not. When every single area converges, the algorithm terminates and the system wide state vector is produced. Observability analysis and distributed state estimation algorithms are tested with the IEEE 14-bus system, and two realistic systems in Rhodes Island. Results concerning Rhodes's system are presented in section 4.
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Synchrophasor measurement technology has been rapidly deployed in modern power systems and in conjunction with information and communication technology enables situational awareness, one of the key steps for the development of smart... more
Synchrophasor measurement technology has been rapidly deployed in modern power systems and in conjunction with information and communication technology enables situational awareness, one of the key steps for the development of smart grids. Smart grid monitoring and control are crucial functions for the satisfaction of consumer energy demand. The developed applications to achieve these tasks are based on complicated models and powerful mathematical programming solving tools. This paper presents the synchrophasor measurement technology background, emphasizing in power grid applications using semidefinite programming, a major subclass of conic linear programming. Illustrative test cases from different research topics are analytically described and simulated to validate the effectiveness of the proposed techniques.
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The most crucial functions of modern power systems are monitoring and control. These tasks can be efficiently accomplished using synchronized phasor measurement units (PMUs) which are extremely accurate devices installed at substations... more
The most crucial functions of modern power systems are monitoring and control. These tasks can be efficiently accomplished using synchronized phasor measurement units (PMUs) which are extremely accurate devices installed at substations providing measurements of the voltage phasor at the installation bus and the current phasors in the branches originated from that bus. Worldwide many utilities have scheduled the installation of a large number of PMUs in the near future, rendering their optimal deployment at substations a problem of major significance. This paper proposes a semidefinite programming algorithm for optimal PMU placement at substations including also the transformer tap settings as state variables, by adding a fictitious bus and branch for each tap-changing transformer. Simulation results for the IEEE 14-bus and 30-bus test systems prove the effectiveness of the proposed algorithm.
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This paper proposes an optimization method to optimally place meters in transmission systems aiming at enhanced state estimation accuracy and minimized number of installed meters. Two optimization criteria are considered for the meter... more
This paper proposes an optimization method to optimally place meters in transmission systems aiming at enhanced state estimation accuracy and minimized number of installed meters. Two optimization criteria are considered for the meter placement formulation, both yielding objective functions with integer decision variables subject to linear matrix inequality constraints. An efficient mixed integer semidefinite programming algorithm is used for solving the problem. The validity of the proposed method is evaluated via numerical simulations on the IEEE 14- and 30- bus benchmark systems.
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This paper presents a unified binary semidefinite programming (BSDP) model with binary decision variables, for optimal placement of phasor measurement units, considering the impact of pre-existing conventional and synchronized phasor... more
This paper presents a unified binary semidefinite programming (BSDP) model with binary decision variables, for optimal placement of phasor measurement units, considering the impact of pre-existing conventional and synchronized phasor measurements as well as the limited channel capacity of phasor measurement units. A linear objective function is minimized subject to linear matrix inequality observability constraints. The developed method is solved with an outer approximation scheme based on binary integer linear programming. The proposed method is illustrated using the IEEE 14-bus test system. Simulations are conducted on the IEEE 57-bus and 118-bus test systems to prove the validity of the proposed method.
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This paper presents a semidefinite programming (SDP) formulation with binary decision variables, for the optimal placement of phasor measurement units (PMU), considering the existence of conventional measurements and the impact of limited... more
This paper presents a semidefinite programming (SDP) formulation with binary decision variables, for the optimal placement of phasor measurement units (PMU), considering the existence of conventional measurements and the impact of limited channel capacity (OPP-LCC). The proposed problem minimizes a linear objective function subject to linear matrix inequality (LMI) observability constraints. Simulations, using a Matlab-based SDP software, are conducted on different IEEE systems to prove the validity of the proposed method.
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The coordination of directional overcurrent relays (DOCRs) in meshed power grids with multiple sources is a constrained optimization problem, which has been stated in recent literature as linear (LP), nonlinear (NLP), and mixed-integer... more
The coordination of directional overcurrent relays (DOCRs) in meshed power grids with multiple sources is a constrained optimization problem, which has been stated in recent literature as linear (LP), nonlinear (NLP), and mixed-integer nonlinear programming (MINLP) problem. In this paper, the DOCR coordination NLP problem is reformulated as an equivalent quadratically constrained quadratic programming (QCQP) model, leading to significant reduction of problem complexity. Another contribution of this work is the systematic problem statement using graph theory concepts. The proposed method is applied to three different meshed power systems, employing state-of-the-art optimization software. Simulation results demonstrate the efficacy and superiority of the proposed QCQP model over the prevailing NLP approach.
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The constantly increasing integration of distributed generation (DG) using renewable energy resources, as well as the wide application of microgrid conception, has posed several challenging problems to the existing protection and control... more
The constantly increasing integration of distributed generation (DG) using renewable energy resources, as well as the wide application of microgrid conception, has posed several challenging problems to the existing protection and control systems. Hence, modern adaptive protection schemes, capable of anticipating potential protection issues, are being developed and implemented. In this paper, the prospect of integrating optimal relay coordination methods with adaptive protection schemes is introduced. The efficacy of the proposed strategy is assessed by simulating two different DG penetrated networks with various configurations, and the obtained results are discussed in detail.
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State estimation (SE) is an essential tool of energy management systems (EMS), providing power system operators with an overall grasp of the actual power system operating conditions and aiding them in sustaining reliable and secure... more
State estimation (SE) is an essential tool of energy management systems (EMS), providing power system operators with an overall grasp of the actual power system operating conditions and aiding them in sustaining reliable and secure operation of the grid. In modern transmission sectors, two main measurement systems are deployed, namely the supervisory control and data acquisition (SCADA) and the wide area monitoring systems (WAMS). The multiple advantages of augmenting conventional SCADA-based SE algorithms with synchrophasor measurements from WAMS are already well-established; thus, an abundance of different methodologies has been reported in the field of hybrid SE (HSE). Under this premise, this paper provides a thorough literature review of novel HSE methods in transmission systems and proposes a classification based on the scope and mathematical modeling of each method. Following a brief introduction to the concept of SE based on WAMS and SCADA measurements, an insight into the m...
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ABSTRACT This paper presents a numerical method for observability analysis of a measurement system including phasor measurement units (PMUs) as well as conventional measurements. Traditional power flow measurements and branch current... more
ABSTRACT This paper presents a numerical method for observability analysis of a measurement system including phasor measurement units (PMUs) as well as conventional measurements. Traditional power flow measurements and branch current phasor measurements are used to build topologically flow islands that, in turn, are used to construct a reduced network. Boundary injections at flow islands and bus voltage phasors are considered to form a reduced size Jacobian matrix. Observability checking is carried out analyzing the pivots encountered during the triangular factorization of a Gram matrix associated with this reduced order Jacobian. The additional measurements, that restore the global observability of an unobservable system, are provided by a direct method, using the triangular factors of a Gram matrix associated with a reduced Jacobian including existing and candidate traditional injection measurements as well as PMUs, at boundary buses of the flow islands. The IEEE 14-bus system demonstrates the features of the proposed method.
Research Interests: Engineering, Power Systems, Restoration, Energy Conversion, Numerical Methods, and 14 moreObservability, Flow measurement, Phasor, Electric Power System, Phase measurement, Synchronized Phasor Measurements, Phasor Measurement units, Direct Injection, Phasor Measurement Unit, Direct Method, Measurement System, Reduced Order, Bus Voltage, and Units of measurement
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ABSTRACT This paper proposes a state estimation algorithm for the monitoring of topological changes in distribution networks, using real measurements at substations, pseudo measurements at load and distributed generation buses, and zero... more
ABSTRACT This paper proposes a state estimation algorithm for the monitoring of topological changes in distribution networks, using real measurements at substations, pseudo measurements at load and distributed generation buses, and zero injections at transition buses. This is accomplished by a generalized state estimation formulation, based on a weighted least squares approach with equality constraints, which involves both real and pseudo analog measurements and operational constraints for the switching devices. Estimates of state variables and switching device statuses are simultaneously provided. The normalized residual test is used to effectively identify gross errors in analog and topological data. The network splitting problem, caused by switching operations, is also investigated by introducing appropriate pseudo measurements. An advantage over previous methods is that the proposed approach eliminates the need of repeated state estimation runs for alternative hypothesis evaluation. A 17-bus distribution network is employed to demonstrate its effectiveness.
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This paper presents a hybrid topological/numerical method for power system observability analysis, using conventional measurements, provided by SCADA, as well as synchronized phasor measurements, provided by phasor measurement units... more
This paper presents a hybrid topological/numerical method for power system observability analysis, using conventional measurements, provided by SCADA, as well as synchronized phasor measurements, provided by phasor measurement units (PMUs). A PMU placed at a bus can measure the voltage phasor at that bus, as well as the current phasors in some or all the lines connected to that bus. Branch power flow and current phasor measurements are used to build topologically flow islands that, in turn, are used to construct a reduced network. A gain matrix associated with this reduced network is built, considering boundary injections at flow islands and all bus voltage phasors. Observability checking is carried out analyzing the pivots in the triangular factors of this gain matrix and observable islands are identified in a noniterative manner, by performing back substitutions. Additional measurements for observability restoration are provided by a direct method, using the triangular factors of a reduced Gram matrix associated with existing and candidate injections as well as PMUs at boundary buses of the observable islands. The IEEE 14 and 30 bus systems illustrate the steps of the proposed method.
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Τις τελευταίες δεκαετίες, η βιομηχανία ηλεκτρικής ενέργειας υπόκειται σε πολλαπλές αλλαγές εξαιτίας της απελευθέρωσης της αγοράς ενέργειας. Σ’ αυτό το περιβάλλον, τα δυναμικά φαινόμενα στα συστήματα ηλεκτρικής ενέργειας έχουν κάνει... more
Τις τελευταίες δεκαετίες, η βιομηχανία ηλεκτρικής ενέργειας υπόκειται σε πολλαπλές αλλαγές εξαιτίας της απελευθέρωσης της αγοράς ενέργειας. Σ’ αυτό το περιβάλλον, τα δυναμικά φαινόμενα στα συστήματα ηλεκτρικής ενέργειας έχουν κάνει περισσότερο από ποτέ επιτακτική την ανάπτυξη αξιόπιστων εργαλείων για την εποπτεία και τον έλεγχό τους. Ένα αποτελεσματικό εργαλείο για τη στενή παρακολούθηση των συνθηκών λειτουργίας τους είναι ο εκτιμητής κατάστασης, ο οποίος βασίζεται σε μετρήσεις πραγματικού χρόνου, οι οποίες παρέχονται μέσω του συστήματος SCADA (Supervisory Control and Data Acquisition). Οι μετρήσεις αυτές συλλέγονται μέσω απομακρυσμένων τερματικών μονάδων (Remote Terminal UnitsRTUs) που είναι εγκατεστημένες στους υποσταθμούς Υ.Τ. Η φασική γωνία των τάσεων ζυγών δε μπορεί να μετρηθεί εύκολα εξαιτίας τεχνικών δυσκολιών που σχετίζονται με τον συγχρονισμό των μετρήσεων στα RTUs. Το παγκόσμιο σύστημα προσδιορισμού θέσης (GPS) εξάλειψε αυτές τις αδυναμίες και οδήγησε στην ανάπτυξη των μο...
An important tool for real-time monitoring and control of power systems, terrestrial or shipboard, is state estimation. The estimated state vector is determined based on measurements well distributed throughout the network. Traditionally,... more
An important tool for real-time monitoring and control of power systems, terrestrial or shipboard, is state estimation. The estimated state vector is determined based on measurements well distributed throughout the network. Traditionally, these measurements are commonly provided by the SCADA (Supervisory Control and Data Acquisition) system. The utilization of global positioning system (GPS) has led to the development of modern measurement devices for real time power system monitoring (e.g. phasor measurement units), improving the state estimation performance and redundancy. The phasor measurement unit (PMU) is a new high-precision measuring device, which can measure voltage and current phasors. With the increasing use of PMUs in recent years, the optimal placement problem has become a critical task for the researchers. The objective of the optimal PMU placement (OPP) problem is to determine their minimum number and corresponding installation sites, ensuring the power system observa...
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Research Interests: Engineering, Algorithms, State Estimation, Observability, Polar Spherical Coordinates, and 12 moreEstimation, Phasor, Phase measurement, Synchronized Phasor Measurements, Uncertainty propagation, IEEE bus system, Electrical And Electronic Engineering, Accurate Measurement, Phasor Measurement Unit, Bus Voltage, Non-Iterative, and Units of measurement
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Research Interests: Mathematics, Computer Science, Algorithms, Distributed Computing, State Estimation, and 12 moreComputer Software, Phasor, Phase measurement, Synchronized Phasor Measurements, Estimator, Electrical And Electronic Engineering, Initialization Stage, State Variables, State estimator, Numerical Problems, Computers and Electrical Engineering, and Units of measurement
Conventional state estimators (SE) are based on real-time measurements, consisting of bus voltages and active and reactive power flows and injections, and estimate the voltage phasors of the network buses. Until recently, these... more
Conventional state estimators (SE) are based on real-time measurements, consisting of bus voltages and active and reactive power flows and injections, and estimate the voltage phasors of the network buses. Until recently, these measurements were obtained only through SCADA. With the advent of GPS synchronized measurements obtained by phasor measurement units (PMU), effective techniques are required to incorporate the extremely
Research Interests: Computer Science, Medicine, Electric Power Systems, SCADA, Real Time Systems, and 15 moreReactive Power, Estimation, MEASUREMENTS, Real Time, Lancet, Phase measurement, Data Handling, Data Processing, Scada, Non Linear, Electrical And Electronic Engineering, Real Time Measurements, Phasor Measurement Unit, Numerical Problems, and Bus Voltage
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ABSTRACT Phasor measurement units (PMUs) are essential tools for monitoring, protection and control of power systems. The optimal PMU placement (OPP) problem refers to the determination of the minimal number of PMUs and their... more
ABSTRACT Phasor measurement units (PMUs) are essential tools for monitoring, protection and control of power systems. The optimal PMU placement (OPP) problem refers to the determination of the minimal number of PMUs and their corresponding locations in order to achieve full network observability. This paper introduces a recursive Tabu search (RTS) method to solve the OPP problem. More specifically, the traditional Tabu search (TS) metaheuristic algorithm is executed multiple times, while in the initialisation of each TS the best solution found from all previous executions is used. The proposed RTS is found to be the best among three alternative TS initialisation schemes, in regard to the impact on the success rate of the algorithm. A numerical method is proposed for checking network observability, unlike most existing metaheuristic OPP methods, which are based on topological observability methods. The proposed RTS method is tested on the IEEE 14, 30, 57 and 118-bus test systems, on the New England 39-bus test system and on the 2383-bus power system. The obtained results are compared with other reported PMU placement methods. The simulation results show that the proposed RTS method finds the minimum number of PMUs, unlike earlier methods which may find either the same or even higher number of PMUs.
Research Interests: Engineering, Power System, Metaheuristics (Operations Research), Tabu Search, State Estimation, and 14 moreElectric Power Systems, Power System Protection, Energy Management, Power System Protection Engineering, Metaheuristic Algorithms, Power System State Estimation, Observability, PMU, Phasor, PMU based monitoring and control, Mathematical Optimization, Phasor Measurement units, Electrical And Electronic Engineering, and Optimal PMU placement
Research Interests: Engineering, Computer Science, Genetic Algorithm, Electric Power Systems, Energy Management, and 15 moreOptimization, Literature Review, Metaheuristic Algorithms, Observability, PMU, PMU based monitoring and control, Electric Power System, Heuristic Algorithms, Phasor Measurement units, Mathematical Algorithms, Optimization Method, Electrical And Electronic Engineering, Phasor Measurement Unit, Optimal PMU placement, and Heuristic algorithm
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The increasing availability of phasor measurement units (PMUs) at substations enables the synchronized measurements to various applications, such as the monitoring of system state under normal operations or the protection and control of... more
The increasing availability of phasor measurement units (PMUs) at substations enables the synchronized measurements to various applications, such as the monitoring of system state under normal operations or the protection and control of power systems during abnormal operation. The objective of the optimal PMU placement (OPP) problem is to determine a minimal set of PMUs such that the whole system is observable. To solve the OPP problem, mathematical programming, heuristic, and meta-heuristic optimization techniques, have been proposed. This paper provides a comprehensive literature review on the OPP problem and the solution methodologies. Due to the vast number of publications in this field, the most representative papers are reviewed.
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The presence of renewable energy resources and conventional distributed generation (DG) in modern distribution networks challenges the traditional protection schemes, since the radial single-fed concept is no longer adopted. In this... more
The presence of renewable energy resources and conventional distributed generation (DG) in modern distribution networks challenges the traditional protection schemes, since the radial single-fed concept is no longer adopted. In this paper, a new adaptive protection system, which takes advantage of multiple relay setting groups (SGs) and optimisation techniques, is introduced. Moreover, a hardware-in-the-loop (HIL) configuration appropriate for testing adaptive protection systems is presented. A distribution test system with large DG penetration is used to demonstrate the efficacy of the proposed solution, and simulation results are thoroughly discussed.