Power System Topology Research Articles

A novel and fast voltage estimation scheme for assessment of power system component outages

Purpose – The purpose of this paper is to pursue two following main goals: first, theorizing a new concept named as equivalent bus load in order to make a promising simplification over power system analysis. Second, proposing an outstanding fast and simple approach based on introduced concept for voltage estimation after multiple component outages while satisfying required accuracy. Design/methodology/approach – Equivalent load bus theory introduces three transfer matrices that describe power system topology. Mentioned matrices could be calculated simply after system reconfiguration without matrix inversion. Using transfer matrices a large-scale power system can be modeled by a simple two-bus power system from the viewpoint of any desired bus so that load flow calculation leads to same value. The analysis of simplified power system yields to extract a new incremental model based on equivalent bus load theory that will be distinguished as an outstanding fast method for voltage estimation aim. Findings – A deep study for fast voltage estimation aim is dedicated to evaluate proposed method from the accuracy and quickness point of view and the outcomes are compared to a well-known method as Distribution Factors (DF). Results and computational times unveil that presented approach is more accurate and much faster. Originality/value – A novel and new fast voltage estimation method for assessment of power system component outages is introduced.

Topology Control for Load Shed Recovery

This paper introduces load shed recovery actions for transmission networks by presenting the dc optimal load shed recovery with transmission switching model (DCOLSR-TS). The model seeks to reduce the amount of load shed, which may result due to transmission line and/or generator contingencies, by modifying the bulk power system topology. Since solving DCOLSR-TS is computationally difficult, the current work also develops a heuristic (MIP-H), which improves the system topology while specifying the required sequence of switching operations. Experimental results on a list of N-1 and N-2 critical contingencies of the IEEE 118-bus test case demonstrate the advantages of utilizing MIP-H for both online load shed recovery and recurring contingency-response analysis. This is reinforced by the introduction of a parallelized version of the heuristic (Par-MIP-H), which solves the list of critical contingencies close to 5x faster than MIP-H with 8 cores and up to 14x faster with increased computational resources. The current work also tests MIP-H on a real-life, large-scale network in order to measure the computational performance of this tool on a real-world implementation.

Power system voltage stability monitoring using artificial neural networks with a reduced set of inputs

This paper presents an artificial neural network (ANN)-based approach for online monitoring of a voltage stability margin (VSM) in electric power systems. The VSM is calculated by estimating the distance from the current operation state to the maximum voltage stability limit point according to the system loading parameter. Using the Gram–Schmidt orthogonalization process along with an ANN-based sensitivity technique, an efficient feature selection method is proposed to find the fewest input variables required to approximate the VSM with sufficient accuracy and high execution speed. Many algorithms have already been proposed in the literature for voltage stability assessment (VSA) using neural networks; however, the main drawback of the previously published works is that they need to train a new neural network when a change in the power system topology (configuration) occurs. Therefore, the possibility of employing a single ANN for estimating the VSM for several system configurations is investigated in this paper. The effectiveness of the proposed method is tested on the dynamic models of the New England 39-bus and the southern/eastern (SE) Australian power systems. The results obtained indicate that the proposed scheme provides a compact and efficient ANN model that can successfully and accurately estimate the VSM considering different system configurations as well as operating conditions, employing the fewest possible input features.

Narrowband Power Line Communications: Enabling the Smart Grid

Without question, information and communication technologies will play a vital role in enabling the next-generation power systems to be more energy efficient and reliable than currently existing power systems. In particular, on the LV and MV grids, NB-PLC technologies are particularly attractive as a communications solution due to their low cost of deployment and ability to communicate across the transformer. This ability to cross the transformer is vital in power system topologies with lower population densities. It was ascertained that wideband interfering noise sources, such as defective lighting systems, hampered communication in both PRIME and G3-PLC systems. Additionally, the next-generation NB-PLC standards ITU-T G.hnem and IEEE 1901.2 were investigated. ITU-T G.hnem and IEEE 1901.2 seek to unify NB-PLC technologies and promise higher data rates than PRIME or G3-PLC. Surely, narrowband PLC technologies have a critical role in enabling a more efficient and reliable power grid.

SOCCA: A Security-Oriented Cyber-Physical Contingency Analysis in Power Infrastructures

Contingency analysis is a critical activity in the context of the power infrastructure because it provides a guide for resiliency and enables the grid to continue operating even in the case of failure. In this paper, we augment this concept by introducing SOCCA, a cyber-physical security evaluation technique to plan not only for accidental contingencies but also for malicious compromises. SOCCA presents a new unified formalism to model the cyber-physical system including interconnections among cyber and physical components. The cyber-physical contingency ranking technique employed by SOCCA assesses the potential impacts of events. Contingencies are ranked according to their impact as well as attack complexity. The results are valuable in both cyber and physical domains. From a physical perspective, SOCCA scores power system contingencies based on cyber network configuration, whereas from a cyber perspective, control network vulnerabilities are ranked according to the underlying power system topology.

On eigenvalues to the Y-bus matrix

The topology of a power system has a profound impact on its reliability. If a power system faces a contingency, for example a loss of a transmission line or a transformer, this contingency might, in worse case, lead to a blackout. Since the Y-bus matrix contains information about the structure, the line impedances, the loading in each bus and is commonly used in power system calculations it can be used to evaluate the topology of the transmission system. This paper reports on the relation between the eigenvalues to the Y-bus matrix and the underlying graph representing the topology of the transmission system. The paper also proposes four different indices’ based on the spectrum to the Y-bus matrix and the corresponding Laplacian matrix to be used to evaluate power system topologies. In addition, this paper will also show how the so called algebraic connectivity and the mean impedance in a graph is related and how the mean impedance can be calculated through the eigenvalues to the Laplacian matrix and the Y-bus matrix. In a numerical example, the indices’ on the Nordic32 system is presented.

Towards an Auto-Associative Topology State Estimator

This paper presents a model for breaker status identification and power system topology estimation based on a mosaic of local auto-associative neural networks. The approach extracts information from values of the analog electric variables and allows the recovery of missing sensor signals or the correction of erroneous data about breaker status. The results are confirmed by extensive tests conducted on an IEEE benchmark network.

Impact of Connections on Power System State Estimation

Power system state estimation plays an essential role in modern computer systems in a dispatcher centre. Apart from reliability, it should have such features as: high accuracy of results, short performance time in each possible situation, i.e. it should ensure equally beneficial results for different states as well as for different connections in a power system. In the paper, the impact of power system topology on properties of state estimation is considered. To show differences of properties of state estimation for different power system topology, results of analysis for the IEEE 14-bus test system are presented. In the analysis, one takes into account the state of calculation process, the accuracy of estimation results and the number of iterations. At the end, from the point of view of power system state estimation, attention is paid to the most important consequences of a change of power system topology.

The Reconfigurable-Hardware Real-Time and Faster-Than-Real-Time Simulator for the Analysis of Electromagnetic Transients in Power Systems

The reconfigurable-hardware real-time power system simulator (RH-RTS) is a field-programmable gate-array (FPGA)-based real-time simulator that is developed based on the concept of simulators hardware reconfigurability (i.e., to change the underlying hardware architecture of the simulator to accommodate various power system topologies). The uniqueness of the RH-RTS is the underlying hardware architecture. The RH-RTS has a massively parallel customized hardware architecture that is tailored to the solution of the mathematical model of the power system under consideration. The RH-RTS enables the simulation of large power systems with a computation-time per simulation time-step in the range of tens of nanoseconds. Not only does the RH-RTS provide a means for real-time operation (e.g., for closed-loop testing of physical control/protection platforms in hardware-in-the-loop (HIL) configuration), it also provides a means for faster-than-real-time operation (e.g., for statistical switching studies). This paper provides validation and evaluation of the performance of the RH-RTS. This paper presents a case study involving the simulation of a power system in both real time and faster than real time. The computation time per simulation time-step is as low as 24 ns, for realistic size systems, which is, by far, the lowest computation time reported in the technical literature.

Scada Based Online Circuit Breaker Monitoring System

This paper presents the online monitoring of circuit breakers used in the transmission and distribution of power system, to connect and disconnect the power flow at the generator, substation, or load location. The circuit Breakers are capable of making, carrying, and breaking currents under normal circuit conditions. The objective of this paper is to investigate feasibility, specify requirement and propose the implementation architecture of an automated circuit breaker monitoring device that enables continuous and reliable system monitoring. It is very essential to implement an online system for efficient circuit breaker monitoring because of many infrequent cases. To improve reliability of the power system through various analysis functions it is necessary to know power system topology configuration. Real time and on-line monitoring seems to be perfect solution for circuit breaker conditions and status monitoring. SCADA is a system used for this purpose. This system monitors status of CB mechanical contacts and transfers it in real time to a central place.

Concepts of Reactive Power Control and Voltage Stability Methods in Power System Network

The intent of this paper is to present an analysis of reactive power control and voltage stability in power systems. It identifies a new model used to enhance voltage stability and exposes several key issues that had remained as research challenges in this area. The steady state voltage and reactive power control in distribution systems can be properly controlled by coordinating the available voltage and reactive power control equipment, such as on-load tap-changers, substation shunt capacitors and feeder shunt capacitors. It began with an overview of reactive power and voltage stability in transmission, distribution and load, and the importance of providing reactive power locally. The description of selected control features of shunt power systems such as SVC (Static Var Compensator) - static compensators of reactive power, STATCOM-type systems (Static Compensator), static reactive power generators and systems that combine both these solutions, which are referred to as SVC based on STATCOM were not left out. It explains the need to improve the voltage stability of Power system, as well as the increasing requirements for energy quality and security. It also discusses the techniques that were adopted in controlling and monitoring of the rate of power flow in the entire power system topology. This investigates the system to an optimal level in order to reduce losses and ensures sufficiency of reactive power control during normal and emergency conditions and to prevent voltage collapse.

The Study on Power System Protection Algorithms and Fault Detection Using Model-Based Methodology Based on Structural Analysis

This study presents a model-based methodology based on structural analysis that has the potential of having a technological impact on the design of diagnostic systems for power systems. The methodology utilizes the analytical redundancy inherent in the system structure and provides a strategy for systematic and automatic evaluation of power system topologies with respect to their monitoring (fault detection and isolation) potential.

Advanced State Feedback Control of Grid- Power Inverter

This paper shows the topology of grid-connected green power system and the performances of the front-end threephase power inverter by applying an advanced state feedback control. The proposed topology benefits a common DCAC inverter which injects the generated power into the grid. The control structure of the power inverter is of vector control type, in synchronous reference frame, and it uses the power balance concept. The solution presented in this paper adds supplementary benefits to the power system beside to the conventional state feedback control: the designed input filter assures zero steady state error and an adequate component is added for dynamic rejection of the load disturbance. The obtained experimental results are shown.

Stability Enhancement of HVDC System using Fuzzy based STATCOM

The necessity to deliver cost effective energy in the power market has become a major concern in this emerging technology era. Therefore, establishing a desired power condition at the given points are best achieved using power controllers such as the well known High Voltage Direct Current (HVDC) and Flexible Alternating Current Transmission System (FACTS) devices. High Voltage Direct Current (HVDC) is used to transmit large amounts of power over long distances or for interconnections between asynchronous grids. The system planner must consider DC alternative in transmission expansion. The factors to be considered are Cost, Technical Performance and Reliability. All these equipment provide controllability to the AC transmission system by adjusting the transmission parameters. In recent years fuzzy logic control is beginning to receive more attention. Power system operation conditions and topologies are time varying and the disturbances are unforeseeable. These uncertainties make it very difficult to effectively deal with power system stability problems through conventional controller that is based on linearized system model. Therefore the fuzzy logic control approach, is one area of artificial intelligence, has been emerging in recent years as a complement to the conventional approach. The focus of this Paper is to identify the improved transient Stability through control scheme and comprehensive analysis for a Static Synchronous Compensator (STATCOM) on the basis of theory computer simulation. By Introducing FACTS Controller into HVDC system we can improve the power transmission capability and System stability.

A Dependency Graph Approach for Fault Detection and Localization Towards Secure Smart Grid

Fault diagnosis in power grids is known to be challenging, due to the massive scale and spatial coupling therein. In this study, we explore multiscale network inference for fault detection and localization. Specifically, we model the phasor angles across the buses as a Markov random field (MRF), where the conditional correlation coefficients of the MRF are quantified in terms of the physical parameters of power systems. Based on the MRF model, we then study decentralized network inference for fault diagnosis, through change detection and localization in the conditional correlation matrix of the MRF. Particularly, based on the hierarchical topology of practical power systems, we devise a multiscale network inference algorithm that carries out fault detection and localization in a decentralized manner. Simulation results are used to demonstrate the effectiveness of the proposed approach.

Wind power and hydrogen generation system with cooperatively controlled three‐level NPC‐VSC based energy capacitor

AbstractOne of the recent challenges for transmission system operators (TSO) or power grid companies is to smoothen the output power fluctuation of wind generator due to the random variation of wind speed. In addition to the output power fluctuation of fixed‐speed wind turbine generator system (WTGS), it suffers greatly from terminal voltage fluctuation. The fixed capacitor bank connected to its terminal cannot maintain constant terminal voltage under randomly varying wind speed. On the other hand, besides the continuous growth of wind power, hydrogen generation system is also becoming very popular nowadays using the electrical energy from wind power plants. This study proposes a three‐level neutral point clamped voltage source converter (NPC‐VSC) based energy capacitor system (ECS), composed of electric double layer capacitor (EDLC) and power electronic converters, to smoothen output power and terminal voltage fluctuations of grid connected fixed speed wind farm. A simple low pass filter (LPF) is adopted in this study to generate the power reference of ECS. Another salient feature of this study is the generation of hydrogen by using wind generator output power. Effective topology of wind power and hydrogen generation system with cooperatively controlled NPC‐VSC based ECS is proposed from the cost and performance points of view. Copyright © 2009 John Wiley & Sons, Ltd.

Novel Dynamic Representation and Control of Power Systems With FACTS Devices

FACTS devices have been shown to be useful in damping power system oscillations. However, in large power systems, the FACTS control design is complex due to the combination of differential and algebraic equations required to model the power system. In this paper, a new method to generate a nonlinear dynamic representation of the power network is introduced to enable more sophisticated control design. Once the new representation is obtained, a back stepping methodology for the UPFC is utilized to mitigate the generator oscillations. Finally, the neural network approximation property is utilized to relax the need for knowledge of the power system topology and to approximate the nonlinear uncertainties. The net result is a power system representation that can be used for the design of an enhanced FACTS control scheme. Simulation results are given to validate the theoretical conjectures.

Comparison of impedance based fault location methods for power distribution systems

Performance of 10 fault location methods for power distribution systems has been compared. The analyzed methods use only measurements of voltage and current at the substation. Fundamental component during pre-fault and fault are used in these methods to estimate the apparent impedance viewed from the measurement point. Deviation between pre-fault and fault impedance together with the system parameters are used to estimate the distance to the fault point. Fundamental aspects of each method have been considered in the analysis. Power system topology, line and load models and the necessity of additional information are relevant aspects that differentiate one method from another. The 10 selected methods have been implemented, tested and compared in a simulated network. The paper reports the results for several scenarios defined by significant values of the fault location and impedance. The estimated error has been used as a performance index in the comparison.

Studer introduces the Xtender series

This paper presents the design and technical-economic analysis of a solar power system for a residential consumer. One of the main objectives is to design an optimal power system based on solar energy resources for a chosen power consumer. The power consumer represents the starting point of the analysis, contains both AC and DC users and, before the design process, the type and variety of the electrical loads has to be well known. This aspect is important in designing the power system topology, to be more economical and compatible with all the power consumers. The aim of the paper is to present the design and functionality of the solar power system, determining the energy production and consumption for the proposed system. Also an important aspect of the paper is the analysis of the system from technical and economical point of view, to present the overall results. The approach is to study the power system, starting from the solar radiation data, which is a known parameter, to calculate the system equipment sizes and power losses and to find an optimal energy production/consumption ratio. To fulfill this task the proposed research methodology is to configure the optimal system structure (solar panels, chargers, inverters), to gather information about the value of the equipment and to deduct the payback period of the system, under normal functioning conditions.

A New Algorithm to Locate Power-Quality Event Source With Improved Realization of Distributed Monitoring Scheme

This paper presents a systematic algorithm to locate the power-quality (PQ) event source in the distributed monitoring system. Firstly, this paper proposes an improved realization of a distributed monitoring scheme for PQ diagnosis. The algorithm utilizes the topology of power system and the direction of PQ events. As a result, the coverage matrix and the direction matrix are constructed. The algorithm determines the candidate areas for an event source by manipulating these two matrices. For more accurate results, it calculates the distance from the PQ monitor to the location of the PQ event source. It is explained with an illustrative example and is applied to IEEE test feeder in order to validate the accuracy. The proposed algorithm can replace the expert's analysis on the PQ event source with an automated computer program.