Showing papers on "Power-system protection published in 2018"

Recognition and Vulnerability Analysis of Key Nodes in Power Grid Based on Complex Network Centrality

Abstract: The analysis of blackouts, which can inevitably lead to catastrophic damage to power grids, helps to explore the nature of complex power grids but becomes difficult using conventional methods This brief studies the vulnerability analysis and recognition of key nodes in power grids from a complex network perspective Based on the ac power flow model and the network topology weighted with admittance, the cascading failure model is established first The node electrical centrality is further pointed out, using complex network centrality theory, to identify the key nodes in power grids To effectively analyze the behavior and verify the correctness of node electrical centrality, the net-ability and vulnerability index are introduced to describe the transfer ability and performance under normal operation and assess the vulnerability of the power system under cascading failures, respectively Simulation results of IEEE 30-bus and IEEE 57-bus test cases show that the key nodes can be effectively identified with high electrical centrality, the resultant cascading failures that eventually lead to a severe decrease in net-ability, verifying the correctness and effectiveness of the analysis

Protection of Smart DC Microgrid With Ring Configuration Using Parameter Estimation Approach

Abstract: In a smart dc microgrid, power electronic devices limit the current during fault and therefore, an overcurrent-based relaying scheme cannot provide required sensitivity and selectivity for such a system. For a dc microgrid with ring configuration having bidirectional power flow, the protection design is further complicated. For reliable supply to customers and to avoid unwanted disconnection of renewable resources, selectivity of a protection scheme is important. In this paper, using local voltage and current data, a least square-based technique estimates the parameter of the fault path, from which the direction of the fault is inferred. Using the direction of fault information of both ends of a line segment in a ring system, internal and external faults are discriminated for network protection. Using PSCAD/EMTDC simulations for a ring system, proposed method is tested for various fault situations including high resistance fault, close-in fault, signals with noise, and considering different modes of distributed generation operations. The proposed algorithm is also validated on a scaled-down hardware setup in the laboratory. The method is found to be more accurate compared to available technique.

Fault Detection and Isolation in Medium-Voltage DC Microgrids: Coordination Between Supply Power Converters and Bus Contactors

Abstract: A fast and effective method for detecting and isolating faults in medium-voltage dc microgrids relies on rapid coordination between power supply converters and bus segmentizing contactors to limit currents and isolate faults without any need for fast communication between these active elements. The power converters independently enter current-limiting mode as soon as they recognize a fault condition and the segmentizing contactors autonomously decide whether or not to open based on their local interpretation of time-to-trip curves as functions of apparent circuit resistance. This method allows converters and contactors to use only local measurements when discerning whether or not to trip in order to isolate the faulted section. Simulation and experimental results show that low-impedance short-circuit faults can be isolated within 10–20 ms and the system can be reenergized within 40–60 ms. The method is effective for a wide range of fault and system configurations, and that range can likely be expanded by applying additional discrimination methods.

Vulnerability of Synchrophasor-Based WAMPAC Applications’ to Time Synchronization Spoofing

Abstract: This paper experimentally assesses the impact of time synchronization spoofing attacks (TSSA) on synchrophasor-based wide-area monitoring, protection and control (WAMPAC) applications. Phase angle monitoring, anti-islanding protection, and power oscillation damping applications are investigated. TSSA are created using a real-time (RT) IRIG-B signal generator and power system models are executed using an RT simulator with commercial phasor measurement units (PMUs) coupled to them as hardware-in-the-loop. Because PMUs utilize time synchronization signals to compute synchrophasors, an error in the PMUs’ time input introduces a proportional phase error in the voltage or current phase measurements provided by the PMU. The experiments conclude that a phase angle monitoring application will show erroneous power transfers, whereas the anti-islanding protection mal-operates and the damping controller introduces negative damping in the system as a result of the time synchronization error incurred in the PMUs due to TSSA. The proposed test-bench and TSSA approach can be used to investigate the impact of TSSA on any WAMPAC application and to determine the time synchronization error threshold that can be tolerated by these WAMPAC applications.

Impact of Power-Electronic Sources on Transmission Line Ground Fault Protection

Abstract: Power-electronic sources, such as Type 3 wind turbine generators and static synchronous compensators (STATCOM), interface to the grid through, partial- or full-scale, and power converters that have inherently fast switching capability to control their output current during short circuits The short-circuit current is a function of the specific converter control algorithm and differs significantly from the conventional rotating machine sources without converter interfaces Therefore, if a transmission-line protection scheme is designed for conventional sources, (not taking into account these differences in short-circuit current characteristics), reliability can be at risk Using real-life short-circuit currents on lines supplied by sources having a power converter interface, this paper illustrates the reliability risk to conventional line protection schemes, in particular, to those which use negative-sequence quantities for the detection of unbalanced faults This paper discusses the protection schemes, adopted by BC Hydro–a large Canadian Electric Utility, for transmission lines interconnecting Type 3 wind turbine and STATCOM sources Their application for ground faults is independent of the converter control algorithm as long as the source is interconnected to the grid via a transformer which is a source of zero-sequence current

Real-Time Cascading Failures Prevention for Multiple Contingencies in Smart Grids Through a Multi-Agent System

Abstract: Cascading failures (CF) is complex in nature and difficult to accurately model or solve mathematically. The current industry approach to preventing CF, which leads to blackout event, involves incurring losses. In this paper, a technique based on an adaptive multi-agent system algorithm is implemented to prevent CF without loss incurrence. The algorithm uses mathematical combinations heuristically selected through the use of sensitivities obtained from the economic dispatch history of the power system to redispatch the power from the generators. This approach enables the implementation of the algorithm on systems of any size. The algorithm is experimentally applied in real-time with the consideration of necessary constraints as it halts the occurrence of CF. The test system is an experimental set up of the generation and transmission side of the IEEE 30-bus system using a reconfigurable smart grid laboratory hardware developed for testing algorithms requiring two-way communication capabilities. It was first showed that the test system will experience CF if nothing is done to prevent CF after the occurrence of a contingency. A detailed experimental analysis of the ensuing blackout event is given. The algorithm was used to prevent CF in the system after the occurrence of N-1 and N-1-1 contingencies. The algorithm was also tested on a larger system, the IEEE 118-bus system, through simulation. The experimental and simulation results affirm the efficacy of the proposed algorithm for systems of any size. In fact, it was discovered from our results that the large number of generators in large systems helps the algorithm converge faster than it does for small systems, which have restricted resources and combinations.

A Full-Scale Experimental Validation of Electromagnetic Time Reversal Applied to Locate Disturbances in Overhead Power Distribution Lines

Abstract: Electromagnetic time reversal (EMTR) has emerged as a promising technique to locate disturbances in power grids, thanks to its location accuracy and robustness against parameters uncertainties. Furthermore, in a reflective medium, like the one of a power network, it has been shown that the method requires no more than one single observation point. In this paper, we present an experimental validation of EMTR to locate disturbances in real power networks. The validation is performed on a full-scale unenergized 677-m-long, double-circuit 10-kV overhead distribution line. The disturbance is emulated by a voltage pulse injected between one of the line conductors and the ground using a high-voltage pulse generator. The frequency spectrum of the injected voltage pulse is specified such that the originated electromagnetic transients are compatible with those of power line faults, lightning, and conducted intentional electromagnetic interferences. The transient currents generated by the emulated disturbance are measured at one end of the line, considering two different line configurations. According to the EMTR technique, the measured signals are time reversed and back injected into the system that, in our case, is a simulated model of the considered distribution line. More specifically, it is represented by a constant-parameter line model implemented within the EMTP-RV simulation environment. For both cases, the disturbance is accurately located, and the phase of the circuit at which the pulse was injected is also identified.

A New Adaptive Dependability-Security Approach to Enhance Wide Area Back-Up Protection of Transmission System

Abstract: This paper presents a new methodology to adaptively shift the dependability and security bias of the transmission system protection logic depending on the system state Contingencies such as generator outage, line outage, and line fault can induce stressed system condition Under stressed conditions, protection logic should be more biased toward security Phasor measurement unit information is used at the system protection centre to estimate the system state A data-mining model known as random forest is utilized to accomplish the task of state assessment Two different protection logics are used to make the final relaying decision The first protection logic is the existing distance relay and the second protection logic is based on wide area information Both the protection logics are connected though logic gates to make the final relaying decision The performance of the proposed scheme is validated on the IEEE-39 bus New England system and 246-bus Indian Northern Regional Power Grid system The test results indicate that the proposed algorithm can help in shifting the dependability-security bias of the protection logic adaptively, which will help in mitigating cascaded outages in the power transmission system

Critical Links Identification for Selective Outages in Interdependent Power-Communication Networks

Abstract: Critical infrastructure, such as the smart grid, is vulnerable to failures and attacks. The complex nature of these systems embeds hidden vulnerabilities that threaten their functionality when exploited. In this paper, we perform a vulnerability analysis of the smart grid based on the power flow dynamics and in the presence of the essential communication network. Our analysis identifies a small number of power lines and communication links that can trigger a cascading failure and result in a blackout when removed. We quantify the failure effect in the form of fractional loss in the served load. Moreover, we formulate a mathematical model to present both components of the smart grid and their interdependency. A scalable algorithm is introduced to analyze the output of the model. We evaluate the proposed model and algorithm on the IEEE 14, 30, 57, and 300 Bus systems and associated communication networks, and report on the collected results.

High-Speed Decision Tree Based Series-Compensated Transmission Lines Protection Using Differential Phase Angle of Superimposed Current

Abstract: This paper presents a decision tree based high-speed intelligent scheme for series-compensated transmission line protection using differential phase angle of superimposed current (DPASC). The conventional distance relaying scheme undergoes many shortcomings in transmission line protection in the presence of series compensation devices. The proposed scheme calculates the differential phase angle of current signals using full cycle discrete Fourier transform. The DPASC for each phase is used as an input to the data mining model known as decision tree (DT). The DT is used to generate thresholds to detect and classify the faults since determination of robust thresholds is an important challenge in protective relay engineering. The proposed method has been tested for different operating modes of transmission line in SIMIULINK/MATLAB software. Simulation results indicate that the proposed method is able to detect and classify the faults with acceptable accuracy, in less than half cycle.

Cascading Failure Analysis of Cyber Physical Power System With Multiple Interdependency and Control Threshold

Abstract: The traditional infrastructure in power system is undergoing a transition to the Smart Grid, in which the communication network and power grid will be integrated into a cyber-physical power system (CPPS). Although the traditional topological analysis reveals the mechanism of cascading failure between two networks, it ignores the control redundancy and standby lines from communication network to power grid. The robustness analysis in CPPS requires a more comprehensive model to analyze failure behavior in reality. Here, we propose a cascading failure model with one-to-multiple interdependency and a relevant theoretical framework to analyze CPPS cascading failure. In consideration of real CPPS, in the proposed model we introduce two robustness factors, the number of dependent links and control threshold, which can better describe the control function from communication nodes to power nodes. The remaining fraction under different initial attacking on high voltage transmission network, small world network, double star network, and the different topological combination of CPPS are analyzed. The results show that the proposed model and robustness factors can better reveal the robustness and the mechanism of two networks in cascading failure.

A Robustness-Oriented Power Grid Operation Strategy Considering Attacks

Abstract: Power system operation is facing increasing cyber and physical attack risks, so it becomes pressing to develop effective methods to improve the robustness of electric power infrastructure in the presence of significant attacks. As it is not guaranteed that attacks can always be detected and thwarted before they cause disturbances and damages to the power systems, increased robustness can contribute to reducing the consequence of attacks. In this paper, a holistic robustness framework is proposed by extending the conventional security-constrained optimal power flow (SCOPF) analysis to incorporate the risk caused by attacks. The corresponding solution methodology is proposed by combining particle swarm optimization and primal-dual interior point methods. Case studies conducted based on several test systems demonstrate that the proposed SCOPF model is able to reduce the consequence of attacks. This paper can provide some insight into improving the power system operation robustness in the face of significant attacks.

Identification and Prevention of Cascading Failures in Autonomous Microgrid

Abstract: This paper presents a new method to model and deal with the cascading failures in an autonomous microgrid (MG) in order to protect it against risks that may lead to its complete collapse. Although cascading failure is a term mainly associated with power system networks and transmission lines, its extension to MGs as the future structure of power systems is proposed in this paper. An MG operating as an independent entity in autonomous mode is prone to catastrophic failures due to its limited supply resources and power flow paths; therefore, a blackout model based on ac power flow is extracted that is tailored to these specifications. Based on the associated risks presented by the model for any configuration in advance of the anticipated events, remedial actions are proposed to mitigate the vulnerability of the MG by reconfiguration to alleviate the loadings of the heavily loaded lines. A genetic algorithm is used to find the optimum MG's configuration with less vulnerable lines. Critical loading is also determined for each configuration in order to indicate the necessity of taking remedial actions upon approaching to this level. The effectiveness of the proposed method is investigated by using the IEEE 33 bus sample power network.

A Novel Method of Combined DC and Harmonic Overcurrent Protection for Rectifier Converters of Monopolar HVDC Systems

Abstract: This paper presents a novel protection method for monopolar high-voltage direct current (HVDC) converters. This method uses the secondary and tertiary currents of the converter transformers and based on dc and harmonic contents of the currents decides for the security of the converter. The new protection method detects the location of the fault inside the converter and based on that issues a signal for single-phase disconnection in the ac system to eliminate the fault. It will be shown that the new method is not only faster compared to the conventional protection methods but also can be easily applied to the existing HVDC systems without imposing any significant requirement. The Hydro-Quebec HVDC test system is used to present the simulation results and to ensure the validity and functionality of the proposed protection method.

Adaptive protection system for microgrids based on a robust optimization strategy

Abstract: The development of a proper protection system is essential for the secure and reliable operation of microgrids. In this paper, a novel adaptive protection system for microgrids is presented. The protection scheme is based on a protective device that includes two directional elements which are operating in an interleaved manner, namely overcurrent and undervoltage elements. The proposed protection scheme can be implemented in microprocessor-based relays. To define the settings of the protective device, a robust programming approach was proposed considering a finite set of fault scenarios. The scenarios are generated based on the predictions about the available energy and the demand. For each decision step, a robust optimization problem is solved online, which is based on forecasting with a confidence band to represent the uncertainty. The system is tested and compared using real data sets from an existing microgrid in northern Chile. To assess the performance of the proposed protection system, fault scenarios not considered in the optimization were taken into account. The results obtained show that the proposed protective device is able to manage those failure scenarios, as well as those included in the tuning of the settings. Practical considerations are also discussed.

Vulnerability Assessment of a Large Electrical Grid by New Graph Theory Approach

Abstract: In previous research a novel methodology to assess structural vulnerability was proposed and applied in IEEE test system and high voltage transmission networks of 94 buses, by using graph theory to investigate various risk scenarios that can trigger cascading failures. In this paper we validate the application of this methodology in larger networks by applying a case study on the transmission network 230 and 400 kV of Mexico. The events of cascading failures are simulated through two elimination strategies: by deliberate attacks on critical nodes or by random errors. Iterations are performed by running successive N-1 contingencies on a network that is constantly changing its structure with the elimination of each node. The power flows are not necessary and only the calculation of the graph statistical parameter “geodesic vulnerability” is required. This reduces the computation time and leads to a comparative analysis of structural vulnerability.

Detection of PMU spoofing in power grid based on phasor measurement analysis

Abstract: In some recent articles, the vulnerability of phasor measurement unit (PMU) to the time synchronisation attack by spoofing its global positioning system (GPS) has been highlighted as a threat to power grid protection, control and monitoring system. Having spoofed PMU GPS signals, one can manipulate the measurements and inject bad data to power grid protection and monitoring system. The existing anti-spoofing methods are all based on GPS signal analysis. The mentioned methods are just able to detect spoofing without any data refinement as the data of power grid has not been practically used in calculations. Furthermore, some of these methods lose their certainty in noisy and harsh environments due to low power of GPS signals. A novel anti-spoofing algorithm has been proposed based on power grid infrastructures which can join to any of the existing anti-spoofing algorithm to empower spoofing detection process. The proposed algorithm adopts phasor measurement analysis and state estimation methods to detect spoofing. The composite of this algorithm with any of the existing algorithms will not only cover the probable malfunctioning in spoofing detection but also be able to refine counterfeit measurements.

Real-Time Analysis of Power System Protection Schemes Using Synchronized Data

Abstract: An error in a power system protection scheme can result in unwanted tripping of healthy lines or delay in the removal of a fault from the network, thus affecting the power system stability. Online identification of such an error provides scope to initiate remedial measures, thereby preventing possible cascade tripping situations. In this paper, a method for real-time analysis of protection decision in a power system is proposed. This method identifies the relay, which has maloperated for an event in the network. For analysis of a relay operation, synchrophasor data from selected locations are obtained depending on the network topology. A function is developed utilizing indices calculated from the synchronized data. Based on the calculated value of the function during an event, the correctness of the protection decision is validated. Results obtained from PSCAD/EMTDC simulations for the New England 39-bus system demonstrate the performance of the proposed method.

Research on the Protection of Hybrid HVDC System

Abstract: The traditional and conventional HVDC system has the advantages of lower installing cost and it is a mature state of the art, but it also has some drawbacks like huge reactive power absorption and commutation fault in the system. Similarly, HVDC based on VSC (Voltage Source Converter) is easily operational and flexible in control but it needs high cost for the installation that’s a drawback. A theoretical type of hybrid HVDC transmission scheme is presented in this manuscript after the combination of above-mentioned advantages of two HVDC systems. In this proposed scheme two control techniques are merged like PCC (Phase Control Converter) at sending terminal and VSC at receiving terminal of HVDC transmission system. Furthermore, the stability and steadily operation of the proposed system are verified by generating single phase to ground fault or short circuit fault in all phases. After getting the simulation results, it is observed that proposed hybrid HVDC system is capable of restoring the system rapidly by minimizing the effect of these faults.

Network Hierarchy Evolution and System Vulnerability in Power Grids

Abstract: The seldom addressed network hierarchy property and its relationship with vulnerability analysis for power transmission grids from a complex-systems point of view are given in this paper. We analyze and compare the evolution of network hierarchy for the dynamic vulnerability evaluation of four different power transmission grids of real cases. Several meaningful results suggest that the vulnerability of power grids can be assessed by means of a network hierarchy evolution analysis. First, the network hierarchy evolution may be used as a novel measurement to quantify the robustness of power grids. Second, an antipyramidal structure appears in the most robust network when quantifying cascading failures by the proposed hierarchy metric. Furthermore, the analysis results are also validated and proved by empirical reliability data. We show that our proposed hierarchy evolution analysis methodology could be used to assess the vulnerability of power grids or even other networks from a complex-systems point of view.

Power System Frequency Estimation Using Adaptive Accelerated MUSIC

Abstract: Frequency estimation is vital for monitoring, control, and protection of power systems. Multiple signal classification (MUSIC) method has been used for frequency estimation in communication systems. This method requires wide range of frequency scanning and heavy computations, which is inappropriate for power system applications. This paper proposes an adaptive accelerated MUSIC algorithm for frequency estimation in power systems. The algorithm accelerates the frequency scanning and adapts itself to transient conditions of power systems, to keep the accuracy of the frequency estimation with minimum computations. Experimental signals besides several static and dynamic test signals are used to evaluate and compare the performance of the proposed algorithm with recent methods. These comparisons show that the proposed algorithm provides faster convergence speed, lower computation burden, and more robustness to noise and grid disturbances. These significant advantages make the proposed algorithm appropriate for power system protection and control applications.

Modeling and Analysis of Asymmetrical Latency in Packet-Based Networks for Current Differential Protection Application

Abstract: Current differential protection typically requires symmetrical communications channels—with equal latency in each direction—for correct operation. Conventionally, this has been delivered using protocols such as IEEE C37.94 over a time-division multiplexing wide-area network (WAN). Modern packet-based WANs offer improvements in efficiency, flexibility, and cost-effectiveness for utility applications. However, jitter is unavoidable in packet-based networks and, in extreme cases, jitter inevitably results in substantial asymmetrical latency in communications paths. This paper clearly defines how a new source of asymmetry arises due to the use of “de-jitter” buffers, which can jeopardize critical protection services. This is demonstrated using an analytical modeling approach, which precisely quantifies the degree of risk, and through real-time demonstration with actual devices, involving current differential protection over an IP/MPLS WAN. Using a novel method of real-time manipulation of Ethernet traffic to emulate large WANs, the modeling approach has been validated. It is shown how the sensitivity of relays to asymmetry depends on the protection settings and the magnitude of the measured load current. To address the risk of protection maloperation, a new approach for compensating for asymmetrical latency has been comprehensively validated. These developments will be of immediate interest to utilities operating, or migrating to, a packet-based infrastructure.

Application of a Continuous Particle Swarm Optimization (CPSO) for the Optimal Coordination of Overcurrent Relays Considering a Penalty Method

Abstract: In an electrical power system, the coordination of the overcurrent relays plays an important role in protecting the electrical system by providing primary as well as backup protection. To reduce power outages, the coordination between these relays should be kept at the optimum value to minimize the total operating time and ensure that the least damage occurs under fault conditions. It is also imperative to ensure that the relay setting does not create an unintentional operation and consecutive sympathy trips. In a power system protection coordination problem, the objective function to be optimized is the sum of the total operating time of all main relays. In this paper, the coordination of overcurrent relays in a ring fed distribution system is formulated as an optimization problem. Coordination is performed using proposed continuous particle swarm optimization. In order to enhance and improve the quality of this solution a local search algorithm (LSA) is implanted into the original particle swarm algorithm (PSO) and, in addition to the constraints, these are amalgamated into the fitness function via the penalty method. The results achieved from the continuous particle swarm optimization algorithm (CPSO) are compared with other evolutionary optimization algorithms (EA) and this comparison showed that the proposed scheme is competent in dealing with the relevant problems. From further analyzing the obtained results, it was found that the continuous particle swarm approach provides the most globally optimum solution.

Robust Testing of Cascading Failure Mitigations Based on Power Dispatch and Quick-Start Storage

Abstract: We present a formal robust testing method for power system cascading failure mitigations. The approach is model-based, using simulated trajectories of the system and proving that uncertainties, e.g., in the initial states or disturbances, do not perturb the trajectories beyond a robust neighborhood around them. We model power systems as hybrid systems with locations representing different swing dynamics and relay dynamics. We present implementations of our robust testing approach in a three-machine system model from the 2003 Italian Blackout and the IEEE 39-bus system model. We apply the robust testing method in two scenarios for averting the cascading failures: 1) robust testing of safety for various generator mechanical power dispatch schedules and 2) robust testing of safety for postfault remedial actions based on quick-start storage.