Real-time Contingency Analysis Research Articles

Mitigation of Saturated Cut-Sets During Multiple Outages to Enhance Power System Security

Ensuring reliable operation of large power systems subjected to multiple outages is a challenging task because of the combinatorial nature of the problem. Traditional approaches for security assessment are often limited by their scope and/or speed, resulting in missing of critical contingencies that could lead to cascading failures. This paper proposes a two-component methodology to enhance power system security. The first component combines an efficient algorithm to detect cut-set saturation (called the feasibility test (FT) algorithm) with real-time contingency analysis (RTCA) to create an integrated corrective action (iCA), whose goal is to secure the system against cut-set saturation as well as critical branch overloads. The second component only employs the results of the FT to create a relaxed corrective action (rCA) to secure the system against post-contingency cut-set saturation. The first component is more comprehensive, but the latter is computationally more efficient. The effectiveness of the two components is evaluated based upon the number of cascade triggering contingencies alleviated, and the computation time. The results obtained by analyzing different case-studies on the IEEE 118-bus and 2000-bus synthetic Texas systems indicate that the proposed two-component methodology successfully enhances the scope and speed of power system security assessment during multiple outages.

$N-1$ Reliability Makes It Difficult for False Data Injection Attacks to Cause Physical Consequences

This paper demonstrates that false data injection (FDI) attacks are extremely limited in their ability to cause physical consequences on N-1 reliable power systems operating with real-time contingency analysis (RTCA) and security constrained economic dispatch (SCED). Prior work has shown that FDI attacks can be designed via an attacker-defender bi-level linear program (ADBLP) to cause physical overflows after re-dispatch using DCOPF. In this paper, it is shown that attacks designed using DCOPF fail to cause overflows on N-1 reliable systems because the system response modeled is inaccurate. An ADBLP that accurately models the system response is proposed to find the worst-case physical consequences, thereby modeling a strong attacker with system level knowledge. Simulation results on the synthetic Texas system with 2000 buses show that even with the new enhanced attacks, for systems operated conservatively due to N-1 constraints, the designed attacks only lead to post-contingency overflows. Moreover, the attacker must control a large portion of measurements and physically create a contingency in the system to cause consequences. Therefore, it is conceivable but requires an extremely sophisticated attacker to cause physical consequences on N-1 reliable power systems operated with RTCA and SCED.

Sensitivity factors based transmission network topology control for violation relief

Transmission networks consist of thousands of branches for large-scale real power systems. They are built with a high degree of redundancy for reliability concern. Thus, it is very likely that there exist various network topologies that can deliver continuous power supply to consumers. The optimal transmission network topology could be very different for different system conditions. Transmission network topology control (TNTC) can provide the operator with an additional option to manage network congestion, reduce losses, relieve violation, and achieve cost saving. This paper examines the benefits of TNTC in reducing post-contingency overloads that are identified by real-time contingency analysis (RTCA). The procedure of RTCA with TNTC is presented and two algorithms are proposed to determine the candidate switching solutions. Both algorithms use available system data: sensitivity factors or shifting factors. The proposed two TNTC approaches are based on the transmission switching distribution factor (TSDF) and flow transfer distribution factor (FTDF) respectively. FTDF based TNTC approach is an enhanced version of TSDF based TNTC approach by considering network flow distribution. Numerical simulations demonstrate that both methods can effectively relieve flow violations and FTDF outperforms TSDF.

Enhanced Energy Management System With Corrective Transmission Switching Strategy—Part I: Methodology

The flexibility in transmission networks is not fully utilized in existing energy management systems (EMSs). Corrective transmission switching (CTS) is proposed in this two-part paper to enable EMS to take advantage of the flexibility in transmission systems in a practical way. This paper proposes the following two EMS procedures: first, Procedure-A connects real-time security-constrained economic dispatch (RT SCED) with real-time contingency analysis (RTCA), which is consistent with industrial practice; and second, Procedure-B, an enhanced version of Procedure-A, includes CTS in EMS with the proposed concept of branch pseudo limit used in RT SCED. Part-I of this paper presents the methodology, whereas Part-II includes detailed results analysis. It is demonstrated that Procedure-A can effectively eliminate the base case overloads and the potential post-contingency overloads identified by RTCA, and Procedure-B can achieve significant congestion cost reduction with consideration of CTS in RT SCED. Numerical simulations also illustrate that integrating CTS into RT SCED would improve social welfare.

Enhanced Energy Management System With Corrective Transmission Switching Strategy—Part II: Results and Discussion

This paper presents a novel procedure for energy management system (EMS) that can utilize the flexibility in transmission networks in a practical way. With the proposed enhanced EMS procedure, the reliability benefits that are provided by corrective transmission switching (CTS) in real-time contingency analysis can be translated into significant cost savings in real-time security-constrained economic dispatch. Simulation results show that the congestion cost with consideration of CTS is largely reduced as CTS can relieve potential post-contingency network violations. The effects of integrating CTS in existing EMS procedure on markets are also analyzed. In conclusion, this two-part paper shows that CTS can achieve substantial reliability benefits, as well as significant cost savings.

Enhancing Power System Cyber-Security With Systematic Two-Stage Detection Strategy

State estimation estimates the system condition in real-time and provides a base case for other energy management system (EMS) applications including real-time contingency analysis and security-constrained economic dispatch. Recent work in the literature shows malicious cyber-attack can inject false measurements that bypass traditional bad data detection in state estimation and cause actual overloads. Thus, it is very important to detect such cyber-attack. In this paper, multiple metrics are proposed to monitor abnormal load deviations and suspicious branch flow changes. A systematic two-stage approach is proposed to detect false data injection (FDI) cyber-attack. The first stage determines whether the system is under attack while the second stage identifies the target branch. Numerical simulations verify that FDI can cause severe system violations and demonstrate the effectiveness of the proposed two-stage FDI detection (FDID) method. It is concluded that the proposed FDID approach can efficiently detect FDI cyber-attack and identify the target branch, which will substantially improve operators' situation awareness in real-time.

Bases Conceptuales para la Utilización del Análisis de Contingencias en Tiempo Real con Criterios de Consciencia Situacional, Caso Centro de Control de CENACE-Ecuador

La operación segura de sistemas eléctricos requiere que los Operadores, sobre los cuales recae esta gran responsabilidad, reconozcan de forma permanente el estado en que se encuentra la red supervisada y dispongan de los recursos para identificar amenazas probables, que le permitan anticipar y reaccionar de manera segura frente a eventos fortuitos de consecuencias predecibles, como ocurren cuando hay la salida de equipos durante la operación. En el ámbito de la Consciencia Situacional se dispone de una metodología que adecuadamente integrada con herramientas como el Análisis de Contingencias, posibilitan capacidades avanzadas de supervisión. Esto solo es posible, si se desarrollan a cabalidad tres fases de implementación, que se proponen conceptualmente en este trabajo como son; Modelación – Sintonización y Personalización. Siendo la Personalización la extensión metodológica clave para el logro de la integración planteada en este trabajo basado en años de experiencia de los autores en sistemas SCADA-GMS-EMS.

Real-Time Contingency Analysis on Massively Parallel Architectures With Compensation Method

Real-Time Contingency Analysis on Massively Parallel Architectures With Compensation Method

Efficient method for the real‐time contingency analysis of meshed HVDC power grids fed by VSC stations

An efficient method for the real-time contingency analysis of meshed high-voltage direct current (HVDC) power grids fed by voltage source converter (VSC) stations is introduced here. A linearised AC/DC grid model is initially determined considering the control strategies of the various VSC units. This lays the foundations for the determination of linear sensitivity factors with which the contingency analysis is carried out to evaluate the real-time N−1 criterion in AC/DC grids, as demanded by system control centres. Distribution and power-injection factors are subsequently derived for efficiently assessing the impact of AC/DC transmission line outages and load/generator disconnections on the HVDC grid. Conversion factors are also derived to estimate the impact of the loss of VSC stations on the AC/DC network, this being another inherent contribution of this work. The efficiency and validity of this timely approach, which finds practical applicability to the real-time operation of HVDC power grids, is confirmed using a meshed DC network fed by three VSC stations. The disconnection of AC and DC transmission lines, generators, and VSC stations are dynamically simulated using Simulink and their post-disturbance steady-state conditions are compared against those computed by the introduced method where it is confirmed that both solutions concur very well with each other.

Real-Time Contingency Analysis on Massively Parallel Architectures With Compensation Method

Real-time contingency analysis (RTCA) is paramount for modern power systems as it forms the basis for important operator actions that help to improve system stability, optimize generator dispatch, manage disparate resources, prevent cascading outages, and enhance market operations. With increasing system size and the number of contingency scenarios, RTCA is faced with computational challenges. To alleviate this situation, massively parallel graphics processing units (GPUs) are introduced for the acceleration of RTCA solution in this paper, where the compensation method (CM) is utilized for the concurrent AC power flow solution. Strategies and principles on the data structure, kernel function, and memory management are provided. Five benchmark systems (ranging from 300- to 13,659-bus) are employed for case studies. Based on the sequential CM implemented on single-thread CPU, the performance analysis related to execution time and speedup is carried out for parallel CMs running on other architectures, including multi-thread CPU, single-GPU, and multi-GPUs. Results indicate that the parallel CM with multi-GPUs has sufficient accuracy, convergence, and scalability. Finally, the potential of the proposal for practical RTCA has been discussed with the reviewing of other state-of-the-art parallel computing methods reported in the literature.

Real-Time Contingency Analysis With Corrective Transmission Switching

Transmission switching (TS) has gained significant attention recently. However, barriers still remain and must be overcome before the technology can be adopted by the industry. The state-of-the-art challenges include AC feasibility, computational complexity, the ability to handle large-scale real power systems, and dynamic stability. This paper investigates these challenges by developing an AC corrective TS (CTS) based real-time contingency analysis (RTCA) tool that can handle large-scale systems within a reasonable time. The tool quickly proposes multiple high-quality corrective switching actions for contingencies with potential violations. To reduce the computational complexity, three heuristic algorithms are proposed to generate a small set of candidate switching actions. Parallel computing is implemented to further speed up the solution time. Moreover, time-domain simulations are performed to check for dynamic stability of the proposed CTS solutions. The promising results, tested on the Tennessee Valley Authority (TVA) system and actual energy management system snapshots from the PJM Interconnection (PJM) and the Electric Reliability Council of Texas (ERCOT), show that the tool effectively reduces post-contingency violations. It is concluded that CTS is ripe for industry adoption for RTCA application.

Real-Time Contingency Analysis With Transmission Switching on Real Power System Data

Transmission switching (TS) has shown to be an effective power flow control tool. TS can reduce the system cost, improve system reliability, and enhance the management of intermittent renewable resources. This letter addresses the state-of-the-art problem of TS by developing an AC-based real-time contingency analysis (RTCA) package with TS. The package is tested on real power system data, taken from energy management systems of PJM, TVA, and ERCOT. The results show that post-contingency corrective switching is a ready to be implemented transformational technology that provides substantial reliability gains. The computational time and the performance of the developed RTCA package, reported in this letter, are promising.

Towards smart corrective switching: analysis and advancement of PJM's switching solutions

Transmission switching, as a power flow control mechanism that can reduce costs and improve reliability, has gained a lot of attention during the last decade. Despite its benefits, industry adoption has been very limited due to its computational complexity, stability and AC performance concerns. Pennsylvania New Jersey Maryland (PJM) has published a list of corrective switching solutions to relieve actual and post-contingency network violations. The list is developed based on operators’ prior knowledge and offline studies. This study employs a fast AC-based real-time contingency analysis (RTCA) tool with corrective transmission switching (CTS) functionality to analyse PJM's switching solutions with actual PJM data. The results show that the RTCA CTS tool is almost always able to find solutions that perform better than, or equally as well as, PJM's solutions. The results also show that PJM's list identifies solutions for only 3% of the problematic contingencies with post-contingency violations over the course of one week. The RTCA CTS tool, however, is able to find corrective TS solutions for almost all the cases. The results suggest that CTS is ripe for industry adoption. The tool provides significant savings and would pave the road towards a smarter transmission network as an essential ingredient of the future smart grid.

Real time complete model estimation for contingency study: field experience

The authors describe field experience with external network modeling for real-time contingency analysis. Contingency simulations using an unreduced external modeling approach were conducted in a real-time environment. The response of the external network model to outages of major 345 kV lines was compared to data obtained by measurement. The real-time contingency test results obtained by using the latest state-estimation-based external network modeling approach are superior to those obtained by the previously used load-flow-based approach.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>