On-line voltage security assessment of the hellenic interconnected system

Power system security is one of the major concerns in recent years due to the deregulation of power systems which are forced to operate under stressed operating conditions. In such environment, online voltage stability evaluation plays a significant role in secure operation of power systems. This paper presents a new approach for estimating voltage stability security assessment accounting uncertainties in the line parameters and control variables. Security index has been evaluated using Monte-Carlo simulation with & without consideration of unavailability of transmission lines, which is used to contingency selection and compared with well-established methods. Further, evaluation of probabilistic insecurity index (PISI) using cut-set method for single & double line outages at various loading conditions considering voltage stability limit. Static voltage stability limit for various sampled values of system parameters and control variables have been obtained using continuation power flow methodology. The applicability of PISI has been made on-line using radial basis function (RBF). Since voltage security assessment is possible on-line using RBFNN. Proposed algorithms have been implemented on IEEE 6-bus 7-line test systems.

With the integration of large scale wind power, the characteristics of power system operation has been changing, and, some problems come forth. On-line security assessment and control decision support system provides the stability and security state message for dispatcher in time, and, some suggestions to improve the level of power system stability and security. To suit the requirements of large amount wind power integrated power system, the technology of on-line security assessment and control decision support must be modified. This paper focuses on the technology of on-line security assessment and control decision for operation of power system with large scale wind power and designing the support system. In the paper, the study and application of on-line security assessment and control decision support technology in China are introduced. Considering the wind power in China having some distinct characteristics such as large scale, centralized development, long-distance and high voltage transportation, the new requirements to on-line security assessment and control decision support are analyzed. They includes need for new information, on-line modelling with large scale wind farm, transfer limitation calculation under the constraint condition of wind power integration requirement, auxiliary preventive control decision based on the forecasting and adjustment properties of wind power output, coordinated emergency control wind power with hydraulic and thermal power. On the basis of technical rule for connecting wind farm into power grid and the interaction between wind power and power grid, the advices on engineering application of on-line security assessment and control decision support technology for large amount wind power integrated power system, are proposed, for example, with respect to the standard of security assessment and selection of pre-contingency sets. (7 pages)

On-line steady-state security assessment of power systems

On-line voltage stability assessment using radial basis function network model with reduced input features

A fuzzy-based power system reliability evaluation

This paper presents a new candidate method for on-line transient security assessment and enhancement based on Pattern Recognition techniques. Transient state variables are used as primary features and the classifier is obtained in two phases, through the combination of an optimum discriminant transformation together with a probabilistic procedure. The proposed security functions can be further refined by means of a second level classifier based on an optimal discriminant plane and using a weighted K nearest neighbour rule. Finally it is shown that this method provides also an efficient and simple tool for on-line preventive control. Extensive results obtained for several contingencies in the CIGRE test system are presented and discussed.

After decades of research and development in the direct methods, it has become clear that the time-domain method approach in stability analysis cannot be completely replaced. Instead, the capabilities of the direct methods and the time-domain method should be used to complement each other. The current direction of development is to combine a direct method and a fast time-domain method into an integrated power system stability program to take advantage of the merit of both methods. The TEPCO-BCU is developed under this direction by integrating BCU method, improved BCU classifiers, and BCU-guide time-domain method. TEPCO-BCU has been evaluated on several practical power system models. The evaluation results indicate that TEPCO-BCU works well with reliable transient stability assessment results and accurate energy margin calculations on several study power systems including a 50,000-bus planning case system. Detailed study of TEPCO-BCU and of a commercial time-domain package on planning cases are conducted. The incorporation of uncertainty into power system planning is also discussed.

A new fast time-domain method is proposed to calculate the overvoltages in transformer winding under the very fast transient overvoltage (VFTO). Based on multiconductor transmission line (MTL) model, which combines the theory of compact finite difference (CFD) with the precise integration method (PIM), using vector fitting and recursive convolution to calculate the frequency-dependent parameters. By comparison with traditional MTL approach, the proposed method can improve the calculation efficiency. For validation, the calculated results are compared with the measurements on a transformer winding model and the result is satisfactory. (6 pages)

This work is concerned with the development of an algorithm for lowering the power consumption of the tester used in digital circuits with on-line testing (OLT) capability. The proposed scheme is generic and flexible in terms of tradeoffs regarding fault coverage and detection latency versus power and area overheads. Most of the works presented in the literature on OLT have emphasised on minimising area overhead and maintaining high fault coverage. However, power, which was mainly a concern for handheld devices, is now a first order impact factor for deep sub-micron designs. Its increased importance for OLT can be realised from the fact that the tester is executed concurrently with the circuit. The proposed technique can handle generic digital circuits with cell count as high as 15,000 and having the order of 2500 states. Results for design of on-line fault detectors for various ISCAS89 benchmark circuits are provided. The results illustrate that with marginal impact on performance in terms of coverage and latency, the proposed technique can lower the power and area consumption significantly, compared to traditional approaches.

In this work, we evaluate bi-directional and unidirectional FPGA routing architectures in terms of energy and power consumption using an updated power estimation framework compatible with VPR 5.0. The goal of this research is to help FPGA vendors find the best FPGA architectures. Initially, we make some general observations on how two types of routing architectures affect speed, area consumption, and power consumption. We observe how routing buffer sizing affects both the critical path delay and power and energy consumption of FPGAs with certain routing architectures. Our results show that uni-directional routing architecture, in all but one case, is the most energy efficient choice both in the traditional FPGA domain and the mobile domain where clock frequencies are fixed.

Existing memory subsystems and TDM NoCs for real-time systems are optimized independently in terms of cost and performance by configuring their arbiters according to the bandwidth and/or latency requirements of their clients. However, when they are used in conjunction, and run in different clock domains, i.e. they are decoupled, there exists no structured methodology to select the NoC interface width and operating frequency for minimizing area and/or power consumption. Moreover, the multiple arbitration points, one in the NoC and the other in the memory subsystem, introduce additional overhead in the worst-case guaranteed latency. These makes it hard to design cost-efficient real-time systems. The three main contributions in this paper are: (1) We present a novel methodology to couple any existing TDM NoC with a realtime memory controller and compute the different NoC interface width and operating frequency combinations for minimal area and/or power consumption. (2) For two different TDM NoC types, one a packet-switched and the other circuit-switched, we show the trade-off between area and power consumption with the different NoC configurations, for different DRAM generations. (3) We compare the coupled and decoupled architectures with the two NoCs, in terms of guaranteed worst-case latency, area and power consumption by synthesizing the designs in 40 nm technology. Our experiments show that using a coupled architecture in a system consisting of 16 clients results in savings of over 44% in guaranteed latency, 18% and 17% in area, 19% and 11% in power consumption for a packet-switched and a circuit-switched TDM NoC, respectively, with different DRAM types.

Debate continues as to the most effective method to determine the operational integrity of valve-regulated lead acid (VRLA) batteries used in critical standby power applications. This paper promises a potential breakthrough in VRLA 'online testing', having the capability of determination of the Randles equivalent circuit components and relating this to battery health. It presents the results to date of a UK Government award sponsored development effort for a portable battery monitor based on this principle.

The secure integration of renewable generation into modern power systems requires an appropriate assessment of the security of the system in real-time. The uncertainty associated with renewable power makes it impossible to tackle this problem via a brute-force approach, i.e. it is not possible to run detailed online static or dynamic simulations for all possible security problems and realizations of load and renewable power. Intelligent approaches for online security assessment with forecast uncertainty modeling are being sought to better handle contingency events. This paper reports the platform developed within the iTesla project for online static and dynamic security assessment. This innovative and open-source computational platform is composed of several modules such as detailed static and dynamic simulation, machine learning, forecast uncertainty representation and optimization tools to not only filter contingencies but also to provide the best control actions to avoid possible unsecure situations. Based on High Performance Computing (HPC), the iTesla platform was tested in the French network for a specific security problem: overload of transmission circuits. The results obtained show that forecast uncertainty representation is of the utmost importance, since from apparently secure forecast network states, it is possible to obtain unsecure situations that need to be tackled in advance by the system operator.

Preface. Contributors. 1 The Real-Time and Study-Mode Data Environment in Modern SCADA/EMS ( Sudhir Virmani and Savu C. Savulescu ). 1.1 Introduction. 1.2 SCADA/EMS Architectures. 1.3 Integrating Stability Applications with the SCADA/EMS. 1.4 References. 2 Overview of Key Stability Concepts Applied for Real-Time Operations ( Savu C. Savulescu ). 2.1 Introduction. 2.2 In Search of the Stability Limits. 2.3 Transient and Voltage Stability Limits. 2.4 Steady-State Stability Limits. 2.5 Concluding Remarks. 2.6 References. Annex 1-1. Reactive Power Steady-State Stability Criterion dDELTAQ / dV. 3 LIPA Implementation of Real-Time Stability Monitoring in a CIM Compliant Environment ( Loris Arnold, Janos Hajagos, Susan M. Manessis, and Anie Philip ). 3.1 Introduction. 3.2 Static and Dynamic Security Assessment at LIPA. 3.3 Benchmarking the Real-Time Stability Application. 3.4 Practical Experience and Outlook. 3.5 References. 4 Real-Time Stability Monitoring at the Independent System Operator in Bosnia and Herzegovina ( Dusko Vickovic and Roland Eichler ). 4.1 Introduction. 4.2 Interim Implementation of Real-Time Stability Assessment at NOS BiH. 4.3 Real-Time Stability Assessment in the New SCADA/EMS Environment. 4.4 Conclusions and Recommendations. 4.5 References. Annex 4-1. TSL, TTC, and the Stability Envelope. Annex 4-2. Siemens Implementation of the Continuation Power Flow. 5 Experience with Real-Time Stability Assessment at Transelectrica ( Horia S. Campeanu, Cornel Erbasu, and Cornel Aldea ). 5.1 Introduction. 5.2 Security Assessment Philosophy and Criteria. 5.3 Real-Time Steady-State Stability Assessment and Monitoring. 5.4 Off-Line Stability Tools in Support of System Operations. 5.5 Conclusions and Outlook. 5.6 References. 6 Implementation of Online Dynamic Security Assessment at Southern Company ( Kip Morison, Lei Wang, Fred Howell, James Viikinsalo, and Alan Martin ). 6.1 Introduction. 6.2 DSA Implementation Fundamentals. 6.3 Transient Security Assessment Implementation at Southern Company. 6.4 Conclusions. 6.5 References. Annex 6-1. Further Details of the DSA Software and Hardware Architecture. Description of the Core DSA Software. Online DSA Implementation Using DSATools. 7 Online Security Assessment for the Brazilian System A Detailed Modeling Approach ( Jorge L. Jardim ). 7.1 Introduction. 7.2 Security Criteria and Functions. 7.3 Solution Methods and Architecture. 7.4 Practical Implementation Aspects. 7.5 User Interface And Performance. 7.6 Concluding Remarks. 7.7 Acknowledgments. 7.8 References. 8 Dynamic Network Security Analysis in a Load Dispatch Center ( Guenther Beissler, Olaf Ruhle, and Roland Eichler ). 8.1 Introduction. 8.2 Siemens Approach to Dynamic Security Assessment. 8.3 Case Studies: Challenges, Implementation Approach, and Solution Features. 8.4 References. Annex 8-1. Further Dynamic Simulation Capabilities. Time Frame for Dynamic Simulations. Simulation in the Frequency Domain. Eigenvalue and Modal Analysis. 9 Real-Time Transient Security Assessment in Australia at NEMMCO ( Stephen J. Boroczky ). 9.1 Introduction. 9.2 Transient Security Assessment at NEMMCO. 9.3 Performance and Reliability. 9.4 Experience, Benefits, and Outlook. 9.5 References. 10 Online Voltage Security Assessment in the Hellenic Interconnected System ( Costas Vournas, George Christoforidis, and Thierry Van Cutsem ). 10.1 Introduction. 10.2 The Control Center of HTSO. 10.3 Online VSA in the Hellenic System. 10.4 Use of Online VSA For Arming Load-Shedding Protection. 10.5 Conclusion. 10.6 References. Annex 10-1. Quasi-Steady-State Simulation. Principle of the QSS Approximation. Handling of Frequency in QSS Simulation. QSS Model of the Synchronous Machine and its Regulations. Numerical Integration of the QSS Model. 11 The Real-Time Supervision of Transmission Capacity in the Swedish Grid ( Lars Sandberg and Klas Rouden ). 11.1 Introduction. 11.2 Prior and Current Application Development at SVK. 11.3 Voltage Security Assessment with SPICA. 11.4 Benefiting from the Knowledge of the Current Transmission Capacity. 11.5 Additional SPICA Functionality. 11.6 Summary. Appendix A Dimo's Approach to Steady-State Stability Assessment: Methodology Overview, Numerical Example, and Algorithm Validation ( Roberto D. Molina Mylius, Martin Cassano, and Savu C. Savulescu ). A.1 Methodology Overview. A.2 Numerical Example Independent Testing of Algorithm Implementation. A.3 Benchmarking the Methodology. A.4 Conclusions. A.5 References. Appendix B SIME: A Comprehensive Approach to Transient Stability ( Mania Pavella, Daniel Ruiz-Vega, and Mevludin Glavic ). B.1 Introduction. B.2 Basic Formulation. B.3 Preventive SIME. B.4 Emergency SIME. B.5 Postface. B.6 References. Notation. Abbreviations and Acronyms. Appendix C Detection and Evaluation of Stability Constrained ( Marius Pomarleanu and Savu C. Savulescu ). C.1 Introduction. C.2 Approach. C.3 Conclusions. C.4 References. Index.

Energy-efficiency has become a major concern in designing computer systems. One of the most promising solutions to enhance power and energy-efficiency in error tolerant applications is approximate computing that balances accuracy, area, delay, and power consumption based on the computational needs. By trading accuracy of computation, approximate computing may achieve significant improvements in speed, power, and area consumption.