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System Security (system + security)

Distribution by Scientific Domains

Engineering	85%

Selected Abstracts

Incorporating power system security into market-clearing of day-ahead joint energy and reserves auctions

EUROPEAN TRANSACTIONS ON ELECTRICAL POWER, Issue 2 2010
J. Aghaei
Abstract This paper is intended to introduce a technique for incorporating system security into the clearing of day-ahead joint electricity markets, with particular emphasis on the voltage stability. A Multiobjective Mathematical Programming (MMP) formulation is implemented for provision of ancillary services (Automatic Generation Control or AGC, spinning, non-spinning, and operating reserves) as well as energy in simultaneous auctions by pool-based aggregated market scheme. In the proposed market-clearing structure, the security problem, as an important responsibility of ISO, is addressed and a nonlinear model is formulated and used as the extra objective functions of the optimization problem. Thus, in the MMP formulation of the market-clearing process, the objective functions (including augmented generation offer cost, overload index, voltage drop index, and loading margin) are optimized while meeting AC power flow constraints, system reserve requirements, and lost opportunity cost (LOC) considerations. The IEEE 24-bus Reliability Test System (RTS 24-bus) is used to demonstrate the performance of the proposed method. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Application of differential evolution algorithm for optimal location and parameters setting of UPFC considering power system security

EUROPEAN TRANSACTIONS ON ELECTRICAL POWER, Issue 7 2009
Husam I. Shaheen
Abstract Unified power flow controller (UPFC) is one of the most effective flexible AC transmission systems (FACTS) devices for enhancing power system security. However, to what extent the performance of UPFC can be brought out, it highly depends upon the location and parameters setting of this device in the system. This paper presents an approach based on evolutionary algorithms (EAs) techniques to find out the optimal placement and settings of UPFC for enhancing power system security under single line contingencies (N-1 contingency). Firstly, we perform a contingency analysis and ranking process to determine the most severe line outage contingencies considering line overloads and bus voltage limit violations as a performance index. Secondly, we apply an evolutionary optimization technique, namely: differential evolution (DE) to find out the optimal location and parameters setting of UPFC under the determined contingency scenarios. To verify our proposed approach and for comparison purposes, we perform simulations on an IEEE 14-bus and an IEEE 30-bus power systems. The results we have obtained indicate that DE is an easy to use, fast, and robust optimization technique compared with genetic algorithm (GA). Installing UPFC in the optimal location determined by DE can significantly enhance the security of power system by eliminating or minimizing the overloaded lines and the bus voltage limit violations. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Unit commitment at frequency security condition

EUROPEAN TRANSACTIONS ON ELECTRICAL POWER, Issue 2 2001
X. Lei
In island grids and weakly interconnected power systems, the loss of a large proportion of generation will cause the system frequency to fall dramatically. In order to ensure a stable operation with the lowest impact to the system, the disturbed power balance must be equalized within a short specified time by activating the second-reserve of on-line units or by load shedding or both. Unit commitment procedures shall consider these factors to ensure a reliable power supply while minimizing the fuel costs. This paper presents a unit commitment procedure taking the frequency security condition of systems into account. The procedure commits and optimizes units, calculates necessary second-reserve capability, and allocates them among the available on-line units. Parallel to the minimization of daily fuel costs, a specified frequency minimum following the loss of generation is employed as a criterion for maintaining system security. A case study on typical island systems with a large number of different units is demonstrated using the proposed procedure. Results from the study validated robust performance of the proposed procedure that minimizes fuel costs while maintaining frequency security condition. This paper considers only the frequency security condition to be handled. However, it can also be extended with other criteria such transmission capability during transient conditions of interconnected systems. [source]

Holiday users of the Internet , ease of use, functionality and novelty

INTERNATIONAL JOURNAL OF TOURISM RESEARCH, Issue 4 2008
Chris Ryan
Abstract This study is based upon a sample of 517 international visitors to New Zealand. It suggests that Internet usage is based upon perceived usefulness and ease of system use. Of additional importance is user confidence about system security. Functional issues of purchasing seem to take priority over information search as users become more familiar with web pages. An additional finding is that entertainment needs are arguably better met by other Internet functions than those provided by destination web pages. Novelty on the Net is perhaps sought from specific sources, and not from the Net generally. Implications are discussed for both measurement and marketing. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Hiding role assignment in mission-critical collaborative systems

QUALITY AND RELIABILITY ENGINEERING INTERNATIONAL, Issue 3 2002
Xinwen Fu
Abstract In a mission critical collaboration system, a group of roles are assigned to computer nodes connected by a communication network. Role assignment is mission-critical information and needs to be protected. In this paper, we develop methods to effectively and efficiently protect the information of role assignment from traffic analysis, a passive attack. To measure the system security, we introduce a metric of detection probability, defined as the probability that a role assignment can be discovered. A heuristic greedy algorithm is given to minimize the resource consumption while guaranteeing a low detection-probability level. Our performance evaluation shows that the algorithm proposed in this paper performs well in terms of execution time and resource usage compared to an exhaustive search algorithm. We also propose to use additional means (e.g. additional nodes) to further increase the security level of a system at the cost of a mild resource consumption increase. Copyright © 2002 John Wiley & Sons, Ltd. [source]