Sharif Digital Repository

In this paper, the Markov models, eigenvectors and eigenvalue concepts are used to propose a methodology for analyzing the transient reliability of a system with identical components and identical repairmen. The components of the systems under consideration can have two distinct configurations, namely; they can be arranged in series or in parallel. A third case is also considered, in which the system is up (good) if k-out-of-n components are good. For all three cases, a procedure is proposed for calculating the transient probability of the system availability and the duration of the system to reach the steady state. © Sharif University of Technology, February 2007  

The reliability analysis of critical systems is often performed using fault-tree analysis. Fault trees are analyzed using analytic approaches or Monte Carlo simulation. The usage of the analytic approaches is limited in few models and certain kinds of distributions. In contrast to the analytic approaches, Monte Carlo simulation can be broadly used. However, Monte Carlo simulation is time-consuming because of the intensive computations. This is because an extremely large number of simulated samples may be needed to estimate the reliability parameters at a high level of confidence. In this paper, a tree model, called Time-to-Failure tree, has been presented, which can be used to accelerate the... 

With the expansion of electricity networks, increasing operational complexities, improved knowledge of the system operators, all with the subsidies elimination in some countries such as Iran and experiencing the real price of electricity by then, it necessitates a more reliable power to be delivered to the system customers. Power system automation is regarded as an efficient solution and the effective key to this problem. However, the great number of substations in power distribution systems has led to the fact that it is neither feasible nor economic to automate all of them. This calls for a comprehensive scheme on the placement of the distribution substations to be automated. In this... 

High reliability against noise, low energy consumption and high performance are key objectives in the design of on-chip networks. Recently some researchers have considered the various trade-offs between two of these objectives. However, as we will argue later, the three design objectives should be considered jointly and simultaneously. The first aim of this paper is to analyze the impact of various error-control schemes on the simultaneous trade-off between reliability, performance and energy when voltage swing varies. We provide a detailed comparative analysis of the error-control schemes using analytical models and SPICE simulations. The second aim of this paper is to analyze the impact of... 

Speed and accuracy of under frequency load shedding (UFLS) has a vital role in its effectiveness for preserving system stability. In any case load-shedding still remains the ultimate resource for emergency condition. Initial rate of change of frequency is a fast and potentially useful signal to detect the overload when a disturbance happens. In order to improve the under-frequency load shedding performance, in this paper, a global load shedding scheme integrated with rate of frequency decline as an extra variable is proposed. The new SCADA based scheme is devised to overcome the shortcomings of previous adaptive UFLS procedures, and to provide a fast and yet reliable method to maintain... 

Unsafe driving behavior and hazardous environmental conditions lead lo traffic crashes and injuries. The annual rale of road crashes in Iran is twenty times higher than the world's average. Motorcycle crashes have higher fatality rates than other motor vehicle crashes, and they exert psychological pressure on the communities and have adverse economic consequences for the societies. This paper analyzes Tehran's motorcycle crash data and investigates the effective underlying factors. Seven strategies were presented and prioritized to reduce the number and severity of motorcycle crashes. The fuzzy Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) combined with the... 

Wind generation is one of the most successful sources of renewable energy for the production of electrical energy. The technical characteristics of wind generation make existing conventional generation models not directly applicable. This paper presents an analytical method for the reliability assessment of the flat-rated wind turbine generation systems. An example of flat rating is that of the MOD-2, a second-generation class of wind turbines. The power-velocity characteristic of the flat-rated wind turbines is employed in this paper to model the operating behavior of the installed wind turbine generators. For wind-power potential estimation, the Weibull distribution model is used. The... 

Recognition of the circuit-breaker's (CB) vital role in reliable operation and protection of power systems (i.e., during energization, disconnecting loads, and clearing faults), helps to understand the requirement and importance of its maintenance management as well as maintenance scheduling. Condition-based maintenance (CBM), employing online monitoring (OLM) of CBs, has been long reported as the most practical maintenance policy on the power system CBs. There are a large number of CBs in a power system to be monitored; however, to address the financial limitations for OLM implementation (in utilities), a method will be proposed to find the most critical breakers for enforcing effectively... 

In this paper, a new method for designing procedure of Reward-Penalty Scheme (RPS) in distribution system is proposed. Being fair and adoptable in viewpoint of distribution companies (DisCos) are main superiorities of the proposed RPS. Established based on concept of the Yardstick theory, its application can ensure regulators that a perfect competition will be created between DisCos to improve the service reliability. Also, such a regulation scheme can be a key for power system decision makers in order to prevent the DisCos from decreasing service reliability. Aimed to reach a fair mechanism, the proposed RPS rewards/penalizes the DisCos only compared with the other ones owning similar... 

As the electricity market undergoes continuous evolutions, along with the outdated nature of the grid, system operators would have to be able to more effectively manage the operation costs since waves of maintenance costs and equipment investments would be anticipated in the years to come. Strategic implementation of cost-effective reliability centered maintenance (RCM) approaches seems to be a key solution. This paper proposes an efficient method to assess the component criticality for the system overall reliability and further maintenance focuses. A solution concept of game theory, called Shapely Value, that is able to fairly identify the contribution of each single equipment to the system... 

With the rapid evolution of electricity markets and the need for higher economic efficiency of power industry, attempts for lowering down the maintenance costs as a large portion of system operation expenses seem imperative. Recognised as a crucial step in practical implementation of modern maintenance paradigms, e.g. reliability-centred maintenance, this study proposes an efficient method to quantify the generating units' criticality on the bulk power system reliability performance. The proposed approach utilises a solution concept of game theory and evaluates the contribution of each generating unit on the overall system reliability when a higher-order contingency occurs. The suggested... 

As the electricity market undergoes continuous evolutions, along with the widely-recognized outdated nature of the grid, system operators would have to be able to more effectively manage the system operation expenses since waves of maintenance costs and equipment investments would be anticipated in a few years to come. Strategic implementation of cost-effective reliability-centered maintenance (RCM) approaches seems to be a key solution. This paper proposes an efficient method to assess the component criticality for system overall reliability and further maintenance focuses. A solution concept of game theory, called shapely value, is proposed that is able to fairly identify the contribution... 

Nowadays automation in distribution systems is growing largely. Automated and remote controlled switches play prominent rules in automated distribution systems. By opening and closing these remote controlled switches in emergency states when a fault has been occurred we can manage fault and restoration process in order to minimize interruption time and costs. In the normal states feeder load management and power loss minimization can be controlled by these remote controlled switches. Finding optimum numbers and optimum locations for installing these switches is the main concern in this between. Up to now a number of algorithms have been developed for optimum switch placement. In this paper a... 

Considerable attention has been devoted to demonstrate reliability enhancement of power systems with power wheeling transactions. The impacts of power wheeling on power systems depends on various factors such as direction, amount of power/energy wheeled, system topology and sink or source nodes of power system. The effects on Iran Composite Power System (ICPS) reliability of wheeling energy from Azerbaijan to Turkmenistan are presented in this paper. This transaction is done through the transmission facilities on north part of ICPS. The sensitivity of ICPS to the direction and amount of power wheeling is attended. Finally, the optimum value for power wheeling is determined and the associated... 

Protection systems play a major role in the performance of electric power systems. There are a number of techniques such as redundancy within the relay system or local and remote backup methods to improve protection system reliability to remove faults as fast as possible, coordination of protective relays is very important. Also availability to neighboring systems affects significantly on repair time after occurring an event. An approach is presented in this paper to incorporate relay coordination and alternative supply availability on radial sub-transmission system reliability. For this purpose, a computer program has been developed. As a case study, a practical 63 KV sub-transmission... 

We propose a robust deviation framework to deal with uncertain component reliabilities in the constrained redundancy optimization problem (CROP) in series-parallel reliability systems. The proposed model is based on a linearized binary version of standard nonlinear integer programming formulations of this problem. We extend the linearized model to address uncertainty by assuming that the component reliabilities belong to an interval uncertainty set, where only upper and lower bounds are known for each component reliability, and develop a Min-Max regret model to handle data uncertainty. A key challenge is that, because the deterministic model involves nonlinear functions of the uncertain... 

The reliability of wireless sensor networks (WSNs) depends on both sensing coverage and reliable transmission of collected data provided by the target cluster of sensors in the proximity of the phenomenon to the observer. In this paper, we establish a probabilistic fundamental quantitative notion for performance-critical applications on reliable information transfer and propose a new analytical model to calculate the coverage-oriented reliability of cluster-based WSNs. Here, the packet loss probability is modeled as a function of two main parameters. The first is the probability of link failure when the node's buffer at the end point of the link is full (discarding the packet) or when the... 

Distribution feeder reconfiguration (DFR) is a precious operation strategy that can improve the system from different aspects including total cost, reliability, and power quality. Nevertheless, the high complexity of the new smart grids has resulted in much uncertainty in the DFR problem that necessities the use of a sufficient stochastic framework to deal with them. In this way, this paper proposes a new stochastic framework based on cloud theory to account the uncertainties associated with multiobjective DFR problem from the reliability point of view. Cloud theory is constructed based on fuzzy theory and probability idea. In comparison with the Monte Carlo simulation method, cloud models... 

Substations and switching stations are critical segments in an electric power system. Their impacts on system operation and the consequential effects of their components failure are usually more dominant in overall power system reliability. There is always a degree of uncertainty in the practical input data used in reliability analysis. This paper presents a conceptual possibilistic approach using fuzzy set theory to manage the uncertainties in the reliability input data such as failure rate, repair time and operation of protective devices. Suitable fuzzy numbers are proposed for components reliability data. Load of feeders are also represented by fuzzy numbers and their impact on ENS... 

Distributed generation is expected to play an increasing role in emerging power systems. They use different type of resources and technologies to serve energy to power system. DG has positive and negative effects for both the utilities and customers. System and load point reliability indices are normally improved if DG is installed in a distribution network. On the other hand, DG has some specific characteristics which distinguish it from conventional generating units. Therefore, they should not be treated as conventional generating units to perform reliability evaluation. An appropriate model is required to be developed in order to assess impacts of DG on reliability indices. Impacts of DG...