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Reliability is an essential factor in distribution networkt expansion planning. However, standard distribution reliability assessment techniques rely on quantifying the impact of a pre-specified set of events on service continuity through the simulation of component outages, one at a time. Due to such a simulation-based nature, the incorporation of reliability into distribution network expansion planning has customarily required the application of heuristic and metaheuristic approaches. Recently, alternative mixed-integer linear programming (MILP) models have been proposed for distribution network expansion planning considering reliability. Nonetheless, such models suffer from either low computational efficiency or over-simplification. To overcome these shortcomings, this paper proposes an enhanced MILP model for multistage reliability-constrained distribution network expansion planning. Leveraging an efficient, yet accurate reliability evaluation model, proposing a customized technique for effectively imposing radial operation, as well as utilizing pragmatic measures to model reliability-related costs are the salient features of this work. In this respect, practical reliability-related costs are considered based on reliability incentive schemes and the revenue lost due to undelivered energy during customer outages. The proposed planning approach is tested on four networks with 24, 54, 86, and 138 nodes to illustrate its efficiency and applicability. [ABSTRACT FROM AUTHOR]

Flexible ramping product (FRP) has been recently launched in a number of electricity markets to enhance the power grid flexibility and accommodate additional deals of uncertainty introduced by renewable energy resources. The FRP procures additional ramp capacities provided by the dispatchable generating units and consumers in the real-time market (RTM) with the aim to enhance the ability of supply to closely follow the net-load at the next immediate time-interval. An important challenge in widespread adoption of this technology is a key question: Does the available energy capacity of the RTM participants contain sufficient ramp capacity to tackle the net-load uncertainties? Indeed, shortage of the systems ramp capacity may not only jeopardize its flexibility, but also may cause drastic fluctuations in the RTM energy prices. To address this challenge, this paper proposes a novel optimization framework to harness the procured spinning reserve services in the day-ahead market (DAM) for FRP provision in the RTM while meeting the system reliability requirements. On this basis, the FRP will be simultaneously procured from the RTM energy and DAM spinning reserve capacities. Furthermore, a new payment mechanism is proposed to compensate the portion of spinning reserve utilized for FRP procurement in the RTM. The proposed framework is simulated on the IEEE 118-bus test system and the results verify its effectiveness in modern electricity markets. [ABSTRACT FROM AUTHOR]

This paper aims at proposing a mixed-integer linear formulation to incorporate reliability-oriented costs into the expansion planning model of electricity distribution networks. In this respect, revenue lost associated with the undelivered energy caused by network interruptions as well as costs incurred by the widely used reward–penalty regulations is considered as the major reliability-related costs from distribution companies point of view. A set of mixed-integer linear equations is proposed to calculate the most common distribution system reliability indices, i.e., expected energy not served, system average interruption frequency index, and system average interruption duration index. It is found that these equations can also facilitate the formulation of radiality constraint in the presence of distributed generation units. Moreover, application of the proposed method is investigated through various case studies performed on two test distribution networks with 24 and 54 nodes. [ABSTRACT FROM AUTHOR]

Reliability cost is considered as an inevitable criterion in expansion planning studies of distribution systems. However, nonlinear expressions of reliability indices aggravate complexity of planning studies. To address this issue, this letter proposes a novel method to linearize mathematical model of the reliability-based distribution expansion planning problem. Using this variant of reliability indices, reliability costs can easily be involved in mixed-integer linear programming model of distribution expansion planning. Validity of the derived expressions is tested by simulation results. [ABSTRACT FROM AUTHOR]

In power distribution systems, sometimes, system reliability indices are available, where some components’ reliability parameters are unknown. This letter presents the inverse reliability evaluation (IRE) problem in radial distribution systems to find unknown components’ parameters from the known system reliability indices. To this end, a nonlinear system of equations is presented and solved. The solutions are analyzed in the RBTS bus 2 to verify the applicability of the proposed approach and to show the importance of the IRE problem. [ABSTRACT FROM AUTHOR]

This paper develops a general framework for reliability assessment of multi-microgrid (MMG) distribution systems. It also investigates reliability impacts of coordinated outage management strategies in a MMG distribution network. According to the proposed reliability evaluation framework, which is based on sequential Monte Carlo simulation method, distribution system is divided into smaller sections/microgrids based on protection system configuration and operating measures are efficiently simulated considering different operation modes. In order to demonstrate the role of outage management strategy in reliability performance of MMG distribution systems, at first, the required features of an outage management strategy are identified. Then, suitable centralized and hierarchical schemes are introduced for operation of such systems during outage events. The proposed schemes, which are based on model predictive control approach, minimize total load curtailments in the system. Moreover, they are flexible and can effectively deal with multiple contingencies as well as uncertainties of outage duration. The developed reliability assessment framework is applied to a test system and performance of the presented outage management schemes are explored through extensive case studies. Obtained results suggest that implementation of an appropriate coordinated scheme is crucial to reliable operation of MMG distribution systems. [ABSTRACT FROM PUBLISHER]

Renewable energies especially Run-Of the-River (ROR) power plants are increasingly used for the electricity generation in the power systems. The uncertain and intermittent nature of these plants arisen from variability of water flow, however, has led to some problems in their integration to power systems. Thus, the operating reserve requirement in a power system containing large ROR plants is a main challenge, which has to be addressed properly. In this way, this paper presents an analytical approach to determine the adequate spinning reserve based on the well-being approach during the system operation. The reliability model based on the components failures and uncertainty nature of water flow is introduced for ROR plants operation studies. This approach not only evaluates the interaction between these energies and conventional units, but also determines the contribution that ROR power plants can make in load carrying capability of a power generating system. Two reliability test systems, utilized from water flow data of Sheshpir River in Iran, are examined to demonstrate the effectiveness of the proposed model. [ABSTRACT FROM AUTHOR]

Maintenance scheduling of generating units in restructured power systems is a collaborative and interactive process between independent system operators (ISOs) and generating companies (GENCOs). The ISO should comply with GENCO maintenance preferences subject to targeted system reliability levels. This process might be multistage since the admission of all initial unit outage requests may threaten system reliability. Hence, the ISO accepts some proposals and determines alternatives for the remaining units. The GENCOs are then allowed to confirm the alternatives or revise them. In this paper the ISO problem of generating unit maintenance scheduling is tackled. The objective function is to minimize the deviation of awarded schedule from the requested schedule, as measured in MW weeks. A novel and effective optimization technique is developed to solve the problem at hand. In the proposed methodology, risk leveling and dynamic programming optimization algorithms are concurrently utilized to lessen the computation burden and enhance the solution process. The effectiveness of the proposed method and its applicability to real-life systems are verified by examining the generation section of the IEEE reliability test system (IEEE-RTS). The performance of the new method is also compared with that of the individual risk leveling approach. [ABSTRACT FROM AUTHOR]

Highlights: [•] A new formulation for composite system reliability assessment is proposed. [•] The new formulation relies on an approximated AC power flow model. [•] The new model is linear and more attractive in terms of computational burden. [•] Accuracy of the model is compared with that of the conventional methods. [•] Performance of the model in different conditions is shown by sensitivity analyses. [ABSTRACT FROM AUTHOR]

This paper approaches the topic of protection system reliability from an economic point of view by 1) designing an optimal modern protective relay based on a prescribed level of reliability subject to economic constraints and 2) determining optimal routine test intervals by balancing the cost of routine tests and losses due to relay failure. This paper proposes a method that enables the designer to optimally select hardware and software components of a digital protective relay to gain the highest possible overall reliability with a restricted budget. This design can be viewed as a reliability and redundancy allocation problem for which a new easy-to-implement algorithm is proposed. In contrast to the existing literature that views the problem of routine test interval optimization solely from a reliability viewpoint, this paper proposes an optimization procedure for determining optimal test intervals. The optimization objective function consists of three terms: cost of routine tests, losses due to relay unresponsiveness, and losses due to relay maloperation. The value of the objective function is calculated based on a new, simple, and comprehensive Markov model. Illustrative numerical examples clarify the application of the proposed methods and demonstrate their effectiveness in achieving an optimum for both cases. [ABSTRACT FROM PUBLISHER]

Automation is acknowledged by distribution utilities as a successful investment strategy to enhance reliability and operation efficiency. However, practical approaches that can handle the complex decision-making process faced by decision makers to justify the long-term financial effects of distribution automation have remained scarce. An automated and remote-controlled sectionalizing switch play a fundamental role in an automated distribution network. This paper introduces a new optimization approach for distribution automation in terms of automated and remotely controlled sectionalizing switch placement. Mixed-integer linear programming (MILP) is utilized to model the problem. The proposed model can be solved with large-scale commercial solvers in a computationally efficient manner. The proposed sectionalizing switch placement problem considers customer outage costs in conjunction with sectionalizing switch capital investment, installation, as well as annual operation and maintenance costs. The effectiveness of the proposed approach is tested on a reliability test system and a typical real size system. The presented results indicate the accuracy and efficiency of the proposed method. [ABSTRACT FROM PUBLISHER]

The deployment of flexible ac transmission system (FACTS) devices, despite miscellaneous benefits and applications, has been restricted mainly due to their large investment costs. Accordingly, the notion of distributed FACTS (D-FACTS) was recently proposed. Distributed static series compensators (DSSCs), as a new member of D-FACTS, are directly clamped to conductors of transmission lines. The possibility of controlling the compensation rate of DSSCs from the control center affords the active control of network power flow. This paper presents a comprehensive reliability model for the DSSC. The model is then reduced and a state-space representation is extracted for a transmission line with a number of DSSCs. To illustrate the worth of DSSC utilization, the increment in the expected interruption cost is computed by using a composite reliability assessment. In the contingency analysis procedure, incorporating the active control of power flow provided by DSSCs makes the optimal load curtailment subproblem nonlinear. In order to linearize the subproblem, a novel set of inequalities is extracted. Numerical analysis on the IEEE Reliability Test System (RTS) is conducted to examine the effect of DSSC on composite reliability indices. The results reveal the effectiveness of proposed models and illustrate that DSSCs enhance the system reliability. [ABSTRACT FROM AUTHOR]

In this paper, an analytical approach for the reliability modeling of large wind farms is presented. A systematic method based on frequency and duration approach is utilized to model a wind farm like a multistate conventional unit, where the probability, frequency of occurrence, and departure rate of each state can be obtained using the regional wind regime of wind farm and wind turbine characteristics. The proposed method is capable of finding both annual frequency and average time of load curtailment analytically in the presence of wind power. A wind farm in the northern region of Iran with the wind speed registration of one year is studied in this paper. To accommodate time-varying patterns of wind speed, reliability analysis considering seasonal patterns of wind speed is also carried out. The results show that seasonal patterns significantly affect the reliability indexes. A reliability analysis is also performed using a load profile similar to that of Iran power network. It will be shown that the coincidence of high-load-demand and high-wind-speed periods makes the North Iran wind farm projects highly attractive from a reliability point of view. [ABSTRACT FROM AUTHOR]

By the introduction of competitive supply, modern electric utilities are forced to operate their systems closer to their security limits. Under such fragile conditions, any disturbance could endanger system security and lead to system collapse. There is, therefore, a need to develop new methods which could evaluate optimal scheduling of operating reserve and forewarn the system operators to take necessary preventive actions in case need arises. An effective method is proposed in this paper to optimally allocate spinning reserve based on a well-being model. The method used in conventional well-being framework for classifying power system comfort zone into healthy and marginal states is initially revised. The optimal value of health index and system spinning reserve requirements are then evaluated on the basis of a trade off between the total cost of spinning reserve and the expected cost of energy not served. The effectiveness of the proposed method is examined using the IEEE-RTS. [ABSTRACT FROM AUTHOR]

Presents a study which examined the impact of a unified power flow controller on power system reliability. Impact of the ability to control power flow in an electric power system; Results; Conclusions.

Adequate operating reserve is required in an electric power system in order to maintain a desired level of reliability throughout a given period of time. Interruptible load can be considered as a part of the system operating reserve if it is required. The inclusion of interruptible load in the assessment of unit commitment in interconnected systems is illustrated in this paper using a well-being framework. A technique is presented to determine the well-being indices of both isolated and interconnected systems with the inclusion of interruptible load. The impacts on the required number of committed units and the well-being indices of the amount of interruptible load and the corresponding interruption time are examined in this paper by application to a hypothetical system and to the IEEE-RTS. © 1998 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

System reliability evaluation can be performed using the two broad categories of deterministic and probabilistic techniques. The basic weakness associated with deterministic methods is that they do not specifically take into account the likelihood of component failures in the evaluation. There is, however, considerable reluctance to using probabilistic techniques in many engineering areas owing to the difficulty in interpreting the resulting numerical indices. An approach is presented in this paper to alleviate this difficulty by combining deterministic considerations with probabilistic indices to monitor the system well-being in the form of system health and margin states in addition to a conventional risk index. The concept of system well-being is illustrated using relatively simple network configurations. The proposed technique is also applied to a power system network to determine the degree of well-being of the various load points and the overall system. © 1997 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Remote control switches (RCSs) are often assumed to be fully reliable in reliability and cost/worth analyses. This assumption, however, overestimates their merits, thereby misguiding network owners about their optimal implementation. This letter extends the current reliability evaluation procedure to incorporate probability of RCS malfunctions. Then, the extended procedure is applied to a network equipped with a few RCSs. The numerical studies reveal that RCS malfunctions degrade their worth, which may even affect their optimal number and locations. [ABSTRACT FROM AUTHOR]

This paper presents an original approach for the evaluation of reliability of active distribution networks with unknown topology. Built upon novel reformulations of conventional definitions for distribution reliability indices, the dependence of system-oriented reliability metrics on network topology is explicitly formulated using a set of mixed-integer linear expressions. Unlike previously reported works also modeling mathematically the relationship between reliability assessment and network topology, the proposed approach allows considering the impact of distributed generation (DG) while accounting for switching interruptions. Moreover, for the first time in the emerging closely related literature, the nonlinearity and nonconvexity of the customer average interruption duration index are precisely characterized. The proposed mixed-integer linear model is suitable for various distribution optimization problems in which the operational topology of the network is not specified a priori. Aiming to exemplify its potential applicability, the proposed formulation is incorporated into a distribution reconfiguration optimization problem. The effectiveness and practicality of the proposed approach are numerically illustrated using various test networks. • Active distribution system reliability assessment can be performed by MILP models. • MILP reliability models ease optimal planning and operation of distribution grids. • Nonlinear CAIDI can be expressed by MILP-based formulations. • DG units can significantly improve interruption duration-based reliability indices. • A small alteration in distribution grid topology can notably change reliability. [ABSTRACT FROM AUTHOR]

Power plant successful operation is always a function of its constituent sub-systems and components. Due to the current financial constraints in power industry, power plant operators are continuously facing a wide range of challenges when dealing with maintenance scheduling and asset management practices of the plant sub-systems. Knowledge on the roles and criticality of the constituent components on the plant overall performance will help in establishing the plans for its smooth, safe, and economic operation. To ensure making the techno-economical decisions on the maintenance of power plant equipment, this paper focuses on the reliability modeling of the combined cycle power plants (CCPP). Reliability models are first developed for the gas turbine power plants (GTPP) and steam turbine power plants (STPP) which provides the input to evaluate the reliability of the overall CCPP from an engineering system perspective. Reliability-oriented sensitivity indices are proposed the aforementioned types of power plants to identify the plant critical components, i.e., those with the most considerable influences on the system reliability and availability targets. Having the system critical components recognized, one can then decide on the efficient maintenance strategies for the power plant components so that the available resources can be well planned and allocated techno-economically. [ABSTRACT FROM AUTHOR]