Composite System Adequacy Research Articles

Reliability enhancement and voltage profile improvement of distribution network using optimal capacity allocation and placement of distributed energy resources

In the radial distribution system, reliability is the most critical performance criterion. Additionally, optimizing the voltage profile is critical. This work proposed the optimal placement of distributed energy resources (DERs) to enhance the reliability and improve the voltage profile of the distribution feeder. To perform this research, two practical feeders of the Debre Markos (D/M) city distribution network, Ethiopia were used, which were affected by the outages. A composite system adequacy assessment, which includes the two main components of the power grid, i.e. generation and distribution, is performed using Monte Carlo simulation. The computed results show that integrating DER units improved the overall system's reliability. Further, the effect of varying DER penetration on reliability and voltage profile is also analyzed. ETAP and DIgSILENT software environments are used to perform this research.

Assessment of the Capacity Credit of Renewables and Storage in Multi-Area Power Systems

Capacity credit (CC) can be defined as the capacity of conventional generators that can be replaced by renewable energy sources (RES) and/or other resources such as energy storage without reducing system reliability. Conventional approaches for calculating CC typically treat the power system as a single area without considering transfer constraints and reliability of interconnectors. However, in multi-area power systems locational aspects are key to assess tradeoffs and synergies arising from transmission, storage and RES in providing adequacy of supply. In this work, we propose a new methodology to quantify the CC of RES and storage in a multi-area power system. Due to the large computational burden brought about by composite system adequacy evaluation, a new accelerated sequential Monte Carlo simulation strategy and a new adaptive sampling approach are specifically developed to achieve computation efficiency. The proposed methodology is tested by demonstrating the impact of interconnectors' transfer constraints and availability on RES-storage CC in the case of the Australian National Energy Market (NEM) multi-area power system, with applications to wind, solar, and pumped hydro storage plants. The results from several realistic NEM case studies highlight how the proposed model can inform strategic, reliability-aware integrated system planning of large-scale interconnected low-carbon power systems.

Composite System Reliability Evaluation With Essential Reliability Services Assessment of Wind Power Integrated Power Systems

With the increasing penetration of renewable resources and the retirements of conventional coal-fired generation units, power systems are undergoing significant transformation with the instantaneous renewable generation penetration sometimes approaching over 50 percent of the demand. This transformation makes the need for comprehensive reliability assessment critical to properly account for the composite system adequacy and the sufficiency of essential reliability services (ERSs). This paper introduces a probabilistic approach to evaluate the reliability of wind power integrated power systems considering ERSs including frequency and voltage support, in conjunction with resource adequacy. To consider stochasticity in system operating conditions, the proposed approach utilizes sequential Monte-Carlo Simulation (SMCS) as the probabilistic analysis methodology and formulates probabilistic reliability metrics representing the composite system adequacy and the ERSs. The proposed approach and metrics are demonstrated on a synthetic test system. Simulation results illustrate the efficacy of the proposed approach and its importance in analyzing the impact of increasing wind power penetration as well as wind turbine generators (WTGs) providing ERSs on system reliability.

Power System Reliability Assessment in a Complex Restructured Power System

The basic purpose of an electric power system is to supply its consumers with electric energy as parsimoniously as possible and with a sensible degree of continuity and quality. It is expected that the solicitation of power system reliability assessment in bulk power systems will continue to increase in the future especially in the newly deregulated power diligence. This paper presents the research conducted on the three areas of incorporating multi-state generating unit models, evaluating system performance indices and identifying transmission paucities in complex system adequacy assessment. The incentives for electricity market participants to endow in new generation and transmission facilities are highly influenced by the market risk in a complex restructured environment. This paper also presents a procedure to identify transmission deficiencies and remedial modification in the composite generation and transmission system and focused on the application of probabilistic techniques in composite system adequacy assessment

Adaptive sequential importance sampling technique for short‐term composite power system adequacy evaluation

The well-known sequential Monte Carlo simulation is a powerful tool to analyse short-term reliability of complicated composite power system. However, the corresponding computational burden is tremendous when applied to a highly reliable system. Aiming at improving the simulation efficiency, an adaptive importance sampling technology is proposed in this study. The proposed method, on the basis of component state duration sampling technique combined with cross-entropy method, is able to provide reliability evaluation of highly reliable non-homogeneous Markov system. The Weibull and lognormal distributions are considered to describe repair time of individual components comprising a system. Through the case studies conducted on a reinforced Roy Billinton reliability test system, it is validated that the proposed method is effective and of high efficiency and the efficiency gain against the crude sequential Monte Carlo simulation is robust to variation of load level and lead timescale. The proposed method is useful and efficient to timely monitor the system operating pressure under different lead timescales.

Composite power system adequacy assessment based on postoptimal analysis

The modeling and evaluation of enormous numbers of contingencies are the most challenging impediments associated with composite power system adequacy assessment, particularly for large-scale power systems. Optimal power flow (OPF) solution, as a widely common approach, is normally employed to model and analyze each individual contingency as an independent problem. However, mathematical representations associated with diverse states are slightly different in one or a few generating units, line outages, or trivial load variations. This inherent attribute brings a promising idea to speed up the contingency evaluation procedure. In this paper, postoptimal analysis (POA), as a well-recognized technique to attack a set of similar problems with minimal effort, is adopted to solve the contingency OPFs. Instead of solving all similar problems independently, POA exploits the similarity among them and accelerates the solving procedure. The proposed method here derives a base case model and obtains its respective solution. Thereafter, the solution associated with a contingency is determined by imposing differences due to unit or line outages or load variation with respect to the base case solution. The proposed approach is applicable in both sorts of analytical and simulation-based evaluation methods. The Roy Billinton test system, the IEEE reliability test system, and the IEEE 118-bus test system are used to demonstrate the performance and efficiency of the proposed approach. A significant reduction in the computational efforts is experienced.

Probabilistic Analysis for Maximizing the Grid Integration of Wind Power Generation

This paper presents a sequential Monte Carlo simulation algorithm that can simultaneously assess composite system adequacy and detect wind power curtailment events. A simple procedure at the end of the state evaluation stage is proposed to categorize wind power curtailment events according to their cause. Furthermore, the dual variables of the DC optimal power flow procedure are used to identify which transmission circuits are restricting the use of the total wind power available. In the first set of experiments, the composite system adequacy is assessed, incorporating different generation technologies. This is conducted to clarify the usual comparisons made between wind and thermal technologies which, in fact, depend on the performance measure selected. A second set of experiments considering several wind penetration scenarios is also performed to determine the operational rules or system components responsible for the largest amount of wind energy curtailed. The experiments are carried out on configurations of the IEEE-RTS 79 power system.

Incorporating multi‐state unit models in composite system adequacy assessment

AbstractComponents are usually represented by a two state model in conventional generating capacity and composite generation and transmission system reliability studies. Multi‐state generating unit models create a significant increase in the number of generation contingency states and can result in a considerable increase in the overall solution time. In order to avoid this problem, the derated states are usually amalgamated with the totally forced out state to create the derating‐adjusted forced outage rate (DAFOR). This statistic is also known as the equivalent forced outage rate (EFOR). Studies have shown that modeling large generating units in generating capacity adequacy assessments using DAFOR can provide pessimistic appraisals. Many utilities therefore use multi‐state generating unit representations to assess generating capacity adequacy, in order to obtain more accurate appraisals. There is relatively little published material dealing with the effects of using multi‐state generating unit representations in composite system adequacy assessment. This paper illustrates these effects by application to the IEEE‐Reliability Test System (RTS). Load point and system indices for the test system are presented to illustrate the impact of incorporating multi‐state representations in composite system adequacy assessment. Attention is focused on the effects of model variations including how many derated states should be used in a multi‐state model to obtain a reasonably accurate appraisal. Copyright © 2007 John Wiley & Sons, Ltd.

Selected considerations in utilizing Monte Carlo simulation in quantitative reliability evaluation of composite power systems

The reliability of the generation and major transmission facilities are important factors in modern electric energy supply. These facilities form what is known as the bulk electricity system. An evaluation of these systems involves the composite analysis of the generation and transmission facilities and can be conducted using analytical techniques, Monte Carlo simulation or a combination of these methods. This paper is focused on considerations that arise when utilizing Monte Carlo simulation in composite system adequacy evaluation. Two test systems are utilized to illustrate solution convergence characteristics, the effect of load curtailment priority orders, common mode failures and the inclusion of substations and switching stations in composite system analysis.

Composite power system adequacy assessment in terms of well-being

This paper presents a system well-being evaluation method that divides the composite power system operating condition into several states depending on the level to which the adequacy and security constraints are satisfied. Conventional composite system reliability indices typically do not reflect the ability of the system to withstand, without resulting in load curtailment or other violations, the abrupt loss of system components. The well-being evaluation method provides an extra index for system planners or designers to decide whether or not the power system is capable, based on the deterministic criteria, to withstand unplanned outages of system components without violation of specified constraints. The well-being indices, which are the probabilities of the system being in the healthy, marginal and at risk states, provide this important and intuitively interpretable information for system planning and operations. Studies on two test systems were done to examine the effect of load levels, system component removal and addition on the well-being indices. The bus well-being indices for selected buses of the two test systems were also calculated and compared with the system well-being indices.

Adequacy equivalent development of composite generation and transmission systems

This paper presents a technique for the development of adequacy equivalents for composite generation and transmission systems using a d.c. load flow approach. Adequacy equivalent concepts can be very useful in large composite power system adequacy evaluation where extremely long computation times are usually required. The computation time burden can be effectively alleviated by using a reduced equivalent model to represent the unchanging portion of a composite system. These reduced models, designated as reliability or adequacy equivalents, retain the essential elements in their desired form but eliminate much of the system detail. Network flow methods are usually used to develop adequacy equivalents for composite systems. The d.c. load flow technique, however, is a more widely accepted procedure for composite system analyses as it can provide more accurate solutions than a network flow method. The concepts associated with developing adequacy equivalents using a d.c. load flow method are illustrated using simple power networks. Results and analyses of system studies based on two test systems are presented in the paper.

Effects of Rounding Adequacy Equivalents of Composite Power Systems

This paper presents a rounding technique for reducing adequacy equivalents of composite generation and transmission systems into different sizes. The effects of using the adequacy equivalent reduction in composite system adequacy evaluation are illustrated. The adequacy equivalent concept can be very useful in large composite power system evaluation in which extremely long computation times are usually required. The burden of long required computation times can be effectively alleviated by using a reduced equivalent model to represent the unchanging portion of a composite system. These reduced models retain the essential elements in their desired form but eliminate much of the system detail. The rounding technique is illustrated using a simple example. System studies on two reliability test systems are used to illustrate the effects of the equivalent rounding technique in composite system adequacy evaluation.

Adequacy equivalent development of composite generation and transmission systems using a d.c. load flow

Abstract This paper presents a technique for the development of adequacy equivalents for composite generation and transmission systems using a d.c. load flow approach. Adequacy equivalent concepts can be very useful in large composite power system adequacy evaluation where extremely long computation times are usually required. The computation time burden can be effectively alleviated by using a reduced equivalent model to represent the unchanging portion of a composite system. These reduced models, designated as reliability or adequacy equivalents, retain the essential elements in their desired form but eliminate much of the system detail. Network flow methods are usually used to develop adequacy equivalents for composite systems. The d.c. load flow technique, however, is a more widely accepted procedure for composite system analyses as it can provide more accurate solutions than a network flow method. The concepts associated with developing adequacy equivalents using a d.c. load flow method are illustrated using simple power networks. Results and analyses of system studies based on two test systems are presented in the paper.

Voltage stability considerations in composite power system reliability evaluation

This paper presents an approach which includes voltage stability considerations in the adequacy assessment of a composite power system. A fast technique for the probabilistic assessment of voltage stability is presented which can be used in conjunction with detailed contingency evaluation in a composite system adequacy assessment. Voltage stability is quantified using an indicator that can be easily included in the framework of an existing composite power system adequacy program. The effect on the adequacy indices (load point and system indices) of incorporating voltage stability constraints is illustrated by application to the IEEE-Reliability Test System.

Incorporation of voltage stability operating limits in composite system adequacy assessment: BC Hydro's experience

This paper presents an approach for incorporating actual voltage stability operating limits (VSOL) in the composite power system adequacy evaluation. The VSOL curves are fitted into simplex-type straight lines and added in the linear programming model for minimizing load curtailment as additional constraints. The incorporated voltage stability limits are those calculated for the operators in the power system control center. The introduction of the actual limits therefore leads to adequacy evaluation closer to the operation reality with very little overhead since the voltage stability operating limits are pre-calculated for system operation. The case studies for BC Hydro's 500/230 kV system are given and discussed.

Algorithm for failure frequency and duration assessment of composite power systems

Failure frequency and duration (F&D) indices are important load-point and system parameters in composite generation and transmission system adequacy evaluation. Several papers have been published in the past few years that focus on developing algorithms for more accurate assessment of the F&D indices, and considerable progress has been made. A new efficient and effective algorithm is presented in the paper, which provides a more accurate assessment of the F&D indices, when compared with previous approaches, without increase in computational effort. The new algorithm also provides an estimate of the failure frequency with an exact and controllable error limit. The required concepts are developed and illustrated using simple networks, and practical application is illustrated using two reliability test systems.

Composite system adequacy assessment using sequential Monte Carlo simulation with variance reduction techniques

Estimation of composite system adequacy indices using sequential Monte Carlo simulation approach with time-varying loads at each load bus is computationally quite expensive. Variance reduction techniques can be used together with the sequential simulation process to enhance the efficiency of the simulation. The paper discusses two commonly used techniques - control variates and antithetic variates with reference to the sequential simulation method used for adequacy analysis. The paper also utilises optimum control coefficients associated with the regression term in the control variate method to further improve the correlation between the control variate and the variable to be estimated. Case studies are conducted on two test systems.

96/05090 Impact of power wheeling on composite system adequacy evaluation

96/05090 Impact of power wheeling on composite system adequacy evaluation

Impact of power wheeling on composite system adequacy evaluation

One of the many possible uses and benefits of interconnection between neighbouring electric power systems is the opportunity to wheel energy through the transmission facilities of one system in order to serve another system. Wheeling of energy can also occur within a system when an independent power producer serves a load located at some other point in the system. iower wheeling transactions are recognized to have a definite impact on the utility's system losses depending upon the system topology, the amount of power/energy wheeled and the wheeling distance involved. These factors currently form the basis for determining service charges associated with power wheeling. Quantification of the reliability impacts of power wheeling is also important in order to understand fully the impacts of wheeling options. This paper discusses the effects of power wheeling on the composite power system adequacy indices of two test systems. The impacts associated with both intra-system and inter-system power wheeling are illustrated. The results presented were obtained using a basic computational tool for composite power system adequacy assessment.

Adequacy and reliability cost/worth implications of nonutility generation

The electrical energy component provided by conventional generating sources is expected to decline slightly in the future due to environmental concerns and the penetration of new sources of energy. Renewable forms of energy such as nonutility generation (NUG) and cogeneration will increase their market share of the total energy mix as a result of the energy policies currently being adopted by many governments and power utilities around the world. A significant portion of future power plant investments will be made by NUG and cogeneration industries, therefore, the task of evaluating the merits and demerits of such options is becoming an important function in the power utility system planning. The NUGs and cogeneration facilities are normally small generating capacity units injected at load points within the system. The reliability and economic implications of capacity additions from independent power producers (IPP) can be quite significant. The paper discusses the impacts of NUGs on the adequacy and reliability cost/worth indices in a generating capacity system and the cost of customer interruptions in a composite system adequacy assessment.