Composite System Adequacy Evaluation Research Articles

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.

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.

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.

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.

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.

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.

Effects of nonutility generators on composite system adequacy evaluation

A significant component of the overall system electrical energy requirements of many power utilities is now being provided by independent power production facilities in the form of nonutility generators (NUGs) and cogeneration facilities. The authors discuss the impacts of NUGs on the composite power system adequacy indices of two test systems. They illustrate the effects on the calculated adequacy indices of using different system load curtailment philosophies in composite system adequacy assessment. Results obtained using an analytical approach and using a Monte Carlo simulation program as the computational tools are illustrated and presented.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A novel method for incorporating weather effects in composite system adequacy evaluation

The proposed method can recognize regional weather aspects including those situations in which transmission lines traverse several geographical regions which undergo different weather conditions. The method uses a Monte Carlo approach which can be readily applied to large-scale transmission systems. Case studies conducted using a program developed at the University of Saskatchewan show that neglecting all consideration of weather effects can lead to an optimistic assessment of system adequacy while ignoring regional weather conditions can result in overestimation of the resulting failure bunching effects due to adverse weather. The effects of weather variations on annualized indices are discussed, and the need to establish suitable and practical procedures for collecting adverse weather data which can be utilized in realistic composite system adequacy assessment is addressed. The modeling procedure also provides a realistic framework for practical data collection.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Effect of bus load uncertainty and correlation in composite system adequacy evaluation

A tabulating technique of normal distribution sampling is used to simulate bus load uncertainty and a correlation sampling technique is utilized to simulate bus load correlation including those situations in which bus loads are completely dependent or independent. These techniques have been incorporated in the MECORE computer program developed at the University of Saskatchewan for composite system reliability evaluation. Case studies include comparisons between the normal distribution sampling technique and a discrete interval enumeration model, effects of bus load uncertainty and correlation on annualized and annual indices for different systems, and effects of different load uncertainty standard deviations and different degrees of bus load correlation on the inadequacy indices.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Indices for use in composite generation and transmission system adequacy evaluation

The adequacy of a composite power system involving both generation and transmission components can be expressed by computing a set of appropriate indices for both the individual load points and the entire system. A wide range of indices have been proposed in adequacy studies by power utilities, research organizations and educational institutions. The selection and definition of these indices are very dependent upon the intent behind the studies and the methodologies used. The absence of a uniform set of meaningful indices is a significant obstacle in any comparison of the different methodologies used for adequacy evaluation. This paper describes a set of load point and system indices that can be used in adequacy studies. These indices have been computed using the COMREL program developed at the University of Saskatchevan. The application of the indices using COMREL is illustrated by evaluating the adequacy of a small test system. The indices proposed and illustrated in this paper provide a basic framework for quantitatively assessing the adequacy of a composite generation and transmission system. It is expected that the indices presented in this paper will make a major contribution to the development of a standard set of overall system adequacy indices.

Monte Carlo approach in planning studies: an application to IEEE RTS

The authors describe two versions ('fast' and 'detailed') of the Monte Carlo SUCRET program for the probabilistic assessment of system adequacy and production cost during the planning of composite generation/transmission systems. Also considered is the adequacy analysis of the IEEE RTS (Reliability Test System). The application of ENEL methodology to the RTS shows that the investments related to the transmission system can be considerably reduced. A revised configuration of the RTS is thus proposed. The authors also provide RTS users with a series of indications on the behavior of the RTS transmission system and to stimulate comparison with the other alternatives that can be found by applying to the RTS other methodologies of composite system adequacy evaluation. >

Low Bus Voltage and III-Conditioned Network Situations in a Composite System Adequacy Evaluation

Low Bus Voltage and III-Conditioned Network Situations in a Composite System Adequacy Evaluation

Low Bus Voltage and Ill-Conditioned Network Situations in a Composite System Adequacy Evaluation

The adequacy assessment of bulk power systems generally involves solution of a network configuration under different outage events. Various solution techniques, depending upon the adequacy criteria employed and the intent behind the studies are available in order to analyze the adequacy of a power system. Transportation models [1,2] D.C. load flow and A.C. load flow solutions [3,14,5] are the most commonly used techniques. The transportation model approach and the D.C. load flow techniques do not take into account bus voltage violations and generating unit VAr limit violations in a network. In order to include these considerations, it is therefore necessary to employ an A.C. load flow technique to evaluate the adequacy of the system. A.C. load flow techniques are computationally more expensive and require larger storage than approximate techniques. A drawback of an A.C. load flow technique is the possible non-convergent situation for a network. Under these circumstances, it is not possible to calculate adequacy indices for the system. This paper clearly illustrates these non-convergent situations in two test systems on which adequacy studies were conducted. A heuristic approximate technique to handle these non-convergent or ill-conditioned network situations is also presented and illustrated by application to the two test systems.

Station-initiated outages in composite-system adequacy evaluation

Failure events originating in terminal stations can result in multiple outages of generators and/or lines or loads in a power system. Failures of breakers, transformers and busbar sections are major causes of these multiple outages. The effect of these outages in composite-system reliability evaluation can be quite significant. The effect of station-related multiple outages can be quite dominant and may, therefore, obviate the need to consider higher-order independent outages of major components such as generating units, transmission lines and transformers. In this paper, models are presented and discussed for various possible failure events originating in the stations. Expressions in terms of probability and frequency of appropriate states are developed for each of the failure events. These expressions are then utilised in the adequacy assessment of a composite 6 busbar test system.

Effect of higher-level independent generator outages in composite-system adequacy evaluation

Effect of higher-level independent generator outages in composite-system adequacy evaluation

Incorporation of weather effects in transmission system models for composite system adequacy evaluation

This paper illustrates the development and analysis of several transmission system models which include varying weather conditions for composite system reliability assessment. The failure rate of an outdoor component can be much higher in stormy weather than that in normal weather periods. The probability of overlapping failures in stormy weather, therefore, can be much greater than that in normal weather periods. This phenomenon is often called `failure bunching' due to the fact that components are fully or partially exposed to a common weather condition. Several methods, designated as the constant weather model, the full Markov process approach, the 4-state approximate method and the line or area addition approach are presented. The impact of these weather models in composite generation and transmission system adequacy evaluation is examined and illustrated in this paper using the IEEE reliability test system.