Features that influence composite power system reliability worthassessment

Reliability worth assessment using customer interruption costs is an important element in electric power system planning and operation. This paper deals with two features that affect the composite generation-transmission system reliability worth assessment. One feature is the incorporation of temporal variations in the cost of interruption. This paper illustrates the effect on the expected annual system outage cost of temporal variation in the interruption costs for the residential, agricultural, industrial, commercial and large user sectors. The other aspect considered in this paper is using a probability distribution approach to represent the cost of interruption model. The conventional customer damage function approach utilizes average customer costs while the probability distribution approach recognizes the dispersed nature of the customer outage data. These two methods of cost evaluation are applied to reliability worth assessment in this paper. A sequential Monte Carlo approach incorporating time varying loads is used to conduct all the studies. Case studies performed on two composite test systems show that incorporating time varying costs of interruption for the industrial sector resulted in a significant reduction in the expected outage cost. A comparison of the reliability worth obtained using the customer damage function method (CDF) with the probability distribution approach suggests that using the CDF method may significantly undervalue the reliability worth by a factor of three to four     

Bibliography on the application of probability methods in powersystem reliability evaluation: 1982-7

The authors present a bibliography of selected papers on the subject of power system reliability evaluation. The following topics are considered: static generating capacity reliability evaluation; multiarea reliability evaluation; composite generation-transmission reliability evaluation, operating reserve reliability evaluation; transmission and distribution system reliability evaluation; equipment outage data; and reliability cost/worth analysis     

Distributed nature of residential customer outage costs

Reliability worth assessment is an important factor in power system planning and operation. An equally important issue is how to use customer costs of electric supply interruptions as surrogates to appropriately quantify reliability worth. Postal or in-person surveys of electric customers are often used to determine interruption costs. The results obtained from the surveys are transformed into customer damage functions which are applicable to individual customer classes and sectors. Standard customer damage functions use aggregate or average customer costs for selected outage durations. This paper develops a practical alternative to the customer damage function method of describing the interruption cost data. The alternate technique, which is designated as the probability distribution approach, is capable of recognizing the dispersed nature of the data. The proposed probability distribution method is illustrated in this paper using the interruption cost data collected in a 1991 survey of the Canadian residential sector     

城市电网用户停电损失估算及评价方法研究

合理地估算和评价城市电网中各类用户的停电损失,为电力企业在提高城市电网的可靠性水平及应急电源优化配置的投资和决策方面提供依据。在对受停电影响造成的各类用户的经济损失进行分类调查的基础上,以峰荷时刻的停电损失为基准,建立了表示综合用户停电损失和停电持续时间关系的综合用户停电损失函数,用以估算每类用户的综合停电损失。基本计算过程为,根据各类用户的综合用户停电损失函数和停电次数的统计结果,采用停电损失评价率和每次事故停电损失2个指标来评价每类用户的停电损失。采用青岛地区53个重要用户的数据为实际算例,估算并评价了各类用户的停电损失。所得结果表明,所提出的估算和评价用户停电损失的方法,有助于电力企业确定不同可靠性水平下的应急电源优化配置成本。     

基于可靠性成本- 效益分析的电网规划

传统电网规划是以电网的直接投资费用最小为目标来满足一定可靠度的电网规划。电网规划的目的是保证电网的供电可靠性,而没有考虑由于电网的扩展所产生的经济效益,这样规划出的电网并不能获得最佳的社会效益。该文通过引入缺电成本,将可靠性与经济性结合在一起,在此基础上提出了一种新的电网规划成本-效益分析方法与数学模型,该方法将缺电成本作为供电总成本的重要组成部分,并且用缺电成本的大小来衡量可靠性效益的高低,将规划的可靠性成本与可靠性效益统一在对电网的经济性评估上。对规划方案进行了分析和评价,进一步完善了成本-效益分析方     

Reliability worth assessment in a developing country-residentialsurvey results

This paper presents the results of a residential customer survey conducted in service areas of the Nepal Integrated Electric Power System (NPS). The objective was to determine the power interruption costs incurred by the residential customers of a developing country, and extend the customer survey approach to reliability worth evaluation in a developing environment. Interruption cost estimates were obtained using in-person interviews with 944 sample customers. The results indicate the implications of service reliability to residential customers of Nepal, and show that reliability worth evaluation in a developing country is both possible and practical     

Evaluation of the marginal outage costs of generating systems forthe purposes of spot pricing

This paper describes a methodology based on quantitative power system reliability evaluation for calculating the marginal outage costs of generating systems. The proposed method involves the calculation of the incremental expected unserved energy at a given operating reserve level and lead time and the multiplication of this value by the interrupted energy assessment rate of the system. The method is illustrated in this paper by calculating the marginal outage cost profile of the IEEE-Reliability Test System and by examining the effect of various modelling assumptions on that profile     

Value of service reliability

The authors present the value of service (VOS) reliability evaluation approach, which explicitly incorporates into the planning process customer choices regarding reliability `worth' and service costs. Using the least-cost planning framework and taking advantage of the recent advances in the quantification of outage costs, this approach determines the optimal level of reliability for the utility and its customers. The approach considers system operational measures-the so-called emergency actions-that the operators invoke in times of dwindling reserves. Information on customer outage costs associated with such actions is incorporated using a probabilistic framework. This approach permits utilities to plan for levels of reliability commensurate with the customers' willingness to pay. The application of this methodology to planning problems is discussed. Numerical results for a large utility are presented     

Comparison of subtransmission system reliability worth for diverse systems by including health considerations

The fundamental concepts associated with quantitative reliability assessment of electric power systems are reasonably well established and accepted by the power industry. The evaluation of the costs and benefits of competing investments has now become a standard practice in power system planning. In order to make a consistent appraisal of economics and reliability, it is imperative to compare the investment cost needed to attain a specified level of reliability with the reliability worth or benefits derived by the society at that level of system reliability. Customer interruption costs, which serve as surrogates for the perceived worth of supply reliability, have been determined for several jurisdictions, areas, provinces, and countries as diverse as Canada, United Kingdom, Nepal, and Thailand, among others. This paper extends the well-being framework to include the societal worth of electric service reliability in subtransmission systems associated with the above four countries/systems. Systems well-being is defined in terms of the three system states of healthy, marginal, and at risk, thus combining the deterministic and probabilistic approaches into a single framework. The main objective of the paper is to present results of reliability worth indices of expected cost of interruptions (ECOST) and interrupted energy assessment rate (IEAR), for both the healthy and at risk states in the well-being framework. The concepts associated with extending the well-being framework to include reliability worth parameters are illustrated by application to a small reliability test system designated RBTS. Customer interruption data from the four countries are used in conjunction with the RBTS subtransmission system in order to obtain the reliability worth indices.     

电网供电可靠性与经济性综合评估研究

提高供电可靠性意味着巨额的投资。如何在有限资金下最大程度地提升供电可靠性指标、合理优化可靠性提升策略等问题成为电网可靠性发展面临的关键问题。建立了用户停电损失模型、可靠性评估预测模型、可靠性费用预测模型,并根据成本一效益分析法,以用户停电损失和可靠性费用之和为成本,以可靠性为效益,建立可靠性与经济性综合评估模型。可靠性与经济性综合评估协调了投资和可靠性的关系,并在此基础上制定科学合理的可靠性提升措施。     

Comparison of alternative techniques for evaluating the marginaloutage costs of generating systems

Quantitative evaluation of the marginal outage costs associated with generating systems involves, among other things, the construction of a model of the system capacity outages. This model is inherently discrete and application of the well-known and basic recursive technique requires lengthy computations when applied to large power systems. Alternatively, continuous distributions and fast Fourier transforms can be used to approximate the generating system capacity model. These techniques can in some cases introduce inaccuracies in the results, which depend on the system under consideration. Several authors have used these approximate techniques in the calculation of capacity outage probabilities, the study of parameter uncertainty in generating capacity reliability evaluation, the calculation of the expected energy production costs and the maintenance scheduling of generating facilities. This paper discusses the potential application of the approximate techniques in the evaluation of the marginal outage costs of a power system. The results of the approximate techniques are illustrated by comparison with those produced by the exact recursive technique for the IEEE-Reliability Test System     

Outage costs quantification for benefit–cost analysis of distribution automation systems

Deregulation of electric power industry has motivated electricity customers to pay more attention in evaluating both the direct cost of electric service and the monetary value of reliable electric service. This movement has been recognized by the utilities and the value-based aspects are introduced into the planning and design of power systems to consider the outage costs. The value of service reliability that can portray and respond to actual utility and customer impacts as a result of power interruptions plays a major role on justifying whether a distribution automation (DA) system is beneficial or not. However, for the value of service reliability, there are a number of factors that can affect it. To exactly evaluate the service reliability value, two formulas for quantifying the customer interruption costs and utility reduced energy revenues associated with power failures are derived in this paper. The customer types, feeder loads, feeder failure rate, number of switch, restoration time, and repair time are taken into account. The proposed formulas can provide an exact estimate in outages costs of a feeder and their computation is simplified and straightforward. The estimated outage costs can then be used to calculate the reliability improvement benefit of DA systems for the system benefit–cost analysis. A practical DA system implemented by Taiwan Power Company is used to illustrate the proposed formulas and the benefit–cost analysis result is presented. Sensitivity analysis is also performed to reduce the effects of benefit–cost analysis parameters on the analysis result.     

Implications of on-site distributed generation for commercial/industrial facilities

Next-generation distributed generation (DG) is poised to become a key element in our energy future. Recognizing the increased need for a higher reliability energy system and a cleaner environment, This work presents a technique that helps to identify the impact of grid-connected DG on the reliability of on-site electric power. This analysis shows the optimal DG mix at various facility outage costs with and without an emission restriction. The impact of varying the grid reliability and the capital costs of DG units on the decision to invest in backup power is discussed. The break-even costs of microturbines are also estimated at various facility outage costs and microturbine forced outage levels.     

Evaluation of the marginal outage costs in interconnected andcomposite power systems

The structure of electric utilities is undergoing dramatic changes as new and expanded service options are added. The concepts of unbundling the electric service and offering customers a range of new services that more closely track actual costs are expanding the options open to customers. Spot pricing provides the economic structure for many of these new service options. An important component of spot prices is the marginal outage cost incurred by customers due to an incremental change in load. This paper presents a formalized approach of calculating the marginal outage cost in interconnected generating systems and composite generation and transmission systems using quantitative reliability techniques. The effects of selected pertinent factors on the marginal outage cost in composite systems are also presented. The proposed methods are illustrated by application to the IEEE-Reliability Test System (IEEE-RTS)     

基于改进遗传算法的风力－柴油联合发电系统扩展规划

提出基于改进遗传算法的风力-柴油联合发电系统容量扩展规划模型,在满足系统规划和运行等非线性约束条件下,寻求总成本最小的容量扩展方案。在规划总成本中除了计及机组建设的投资费用和运行费用以外,还考虑了因电力供给不足所造成的需求侧停电损失成本。在模型中采用蒙特卡罗方法计算系统的概率性发电成本,不仅考虑了风速随机性、机组随机停运、风速序列和负荷序列相关性,而且考虑了风电穿透功率极限的约束。算例表明,文中所提出的模型和算法是可行的,能对风力发电的规划设计提供一定的帮助。     

Effective techniques for reliability worth assessment in compositepower system networks using Monte Carlo simulation

Reliability cost/reliability worth assessment plays an important role in electric power system planning and operation. The paper proposes a technique for evaluating the costs of interruption and hence, the reliability worth in a composite power system network with time varying loads at load buses using sequential Monte Carlo simulation. A generalized methodology of determining the interruption costs, without considering the time varying aspect of the loads is discussed and the results are compared with those obtained by utilizing a load duration curve to represent the time dependent loads. Case studies conducted on the IEEE Reliability Test System (IEEE-RTS) are presented and discussed     

同时计及设备老化与不完全维修的电力系统可靠性评估

在电力系统可靠性评估中,建立精确的元件停运模型至关重要。传统模型忽视了设备老化与维修更新性的影响,导致评估误差随着元件运行时间增长而不断增大。针对这一严重不足之处,提出了计及设备老化与不完全预防性维修的元件时变停运概率模型。该模型采用虚拟年龄与改善因子表征预防性维修对故障率的降低效应,采用威布尔模型表征时间对故障率的增长效应。应用所提出的模型对改进的IEEE RTS-79系统进行了可靠性评估。通过改变部分系统元件的维修成本和预防性维修周期模拟实际维修,给出了新模型中不同维修策略的系统可靠性评估结果,并与传统方法进行了对比分析。结果表明提出的模型能更准确地反映实际维修效果,更精确地预测电力系统中长期可靠性水平。     

Farm losses resulting from electric service interruptions-aCanadian survey

A summary of results is presented of a postal survey of Canadian farm operators conducted to evaluate the direct and short-term costs and impacts resulting from local random electrical supply interruptions. Statistics Canada's Standard Industrial Classification (SIC) was used to categorize farms into groups and subgroups, and the composition of the survey sample was intended to reflect the relative importance of the various farm categories to the geographical regions across Canada. Most Canadian utilities which serve farm customers participated in the project. The survey was designed to obtain the consumer's valuation of interruption costs using three approaches: an indirect worth evaluation based on the preparatory actions the consumer predicted he would take given a specified (un)reliability, a direct estimate of worst-case costs, and an attempt to indicate expected rate reductions commensurate with a specified reduction in reliability. Principal variations of cost estimates are briefly discussed. Information concerning primary effects of interruptions is presented, and the availability, type, and size of standby equipment are reported     

可靠性与经济性协调的输电线路最大利用率评估方法

电网运行由于受各种因素制约,若仅以可靠性作为判据进行评估,则输电线路最大利用率处于较低水平。针对这一问题,通过对年持续负荷曲线的分析,提出一种基于经济性与可靠性协调的输电线路最大利用率评估方法,通过协调电力系统可靠性与经济性,得出现有线路年平均利用率真正能够达到的最高水平。评估中首先计算系统满足可靠性约束的年最大负荷,进而对持续负荷曲线超过年最大负荷部分作为过负荷切除,并按照可中断负荷方式给予切负荷赔偿;对于年持续负荷曲线中保留部分,针对其电量不足期望值给予停电损失赔偿。二者共同组成可靠性的经济代价,将其增长速度与电网售电带来的经济效益增速比较,只要可靠性的经济代价增速更慢,评估中系统最大年利用率就仍有提升空间。将该方法应用于IEEE RTS79系统,结果表明此评估方法较传统安全评估结果更高,能够进一步开发线路利用空间,充分利用输电线路的可用容量。     

考虑微网源荷不确定性的旋转备用容量优化

电力市场环境下,为应对微网源荷波动和可控机组随机故障,提升其供电可靠性,提出了一种考虑微网源荷不确定性的旋转备用容量优化方法。计及日前预测误差,采用序列理论对源荷随机概率性序列以及可控机组随机故障序列进行离散化处理,生成微网综合不确定性离散分布模型;在此基础上,以微网运行成本、备用成本和停电损失的总成本最小为目标函数,建立旋转备用容量优化模型,并结合蒙特卡罗与粒子群算法对该模型进行求解,获得各时段的旋转备用优化配置容量。以某地微网系统为例,仿真验证了所提方法的有效性和合理性。