Current practices and customer value-based distribution system reliability planning

Among the major issues facing utilities in today's competitive electricity market is the pressure to hold the line on rates and provide electricity with adequate quality and reliability. Utilities are increasingly recognizing that the level of supply reliability planned and designed into a system has to evolve away from levels determined basically on a technical framework using deterministic criteria, and toward a balance between minimizing costs and achieving a sustainable level of customer complaints. Assessment of the cost of maintaining a certain level of supply reliability or making incremental changes therein must include not only the utility's cost of providing such reliability and the potential revenue losses during outages, but also the interruption costs incurred by the affected customers during utility power outages. Such a cost-benefit analysis constitutes the focal point of the value-based reliability planning. Value-based reliability planning provides a rational and consistent framework for answering the fundamental economic question of how much reliability is adequate from the customer perspective and where a utility should spend its reliability dollars to optimize efficiency and satisfy customers' electricity requirements at the lowest cost. Costs to customers associated with varying levels of service reliability are significant factors that cannot be ignored. Explicit considerations of these customer interruption costs in developing supply reliability targets and in evaluating alternate proposals for network upgrade, maintenance, and system design must, therefore, be included in system planning and design process. The paper provides a brief overview of current deterministic planning practices in utility distribution system planning, and introduces a probabilistic customer value-based approach to alternate feed requirements planning for overhead distribution networks.     

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     

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     

Distribution system reliability cost/worth analysis usinganalytical and sequential simulation techniques

The requirements for extensive justification of new facilities and emphasis on the optimization of system cost and reliability are steadily increasing. Customer interruption cost analysis provides valuable input to electric power supply reliability worth assessment. This paper presents both a generalized analytical approach and a time sequential Monte Carlo simulation technique for evaluating the customer interruption cost in complex radial distribution systems. Studies are conducted on two practical distribution systems. The results obtained using the analytical technique incorporating average restoration times are compared with those obtained using the time sequential simulation method and random restoration times. The effects on customer interruption cost indices associated with alternate supply and protection devices are also considered     

英国供电安全工程建议ER P2/6浅析

英国电力委员会制订的供电安全工程建议ER P2/6是英国关于配电网规划的指导性文件,该文件以最终客户的供电可靠性为规划目标,将系统安全性与客户负荷大小相关联,应用停电频率、停电持续时间等主要的电网可靠性指标,结合运行方式及其他有关数据来估计系统的运行特性及发展趋势,对可靠性投资费用和效益进行分析,为正确的投资决策提供依据。文章分析了ER P2/6的背景、内容、特点、理论基础和实际应用,并通过实际案例验证了该文件的实效性。文章还以ER P2/6为参考,客观地审视了我国目前电网规划设计和调度运行中有关电力可靠性标准的理念及标准应用方面的不合理之处,提出了相关意见和建议。     

计及可靠性评估的中压配电网规划方案比选

从可靠性参数搜集及计算方法和备选规划方案比选两方面切入,进一步丰富DL/T 1503—2016中压配电网可靠性评估导则在规划中的应用,提出了基于可靠性评估的中压配电网的方案形成与比选方法,内容包括相关参数的搜集、可靠性计算方法和方案比选。综合考虑可靠性与经济性,基于"有无对比法"给出配电网投资的增量净效益计算模型,并分析不同网架供电能力与负荷需求关系下净效益简化模型与全寿命周期成本最小化比选方案的异同。基于全寿命周期净现值、净现值率等动态指标进行投资成本效益分析,可用于多个方案的比选。案例表明,本文方法有效。     

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.     

A Framework to Implement Supply and Demand Side Contingency Management in Reliability Assessment of Restructured Power Systems

This paper presents a framework to implement supply and demand side contingency management in the reliability assessment of hybrid power markets. A model for the independent system operator (ISO) to coordinate reserve and load curtailment bids for contingency states is introduced to balance reliability worth and reliability cost. The load curtailments and generation re-dispatch for a contingency state are determined based on minimizing the market interruption cost using an optimization technique. A nonsequential Monte Carlo simulation technique based on this framework has been proposed to evaluate the customer reliability of restructured power systems with the hybrid market model. The modified IEEE Reliability Test System (RTS) is used to illustrate the proposed technique     

配电网供电可靠性提升及定量测算分析

本文针对供电可靠性提升的各种措施,通过可靠性评估软件对其进行仿真计算,对提升供电可靠性的各类措施运用收益增量/成本增量的评估方式进行逐一比较,选出最优方案,并绘制Pareto曲线。     

基于停电损失费用的变电站经济容量研究

考虑供电可靠性并将其转化为停电损失费用来进行经济分析是城市电网规划的必然趋势。在综合考虑电网的建设投资、运行费用的基础上,将停电损失费用有机地结合到电网规划的优化目标中,以单位供电面积的年费用最少为原则,提出了确定变电站经济容量的计算方法,并给出了相应的计算流程。以佛山电网为计算实例,说明确定变电站经济容量时考虑停电损失费用的必要性,验证了该方法的合理性和有效性。     

配电网用户感知停电事故严重性分析及可靠性评估

可靠性评估对于指导配电网规划设计具有重要意义。传统配电网可靠性评估主要从系统侧供电的角度,建立评估指标体系并进行分析,较少考虑停电发生时用户侧的用能需求差异,忽视了不同用户对于同一停电事故严重性的差异化感知,进而造成了传统可靠性指标不能完全准确反映停电事件对于不同用户在不同时段的差异化影响。为解决上述问题,首先,提出了用户感知可靠性的概念,并提出了一种用户对停电事故严重性感知的量化方法,以分析不同用户对停电事故的严重性感知程度及停电容忍程度;然后,分别从用户侧和系统侧提出了一系列基于用户感知的配电网可靠性评估新指标,建立了相应指标体系,并围绕该体系对配电网系统的可靠性评估开展了研究;最后,运用IEEE-RBTS标准算例对所提出的方法、指标进行了计算验证,证明了其可行性及正确性;并通过与传统可靠性指标的对比分析,体现了用户感知可靠性指标相较于传统评估指标的客观优势。     

配电网可靠性定量评估及成本/效益分析软件包研究

在综合应用配电系统可靠性理论、成本 /效益分析理论、图论以及面向对象的计算机编程技术基础上 ,研究开发了用于定量评估配电网供电可靠性以及进行可靠性成本 /效益分析的软件包系统。介绍了该系统的设计开发思路、软件包工作流程和功能以及有关的主要技术特点等。最后 ,应用该软件包系统对我国某地区中压配电网的供电可靠性进行了定量计算 ,并对为提高可靠性而投入的成本以及所获得的效益进行了分析比较。研究结果可以为电网的规划人员与运行管理人员提供决策依据     

供电可靠性承诺/赔偿法

可靠性的经济性评估可分为3个层次。第1层次是将电力系统作为一个整体，研究投资与可靠性之间的关系；第2层次是将社会作为一个整体，研究提高可靠性的收益与停电损失之间的关系；第3层次以供电企业为整体，研究可靠性承诺与赔偿之间的关系。文中提出适合国情的城网可靠性承诺/赔偿方法，可用于城网改造的效益评估。该方法基于成本/效益分析法，按市场经济原则对电力这种特殊商品的价格进行分析。新方法将电价机制与可靠性有机地结合起来，为建立优质优价、停电赔偿的新电价体制提供了理论支持，努力达到电力公司和用户双赢的目标。     

基于GA的发输电合成系统最优可靠性计算新方法

将可靠性和经济性相结合,提出了基于总拥有费用法的发输电合成系统最优可靠性算法的总体框架,进而在概率安全性和概率充裕度综合评估基础上,将综合评估风险指标和可靠性经济评估理论相结合,建立了基于遗传算法和蒙特卡罗仿真相结合的最优可靠性计算模型和算法。算法使最终求得的各元件的最优解所对应的规划方案的总成本最小。最后对IEEE—RTS标准测试系统进行了计算,结果表明所提模型和算法是可行的。     

一种基于半马尔柯夫过程的配电系统可靠性经济评估方法

针对配电系统故障时间分布不确定的特点,提出了基于半马尔柯夫过程的可靠性经济评估通用方法。建立元件寿命、预防维修时间和修理时间服从任意分布的可靠性评估模型,引入用户停电损失函数研究系统在不完善预防维修情况下的停电损失;通过实例证明了该方法的正确性,显示出该方法对Homogenous M arkov和W e ibu llM arkov算法的兼容性、有效性,同时更清晰地反映了元件故障持续时间分布对系统可靠性经济指标的影响。     

Power Distribution Protection System Design with Momentary Interruption Consideration

An objective of protection system design is to support the system to serve its customers with highly reliable and low-cost power supply. In this paper, a radial distribution protection system design is formulated as a binary integer programming problem to identify number, types, and locations of the protective devices in order to optimize system total cost. The formulated problem takes into account not only the reliability of system components' but also the cost of utility investment and customer interruption, which comprises permanent and momentary interruption. The proposed method has been tested with an actual system with satisfactory results, from which it clearly shows the necessity of the inclusion of the customer interruption cost into the design problem. Copyright © 2009 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

电网规划中的可靠性成本-效益分析研究

通过定义可靠性边际成本与可靠性边际效益概念,阐明电网规划中的可靠性成本＿效益分析问题。以用户缺电成本大小衡量可靠性效益高低,将规划的可靠性成本性效益统一在对电网的经济性评估上;通过构造缺电损失评价率给出缺电成本计算方法。最后通过计算缺电损失评价率以及相应的缺电成本,说明了所提方法的可行性。     

基于序贯蒙特卡罗仿真的配电网可靠性评估模型

提出了考虑线路容量约束和潮流分布的基于序贯蒙特卡罗仿真和时变负荷模型的评估配电网可靠性的模型.模型中切负荷策略综合考虑了停电损失费用、停电电量、网损和停电时间,因而该模型在模拟配电网的故障和负荷点停电情况方面更加符合实际运行情况,并可以评估不同调度策略下的可靠性风险指标和可靠性效益指标的影响.经采用IEEE RBTS配电系统测试,结果表明该模型是合理的、有效的.     

考虑可靠性成本的配电网多阶段扩展规划方法

传统的配电网可靠性评估通过模拟组件中断来量化一组事件对供电可靠性的影响,这种基于模拟的可靠性评估方法使得其纳入到配电网扩展规划中需要采用启发式或元启发式方法求解。为了克服启发式或元启发式方法收敛性和局部最优的缺点,文中提出了考虑可靠性成本的配电网多阶段扩展规划的混合整数线性优化模型。该模型建立了配电网可靠性指标(即系统平均停电持续时间指标、系统平均停电频率指标和系统缺供电量)的显式评估表达式,并将其相关的可靠性成本纳入到配电网多级扩展规划目标函数中,以系统运行约束等为约束条件。在24节点、54节点、86节点和138节点四个算例系统上验证了所提出的方法的有效性和适用性。     

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.