Utilization of time varying event-based customer interruption cost load shedding schemes

Load curtailments occurring under emergency conditions can have significant monetary impacts on the system customers. Customer satisfaction is becoming increasingly important in the new deregulated electric utility environment, and the customers in some jurisdictions are beginning to receive monetary compensation for power supply failures. Minimizing the customer interruption costs associated with a load curtailment event is an important factor in maintaining customer satisfaction. Customer interruption costs depend on many factors such as the customer types interrupted, the actual load demand at the time of the outage, the duration of the outage, the time of day and the day in which the outage occurs. This paper focuses on incorporating these interruption cost factors in a load shedding strategy. The load shedding algorithm was developed using an approximate event-based customer interruption cost evaluation technique to identify and determine the priority of the distribution feeders on a given bus during an emergency. The developed algorithm incorporates a time dependent feeder cost priority index (FCP). The optimum load shedding set determined using the FCP is a feeder or group of feeders that meet a capacity deficiency, and result in the lowest customer interruption cost for the specified emergency situation. This paper illustrates the algorithm development for a load shedding scheme and demonstrates the utilization of the technique on a sample load bus.     

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。     

Economic Evaluation of a Distribution Automation Project

To deal with the deregulated challenges in future power system operations, Taiwan Power Company (Taipower) has taken a strategic approach to implement an extensive Distribution Automation (DA) project including feeder automation (FA), trouble call management, load management, and remote metering functions in its Tai-Chung District. The project was completed in December 2002. For future extension purposes, Taipower tries to develop a comprehensive generalized step-by-step methodology for the economic evaluation of the DA project. This paper presents the methodology and results for the economic evaluation of the Tai-Chung DA project. The potential benefits of the implemented DA functions are quantified using standard mathematic formulas. An economic evaluation method using value-based analysis and present-worth analysis is performed to identify the most beneficial functions in the Taipower's implemented DA functions. Those DA functions that have great benefits should have high priority to be implemented in other distribution districts. Moreover, to find the candidate feeders for further FA extension, the sensitivity analysis of the benefit/cost ratio with respect to different customer types, feeder loads, feeder lengths, numbers of switch, and failure rates is also conducted. Accordingly, the optimum number of switch can be determined under the expected service reliability. The results and formulas obtained in this paper can also be used for return-of-investment or possible performance measure of the DA systems.     

A value-based probabilistic approach to designing urban distribution systems

Achieving high distribution reliability levels and concurrently minimizing capital costs can be viewed as a problem of optimization. Assuming given outage rates and repair times, distribution system design is the remaining factor in determining customer reliability. Including customer value of reliability in an economic analysis allows for optimization of the major components of distribution system design. Using mathematical models and simulations, a comparison of design concepts can be performed to compute the optimal feeder section length, feeder loading level, and distribution substation transformer loading level. The number of feeder ties and feeder tie placement are also optimized through the models. The overall outcome of this analysis is that capital costs can then be directed towards system improvements that will be most cost-effective in improving system reliability. This paper presents a value-based probabilistic approach to designing urban distribution systems. The value-based reliability methodology is illustrated using a practical urban distribution system of MidAmerican Energy Company.     

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     

An electric power purchase strategy for bilateral contracts focusing on reliability of customers

With the introduction of the competitive electrical power market, large‐scale customers can select electric power suppliers. Customers need to consider not only the economical efficiency but also reliability, to decide the amount of electrical power to purchase. This paper develops an economic electric power purchase strategy for customers focusing on reliability. A bilateral contract model expressing electric power suppliers as generators with a forced outage rate is proposed and introduced to assess potential outage risks of the bilateral contract between an electric power supplier and a customer. The outage‐related cost, consisting of potential outage risks and the estimated outage cost, is also proposed and introduced as an index of the reliability on the customer side, and an optimal reliability level of a customer is obtained by using the index. Several numerical examples demonstrate the availability of the proposed electric power purchase decision method and reliability improvement strategies for customers are discussed. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 156(4): 9–21, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20345     

Fast tripping of utility breakers and industrial load interruptions

Some industries are very sensitive to electric power interruptions and voltage sags, which are a normal consequence of the utility fault-clearing process. Typically, US utilities will try once or twice to clear faults without blowing any tap fuses, which would require dispatching a trouble crew to replace. To reduce complaints and to improve power quality for critical customers with high economic impact of interruptions, some utilities have been eliminating fuse-saving practices on feeder breakers and reclosers. The impact on overall reliability and the number of interruptions is evaluated based on distribution feeder power quality data. Some degradation in overall reliability can be expected, but this can be minimized with judicious placement of line reclosers. Critical customers can expect a significant reduction in the number of interruptions. A value-based economic analysis, including both utility and customer costs, shows that the practice has a high overall benefit-to-cost ratio. The utility experiences increased costs, but these are frequently overshadowed by the potential customer savings. However, removing fast tripping may correct for only a small portion of the utility-related events that might disrupt sensitive industrial processes. This article analyzes the impacts of removing fast tripping on reliability indices and on power system economics     

Optimal transmission expansion planning for electric power systems

This paper presents a new method for transmission expansion planning in which the utility loss revenue and the customer outage cost resulting from service outages are incorporated. A new algorithm based on the total probability formula is developed for evaluating the expected value of demand not served (EDNS) and the expected value of energy not served (EENS). These reliability indices are employed to determine the utility loss revenue curve. The system expansion cost curve is obtained by using a maximum reliability design algorithm. The optimal reliability level of a transmission expansion plan is determined by minimizing the sum of the investment cost, the utility loss revenue, and the customer outage cost. An example is presented for illustration of the proposed method.     

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     

Value-based distribution system reliability planning

Society is becoming increasingly dependent on a cost-effective reliable electric power supply. Unreliable electric power supplies can be extremely costly to electric utilities and their customers. Predictive reliability assessment combines historical outage data and mathematical models to estimate the performance of specific network and system configurations [e.g., IEEE Std. 493-1990]. This paper is concerned with the value-based assessment of proposed modifications to an existing industrial distribution system configuration to minimize the costs of interruptions to both the utility and its industrial customers. This paper presents a series of case studies of an actual industrial load area supplied by two feeder circuits originating from two alternate substations. Each case study reveals the impact on the cost of industrial load point interruptions and the frequency and duration of industrial load point interruptions when various system constraints (e.g., ideal and nonideal protection coordination schemes, substation capacity restrictions, etc.) are imposed on the distribution system. The paper discusses in some detail the variance in reliability performance indexes and their impact on the cost of load point interruptions. A basic conclusion of this paper is that expansion plans of an industrial distribution system can be optimized in terms of reliability by using an economic criterion in which the sum of both the industrial facility interruptions and the utility system costs are minimized     

Estimating Power Outage Costs Based on a Survey of Industrial Customers

Thousands of factories in Japan responded to a survey on power outage costs for industrial customers. From across the country, 5139 facilities designated as energy management factories answered questions about their power consumption and the loss of production value due to a hypothetical hour‐long power outage on a summer weekday. Using their responses, we estimated the median unit cost of a power outage across all sectors to be 672 yen/kWh. The service sector of amusement and hobbies and the manufacturing sector that makes electronic information and communication equipment have relatively high unit costs for power outages. The direct cost of damage from a specified power outage across all sectors totaled 77 billion yen. Using input–output analysis, we estimated the indirect damage costs caused by the repercussions of halting production. Indirect damages across all sectors totaled 91 billion yen. The wholesale and retail trade sector had the largest direct damage costs, while the transportation equipment manufacturing sector has the largest indirect damage costs. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 185(4): 25–32, 2013; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.22306     

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     

分级电价的研究

分级电价考虑了用户的用电特性和缺电成本，通过弹性化的电价方案来达到负荷管理的目的。我国电力短缺，资金匮乏，应重视这方面的研究。本文阐述了分级电价的概念及其意义，探讨了分级电价与缺电成本的关系，并介绍了分级电价的制订成本。     

Distribution Feeder Scheduling Considering Variable Load Profile and Outage Costs

In a deregulated power market, customers would have more choices for their power service and the improvement of service quality has become a challenge to power transmission and distribution companies. Distribution system reliability that was traditionally considered within the planning activities is now incorporated in the operational environment. This paper presents study results of a multiobjective feeder operation optimization problem that considers how to balance network efficiency, switching and reliability costs in a distribution network. The proposed method divides annual feeder load curve into multiperiods of load levels and optimizes the feeder configurations for different load levels in annual operation planning. Customer load profiles and seasonal varying data of feeder section failure rates and customer interruption costs are considered. Numerical simulations demonstrate the time-varying effects on the optimal distribution feeder configuration and operation costs. A binary particle swarm optimization (BPSO) search is adopted to determine the feeder switching schedule. Test results indicate that not considering time-varying effects and using only simplified fixed load and reliability parameters could underestimate the total loss to the utility and its customers.     

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     

缺电成本及其调查估算方法的探讨

介绍了缺电成本的类型及其影响因素,通过构造用户停电损失函数和利用缺电功率、缺电电量方法以及通过近似构造停电损失评价率,分别介绍了缺电成本的三种调查估算方法,并以此阐述了缺电成本与经济可靠性的关系。缺电成本的调查估算方法在实地应用后,说明缺电成本的调查估算方法是可行的。     

Distribution feeder reliability studies

As the power industry moves into a new competitive era, the reliability of radial distribution feeders becomes a primary issue in comparing the “new” versus the “old” way of serving customers. In order to make the comparison, a distribution engineer needs to have the analysis tools to perform the necessary reliability studies. For the purposes of this paper, the reliability studies will be limited to the calculation of the annual “outage rate” and associated “restoration time” for a typical customer on a radial distribution feeder. This paper develops the background and theory for computing these reliability indices. The method can be applied to demonstrate how different devices and/or feeder configurations affect the average customer on a specific feeder     

Factors Affecting the Development of a Commercial Customer Damage Function

The assessment of reliability cost/reliability worth is an important aspect of power system planning and operation. Reliability cost evaluation has become a relatively well established procedure compared with reliability worth evaluation. This paper presents the results of an investigation of the effect of standby equipment on both the consumption and demand normalized outage costs in the commercial sector. The results of a comprehensive study to find the outage costs for respondents with and without standby systems, and the seasonal variation of these costs, are presented. The development of a localized customer damage function utilizing the data is explored.     

基于GE Smallworld GIS的停电分析系统研究

本文提出了基于GE Smallworld GIS的停电分析系统,它是建立和维护从变电站至用户馈线连通性模型的工具.该系统可对配电网有关信息进行地理聚焦定位,可在GIS视图中进行停电范围分析和模拟停电分析,是配电网操作人员的一个决策支持工具.在综合环境中它可与企业的其它信息系统相互作用,是配网综合停电管理系统成功设计和实施的关键.研究的结果表明,该系统有很好实用价值,在停电管理方面的性能非常好.     

分界负荷开关在10 kV架空线路上的应用

分界负荷开关在10 kV馈电架空线路上的应用可大大减少无故障线路连带性的事故停电、缩小故障停电范围、缩短用户停电时间,从而提高所带用户的供电可靠性。