Evaluation of reliability indices accounting omission of random repair time for distribution systems using Monte Carlo simulation

This paper describes a methodology for reliability assessment of electrical distribution system accounting random repair time omission for each section. A distributor segment in a distribution system has failure rate and repair time which decide mean up time (MUT) and mean down time (MDT) at load points. Usually the reliability analysis is based on exponential failure and repair laws. The repair time is a random variable. Certain values of repair times are smaller which may be neglected based on the tolerance time of consumers at each load point. Complete reliability analysis with repair time omission has been presented. Modified mean up time, mean down time and unavailability (h/year) have been obtained at each load point using state transition sampling technique. These have been obtained accounting outage due to random repair time omission. The methodology has been implemented on two distribution systems.     

Differential evolution based technique for reliability design of meshed electrical distribution systems

This paper describes a methodology for allocating repair times and failure rates to segments of a meshed distribution system using differential evolution (DE) technique. A cost function based on Duane’s reliability growth testing model has been proposed. Constraints on basic reliability indices i.e. failure rate, average interruption duration and average interruption duration per year have been accounted. The algorithm has been implemented on a meshed distribution system and results have been compared with those obtained using particle swarm optimization (PSO) and co-ordinated aggregation based PSO (CAPSO).     

Probabilistic reliability indices evaluation of electrical distribution system accounting outage due to overloading and repair time omission

This paper presents a methodology for modifying failure rate and repair time of a distributor segment accounting the outage due to overloading and omission of critical repair time termed as repair tolerance time. Necessary relations have been derived for modifications of failure rate and repair time of a distributor and these modified failure rate/repair time have been used to evaluate average failure rate, average outage duration and average outage duration per year for distribution systems. The methodology has been implemented on a meshed distribution network and results have been compared with those obtained with unmodified failure rates/repair times.     

Analytical Complex Distribution System Reliability Evaluation Considering Stochastic Interruption Durations and Network Reconfigurations

A reliability enhancement scheme for an electric distribution system is impossible to be cost-effective without the guidance of accurate reliability index estimations. As one of the widely used basic reliability indices, average interruption duration is of foremost concern, due to being a straightforward indicator of the electric power supply quality in the aspect of customer satisfaction to the incident response capability of electric utilities to outage events. This paper proposed an analytical distribution system reliability evaluation method that allows for considering stochastic load point interruption durations together with stipulated network reconfiguration constraints. Through case studies on the Roy Billinton Reliability Test System, advantages of the proposed method over a traditional section technique-based reliability evaluation method are discussed. The proposed method is validated to yield more realistic estimations in the case of considering stochastic interruption durations and post-fault network reconfigurations, thus is expected to be capable of supporting economical system reliability-enhancing decision-making.     

A probabilistic method for establishing the transformer capacity insubstations based on the loss of transformer expected life

A method is presented for computing reliability indices, probability, duration frequency, and the loss of transformer expected life. The probabilistic model takes into account the variables affecting the loss of transformer expected life, daily load curve, transformer forced outage rate, outage duration, occurrence time of forced outage and expected overload duration. Comparing the results of this model with those of Monte Carlo simulation an acceptable degree of accuracy is achieved. From the reliability indices, a reliability criterion is obtained for rating transformers in substations, which have traditionally been rated on the basis of conservative deterministic criteria     

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。     

基于Semi-Markov的配电可靠性成本估计

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成本评估通用方法。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 Markov和Weibull Markov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。     

基于混合算法的复杂配电系统可靠性评估

提出了基于状态转移和蒙特卡洛模拟(M on te C arlo s im u lation,M CS)的配电系统可靠性评估算法。算法根据配电系统中断路器、分段开关、联络开关等可操作性元件的动态特性对系统建立彼此独立的状态转移链,并利用M CS法模拟元件故障事件发生状态转移,统计各元件及各状态的故障频率、故障发生时间和故障持续时间等参数,最后利用这些参数计算各负荷点的基本可靠性指标及其概率分布。文章通过对RBTS(re lia-b ility test system)算例的计算分析,验证了所提算法的有效性。并分析了TTR(tim e to repa ir)、TTS(tim e tosectiona lize)的概率分布以及熔断器的可靠度对可靠性指标的影响。     

Fuzzy Reliability Assessment of Distribution System with Wind Farms and Plug-in Electric Vehicles

Abstract

The equipment failures are highly uncertain in nature and simple average failure rate will not reflect this uncertainty. The uncertainty level further increases in reliability evaluation due to the integration of wind farm (WF) because of the intermittent nature of wind speed and random charging patterns of plug-in electric vehicles (PEVs). In this work, the uncertain variables in the distribution system (failure rate, repair time, WF output, PEVs charging and system load factor) are represented as fuzzy numbers to handle the uncertainty. The available uncertain data are used to find the probability distribution function (PDF) of that parameter and is converted into fuzzy membership function using transformation techniques. Failure rate of equipment is converted into failure probability using Monte Carlo simulation (MCS) method. Sampling method is applied to create the PDF of a variable which has average value. Fuzzy severity index (FSI) is proposed to find the importance of an equipment on reliability and is evaluated by measuring the fuzzy distance between the fuzzy reliability indices. The proposed assessment method is validated on modified RBTS bus 2 by comparing with analytical and MCS methods. The proposed method has been tested with integration of WFs and PEVs.     

The evaluation of reliability of supply to receivers from a network node with an automatic reserve switching system

The paper presents basic equations for determining reliability indices of network nodes equipped with automatic reserve switching systems (ARSSs).These equations can be applied to large networks with multiple sources and different configurations.A method is presented for calculating the failure rate and expected frequency of interruption of transmission and distribution systems equipped with an ARSS.The average time duration of an interruption for each network node with an ARSS can be determined.Time duration of manual switching to the reserve supply system, in the case of malfunction of the ARSS, has been taken into consideration in determining reliability indices for network nodes. Automatic protective system misoperation and faulty switch-gear operation have also been considered.     

Reliability design of distribution systems using modified genetic algorithms

This investigation presents an evolutionary algorithm to reliably design a distribution system. Adopted reliability indices include failure rate and interruption duration, which are both commonly used in distribution systems. The total cost including the apparatus investment cost and the system interruption cost, is the objective function to be minimized. Reliability constraints on a load point are addressed to ensure the adequacy of the power supply of the load point. The evolutionary optimization algorithm is a modified genetic algorithm (GA), which uses binary and floating-point representations. The proposed GA is compared with the conventional generalized reduced gradient (GRG) method. A secondary substation of the Taiwan Power Company is used in an example of the method's application. The discussed method is simple and effective and is useful for expanding the existing systems and constructing new systems.     

Impact of manual versus automatic transfer switching on the reliability levels of an industrial plant

Detailed reliability modeling and analysis of industrial plants provides an estimate of the frequency and duration of load point interruptions. The duration of repair and switching activities necessary to restore a unique power system configuration to a normal operating state from an outage state has a significant impact on the power system reliability levels of industrial power systems. This paper presents and discusses the significant variations in the frequency and duration of load point interruptions at an industrial plant due to manual and automatic switching activities. Three case studies with different percentages of open- and short-circuit failure modes of circuit breakers and fuses will also be presented and discussed for both manual and automatic switching restoration activities.     

配电系统中变电站智能化升级策略

代表变电站技术发展趋势的智能变电站是智能电网的重要组成部分。智能变电站的配置对系统安全与经济运行具有重要影响,是值得研究的重要问题。在此背景下,研究了计及可靠性的配电系统中变电站智能化升级问题。首先,以变电站智能化升级成本和用户停电损失之和最小化为目标函数,考虑系统平均停电时间(system average interruption duration index,SAIDI)和电量不足平均值(average energy not supplied,AENS)这2个可靠性指标不超过给定阈值等约束条件,构建了配电系统中变电站的智能化升级优化模型。之后,发展了针对配电系统故障的故障清除模型,提出了评估用户停电时间的比较准确的方法。接着,对用户停电时间和用户停电损失函数进行线性化处理,得到变电站智能化升级问题的混合整数线性规划模型,并采用高效商业求解器求解。最后,以IEEE RBTS-Bus 4配电系统和丹麦某中压配电系统为例来说明所提方法的基本特征。     

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。     

基于元件层级和电源可达性的配电网可靠性评估混合算法

提出一种配电网可靠性快速评估算法以解决重复遍历网络拓扑的问题。以开关元件为界形成配电系统元件分区和负荷分区。提出建立元件等级和开关层级以直接判断动作保护元件的位置,结合高度稀疏的等效支路连接矩阵快速分析负荷与电源及备用电源之间的可达性,建立等效负荷故障后果模式列表。采用序贯蒙特卡罗模拟,根据元件所属分区搜索负荷故障类型,统计故障停电次数和停电时间,计算可靠性指标。分别以各元件分摊的负荷故障时间和系统缺供电能量辨识负荷点和系统的薄弱环节。算例验证结果表明,该算法能正确高效地计算可靠性指标,适用于复杂配电网可靠性评估。     

基于FD—MonteCarlo混合法的节点电价和节点可靠性指标评估

电力市场环境下,节点电价和节点可靠性指标能提供系统运行的经济信息和风险信息。为研究市场条件下元件随机故障和计划检修对节点电价和节点可靠性指标的影响,在应用MonteCarlo法模拟系统状态转移的过程中,采用Frequency—DurationTime（FD）法解析地计算确定性事件和随机事件发生后状态的期望持续时间。考虑到可中断负荷缓解系统阻塞和抑制节点电价的作用,设计了一个2层优化模型来确定节点电价和负荷中断量,并提出了一种启发式算法进行求解。最后以一个6节点的可靠性测试系统（RBTS）为例对所提模型和算法进行了说明。     

A basic framework for sub-transmission system health analysis

The reliability of supply in sub-transmission systems is usually quantified in terms of two sets of indices, the individual supply/load point indices (average failure rate, average outage duration and average annual unavailability) and the system performance indices (SAIFI, SAIDI, CAIDI, ASUI, ASAI, etc.). These probabilistic indices are very useful not only for assessing the severity of system failures in future reliability predictions but also in assessing the system’s past performance. Many utilities, however, continue to use deterministic methods (rule-of-thumb methods) to assess the reliability of their systems. This paper presents a method designated as system well-being analysis, which in addition to the conventional probabilistic risk index of supply point unavailability, also incorporates the specified deterministic criteria in defining additional system healthy and marginal states. The proposed method is illustrated in this paper to calculate the well-being indices of electric sub-transmission systems. The proposed technique, which can be used to evaluate the adequacy of sub-transmission systems, is applied in this paper to a small but comprehensive test system to show the effects of some pertinent factors and deterministic criteria on the system well-being indices.     

Bus-based reliability indices and associated costs in the bulkpower system

This paper presents a methodology to evaluate the reliability and to calculate interruption costs at the load bus level in the bulk power system (Hierarchical Level II). The method is based on a nonsequential Monte Carlo simulation combined with a linear optimization model in which the load at every bus is represented by two components, a firm and a nonfirm (curtailable) portion. Expected values of not served energy (EENS), not served demand (EPNS) and loss of load probability (LOLP) are computed for the whole system (global indices) as well as for each load bus. The paper includes a sensitivity analysis taking into consideration variations of the indices due to factors such as interruption costs and load shedding policies. In a number of countries the evaluation of bus-based reliability indices has become a key component in the negotiation of supply contracts in the open access environment. The same indices are useful to assess the reliability of the supply at the delivery point to both distribution utilities and large industrial customers     

Generating Capacity Reliability Evaluation Based on Monte Carlo Simulation and Cross-Entropy Methods

This paper presents a new Monte Carlo simulation (MCS) approach based on cross-entropy (CE) method to evaluate generating capacity reliability (GCR) indices. The basic idea is to use an auxiliary importance sampling density function, whose parameters are obtained from an optimization process that minimizes the computational effort of the MCS estimation approach. In order to improve the performance of the CE-based method as applied to the GCR assessment, various aspects are considered: system size, rarity of the failure event, number of different units, unit capacity sizes, and load shape. The IEEE Reliability Test System is used to test the proposed methodology, and also various modifications of this system are created to fully verify the ability of the proposed approach against both, a crude MCS and an extremely efficient analytical technique based on discrete convolution. A configuration of the Brazilian South-Southeastern generating system is also used to demonstrate the capability of the proposed CE-based MCS method in real applications.      

风/柴/储能系统发电容量充裕度评估

提出一种用于含风能和能量储存设备的小型孤立电力系统(SIPS)发电容量充裕度评估仿真方法。该仿真方法根据每小时计算的随机事件模拟发电系统的运行历史记录,考虑现场风资源的时序性、系统中发电机组的故障和修复特性。使用几个样例系统说明了该方法的应用,该系统的充裕度取决于许多因素,它们是能量储存容量、系统负荷需求、风能注入水平、发电机组强迫停运率(FOR)和其地理位置。能量储存设备对该系统可靠性能有积极的影响;SIPS随着系统负荷的增加,充裕度减少;风力发电机组FOR的变化对系统充裕度的影响不大;增加风能注入水平可以改善可靠性;位于高平均风速处的系统明显比低平均风速处的系统可靠性高。