Distribution feeder loss analysis by using an artificial neural network

This paper proposes an artificial neural network (ANN) based feeder loss analysis for distribution system analysis. The functional-link network model is examined to form the artificial neural network architecture to derive various loss calculation models for distribution feeders with different configurations. The ANN is a feedforward network that uses a standard back-propagation algorithm to adjust the weights on the connection path between any two processing elements. The typical daily load curve of the study feeder for each season is derived to field test data. A three-phase load flow program is then executed to create the ANN training sets to solve the exact feeder loss. A sensitivity analysis is performed to determine the key factors of feeder loss, which are feeder loading and power factor, primary and secondary conductor length, and transformer capacity. The above key factors form the variables of the ANN input layer. By applying the artificial neural network with pattern recognition capability, this study has developed the seasonal loss calculation models for both an overhead and an underground distribution feeder. Two practical feeders in the Taiwan Power Company (Taipower) distribution system have been selected for computer simulation to demonstrate the effectiveness and accuracy of the proposed ANN loss models. By comparing the loss models derived by the conventional regression technique, it is found that the proposed loss models can estimate feeder loss in a very effective manner and provide a better tool for distribution engineers to enhance system operation efficiency.     

Simplified three-phase lateral and feeder models for fast distribution system calculations

This paper introduces three simplified three-phase lateral models for fast distribution system calculations. The models can also be applied to model a feeder with short laterals, whose impedances are negligible. These models are formulated using three lumped individual phase loads to represent single-phase, three-phase unbalanced, and nonuniformly distributed loads along a lateral or feeder. Proposed voltage-drop and line-loss models are developed to accurately simulate the total series voltage drop at the end and the total copper loss of a given lateral, respectively. A hybrid model is then developed to simulate both voltage drop and line loss accurately. All of the proposed models are used to represent the unbalance features of a physical distribution system in which various transformer connections are presented. The proposed models are applied to a physical feeder of Taiwan Power Company (Taipower). The simulation results show that it is possible to simplify complicated laterals or feeders to simple equivalent models in the calculations of voltage profiles and line losses with negligible error, even if there are various transformer connection schemes in the lateral or feeder.     

树状配电线路并联电容器无功优化规划

为解决含分支树状配电线路无功补偿问题,提出了在树状配电线路安装多台固定容量电容器的无功优化规划方法。该方法以净节约金额最大为目标函数,采用等效负荷法将树状配电线路转化为多个梳状配电线路,分别对各个等效线路进行优化规划,将目标函数值最大者对应的方案确定为最优规划方案。实例分析和规划结果验证了该方法的正确性和可行性。     

Feasibility study of upgrading primary feeders from radial and open-loop to normally closed-loop arrangement

The feasibility study of upgrading primary feeders from radial and open loop to a normally closed-loop arrangement have been explored in this paper. First, three possible feeder arrangements for forming a normally closed loop are discussed, and then the factors that may predominantly affect the system-type upgrading are discussed theoretically. Next, four existing distribution feeders with original radial arrangements, fed by three power transformers that are located at two different distribution substations of Taiwan Power Company (Taipower) are employed as sample systems. To form three types of closed-loop arrangement, all of the four radial feeders were tied together at their ends, two feeders at a time. The power flows, voltage profiles and short-circuit capacities of the feeders under both the tie breaker normally open and closed cases have been evaluated, and the impacts of the upgrading of system type on the distribution system and customers assessed. Finally, the required supporting measures for these kinds of upgrading have been listed, and the most suitable and feasible arrangement was recommended to Taipower.     

计及馈线自动化故障处理全过程的配电终端优化布置方法

为了进一步提高配电网供电可靠性,提出了一种计及馈线自动化(feeder automation, FA)故障处理过程的配电终端优化布置方法。首先以自适应综合型FA模式为例,分析FA的故障定位、隔离与恢复供电的故障处理全过程,并基于电力系统仿真软件DIgSILENT建立了配电终端的动作信号逻辑模型。其次,在考虑了FA故障处理过程的条件下,计算包括故障区域与非故障区域的总负荷停电损失成本,与总投资成本共同构成模型目标函数。考虑系统平均供电可用率指标约束等因素,建立配电终端优化布置模型。然后,基于整数编码的人工蜂群算法确定配电终端最优安装总数,制定配电终端最优配置方案,计算出配电终端最优选址方案。最后,以冀北某地区10 k V配电网作为仿真算例,基于DIgSILENT模拟FA故障处理全过程,验证所提方法的有效性和适用性。     

Multi-Objective Approach for Reconfiguration of Distribution Systems with Distributed Generations

This paper presents a fuzzy multi-objective based heuristic algorithm for network reconfiguration of distribution systems considering distributed generations (DGs). The objectives of reduction of real power loss, branch current carrying capacity limit, maximum and minimum voltage constraints, and feeder load balancing are considered for performance enhancement of the distribution system. Since these objectives are non-commensurable and difficult to solve simultaneously using conventional approaches, they are converted into fuzzy domain and a fuzzy multi-objective function is formulated. A sensitivity analysis based on voltage profile improvement and real power loss reduction is used for obtaining optimal locations of DGs and genetic algorithm is used for optimal sizing of DGs. The proposed reconfiguration algorithm is implemented in two stages, initially in the first stage without incorporating DGs and in the second stage incorporating DGs for obtaining an optimal distribution system network reconfiguration. The advantage of the proposed method is demonstrated through a seventy node four feeders and a sixteen node three feeders distribution systems.     

基于馈线偶的配电网快速减小网损重构方法

作为配电网自动化高级应用模块,网络重构应满足快速性的要求而达到在线应用的目的。而许多配电网重构方法因追求全局最优或多次潮流计算而不能满足该要求。文中提出一种基于馈线偶的快速减小网损重构方法。该方法利用馈线偶内网损估算公式推导馈线偶内最佳转移负荷来寻找最优分段开关,可以避免多次潮流计算,完成馈线偶内重构。以馈线偶内重构为基础,并按照全网所有馈线偶的联络开关两侧压差的大小顺序进行全网网络重构。全网重构时对所有馈线进行"优化标定",可以起到避免重构死循环和结束全网重构的作用。最后采用13节点和185节点配电网进行了编程计算,结果表明了该方法的快速性和有效性,可以满足配电网重构在线应用的要求。     

计及全年风光资源的分布式电源选址方法

针对分布式电源优化选址问题,现有方法一般都简化处理全年风光资源和负荷数据,且算例规模较小,不能完全满足实际应用要求。提出了计及全年风光资源和负荷数据的大规模多馈线配电网分布式电源选址方法。首先,建立计及全年风光资源的大规模多馈线配电网分布式电源优化选址模型,然后基于遗传算法给出优化模型的求解策略,最后采用实际大规模多馈线配电网算例进行验证。结果表明,由于考虑到风机位置会受到全年负荷及风能资源时序特性的影响,因此风机位置优化后的网损更低;采用大规模多馈线整体优化的方案后,采用该方法计算的网损结果也明显优于单馈线范围内的优化结果。     

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.     

基于配电网谐波责任划分的分布式有源滤波系统

随着电力电子装置的广泛应用和多种分布式能源的接入,低压配电网的电能质量问题已日益突出。为改善多馈线型低压配电网公共连接点(PCC)处的电能质量,降低其电压谐波失真,以具有谐波补偿功能的单相光伏并网设备为基本单元,构建了一个分布式有源滤波系统。通过分析低压配电网中各馈线对PCC处电压谐波的责任,对各馈线的谐波补偿任务进行了优化调整。此外,采用基于虚拟谐波阻抗的下垂控制方法,实现了多设备并联时的自主协调,并提出了一种参考PCC处谐波责任的谐波补偿容量分配算法,提升了在输出容量限制情况下分布式有源滤波系统的谐波补偿效果。最后,通过软件对上述模型和控制策略进行了建模与仿真,仿真结果验证了该系统的可行性和有效性。     

System wide MV distribution network technical losses estimation based on reference feeder and energy flow model

This paper presents an integrated analytical approach to estimate technical losses (TL) of medium voltage (MV) distribution network. The concept of energy flow in a radial MV distribution network is modelled using representative feeders (RF) characterized by feeder peak power demand, feeder length, load distribution, and load factor to develop the generic analytical TL equations. The TL estimation approach is applied to typical utility MV distribution network equipped with energy meters at transmission/distribution interface substation (TDIS) which register monthly inflow energy and peak power demand to the distribution networks. Additional input parameters for the TL estimation are from the feeder ammeters of the outgoing primary and secondary MV feeders. The developed models have been demonstrated through case study performed on a utility MV distribution network supplied from grid source through a TDIS with a registered total maximum demand of 44.9 MW, connected to four (4) 33 kV feeders, four (4) 33/11 kV 30 MVA transformers, and twelve (12) 11 kV feeders. The result shows close agreement with TL provided by the local power utility company. With RF, the approach could be extended and applied to estimate TL of any radial MV distribution network of different sizes and demography.     

实现最大供电能力的配电网馈线与主变压器容量匹配

提出了一种新的配电网规划中馈线与变电站主变压器容量的匹配方法。首先,定义了达到最大供电能力下的馈线平均负载率和主变压器平均负载率两个指标,再分析其随馈线容量与主变压器容量比值的变化规律,发现两个指标无法同时达到最大。然后,根据馈线与变电站的建设成本差异,确定馈线与主变压器容量的最优配比,在该配比下单位供电能力的电网建设总投资最小。最后,分析得到多个算例的不同情况的馈线与主变压器容量的最优配比,该值随着馈线相对变电站造价比值的增加而减小;并随着馈线联络均衡度的增加而增加。在现有城网造价水平下建议配比取1.0~1.6,明显低于传统配电网以及规划经验值约1.5~2.0的区间。     

计及分布式发电的配电网快速潮流算法

通过研究配电网络的拓扑结构和无分支单馈线的潮流特性,对传统的前推回代潮流算法进行改进,提出一种新的基于辐射状网络的潮流计算方法.该方法将包含多条分支或非终端的配电馈线分解成一级一级的数条无分支单馈线进行潮流计算.此外,由于分布式电源和并联电容器在配电网侧的大量引入,考虑在潮流计算过程中将分布式电源和并联电容器作为PQ节点进行处理.并通过算例验证了该方法的快速有效性.     

含分布式电源的配电系统规划研究

研究分布式发电(DG)对电网的支撑作用及其对配电网规划的影响,提出DG的布点规划流程和含DG的配电网规划流程,给出分布式电源(DGS)在径向馈线中的最佳位置的确定方法,并以分布特性不同的三种馈线负荷分布为例验证了DGS在馈线中的合理布置会大大降低系统的功率损耗。     

A rule-based expert system with colored Petri net models for distribution system service restoration

A rule-based expert system with a colored Petri net (CPN) inference model is developed for service restoration of distribution systems. The CPN models of distribution components such as four-way line switches are proposed to derive the proper restoration plan after the faulted location has been identified and isolated. The unfaulted but out of service areas are restored by applying parallel-like reasoning in the CPN for multiple contingencies simultaneously. To assure the restoration plan can comply with the operation regulation, heuristic rules based on the standard operation procedures of Taipower distribution system are included in the best first search of the CPN. For the fault contingency during summer peak season, the load shedding is executed and the CPN models are designed to restore service to as many key customers and loads as possible. The priority indices of each feeder and service zone are determined according to the key customers within the service territory. A Taipower distribution system with 18 feeders is selected for computer simulation to demonstrate the effectiveness of the proposed methodology. It is found that the service restoration of distribution system can be obtained very efficiently by applying the proposed CPN model.     

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.     

基于成本分析的柔性直流配电网综合规划方案研究

随着直流分布式发电的高渗透率以及敏感直流电子负载的不断增长,柔性直流配电网络的应用越来越广泛,为比较柔性直流系统与传统交流配电系统,提出基于成本分析的柔性直流配电网规划方案。该方案可确定最优的交直流变电站位置和规模、交直流馈线的布线路线以及中低压侧交直流馈线的长度和容量,其目标函数由投资成本和运营成本组成。提出的柔性直流配网规划方案是在没有预先分配配电系统的地区实施的,并与传统交直流规划方案进行了比较。最后算例结果表明,与常用的交流配电系统相比,采用柔性直流配电方案可降低敏感负载下的总成本,并能提高分布式电源的渗透率。     

电力市场中分布式发电孤岛模式对配电公司费用的影响

在分布式发电参与的电力市场中,提出了一种考虑可中断负荷及其费用的配电公司最小总费用模型。在对传统运行模式、孤岛运行模式,以及非故障馈线支援模式进行比较的基础上,重点分析了不同负荷水平下分布式发电孤岛运行模式对配电系统的有功网损、配电网络的节点边际电价和配电公司购电费用的影响。数值计算和算例仿真表明,当配电网出现故障时,利用分布式发电形成的安全孤岛可以减少整个系统的失电负荷量、降低配电公司的购电总费用。同时,可以根据非故障馈线的容量裕度,实施最佳的支援方式。     

遗传粒子群混合算法在配电网络重构多目标优化中的应用

针对配电网络重构多为单一性能最优重构的问题,文章提出了使配电网线损、负荷均衡、供电电压质量最佳的多目标配网优化模型。结合GA中的进化思想和粒子群算法(PSO)中的群体智能技术,采用遗传粒子群混合算法寻优,通过随机权重方法来获得目标是Pareto前沿面的可搜索方向,体现出较GA和PSO更好的寻优性能。寻优过程中,部分个体以PSO方法迭代,其它个体进行GA中的选择、交叉和变异操作,整个群体信息共享,同时采用自适应参数机制和优胜劣汰的思想进化。在此基础上制定的配网优化方案能够在保证配网呈辐射状、满足馈线热容、电压降落要求和变压器容量等的前提下,最大限度地提高配电系统安全性和经济性。算例表明该算法在求解性能和效率两方面都有比较显著的优势。     

配电网部分馈线的剩余供电能力

现有配电系统剩余供电能力模型(RSC)研究了配电网在已有负荷下时,全网以及所有馈线或馈线段的剩余供电能力,适用于定量指导新增负荷接入。本文改进了已有的RSC模型,得到了一种能计算配电网部分馈线或馈线段剩余供电能力的计算方法。首先,简要介绍了现阶段配电网的RSC以及存在的问题;其次,介绍了已有配电网剩余供电能力的数学模型、求解方法;再次,改进了已有的剩余供电能力模型,得到了一种能求解部分馈线或馈线段剩余供电能力的数学模型,并给出了求解方法;最后,结合算例说明本文的剩余供电能力所具有的特点,以及适用的场景。本文工作研究了配电网中,部分馈线或馈线段的剩余供电能力计算方法,能够充分挖掘部分馈线的供电潜力,完善了剩余供电能力的理论体系,其具有更好的实用性和经济性,有利于高效利用配电网的供电潜力、提高资产利用率。