Cross-phase voltage sag compensator for three-phase distribution systems

Voltage sags are one of the most important and frequent problems in distribution systems. Voltage sags lead to huge financial losses all over the world which makes them more important for sensitive load centers. In this paper, a three-phase voltage sag compensator is proposed. The proposed voltage sag compensator is based on the ac–ac conversion eliminating the energy storage elements and dc link capacitors in the conventional voltage sag compensators such as dynamic voltage restorers (DVRs). The proposed topology in this paper energizes the compensator of each phase from the other two phases. Regarding that the single-phase voltage sags are the most frequent types of voltage sags, the faulted phase will be supplied by the two healthy phases in the most cases of voltage sags. This results in a more successful operation under very deep single-phase voltage sags. Even if one phase is lost, the proposed compensator will continue to supply all three phases of the sensitive load. Beside the single-phase voltage sags, the compensator can compensate for any balanced and unbalanced voltage sag accompanied with phase jump. The proposed voltage sag compensator is validated using digital simulation case studies with PSCAD/EMTDC software and experimental results from a laboratory-scale prototype.     

Minimization of voltage sag induced financial losses in distribution systems using FACTS devices

Voltage sag can have significant economic consequences for different types of industries. Flexible AC Transmission System (FACTS) is originally developed for transmission networks but similar ideas are now starting to be applied in distribution systems. FACTS devices have become popular as a cost effective solution for the protection of sensitive loads from voltage sag. This paper presents the modeling of FACTS devices to minimize the voltage sag induced financial losses. The overall system financial losses due to voltage sag could be significantly reduced depending on the type of FACTS devices used. The short circuit analysis approach is used to incorporate the effect of these devices on financial losses. Voltage sag produced by balanced and unbalanced short circuits is analyzed by means of an analytical approach using system impedance matrix (Z_Bus) which incorporates FACTS devices. Two types of FACTS devices, which are most often used in practical applications, are considered in this study: Distribution Static Compensator (D-STATCOM) and Static VAR Compensator (SVC). Case studies based on a real Indian distribution system are used to illustrate the modeling method and the effectiveness of these devices in minimization of financial losses.     

电压暂降特征值统计分析及暂降传播特性

进行电压暂降评估及其对敏感设备影响的分析,制定电压暂降有效缓解措施,均应建立在对电压暂降特征值充分了解的基础上,但目前有关描述电压暂降特征量典型取值范围及其分布特征方面的研究还较少。该文就暂降特征值统计分析、分类研究、传播计算及负荷侧暂降计算四个问题进行了研究,旨在为电网及敏感设备暂降评估与治理等研究奠定基础。首先基于我国多个地区电能质量监测系统记录的大量电压暂降事件及其实测波形的统计与分析,给出了电压暂降幅值、持续时间、暂降起始点、相位跳变四个特征量的分布特征、范围;然后在原有电压暂降分类基础上,将相位跳变考虑其中,提出了更一般化的电压暂降分类方法,并研究了变压器对不同类型暂降相位跳变的影响;最后为方便计算负荷及相关节点暂降,提出了变压器、线路叠加计算及多变压器、负荷联结方式等效计算方法,完善了电压暂降的传播特性研究。     

电压暂降的计算及故障点电压暂降系数确定

由于电力系统中新型电力电子设备的广泛应用,电压暂降已逐渐成为影响设备正常运行的主要电能质量问题之一,为避免电压暂降对设备正常运行造成危害,电压暂降计算已成为电力系统运行分析不可缺少的一部分。采用故障定位法,设计了电力系统电压暂降计算软件,从而实现查找、统计、分析、预估等功能,实现电力系统的电压暂降计算,并提出一种故障点电压暂降系数(FPSC)的量化指标,对电力系统不同的故障点进行了FPSC的计算,根据FPSC的数值确定对全网电压暂降影响严重的故障区域;并利用电压暂降分析程序的输出结果对欲购进新设备的电压敏感性进行了评价;以某实际工业配网为算例,利用所设计计算软件对该本地配网进行了电压暂降的分析计算,所做工作可以为用户采取电压暂降抑制措施提供理论指导。     

Classification of sags gathered in distribution substations based on multiway principal component analysis

Voltage sags, whether they occur in transmission or distribution systems, may severely damage the loads connected to the power system. As these problems could cost a great deal financially, electric utilities are very interested in finding the origins of sags, that is, whether they have been originated in the transmission network (high voltage (HV)) or in the distribution system (medium voltage (MV)). In addition to the needs of utilities and regulators, many researchers have been prompted to develop reliable methods to properly classify sags. Several of these methods, based on classifying meaningful features extracted from data and waveforms, have been proposed in the literature. Unlike those methods, though, we propose a systematic transformation of data, based on multiway principal component analysis (MPCA), to develop a new voltage sag classification procedure. Sampled voltage and current waveforms of previously registered sags are used together with the MPCA technique to obtain a lower dimensional model. This model is then used to project new sags and classify them according to their origin in the power system. Different classification criteria and parameters are examined to maximize the classification rates of not yet seen sags. Applying the proposed method to real sags recorded in substations demonstrates its applicability and power.     

计及电压暂降和保护性能的配网可靠性算法

提出一种计及电压暂降和保护性能的配电网可靠性算法。运用蒙特卡洛法模拟故障的各种信息;采用故障电流补偿法计算系统故障后各节点电压;根据系统故障后线路保护的动作性能确定各负荷节点的电压暂降持续时间,从而进一步判断敏感负荷是否停运;将故障点法与临界距离法相结合,提出一种计算电压暂降域的方法。最后比较了计及电压暂降和保护性能前后的配电网可靠性指标变化。该算法采用的模型是RBTS测试系统的第6母线,运用上述算法计算了它的暂降域和可靠性指标。     

电压暂降评估指标(Ⅱ)——设备停运概率指标

电压暂降对敏感设备的影响明显,容易造成敏感设备停运。用户将敏感设备调整至电压暂降发生概率低的进线上,能够有效抑制电压暂降对敏感设备的影响,该方法投资小,实现简单。设备停运概率指标是针对电力用户进行敏感负荷调整提出的评估指标。通过对每回进线电压暂降事件进行统计,获得电压幅值和持续时间的概率分布。结合电压暂降造成设备停运的条件,得出设备在每一回进线下的停运概率指标。通过指标的大小,指导用户将敏感设备连接到指标小的进线上,减小设备停运带来的经济损失。     

基于平均点线距的电压暂降系统级评估方法

为系统比较不同区域电压暂降的严重程度,从电网电压暂降整体水平出发,提出了系统级的电压暂降严重程度评估方法。该方法通过聚类分析确定持续时间区段,求取不同持续区段内残余电压的中位数并绘制中位数线。随后提出平均点线距指标以量化评估各个区域电压暂降严重程度,并根据不同区域的指标分布特征进行电压暂降水平等级划分。某市实际监测数据的评估验证了所提方法的正确性与合理性。该方法能在大量监测数据中有效提取不同区域电压暂降的严重程度信息,从残余电压和持续时间2个维度实现电压暂降的系统级评估,有利于区域间电压暂降水平的对比。     

A voltage sag study in an industry with adjustable speed drives

This article presents voltage sag measurements and their analysis, which were performed in two industries for a period of 17 months. Voltage sags are caused by faults in the utility's transmission system, since both industries are fed by a 115 kV line, but from different circuits. Even faults in 230 or 400 kV lines are felt by the industries' entrance substation as voltage sags. These events cause interruptions in important continuous processes because the adjustable speed drives (ASDs) involved are sensitive to voltage variations. It is shown that, with the measurements made, ASDs are more sensitive to voltage sags than data processing equipment, according to the tolerance curve shown in C51. Also identified were ASDs that tripped more frequently with voltage sags. This allowed the selection of problem areas in both industrial plants, requiring a more detailed analysis in order to select some type of power line conditioning equipment     

雷电引起的电压暂降严重程度自学习评估方法

雷击故障是造成电网电压暂降的主要原因之一,准确评估雷电造成的电压暂降严重程度可以为制定最优治理方案和敏感用户选址提供依据。文中提出一种数据驱动的电压暂降严重程度自学习评估方法。首先,基于雷电造成的电压暂降机理,结合雷电定位系统和电能质量监测系统中的监测信息选取参与挖掘的参数;其次,减少离散化结果对规则准确性的影响,使用离散化评价系数确定不同参数的离散区间数目;然后,针对电网数据库动态变化时挖掘算法效率过低的问题,使用基于增量式学习的关联规则挖掘算法持续更新挖掘规则,从而赋予其自学习的能力;最后,提出基于综合赋权法的加权欧氏距离评估实际场景的电压暂降严重程度。通过某地区电网的监测数据和IEEE 30节点系统仿真数据进行实证分析,结果证明文中方法能在实际应用中准确挖掘有价值规则,实现关注节点的电压暂降严重程度评估。     

基于平均点线距的电压暂降系统级评估方法

为系统比较不同区域电压暂降的严重程度,从电网电压暂降整体水平出发,提出了系统级的电压暂降严重程度评估方法。该方法通过聚类分析确定持续时间区段,求取不同持续区段内残余电压的中位数并绘制中位数线。随后提出平均点线距指标以量化评估各个区域电压暂降严重程度,并根据不同区域的指标分布特征进行电压暂降水平等级划分。某市实际监测数据的评估验证了所提方法的正确性与合理性。该方法能在大量监测数据中有效提取不同区域电压暂降的严重程度信息,从残余电压和持续时间2个维度实现电压暂降的系统级评估,有利于区域间电压暂降水平的对比。     

Probability evaluation method of equipment failure due to voltage sags considering multi-uncertain properties

The existing problem with probability evaluation of sensitive equipment failure arising from voltage sags is how to measure the uncertain properties and determine the mathematical models of influencing factors. In this paper, the uncertain properties of voltage sags, voltage tolerance of sensitive equipment, and equipment operation states are explored. The intension and extension uncertainties of influencing factors are used to distinguish the mathematical properties. Stochastic and fuzzy variables are introduced to quantify these uncertainties. The corresponding models are proposed. A multi-uncertainty evaluation method of sensitive equipment failure probability is presented also. With the proposed method, the maximum entropy method is used to extract the probability distribution of voltage sag intensity while the determination principle of membership function of fuzzy safety event is applied to determine the multi-uncertainty evaluation model. As a case study, a personal computer is simulated. The results show that the proposed method is feasible and effective, and can be deployed in other fields.     

基于网络传播特性的配电网电压暂降随机预估方法

敏感负荷的大量投运使得用户对电能质量的要求不断提高,电压暂降的快速有效预估成为当前电压暂降研究的一项重要内容。提出了一种基于网络传播特性的配电网电压暂降随机预估方法。首先基于配电网拓扑搜索电压暂降传播路径,通过序分量法获得不同路径下电压暂降的垂直/水平传播特性。进而根据路径搜索结果建立故障源至负荷侧的配电网电压暂降传播方程。最后结合不同故障类型及线路故障率计算暂降凹陷域和相应预估指标。对某实例配电网系统开展算例分析,验证了所提方法的有效性与优越性。     

配电线路电流保护的跌落保护性能评估

系统中大部分电压跌落由故障引起,快速可靠地判断并切除故障是继电保护的主要职责.然而,目前的电压跌落治理方案均缺乏对继电保护技术的评价和应用.文中将三段式电流保护动作特性引入CBEMA(Computer Business Equipment Manufacturing Association)敏感特性曲线中,提出了电流保护的电压跌落安全域评估模型及保护性能评估模型,有效地衡量了线路电流保护可以提供给敏感设备安全运行的有效区域以及最大电压跌落保护能力.相关理论与算例分析表明,继电保护技术可以提供一定的电压跌落治理能力;改善电流保护的电压跌落保护性能,只能从增大无时限电流速断(I段)保护的保护范围入手.     

基于互近似熵的电压暂降波形匹配方法

随着越来越多电压暂降敏感设备接入电网,因电压暂降干扰带来的直接及间接经济损失日趋严重,这对供电质量提出了更高要求,准确识别暂降源是治理电压暂降问题中必不可少的步骤。文中分析了各类短路故障引起的电压暂降类型及其经变压器传变后暂降波形的变化情况,并根据理论分析建立各类暂降的标准样本波形。提出了一种基于互近似熵原理的电压暂降源辨识方法,通过计算实测波形与样本波形之间的互近似熵,直接进行相似度匹配,实现故障暂降类别的准确识别,并利用电网实测数据对该方法进行验证。结果表明该方法与实际工程相贴合,具有很强的实用性。     

考虑设备敏感特性的单次电压暂降事件分级评估方法

对于单次电压暂降事件,得到其评估值后,在没有比较基准的情况下,无法直观地知晓其严重程度。本文提出了考虑设备敏感特性的单次电压暂降事件分级评估方法。在暂降能量指标的基础上,根据典型的设备耐受曲线的严重性评估结果拟合设备免疫水平概率分布函数;计算单次事件引起设备的故障概率,基于层次分析法得到设备综合故障率;利用设备故障率构造修正函数来修正暂降能量指标,基于电网中490组历史暂降样本,通过对修正后的暂降能量指标进行概率统计分析,拟合其概率分布函数,计算其概率分位数,作为比较基准值;根据单次事件修正后的评估指标与基准值的大小关系建立电压暂降严重性评估等级。通过对电网中100组实测暂降样本进行分级评估,将暂降能量指标修正前后的结果进行对比,验证了本文方法能有效地克服暂降能量指标的过度评估,并且评估结果更加直观、合理。     

考虑敏感区域的电压暂降监测装置优化配置

电压暂降无法避免且对敏感负荷危害严重,合理配置有限监测装置可以降低监测成本,并为暂降治理、降低暂降危害提供数据支撑,因此暂降监测装置的优化配置有重要意义。本文针对传统方法忽略不同区域发生暂降危害程度不一致的问题,提出一种考虑暂降敏感区域监测可靠性和同步相量测量装置（phasor measurement unit,PMU）布点的暂降监测装置联合优化配置模型。该模型以暂降可观为约束条件,以监测装置数目最少,覆盖暂降敏感区域范围最广为目标,并进一步配置PMU用于辅助监测电压暂降。此外,本文采用Zeroin方法提高了暂降域计算的准确性。IEEE30系统仿真表明本文方法可以保证装置数目最少并对敏感负荷高冗余度覆盖,保障其经济效益。本文所提方法克服了难以平衡监测成本与敏感区域监测能力的困难。     

基于凹陷域分析的电压暂降监测点优化配置

提出一种基于凹陷域分析的电压暂降监测点优化配置的新方法,以监测点数目最小为目标函数,以全网敏感性负荷节点电压暂降可观测性为约束条件,利用整数线性规划方法,通过MATLAB编程求取符合要求的最少数目监测点。在构造电压暂降幅值矩阵的计算中,考虑到了每一个节点故障可能引发系统其余节点电压暂降的情况。在IEEE 39节点系统上进行仿真计算,成功求得了保证全网敏感性负荷节点电压暂降可观测的最少数目的监测点。     

Stochastic evaluation of voltage sags in series capacitor compensated radial distribution systems

Voltage sags, also known as dips, are important to industrial reliability. This paper presents a Monte Carlo-based approach to evaluate the maximum voltage sag magnitudes in series capacitor compensated radial distribution systems. In this context, investigations have been conducted on a sample distribution system model taking into consideration the uncertainty of several factors associated with the practical operation of a power system. The power system blockset of MATLAB is used in the simulation studies.     

An evaluation method of voltage sag using a risk assessment model in power distribution systems

In this paper we explore a new method for evaluating the impact of voltage sags in the power distribution systems. The proposed method incorporates the generalization of the evaluation method as well as the effects of voltage sags on customers. To generalize the evaluation method, historical reliability data will be used. We take into account the impact of voltage sags on customers using a representative power acceptability curve and a fuzzy model. The final result of the evaluation model yields on a yearly basis the magnitude of customers’ risk caused by voltage sags. The evaluation methodology is divided into the analytic and probabilistic method. The time sequential Monte Carlo simulation is used as probabilistic method. The proposed method is tested using the modified Roy Billinton Test System (RBTS) form and the reliability data of Korea Electric Power Corporation (KEPCO) system. Through the case study, we verify that the proposed method evaluate the actual impact of voltage sags and can be effectively applied to the real system using the historical reliability data as the conventional reliability indices in power distribution systems.