Restoration of Directional Overcurrent Relay Coordination in Distributed Generation Systems Utilizing Fault Current Limiter

A new approach is proposed to solve the directional overcurrent relay coordination problem, which arises from installing distributed generation (DG) in looped power delivery systems (PDS). This approach involves the implementation of a fault current limiter (FCL) to locally limit the DG fault current, and thus restore the original relay coordination. The proposed restoration approach is carried out without altering the original relay settings or disconnecting DGs from PDSs during fault. Therefore, it is applicable to both the current practice of disconnecting DGs from PDSs, and the emergent trend of keeping DGs in PDSs during fault. The process of selecting FCL impedance type (inductive or resistive) and its minimum value is illustrated. Three scenarios are discussed: no DG, the implementation of DG with FCL and without FCL. Various simulations are carried out for both single- and multi-DG existence, and different DG and fault locations. The obtained results are reported and discussed.     

含低电压穿越型分布式电源配电网的短路电流计算方法

换流器型分布式电源(DG)在配电网中的应用使传统配电网的短路电流计算方法不再适用。根据DG在配电网故障点前后位置的不同,将DG处理为不同类型的故障等效模型,故障点上游DG采用低电压穿越故障等效模型,故障点下游DG采用恒定电流源故障等效模型。提出了一种基于叠加定理的短路电流迭代计算方法,在每一次迭代过程中,根据当前节点电压和DG的故障等效模型分别修正故障点上游DG和下游DG的输出短路电流,并利用节点电压方程求解配电网的短路电流和节点电压分布,直到满足收敛条件。通过对算例系统的分析计算,验证了所提方法的正确性。该方法可应用于含DG的大规模配电网的短路电流求解。     

含分布式电源配电网保护方案

分布式电源（DG）接入配电网会对传统的配电线路电流保护产生影响,可能导致保护不正确动作。针对这一问题,文中提出一种新的保护方案,对传统的配电线路保护配置进行了改进。该保护方案根据DG接入点的位置,对被保护馈线进行了分区,在DG的上游区域配置了方向纵联保护,而整条馈线则保留了过电流保护。为了能方便整定工作以及更快地切除故障,根据DG接入位置的不同,馈线的过电流保护分别采用定时限或反时限形式。采用该保护方案后,无论DG的输出功率如何变化,故障都能被可靠切除。最后,对一个10 kV配电系统进行了仿真,验证了保护方案的有效性。     

利用暂态分量的含分布式电源配电系统故障诊断

在智能配电系统快速发展的背景下,分布式电源（distributed generation,DG）越来越多地接入配电系统,传统的针对单端电源的配电系统故障诊断方法不再适用。在此背景下,针对含有DG的配电系统,提出一种基于故障暂态分量和遗传算法的配电系统故障诊断方法。针对DG接入使故障点的暂态零序电流方向复杂化的问题,通过给定开关上下游电源的方式改善了终端的状态编码环节,且考虑了故障线路诊断的优先级。采用小波分析方法提取故障暂态分量,能够很好地适应我国中压配电系统广泛采用的小电流接地方式,在相当程度上解决了单相接地短路稳态故障信息不明显的问题。最后,用算例说明了所提出方法的可行性,分析了其对故障信息畸变和丢失的容错性能。     

A Fault Location Scheme for Active Untransposed Distribution Systems Using a Limited Number of Synchronized Measurements

Abstract

This paper presents a fault location scheme for unbalanced and untransposed distribution systems which contain different types of distributed generation (DG). A general formula has been derived for any fault type using a limited number of synchronized measurement points. To avoid having to synchronize all the measurement points, the voltage and current measured locally at the DGs are processed locally to calculate the equivalent impedance of the DG at the non-fundamental frequencies. This is then used in the fault location process. The IEEE 34-bus feeder is simulated using the distributed parameter model for the lines and is used to validate the proposed scheme. Uncertainties associated with fault type, fault location, fault resistance, inception angle, noise in measurements and load profile are considered in the evaluation. The simulation studies demonstrate that the scheme can have a high accuracy and is robust.     

适用于柔性直流互联交流系统的无电压方向元件判据

背靠背柔性环网控制装置的应用使配电网由单端电源供电的辐射状网络变为多端电源供电网络,三段式电流保护无法判断故障方向。为了既保证配电网保护动作可靠性又保留三段式电流保护,需要为保护安装方向元件。文中通过研究背靠背柔性环网控制装置接入的交流配电网发生不同位置相间故障时序电流间的相位规律,提出了基于流过保护的负序电流和同一母线上无源支路正序电流间相位关系的故障方向判别元件,并给出了正反方向故障时方向元件的动作区间。该方向元件适用于由传统电源、采用负序电流抑制的柔性环网控制装置或分布式电源构成的且母线含无源支路的多端供电网络。该元件受过渡电阻影响小,无需安装电压互感器,在三相对称故障时仍可保证保护的正确动作,不存在传统功率方向元件出口三相故障时的死区问题。经PSCAD仿真验证了该方向元件在系统不同位置发生各种相间故障时的正确性和有效性。     

Determination method for loss‐minimum configuration considering reconnection of distributed generators

In the field of electrical power system, various approaches, such as utilization of renewable energy, loss reduction, and so on, have been taken to reduce CO₂ emission. So as to work toward this goal, the total number of distributed generators (DGs) using renewable energy connected into 6.6‐kV distribution systems has been increasing rapidly. The DGs can reduce distribution loss by appropriate allocation. However, when a fault occurs such as distribution line fault and bank fault, DGs connecting outage sections are disconnected simultaneously. Since the simultaneous disconnection of DGs influences restoration configuration and normal configuration after the restoration, it is necessary to determine the system configuration in the normal state considering simultaneous disconnection of DGs. In this paper, the authors propose a computation method to determine the loss minimum configuration in the normal state considering reconnection of DGs after simultaneous disconnection by fault occurrence. The feature of determined loss minimum configuration is satisfying with operational constraints even if all DGs are disconnected from the system. Numerical simulations are carried out for a real‐scale distribution system model with 252 sectionalizing switches (configuration candidates are 2²⁵²) and 120 DGs (total output is 38.46 MW which is 23% of total load) in order to examine the validity of the proposed algorithm. © 2011 Wiley Periodicals, Inc. Electr Eng Jpn, 176(4): 7–14, 2011; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21142     

含分布式电源的配电网智能电流保护策略

以含有多分布式电源(distributed generation,DG)的配电网为模型,提出一种基于多智能体(Agent)的新型分布式电流保护策略。该策略以简单的工频电流比较为基础,运用智能体的分布式处理优势,实现对故障的在线搜索和定位。阐述了利用工频电流变化量幅值和相位比较法进行故障区域搜索、故障线路判定的原理：首先利用DG接入形成的T型节点判断故障搜索的正方向,确定一个较小范围的故障搜索区域;然后通过比较线路两端故障电流幅值或相位确定故障发生的最小区域,并最终完成故障隔离。文章在多智能体分布式处理与主动协作的基础上,提出了分布式电流保护的基本框架和算法流程,并在含有2个DG的配电网模型上进行了仿真验证,仿真结果证明了保护算法的正确性。该保护策略对分布式发电条件下配电网网络结构和运行方式的随机变化具有良好的适应性。     

Fault analysis of unbalanced radial and meshed distribution system with inverter based distributed generation (IBDG)

The fault current contribution of inverter based DGs (IBDGs) may affect the operation of protective devices present in the system. Hence, it is necessary to consider the presence of IBDGs in short-circuit analysis of distribution system. A short-circuit analysis approach for unbalanced distribution system with IBDG, incorporating different voltage dependent control modes, is proposed in this paper. Comparison of the results obtained by the proposed method with those obtained by the time domain simulation studies carried out using PSCAD/EMTDC software, shows the accuracy of the proposed technique.     

含分布式电源配电系统中计及警报错误的故障定位

现有针对含分布式电源配电系统的故障定位方法在实际应用时如果存在警报漏报与误报就可能发生误判。针对这一问题,提出了一种综合利用遥信和遥测信息的配电系统故障定位两层模型。首先,利用遥信信息建立故障定位的上层解析模型,然后在此基础上通过遥测数据建立下层模型。所提出的两层模型可以较好地处理含分布式电源配电系统的故障定位,并能给出漏报和误报的警报。最后,采用算例系统说明了所发展的两层模型的基本特征。     

有源配电网中性点接地方式的选择问题

中性点接地方式选择是配电系统的基础问题,对于分布式电源(DG)大量接入的有源配电网,其接地方式将由主网和DG共同决定,单相接地故障电流和过电压等问题也将更为复杂,需要重新审视。文中给出了有源配电网中主网和DG接地方式可能的组合;针对DG并网、脱网不同运行状态以及接地故障后主网线路保护、孤岛保护等不同故障处理阶段,分析了可能面临的接地方式与故障电流、过电压等转变问题;提出了接地方式已确定的现有配电网中DG接地方式选择以及脱离现有配电网条件约束的有源配电网接地方式选择的基本思路,为有源配电网中性点接地方式技术的研究和应用作初步探讨。     

基于分布式电源电流变化率的主动配电网单相断线保护方法

分布式电源的应用,改变了配电网断线故障的特征,加剧了断线故障的威胁。但是目前不仅缺乏含分布式电源(DG)的配电网断线故障保护方法,甚至电网断线故障下DG的输出特性也不清晰。基于主动配电网的可观测性,提出了一种根据DG电流变化率识别配电网断线故障的新思想。首先,分析了配电网单相断线故障下DG的输出特性,并建立了DG的等值模型。然后,建立了含DG的配电网单相断线故障等效电路,推导了故障前后DG输出电流的表达式。随后,分析了故障前后DG输出电流的变化特征,建立了基于DG电流变化率的辐射状配电网单相断线故障保护判据。仿真表明,所提单相断线故障保护方法能够迅速识别断线故障并准确定位。     

分布式电源短路计算模型及电网故障计算方法研究

分布式电源的发电模式及并网方式多样,其馈入电网的故障电流特性与传统交流同步发电机相比存在较大差异,使以传统交流同步电机供电电源为基础的短路电流分析理论和方法难以满足分布式电源接入后电网故障分析的要求,给继电保护原理研究和整定计算提出了新的课题并备受关注。根据不同类型分布式电源的低压穿越运行技术要求,建立逆变型电源的短路计算模型。并考虑异步型电源撬棒保护的动作行为特征,建立了异步型电源在电网严重和非严重故障条件下的等值计算模型。进而,提出了含分布式电源接入的电网故障计算方法。仿真对比分析表明,电网故障计算方法精度较高,能更好地满足工程应用要求。     

含分布式电源的配电网故障分析叠加法

传统的配电网故障分析方法已不能满足未来分布式发电系统的需求。为此,文中针对含分布式电源的配电网故障分析展开研究。将常见分布式电源节点划分为PQ节点、PI节点、PV节点和PQ(V)节点几种类型,并根据各节点类型的特点,提出了在故障分析中的处理方法。根据含分布式电源的三相不平衡弱环配电网的特点,在前推回推类方法的基础上,提出了一种含分布式电源的配电网三相故障计算的叠加方法。该方法既能用于辐射型网络,也能用于弱环网络。采用13节点算例对所述方法进行了测试,算例结果证明了该算法的可行性和有效性。     

计及逆变型分布式电源控制特性的配电网故障分析方法

随着分布式电源(DG)的大量接入,DG的故障穿越行为对配电网的故障特性影响很大。而传统的等值模型均未计及DG的控制策略,从而造成含DG的配电网故障分析存在不可忽略的局限性。为此,文中在系统分析DG控制策略和动作行为的基础上,建立了计及控制策略的逆变器并网方式下DG压控电流源等值模型,更加真实地体现出DG故障电流的输出特性。在此基础上,通过建立故障前后电网支路电流和节点电压关系方程,推导出故障穿越时DG输出电流与公共连接点电压的求解方程组,从而建立故障精确分析方法。最后,基于DIgSILENT建立含DG的10kV配电网仿真模型,验证了所述方法的正确性和有效性。     

运用MAS的配电网保护和控制

随着信息设施的不断改善,大量的分布式发电机(DGs)将会接入配电网.为此,运用多代理技术提出了一个新的配电网保护方案.该方案中,各种不同的继电器被设计成继电器代理,区域内的继电器相互合作以定位和隔离故障.通过感知在继电器处的电流突然变化,来选择二元状态信号(电流的方向,幅值大小等)作为保护用信号.每个继电器同时利用同一...     

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.     

Experimental Study of Islanding‐Prevention Method by Harmonic Injection Synchronized with Exciting Current Harmonics of Pole Transformer

As distributed generators (DGs) such as photovoltaic (PV) systems are increasingly used in distribution systems, quick prevention of islanding caused by power system failure is essential to assure electrical safety. Various islanding protection methods have been used practically, but the conventional active systems tend to increase the detection time, because mutual interference occurs between active signals due to asynchronous states. A new active islanding detection method, the frequency feedback method with step reactive power injection, also has the possibility of extending the detection time in the so‐called perfect balance area (PBA). Thus we propose a novel method of islanding‐prevention by harmonic injection synchronized with the exciting current harmonics of the pole transformer. We performed an experimental study using prototype inverters equipped with the proposed method. We have shown the feasibility of detecting islanding quickly and reliably, even if the islanding state is in the PBA. The experimental results demonstrate that mutual interference does not occur due to asynchronous states between active signals, and also that the proposed method is applicable to islanding detection system in clustered installation of PV systems.     

适用于逆变型电源接入的配电网故障方向判别元件

分布式电源接入配电网使得传统的单电源辐射状网络变成部分线路多电源供电的复杂网络,仅依靠阶段式电流保护已不再适用,因此急需对配电网原有保护进行改造。而由于分布式电源的结构特征与控制方法不同于传统发电机,传统方向元件的灵敏性大大降低甚至存在误判的可能性。以逆变型电源接入配电网为例,提出一种新的方向判别元件。通过限制逆变型电源接入位置实现短路电流性质区分;设置电流整定值,将各保护进行分类并采用不同的方向判别逻辑,仅根据短路电流与整定值之间的大小关系,便能准确区分正、反方向故障。     

一种基于有向图的配电网故障定位方法

为提高配电网的故障定位效率,减少因故障停电带来的损失,本文基于有向图提出了一种配电网故障定位的新方法。它利用主站接收到的故障指示器动作信号,通过构造节支关联矩阵和线路电流向量,进行两者相乘运算,确定故障所在区段。所提方法无需规格化处理,可实现含分布式电源接入、多重故障和闭环运行的复杂配电网故障定位,具有较强的容错能力。文中不仅应用KCL电流定律从理论证明了方法的正确性和适用性,而且还在某市配电网系统上进行了仿真。结果表明了该方法可以用于实际配电网,具有很大的应用前景。