A novel neural network and backtracking based protection coordination scheme for distribution system with distributed generation

With the increased installation of renewable energy based distributed generations (DGs) in distribution systems, it brings about a change in the fault current level of the system and causes many problems in the current protection system. Hence, effective protection schemes are required to ensure safe and selective protection relay coordination in the power distribution system with DG units. In this paper, a novel adaptive protection scheme is proposed by integrating fault location with protection relay coordination strategies. An automated fault location method is developed using a two stage radial basis function neural network (RBFNN) in which the first RBFNN determines the fault distance from each source while the second RBFNN identifies the exact faulty line. After identifying the exact faulty line, then protection relay coordination is implemented. A new protection coordination strategy using the backtracking algorithm is proposed in which it considers the main protection algorithm to coordinate the operating states of relays so as to isolate the faulty line. Then a backup protection algorithm is considered to complete the protection coordination scheme for isolating the malfunction relays of the main protection system. Several case studies have been used to validate the accuracy of the proposed adaptive protection schemes. The results illustrate that the adaptive protection scheme is able to accurately identify faulty line and coordinate the relays in a power distribution system with DG units. The developed adaptive protection scheme is useful for assisting power engineers in performing service restoration quickly so as to decrease the total down time during faults.     

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...     

New coordination approach to minimize the number of re-adjusted relays when adding DGs in interconnected power systems with a minimum value of fault current limiter

The presence of DGs in power networks tends to negatively affect relays coordination. Adding fault current limiters FCLs is one of the possible solutions to mitigate negative impacts of DGs addition on protection systems. Traditional schemes have estimated the minimum value of FCL to restore relays coordination when adding DGs without resetting of any relays. That minimum value of FCL in such case is called a critical value, where below this value the relays coordination will be lost.Nowadays, designing FCL to simultaneously achieve two conflicted objectives of good performance and low cost is considered a great challenge. The paper introduces a new scheme to determine to what extent we could decrease FCL impedance value below its critical value with re-adjusting the original settings of only one adaptive relay to get relays coordination. Decreasing FCL value below its critical value will reduce the cost especially for superconductivity FCL. The proposed scheme can determine the location of that selected relay to be an adaptive one and estimate its re-adjusted new settings to be applied when DGs are added while inserting the reduced value of FCL.Actually the proposed scheme can be applied for any networks irrespective of the number of added DGs and their capacities; while having an adaptive relay is the only requirement to implement it.The proposed approach is implemented and effectively tested on the large well-known interconnected IEEE-39 bus test system with 84 relays. Its results are compared with other approaches where, no re-adjusted relays settings are applied. A noteworthy advantage of the proposed scheme is the ability to implement a reduced FCL value than the critical value, by adjusting only one relay settings in the whole network. The proposed scheme may also be extended to re-adjust settings of more than one relay and get further reduced value of FCL. Furthermore, it is also shown that a more optimum value of the total operating time of all primary relays for near end faults is achieved when applying the proposed method rather than other traditional schemes.     

基于状态量信息的含分布式电源配电网保护新方案

为消除分布式电源(DG)接入对保护的影响,同时尽量减少改造成本,提出了一种基于多点状态量信息的含DG配电网保护新方案。对于DG下游辐射状线路和无DG接入的馈线,所提方案根据过电流保护动作信息实现故障定位。另外,基于馈线首端和DG并网点处的电压和电流信息,提出了补偿阻抗极性信息的新判据及其故障定位方法。当DG上游区域发生故障时,所提方案无需加装电压互感器,即可快速准确地切除DG上游区域的故障线路。最后,通过PSCAD/EMTDC软件对一个含DG的10 kV配电网进行故障仿真与分析,结果验证了所提方案的有效性和正确性。     

A theory of maximum capacity of distributed generators connected to a distribution system using electric power density model

Recently, the number of distributed generators (DGs) connected to distribution systems has been increasing. System operators should know the maximum capacity of DGs that can be connected without problems to one feeder of the system in order to control the system appropriately. Many studies of the maximum capacity of the DG have been presented, but they have produced limited results calculated by a typical or average‐value model. However, many DGs will access one feeder if deregulation of the electric power industry is accelerated in the near future. In order to deal with this situation, the authors have derived a general formula to calculate the range of the maximum DG capacity per feeder. Copyright © 2004 Wiley Periodicals, Inc. In order to deal with sets of DGs that are dispersed completely on the distribution line, the authors have derived a differential equation for the complex power and one for the voltage drop, which are expressed as functions of distance from the substation. The general formula to calculate the range of the maximum DG capacity connected to the system is determined by solving these equations under the constraints of the line voltage, the line current, and the power factor of the DGs. By a numerical analysis, the authors have calculated the maximum capacity of DGs depending on many parameters, such as the length of the feeder, the DG power factor, and the like. In a short‐length system, the maximum DG capacity is governed by the current constraint, but in a long length system, it is governed by the upper voltage constraint. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 155(3): 18–28, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20330     

基于二进制莱维风驱动算法的船舶岸电系统并网故障诊断方法研究

针对船舶岸电无缝并网过程中出现的过流和继电保护误动作等问题,提出了一种基于改进二进制风驱动算法的船舶岸电并网故障诊断方法。分析船舶岸电系统的继电保护方案,在继电器、断路器拒动/误动条件下研究多种继电保护之间的状态关系及其对岸船电力系统的综合影响。选取适合船舶岸电电力系统故障诊断的数学模型,并利用改进的二进制风驱动算法对模型进行求解。最终,通过故障算例验证了该模型的合理性和改进算法的可靠性。     

新型继电保护发展现状综述

介绍了近年来国内外继电保护与故障测距新原理、新技术的现状及发展。简单总结了计算机对电力系统继电保护发展的影响。介绍了对故障信息的进一步利用;小波变换、神经网络等数学方法在继电保护领域中的应用;自适应原理继电保护的发展。新型继电保护的发展趋势是高速化、智能化、一体化,尽量避免测量元件对继电保护装置的影响。对故障信息的研究和充分利用是发掘继电保护新原理的基础,计算机在继电保护中的应用为充分利用故障信息     

A novel scheme for current-only directional overcurrent relay

Overcurrent relays are widely used as main protection in sub-transmission and distribution systems. In mesh and multi-source networks, application of directional relay is unavoidable. Traditional directional overcurrent relays use the reference voltage phasor as the polarizing quantity to estimate the direction of the fault. Traditional direction distinguishing scheme is unreliable in the case of close-in faults. In this paper, a novel algorithm for directional overcurrent relay is proposed. The new algorithm uses only current signals for determining the fault direction. It uses superimposed component of the current signal and does not require phasor estimation. This new algorithm uses pre-fault current signal as the polarizing quantity. The proposed method is tested on simple power system in different situations. The results show it leads to fast and reliable directional protection.     

基于模型识别的有源配电网单相接地故障定位方法

分布式电源(distributed generation, DG)大量接入使配电网继电保护面临严峻挑战。单相接地故障发生概率大,但故障信息十分微弱,特别是在DG多样化故障输出特性的影响下,有源配电网单相故障定位的准确性常难以保证。为此,提出了一种基于模型识别的有源配电网单相接地故障定位方法。分析了配电网单相接地故障下DG的输出特性,建立了在不同故障位置下有源配电网的正序增广网络,构建了故障位置关于馈线出口以及DG输出电流的函数,建立了配电网单相接地故障位置模型,利用不同故障位置下短路电流矢量占比系数的差异性构建了新的故障定位判据。通过将单相接地故障定位问题转化为故障位置模型系数的求解问题,提高了故障定位的准确性和实用性。理论和仿真分析表明,在不同故障位置、不同过渡电阻下均能准确定位单相接地故障,具有原理清晰、故障特征量采集便捷、灵敏性和可靠性高的优点。     

零序导纳法馈线接地保护的研究

提出了采用测量线路零序导纳进行接地保护的新原理,讨论了直线式导纳继电器的接地保护判据。该原理克服了传统的小电流接地系统故障选线方法安装不便,可靠性不高等不足。只需测量本线路的零序电压、零序电流基波分量,适合在馈线保护中实现和就地终端单元（FTU）上安装,可行性高。经EMTP仿真分析表明：该方法具有较高的保护精度,能满足高阻接地保护的要求。     

Distribution system fault identification by mapping of characteristic vectors

A new fault-locating scheme using the concept of characteristic vector is proposed. Utilizing digital overcurrent (O/C) relays, the proposed scheme can locate either a bus fault or a feeder fault by mapping corresponding fault current vector with the characteristic vectors in a pre-built database. By updating the characteristic vector database, the proposed scheme can be applied to the changed system as well, thereby achieving adaptive feature. No complex optimization technique is required. A simplified distribution system is employed to test the proposed scheme and its adaptive aspect. Test results show that the scheme has very good performance.     

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。     

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。     

Agent-based self-healing protection system

This paper proposes an agent-based paradigm for self-healing protection systems. Numerical relays implemented with intelligent electronic devices are designed as a relay agent to perform a protective relaying function in cooperation with other relay agents. A graph-theory-based expert system, which can be integrated with supervisory control and a data acquisition system, has been developed to divide the power grid into primary and backup protection zones online and all relay agents are assigned to specific zones according to system topological configuration. In order to facilitate a more robust, less vulnerable protection system, predictive and corrective self-healing strategies are implemented as guideline regulations of the relay agent, and the relay agents within the same protection zone communicate and cooperate to detect, locate, and trip fault precisely with primary and backup protection. Performance of the proposed protection system has been simulated with cascading fault, failures in communication and protection units, and compared with a coordinated directional overcurrent protection system.     

基于故障稳态分量的含DG配电网自适应方向电流保护方案

针对分布式电源(DG)大量接入配电网后保护可靠性低的问题,提出一种基于故障稳态分量的自适应方向电流保护方案。分析不同类型DG的故障暂态特性以及故障等值方法,计算系统短路电流所含分量,并揭示短路电流三相分量之间的关系。在此基础上,根据故障边界条件,获取系统故障稳态分量,再结合保护安装处的测量电压及测量电流,计算保护背侧等值电压和等值阻抗,构造不同故障类型下自适应方向电流保护判据。仿真结果表明该方案不受DG类型、DG出力以及系统运行方式影响,并能有效地防止电压跌落引起的延时保护拒动。     

Overcurrent protection for distribution feeders with renewable generation

Distribution systems in Taiwan are typically radial type or normally open loop type. Distribution feeders have a simple protection system that usually employs overcurrent relays. When renewable generation (RG) is connected to the distribution feeder, the feeder changes from a single-source system to a complex multi-source system, which causes loss of the original coordination among feeder protection devices. The operation of RG units can cause protection failure. Fault current produced by RG units may reduce the current measured by the feeder relay. Therefore, this paper proposes connecting RGs to the feeder via four-way circuit switches with overcurrent relays, and dividing the feeder into several protection zones. Each protection zone is capable of isolating fault itself.The algorithm process and design procedure of overcurrent protection are also proposed for distribution feeders with RG. Results of this research provide a valuable reference for overcurrent protection that improved protection coordination and system reliability.     

基于电流相角突变量方向的有源配电网保护

随着分布式电源(DG)的大量接入,配电网的结构由传统的辐射型改变为多端电源系统。由于DG出力的随机性,传统的基于电流幅值的保护方案很难整定。通过研究故障前后电流相角的变化,得出了电流相角突变量方向与故障位置的关系,并由此提出一种新的电流纵联方向保护方案。由于该方案只利用电流信息,避免了安装电压互感器。对于规模巨大的配电网,具有经济性。由于只需传输判定结果,降低了对通信通道的要求。最后,通过仿真分析,对保护方案进行了验证。     

分布式发电对重合器模式馈线自动化的影响

研究了实施重合器模式馈线自动化(FARM)的配电网馈线在接入分布式电源(DG)后发生相间短路故障时自动开关设备的保护配合动作行为.基于馈线上2个自动开关设备间的配合,考虑实际运行中发生故障时DG有可能没有及时退出的情形,针对DG的不同接入方式以及短路故障发生的不同位置,详细分析了FARM系统中典型的重合器-熔断器配合、重合器-分段器配合、重合器-重合分段器配合以及重合器-重合器配合在DG接入后的运行状况.得到了FARM系统中按传统配合方式整定的自动开关设备面对DG接入在短路故障时出现误动、拒动、配合紊乱等情形的内在机理.提出了DG接入后保证FARM系统中自动开关设备保护配合准确的DG容量与接入位置的限制策略.     

分布式发电条件下的新型电流保护方案

根据分布式发电（DG）接入配电网后网络结构和故障电流的变化特点,提出了一种新型电流保护方案。该方案利用电流综合幅值的比较将故障范围缩小到一个故障搜索区域之间,然后利用该区域电流间的相位关系对故障线段进行定位。文中详细论证了故障搜索的电流幅值判据和故障判断的电流相位判据,并分别提出了其矩阵算法,该算法对DG投退造成的网络结构的随机变化具有自适应性,对智能电子设备（IED）故障具备一定的容错能力,满足DG接入对配电网保护提出的要求。利用IED进行分布式处理,降低了保护对通信系统的要求,同时,由于仅利用电流量进行故障搜索判定,工程上较容易实现。文中对该电流保护方案进行了算例仿真,证明了方案的正确性。     

继电保护配合提高配电自动化故障处理性能

为了提高配电网的故障处理性能,论述了多级级差实现配电网继电保护配合的可行性。分析了装设瞬时电流速断保护情况下级差配合的适应范围。给出了多级级差保护与配电自动化协调配合的配电网故障处理策略的配置原则,讨论不具备多级级差保护配合条件时的处理和分布式电源接入带来的影响。研究结果表明:配电网多级级差继电保护配合是可行的,可以实现用户故障不影响分支,分支故障不影响主干线。即使安装了瞬时电流速断保护的情形仍然有一部分区域具备级差配合的条件。配电自动化与继电保护协调配合,能够显著提高故障处理性能。