Sensitivity improvement of time overcurrent relays

In this paper, we recommend a new adaptive function for time overcurrent relays. The purpose of the adaptation process is to improve the sensitivity of time overcurrent relays, which then operate with a dynamic pickup setting such as a load current. The results obtained from time overcurrent adaptive relays are collated, and the results from analysis of negative sequence relays and conventional time overcurrent relays are also presented. In this article, we describe the control logic structure of an adaptive pickup current and its performance under different operating states.     

Application of a proposed overcurrent relay in radial distribution networks

This paper contains the application criteria and coordination process for a proposed overcurrent relay in a radial power system with feed from one or multiple sources. This relay uses independent functions to detect faults and to calculate the operation time. Also this relay uses a time element function that allows it to reduce the time relay operation, enhancing the backup protection. Some of the proposed approaches improve the sensitivity of the relay. The selection of the best approach in the proposed relay is defined by the needs of the application. The proposed protection can be considered as an additional function protection to conventional overcurrent relays.     

Coordination of dual setting overcurrent relays in microgrid with optimally determined relay characteristics for dual operating modes

Fault current magnitude in a microgrid depends upon its mode of operation, namely, grid-connected mode or islanded mode. Depending on the type of fault in a given mode, separate protection schemes are generally employed. With the change in microgrid operating mode, the protection scheme needs to be modified which is uneconomical and time inefficient. In this paper, a novel optimal protection coordination scheme is proposed, one which enables a common optimal relay setting which is valid in both operating modes of the microgrid. In this context, a common optimal protection scheme is introduced for dual setting directional overcurrent relays (DOCRs) using a combination of various standard relay characteristics. Along with the two variables, i.e., time multiplier setting (TMS) and plug setting (PS) for conventional directional overcurrent relay, dual setting DOCRs are augmented with a third variable of relay characteristics identifier (RCI), which is responsible for selecting optimal relay characteristics from the standard relay characteristics according to the IEC-60255 standard. The relay coordination problem is formulated as a mixed-integer nonlinear programming (MINLP) problem, and the settings of relays are optimally determined using the genetic algorithm (GA) and the grey wolf optimization (GWO) algorithm. To validate the superiority of the proposed protection scheme, the distribution parts of the IEEE-14 and IEEE-30 bus benchmark systems are considered.     

基于负序电压极化的自适应阻抗继龟器研究

提出了一种基于负序电压极化的自适应接地阻抗继电器方案,并对其动作特性进行了分析。该继电器可根据接地电阻的大小自动调整继电器的动作边界,对接地电阻有极强的自适应能力。同时,继电器不存在动作的“电压死区”,具有明确的方向性。通过Matlab仿真分析结果证明,该继电器具有优良的动作特性,在500kV的高压线路上有良好的耐受过渡电阻能力。     

基于负序电压极化的自适应阻抗继电器研究

提出了一种基于负序电压极化的自适应接地阻抗继电器方案,并对其动作特性进行了分析。该继电器可根据接地电阻的大小自动调整继电器的动作边界,对接地电阻有极强的自适应能力。同时,继电器不存在动作的“电压死区”,具有明确的方向性。通过Matlab仿真分析结果证明,该继电器具有优良的动作特性,在500kV的高压线路上有良好的耐受过渡电阻能力。     

Adaptive overcurrent protection scheme coordination in presence of distributed generation using radial basis neural network

The operational performance of conventional overcurrent protection relay coordination connected to a distribution network is adversely afected by the penetration of distributed generators (DG) at diferent buses in the network. To address this problem, this paper proposes a novel adaptive protection coordination scheme using a radial basis function neural network (RBFNN), which automatically adjusts the overcurrent relay settings, i.e., time setting multiplier (TSM) and plug setting multiplier (PSM) based on the penetration of DGs. Short circuit currents and voltages measured at diferent buses are acquired using the remote terminal units (RTU) connected to diferent buses within the terminal network. Communication between the various remotes and local end station RTUs is through hybrid communication systems of fber optic and power line communication system modules. The new adaptive overcurrent protection scheme is applied to the IEEE 33-bus distribution network with and without DGs, for single and multi-DG penetration using both the ETAP and MATLAB software. The simulation results show the proposed scheme signifcantly improves the protection coordination.     

反时限距离保护原理的改进

反时限距离保护是解决近范围快速动作与保护范围末端可靠动作之间矛盾的最好策略。鉴于距离保护动作特性的二维性,目前均采用阶段式开放距离范围的策略达到反时限的效果。提出了一种新型反时限距离保护实现方法,采用相似动作区域的概念,首先根据测量阻抗,确定其所在的二维动作区域边界,根据参考点(一般选择动作原点)将此二维动作区映射为对应的一维同比缩放因子,然后依据此缩放比例因子构造反时限动作方程,由此实现了距离保护的连续反时限动作特性。理论分析表明此方法的合理性,并结合距离保护装置开发实际,给出了具体的实现方案。大量ATP仿真分析表明,此方法可行、有效。     

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.     

一种新型的微网自适应过流保护方法

微网灵活的运行模式给保护带来了严峻的挑战,对此提出了一种新型的微网自适应过流保护方法。以微网三处典型的故障为案例,从并网和离网角度剖析了微网自适应保护应具备的功能。以此为基础,给出了微网自适应保护方案并阐述了集中式微网保护的主从工作机制;提出了三段式自适应保护的过电流整定算法,设计了故障识别流程;基于分析传统过电流保护时限配合在微网保护中存在的弊端,提出了微网自适应保护在并网和孤岛时的动作时限优化方案,结合案例分析了其优点。理论和案例分析表明,所提自适应保护方法能够快速可靠地识别故障区域,满足微网对保护的要求。     

A comparative study for current transformer dimensioning in overcurrent relay

Dimensioning a current transformer (CT) is one of the most important tasks during the substation planning process. The installation of a correctly specified CT will ensure the integrity of the protection scheme. However, some parameters required for dimensioning a CT can be obtained only after the CT is installed in the substation. Because of the conflicting requirements, utility companies commonly adopt a simplified approach in compensating for the missing parameters. Two other methods for dimensioning CT under the given constraint during the planning stage have also been proposed by several authors. In view of the availability of the three methods of approximating CT specifications, this paper will conduct a comparative study to evaluate their accuracies. The approximated specifications of the CT during the planning stage are compared against those measured from a practical substation. Based on the findings from the comparative studies, the most reliable approach for CT dimensioning during the planning stage is proposed. © 2016 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

超高压电网反时限零序过流保护简化整定方法

随着国内超高压电网中传统四段式定时限零序电流保护的整定配合越来越困难,反时限零序过流保护作为后备保护逐渐得到应用。但目前其定值整定多依赖工程经验,缺乏理论支撑,给实际应用带来诸多限制。为此,首先结合超高压电网变电站装设接地变压器的结构特点,分析了零序网络电流的自然差异分布特性,给出了简化整定的理论基础。然后提出采用全网统一定值整定原则的反时限零序过流保护简化整定方法。最后通过理论分析说明了简化整定后仍可保证选择性与灵敏性。利用国内某区域电网500 kV局部输电网算例进行计算,其结果证明了所提简化整定方法有效且合理。     

电子式过载保护继电器的研究

详细介绍了一种智能化电子式过载保护继电器。该过载保护继电器以电流幅值、正序分量、负序分量、零序分量及电压幅值的不同排列组合作为电动机的保护判据,以PIC16F877单片机作为核心部件,具有过载、断相、短路等多种故障自动诊断及串行通信等功能,从而达到了电动机保护智能化的要求。     

配电网输电线路反时限过流保护探讨

讨论了传统的反时限过电流保护的实现方法 ,如分区查表法 ,插值方法的实现方式及其误差特性 ;提出了适用于配电网的过电流保护的冷备用方案 ;论述了一种用DSP技术实现反时限特性曲线的新技术 ,提出了在DSP技术下计算动作时限的新方法。该方案能够根据故障电流的大小实时计算出过电流保护的动作时限 ,所需要的内存较小 ,且计算速度快 ,在配电网的自动化技术中 ,具有较强的实用性     

Numerical inverse definite minimum time overcurrent relay for microgrid power system protection

Access of distributed generation gets complicated at the distribution level, and hence managing these systems effectively becomes highly challenging. Microgrids have been proposed as a way of integrating a large number of distributed renewable energy sources with a distribution system. They are low to medium voltage networks of small load clusters with distributed generation sources and storages. Microgrids can be operated in the islanded mode or the grid‐connected mode. If a microgrid is connected to the system, it is seen as a single aggregate load. One of the potential advantages of a microgrid is that it could provide more reliable supply to customers by islanding itself from the system in the event of a major disturbance. However, a major problem with microgrid implementation in islanded operation is designing a proper protection scheme. The fault currents for grid‐connected and islanded microgrids are significantly different. Additionally, high penetration of inverter‐connected distributed generation sources leads to conditions where no standard overcurrent protection method will work. Overcurrent protection is considered as the backbone of any protection strategy, especially in distribution systems. Distribution systems constitute the largest portion of the power system network, and therefore the diagnosis of faults in this system is a challenging task. Faults occurring in distribution systems will affect the reliability, security, and quality of a power system. Field‐processable gate array (FPGA) Xilinx Zynq‐based numerical overcurrent relay protection is provided to the microgrid that is operated in islanded mode. This results in faster discrimination and quicker isolation of the faulty section from the microgrid. This improves the reliability of the microgrid because the fault is rapidly diagnosed and isolated from the healthy part, thanks to the high‐speed operation of the 800‐MHz FPGA Xilinx Zynq‐based numerical overcurrent relay. This system is simulated using MATLAB Simulink SimPower system tool box and LabView software. © 2014 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

静态时间继电器抗扰分析

直流回路受到交流电压干扰,是控制回路中容易产生的现象.认识并消除其危害,是抗干扰应采取的措施.通过对静态时间继电器的抗干扰试 验和比较,提出对应方法.     

Comprehensive coordination of combined directional overcurrent and distance relays considering miscoordination reduction

This paper presents a novel approach to solve the miscoordination problem of combined directional overcurrent and distance relays in transmission and subtransmission systems. In order to reduce relays miscoordinations, a general objective function is presented to find optimum directional overcurrent relays time setting multipliers, characteristics, and pickup currents by optimization algorithms. In previous researches, different approaches have been presented but they cannot find a reliable solution to avoid from having negative discrimination times between the backup and main relay (miscoordination), which means operation of the backup relay before the main relay. Using proposed approach, not only the number of miscoordinations can be greatly decreased but also the positive discrimination times can be minimized. The proposed method is tested on 9-bus and 39-bus test system. Genetic algorithm and human behavior-based optimization are used as optimization tools to find optimum settings. The results indicate that the proposed approach is capable of solving the miscoordination problem, in addition to minimization of discrimination and relay operation times compared with previous approaches.     

自适应电流速断保护中实时计算系统参数算法研究

研究了自适应电流速断保护中实时计算系统等值参数的一种傅氏算法。首先,分析了一般全周傅氏算法在计算系统等值内阻抗时的实现方法．计算示例显示该方法由于受短路电流非周期分量的影响,会产生很大的误差。然后,研究了带补偿的傅氏算法计算系统等值内阻抗的实现方法,应用相同的计算示例对各种不同相电势初相角下的系统等值内阻抗进行了计算。结果表明带补偿的傅氏算法具有很高的精度。最后,提出了利用记忆在计算机存储器内的故障前测量电压、电流采样值计算系统等值相电势的方法,并用计算示例证实了算法具有很高的精度。     

曲线拟合法在反时限过流继电器中的应用

对通用的三种标准反时限特性曲线的数学模型进行了分析,提出了一种用曲线拟合的算法,根据拟合结果研制成的微机线路保护装置,经测试:继电器的动作特性较好,具有较高的工程实用价值。     

配电变压器过流保护配置分析及完善方法

随着国民经济的迅速发展 ,电力需求日益增加 ,安全可靠供电显得越来越重要。用户对电能质量及年可靠供电时间有了更高的要求 ,除了提高配电网系统自动化水平外 ,对现场常用Y Y0 接线和Δ Y0 接线的配电变压器 ,选择适应系统特点的继电保护装置显得更为突出。由于诸多城市小区智能楼宇的兴起 ,大型厂矿企业等用电大户基本上都应用这两种方式供电 ,致使传统的熔断器和继电器保护上下级之间的电流定值难以配合 ,常常造成短路容量增加。该文通过对不同接线方式配电变压器的分析 ,进行模拟现场实验 ,确定出在使用上述配电变压     

桐柏抽水蓄能电厂机组负序电流保护改进

介绍了桐柏抽水蓄能电厂大容量发电电动机负序电流保护整定配合,讨论了其在实际运行中存在的问题。针对桐柏电厂机组内桥接线方式下的特点,提出符合系统需求和机组特性的负序电流保护整定改进方案,以满足大容量机组对保护选择性、灵敏性和可靠性的要求。