Performance of frequency relays for distributed generation protection

This paper investigates the efficiency of under/over frequency relays for protection of distributed synchronous generators considering islanding detection and frequency-tripping requirements. Comparison between frequency and vector surge relays, which are islanding detection-dedicated devices, shows that the former can be as effective as the latter. This feature supports the idea that frequency relays can replace vector surge relays for islanding detection purpose. In this case, frequency relays must also meet the generator manufacturer recommendations and the utility frequency-tripping requirements. In order to investigate the relay capability to meet both necessities, it is proposed the concept of application region, which defines a region in the detection time versus active power imbalance space where frequency-based relays can be adjusted to satisfy the anti-islanding and frequency-tripping requirements simultaneously. The paper also presents a set of formulas to determine directly the application region.     

Power imbalance application region method for distributed synchronous generator anti-islanding protection design and evaluation

This paper presents a novel graphical approach to adjust and evaluate frequency-based relays employed in anti-islanding protection schemes of distributed synchronous generators, in order to meet the anti-islanding and abnormal frequency variation requirements, simultaneously. The proposed method defines a region in the power mismatch space, inside which the relay non-detection zone should be located, if the above-mentioned requirements must be met. Such region is called power imbalance application region. Results show that this method can help protection engineers to adjust frequency-based relays to improve the anti-islanding capability and to minimize false operation occurrences, keeping the abnormal frequency variation utility requirements satisfied. Moreover, the proposed method can be employed to coordinate different types of frequency-based relays, aiming at improving overall performance of the distributed generator frequency protection scheme.     

5G通信自同步配网差动保护研究与应用

随着分布式电源的高度渗透和环网结构的逐步增多,配电网迫切需要电流差动保护应对过流保护面临的挑战。基于5G的商用化契机,研究开发一种基于5G通信的配电网分布式差动保护。该保护采用基于移动边缘计算的切片网络作为数据通道,具有超低延时和超高可靠的特点;采用基于故障时刻的自同步方法解决差动保护两端的数据同步问题,无需增加额外对时装置。在5G智能电网应用示范区,对所开发装置进行了单基站和跨基站环境下的综合测试,并投入10 kV线路试点运行。现场测试结果与试运行数据表明,差动保护性能满足配电网工程应用要求。     

All your eggs in one basket [back-up protection using multifunction relays]

Multifunction microprocessor-based relays are commonly used in modern installations due to the many advantages they offer, such as communications, measurements, simplified wiring, self monitoring, and reduced space requirements. A reliable protection scheme is very important in order to protect capital equipment and operating personnel and reduce down time by selectively clearing faults. Back-up protection is also normally provided to ensure the elimination of faults should the primary protection circuit fail. In this article, the authors show how the features of modern multifunction relays can be used to enhance back-up protection. To better understand why multifunction relays can improve back-up protection, it is necessary to first review what back-up protection is and how it has been implemented in the past. This review is based on the electrical distribution system typically found in large petrochemical installations.     

基于用户自定义特征的反时限有源配网保护方案

由于分布式电源输出功率的随机性与波动性,当分布式电源大量接入配电网后,传统的反时限过电流保护方案很难满足配电网保护选择性和速动性的要求。为此,文章通过研究数字反时限过流保护继电器,提出一种基于用户自定义特征的反时限过电流保护方案。保护方案将反时限继电器的特性常数(A)和反时限的类型常数(B)同继电器的时间整定系数、启动电流共同作为待优化的连续变量,并以最小故障电流时所有保护动作时间之和最小为目标函数,利用内点法求解保护的最优配置。方案保证了线路出口处故障时保护能快速动作,满足了配电网保护选择性和速动性的要求。最后,通过仿真分析,对保护方案进行了验证。     

Differential Protection for Special Industrial Transformers

Power transformer differential protection has been used for decades on standard three-phase power transformers. However, special industrial transformers, such as 24-pulse converter transformers, could not typically be protected easily with the standard power transformer differential relays. The main reason is the nonstandard phase angle shift of 24-pulse converter transformers. Such 24-pulse converter transformers are often used in industrial and railway applications. This paper will show that it is possible to provide differential protection for such special transformers by using standard numerical transformer differential protection relays and external interposing current transformers (CTs). However, the external interposing CTs can be designed in a standardized way. This approach will significantly simplify the application of differential protection for special industrial transformers.     

考虑DG接入位置和容量的配电网保护综合改进方案

为了解决分布式电源(distributed generations,DG)接入配电网后引起的传统配电网继电保护拒动、误动、灵敏度降低等问题,提出一种适应DG大量接入配电网的改进保护方案。从DG接入位置和容量角度,分析接入母线和馈线对传统配电网三段式电流保护和反时限过电流保护的影响,并计算传统配电网三段式电流保护允许接入容量。通过配置低电压加速反时限过电流保护,以及加装少量方向元件对传统配电网继电保护进行改进来满足含大量DG的配电网保护要求。利用PSCAD/EMTDC对含DG的10 kV配电系统进行了仿真分析,仿真结果表明,该改进方法能够满足不同容量的DG接入配电网保护要求,具有很好经济性和实用性,符合我国当前配电网发展现状。     

Trade-Offs in Overload Protection for Low Voltage Motors

Running overcurrent protection for motors rated 600 V or less is available in a variety of devices. Thermal overload relays, thermal protectors, magnetic and solid-state overload relays, multifunction solid-state motor protectors, and even short-circuit protective devices selected according to certain rules of the National Electrical Code (NEC) can provide varying degrees of protection. Selection of the running overcurrent protective device is based upon application requirements, cost, convenience, and performance. The advantages and disadvantages of each method of providing overload protection for three-phase low-voltage motors in a concise manner are outlined, so that an individual selecting overload protection for a motor circuit can be aware of the many considerations and select the overcurrent protective means that optimizes the concerns he feels are most important.     

IEC 61850数字化保护动模测试系统设计与实现

IEC 61850标准的应用给变电站自动化系统带来了重大变革。在此类变电站中,保护装置可以直接从电子式互感器处获取所需的电流、电压数字量信息,并向智能开关控制器发送数字化跳闸命令。这种数字化保护与传统的微机型保护在硬件结构和信号处理方面都存在差异,传统的保护测试方法将不再适用。文章分析了基于IEC 61850的数字化保护装置的测试要求,提出通过对传统的物理模拟系统进行升级改造,建立符合要求的测试系统。根据这一思路,该新型测试系统在山东大学电力系统动态模拟实验室的基础上开发而成。初步试验结果表明,测试平台能够提供所需要的二次接口特征和测试环境,可以对不同种类的IEC 61850保护装置进行动模测试。     

基于风险的继电保护定值薄弱区域在线辨识

在线校核对于提高电网的运行水平具有重要作用,但在应用于大规模电网时,由于不满足校核要求的保护数目较多,用户很难确定这些保护定值的薄弱程度。基于此,文中以距离保护为例分析了不满足校核要求时保护不正确动作的概率,并选取相对负荷损失量度其后果,实现了当前运行方式下基于风险的定值薄弱区域在线辨识;同时,从系统运行波动角度给出了历史运行方式下的定值薄弱分析。两者相辅相成,共同为用户及时制定合理的定值维护策略提供依据。工程示例验证了该方法的合理性和可行性。     

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.     

A comprehensive method for break points finding based on expert system for protection coordination in power systems

Interconnected power systems are multi-loop structured. In such networks, the determination of settings for all overcurrent relays can be carried out in different forms and may be quite complicated. The main problem for coordination is the determination of starting points, i.e. the location of starting relays in the procedure for settings, which is referred to as break points. In this paper, a powerful approach based on expert system is applied. The rules of the expert system include network configuration, protection systems, fault levels, etc. The method is applied to two networks with different configurations, pilot protection and other protection systems. From the obtained results, it is reviled that the new method is efficient, accurate, comprehensive and more optimal than the previously used graph theory.     

一种适用于微电网的分散式自适应过电流保护

针对传统的定流继电保护不能及时响应微电网拓扑结构变化的问题,文中提出一种分散式自适应过电流保护方案。根据微电网的故障特性将微电网中的馈线以分布式电源为中心分为上游区域和下游区域。针对不同区域分别配置基于瞬时继电器的分散式保护法。最后,在电磁暂态仿真软件PSCAD/EMTDC平台上建立微电网模型,验证所提方法。结果表明,所提方法能正确地切除微电网在不同运行模式、拓扑结构、DG运行状态下的故障,提高了保护的可靠性。     

The new science of protective relaying in the petrochemicalindustry

The multifunction digital relay has greatly expanded the science of protective relaying. The new science of protective relaying has resulted in the following improvements and benefits to the petrochemical industry. The multifunction relays typically have a large array of functions that can be used for electrical equipment protection. The multifunction relays are typically less costly than the equivalent package of discrete electromechanical and solid state relays. The programming logic provided by most multifunction relays allows for sophisticated protection schemes that were either not possible or economical with the discrete protection components of the past. The burden requirements of the multifunction relays are typically very low. With increases in technology, the testing and calibration of protective relays is changing. Advances in technology in the future may result in a decreased life expectancy of protective relay packages of the future     

Non-communication protection method for meshed and radial distribution networks with synchronous-based DG

This paper presents an efficient protection method which can be used for both meshed and radial distribution networks (DNs) with synchronous-based distributed generation (SBDG) units. The method does not require any communication system in the both grid-connected and islanded modes of operation. The microprocessor-based relays used in the DNs are programmed with a new time-current-voltage characteristic utilising only local fault voltage and current magnitudes. The proposed method is verified by simulation study on the DN of IEEE 30-bus test system as a meshed network in grid-connected mode. The method is also tested on an Iranian practical radial DN in the both grid-connected and islanded modes of operation. The test cases include different fault conditions, with SBDG at various locations and different DG penetration levels, and also without any SBDG in the networks. It is shown in a comparative study that the new time-current-voltage characteristic achieves a notable reduction in total relay operating times without any communication links. In addition, the method uses the same protection settings for the both grid-connected and islanded modes of operation.     

Algorithmic-knowledge-based adaptive coordination in transmission protection

Changes in power system operating conditions can affect both the reach point of distance relays and the coordination of distance and overcurrent relays. To improve the performance of the protection system, an adaptive scheme of relay settings is proposed. That is possible since the protection relays became digital . This paper describes a system for online adaptive setting and coordination of protection relays in meshed networks where the backup protection is achieved in remote form. After changes in the state of the network, an expert system (ES) performs the detection and proposes the correction of erroneous settings of protection zones and miscoordinations between relays at different stations; through an algorithm based on a fast determination of a nonminimal set of "break-points" (BPs) relays , new time characteristics for the coordination are found. The results of the application of the developed system to a test network of 34 nodes, 55 branches, and 110 relays are shown.     

IEEE-C37.94标准在继电保护设备中的应用

为提高继电保护装置的光纤通道故障监测能力和定位能力,尝试将IEEE-C37.94光接口标准应用到继电保护装置,并研究该标准应用到继电保护装置中的优势及局限性。通过解读IEEE-C37.94光接口标准帧格式的协议,结合国内继电保护装置的光纤传输要求,验证该标准可以允许不同厂家的保护设备与数字复接接口设备在光接口处能够互通,并且对不同链路的通信故障能够有效定位。但也存在传输带宽不高问题,宽松的校验措施也给其应用于继电保护设备带来了一些局限性。实际应用情况表明,IEEE-C37.94标准应用于继电保护设备是可行的。     

Protection and commissioning of multifunction digital transformer relays at medium voltage industrial facilities

The application of multifunction digital relays to protect medium voltage power transformers has become a common industrial practice. Industrial transformers, unlike utility transformers, frequently use neutral grounding resistors to limit ground current during faults to the 200-400-A level on medium voltage systems. This paper will discuss why these types of transformers require sensitive ground differential protection. The paper will also discuss the basics of transformer protection including phasing standards, through-fault withstand capability, differential/fusing/overcurrent protection, slope, current transformer (CT) requirements, and harmonic restraint, and communicating these properly to new digital relays. The rationale for providing transformer overexcitation protection on all major transformers within mill facilities is also addressed. Advancements in digital technology have allowed relay manufacturers to include more and more relay functions within a single hardware platform as well as address increasingly more transformer winding configurations. This has resulted in digital transformer relays requiring an Einstein to set and an Edison to commission. Since there are few Einsteins or Edisons among us, the next generation of transformer relays needs to concentrate on this complexity issue in addition to technical improvements. This paper addresses these issues that the author believes are the major shortcomings of existing digital transformer protective relays.     

基于网络的继电保护整定计算和短路电流计算程序设计

为适应继电保护信息管理网络化的趋势 ,作者根据多年的继电保护整定和运行经验 ,编制了与继电保护整定和运行有关的一整套程序 ,且边开发边验证该套程序。文章介绍了一种继电保护整定计算和短路电流计算程序设计的新思路 ,它将和 DMIS网相结合 ,各程序之间是有机结合的 ,计算是基于网络的计算模式 ,编制过程中强调优化算法     

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.