Applying CTs with digital ground relays

Industrial power distribution system substation transformers and generator step-up transformers in power stations often use resistance-grounded wye secondary windings for medium-voltage power distribution. The purpose of this is to limit damage due to ground-fault currents, while providing sufficient fault current for the operation of ground-fault relaying. The relaying used to protect against ground faults in the system may not provide sufficient protection of the transformer winding against internal faults because the backup ground overcurrent relay in the transformer neutral-to-ground connection must be set to coordinate with downstream relays. In order to protect the winding itself, special relays are utilized. Ground differential protection can be provided by digital overcurrent relays in conjunction with auxiliary ratio matching transformers. Ground differential protection can also be provided in multifunction digital relays. Transformer protection relays may include this feature with one of the schemes used with component relays. If a feeder-protection relay is used on the secondary, in some cases, this may have a ground-directional feature that can be utilized for ground-differential protection     

Multifunction digital relay commissioning and maintenance testing

This paper discusses with the protective relay technology over the past 25 years has evolved from single-function electromechanical (EM) relays, to static (electronic) relays, and, finally, to digital multifunction relays. A significant number of these multifunction digital relays are being installed on medium-voltage electric power systems within industrial and commercial facilities. As was required in earlier EM and static relay technologies, digital relays also require commissioning and relay-setting verification. This article discusses the unique challenges the user faces in testing and commissioning digital multifunction relays. It also explores the impact on maintenance testing of self-diagnostics, the digital relay's internal capability to check itself for failures.     

采用光纤通信后的220 kV线路保护配置

随着光纤技术在电力通信领域的广泛应用,已使利用光纤通道传输继电保护信息成为现实。由于通道类型的不同,奉引起保护配置上的变化。文中在简单介绍一种专门适用于光纤通道的220kV线路继电保护装置的基础上,为实现220kV线路保护的双重化,对采用光纤通道后220kV线路保护提出的2种不同配置方案进行比较,并选择出最佳方案。     

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.     

Microprocessor-based protective relays

This article describes the benefits of microprocessor (μP) relay performance and its capabilities beyond previous protective relaying technologies. This article also discusses a multiple quality-measurement approach to observing, measuring, and then calculating μP relay reliability and unavailability. This is an important consideration for industrial and commercial facilities that are being required to repair or replace old electromechanical or solid-state (analog and digital) protective relaying equipment because of equipment malfunctions, misoperations, accidental tripping, or obsolescent parts. Although lP relays have been commercially available for more than 20 years and researched for the past 40 years, industrial and commercial plant engineers tend to be more reluctant to embrace the μP technology. Electric power utilities in North America have aggressively selected to replace older protection equipment by upgrading and replacing the equipment with new μP relays whenever and wherever possible.     

Relay setting considerations and operational experience of a long500 kV transmission line

The large capacitive susceptance, large load magnitude, and substantial phase unbalance before and after a single-pole trip operation have a substantial effect on the performance of the protective relaying systems of the Minneapolis-Duluth 500 kV line. Computer simulation studies show that correct operation of the relays can be assured if these effects are taken into consideration in determining relay settings. The selection, performance, and operation of the primary and secondary relay system are discussed, indicating that the relaying protection used achieved substantial security and dependability     

Application of transformer ground differential protection relays

Transformer ground differential protection relays (device 87G) have been used to protect the windings of resistance-grounded transformers. A number of strategies have been utilized with electromechanical relays in the past. With the advent of the multifunction digital protective relay, these strategies can be adapted to continue this form of protection     

A virtual environment for protective relaying evaluation and testing

Protective relaying is a fundamental discipline of power system engineering. At Georgia Tech, we offer three courses that cover protective relaying: an undergraduate course that devotes one-third of the semester on relaying, a graduate course entitled "Power System Protection," and a three-and-a-half-day short course for practicing engineers. To maximize student understanding and training on the concepts, theory, and technology associated with protective relaying, we have developed a number of educational tools, all wrapped in a virtual environment. The virtual environment includes a) a power system simulator, b) a simulator of instrumentation for protective relaying with visualization and animation modules, c) specific protective relay models with visualization and animation modules, and d) interfaces to hardware so that testing of actual relaying equipment can be performed. We refer to this set of software as the "virtual power system." The virtual power system permits the in-depth coverage of the protective relaying concepts in minimum time and maximizes student understanding. The tool is not used in a passive way. Indeed, the students actively participate with well-designed projects such as a) design and implementation of multifunctional relays, b) relay testing for specific disturbances, etc. The paper describes the virtual power system organization and "engines," such as solver, visualization, and animation of protective relays, etc. It also discusses the utilization of this tool in the courses via specific application examples and student assignments.     

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.     

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     

Digital defense

This article deals with the advances in digital technology, which has provided relay designers with the tools to increase the capabilities of modern digital relays to provide more complete protection of generators. This article discusses field-ground protection and brush lift-off detection, which is recently incorporated into the multifunction digital generator relay. The scheme presented in this article addresses field-ground detection on generators with brushes and an external source of DC field current and voltage.     

Benefits of upgrading: paper mill generator protection

There are a number of functional protection areas on paper mill generators 20 years or older that have significant shortcomings when compared to current IEEE recommended generator-protection practices. This article identifies these protection areas and the risks of not addressing the shortcomings. It also points out the advantages of using multifunction digital relaying to upgrade generator protection as a technology that offers many advantages over older electromechanical relays. The completed upgrade project at MeadWestvaco's Luke Mill in Maryland provided a number of examples of these benefits in uncovering mill problems that, if they had gone undetected, could have resulted in costly mill shutdowns or damage to mill generators.     

Proposed statistical performance measures for microprocessor-basedtransmission-line protective relays. I. Explanation of the statistics

The paper presents practical calculations and novel techniques for collecting performance data from protective relays. The methods are focused on, but not limited to, microprocessor-based transmission line relaying systems. Standard definitions are presented for availability, dependability, security, hardware MTBF, relaying MTBF, repair time, and other measures of interest for specific relay types. The paper explains the novel concept of exposures, the key to a standardized security measure. With these standard measures, relay users will be able to compile the first consistent industry-wide data base for relay performance assessment     

A Microprocessor-Based Scheme for Testing Protective Relays

ABSTRACT

This paper presents a general hardware scheme for testing protective relays using microprocessor based systems. The microprocessor simulates the relaying signals for test purpose and monitors the relay performance. Based on the proposed hardware, a teat procedure for directional overcurrent relays is presented in detail. Typical test results of various routine tests conducted on a commercial single phase directional over-current relay clearly demonstrate the efficacy of the proposed technique for conducting tests on commercial relays.     

根据GB/T14285-2006设计发变组保护探讨

根据<继电保护和安全自动装置技术规程>GB/T 14285-2006归纳了发电机变压器组继电保护的主要特点,对发电机变压器组单元接线继电保护配置的部分条款要求作了解释,详细论述了应考虑装设的保护和各种保护出口的设置原则,并对目前电气量保护全双重化存在的问题提出了一些看法和建议,突出强调了发电机变压器组公共保护的主要特点和设计方案.最后,对大型发电机变压器组继电保护的配置和保护出口的设计原则提出了几个值得注意的事项.     

继电保护技术的新进展

电力系统继电保护技术的发展方兴未艾。将近一个世纪以来,它已经历了三个发展阶段、两次飞跃。在简要回顾继电保护技术发展史的基础上,介绍了继电保护技术的新进展,其中包括有：利用故障分量的继电保护,自适应继电保护,小波变换与继电保护,ＧＰＳ在继电保护中的应用。     

Applying the directional neutral, 67N, function in microprocessor multifunction relays

This paper is a case study of the application of the 67N function in a digital multifunction relay. The directional neutral current relay, function number 67N, is often found to be critical to the proper operation of a protective scheme. Furthermore, a false trip of a 67N will usually be devastating. The 67N is a complex function that always required more wiring than almost any other relay. The 67N is now available as one of many functions in digital multifunction relays. However, the digital 67N may be even more difficult to set and test than it was as a single function in an old electromechanical relay.     

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.     

Protection, metering, monitoring, and control of medium-voltage power systems

Traditional practices for industrial and commercial medium-voltage power systems to provide protection, metering, monitoring, control, power quality analysis, disturbance recording, and automation have changed. The new multifunction numerical protection relays using the processing power of the present generation of microprocessors have very high functionality. Many functions can be integrated into one device, allowing new power system problem-solving capabilities while permitting significant cost savings as compared with discrete protective relays, instruments, meters, recorders, and transducers of the past. This paper describes the vast capabilities and recent enhancements of these devices, which will be called intelligent electronic devices in this paper. Included are anecdotes obtained from an installation on a large industrial power system.     

Application of multifunction generator protection systems

The introduction of microprocessor technology enabled multiple protection functions to be integrated into a common protection platform which has advantages when applied to generator protection. This paper provides an insight into industry application experience in using multifunction generator protection systems on various sizes and types of generators. Included are discussions on application and performance differences between multifunction protection systems and single function static and electromechanical relaying devices. Also included is a summary of the various types of tests performed on the multifunction protection systems by the user. The paper additionally addresses the need for application of redundancy and backup protection when applying multifunction generator protection systems on large or important generators