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.     

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     

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.     

Computer aided coordination of directional relays: determination ofbreak points

The directional overcurrent and distance relays of a multiloop network must be set in a sequence to ensure coordination. The starting points of the sequence are called break points. An algorithm to determine the minimum number of break points is presented. It can be readily implemented on a computer and forms a basic component of a computer-aided-design package for a protective system     

Study of Solving the Coordination Curve Intersection of Inverse-Time Overcurrent Relays in Subtransmission Systems

This paper presents a practical and effective novel approach to solve the coordination problem caused by the curve intersection of overcurrent relays in subtransmission systems. Based on the IEEE and IEC standard characteristic curve equations of digital overcurrent relays, as well as the simulation curve equation for electromagnetic overcurrent relays, lever setting adjustment equations for a selected point on the characteristic curve is derived. Then, centered on the derived equations, a dedicated software program is developed to compute the corresponding relay lever setting with different tap value in order that, passing through the selected point, another curve with the new lever setting is chosen. Finally, assisting with the graphical capability of the commercial ASPEN OneLiner, the proposed fixed-point coordination curve adjustment procedure can completely eliminate the coordination curve intersections. In addition, an actual case of a subtransmission network in Taiwan Power Company is simulated to validate the feasibility of the technique proposed.     

Enhanced time overcurrent coordination

In this paper, we recommend a new coordination system for time overcurrent relays. The purpose of the coordination process is to find a time element function that allows it to operate using a constant back-up time delay, for any fault current. In this article, we describe the implementation and coordination results of time overcurrent relays, fuses and reclosers. Experiments were carried out in a laboratory test situation using signals of a power electrical system physics simulator.     

Protective relaying for multi-source generator buses

The reliability of an industrial power system can be increased by proper selection and application of protective relays. This is especially true for the medium-voltage distribution system. An effective protective relay application scheme is presented that uses devices widely used in present pulp and paper mill power distribution systems. The effective use of summation overcurrent and directional overcurrent relays for multisource generator buses makes it possible for the power system protective engineer to achieve good selective operation between source buses for both phase and ground fault current conditions. This greatly enhances the reliability of the power distribution system     

Combined use of definite and inverse time overcurrent elementsassists in transmission line ground relay coordination

In some cases the coordination of ground time overcurrent relays in transmission line protection applications can be difficult. The combined use of definite and inverse time overcurrent characteristics sometimes provides significantly improved protection speed and sensitivity. Two cases are discussed where the use of hybrid characteristics has achieved improvements. The application of hybrid characteristics is limited by difficulties in dynamic coordination. The technology to overcome the dynamic problems would appear to be technically feasible     

F35型多功能馈线管理继电器在单母线分段系统中的应用

F35型多功能馈线管理继电器是建立在通用平台上的新一代模块式数字化继电器，用于电气自动化及变电所的保护和控制、测量，以及管理电能质量、数字故障记录及预见性维修。标准应用为多馈线的保护和测量，当有母线电压测量时为5回线路，无母线电压测量时为6回线路。文中介绍如何用F35型多功能馈线管理继电器完成单母线分段系统的进线、母联及电压互感器的全部保护、控制、测量及其他功能。     

Optimal coordination of directional overcurrent relays consideringdefinite time backup relaying

A methodology is presented for the consideration of definite-time backup relays in the optimal coordination of directional overcurrent relays using linear programming. It is shown that the influence of considering second-zone distance relays and breaker failure relays impose important requirements for the determination of the time dial settings of directional overcurrent relays. The paper introduces a revised formulation of the optimization problem. Results are presented for the application of the methodology on a power system with 2 generators, 9 buses, 2 transformers and 7 transmission lines     

The universal overcurrent relay

A comprehensive list of nondirectional overcurrent relays would include thermal overload, inverse-time, definite time, and instantaneous relays. The list could be further classified by operating quantities including individual phase, residual, and negative-sequence current. Taken collectively and depending on the characteristic shape, pickup and time range, and dynamics, these relays span the applications for motor, feeder, and breaker failure protection. Because of the past necessity for using either discrete or specialized system relays, overcurrent characteristics for these applications may appear diverse and unrelated. However, microprocessor relay technology has advanced to where it is not only feasible, but it is of distinct economic advantage, to consider all these characteristics collectively as attributes of a universal overcurrent relay. This universal relay concept is used here to discuss the commonality, the differences, and the coordination of the elements required for feeder, motor, and breaker failure protection. The article goes on to discuss the rules for the coordination of negative-sequence overcurrent characteristics for sensitive phase-to-phase fault protection in feeders, as well as for unbalanced current protection of induction motors     

Coordination of directional overcurrent relays in transmissionsystems-a subsystem approach

A new concept, called subsystem coordination, for efficiently computing proper settings of directional overcurrent relays on transmission systems in response to changes in system topology and load levels is proposed. An automatic window identification and coordination algorithm has been developed, implemented, and tested on a realistic transmission system. The test results have been validated through a full system coordination study, and the significant reduction in computer time required by the subsystem approach has been demonstrated     

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.     

矿井高压电网的自适应过流保护研究

针对目前矿井高压电网过流保护经常误动或拒动的问题,提出一种基于自适应控制技术的定值整定方案。该方案通过对每条线路的电压、电流进行实时监视和分析,自动改变继电保护的整定值和特性以提高过流保护装置的灵敏性、可靠性,并通过常态闭锁、延时配合实现了保护的纵向选择性,为消除矿井高压电网长期存在的因短路故障而引起越级跳闸的安全隐患提供了技术支持。     

Optimal coordination of directional overcurrent relays ininterconnected power systems

The authors present a new methodology based upon the principles of optimization theory, to treat the problem of optimal coordination of directional overcurrent relays in interconnected power systems. With the application of the proposed technique, this coordination problem is stated as a parameter optimization problem, which in general, is of a large dimension, especially when many different system configurations and perturbations are to be considered. Several optimization procedures, including direct methods and decomposition techniques, for solving this large scale coordination problem are described, and results of optimally coordinating directional overcurrent relays in power systems with up to 30 buses are presented     

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.     

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。     

LOCAL OPTIMAL COORDINATION BASED ADAPTIVE COORDINATION

ABSTRACT

This paper presents the development of an adaptive coordination scheme for the coordination of directional overcurrent relays for large interconnected power systems, using the concept of local optimal coordination under the changed system conditions. In response to a structural change or an operational change in the power system, the developed adaptive local optimal coordination algorithm automatically identifies the local disturbed region and re-coordinates only the settings of the relays which fall inside this identified local region in an on-line manner. The scheme developed is applied to the IEEE 57-bus test power transmission system. The results are validated through a full system coordination study and the usefulness of the reported algorithm is demonstrated.     

New overcurrent RST80 relays and their time-current characteristics

The problems are considered of the operation of electromechanical overcurrent relays and construction of relay protection using their time-current characteristics. The distinctive features of new static overcurrent RST80 relays are presented. It is shown that the four types of time-current characteristics implemented in the RST80 relay provide flexible coordination with the characteristics of the protection of the adjacent equipment.     

An interior point method based protection coordination scheme for directional overcurrent relays in meshed networks

In this work, interior point method based protection coordination schemes are presented for coordinating directional overcurrent relays. Also, for minimizing the operating times of primary and backup relays simultaneously, a new objective function (NOF) is developed. The effectiveness of the proposed solution methods and the developed objective function has been investigated on two test systems (one small and one large). The suitability of the proposed method for coordination of directional overcurrent relays in meshed networks has been established by comparing its performance with that obtained by genetic algorithm, differential evolution and two hybrid algorithms for the developed objective function. Also, the superiority of the develop objective function has also been established by comparing the protection coordination results obtained by using NOF with those obtained by the other objective functions reported in the literature.