Gravitational Search Based Algorithm for Optimal Coordination of Directional Overcurrent Relays Using User Defined Characteristic

Due to dependency on Plug Setting (PS), Time Dial Setting (TDS), size of the network, more than one back-up relays for one primary relay and other technical constraints, coordination of Directional Overcurrent Relays (DOCRs) is an extremely constrained and nonlinear optimization problem. In this paper, a new Gravitational Search (GS) based algorithm is presented for achieving optimal coordination of directional overcurrent relays. The proposed algorithm utilizes user defined characteristic for inverse time overcurrent relays than the predefined standard curves. The user defined relay characteristic deals with constants that control the shape of the characteristics as variable adjustable values which are optimally chosen along with TDS and Plug Setting Multiplier (PSM). The performance of the proposed algorithm has been evaluated on 8-bus, 15-bus and IEEE 30-bus distribution network at different fault locations (near-end, far-end and middle point). In addition, the time of operation of some of the primary relays at different fault locations on IEEE 30-bus distribution network is also presented. At the end, comparative evaluation of the proposed algorithm with other optimization algorithms having different relay characteristics presented in the literature clearly indicates its effectiveness and superiority in terms of the sum of total primary relays operating time.     

Adaptive non-communication protection for power lines BO scheme3-The accelerated operation approach

This paper presents the accelerated operation scheme of the adaptive noncommunication protection technique for power lines with complex configurations, such as multi-end feeders and ring mains. In the scheme, the overcurrent directional relays are arranged in two operating modes, the fixed time operation and accelerated operation. The relays with faster operating time in the conventional time grading coordination remain unchanged. The new technique is employed to enable accelerated operation to be achieved for the relays which are in the positions for which slow operating time is set when using conventional time grading technique. For a fault occurring on the protected system, the relays of fixed time operation mode will operate at the preset time for the fault within its protected direction. The relays which are programmed to use accelerated operation mode will determine whether a fault is on the protected section or not by using the BO technique, that is to detect the circuit breaker operation by determining whether the line section is in a balanced operation condition or not. The relay makes accelerated tripping decisions for a fault on its protected section. Simulation studies of the responses to various system and fault conditions show that the scheme can significantly increase the speed of the relay responses in the protection of power line systems with complex configurations     

A Novel Multi-Objective Protection Coordination Scheme for a Microgrid with Optimal Deployment of Dual-Setting ROCOV Based Relays

Relay coordination is crucial in electrical power systems to protect against malfunctions and damage caused by unexpected events like short circuits. To address the challenge associated with the reverse direction of fault current, dual-setting (DS) directional over-current relays have evolved but failed to provide proper coordination during changes of load, generation, and network. In the meantime, with the increasing number of DS relays, the total relay operating time tends to saturate. Therefore, this paper proposes a protection scheme based on the optimal deployment of conventional and dual-setting rate of change of voltage (DS-ROCOV) relays in distribution systems. This holds true for varying network topologies and is unaffected by variations in load and generation. The objective of the proposed scheme is to ensure reliable and efficient protection against faults in distribution systems by minimizing the overall operating time with the optimal number of DS-ROCOV relays. The proposed protection scheme''s performance is evaluated for different coordination time interval values as well as in different microgrid scenarios. This paper outlines the design and implementation of the proposed protection scheme which is validated on the modified IEEE 14-bus system using simulations in Matlab/Simulink.     

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.     

A novel fault protection system using communication-assisted digital relays for AC microgrids having a multiple grounding system

This paper develops a novel fault protection system for AC microgrids having a multiple grounding system. Communication-supported digital relays which have different protection modules are used for this novel microgrid protection system. The protection modules in a digital relay have various functionalities to protect AC microgrids from various fault types, such as: low/high-impedance ground faults and short-circuits. To effectively use the developed novel microgrid protection system, the first step is to reconfigure different microgrid structures into a standard microgrid configuration having a multiple-grounding system through using delta/wye-grounded or wye-grounded/wye-grounded transformers. Then, a fast–dependable–adaptable (FDA) fault protection algorithm is developed to protect AC microgrids from faults occurring at trunk lines, common buses or branch lines. At an islanded operation mode of AC microgrids, by using digital relays, a new protection module is designed to detect, locate, and classify the faults occurring at trunk lines and common AC buses, while other protection modules can use the existing protection methodologies (e.g. directional/non-directional overcurrent protection principles, etc.) to detect and clear the faults at source branches or load branches of the microgrids. At a grid-connected operation mode, standard overcurrent protection modules are applied for the FDA fault protection system. Simulation and experiment results obtained from various fault cases at a real low-voltage AC microgrid have validated the effective operation of the FDA fault protection system.     

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。     

Optimal computation of distance relays second zone timing in amixed protection scheme with directional overcurrent relays

This paper describes a technique to determine the optimal time setting for the second zone of distance relays when used in a mixed protection scheme with directional overcurrent relays. The technique consists of including the second zone operation time as a new variable in the original problem statement of optimal computation of directional overcurrent relays settings. It is shown that the influence of distance relays and directional overcurrent relays must be considered when the settings of these relays are computed. Numerical results obtained with the proposed method for a realistic power system are presented     

A novel method for optimal coordination of directional overcurrent relays considering their available discrete settings and several operation characteristics

For optimal coordination of directional overcurrent relay we propose to consider operation characteristics, pickup current and time multiplier setting of relays as optimization parameters. Each parameter is optimized independently with the aid of linear formulation of the coordination problem. First, optimal discrete values of pickup current are selected. Second, adequate operation time characteristics of relays are selected. Third, optimal discrete values of time multiplier setting are determined. The proposed method is tested on two networks: an 8-bus system and the IEEE 30-bus system. Its performances are evaluated and compared with those of the linear and nonlinear programming techniques.     

Optimal coordination of directional over-current relays using Teaching Learning-Based Optimization (TLBO) algorithm

Relay Coordination in a big distribution system with multiple meshes and bidirectional power feed becomes very Complex for protection engineers. Manual and graph theory based approaches were applied successfully in small power system. In a big distribution system linear and non-linear programming based optimizing techniques are applied for relay coordination. Presently, artificial intelligence techniques are applied for optimal co-ordination of directional overcurrent relays. This paper discusses the application of Teaching Learning Based Optimization (TLBO) algorithm for optimal coordination of DOCR relays in a looped power system. Combination of primary and backup relay is chosen by using Far vector of LINKNET structure, to avoid mis-coordination of relays. Coordination of DOCR is tested for IEEE 3, 4 and 6 bus systems using the TLBO. Also, the objective function is modified to optimize the operating time between backup and primary relays. The results are compared with the optimized values of Time dial setting and Plug setting values obtained from modified differential evolution algorithm. The proposed algorithm TLBO gives optimal coordination margin between 0.3 and 0.8 s and no miscoordination between primary and backup pairs. Results are also verified using Digsilient power factory simulation software.     

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     

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。     

A new approach for optimal coordination of distance and directional over-current relays using multiple embedded crossover PSO

Proper coordination between distance relays and Directional Over-Current Relays (DOCRs) in power systems is one of the important conditions for the system security. The coordination problem in interconnected systems, because of complexity of the system, is complicated and a powerful optimization program must be used in order to do the best and optimal relay coordination.In this paper at first, a new problem formulation for optimal coordination of distance relays in presence of DOCRs, as the backup relays, is proposed. Then to deal with this complex problem, as another contribution, a new Multiple Embedded Crossover PSO (MECPSO) is proposed. In the presented MECPSO by updating velocity vector, diversity of the swarm is enhanced and exploration and global search capabilities of the PSO is improved as well. In the proposed approach, with considering the effect of in-feed or out-feed currents, the optimal second zone timing of distance relays and optimal settings of DOCRs are computed. The proposed method is tested on two case studies and encouraging optimal results are obtained.     

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.     

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.     

Advanced Coordination Method for Overcurrent Protection Relays Using Nonstandard Tripping Characteristics

This paper describes an advanced coordination method for an optimized protection time grading based on a new nonstandard tripping characteristic for overcurrent protection relays. The intention is the highest possible reduction of tripping times for a selective fault clearing in distribution networks protected by overcurrent relays without communication links. The new nonstandard tripping characteristic will be described from its basic idea to its constraints of the optimization problem. The optimization is solved by the method of Lagrange generalized with the Karush-Kuhn-Tucker conditions and is aimed at selective fault tripping with shorter tripping times as standard characteristics and conventional coordination methods. Overcurrent relay coordination becomes a mathematical optimization task. A comparison with the standard characteristics and conventional coordination methods shows a notable advancement regarding their average and maximum tripping times which can be achieved using this new method.     

Optimum coordination of directionalovercurrent relays for combined overhead/cable distribution system with linearprogramming technique

Heavy fault currents flow in the event of fault at the loads connected in distribution system. To protect these loads, circuit breakers and relays are required at appropriate places with proper coordination between them. This research paper focuses on finding optimum relay setting required for minimum time to interrupt power supply to avoid miscoordination in operation of relays and also investigates effect on time multiplier settings (TMS) of directional overcurrent relays in a system with combined overhead lines-underground cables. Linear programming problem (LPP) approach is used for optimization. It is interesting to know the quantitative variations in TMS as the underground cables have different characteristics than overhead lines.     

基于复合故障补偿因子的微电网反时限电流保护方法

为了解决逆变型分布式能源(Distributed Generator, DG)对微电网保护速动性和协调性的影响,提出了一种基于复合故障补偿因子和天牛须搜索(Beetle Antenna Search, BAS)算法的改进反时限微电网电流保护方法。首先,通过分析故障时保护安装处的电压分布特性,并结合测量阻抗特征构建复合故障补偿因子,以解决反时限过电流保护由于短路电流变化引起的动作延时问题,提高保护速动性。同时,为了解决DG接入、微电网运行方式改变等因素引起的微电网保护协调问题,利用BAS算法对改进反时限电流保护的参数进行优化,以保证相邻保护的协调配合。最后,在DIgSILENT/PF软件中建立微电网仿真模型,以验证改进方法的有效性。仿真结果表明,与传统反时限过电流保护相比,改进保护方法在速动性方面明显提升,且在微电网不同运行模式、故障条件下均满足协调性要求。     

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。     

Considering Different Network Topologies in Optimal Overcurrent Relay Coordination Using a Hybrid GA

The directional overcurrent relays (DOCRs) coordination problem is usually studied based on a fixed network topology in an interconnected power system, and is formulated as an optimization problem. In practice, the system may be operated in different topologies due to outage of the transmission lines, transformers, and generating units. There are some situations for which the changes in the network topology of a system could cause the protective system to operate without selectivity. The aim of this paper is to study DOCRs coordination considering the effects of the different network topologies in the optimization problem. Corresponding to each network topology, a large number of coordination constraints should be taken into account in the problem formulation. In this situation, in addition to nonlinearity and nonconvexity, the optimization problem experiences many coordination constraints. The genetic algorithm (GA) is selected as a powerful tool in solving this complex and nonconvex optimization problem. In this paper, in order to improve the convergence of the GA, a new hybrid method is introduced. The results show a robust and optimal solution can be efficiently obtained by implementing the proposed hybrid GA method.     

含超导元件的配电网继电保护方案研究

随着分布式电源（DG）在电力系统中的大量应用,电力系统继电保护的拒动、误动及保护配合失败问题成为影响电网稳定运行的重要问题。首先分析了DG对传统保护的影响机理,提出一种基于微处理器的新型电流-电压-时间继电保护特性的方向过流继电器,可用于减少继电保护动作时间,恢复被DG破坏的保护之间的配合。利用超导器件遏制短路电流的特性解决误动问题,提出以超导器件与所提新型继电器相配合的含DG的配电网继电保护方案,并以IEEE-14节点系统为例,验证了所提方案的有效性。