This paper presents an overview on optimalovercurrentrelaycoordination in protection system and protective relays. Efforts have been made to include all methods used for the coordination of overcurrent relays. It includes techniques, such as Artificial Intelligence (AI) and Nature Inspire Algorithm (NIA) as well as other conventional methods used for overcurrent protection. A brief mentioned is made about conventional methods while more prominence is given on the application of AI and NIA for the protection of overcurrent relays. This paper presents a set of references of all respective papers related and provides a brief summary of the research work. In addition, the results of these techniques also provided in the respective references.
many years, power system engineers have relied on conventional methods for overcurrentrelaycoordination. These methods are based on trial and error approach that can be laborious and time consuming depending on the size and the complexity of the network. As a result, it has been proposed to automate the relaycoordination pro- cedure using computer programs  . However, these automated methods do not provide optimal solutions but rather the best of the tried solutions . Consequently, new methods that can provide optimalovercurrentrelaycoordination have been proposed. A comprehensive review of different optimalcoordination methods to overcome this problem is given in  .
Abstract. The integration of system compensation such as Series Compensator (SC) into the transmis- sion line makes the coordination of directional overcur- rent in a practical power system important and com- plex. This article presents an efficient variant of Par- ticle Swarm Optimization (PSO) algorithm based on Time-Varying Acceleration Coefficients (PSO-TVAC) for optimalcoordination of directional overcurrent re- lays (DOCRs) considering the integration of series compensation. Simulation results are compared to other methods to confirm the efficiency of the proposed variant PSO in solving the optimalcoordination of di- rectional overcurrentrelay in the presence of series compensation.
Abstract: The aim of the relaycoordination is that protection systems detect and isolate the faulted part as fast and selective as possible. On the other hand, in order to reduce the fault clearing time, distance protection relays are usually equipped with pilot protection schemes. Such schemes can be considered in the Distance and Directional Over-Current Relays (D&DOCRs) coordination to achieve faster protection systems, while the selectivity is maintained. Therefore, in this paper, a new formulation is presented for the relaycoordination problem considering pilot protection. In the proposed formulation, the selectivity constraints for the primary distance and backup overcurrent relays are defined based on the fault at the end of the transmission lines, rather than those at the end of the first zone of the primary distance relay. To solve this nonlinear optimization problem, a combination of Genetic Algorithm (GA) and Linear Programming (LP) is used as a Hybrid Genetic Algorithm (HGA). The proposed approach is tested on an 8-bus, the IEEE 14-bus and the IEEE 39-bus test systems. Simulation results indicate that considering the pilot protection in the D&DOCRS coordination, not only obtains feasible and effective solutions for the relay settings, but also reduces the overall operating time of the protection system. Keywords: Directional OvercurrentRelay, Distance Relay, Pilot Protection, RelayCoordination.
Due to the complexity of nonlinear optimal programming techniques, the coordination of over current relays is commonly performed by linear programming techniques, including the simplex, two phase simplex and dual simplex methods. In these methods the current setting of the relays are assumed to be determined prior, and only find the time multiplier setting of the relays. In this paper, an optimalcoordination method for over current relays is proposed. The current setting and time multiplier setting of all relays are considered as optimization parameters and they are obtained simultaneously in an optimal manner. It is shown that lower protection operating time is achievable if the pickup current of the relays are determined in the optimization procedure. Over current relays are the most widely used protection system relays to detect and isolate faults in power systems. There are two types of over current relays: 1) the instantaneous over current relays, operate instantaneously when the current reaches a predetermined value and 2) time delay relays which require that both the current and the time to exceed the setting values before the relay can operate. For time delay overcurrent relays, relaycoordination involves setting the pickup current and time multiplier parameters. The most important parameter for the overcurrentrelaycoordination is the time multiplier which has a direct influence on the operating time of the relay.
Abstract: Most studies in relaycoordination have focused solely on coordination of overcurrent relays while distance relays are used as the main protection of transmission lines. Since, simultaneous coordination of these two types of relays can provide a better protection, in this paper, a new approach is proposed for simultaneous coordination of distance and directional overcurrent relays (D&DOCRs). Also, pursued by most of the previously published studies, the settings of D&DOCRs are usually determined based on a main network topology which may result in mis-coordination of relays when changes occur in the network topology. In the proposed method, in order to have a robust coordination, network topology changes are taken into account in the coordination problem. In the new formulation, coordination constraints for different network topologies are added to those of the main topology. A complex nonlinear optimization problem is derived to find the desirable relay settings. Then, the problem is solved using hybridized Genetic Algorithm (GA) with Linear Programming (LP) method (HGA). The proposed method is evaluated using the IEEE 14-bus test system. According to the results, a feasible and robust solution is obtained for D&DOCRs coordination while all constraints, which are due to different network topologies, are satisfied.
V. S IMULATION R ESULTS A ND D ISCUSSION The previous section proposed a brief information about (GA, MFO, GWO, and SSA) techniques. These techniques are applied for obtaining the optimal setting for 14 directional overcurrentrelay in an IEEE 8 bus test system. Tables (III to VI) shows the coordination results between the backup and primary relays based (GA, MFO, GWO, and SSA) techniques.
Over current relays are usually employed as backup protection. In distribution feeders, they play a more important role and there it may be the only protection provided [1,2]. The problem of coordinating protective relays consists of selecting their suitable settings such that their fundamental protective function is met under the requirements of sensitivity, selectivity, reliability, and speed [3,4]. If backup protections are not well coordinated, mal-operation can occur and, therefore, OC relaycoordination is a major concern of power system protection . Each protection relay in the power system needs to be coordinated with the relays protecting the adjacent equipment. The overall protection coordination is thus very complicated. The OC relaycoordination problem in distribution system can be defined as constrained optimization problem. The objective is to minimize the operating time of relay for fault at any point. A protective relay should trip for a fault in its zone and should not, for a fault outside its zone, except to backup a failed relay or circuit breaker traditionally; a trial and error procedure is employed for setting relays in multi loop networks. In the past few years, several mathematical techniques have been reported. warakanath and Nowitz  suggested a systematic approach for determining the relative sequence setting of the relays in a multiloop network. They used a linear graph theory approach which provided a directional loop matrix. A minimal set of break points spanning all loops of the system graph were obtained from this matrix.Damborg et al.  extended the graph theoretic concepts and proposed a systematic algorithm for determining a relative sequence matrix corresponding to a set of sequential pairs which reduced the number of iterations. Jenkins et al.  proposed a functional dependency concept for topological analysis of the protection scheme. They expressed the constraints on the relay settings through a set of functional dependencies. A arametric optimization approach was reported by Urdeanneta et al.  that optimized the time multiplier settings (TMS) using the Simplex method. Optimal values of the pick-up currents for selected TMS were then determined by using a generalized reduced gradient technique. The objective of this paper is to present some of the optimization concepts and their use in the project.
This paper proposed IGWO algorithm for optimalcoordination setting of the overcurrent relays problem. Some modification has been recommended to improve the exploration ability of the grey wolves. This exploration ability has been proven to improve the conventional GWO convergence characteristic. Three test cases are utilized to confirm the reliability of the IGWO. Comparison results between IGWO, conventional GWO and with other identified algorithm such GA-NLP and CSA indicated that IGWO has improved the convergence performance when applied to the optimization problem of overcurrent relays coordination. In addition, proposed modification has counteracted the argument of randomness exploration activity. As the conclusion, the IGWO is appears to be an efficient and robust optimization algorithm for optimal solution of overcurrentrelaycoordination problem in electrical network system.
The results obtained from the proposed MPSO Algorithm displayed in Table 7 shows an improvement in the overall tripping timing of the relays. The optimal tripping time of all the primary relays of the 6 Bus microgrid comprising of 14 DOCRs was 3.7903s while that obtained for the existing Katempe-Life Camp feeder for just 2 relays was 3.68s. Using the optimized Relay settings to run fault studies on Line 7 and Single Busbar 2 gave various tripping times for both Clockwise Looping and Anticlockwise Looping Relaycoordination as shown in Figures 3 to Figures 12. Table 8 and 9 shows the Relay settings before and after optimization respectively.
Protection of distribution networks is one of the most important issues in power systems. Overcurrentrelay is one of the most commonly used protective relays in these systems. There are two types of settings for these kinds of the relays: current and time settings. A proper relay setting plays a crucial role in reducing undesired effects of faults on the power systems [1, 2]. Overcurrent relays commonly have plug setting (PS) ranging from 50 to 200% in steps of 25%. The PS shows the current setting of the overcurrent relays. For an overcurrentrelay, PS is defined by two parameters: the minimum fault current and the maximum load current. However, the most important variable in the optimalcoordination of overcurrent relays is the time multiplier setting (TMS) . So far, some research has been carried out on coordination of overcurrent relays [3-7]. Due to the difficulty of nonlinear optimal programming techniques, the usual optimalcoordination of overcurrent relays is generally carried out by linear programming techniques, including simplex, two-phase simplex and dual simplex methods . In these
applications for tripping acceleration. But this method depends on current transformer (CT) whose dynamic behavior inﬂuences the protection stability. Ref.  proposes utilizing the distribution automation system capabilities for protection coordination. One drawback of this method is that the number of protection zones increases when the number of DGs increases. So, many isolating circuit breakers will be needed and the scheme may not be economic. Communication- assisted digital relay approach is presented in  to achieve coordinated operation of OCRs. Complexity and enlarged fail- ure rates are major concerns in this method. Ref.  reviews the protection schemes and coordination techniques in micro- grid systems. A neural network and backtracking-based
and BFGS . MR Asadi dan SM Kouhsari (2009) Using the particle swarm optimization (PSO) method to obtain a optimum settings solution for coordinationovercurrentrelay. This study found that the use of PSO method can improve coordination and relay operation time, looking for optimal points in absolute terms and not being trapped in optimal local points . Manohar Sigh, B.K Panigrahi dan Rohan Muherje (2012) Apply Covariance Matrix Adaptation Evolution Strategy (CMA-ES) to solve the problem of overcurrent protection coordination. This method is tested in a loop system and provides optimalcoordination results and there is no coordination error between the primary relay and the backup relay . Hebatallah Mohamed Sharaf, Doaa Khalil
Where and are the minimum and maximum values for operating time which values are equal to 0.05 and 1.00 respectively. The coordination time interval between the primary and the backup relays must be confirmed during optimization procedure. In this paper, the chronometric coordination between the primary and the backup relays is given as in equation:
coordinated correctly so as to prevent mal-operation and therefore to avoid the unneeded outage of healthy section of the system. The overcurrent relays are usually the foremost protection product in a distribution system. Overcurrentrelay is typically used as backup protection. But in a number of situations it may become the only protection supplied. Power system includes many variety of equipment. A lot more amount of circuit breakers and relays are necessary to protect the system. Optimization of over current relay settings is a major problem in protection of electrical power systems. This paper describes the Firefly algorithm for optimal time coordination of these relays. The algorithm has been implemented in MATLAB and tested on a radial system, as well as a single end fed system with a parallel feeder. The results obtained by the Firefly algorithm (FA) are compared with those obtained by the Cuckoo search Algorithm (CSA) and Genetic algorithm (GA). The novel feature of this paper is the application of the Firefly algorithm to the problem of over-current relaycoordination.
Deregulation of electricity has brought new suppliers into the electicity market resulting in the power system operating close to its peak limit and requires good protection system against any fault. Protection system for power system has been developed to minimize damage and make sure supply is safe, continous and economical. This is a achieved using relay. A relay is device that makes measuremt or receivers signal that causes it to operate and effect the operation of other equipments. It responds to abnormal conditions in faulty section of the system with minimum interruption of supply. Relay co-ordination plays an important role with protection scheme. It is an integral part of the overall system protection and is absolutely necessary to Isolate only the faulty circuit, prevent tripping of healthy circuit. The main purpose of this paper is to design a computer model to calculate the time setting multiplier (TSM) and pick up current Iset of each relay so that the overall operating time of the primary relays is minimized properly. For optimalcoordination, these parameters should fulfill all constraints under the operating time and lead to optimalcoordination of overcurrentrelay. Each part of the system is protected by a main and back up relay and no interference could occur in relay operation . For a good protection scheme, a reliable back up should exist in case the main protective system fails. This backup protection should act as a backup either in the same station or in the neighbouring lines with a time delay according to the selective requirement .
 Urdaneta A. J, Ramon N., Luis G.P.J “OptimalCoordination Of Directional Overcurrent Relays In Interconnected Power Systems”, IEEE Transactions on Power Delivery, Vol. 3, No. 3, July 1988.  Rashesh P Mehta, OptimalRelayCoordination, Journal Of Engineering And Technology, Sardar Patel University, Vol. 19, December 2006.
Recently, multiple-input multiple-output (MIMO) relay technique has been received great attention due to its prominent ability to provide broad coverage and enhance the link reliability and spectral efficiency. In this paper, an overview of optimal design for single user and multiuser non-regenerative MIMO relay systems is proposed. We explore some key designs of source node and destination node as well as relay node processing matrices using minimum mean square error (MMSE) criterion under the transmit power constraints. Simulation results compare different methods in terms of the MSE and bit error rate (BER) performance.
Fig. 1 illustrates a two-hop MIMO relay communication system consisting of one source node, K parallel relay nodes and one destination node. We assume that the source and destination nodes have Ns and Nd antennas, respectively and each relay node has Nr antennas. The generalization to the system with different number of antennas at each node is straightforward. To efficiently exploit the system hardware, each relay node uses the same antennas to transmit and receive signals. Due to its merit of simplicity, we consider the amplify and forward scheme at each relay.