This paper deals with the optimal set of Directional overcurrent relays using intelligent methods when the problem has multi-objective functions with different constraints. Due to the linear and nonlinear constraints in the coordination of the Directional overcurrent relays, the method used is based on Pareto Envelope-based Selection Algorithm to obtain optimal values of plug setting, time multiplier setting, and relay characteristic curve by considering all governing constraints setting parameters of the network primary and backup relays. In this study, there is a simultaneous time reduction between the performance of the main and backup relays. Besides, in this method, while solving a multi-objective function without the need for weight factors, a penalty function is used to check the correct coordination of the primary and backup relays. The proposed method is implemented in two different standard networks, i. e. 3-bus and modified IEEE 14-bus networks. The results show the efficiency of the method used and the optimality of the values compared to other algorithms.

Directional overcurrent relays are used to protect transmission lines against short circuits. Reducing the total operating time of relays has always been a challenge for protection engineers. For this purpose, various optimization algorithms have been introduced, some of which are based on multi-objective optimization. The objective functions of multi-objective algorithms must have the Pareto optimality property, which it’ s ignoring is one of the drawbacks of previous studies. In this paper, new objective functions are proposed for a multi-objective optimization problem. To solve the optimization problem, the Multi-object PSO (MOPSO)algorithm is applied with small but effective changes to get the fastest settings of relays. These changes include a leader selection method, a removal method of repository surplus members, and a new velocity vector for particles based on the value of the objective function in the previous iteration. The proposed algorithm is evaluated in IEEE 30-bus network and compared with the standard MOPSO. There is also a comparison with the recent outstanding papers. The proposed method, compared to the 15 algorithms of other papers, results in the lowest total operating time of relays with a 7% reduction.

Directional overcurrent relays (DOCRs) are the essential protective devices in distribution networks which are usually set without considering any contingencies. However, the current challenge in power systems is the existence of uncertainty and its unfavorable consequences. It sometimes appears that some elements simultaneously fail which makes other parts to be overloaded to the extent that it leads to cascading outages. Therefore, DOCRs may have mal-operation which ends in unwanted trips when there is no fault, or they may not operate in the case the fault is located within their reach point. In such cases, the coordination setting will need complex programming with many related non-linear inequality constraints. In this paper, a novel hybrid method is proposed based on multi-objective optimization including new objective functions by using the genetic algorithm (GA). Also, the cascading outages are considered in the presented method based on network data analysis. This approach is performed on distribution part of the IEEE 14-bus meshed system, and a real industrial radial feeder named TOSEE, located in Iran. The simulations have been implemented in MATLAB and Power Factory-DIgSILENT software packages in different models, and the results are evaluated.

The relay coordination problem of Directional overcurrent has been an active research issue in distribution networks and power transmission. In general, the problem of relay coordination is the nonlinearity of the optimization problem, which increases or decreases with different network structures. This paper presents a new method with Directional overcurrent relay coordination approach to reduce the operating time of the relays between the primary and backup relays by using hybrid programming of ILP (interval linear programming) and DE (differential evolution). Due to the difference in short circuit current level from grid connected to the isolated mode, therefore, it is necessary to use a reliable protection solution to reduce this discrimination time and also to prevent the increase of coordination time interval (CTI). The ability of the objective function used in this paper is to reduce the discrimination time of primary and backup relays and simultaneously reduce the operating time of primary and backup relays by introducing a new method. The basic parameters of the Directional overcurrent relay (DOCR) such as time multiplier setting (TMS) and plug setting (PS) have been adjusted such that the relays operation time should be optimized. Optimization is based on a new objective function, described as a highly constrained non-linear problem to simultaneously minimize operating time in backup and primary relays. A function of penalty is also used to check the problem constraints in case the backup relay time is fewer than that of the main relay. The method is implemented on modified IEEE 14-and 30-bus distribution networks. The results demonstrate the efficiency of the method, and the values are optimal compared to those of other algorithms. MATLAB program has also been used to simulate optimization.

The deployment of microgrids (MGs) and smart grids to maximize the benefits from distributed generations (DGs) has increased. Although the MG framework and concept improve system flexibility and reliability, new challenges corresponding to the MG protection system appear compared to conventional passive distribution networks. The adaptive protection schemes, which have been reported to consider various topologies in MG protection, need communication infrastructure. Also, the failure of telecommunication systems and cyber-attacks has drawn attention to unrelated protection schemes using local measurements, taking into account different topologies and related selectivity constraints. The literature shows a research gap in the development of local measurement-based protection schemes considering different operating modes and network configurations due to the unavailability of upstream substations, DGs, and other MGs sub-systems such as lines. This research attempts to fill this research gap by proposing a new protection scheme using dual setting Directional overcurrent relays (DS-DOCRs) based on N-1 contingency topologies. The introduced method is applied to the distribution portion of the IEEE 30-bus test system. The Genetic Algorithm (GA) has been selected as the optimization algorithm, which is implemented in MATLAB, and the power system analyses are done in DIgSILENT. The test results show the advantages of the proposed method compared to the existing designs, only considering the limited operation modes. The test results indicate that mis-coordination for the N-1 contingency-based topologies does not appear using the proposed method.

The change in network topology and operation modes of microgrids is one of the most crucial challenges for protection systems, which might lead to some coordination constraint violations.  Although communication-based and adaptive protection schemes have various advantages, because of their required hardware and software infrastructures, the communication-free schemes have received a great deal of attention. The cyber-attacks and failures in communication-based protection schemes highlight the advantages of communication-free systems. In this paper, the main contribution is to develop a new communication-free method using double setting Directional overcurrent relays considering different operation modes and network topologies. There is a research gap in developing a method incorporating the optimal selection of relay characteristics and curve breakpoints for dual setting Directional overcurrent relays. The proposed method tries to fill such a research gap by proposing a new method using the dual setting relays, while the time settings, current settings, types of relay curves, and curve breakpoints are simultaneously optimized. The microgrids are simulated in DIgSILENT environment, and power flow and short circuit analyses are performed to determine the required data and information for the proposed optimization problem. Thus, the proposed optimization problem for protection coordination of microgrids is solved using the Genetic Algorithm (GA) in MATLAB. Test results of applying the proposed method on the IEEE 8-bus and the distribution portion of the IEEE 30-bus test systems result in 12.42% and 9.56% improvement in the operating time of the protection system, respectively, that illustrate the advantages of the proposed method. Obtained results show that optimizing the curve types for dual setting Directional overcurrent relays besides the optimal selection of curve breakpoints significantly improves the performance of the protection schemes using the dual setting characteristics in various operation modes and network topologies.

To assure the security and optimal protection coordination in meshed distribution networks, clearing faults swiftly and selectively is an essential priority. This priority, when hosting distributed generations (DGs), becomes the main challenge in order to avoid the unintentional DGs tripping. To overcome the mentioned challenge, this paper establishes a truth table to select new settings of Directional overcurrent relays (DOCRs) characteristics which can be defined by users. It concentrates on minimizing the overall relays operating time. Typically, the conventional coordination between pair relays is achieved by two settings: time dial setting (TDS) and pickup current (Ip). Besides these adjustments, the suggested approach, considered the two coefficient constant of the inverse-time characteristics, namely the relay characteristics (A) and the inverse-time type (B), as continuous to optimize. Thus, more flexibility is attained in adjusting relays features. In addition, the inclusion of user-defined settings on numerical DOCRs, not only decreases the overall operating time of relays, but also improves the performance of the backup relays against the fault points. This approach illustrates a constrained non-linear programming model tackled by the combined particle swarm optimization (PSO) and whale optimization algorithm (WOA). The efficiency of the suggested approach is assessed though the IEEE 8-bus and the distribution portion of IEEE 30-bus system with synchronous-based DG units. The obtained results demonstrate the performance of approach and will be discussed in depth. 

Short-circuit current in the power networks, consists of steady and transient states. In the conventional relay coordination method, the transient component of short-circuit current is ignored and the relays are coordinated via fixed currents. The transient component of short-circuit currents causes relays operate fast and thus miscoordinations appear between the main and backup pair relays. In this paper, a relay coordination method considering the transient component of short-circuit current is presented. Dynamic model of inverse time overcurrent relay is used to calculate operating time of relays. In the proposed method, both TSM and IP of relays are calculated considering coordination constraints. It is shown that when the IP is entered to the optimization problem, the objective function is reduced but miscoordinations between relays are increased because of the transient component of short-circuit current. Genetic optimization algorithm is used for relays coordination. The proposed coordination method is implemented on a radial and a meshed network, and the results are compared with the conventional method of coordination.

Increasing the penetration of distributed generation (DG) systems in power systems has many advantages, but it also has problems, including interference with the proper functioning of the protection systems. This problem is severe in microgrid systems that contain many DGs. overcurrent relays are one of the most critical protection equipment of protection systems. The DG sources significantly change the characteristics of fault currents and the protection designs as well as the coordination of overcurrent relays. This paper proposes a coordination method for Directional overcurrent relays with dual adjustment to resolve the interference problem in the protection system of a microgrid in the presence of distributed generation sources based on the electronic power converter (inverter). This is done by considering the curve of different standard characteristics according to the IEC60255 standard in two operating modes, the grid-connected and islanded. A genetic optimization algorithm is used to reduce the total operating time of the relays. The simulation results verify the effectiveness of the proposed coordination method. The results show that the protection coordination scheme with dual adjustment relays and the use of combined characteristic curves can significantly reduce the operating time of the total relays.

In transmission and sub-transmission systems, distance and overcurrent relays have a vital role in protection of transmission lines. Power systems have different topological uncertainties such as planned or unplanned line outages. Such uncertainties affect network impedance matrix, and the distribution and amplitude of fault currents through the relays leads to changes in the coefficients of coordination constraints. Therefore, mal-operation of relays and non-selective operation of protection system may occur. In order to have a robust coordination, coordination constraints from different topologies must be taken into account in the coordination problem. In such conditions, in order to satisfy all constraints, operating time of relays increases. In this paper, the selection of appropriate characteristic among standard characteristics for overcurrent relays is proposed to reduce the operating time of relays despite the existence of robust coordination. The proposed approach is tested on an 8-bus and the IEEE 14-bus test systems. Simulation results show that, by applying the proposed method to the coordination problem of distance and overcurrent relays, the operating time of relays, while maintaining their correct operation of relays, is significantly reduced, despite the network restructuring.