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.

In recent years, the complexity of modern distribution systems has increased due to the integration of dispersed generation resources. Coordinating directional overcurrent Relays (DOCR) for protecting these systems poses a challenging optimization problem. This study introduces the Eel Swarm Optimization Algorithm (ESOA) to address this issue. Inspired by eels' hunting behavior, ESOA effectively explores the solution space. Testing on various error scenarios in 3-bus and 15-bus systems demonstrates ESOA's superior performance in reducing Primary Relay performance time compared to other optimization algorithms. The algorithm demonstrates proficiency in ensuring synchronization between Primary Relay pairs and Backup Relays, reducing the time difference in coordination.

The presence or absence of distributed generation (DG) sources in a distribution network has a probabilistic nature. In the event of connection or disconnection of these sources, the fault current through a Relay and the Relay operating time are affected, which leads to miscoordination. For solving this issue, coordination constraints corresponding to the presence or absence of DGs have to be considered in the overcurrent Relay coordination problem (CP). The incorporation of these constraints increases the operating time (OT) of the conventional overcurrent Relays (OCRs). In this paper, a novel adaptive characteristic is proposed to solve this unwanted effect. Accordingly, a function proportional to the equivalent impedance (EI) seen by the Relay is added to the Relay characteristic. This EI is calculated via in-situ measurement of voltage and current before the occurrence of a fault, continuously; when the fault occurs, the calculated impedance is used in the Relay characteristic to determine the OT. The addition of this function to the conventional overcurrent Relay characteristic, reduces the effects of disconnecting the DGs on the coordination constraint, and in general, improves the OT of the Relay. Based on the analytical relations and simulation results, it is shown that the OTs of the Primary and Backup Relays with the proposed characteristic are improved compared to the Relays with the conventional characteristic.

Distance Relays calculate the path impedance between the fault point and the Relay location by sampling the voltage and current at the Relay location. By using the ratio of the impedance estimated by the Relay to the impedance of the line where the Relay is installed, the location of the fault can be estimated by a distance Relay. However, several factors influence the estimated impedance and proper operation of distance Relays. The most important of these factors is the resistive fault occurrence, which results in an increase in the impedance and deviation of the impedance estimated by the Relay as well as causes Relay under-reach. Therefore, in the present study, an adaptive method is proposed to modify the protection zones of distance Relays settings under different operating conditions and resistive single-line-to-ground (SLG) fault occurrence. Furthermore, the adaptive distance protection of transmission lines, wind farm collector lines and the protection coordination of the Relays in these lines are investigated. In this method, an adaptive coefficient is added to the conventional characteristics of distance Relays to improve the accuracy and coordination. The proposed adaptive method can also maintain the coordination of different protection zones of Primary and Backup Relay pairs. In addition to analytical verification, the numerical results obtained from simulation show the efficiency of the proposed method. The proposed method is implemented on a power system with transmission lines and wind farms and simulated in MATLAB/Simulink environment.