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 presence of Distributed Generation (DG) resources in power system, versus economic benefits, can be cause a miss- coordination in operation of overcurrent Relay. In this paper, a new index is proposed to determine the impact of DG installation on coordination constraints of overcurrent Relay, independent of Relay settings. In the presence of DG in network, the fault current passing through the Backup and Primary Relays change in compare to the no presence of DG. According to this, the proposed index is defined as the difference between the rate of change of fault current passing through Backup Relay and the rate of change of fault current passing through Primary Relay, for each Relay pairs. In the presence of DG, mathematically proven that the sign of the proposed index for each coordination constraints, indicates the increase or decrease of coordination time interval and the measure of proposed index indicates the reduction of coordination time interval. The proposed index for the coordination constraints of overcurrent Relay of an 8-bus test system is determined at each DG location. The results have shown the correctness of proposed index to evaluate the impact of location and capacity of DG on the coordination constraints. Also, the locations and capacities of DG have been ranked base on proposed index.

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.

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.

In a realistic and large power system, the overcurrent Relay coordination problem considering different network topologies and different location of faults is stated as an optimization problem with a large number of constraints. In this paper, a new index is proposed to detect and remove the inactive inequality constraints in Relay coordination problem. This index is defined for each Relay pairs, as the ratio of the variation of fault current passing through the Primary Relay to the variation of fault current passing through the Backup Relay. The proposed index is independent of the overcurrent Relay characteristics and current and time multiplier settings of the Relay, which is the most significant feature of this index. For IEC Relay characteristic, it is shown that without the solving the coordination problem, the proposed index can distinguish the active and inactive inequality constraints. The 14-bus and 30-bus IEEE test systems are used to verify the performance of the proposed index. The presented results show that greater than 90 percent of the inactive constraints can be detected and removed from the set of constrains by using the proposed index.

In this paper, we propose a cognitive radio network which consists of a number of secondary users and one Primary user. The Primary user utilized a successive Relay performance. The successive Relaying technique creates a full duplex Relay performance by two half duplex Relays, which improves spectral efficiency. In the presence of secondary users, we use successive Relay technique in the Primary user to ensure its acceptable performance. Also, the sum rate of secondary users is increased. The challenges of this network are inter-Relay interference and inter user interference. The interference alignment method is utilized to eliminate the interferences in the successive Relay technique and in the cognitive radio network. Besides, the minimum transmitted power of the Primary user is derived to guarantee its quality of service requirement. Two power allocations algorithms are proposed to maximize the sum rate of secondary users and the energy efficiency of the network. In both power allocations algorithms, satisfying the quality of service of the Primary user is considered. The closed-form solutions of these algorithms are studied. The fractional programing approach was employed to solve the energy efficiency optimization in two steps.

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.

We address the throughput maximization problem for downlink transmission in DF-Relay-assisted cognitive radio networks (CRNs) based on simultaneous wireless information and power transfer (SWIPT) capability. In this envisioned network, multiple-input multiple-output (MIMO) Relay and secondary user (SU) equipment are designed to handle both radio frequency (RF) signal energy harvesting and SWIPT functional tasks. Additionally, the cognitive base station (CBS) communicates with the SU only via the MIMO Relay. Based on the considered network model, several combined constraints of the main problem complicate the solution. Therefore, in this paper, we apply heuristic guidelines within the convex optimization framework to handle this complexity. First, consider the problem of maximizing throughput on both sides of the Relay separately. Second, each side progresses to solve the complex problem optimally by adopting strategies for solving sub-problems. Finally, these optimal solutions are synthesized by proposing a heuristic iterative power allocation algorithm that satisfies the combinatorial constraints with short convergence times. The performance of the optimal proposed algorithm (OPA) is evaluated against benchmark algorithms via numerical results on optimality, convergence time, constraints’ compliance, and imperfect channel state information (CSI) on the CBS-PU link.

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.