Minimization of the discrimination time between the backup and main overcurrent relay is one of the most critical issue in relay coordination of power system. Determination of time setting multipliers (TSMs) using evolutionary algorithms has been studied in previous papers. In this paper, TSM, various characteristics of the overcurrent relays and pickup currents are simultaneously considered to improve coordination of main and backup overcurrent relays. Furthermore, the coordination problem can also be considered as an optimization problem which can be solved using artificial intelligent methods. Recently, a novel optimization algorithm, called hyper-sphere search (HSS) algorithm, has been introduced. In this paper, Improved HSS (IHSS) is introduced. Based on the problems mentioned in this paper, the IHSS algorithm is more appropriate for obtaining the characteristics of the overcurrent relays, pickup currents and their TSMs. The result of IHSS is compared with HSS algorithm which has been used in previous studies. The simulation results on the test network show the efficiency of using IHSS and considering pickup currents in term of better relays coordination.

This article discusses about coordination of directional overcurrent relays (DOCRs) in the power system transmission lines. In these relays, 4 characteristics are used as variables to calculate coordination between of them. These 4 variables include PS, TMS, A and B, which are used to obtain optimal coordination between relays. In this article, to obtain optimal coordination, two fault locations are considered. One of them is near the relay (at the 10%-line beginning) and another is fault far from the relay (at the 90%-line end). The problem of coordination of relays is solved and optimized using the PSO optimization algorithm. The proposed method has been tested in the standard distribution 6-Buse IEEE System, and its results are stated. The results of the PSO optimization method that was obtained have been compared with traditional methods such as GA-NLP. Comparing the results of this method with the traditional methods presented in the other articles, found that the presented method obtains more optimal results than other traditional methods. Since the proposed method minimizes the operation time of DOCRs relays. This method is a reliable and effective method for calculating coordination between relays.

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 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.

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.

The analysis of transient stability in electric power systems and the penetration coefficient of scattered productions play important roles in the regulation of protective equipment, so these parameters should be considered two main factors in the electrical protection of power networks. Overcurrent relays are used as one of the simplest and most effective solutions for power system protection. The overcurrent relay has two main variables: time setting factor (TMS) and plug setting (PS). The relay operation time is a function of TMS, PS, and the current seen by the relay. This paper analyzes the transient stability of a distribution network including distributed generation to determine the protective regulation of overcurrent relays. First, the transient stability of scattered products is studied for different fault locations and their different penetration coefficients. Then, the limitations of distributed generation resources are considered in the protection coordination of overcurrent relays. Therefore, a new method is proposed to calculate the modified value of the time adjustment coefficient of the overcurrent relay. In other words, not only the protection limits but also the transient stability limits are considered in the calculation of the time adjustment factor. In fact, by applying the proposed method, not only is the coordination between overcurrent relays maintained but the instability of distributed generation sources is also prevented. The performance of the proposed protection plan is evaluated with the help of simulation in an IEEE 33-bus distribution system using ETAP software. The results show the correct performance of the proposed method for the worst error conditions. It should be noted that to carry out conservation and stability studies, the following steps are performed in order, which ultimately leads to the creation of a conservation-stability algorithm: (A) protection studies in the condition of disconnection of DG resources, (B) transient stability studies in the conditions of connection of scattered production sources, including obtaining the minimum stability time for each of the scattered production, and (C) investigating the simultaneous establishment of CTI and CCT. In this situation, two situations are possible: the simultaneous establishment of CTI and CCT, the establishment of CTI restrictions, and the non-establishment of CCT. The value of CCT for each DG is equal to the time when the speed of the DG or the power angle of its generator becomes zero. As can be seen, in the first, second, fourth, and fifth scenarios, the CCT condition of the distributed generation source is not established, and it is necessary to modify the TDS value of the main relay.

The analysis of transient stability in electric power systems and the penetration coefficient of scattered productions play important roles in the regulation of protective equipment, so these parameters should be considered two main factors in the electrical protection of power networks. Overcurrent relays are used as one of the simplest and most effective solutions for power system protection. The overcurrent relay has two main variables: time setting factor (TMS) and plug setting (PS). The relay operation time is a function of TMS, PS, and the current seen by the relay. This paper analyzes the transient stability of a distribution network including distributed generation to determine the protective regulation of overcurrent relays. First, the transient stability of scattered products is studied for different fault locations and their different penetration coefficients. Then, the limitations of distributed generation resources are considered in the protection coordination of overcurrent relays. Therefore, a new method is proposed to calculate the modified value of the time adjustment coefficient of the overcurrent relay. In other words, not only the protection limits but also the transient stability limits are considered in the calculation of the time adjustment factor. In fact, by applying the proposed method, not only is the coordination between overcurrent relays maintained but the instability of distributed generation sources is also prevented. The performance of the proposed protection plan is evaluated with the help of simulation in an IEEE 33-bus distribution system using ETAP software. The results show the correct performance of the proposed method for the worst error conditions. It should be noted that to carry out conservation and stability studies, the following steps are performed in order, which ultimately leads to the creation of a conservation-stability algorithm: (A) protection studies in the condition of disconnection of DG resources, (B) transient stability studies in the conditions of connection of scattered production sources, including obtaining the minimum stability time for each of the scattered production, and (C) investigating the simultaneous establishment of CTI and CCT. In this situation, two situations are possible: the simultaneous establishment of CTI and CCT, the establishment of CTI restrictions, and the non-establishment of CCT. The value of CCT for each DG is equal to the time when the speed of the DG or the power angle of its generator becomes zero. As can be seen, in the first, second, fourth, and fifth scenarios, the CCT condition of the distributed generation source is not established, and it is necessary to modify the TDS value of the main relay.

In this paper, the influence on the voltage compensation type, active superconducting fault current limiter (ASFCL) is investigated under symmetrical and asymmetrical fault conditions. ASFCL is consisting of three air-core superconducting transformers and a three-phase voltage source converter. In the normal (no fault) state, the flux in air core is compensated to zero, so the ASFCL has no influence on the main circuit. In the case of short circuit, by controlling the amplitude and phase angle of the second winding’s current, the limiting impedance which is in series with the AC main circuit can be regulated, and the fault current will be limited to a certain level. Control strategies consist of fault detection and PWM converter operation is designed. To simplify the design of controllers the mathematical equations can be expressed in synchronous rotating d-q frame. Furthermore, under the condition that the active SFCL is placed behind the relay element, its current-limiting impedance will be added into the measured impedance between the relay and the fault points. As a result, in order to prevent the refused operation of the relay, According to the two different operation modes of the active SFCL, in this paper present the corresponding two modified formulas. Using MATLAB SIMULINK, model of the three phase AC system with ASFCL is created and control strategies test, fault current limiting test, and distance relay operation is investigated.

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.

In this study, we introduce a new two-way relay channel and obtain an inner bound and an outer bound for the discrete and memoryless multiple access relay channels with receiver-source feedback via two-way relay channel in which end nodes exchange signals by a relay node. And we extend these results to the Gaussian case. By numerical computing, we show that our inner bound is the same with one obtained by Hou-Koetter-Kramer, for the channel with relay-source feedback.