In recent years, the distributed generation resources (DGR) have become an essential and inseparable component in power networks and have achieved major success. Improving network power voltage, helping in peak load conditions and reducing load on power lines and transformers, utilizing renewable energies and reducing environmental pollution constitute some of the reasons for their expansion. In contrast to all these advantages in a given network, the increased presence of distributed generation resources has presented new challenges for power networks. One of the most important problems is the impact on system protection functionality. The traditional protection structure of the networks will be impaired and malfunctioned due to the presence of distributed generation resources. In this paper, a new intelligent linear control algorithm is used to restore the protective coordination. The proposed method modifies the protection characteristic curve of the protection system by adjusting the OverCurrent Relay Current coefficient. This control procedure is in accordance with the widely applied OverCurrent Relay curves and complies with the relevant standards. For this purpose, by using a new drop control block and local sampling of Over-Current Relay Current, Current setting of the Relay is recOvered to keep the correct operation of protection system. The proposed method is evaluated on two real micro-grids test system in Isfahan province by ETAP software. The findings indicate the ability of this method in coordinating the protection functionality of micro-grids with high penetration coefficient of DGR.

The design and application of a fuzzy logic based controller to a leakage Current Relay was presented in this paper. A novel approach based on fuzzy logic to form the tripping action of leakage Current Relay was investigated. In addition to the theoretical aspect of fuzzy logic, detection of a leakage Current, measurement of the leakage Current, determination of its duration, trip opening of faulty cases and detailed system architecture were also introduced. The inspected fuzzy logic technique to control the tripping action of the leakage Current Relay was intended to improve the performance of conventional leakage Current Relay control for human safety and system reliability. The relationship between the controlled output of the fuzzy processor and properties of leakage Current for the proposed Relay was explored by using a graphical output expression. It was observed that the proposed leakage Current Relay based on fuzzy logic was more reliable than conventional leakage Current Relay.

Islanded operation of distributed generators is a problem that can happen when they are connected to a distribution system. In this paper an islanding detection method is presented for inverter based Distributed Generation (DG) using under/Over voltage Relay.The method is an adaptive one and is based on the change of DG active power reference (Pref) in inverter control interface. The active power reference has a fixed value in normal condition, if the Point of Common Coupling (PCC) voltage changes, Pref, is determined as a linear function of voltage. The slope of Pref depends on the load active power (Pload) and it should be changed if Pload changes. The Non-Detection Zone (NDZ) of the proposed method is zero. If changing of the PCC voltage is sensed, islanding will be detected when it occurs. Also, it does not have any negative effects on the distribution system under normal conditions. The proposed method is evaluated according to the requirements of the IEEE 1547 and UL 1741 standards, using PSCAD/EMTDC software.

In this paper, we investigate the physical layer security performance of a buffer-aided cognitive Relay network Over Rayleigh fading channels, where an underlay cognitive radio system is employed. In this network, a cognitive transmitter communicates with a cognitive receiver through a buffer-aided Relay, in the presence of an eavesdropper Overhearing the transmitted information. To evaluate the secrecy performance of the system, secrecy outage probability (SOP) has been used as a popular performance metric, where a closed-form expression is obtained. Numerical results obtained from the derived SOP expression, along with the Monte-Carlo simulation results are provided to evaluate the secrecy performance of the system under different system parameters. In addition, the secrecy performance of the system without buffer is evaluated and compared with that of the buffer-aided system. Assuming that the delay caused by buffer is negligible, it is shown that increasing the buffer size from L=2 to L=20 leads to a decrease in SOP from 10-2 to 10-3, indicating a performance improvement in the order of about 10. MoreOver, buffer-aided Relay system achieves 3 dB SNR gain compared to the performance of the system without buffer, at the SOP of 10-3.

Directional OverCurrent Relays utilize the voltage phasor as a reference for determining the direction of the fault. This requires measuring both Current and voltage and makes the directional OverCurrent Relays more costly than the non-directional type. In this paper, a new method for detection the fault occurrence and fault direction is proposed, that is based on Teager energy operator. Teager energy operator is a simple algorithm that is used to signal processing and extraction of instantaneous changes in amplitude and frequency of a signal. To this end, the proposed algorithm uses only three consecutive samples of measured Current signal for detection of fault and its direction. This method does not require phasor estimation and complex calculations. In addition, the method is very fast. This Algorithm is implemented and verified for different types of fault and several conditions using Matlab/Simulink. The simulation results show that the proposed method is fast and has acceptable accuracy.

This paper presents a new AC optimal power flow (AC OPF) model for sub-transmission networks. This model, which consists of sub-transmission and distribution bus-bar switching actions, can avoid undesirable Over-Current (OC) status and subsequent actions of OC Relays. The proposed AC OPF optimizes the bus-bar switching actions along with optimizing sub-transmission control actions. Also, to consider the impact of OC Relays’ actions in the proposed AC OPF, the cost of load shedding caused by these Relay actions is included in the objective function and is minimized along with the sub-transmission operation cost. The bus-bar switching actions are modeled using binary decision variables. Therefore, the proposed AC OPF model is formulated as a Mixed Integer Non-linear Programming (MINLP) optimization problem. The effectiveness of the proposed model is illustrated on a real-world sub-transmission network of Iran’ s power system.

The presence of distributed generation sources (DGs) will affect the extent and duration of system failures. This will inevitably require the need to review the functioning of the system of protection and re-coordination of the relevant equipment. Because the lack of an appropriate coordination between the DG units connected to a distribution system could lead to the exchange of power between these units and the system's instability, improper operation of the system of protection or the unintended islanding of a part of the system. Due to the fact that synchronous machine type DGs (SMDGs) are the most problematic for system coordination (Over-Current Relays) than other types of DGs, in this paper, controlling the output Current of generators Synchronization is proposed by tap changer of the transformer connected to it. In this method, the SMDG's participation in the flow of error is limited by the control of the pincer. Before the fault occurred and in accordance with the system conditions, the transformer tapping device connected to the synchronous generator has been changed and it reduces the flow during an error. This strategy, in addition to reducing the generation error of the generators and transformer assembly installed as a dispersed generation source, also increases the permeability coefficient of these sources. The proposed technique is implemented on a sample distribution system in the ETAP software, the results of the simulation show the effectiveness of the proposed method.