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Islanding is one of the important challenges in power networks in the presence of distributed generation which is considered an undesirable incident due to the possibility of damage to operators, network equipment, and consumers. Therefore, it is necessary to quickly detect islanding and make a decision regarding the connection status of local distributed generation units in the network. In this paper, a passive islanding detection method is proposed using adaptive threshold-based instantaneous frequency droop characteristic. The proposed threshold limit is dynamically changed depending on under-studied conditions to discriminate the island from load changes, capacitor bank switching, motor start-up, and short circuit types. Two medium voltage networks of Cigre and 34-bus IEEE are used to evaluate the proposed method. The simulations are performed in Digsilent software and the proposed method is implemented in MATLAB software. The simulation results indicate that the island is correctly detected with appropriate accuracy in a short period of time from other disturbances in the presence of wind, solar and diesel types of distributed generations. [ABSTRACT FROM AUTHOR]

Islanding is one of the important challenges in power networks in the presence of distributed generation which is considered an undesirable incident due to the possibility of damage to operators, network equipment, and consumers. Therefore, it is necessary to quickly detect islanding and make a decision regarding the connection status of local distributed generation units in the network. In this paper, a passive islanding detection method is proposed using adaptive threshold-based instantaneous frequency droop characteristic. The proposed threshold limit is dynamically changed depending on under-studied conditions to discriminate the island from load changes, capacitor bank switching, motor start-up, and short circuit types. Two medium voltage networks of Cigre and 34-bus IEEE are used to evaluate the proposed method. The simulations are performed in Digsilent software and the proposed method is implemented in MATLAB software. The simulation results indicate that the island is correctly detected with appropriate accuracy in a short period of time from other disturbances in the presence of wind, solar and diesel types of distributed generations. [ABSTRACT FROM AUTHOR]

Reliable overhead transmission lines have a vital role in maintaining the reliability of power systems at a desirable level and ensuring the continuity of electrical energy. In this regard, a proper preventive maintenance program can ensure the reliable functioning of transmission lines. Based on the concept of reliability-centered maintenance, this paper proposes a preventive maintenance strategy that can be implemented in real power systems due to the limited data requirements. The priority of each line for preventive maintenance was obtained by two indices revealing the technical condition and importance of each line in the network. The proposed method was applied to a real transmission network in Khorasan province of Iran. In order to extract the condition index of lines, failure statistics during six recent years as well as technical data of lines were investigated. Moreover, this paper presents a two-stage method to determine the importance index of each line by evaluating the consequences of line failures on the network. The presented results show the efficiency of the proposed approach. [ABSTRACT FROM AUTHOR]

In this paper, the modified bee optimization algorithm is proposed to appropriate switches placement regarding distributed generation to maximize the feeders' reliability of a typical distribution network in Mazandaran. In this regard, actual network information including number of consumers, average consumption, feeders failures, feeders access time, repair time, etc. are used to determine network reliability indices. The optimal location of switches is determined by different scenarios due to the presence of distributed generation and the importance of feeders in the studied network. Moreover, the effect of cut-out fuses and ring points on feeders is considered in determining the appropriate switches placement, which is usually not considered in the reliability analysis of the distribution network and switches placement. Different indices are considered to determine the importance of feeders and a questionnaire has been prepared to utilize the personnel experiences of the distribution company to weigh these indices. Comparing and analyzing the results shows the ability of the proposed method in determining the appropriate switches locations in a real network. [ABSTRACT FROM AUTHOR]

Power transformer protection has a high sensitivity due to its important role in power systems. Various factors such as inrush and sympathetic inrush currents may result in the inappropriate performance of protective relays and cause problems such as power outage or blocking of sensitive loads. Until now, several studies have been performed on the detection and reduction of inrush current, however, the effect of sympathetic inrush current on transformer protection has not been addressed. In this study, the operation of the protection system during the sympathetic inrush current is comprehensively analysed. Furthermore, the use of a fault current limiter is proposed to reduce the undesirable effects of the phenomena. The effects of the limiter on the saturation of power and current transformers are investigated. A real transmission station is simulated using DIgSILENT Power Factory Software to perform these studies by considering the resistive and impedance fault current limiter. Results show that protective relays do not have an improper operation during the phenomena with limiters. Moreover, with the resistive fault current limiter, sympathetic inrush and inrush currents are decreased by 5 and 15% more than the impedance fault current limiter, respectively. Saturation of power and current transformers is significantly reduced with limiters, especially with a resistive fault current limiter. [ABSTRACT FROM AUTHOR]

The number of constraints in coordination of distance and directional overcurrent relays (D&DOCRs) in power systems increases significantly by considering changes in network topology, especially in large power systems. By increasing the number of coordination constraints, the complexity of the D&DOCRs coordination problem is increased. Therefore, in this paper, a new method is proposed to reduce the number of coordination constraints in the D&DOCRs coordination problem. In the proposed method, redundant constraints are identified before solving the coordination problem. The proposed method is independent from D&DOCRs settings and operating characteristics of directional overcurrent relays. In order to evaluate the proposed method, two different test systems, namely, an 8-bus and the IEEE 14-bus test systems, are used. Based on the presented results, it can be seen that the proposed method is efficient, and by utilizing it, many redundant coordination constraints are identified and removed, helping to obtain effective solutions for the optimal settings with less computational effort. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]