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Optimal coordination of the protection devices (PDs) is performed here simultaneous with optimal allocation of them and the DGs. The PDs are a set of directional overcurrent relays (DOCRs) and voltage relays, each with its own fast switch (FS). In previous optimal DG placement studies the coordination of the PDs has been considered as a constraint. So, it was not possible to optimal coordination of the PDs simultaneously. In the present study, the coordination between the PDs is considered in calculating the value of the energy not supplied (ENS) that is a part of an overall cost function. The cost function considered here includes cost of purchase, installation, and maintenance of the DGs and the PDs, cost of the energy losses, cost of the ENS, cost of the purchased energy from the main grid and the DGs, and the penalty cost for emitting environmental pollutants. Here, output of the renewable DGs and the network loads during the year, in a 96‐h model, has been considered as variable. To solve the desired optimization problem, an algorithm based on evolutionary algorithms such as genetic algorithm (GA) is proposed. Finally, various cases have been simulated by considering a standard 33‐bus radial network. [ABSTRACT FROM AUTHOR]

Since the penetration level of the inverter‐based distributed generations (IBDGs) into microgrids (MGs) is increasing, the protection issues of such networks have become more challenging. The present work aims to design a protection framework for fault detection and classification in IBDG dominated MGs. In the proposed approach, the current waveforms measured from one end of the protected lines are processed using superimposed components. Then, the faults are identified using the Euclidean distance concept. A Pearson correlation coefficient‐based approach is also developed to characterize the faulty phases in the proposed fault classification unit. Furthermore, an auxiliary index is defined to discriminate load change conditions from the faults. In addition to being simple and efficient, the proposed technique is highly capable of functioning in different MG operating modes and configurations without changing its settings. Also, it demonstrates robust performance against IBDG impacts, noises, and stimulating fault scenarios. To assess the scheme proficiency, a modified IEEE 15‐bus system with highly penetrated IBDGs is simulated. The results confirm the quickness and high accuracy of the proposed technique. Moreover, the method is validated in an experimental laboratory test bench. Finally, the superiority of the method is confirmed by a comparative study with other recent methods. [ABSTRACT FROM AUTHOR]

Due to increase in penetration of Distributed Generations (DGs) in power systems, fault current level is being increased, which results in some problems in the systems. Fault Current Limiters (FCLs) are attractive devices to tackle these problems for transmission and distribution systems. The utilized FCLs may have considerable impact on the signals used for differential protection of power transformers, which leads to mal-operation of these protections. It seems a comprehensive analysis is necessary for performance evaluation of differential protection algorithms in presence of FCLs. This paper deals with investigation of FCLs impact on power transformers’ differential protection. The performance of some well-known differential protection algorithms for discrimination between internal fault current and magnetizing inrush current with and without presence of FCL are evaluated. [ABSTRACT FROM AUTHOR]

Stand-alone micro-grids (MGs) and grid-connected MGs with high penetration level of Distributed Generation (DG) are growing at a fast rate. In these grids, the power quality disturbances such as harmonics, inter-harmonics and deviation from the fundamental frequency are widespread. The influence of these disturbances on two categories of digital metering algorithms is evaluated in this paper. The first category is related to the measurement of the fundamental frequency component of current and voltage signals, which are used as inputs of the digital protection algorithms. Most of the relays only use fundamental frequency component of their input voltage and current signals to fulfill the desired protective functions. The accuracy of the protective relays highly depends on the performance of the applied algorithms for extracting the fundamental components. The second evaluated category is related to the reactive power calculation algorithms, which are used in the static VAr compensator (SVC) control system. Utilizing SVC is growing due to the DGs such as wind turbines magnify voltage fluctuations called flicker. Since the SVC compensates only the reactive power related to the fundamental frequency component, the reactive power signal should not be sensitive to the harmonics. In addition, the reactive power calculation should be fast enough that SVC can follow the abrupt changes to mitigate the flicker, efficiently. In this paper, frequency deviation, harmonic, and inter-harmonic phenomena are considered as the most causes for power quality problems. Their influence in digital metering algorithms is evaluated. It is confirmed that defining new indices is mandatory to fully reflect algorithms׳ accuracy and efficiency. Furthermore, the field measurements of instantaneous voltage and current of a wind farm and electric arc furnaces are used for the evaluation. [ABSTRACT FROM AUTHOR]

A simple technique is proposed in this study, aimed at the islanding detection of an inverter-based distributed generation (DG). The main advantage of the proposed technique is its reliance on a simple approach for islanding detection with negligible non-detection zone and keeping the unchanged output power quality. This work attempts to detect islanding conditions through computing the rate of change of voltage phase angle (ROCOVPA) of the point of common coupling by phase-locked loop (PLL) in inverter controllers. Because almost all inverter systems are equipped with the PLL, its implementation for inverter-interfaced DGs is simple and economical. Simulation results show that the durability energy of ROCOVPA is different for islanding and non-islanding conditions. In fact, in non-islanding condition the energy of ROCOVPA reduces to a negligible value after a certain time, but in islanding conditions it has considerable variation. The proposed method is evaluated using the conditions dictated by the IEEE 1547 and UL 1741 standards. The simulation results are presented to highlight the effectiveness of the proposed technique. In addition, the proposed method is compared with several passive and intelligent methods and it is confirmed that the proposed method has better performance and more accuracy. [ABSTRACT FROM AUTHOR]

A simple technique is proposed in this study, aimed at the islanding detection of an inverter‐based distributed generation (DG). The main advantage of the proposed technique is its reliance on a simple approach for islanding detection with negligible non‐detection zone and keeping the unchanged output power quality. This work attempts to detect islanding conditions through computing the rate of change of voltage phase angle (ROCOVPA) of the point of common coupling by phase‐locked loop (PLL) in inverter controllers. Because almost all inverter systems are equipped with the PLL, its implementation for inverter‐interfaced DGs is simple and economical. Simulation results show that the durability energy of ROCOVPA is different for islanding and non‐islanding conditions. In fact, in non‐islanding condition the energy of ROCOVPA reduces to a negligible value after a certain time, but in islanding conditions it has considerable variation. The proposed method is evaluated using the conditions dictated by the IEEE 1547 and UL 1741 standards. The simulation results are presented to highlight the effectiveness of the proposed technique. In addition, the proposed method is compared with several passive and intelligent methods and it is confirmed that the proposed method has better performance and more accuracy. [ABSTRACT FROM AUTHOR]

This paper presents simultaneous allocation of distributed generations (DGs) and fast directional protection switches (FDPSs) to decrease energy losses and enhance reliability of the network. The main contribution of the paper is restricting the allowable size of DGs to ensure the correct operation of upstream installed FDPS in all conditions. The paper introduces a method based on genetic algorithm to solve the optimization problem. Finally, to confirm the effectiveness of the proposed method some simulations considering a 33 bus test network are performed. The optimization problem with and without applying protection constraint is solved. Customer’s load is modeled by a three level yearly load. Time value of money and load growth rate are also considered. To assess the importance of the proposed protection constraint, fault studies after adding DGs and FDPSs to a 33 bus test network are performed. Results confirm the importance of the proposed protection constraint. [ABSTRACT FROM AUTHOR]

In this paper allocating of DGs and optimal number, locations and size of solid State Fault Current Limiters (SSFCLs) is performed for a case study contains modern protective devices. Genetic algorithm (GA) is employed for optimal allocating of DGs and SSFCLs. The distribution system contains remote controllable switches in addition to conventional tools such as fuses, relays and circuit breakers. The results demonstrate that minimization of distribution protection system cost, is still valid for a distribution system, which contains modern protective devices. [ABSTRACT FROM AUTHOR]

• Proposing an islanding detection algorithm based on empirical mode decomposition. • Dealing with under the complete match between generation and consumption. • Dealing with various non-islanding conditions including fault, switching, etc. Owning to extensively enhancement of renewable energy resources in the distribution grids, the employment of such sources is also associated with various issues such as the islanding problem. In this paper, an effective method has been proposed for detection of the islanding in the micro-grids comprised of inverter or direct fed types of distributed generations. The proposed method is designed based on the intrinsic modes of the voltage signal measured at the PCC point. More specifically, through the calculation of the positive sequence of the voltage signal variation (PSVSV) and extracting the signal energy of PSVSV's intrinsic modes, the islanding can be detected. The superiority of the proposed islanding detection method is manifested in the condition where the generation of distributed resources is in balance with the loading consumption. The performance of the proposed method has been evaluated considering the conditions where islanding is difficult to detect or might be mistaken with other phenomena given by loads within the NDZ region, different fault types, and loads with different power factors. The performance evaluation has been carried out through simulations, and furthermore has been compared with the state-of-the-art algorithms. [ABSTRACT FROM AUTHOR]

• It has been Mathematically proven that, due to the use of the rate of change of fault current signal, the proposed index has very little sensitivity to the decaying DC component. • Unlike previous methods, the proposed index does not suffer from voltage-drop issues for fault near the directional algorithm. • In the proposed index, a half-cycle moving average indicator is employed and as a result, the presence of the proposed index reduces the sensitivity of the algorithm to noise. • Comparing to the state-of-the-art algorithms, the proposed method requires a low sampling rate. Also, low-complexity. The proliferation of Distributed Generations (DGs) in distribution networks has provided power system operation improvement while raising some protection challenges. Turning to bi-directional, the protection schemes of the deregulated distribution networks should be able to deal with an out-of-zone fault. More specifically, DGs impose bi-directional fault current and directional relay should be employed to identify correct fault direction so that the protective relays are prevented from mal-operation of out-of-zone fault. This paper introduces a current-based directional algorithm that utilizes a pre-fault current signal as the reference. This algorithm is designed based on the pre-fault current and rate of change of the fault current. As it can be inferred from the mathematical basis of the proposed method, it has low sensitivity to decaying DC and noise components. Also, the proposed index has a certain and straightforward range of variation between (-1, 1) for backward and forward fault direction, respectively. The performance of the proposed algorithm is evaluated for different scenarios such as variation of fault resistance, sampling frequency, and types of faults in three simulated systems and a laboratory test bench. The simulation and experimental evaluation results show the accuracy and speed of the proposed algorithm in comparison with similar algorithms. [ABSTRACT FROM AUTHOR]

• This paper proposes a new criterion based on the rate of change of potential energy function. • The proposed criterion discriminates the islanding condition in a short period even under a perfectly matched load and generation. • The proposed islanding detection index does not mal-operate the short circuit fault, load change, capacitor switching. • The presented criterion has straightforward mathematics which leads to low computational cost. Owning to the extensive enhancement of renewable energy resources in the distribution grids, the employment of such sources has also introduced various issues, such as the islanding problem. In this paper, an effective method is proposed for the detection of islanding in micro-grids. The proposed method employs the concept of potential energy function to drive the islanding detection index. Based on swing and potential energy function equations, an islanding detection criterion is derived based on the rate of change of the potential energy function. The islanding detection index (IDI) takes into account the frequency changes and the rate of change of frequency (ROCOF) of DG. The superiority of the proposed islanding detection method is manifested in the condition where the generation of distributed resources is in balance with the loading consumption. The performance of the proposed method has been evaluated considering the conditions where islanding is difficult to detect or might be mistaken for other phenomena given by loads within the Non-Detection Zone (NDZ) region, different fault types, and loads with different power factors. The performance evaluation has been carried out through simulations and, furthermore, has been compared with the state-of-the-art algorithms. [ABSTRACT FROM AUTHOR]