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Although inverter‐interfaced renewable energy sources (IIRESs) have great economic and environmental benefits, their fault current characteristics differ from those of synchronous generators. IIRESs also comply with modern grid code (GC) requirements for injecting reactive current to compensate for voltage drop during fault conditions. Moreover, the limits of renewable energy‐side fault current contribution and the phase angle difference between the local and infeed fault current from conventional sources lead to incorrect reactance estimation by the traditional distance relay at the IIRES substation and negatively affect relay dependability. As a result, the IIRES‐side distance protection is prone to incorrect operation. Furthermore, an improved relaying scheme is proposed to alleviate the adverse effects of IIRES on the reactance calculation. This research aims to improve the performance of the ground distance protection scheme in the case of a single‐phase to ground fault in zone one. The proposed method, with more than 99% accuracy, is solely dependent on the local information and, therefore, no communication link is required to implement the algorithm. Moreover, the algorithm is compatible with the existing pilot protection methods used in the industry. The simulation studies are modeled in the Digsilent Power Factory environment. [ABSTRACT FROM AUTHOR]

The security of energy systems has always been one of the most important issues of energy systems operation. The multi‐carrier multi‐microgrid (MCMMG) is one of the novel structures in the power system. High penetration of renewable resources and their uncertainty, their ability to operate in isolation mode, and the presence of energy hubs in MCMMG systems increase the importance of security assessment in this type of system. This paper presents a decentralized risk‐based security‐constrained optimal power flow model for an MCMMG system. The stochastic nature of wind energy, photovoltaic generation, and electrical and heating loads are considered in the proposed model. In the model, the risk level of the system is determined by considering both the electrical and natural gas (NG) networks' contingencies. The proposed model is decomposed into three types of subproblems with the augmented Lagrangian relaxation (ALR) method: The subproblem related to the multi‐microgrid operator level, the NG network subproblem, and the individual microgrid level subproblem. The decomposed problem is solved using MATLAB software. According to the results, the proposed model can secure the system from high costs that may impose on the system due to the contingency occurrence. [ABSTRACT FROM AUTHOR]

This paper presents a discrete heuristic algorithm to improve voltage stability margins of the power system, during under frequency conditions. Discrete group search optimization algorithm is proposed for the first time in this work and applied to a load shedding problem. Sometimes, after initial frequency drop following severe disturbances, the system frequency might return to its acceptable value, however, the system might become unstable due to voltage problems. This paper proposes discrete group search optimization algorithm to solve the load shedding problem as well as returning system frequency to the acceptable range. The objective of proposed method is to enhance voltage stability margins of the power system. Furthermore, in the paper the load uncertainty as the most critical source of uncertainty in power system is handled using point estimation approach. The proposed method is implemented on the modified IEEE 14-Bus test system as well as 39 bus New England Network to demonstrate its applicability and effectiveness. The performance of discrete group search optimization method is also compared with several methods in terms of enhancing voltage stability margins. The results confirm that the proposed method provides a considerable enhancement in the power system voltage stability margin. [ABSTRACT FROM AUTHOR]

Hilbert-Huang transform (HHT), continuous wavelet transform (CWT) and discrete wavelet transform (DWT) are well-known signal processing methods that are widely utilized for feature extraction and fault detection by protection systems in smart grids. In this paper, we assess the performances of these methods encountering challenging situations in distribution networks, i.e. high impedance arcing fault (HIF) and current transformer (CT) saturation. Low fault current amplitude in HIF case causes the overcurrent protection, which is the predominant protection method in distribution grids, to fail. Furthermore, some faults may lead to CT saturation, which may result in delayed operation of the relay. To overcome the mentioned problems, researchers employ signal processing approaches such as HHT, DWT or CWT for feature extraction from voltage and current waveforms and import the features to artificial intelligence-based algorithms to detect and discriminate the problems from other normal conditions in power networks. In this regard, HHT, CWT, and DWT are compared under different fault conditions, such as HIF and CT saturation, as well as sudden load increasing, capacitor bank switching, and inrush current of distribution transformers as normal conditions. As a result, simulation studies demonstrate that CWT and DWT are more appropriate for applications of CT saturation and HIF detection in protection of power networks. [ABSTRACT FROM AUTHOR]

This paper uses the coordination between the reactive power of a solid oxide fuel cell (SOFC) and a battery to control the frequency within an islanded microgrid. By this coordination, the microgrid frequency regulation becomes faster and better during contingencies. Moreover, the energy storage capacity, which is usually required for the frequency control of islanded microgrids, has significantly been reduced. Furthermore, there will be no need to consider reserve capacity in renewable sources for frequency control. Therefore, renewable energy sources can be operated at their maximum power point. Also, this paper introduces a new frequency-reactive power control concept and a related coefficient that shows the degree of dependence of the microgrid frequency on the injected reactive power changes at each bus. This coefficient determines the priority of buses for the installation of reactive power control devices to control the frequency of the microgrid. Simulation studies have been performed in the MATLAB/Simulink environment. The results show the applicability and accuracy of the proposed coefficient and demonstrate the effectiveness of the coordinated control of reactive power between the SOFC and the battery for frequency control. [ABSTRACT FROM AUTHOR]