Summary Smart grid has been developing nowadays as an initiative to operate modern electric distribution systems (EDSs) in a more reliable and efficient manner. With the decreasing price of the energy storage systems (ESSs), ESSs are highly recommended to be exploited in the operation of EDSs. In this manuscript, a comprehensive framework is introduced for ESS incorporation in service restoration process which proposes 2 roles for ESSs in the service restoration. As the first role, ESSs are exploited in the service restoration to re‐energize customers in interrupted zones, as their backup units. As the second role, ESSs are used in the service restoration to increase the number of interrupted customers which transferred to the backup feeders through acting as storage units. The proposed objective function of service restoration consists of customer interruption cost, energy not sold cost, cost of electricity production in combined heat and power units, and cost of ESS incorporation in service restoration. Moreover, the stochastic characteristics of ESS contribution in service restoration are considered in the proposed problem formulation. Further, the impacts of the uncertainties of the service restoration on the proposed approach for ESS incorporation are investigated. The effectiveness of the proposed methodology is deliberated using a standard reliability test system (RBTS‐4). The obtained results show that the incorporating ESSs as storage units will lead to substantially improve the reliability level of EDS through increasing the adequacy of the EDS during service restoration process.
Summary Community microgrids (CMGs) have been developing nowadays as an initiative to operate modern electric distribution systems in a more economical, reliable, and environmentally friendly manner than the existing centralized electricity grid which benefited both distribution system operator and consumers. In this paper, the optimal energy management of CMGs is formulated considering distributed energy resources and thermal and electrical demands in CMGs. The objective function of the proposed methodology consists of the total cost of CMGs operation, the total cost of energy not supplied in CMGs, and total cost of emission produced in CMGs in order to comprehensively manage the CMG operation. Moreover, the uncertainty of renewable energy resources, electricity price, and demanded power of CMGs are considered in the proposed methodology. In addition, two risk evaluation measures are employed to cope with existing risks in the CMG operation. Furthermore, a number of sensitivity studies are accomplished to investigate the effects of important parameters on the performance of the proposed approach. The effectiveness of the proposed methodology is examined on a test system.
Summary Microgrids have been developing nowadays as an initiative to operate modern electric distribution systems in a more economic and efficient manner which benefited both system operator and consumers. However, system operators confront certain ordeals in microgrid operation. In this paper, a centralized reactive power compensation (CRPC) system is proposed for microgrids which aims at minimizing the total cost of reactive power compensation including power loss cost, capacitor utilization cost, and voltage deviation in the presence of renewable energy resources. Moreover, the stochastic behavior of customers in the microgrid is considered through several scenarios for demanded active and reactive power, electricity price, and the generated power of renewable energy resources. Further, sensitivity of the proposed CRPC system on the weighting coefficient definition in the objective function is investigated. In addition, the performance of the introduced CRPC system is compared with a decentralized reactive power compensation method. The effectiveness of the proposed methodology is examined using a Macauian test system.
SUMMARY Power transformer differential relays may incorrectly operate due to inrush condition or transformer external faults lead to current transformer (CT) saturation. In this paper, a new technique is presented to distinguish internal fault current from magnetizing inrush current in power transformers. The proposed technique applies two moving windows which both of them estimate magnitude of transformer differential current using different methods. The first moving window method is based on full‐cycle Fourier algorithm (long window) which uses one cycle samples of the current and provides precise estimation. The second one is originated from least error square (LES) method that has five sample point input data (short window). LES method has fast response, but its estimation might not be quite accurate. The proposed technique (which is a combination of two mentioned methods) presents a new criterion for discrimination between internal fault currents and inrush currents using the differences between output values of these two estimators. Meanwhile, obtained results demonstrate precise operation of the proposed algorithm for different conditions such as CT saturation and over‐flux condition; therefore, it can be a multi‐objective technique for transformer protection. Also, a general scheme is presented in order to improve differential protection. In this paper, a real part of 400/230 kV Iranian national grid is simulated using PSCAD software for evaluating the performance of the proposed algorithm. Also, additional validation of the proposed technique is tested offline using data collected from a three‐phase, 5 kVA, 60 Hz, laboratory prototype transformer. Copyright © 2013 John Wiley & Sons, Ltd.
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