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In this paper, a new formulation for distribution system reconfiguration (DSR) is proposed for minimizing the annual energy losses considering the variability in active and reactive power demand and distributed generation (DG) profiles. A fuzzy C-means clustering algorithm is used to obtain representative centroids from annual DG and power demand profiles. The DSR study is formulated as a mixed-integer nonlinear programming optimization problem and tested on a 33-bus and an 84-bus system. The minimization is subject to the power balance, bus voltage, and distribution system radiality constraints. Using this formulation, a single optimum configuration that minimizes annual energy losses is found and shown to be different from the optimum configuration, found in previous literature, which focuses on minimizing power losses at peak or average loads. In addition, the prospective advantages of grid automation on DSR are demonstrated to provide further energy loss reduction by including the possibility of interchanging a predefined number of configurations that minimize annual energy losses. [ABSTRACT FROM AUTHOR]

With the integration of distributed generation (DG) to meshed distribution systems, the operating time of the protective system becomes a major concern in order to avoid nuisance DG tripping. This paper proposes a new time–current–voltage tripping characteristic for directional overcurrent relays (DOCRs) that can achieve a higher possible reduction of overall relays operating time in meshed distribution networks. The proposed tripping characteristic is described in detail. Moreover, the protection coordination problem is formulated as a constrained nonlinear programming problem to determine the optimal relay settings. The proposed characteristic is tested on the power distribution system of the IEEE 14 bus and IEEE 30 bus with inverter-based and synchronous-based DG units. The outcome of this study reveals that the new tripping characteristic for DOCRs achieves notable reduction in total relays' operating time over the conventional characteristic. [ABSTRACT FROM AUTHOR]

This paper introduces a novel coordinated voltage-control (CVC) scheme for distributed generations (DGs) that relies on adaptively changing the roles (master or slave) of the devices [inverter-based DG, diesel generator, and online tap changer (OLTC)] within the smart grid, depending on system conditions. In addition, the proposed scheme imposes different control response and bandwidth on the devices to coordinate the reactive power among distributed generations (DGs) and OLTC steps. The main objective of the proposed method is twofold: 1) to maximize the reactive power reserve of DGs and, hence, facilitate reaction during contingency situations and 2) to provide voltage regulation during normal operating conditions. The simulated distribution system includes inverter-based DGs (photovoltaic and wind turbine), diesel generator, and OLTC and the potential of the CVC scheme is evaluated and analyzed in view of improving voltage profile, maximizing the reactive power reserve, enhancing fault ride through and improving the transient stability margin. The control algorithm is examined under steady state, load excursion, and three-phase-to-ground fault conditions. The results demonstrate the ability of the proposed CVC scheme to satisfy the targeted objectives with significant improvement in the maximum critical clearing time. The proposed scheme is independent of real-time measurements and is widely adaptive to the dynamics of power systems, thus making it quite suitable for utility implementation. [ABSTRACT FROM AUTHOR]

In this paper, a new optimization problem is proposed to determine the maximum distributed generation (DG) penetration level by optimally selecting types, locations and sizes of utility owned DG units. The DG penetration level could be limited by harmonic distortion because of the nonlinear current injected by inverter-based DG units and also protection coordination constraints because of the variation in fault current caused by synchronous-based DG units. Hence the objective of the proposed problem is to maximize DG penetration level from both types of DG units, taking into account power balance constraints, bus voltage limits, total and individual harmonic distortion limits specified by the IEEE-519 standard, over-current relay operating time limits, and protection coordination constraints. The DG penetration study is formulated as a nonlinear programming (NLP) problem and tested on the IEEE-30 bus looped distribution network with ten load and DG scenarios. Similarly, feasibility assessment of customer owned DG unit installations considering power quality and protection coordination is also studied. Simulation results show the effectiveness of the proposed approach, which can serve as an efficient planning tool for utility operators. [ABSTRACT FROM PUBLISHER]

This paper presents an optimization procedure that enables the optimal dispatching of distributed generators and storage systems in a medium-voltage islanded microgrid. The network is assumed to be supplied by programmable (dispatchable) and nonprogrammable generators (i.e. nondispatchable, such as renewable energy sources—based units). The optimization goal is to minimize the overall microgrid operating cost and the pollutants emission of the programmable generators, assuming that all of the power made available by the renewable generators (photovoltaic and wind systems) is either directly injected into the network or stored in order to be subsequently delivered according to the proposed storage units' management strategy. The optimization is carried out by a niching evolutionary algorithm (NEA) that is able to find multiple optima and the variation of the objective function in their neighborhood. NEAs allow overcoming the performance of standard algorithms used for optimal power-flow calculations in power systems by avoiding falling into local optima. The optimization procedure is performed on a test microgrid and verified by computer simulations. The numerical results show that the solutions can always improve the microgrid performances irrespective of the network operating conditions in all of the considered cases. [ABSTRACT FROM AUTHOR]

The battle for electricity customers in an increasingly competitive and deregulated market environment is one of the challenges facing the electric power utilities of today. Customers expect a reliable and efficient supply of power from their utilities. One of the advantages that a distributed generator (DG) can provide to the electric utility and to customers is the possibility of improving the continuity of supply by implementing safe intentional islands in the event of upstream utility supply outage. Implementing intentional islanding of DG in a deregulated era will have an impact on electricity market prices. This problem is considered in this paper by solving the optimal power flow problem while accounting for islanded operation. [ABSTRACT FROM AUTHOR]