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In this paper, a stochastic framework is proposed for optimizing replacement strategies of aged XLPE cables in the electric power distribution network. The proposed framework facilitates realizing an economic value for the risk of unplanned outages, thereby shifting the paradigm of replacing aged XLPE cable from a technical decision that is solely based on diagnostic measurements to a techno-economic strategy. The proposed framework constitutes of three main phases: (1) obtaining a distribution for the aging process of XLPE cable due to water-trees, (2) modeling the replacement of the aged XLPE cable as a Markov decision process, and (3) applying a linear programming algorithm in order to solve for the optimal replacement policy. Based on the proposed framework, a critical health index is defined for optimum replacement, depending on the installation costs of a new cable and the unplanned outage cost. [ABSTRACT FROM AUTHOR]

This paper proposes a generic steady-state modeling and power-flow analysis approach for droop- and isochronously controlled microgrids. The proposed framework adopts symmetrical sequence component models, rather than phase-coordinate models, of microgrid elements. Such approach immensely reduces the power-flow execution time, as it breaks down the system model into independent equation sets with considerably reduced sizes. To render the proposed approach practical and generic, it integrates different types and control schemes of distributed generation (DG), including synchronous generator-based DG (SGDG) and electronically interfaced DG units. Furthermore, it incorporates unbalanced loads and feeders, transformer connections, different load characteristics, and configurations, as well as microgrid droop features. A novel power-flow algorithm based on a modified Newton–Raphson method is proposed to solve for the microgrid steady-state voltage magnitudes, angles, and frequency. The accuracy of the models and algorithm is verified through comparison with detailed time-domain simulations in MATALB/Simulink. Additionally, the proposed approach is shown to outperform the reported Newton-Trust Region approach in generality, accuracy, and performance. Two case studies, incorporating IEEE 123-node test microgrid, are further performed to examine the effectiveness of the proposed approach in solving complicated droop-controlled microgrids, and to examine the behavior of droop-controlled DGs in isochronous microgrids. [ABSTRACT FROM AUTHOR]

This paper provides a novel power flow algorithm as a viable tool to accurately analyze the steady-state behavior of islanded hybrid ac/dc microgrids. The operational philosophy of these networks is sophisticated since both the ac frequency and dc voltage are variable, coupled, and sensitive to the control schemes of the distributed generators (DGs) and interlinking converters (ICs). In order to render the analysis generic, mathematical models are developed for control schemes of the DGs and ICs under unbalanced conditions. The presented models are then incorporated into an optimized power flow formulation and the solution is found using the globally convergent Newton-Trust Region (NTR) method. The algorithm accuracy is verified using detailed time-domain simulations in PSCAD/EMTDC environment. The effectiveness of the introduced power flow algorithm is illustrated via two case studies. The first case investigates parallel operation of droop-controlled ICs and highlights the effects of IC settings on load sharing among subgrids and power-transfer sharing through installed ICs. The second case reveals the significance of analyzing the loading condition for each phase of the DGs rather than for the total three-phase power generation, which is commonly followed in steady-state analysis in the reported literature. [ABSTRACT FROM AUTHOR]