Participation of distributed energy resources in the load restoration procedure, known as intentional islanding, can significantly improve the distribution system reliability. Distribution system reconfiguration can effectively alter islanding procedure and thus provide an opportunity to supply more demanded energy and reduce distribution system losses. In addition, high-impact events such as hurricanes and earthquake may complicate the procedure of load restoration, due to disconnection of the distribution system from the upstream grid or concurrent component outages. This paper presents a two-level method for intentional islanding of a reconfigurable distribution system, considering high impact events. In the first level, optimal islands are selected according to the graph model of the distribution system. In the second level, an optimal power flow (OPF) problem is solved to meet the operation constraints of the islands by reactive power control and demand side management. The proposed problem in the first level is solved by a combination of depth first search and particle swarm optimization methods. The OPF problem in the second level is solved in DIgSILENT software. The proposed method is implemented in the IEEE 69-bus test system, and the results show the validity and effectiveness of the proposed algorithm.

Although natural disasters have recently imposed enormous damages to power system infrastructures, resilience enhancement through hardening measures is not usually compensated in conventional power system planning. In this article, a framework is proposed to enhance the resilience of distribution systems against earthquakes. In particular, it focuses on substations’ retrofit whose failure can affect the distribution system, imposing outages to the customers connected to it. A knapsack based heuristic method, which considers the bus configuration of substation is proposed to select the substation components for hardening. The potential failure of substation components that would lead to complete unavailability of substation is evaluated through minimal cut set-fault tree analysis. A criterion for resilience enhancement is proposed, including hardening cost, cost incurred by damaged components, cost of customers’ interruption in the distribution system level, and power generation cost of Distributed Energy Resources. A penalty mechanism taking into account the component repair time is used to estimate interruption costs. The impact of earthquakes on substation components is modeled using fragility curves. A case study with real earthquake characteristics is considered and Monte Carlo simulation is used to capture the stochastic failure of substation components. The results show that power transformers and circuit breakers at 20 kV are the most critical components in the retrofitting strategies.