I- INTRODUCTION

II- INFRASTRUCTURE FRAGILITY MODELS AND RESILIENCE ENHANCEMENT STRATEGIES

III- MATHEMATICAL FORMULATIONS

IV- SOLUTION ALGORITHM

V- NUMERICAL RESULTS

VI- CONCLUSION

REFERENCES

Abstract

This paper proposes an optimal hardening strategy to enhance the resilience of power distribution networks to protect against extreme weather events. Different grid hardening techniques are considered, such as upgrading poles and vegetation management. The problem is formulated as a tri-level optimization problem to minimize grid hardening investment and load shedding in extreme weather events. The first level is to identify vulnerable distribution lines and select hardening strategies, the second level is to determine the set of out-of-service distribution lines so that the damage caused by extreme weather events is maximized, and the third level is to minimize load shedding costs according to load priorities and the set of damaged lines. Since the selection of hardening strategies is coupled with the uncertainty set of out-of-service lines, the original tri-level model is transformed to be an equivalent bi-level problem, which is subsequently solved by a greedy searching algorithm. Case studies demonstrate the effectiveness of the proposed method under multiple severe weather events and different simulation settings.

INTRODUCTION

Enhancing grid resilience to protect against extreme weather events is a key task of grid modernization efforts [1]. The extreme weather-caused outages have resulted in substantial economic losses in recent years in the United States. For example, Hurricane Sandy in 2012 paralyzed power systems of several coastal states and resulted in outages that affected over 8.5 million customers [2]. It is reported that 65% of New Jersey’s customers were disconnected from grids in this severe event [3]. Between 2003 and 2012, roughly 679 power outages, each affecting at least 50, 000 customers, occurred due to weather events in the United States, and 80%−۹۰% of these outages were due to failures in distribution systems [4]. Grid hardening is one of the most effective methods to protect systems against extreme weather events. There are various grid hardening strategies such as overhead structure reinforcement, vegetation management, undergrounding, and integrating black-start resources. Overhead structure reinforcement constitutes a primary hardening strategy which involves upgrading distribution poles to a stronger class, enhancing guying, and refurbishing poles. Extensive vegetation management also can contribute to distribution system hardening, as fallen trees and debris are credited with the majority of power outages that occur during severe storms in the Northeastern part of the United States [5]. Undergrounding distribution lines can reduce the system susceptibility to windinduced damages, lightning, and vegetation contacts, but it extends restoration time with a high installation and repair cost. Elevating substations, integration of DGs, and relocating facilities to areas that are less prone to extreme weather can help protect against floods. Although system hardening could reduce component failures and restoration efforts, hardening and upgrading the entire distribution systems is potentially expensive. As a result, how to cost-effectively design a resilient distribution system against climatic disasters becomes a great challenge.