Fragility of Electric Power Distribution Systems

Abstract eng:
A vital aspect on the restoration of civilization to good working order after earthquakes is the restoration of the power grid. For the past 46 years, ever since the damage at the Sylmar converter station in the 1971 San Fernando earthquake, the focus has been on the damage of high voltage equipment at substations, with very little attention to the damage of low voltage distribution systems. In California, there are now more than 4 million low voltage distribution power poles, and hundreds of thousands of kilometers of low voltage circuits. What is needed are rational methods to analyze this huge inventory, in a way that can develop accurate power outage forecasts, and ideally provide insight as to what actions can be done now to reduce the potential for power outages in future earthquakes. This paper presents a detailed examination of the performance for Pacific Gas and Electric's (PG&E) low voltage distribution system in the 2014 Napa earthquake. In that earthquake, there was no material damage to the high voltage transmission system, but damage to the distribution system resulted in power outages to 70,000 PG&E customers. The last customer had power restored in about 38 hours. This paper examines the damage that caused these outages, what level of effort was needed to make repairs, and describes new fragility models that can accurately forecast this damage.

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