Flood Resilience in Pole-Mounted Substations: Structural Fragility Assessment

Electric Power Networks (EPNs) should ensure a resilient electricity supply even during extreme events. This study focuses on evaluating the resilience of substations, a key component of EPNs responsible for regulating, transforming, and distributing electricity, and often vulnerable to flood hazards. Pole-mounted substations are the type that can effectively mitigate inundation failures by elevating electrical equipment. However, the supporting structures of such substations are often not designed to withstand flood flows and thus are prone to structural failure. In this study, a generalized framework is proposed to quantify the structural failure probabilities of pole-mounted substations and to assess their structural resilience to flooding. This framework is then applied to a case-study location in Malaysia, where serious flood events are common and pole-mounted substations are numerous.

The proposed framework can effectively address data limitations through well-justified assumptions. The study first identifies and quantifies the flood effects on the poles, including pure hydrodynamic forces, the impact of floating debris, debris damming effects, and scouring. The quantified flood effects are then compared with the structural capacity of a typical pole-mounted substation structure and its foundation to derive a capacity threshold curve for structural failure. The failure probability is illustrated via fragility curves for different flood depths and risk curves for different flood and wind return periods, to further assess the substation’s structural resilience. The aforementioned curves are based on a stochastic distribution of flood depths and velocities represented by a normalized Weibull function. A modifiable scale factor λ in this function (determined by the mode of flood depth or velocity) can be used to accommodate different geographical locations, which addresses the inherent uncertainties in assessing the resilience of structural systems to floods.

The research findings revealed that impact and damming effects arising from floating debris contribute the most (e.g., 40%–80%) to structural failure, which verifies that pole-mounted substations need to be designed to withstand flood effects in addition to wind loading. Besides, according to the developed risk curves, a flood return period of 25 years is recommended for designing substations to balance the structural capacity and costs. Overall, this study enhances the understanding of how component resilience relates to system-level risk in EPNs and helps stakeholders, including those designing and managing substation structures, to quantify, assess, and further enhance the flood resilience of EPNs.