Assessing the risk of a power transmission tower and its possible adaptation options to climate change in a Nordic Climate.

The EU-funded RISKADAPT project (GA: 101093939) introduces an innovative, modular, and user-friendly platform, PRISKADAPT, developed in collaboration with end-users to facilitate systemic, risk-informed decision-making for adapting to climate change (CC)-induced compound events. With a focus on structural systems, this study showcases results from one of RISKADAPT's four pilot initiatives, specifically targeting the energy transmission grid in a Nordic climate. Power grid infrastructure is a cornerstone of modern society, underpinning daily activities such as work, communication, transportation, and leisure. The uninterrupted distribution of electricity is essential, with power transmission lines, comprising conductors and steel towers, serving as the "highways" of electricity. Consequently, ensuring their high performance and resilience is of paramount importance. Experience of past events has shown that extreme weather events such as hurricanes, tornados or ice accretions (especially in combination with high winds) may cause failures, usually collapses, of power transmission towers leading to possible long power outages with significant socioeconomical impact. For this reason, evaluating the risk of power transmission infrastructure under adverse weather conditions is crucial. Moreover, climate change makes such risk evaluation more challenging due to the modification of extreme weather trends in terms of frequency and intensity. The aim of this study is to present a risk assessment framework of a steel power transmission tower used in a Nordic climate. More specifically, a 22.20 m high guyed portal frame transmission tower used by the Finnish power operator (Fingrid) is analyzed and its risk, expressed in terms of annual probability of failure, is evaluated under the combination of wind and ice accretion. Different versions of the tower are assessed such as: “as-built” tower using conventional steel, deteriorated versions assuming section loss due to aging (e.g., steel corrosion), restored cases of the deteriorated versions by using Fiber-Reinforced Polymer (FRP) plates, and finally rebuilding options of the tower using High Strength Steel (HSS). For all the above versions of the tower, the fragility, which is the probability of failure, under different combinations of wind speed and ice thickness is estimated and corresponding curves (fragility curves) are produced. Then, in order to estimate the risk of the tower, the fragility estimations will be combined with the hazard. The hazard refers to the probability of occurrence (or exceedance) of wind speed and ice thickness combinations that is provided by appropriate probability distributions (i.e., Generalized Extreme Value - GEV). It should be also noted that for specifying the hazard various climate models for past and future periods are used considering possible effects of the climate change. Finally, a comparison of the risk results of all tower types and climate-change scenarios considering also the associated financial costs and environmental impacts (e.g., CO₂ emissions) is made. All in all, the work presented herein constitutes a framework for evaluating the performance of steel transmission towers and possible adaptation options against climate change. Thus, it could be useful as a decision tool for stakeholders, such as power companies or grid operators in evaluating different options and determine their strategy for grid maintenance, uprates or upgrades.