Failure modelling of overhead lines exposed to worsening gradual and instantaneous weather hazards due to climate change

This paper presents a novel methodology for modelling multi-hazard risks affecting electricity transmission infrastructure. The method is probabilistic, sequential and preserves the statistical relationship between hazard intensities, ensuring modelling is robust. As an exemplar, we consider only OHL conductors, and the methodology is demonstrated for a combination of two hazard types: temperature-accelerated ageing and wind storms. The former is a gradual and cumulative process, while the latter is an acute weather phenomenon that causes highly elevated probabilities of failure for short periods. Both hazards within our example are expected to intensify due to climate change, with more intense heatwaves and more violent storms predicted.

For this stylised example we consider only conductor failures that occur when the maximum instantaneous value of tension, due to the most extreme gusts that are incident on the spans during a storm, exceeds the conductor’s (remaining) tensile strength. The elevated air temperatures associated with heatwaves can lead to extreme conductor temperatures – particularly if there is an increased cooling load during those times, potentially leading to a loss of tensile strength through annealing of the metals. A reduced tensile strength implies an increased probability that it will be exceeded by the maximum instantaneous forces experienced during windstorms.

Both types of extreme weather can also present different types of hazards, e.g. induction of galloping oscillations during windstorms and chemical reactions in the case of extreme heat. However, in this work all such mechanisms other than annealing and wind-friction induced tension are excluded for the sake of clearly demonstrating a novel approach for representing interacting multiple hazards. This exemplar therefore does not produce absolute failure probabilities, but rather demonstrates how these could be produced when all degradation and failure mechanisms are included in the analysis.

A typical 400 kV circuit in the southeast of England was chosen to be modelled, due to anticipation that this region is most susceptible to extreme heatwaves over the next decades.

Multiple IEEE and CIGRE guides, the regional FES workbook [1] and weather time series derived from UK climate projections (UKCP18) [2] were used to model conductor temperatures and the resulting losses in strength. The same climate data was used to generate simulated guststrength time series.