Thermal Impact Assessment on Power Transmission Capacity and Grid Reliability

Abstract

Rising ambient temperatures and intensifying heatwaves, driven by climate change, exert significant thermal stresses on power transmission systems by simultaneously increasing electricity demand for cooling and degrading the thermal performance of overhead conductors, transformers, and associated infrastructure. Higher temperatures elevate conductor resistance, accelerate joule heating, and reduce convective and radiative cooling margins, leading to elevated conductor core temperatures, increased sag, and mandatory derating of line ampacity to maintain safe ground clearances and prevent annealing or mechanical failure. Empirical studies indicate that heatwaves can reduce effective transmission capacity by 1.9–5.8% on average by mid-century under various RCP scenarios, with regional variations (e.g., larger impacts in inland areas like MISO). Concurrent demand surges of 30–50% or more tighten reserve margins, while increased line losses (resistance rises ~0.4% per °C for aluminum) and accelerated aging of transformers further compromise reliability. Data from China show heatwaves increase outage frequency by 3.9–4.0% and duration by 7.9–8.3%, with each additional degree of temperature rise contributing ~0.1% more outages and each extra heatwave day adding ~0.5%. This paper provides a comprehensive thermal impact assessment, detailing physical mechanisms, quantitative effects on ampacity and losses, implications for grid reliability metrics.