Wind variability and its effect on transmission line capacity estimation

Transmission line ampere capacity, i.e. ampacity, can be determined in real time using dynamic thermal rating (DTR). Standard DTR systems rely on weather data averaged over multi-minute windows. While sufficient for most weather parameters, this approach can introduce considerable inaccuracies due to short-term variability of both wind speed and direction. This study investigates the inaccuracies using high-resolution (1-second) wind measurements from an in-service transmission line. We evaluate two commonly used wind-averaging methods and show that variability in wind direction and the relative angle of wind crucially influence the results. In spans with parallel wind, which are often critical spans, i.e. spans that limit the ampacity of the whole line, averaged data commonly underestimates ampacity by more than 10%, with the maximum observed underestimation being over 45%. On the other hand, in perpendicular wind scenarios, averaging may lead to overestimation (by up to 25%), raising operational safety concerns. For transmission system operators, incorporating wind-angle sensitivity and leveraging higher-resolution measurements where feasible can improve ampacity accuracy, enhance grid reliability, and unlock additional transfer capacity - contributing to more efficient and secure energy system operation. • Current wind-averaging practices in dynamic thermal rating pose risk for inaccuracies. • They depend on wind direction variability and relative angle. • Parallel winds cause underestimation; some spans show > 10 % ampacity loss. • Perpendicular winds can lead to overestimation. • Improved wind handling in DTR may boost grid capacity and operational safety.