Assessing Ampacity Performance Through Dynamic Line Rating: A Comparison of IEEE Std 738 and CIGRÉ TB 601

Abstract

Overhead transmission lines (TLs) are typically rated using static methods that assume conservative environmental conditions, such as high ambient temperatures and low wind speeds. These conservative ratings often result in underutilization of the line’s full ampacity, as extreme conditions occur only intermittently. Dynamic line rating (DLR) addresses this issue by utilizing real-time weather and grid load data to dynamically calculate the available ampacity, considering favorable environmental conditions. The DLR continuously updates ampacity calculations, allowing operators to access unused capacity when conditions are more favorable. This approach improves transmission efficiency and enhances grid reliability, ensuring a more adaptive and resilient power system. By integrating real-time weather data, DLR provides a more accurate representation of a TL’s actual capacity than static ratings. Both IEEE and CIGRÉ standards employ the heat balance equation to calculate ampacity, accounting for heat absorption and dissipation. This paper compares the methodologies outlined in IEEE Std 738 and CIGRÉ TB 601, focusing on their approaches to calculating conductor temperature and ampacity. The study examines the impact of different modeling approaches on ampacity calculations and the performance of TLs. The analysis shows significant differences between the two methods. In summer, the IEEE method increases ampacity by 47.2% compared to static line rating (SLR), while the CIGRÉ method increases it by 46.5%. In winter, the IEEE method shows a 36.9% increase, and CIGRÉ shows a 38.6% increase. These results demonstrate the potential of DLR to optimize transmission capacity and improve grid performance by adapting to real-time environmental conditions. Seasonal variations further highlight how factors like temperature and wind speed impact ampacity, reinforcing the value of DLR systems for maximizing TL efficiency year-round.

Cite this article as: Z. Zia and C. F. Kumru, "Assessing ampacity performance through dynamic line rating: A comparison of IEEE std 738 and CIGRÉ TB 601," Electrica, 2025, 25, 0109, doi: 10.5152/electrica.2025.25109.