The line rating given to power transmission lines is determined by calculating a conductor temperature that should not be exceeded. The conductor temperature is affected by the current flowing through the line, the material of the conductor, and the local environmental factors such as ambient air temperature, insolation, and wind speed and direction. At present, utilities typically base line ratings on seasonal extreme values of the environmental variables. Dynamic line ratings (DLR) based upon the weather forecasts of air temperature, insolation, and wind speed and direction could help utilities to take advantage of the additional ampacity present in power transmission lines without exceeding safety margins.
This presentation looks at the potential gains in ampacity that could be realized by using DLR based on short-term forecasts from the High-Resolution Rapid Refresh (HRRR). First, HRRR forecasts are compared to weather station observations from along a power line in Idaho. Margins of safety are then calculated using the forecast-to-observation differences. Next, a DLR transmission line ampacity is calculated using the HRRR forecasts plus the safety margin. Finally, the DLR ampacity is compared to the seasonally set values to determine the additional ampacity that could have been realized by using short-term HRRR forecasts. It is shown that HRRR forecasts can lead to 5-8% capacity improvements over seasonal line ratings while accounting for a safety margin.