A Review of Dynamic Thermal Line Rating Methods With Forecasting

Power flow, on both AC and DC overhead transmission lines, is limited to keep the conductor temperature below a maximum (TC <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">MAX</sub> ) specified to limit both conductor sag and the aging of conductors and splices over time. This power flow limit (line thermal rating) varies with weather conditions along the line corridor but, for simplicity, static line ratings (SLR) are normally calculated for “suitably conservative” annual or seasonal weather conditions. Dynamic line ratings (DLR) change with the real-time weather conditions along the line, are usually higher than SLR, and are more complex to use in system operation. Forecasting of DLR requires forecasting of line corridor weather conditions but makes DLR more useful to power system operations. This paper discusses DLR methods including forecast techniques and presents various field applications.