A Coupled Fluid–Thermal–Stress Simulation Model for Sag of Overhead Transmission Conductors Under Wildfire Conditions

Wildfires near overhead transmission line corridors can cause localized conductor heating, thermal elongation, increased sag, and reduced ground clearance. However, traditional sag-calculation formulas and simplified equivalent-temperature methods have difficulty accurately representing wildfire-induced nonuniform temperature rise. To address this limitation, a fluid–thermal–stress multiphysics model was developed for an LGJ 300/40 ACSR conductor. A prescribed flame-temperature field and surrounding airflow were calculated using a CFD model to obtain the conductor’s nonuniform temperature distribution, which was then transferred to a structural finite-element model to determine thermal expansion and sag deformation. The effects of fire-source location were also investigated. The results show that nonuniform temperature rise leads to sag responses significantly different from those predicted using the three-section equivalent-temperature method. When the average conductor temperature reached approximately 130 °C, the maximum sag increased to about three times the cold-state value. Changing the fire-source location resulted in maximum differences of 73.3 °C in average conductor temperature and 37.1% in maximum sag. These quantitative relationships provide a practical reference for assessing conductor-to-ground clearance and evaluating wildfire-induced sag risk of overhead transmission lines.