The Effect of Conductor Sag on EMF Exposure Assessment for 400 kV Double-Bundle

This study investigates the effect of seasonal conductor sag on electromagnetic field (EMF) exposure to near 400 kV double-bundle overhead transmission lines. The conductor sag study resulted in clearance values of 28.0 m for winter (−10 °C, sag ≈ 7.0 m) and 23.4 m for summer (+35 °C, sag ≈ 11.65 m). For both seasonal examples, the electric field strength and magnetic flux density were calculated at a pedestrian height of 1.5 m, and the image approach to account for ground effects. The winter setup resulted in maximum values of 1.35 kV/m (E) and 27.2 µT (B), while the summer configuration produced higher values of 1.96 kV/m and 38.5 µT, respectively. Autumn field measurements, representing intermediate seasonal circumstances, produced average values of 1.294 kV/m and 1.399 µT, with peaks of 8.39 kV/m and 6.85 µT for electric field and magnetic flux density, respectively. The electric field projections were nearly identical to measurements; however, the magnetic field predictions were significantly higher, most likely due to the model’s assumptions of balanced currents and ideal geometry. These findings suggest that seasonal conductor sag variation is a real and substantial factor in assessing EMF exposure, with the electric field being particularly sensitive to clearance changes. The findings emphasize the need to incorporate a large analysis into EMF compliance assessments, especially in cases where terrain relief between towers may further diminish clearance in mid-span regions.