Underpass structure options for 400 kV line crossings in South Africa

In the past ten years, there has been an increasing need in South Africa for 400 kV line design projects to use underpass structures. These structures are essential for crossing beneath existing transmission lines, allowing access to the appropriate substation bay. The primary option available around the substation was the substation gantry. The current substation gantry design in use has a 13 m attachment height limitation and has a 18 kN tension limit per phase. It is normally used with twin bull (38.25 mm) conductor configuration with a 60 m to 80 m span length and a maximum 15° deviation angle to terminal tower. The 18 kN tension limit is not sufficient for the bigger conductor bundles like quad tern (27 mm), triple Bersfort (35.56 mm), quad IEC 560 (30.1 mm) so there was a need for other structure options to be considered for more complex underpass crossings. The 541 series of steel pole underpasses was considered as an option for projects requiring multiple line crossings and underpasses. The design was successfully tested, with conductor attachment heights ranging from 9.8 m to 14 m. However, due to the high loading requirements