Wind Tunnel Study on Precise Drag Coefficients of UHVDC Transmission Towers

In order to study the wind drag coefficients on main rods and whole structure of an angle-steel transmission tower, high frequency force balance test was carried out to obtain drag force coefficients of main rods of the cross arm and tower body under various wind azimuths. Interference of surrounding rods on drag force was considered during the test. Meanwhile, drag force coefficients of a single plane and whole parts of the tower body and cross-arm were tested under different wind azimuths, respectively, and the corresponding shielding factors were also analyzed. In addition, the obtained experimental results were compared with the current national code provisions. The study showed that drag force coefficients of a main rod were significantly influenced by its location. Most rods of the cross arm and tower body had maximum drag force coefficients larger than 1.3 as recommended by Load Code for the Design of Building structures (GB 50009-2012). Wind loads acting on the upper and lower surfaces of the cross arm contributed a lot to overall wind loads on the cross arm, however. Technical Code for the Design of Tower and Pole Structures of Overhead Transmission Line (DL/T 5154-2012) only considered those on the windward and leeward surfaces of the cross arm, resulting in underestimation of overall wind drag force. The drag force coefficients of a single plane and whole parts of the tower-body were close to those given by the foreign codes, but slightly larger than those in Chinese codes. The tested shielding factors of leeward sides of the cross arm and tower body were 0.73 and 0.62, respectively. Comparing the test results with different code recommended values indicated that the shielding factors in Chinese codes were more conservative.