Wind tunnel test on global drag coefficients of multi-bundled conductors

• Wind tunnel test on global drag coefficients of multi-bundled conductors was carried out.
• Global drag coefficients decrease significantly with the increase of the bundle number and diameter of a single conductor.
• Global drag coefficients vary greatly in different wind attack angles.
• Global drag coefficients of 8-bundled conductor are much lower than the recommended value in the current design codes.

Multi-bundled conductors of large cross-section are becoming popular due to the increasing application of 1000 kV ultra-high voltage (UHV) transmission lines. However, the aerodynamic characteristics of these conductors have not been investigated systematically, especially the global drag coefficient which is of a vital importance to determine the equivalent static wind load on the conductors. Therefore, a series of wind tunnel experiments were carried out to measure the global drag coefficients of multi-bundled conductors with the conductor diameter, bundle number, wind turbulence intensity and wind attack angles varied. Necessary measures were taken to ensure the accuracy of the test results. The results show that the global drag coefficients vary significantly with the wind attack angles and they decrease with the increase of the conductor diameter and bundle number. In any attack angle, the global drag coefficients of multi-bundled conductors are much smaller than those of a single conductor in the same wind velocity. The biggest global drag coefficients corresponding to different conditions investigated in this study are less than those recommended in the design codes worldwide. This suggests that the global drag coefficient of multi-bundled conductors specified in the current codes can probably be reduced by taking proper consideration of the shielding effect. This will lead to economic benefit in the construction of the UHV transmission lines.