Research Of Wind Loading On500kV Multiple-circuit Transmission Tower

Wind loading is one of dominating loads in the design of multiple-circuit transmission tower. The reasonable determination of the wind loading in order to to ensure a safe, economical and reliable design of the tower is of great significance. The difference between a500kV multiple-circuit tower and a tradiontal tower is significant, which are distinguished in arm length, abrupt changes in mass distribution and tower height. As a result, the wind loading on a multiple-circuit transmission tower is much more complicated which has not yet been covered by the current design Codes.Taking a typical multiple-circuit transmission tower as an example, the dynamic characteristics of the tower was analyzed. The wind-induced resposes of the tower were obtained using aeroelastic model wind tunnel tests. The High-Frequency Force Balace (HFFB) wind tunnel tests of the tower in the uniform flow and the open-type flow were carried out to dertmine the aeroelastic forces and body shape coefficients of each part of the tower. The gust loading factors on tower bodies and arms were calculated based on the wind tunnels test data and the quasi-steady assumption. The body shape coefficients, gust loading factors (GLFs), and distributed coffecients under yawed wind angle were justified and their reasonable values were suggested by compared the results from the tests and calculations with those from the design Codes.Results from this study show that, the cross-wind effect can be mainly contributed to the vortex induced by the wind flows around the latticed components of the tower. The maximum aeroelastic forces of the tower take place at15wind azimuth whereas the minimum values take place at90wind azimuth. Considering the effect of Renault Number, the aeroelastic forces obtained from open-type flow need not to be modified and those from uniform flow should to be modified with a suggestive factor of0.7. The body shape coefficients on0and90wind azimuths obtained from the tests are almost the same as the design Codes. The GLFs on tower body are almost coincided between the tests and the Codes, whereas the GLFs of the arm are quite different where the GLFs of the Codes are much more conservative. At0and90wind azimuths, the cross-wind effect is ignored by the design Codes. However, calculations show that the cross-wind loading reachs10-30percents of along-wind loading, indicating that the ignorance of cross-wind load by the Codes may lead to an unsafe design.