Wind Characteristics With Various Topographies And Wind Effects Of Transmission Lines Systems

In recent years,with the continuous construction of China’s UHV transmission line and the optimal allocation of energy structure,the scale of power grid is rapidly expanding.The transmission lines are structures sensitive to wind load,especially to the unsynoptic wind at costal areas and micro-meteorology caused by harsh micro-terrain,which are likely to form wind fields characterized by considerable amplitude of wind velocity and complex turbulence structure.Structures exposed to such wind may suffer wind loads that are far beyond the design level,resulting in the collapse of transmission lines,flashover and other failures,which may be a serious threat to the normal transport of electricity and stable development of the national economy.Therefore,it has important engineering significance and economic value to launch monographic research on wind characteristics with various topographies by sites measurements and atmospheric boundary layer wind tunnel experiment,thus promoting the rationality of wind load calculation parameters and the accuracy of wind effects of transmission lines systems.The research work of this paper mainly includes the following aspects:1.Sites measurement of wind characteristics over open and flat terrain:An intelligent remote distributed monitoring system was constructed and applied to collect the spatially distributed strong winds over the open flat terrain.A nonstationary model was proposed by multivariate empirical mode decomposition to decompose measured wind speed into the deterministic average speed and the zero-mean stationary wind fluctuations.The turbulence intensity was calculated on the basis of this model and was bridged relationship with that of the stationary model.The optimal function describing the probability density distribution of wind fluctuations was discussed.Also,the methods of the longitudinal turbulence length scales for nonstationary wind field were compared and a suitable one was finally given.2.Research on the spatial coherence and the span reduction factor for horizontal wind velocities:The influence of inhomogeneity of wind fields on the wind-induced response of trans-mission lines were studied based on the measured spatially distributed wind records.The relevance between horizontal coherence and different factors,including mean wind speed,distances and attack angles was analyzed;a mathematical model was wherefore constructed to describe the spatial coherence,which was available for separations comparable to the turbulent scales.Based on the finite element method,the influence of horizontal spatial correlation on the wind-induced torsional effect of long cantilever transmission tower was established.The non-stationary model for wind speed was applied to calculate the span reduction factors(SRF).An empirical model for the SRF involved with the amplitude of wind speed and the distances was proposed to measure the inhomogeneity of wind fields.Finally,the model was made comparison with other models specified in the international standards.3.Wind tunnel test of wind characteristics in mountainous topographies:Terrain-induced turbulent characteristics were investigated based on the wind tunnel test of a generic three-dimensional ridge model and a canyon model with inflow conditions similar to wind in flat and open terrain.Through a comprehensive simulation of atmospheric boundary layer in the wind tunnel,the three-dimensional time histories of wind velocity at typical positions were measured,and were verified by numerical simulation.Based on the experimental data,several turbulent characteristics,including amplification factors of standard deviations,power spectral densities and spatial coherence of three-dimensional fluctuating velocities were identified,and made comparison with the turbulent characteristics over the open and flat terrain.4.Evolutionary spectrum of typhoon at coastal China and wind-induced responses spectrum of transmission towers:The evolutionary spectrums of non-stationary random processes were evaluated by Wigner-Ville Method,Short-Time Fourier Transform Method,Wavelet Transform Based Method and a traditional PSD model based method,the advantages and disadvantages of each method were compared.Based on the field measurement data at coastal China,the evolutionary spectra of typhoon Mifa were estimated and the time-frequency characteristics were analyzed.A frequency domain algorithm for the evolutionary spectrum of responses of transmission towers under the non-stationary random wind load were evaluated and made comparisons with that obtained by numerical finite element method to reach finally a better solution for wind induced responses of transmission towers.5.A joint probability density function of wind speed and direction:A bivariate joint probability density distribution model for representing both wind direction and speed was constructed based on the maximum entropy principle.Two cases studies of measured wind velocities and directions over open and flat terrain and the monthly wind data were given to verify the rationality and validity of the joint probability density model.The model was then put into use for the calculation of rate of wind yaw and the reference wind speed,to further demonstrate the practicability of the model.