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- 2014 (3) (entfernen)
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- Englisch (3) (entfernen)
Schlagworte
This paper presents a finite element model of an overhead transmission line using so called cable elements which allow reproducing the cable's nonlinear characteristics accurately employing only a few elements. Aerodynamic damping is considered in the equation of motion by taking into account the relative velocity between the flow of the wind and the moving structure. The wind flow itself is simulated by wave superposition making necessary assumptions on the lateral correlation between the wind velocities along the cable length. As result from the simulation, the following conclusions can be drawn. The first natural frequency of generally used wide spanning cables lies well below 1 Hz where also most of the energy content of the wind excitation is to be expected. Aerodynamic damping is significant for the moving cables holding very low structural damping which leads to a suppression of resonant amplification. This is particularly of interest regarding the support reaction which is dominated by the mean value and the so called background response. The latter is mostly influenced by the randomness of the wind flow, especially lateral to the main wind direction.
Overhead transmission lines are very sensitive structures in regards to wind action. The cables, spanning over a few hundred meters contribute in particular to the overall action on the suspension towers. These slender structures incorporate both structural nonlinearities from the large deformation of the cables and aerodynamic nonlinearities which need to be accounted for when it is to estimate the system response to strong wind events. In this work, a finite element procedure is presented to model an existing power line section using nonlinear cable elements. The wind force is assumed quasi-steady with force coefficients determined in wind tunnel test on a conductor section. Further, aerodynamic damping is incorporated by considering the relative velocity between cable nodes and oncoming wind flow. The results are compared with on-site measurements of the cables support reaction. The results show a significant effect of damping since almost no resonant amplification is visible both in observation and simulation. In addition, wind tunnel tests approved aerodynamic damping to be large for the system of sagging cables, but nonlinear in its nature. It is concluded, that the dynamic response of overhead transmission line cables has to be modeled with care, considering all sources of nonlinearities. That is of particular interest in case of random excitation such as wind because the peak response depends on the probability distribution of the system's response.
Overhead transmission line cables under wind gust loading - measurements and numerical simulations
(2014)
Overhead transmission lines with conductor cables spanning over a few hundred meters are highly
sensitive to the action of wind. Particularly wind acting on the cables signifies a major load on the
suspension towers. In order to identify critical loading parameters and the load-response
mechanism of those structures, measurements are carried out along a high voltage overhead
transmission line capturing the acting wind field as well as the structural response of the cables. A
finite element model of the structure is built and used to simulate the system's response. A method
is presented which allows generating a complete wind field for all the models nodes
incorporating measured wind velocities and estimated parameters of the acting wind. The full
scale measurements of both action and reaction will be compared to the numerical results.