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- ja (7) (entfernen)
Schlagworte
- Overhead transmission lines (3)
- Aerodynamic damping (2)
- Accelerated ageing (1)
- Cable dynamics (1)
- Conductors (1)
- Downburst (1)
- Dynamik (1)
- FEM-Simulation (1)
- Field measurements (1)
- Finite element method (1)
Die Beanspruchung von Freileitungen erfolgt hauptsächlich durch Naturlasten. Dabei spielt für die bemessungsbestimmenden Lastfälle häufig der Wind eine entscheidende Rolle. Die Leiter, die mehrere hundert Meter weit spannen, tragen einen wesentlichen Anteil zur Gesamtbeanspruchung von Tragmasten bei, die wiederum Eigengewicht und Windlasten der Leiter zwischen zwei Abspannmasten abtragen. Wenn die Reaktion der Seile auf Starkwindereignisse abgeschätzt werden soll, müssen sowohl geometrische Nichtlinearitäten durch die großen Verformungen wie auch aerodynamische Nichtlinearitäten berücksichtigt werden. Insbesondere für die Anwendung und Berücksichtigung in Bemessungsvorschriften werden hierfür Vereinfachungen vorgenommen. In diesem Beitrag wird eine umfassende Untersuchung vorgestellt, über Naturmessungen, FEM-Simulationen kombiniert mit Windkanalversuchen und generierten Windzeitreihen. Ziel ist es, existierende Bemessungsvorschriften im Hinblick auf die Abschätzung der Beanspruchung aus Wind auf Leiter zu validieren. Hierbei sind insbesondere die Turbulenzannahmen und das dynamische Verhalten von weitgespannten Leitern wichtig, um die Extremschnittgrößen zu beschreiben. Mithilfe von so genannten Spannweitenfaktoren sollen die relevanten Parameter, wie Spannweite und Windturbulenz, bei der Beanspruchungsabschätzung berücksichtigt werden.
Measurements of downburst wind loading acting on an overhead transmission line in Northern Germany
(2017)
Along an overhead transmission line in Northern Germany, a unique instrumentation of anemometers and force measurements is installed. Details of this test line with wind measurements along a horizontal axis are given. A recent event of a presumable downburst wind event is analyzed by means of available data and precedent works on thunderstorm analysis. The measured response of the conductors at the suspension tower is investigated and compared with time domain simulation of a finite element model.
The paper focuses on a recently launched project of wind measurements along a high voltage overhead transmission line. For reliable information on the actual horizontal distribution of the wind flow, 13 positions along two spans of an overhead electrical line of about 400 m length each are selected for wind measurements. Simultaneously, the structural response is measured at the towers. Preliminary analyses aim at the system identification of long span transmission lines exposed to gusty wind by derivation of a so called joint acceptance function which describes the admittance from wind velocity to the system's response. It can be shown that measured structural response can accurately be described using a statistical model which accounts for the irregularity of the wind as well as the structures behaviour.
Accelerated electrical and mechanical ageing tests of high temperature low sag (HTLS) conductors
(2017)
As part of the Best Paths project, work package 6 of the DEMO #4 combines the R&D tasks for repowering of transmission overhead line corridors. The aim of the presented research work is the electrical and mechanical investigation of high temperature low sag conductors (HTLS) and their respective accessories. In contrast to the conventional ACSR (aluminum conductor steel reinforced) conductors, new material combinations of HTLS technologies result in a better sagging behavior combined with an operation at higher temperatures. Because of missing operational experience, the ageing behavior of HTLS conductor technologies shall be analyzed regarding the operating parameters such as electrical, thermal and mechanical load.
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.
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.
Aerodynamic damping is a decisive parameter influencing the dynamic response of overhead transmission line conductors. Methods of how to account for the effects of aerodynamic damping differ significantly and so might do the results. In this work, the source of aerodynamic damping being the result of the relative velocity between the structure and wind flow will be revised. Based on wind tunnel tests and validated by simulations, the differences of linear movement compared to a pendulum movement of a sagging cable are shown. The reasons for that Deviation are the large deflections, resulting in a movement non-parallel to the acting wind flow. For analysis in frequency domain, it is not possible to incorporate aerodynamic damping implicitly by fluid structure interaction. If the dynamic movement can be linearized at a working point of the mean deflection, a modification to the linear approach is suggested. This approach is validated by simulation with a finite element model of an existing overhead transmission line, calibrated with full scale measurements. Aerodynamic damping is incorporated in time step analysis by Rayleigh damping and modal damping. The differences between both approaches are emphasized and modal damping is shown to be the most adequate.