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- Beitrag zu einem Tagungsband (11) (entfernen)
Schlagworte
- Overhead transmission lines (3)
- Aerodynamic damping (2)
- Accelerated ageing (1)
- Cable dynamics (1)
- Conductor cables (1)
- Field measurements (1)
- HTLS (1)
- High temperature low sag (1)
- High temperature low sag conductors (1)
- In-situ measurements (1)
Im Rahmen eines Forschungsprojekts zur Tragverhaltensstudie von Freileitungsseilen unter Böenbeanspruchung soll durch die Kombination von Naturmessungen, Windkanalversuchen und numerischen Simulationen versucht werden, das mechanische Verhalten von Freileitungsseilen und turbulenter Windbeanspruchung genauer abzubilden. Die Unsicherheiten bei der Modellierung dieses Zufallsprozesses sollen durch Windkanalversuche und Naturmessungen auf ein Minimum reduziert werden. Im vorliegenden Beitrag werden Ergebnisse von Simulationen mit den Beobachtungen aus den Naturmessungen verglichen und bewertet. Ziel des Forschungsvorhabens ist die Bewertung der aktuellen Bemessungsvorschriften für die Berücksichtigung von Wind auf Leiterseile.
The paper focuses on a unique project of wind measurements along a high voltage Overhead transmission line. For reliable information on the 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 velocity measurements. Simultaneously, the structural response is measured at the towers. Preliminary analyses aim at the appraisal of results what is important for the upcoming system identification. It is shown that system identification of long span transmission lines exposed to gusty wind is possible by derivation of a so called joint acceptance function which describes the admittance from wind velocity to the systems response.
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.
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.
Der folgende Beitrag befasst sich mit der analytischen Herleitung eines sog. Spannweitenfaktors zur Berücksichtigung der Korrelation der Windeinwirkung auf weitgespannte Freileitungsseile. Insbesondere zur Abschätzung der Windlast auf Maste trägt dieser Lastfall maßgebend zur Bemessung bei. Mithilfe von Naturmessungen und Simulationen werden zugrunde gelegte Annahmen überprüft und validiert. Die Ergebnisse werden schließlich anhand der einschlägigen Regelwerke verglichen und bewertet.
Aerodynamic damping of nonlinear movement of conductor cables in laminar and turbulent wind flow
(2015)
It is widely accepted that aerodynamic damping is a decisive parameter influencing the dynamic response of overhead transmission line conductors in turbulent wind flow. But anyway, 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 shall be revised leading to the well-known formulation for a linear pendulum being the result of the relative velocity between the structure and wind flow. Based on wind tunnel tests and validated by simulations, the differences 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 some analysis, in particular those in frequency domain, it is practically 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 onsite measurements for wind velocities at lower levels. Further accent is put on the different possibilities to incorporate aerodynamic damping in time step analysis, such as Rayleigh damping or modal damping. The differences between both approaches are emphasized and modal damping is shown to be the most adequate representation of aerodynamic damping.
Investigation on the dynamic behavior of an OHL conductor bundle with light and heavy ice accretion
(2016)
Under a variety of possible cable vibrations which overhead line conductors can suffer, galloping identifies by large amplitudes at rather low frequencies. Changes of the cross-section as by ice-accretion provide the basis for such vibrations through an aerodynamic instability of drag and lift responses under wind excitation. Two different types of light and heavy ice bodies attached to a quad bundle conductor are analysed in wind tunnel tests. The results of aerodynamic drag and lift coefficients are investigated by means of a finite element model under turbulent wind excitation. It was found that instability can be well simulated for the heavy ice accretion but not for the case of lightly iced conductors.
MOSYTRAF - Monitoringsystem zur Tragverhaltensstudie von Freileitungen unter Böenbeanspruchung
(2014)
Im Rahmen des Forschungsvorhabens MOSYTRAF (Monitoringsystem zur Tragverhaltensstudie von Freileitungen unter Böenbeanspruchung)
werden seit Ende 2011 kontinuierlich Windgeschwindigkeiten entlang eines insgesamt 800 m langen Freileitungsabschnitts gemessen. Gleichzeitig wird die resultierende Windkraft aus Wind auf Leiterseile an den Isolatoren erfasst. Dadurch soll der Zusammenhang zwischen Einwirkung und Bauwerksreaktion möglichst zuverlässig ermittelt werden. Dabei ist besonderes Augenmerk auf die kurzzeitigen
Windgeschwindigkeitsspitzen, die Böen gerichtet. Diese erfassen anders als die konstante mittlere Windgeschwindigkeit, nicht die gesamte Länge des Freileitungsabschnitts, sondern nur einen eingeschränkten Bereich. Aus diesem Grund erfolgen die Windmessungen an insgesamt 13 Stellen entlang des Abschnitts und geben ein fein aufgelöstes Bild des Windfeldes. In dem Beitrag werden Messergebnisse beispielhaft präsentiert und einige Plausibilitätskontrollen vorgestellt, da dies einen unerlässlichen Schritt bei Naturmessungen darstellt. Ausgehend von einem Übersichtsdiagramm der bisherigen Messergebnisse wird die Aufgabenstellung und die Zielsetzung der Messkampagne erörtert.
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.
To cope with future requirements, the transfer capacities of distribution systems as well as of transmission systems in Europe need to be increased. Therefore repowering of existing overhead lines with high temperature low sag con-ductors (HTLS) can be one interesting possibility. Because of limited experiences with that technology, current re-search of TU Dresden, the Federal Institute for Materials Research and Testing (BAM) and 50Hertz Transmission GmbH investigates the ageing behaviour of several differ-ent HTLS technologies in a consortium with other Euro-pean partners. In this context, accelerated ageing tests of conductors and its corresponding fittings with combined mechanical and electrical loads are done. To evaluate the changes due to ageing, several mechanical tests of the con-ductors are carried out and the contact behaviour of the fittings is analysed.