Response Of Transmission Tower-line System Research Articles

Seismic responses of transmission tower-line system under multi-component ground motions

In this study, shaking table tests, theoretical research, and finite element modeling analysis were conducted on seismic responses of a transmission tower-line system under multi-component ground motions. The rocking component of ground motion was determined from the original seismic record by the wavelet analysis. The shaking table tests for scale models (single tower and tower-line system) that satisfy the similarity ratio of an actual tower-line system, were performed under multiple directions of motion. Dynamic equations under multi-component (horizontal, coupled horizontal, and tilting (CHT), and coupled vertical, horizontal, and tilting (CVHT)) ground motions were first derived in theoretical studies. The finite element model based on the actual transmission tower line system was built, and the response of the system under the identical working condition was calculated. It is found that the rotational component of the ground motion cannot be overlooked and significantly impacts the seismic response of the tower-line system, which is reflected especially as the vertical motion is coupled. The tilting ground motion, the additional second-order effect, and the foundation tilting jointly cause the increase in the response amplitude and significant asymmetric displacement effect. Since this effect of tilting ground motions, the weakening effect of the transmission line to reduce the responses for the displacement and acceleration of the tower-line system is also weakened. It is, therefore, essential to consider the adverse effects of multi-component ground motions on the designing of transmission tower systems in high-intensity areas.

Study on Wind-Induced Response of Transmission Tower-Line System under Downburst Wind

Downburst is the main source of extreme wind speed in non-typhoon areas, which has caused a large amount of transmission line damage all over the world. In order to reveal the wind-induced vibration response characteristics of a transmission tower-line system under downburst, the nonlinear dynamic analysis of a single tower and tower-line system is carried out, and the amplification effect of tower-line coupling and fluctuating wind on the dynamic response is studied. Then, the effects of three wind field parameters closely related to the average wind profile on the wind-induced response of the tower-line system are studied. The results show that under the action of the downburst, the tower-line coupling weakens the dynamic response to a certain extent, and the dynamic amplification factor of a single tower and tower-line system is 1.1 ~ 1.3; for the self-supporting tower, when the height of the peak wind speed is close to the height of tower, the responses of the structure are more unfavorable. When the vector superposition method is used, the storm moving speed (Vt) has little effect on the wind-induced response of the tower-line system. For large-span structures such as tower-line systems, to ensure the safety of the structural design, the value of the characteristic radius (Rc) should not be too small.

A review of the transmission tower-line system performance under typhoon in wind tunnel test

As a regenerated turbulent wind field process, wind tunnel test has proven to be a promising approach for investigating the transmission tower-line system (TTLS) performance in view of experimental scaled models design, simulation techniques of wind field, and wind induced responses subjected to typhoon. However, the challenges still remain in using various wind tunnels to regenerate turbulent wind field with considerable progress having been made in recent years. This review paper provides an overview of the state-of-the-art of the wind tunnel based on active or passive controlled simulation techniques. Specific attention and critical assessment have been given to: (a) the design of experimental scaled models, (b) the simulation techniques of wind field, and (c) the responses of TTLS subjected to typhoon in wind tunnel. This review concludes with the research challenges and recommendations for future research direction.

A Bidirectional Pounding Tuned Mass Damper and Its Application to Transmission Tower-Line Systems under Seismic Excitations

Failures of transmission tower-line systems have frequently occurred during large earthquakes. It is essential to control the excessive vibrations of transmission tower-line systems to ensure their safe operation in such events. This paper numerically investigates the effectiveness of using a novel bidirectional pounding tuned mass damper (BPTMD) to control the seismic responses of transmission tower-line system when subjected to earthquake ground motions. A finite element model of a typical transmission tower-line system with BPTMD is developed using the commercial software ABAQUS, with the accuracy of the results verified against a previous study. The seismic responses of the system with and without BPTMD are calculated. For comparison, the control effect of using the conventional bidirectional tuned mass damper is also calculated and discussed. Finally, a parametric study is performed to investigate the effects of the mass ratio, seismic intensity, gap size and frequency ratio on the seismic response of the system, while optimal design parameters are obtained.

Influence of multi-component ground motions on seismic responses of long-span transmission tower-line system: An experimental study

Seismic performance is particularly important for life-line structures, especially for long-span transmission tower line system subjected to multi-component ground motions. However, the influence of multi-component seismic loads and the coupling effect between supporting towers and transmission lines are not taken into consideration in the current seismic design specifications. In this research, shake table tests are conducted to investigate the performance of long-span transmission towerline system under multi-component seismic excitations. For reproducing the genuine structural responses, the reduced-scale experimental model of the prototype is designed and constructed based on the Buckingham\'s theorem. And three commonly used seismic records are selected as the input ground motions according to the site soil condition of supporting towers. In order to compare the experimental results, the dynamic responses of transmission tower-line system subjected to single-component and two-component ground motions are also studied using shake table tests. Furthermore, an empirical model is proposed to evaluate the acceleration and member stress responses of transmission tower-line system subjected to multi-component ground motions. The results demonstrate that the ground motions with multi-components can amplify the dynamic response of transmission tower-line system, and transmission lines have a significant influence on the structural response and should not be neglected in seismic analysis. The experimental results can provide a reference for the seismic design and analysis of long-span transmission tower-line system subjected to multi-component ground motions.

Dynamic analysis of transmission tower-line system subjected to wind and rain loads

In order to study the dynamic response of transmission tower-line system induced by wind and rain loads, the calculating method of wind and rain loads acting on the transmission conductor is presented. The wind tunnel test, conducted by Kikuchi et al. (2003), is introduced to determine the drag coefficient under both wind and rain excitations, which is a key parameter to estimate the wind and rain loads for the transmission conductor. Then the three-span conductor and tower-line system are modeled to perform the dynamic analysis subjected to wind and rain loads, of which the results demonstrate that the maximum percentage of average displacement induced by the rain loads relative to the wind loads can reach to 22.00%, indicating strongly that the effect of rain load on the response of tower-line system is not negligible. Meanwhile the influence of wind attack angle on the response of tower-line system induced by wind and rain loads is investigated, and the results show that the most unfavorable wind attack angle is 90° and the rain load has no effect on the most unfavorable wind attack angle. The conductors made up of trapezoidal wires are used to examine the effects of wind and rain loads, and therefore some of the models and findings of the present contribution may not always be applicable. All in all, it can be stated that the rain load has an important effect on the response of tower-line system and should be given more attention.

Nonlinear inelastic responses of transmission tower-line system under downburst wind

Electrical transmission tower-line systems transport the needed electrical energy. These systems are spatially distributed and subjected to extreme natural environmental events such as downbursts. The capacity curve of a single tower has been reported under the downbursts but neglecting the turbulent wind component and potential dynamic tower-wire interaction. This study is focused on the assessment of capacity curve of a tower within the tower-line system considering the turbulent winds and the tower-wire interaction. The incremental dynamic analysis and the nonlinear static pushover analysis are employed to estimate the capacity curve. Moreover, comparison of such a capacity curve to that of a single tower is also presented. It was shown that the turbulent winds introduce variability in the capacity curve. The estimated capacity curve by using the nonlinear static pushover analysis is in close agreement to the average capacity curve obtained based on the curves estimated using the incremental dynamic analysis. Most importantly, it is shown that the capacity curve of a single tower represents adequately that of a tower within a tower-line system, and the effect of the dynamic interaction between the tower and the wires on the capacity curve is negligible.

Analysis on Galloping Responses of Transmission Tower-Line System

Nonlinear finite element model of a transmission tower-line system was set up and galloping of iced bundle conductors in the system was numerically simulated by means of ANSYS software. Based on galloping trajectories, vibration frequency, galloping order, conductor tension; unbalanced tension characteristics of iced conductors, it was shown that values of the conductor amplitudes by the tower-line system model are increased by 20% compared to the conductor model. The values of the strain tower unbalanced tensions by the tower-line system model are decreased by 20% and the values of the suspension tower unbalanced tensions by the tower-line system model are decreased by 62.5% compared to the conductor model conductor-insulator mode1. The galloping order is different for different span, due to the impact of the order of galloping. The amplitude of the vertical galloping is increasing while the increasing span, but it is not linear increase.

Analysis on Wind-Induced Vibration Dynamic Responses of Transmission Tower-Line System

Tower-line system of overhead transmission line are sensitive to wind. Therefore, dynamic effect of wind load should be taken into consideration, for instance, wind-induced vibration coefficient. There might be some errors in the calculation of the coefficient in accordance with ‘Load code for the design of building structures’, for its ignoring the irregular figure, scattered masses and coupling effect of tower-line system. Tower-line system is set up in virtual environment, with tower-line coupling considered, and research wind-induced vibration dynamic responses under Davenport wind speed spectrum. Random vibration theory was applied to calculate the coefficient. Whole tower was divided by hight, and calculated segment’s the wind-induced vibration coefficient seprately. Compare the coefficient from Load Code and random vibration theory, the latter with tower-line coupling effect and tower figure considered, is close to the actual.

Research on the Wind-induced Vibration Coefficient of Transmission Tower-line System

The six different non-linear finite element model of the transmission tower-line system which have different spans and different height difference was established by the finite element analysis software, and wind velocity time series with resorting to weighted amplitude wave superposition (WAWS) was simulated. Based on the established models and the simulated wind velocity time series, the wind-induced response of transmission tower-line system in time history was calculated to achieve wind-induced vibration coefficient of transmission towers of various models. By comparative analyzing, span and height difference on the impact of wind-induced vibration coefficient of transmission towers was studied. The results show that the span and height difference have a certain impact on wind-induced vibration coefficient of transmission towers, and the effects on tower top are more obvious than tower bottom. With the increase of span, wind-induced vibration coefficient reduces gradually, but with the increase of height difference, wind-induced vibration coefficient increases gradually.

Response of a transmission tower-line system at a canyon site to spatially varying ground motions

Collapses of transmission towers were often observed in previous large earthquakes such as the Chi-Chi earthquake in Taiwan and Wenchuan earthquake in Sichuan, China. These collapses were partially caused by the pulling forces from the transmission lines generated from out-of-phase responses of the adjacent towers owing to spatially varying earthquake ground motions. In this paper, a 3D finite element model of the transmission tower-line system is established considering the geometric nonlinearity of transmission lines. The nonlinear responses of the structural system at a canyon site are analyzed subjected to spatially varying ground motions. The spatial variations of ground motion associated with the wave passage, coherency loss, and local site effects are given. The spatially varying ground motions are simulated stochastically based on an empirical coherency loss function and a filtered Tajimi-Kanai power spectral density function. The site effect is considered by a transfer function derived from 1D wave propagation theory. Compared with structural responses calculated using the uniform ground motion and delayed excitations, numerical results indicate that seismic responses of transmission towers and power lines are amplified when considering spatially varying ground motions including site effects. Each factor of ground motion spatial variations has a significant effect on the seismic response of the structure, especially for the local site effect. Therefore, neglecting the earthquake ground motion spatial variations may lead to a substantial underestimation of the response of transmission tower-line system during strong earthquakes. Each effect of ground motion spatial variations should be incorporated in seismic analysis of the structural system.

CONTROL OF WIND-INDUCED RESPONSE OF TRANSMISSION TOWER-LINE SYSTEM BY USING MAGNETORHEOLOGICAL DAMPERS

Transmission tower-line system is a high-rise structure with low damping and it is therefore prone to strong wind excitation. In this paper, the control of wind-induced response of transmission tower-line system is carried out by using magnetorheological (MR) dampers. The effects of brace stiffness of damper are introduced and a multi-degree-of-freedom (MDOF) model is developed for both in-plane/out-of-plane vibration of transmission tower-line system. Two semi-active control strategies are proposed for the vibration mitigation of tower-line system. The first one is based on fixed increment of controllable damper force whereas the second one is a clipped-optimal strategy based on fuzzy control principle. The optimal parameters of the MDOF model of transmission line are investigated. A real transmission tower-line system constructed in China is taken as an example to examine the feasibility and reliability of the proposed approach. A parametric study is conducted for the effects of brace stiffness of MR damper, wind loading intensity, and parameters of MR fluids on the control performance. The results demonstrate that the incorporation of MR dampers into the transmission tower-line system can substantially suppress the wind-induced responses of transmission tower if the damper parameters are optimally determined. The performance of the two kinds of semi-active control approaches is better than that of a passive control approach.