Tower-line System Research Articles

Probabilistic capacity assessment of single circuit transmission tower-line system subjected to strong winds

The safety and resilience of physical infrastructure of the power systems, including the transmission towers and lines for high-voltage transmission as well as the poles and wires for power distribution at a lower voltage level, is critical to avoid and recover from power outages under the extreme weather related loads such as strong winds from hurricanes, tornados, downbursts or isolated thunderstorms. In the current engineering practices, single circuit lattice steel towers linked by transmission lines are widely used to form power transmission systems. Failure of either a structural component (local failures, such as buckling of a local member or breakage of a single wire) or the entire structure (global failures, such as instability of the entire tower) could propagate to their adjacent structural members or systems (such as neighboring towers or lines). Therefore, there is a strong need to identify the root cause of the failure of the transmission tower-line system and identify the weakest link under various extreme weather scenarios. This study is to develop a probabilistic assessment approach for a typical transmission tower-line system subjected to strong wind loadings under synoptic winds (atmospheric boundary layer wind). Due to the complicated structural details and complex wind-structure interactions, wind tunnel experiments were carried out to obtain the static wind load coefficients for different panels of the transmission towers as well as for the transmission lines. Incremental dynamic analysis (IDA) is carried out to obtain the capacity curve for the transmission tower-line system. Uncertainties from the meteorological parameters are also considered in the analysis. The probabilities of failure for the two predefined limit state functions are obtained considering the meteorological uncertainties. Meanwhile, the probabilities of failure at different return periods are presented for a transmission tower-line system subjected to strong winds in a coastal region. Finally, the effects of the aerodynamic damping for the transmission lines on the dynamic responses of the tower-line system are discussed, as well.

Beam-end stiffness identification for a structural health monitoring-oriented finite-element transmission tower model using effective optimization techniques

As an important issue for establishing structural health monitoring–oriented finite element models for large steel pylons, identification of beam-end stiffness draws the attention of the engineering circle. Since the methods adopted by other researchers for parameter identification are impracticable, a beam-end stiffness identification method which combines in situ measurements for the structure’s global dynamic properties with effective multi-variable optimization methods is utilized to improve the accuracy of established finite element models. A 131-m-high large transmission tower is employed as a case study to validate the method. In situ measurements for the tower’s global dynamic characteristics are performed, and identifications of Young’s modulus for 20 semi-rigid connections distributed along each of the tower’s four main chords are undertaken utilizing three multi-variable optimization methods, that is, the first-order method, the subproblem approximation method, and the response surface method. Static numerical simulations on two detailed connection models prove that multiple uncertain parameters can be correctly and simultaneously identified when appropriate optimization techniques are chosen. Finally, the influence of beam-end stiffness identification on the structural health monitoring–oriented structural safety assessment is revealed by calculating the wind-induced dynamic structural responses for the single tower and the transmission tower-line system, which indicates that identification of the correct beam-end stiffness and updating the structural health monitoring–oriented finite element model are indispensable procedures for reliable structural health monitoring.

Study on Mechanical Properties of Steel on Transmission Tower under Icing Load

In order to determine the failure mode of high-voltage transmission tower materials under the condition of ice-coating load in an actual line. The Qidian-Luoping 500kV wine glass type transmission tower is selected as the prototype, and the one tower with two lines model of the whole beam unit is established by using the ANSYS finite element software. The loading mode is static load considering icing load and wind load. The most unfavorable wind direction of the transmission tower is obtained by comparing and analyzing the maximum displacement and the stress of the rod under different directions of wind load in the transmission tower. Then the failure mode of transmission tower is studied by the variable ice thickness of the tower line system. The results show that the direction parallel to the cross arm is the most unfavorable direction in the transmission tower. And under the most unfavorable wind direction, with the increase of ice thickness, it is found that the tower head part is more sensitive to icing load than the tower body part. When the thickness of ice coating reaches 30mm, the weak load-bearing rod will appear locally in the transmission tower and the position of the rod is mainly distributed on the outer upper crank arm, the outer side of the ground bracket and the upper side of cross arm of the transmission tower.

Wind-induced collapse analysis of long-span transmission tower–line system considering the member buckling effect

The collapse problem of transmission tower upon strong winds was well noted in past few years. This article analyses the wind-induced collapse problem of a long-span transmission tower–line system. The member buckling effect was particularly considered. In doing so, a three-dimensional finite element model of the long-span transmission tower–line system was established in ABAQUS based on a practical project. The transmission tower and line were simulated by the frame and truss elements, respectively. The nonlinear behavior of a compressive member was simulated using the Marshall model, and the nonconvergence of numerical calculation was set to be the collapse criterion. The critical wind speed, damage position, and collapse probability were obtained from a collapse analysis of the long-span transmission tower–line system under different wind attack angles. The collapse mechanism of the long-span transmission tower–line system under a wind attack angle of 45° was investigated, and an incremental dynamic analysis was performed to evaluate the collapse-resistant capacity of the transmission tower. The study reveals that the interaction between bending moment and shear deformation is critical to the collapse of transmission tower.

Dynamic Behavior of Transmission Tower-Line Systems Subjected to Insulator Breakage

Ice loads attached to a transmission tower-line system can not only increase the vertical loads on the insulators, but also cause flashover to occur more easily. Both effects can lead to an increased probability of insulator breakage. In this paper, a finite-element model of a transmission tower-line system with three towers and four span lines under the ice loads is established. Dynamic analyses of the tower-line system after insulator breakage are performed to study the dynamic responses of the system and its failure process. In addition, a parametric analysis is conducted to investigate the influence of span length and insulator length on the vibration of the system and the failure mode. The results show that a larger ice load can lead to more severe vibration of the tower-line system due to the insulator breakage. Moreover, as the span length increases, the insulator breakage can result in more serious consequences and even the cascading collapse of the transmission tower-line system. This study provides crucial reference for preventing the failure of transmission tower-line systems in heavy ice regions.

Wind-induced vibration of UHV transmission tower line system: Wind tunnel test on aero-elastic model

A wind tunnel test on the aero-elastic model of UHV transmission tower line system was carried out for researching tower line system's dynamic behavior under different wind speeds. The effect of wires' vibration on tower was particularly addressed in the paper. For comparison, the single tower model and tower line system model were involved. Both alongwind and crosswind responses of tower were investigated. The wire's dynamic strain was traced synchronously for exploring the coupling vibration effect of tower line system. Comparing the responses of the single tower model and the tower line model, it is found that 70–90% displacement and strain are induced by wires. This action is more prominent in the alongwind direction. However, the peak response values of the tower line model are smaller than those of the single tower model. Test results in frequency domain indicate that the dynamic behavior of the tower becomes more susceptible to wind speed when it connects with wires. As to the tower line system, the response power spectra of the tower and the conductors show the tendency of moving to lower and higher frequency region respectively with the crests weakened and vibration energy dispersed when wind speed increases.

Collapse simulations of a long span transmission tower-line system subjected to near-fault ground motions

Observations from past strong earthquakes revealed that near-fault ground motions could lead to the failure, or even collapse of electricity transmission towers which are vital components of an overhead electric power delivery system. For assessing the performance and robustness, a high-fidelity three-dimension finite element model of a long span transmission tower-line system is established with the consideration of geometric nonlinearity and material nonlinearity. In the numerical model, the Tian-Ma-Qu material model is utilized to capture the nonlinear behaviours of structural members, and the cumulative damage D is defined as an index to identify the failure of members. Consequently, incremental dynamic analyses (IDAs) are conducted to study the collapse fragility, damage positions, collapse margin ratio (CMR) and dynamic robustness of the transmission towers by using twenty near-fault ground motions selected from PEER. Based on the bending and shear deformation of structures, the collapse mechanism of electricity transmission towers subjected to Chi-Chi earthquake is investigated. This research can serve as a reference for the performance of large span transmission tower line system subjected to near-fault ground motions.

Stability and Dynamic Analyses of Transmission Tower-Line Systems Subjected to Conductor Breaking

Ice loads exerted on the transmission line can increase the probability of conductor breaking, which will lead to the stability failure of transmission towers. In this paper, a transmission tower-line system is established for two towers and three span lines. Then the nonlinear static stability analysis and nonlinear dynamic stability analysis induced by the conductor breaking are carried out to obtain the load versus displacement curves, while studying the failure modes of the transmission tower-line system. Moreover, the ice load and initial eccentricity are considered in the numerical simulation. In addition, a parametric analysis is performed to investigate the influence of span, insulator length and initial tension force on the stability failure of the system. The results show that the dynamic instability will occur earlier than the static instability due to the dynamic impact effect and conductor breaking with ice loads can lead to the progressive collapse of the transmission tower-line system. Finally, the span length has the greatest effect on the response of transmission tower caused by conductor breaking.

Reliability of Tower and Tower-Line Systems under Spatiotemporally Varying Wind or Earthquake Loads

AbstractTowers or tower-line systems within a power network can experience damages under rare earthquakes or strong winds. The estimation of the failure probability of a tower-line system is rarely...

Effects of bolt slippage on the wind induced responses of transmission tower line system

The wind induced responses of transmission tower line system are studied by finite element method. Firstly, a slip model considering eccentricity and bolt joint slippage in diagonal bracings, tower legs and tower head is built by ANSYS. The slip model has a more accurate result compared with conventional models. Secondly, the finite element models of tower line systems are established and the wind speed time histories are simulated using MATLAB. Finally, the wind induced responses of different tower line systems are studied. The results of a single tower and the tower line systems are compared to study the effects of tower-line coupling effects and bolt slippage on wind induced responses of transmission tower line systems.

Progressive collapse analysis of long-span transmission tower-line system under multi-component seismic excitations

Research on progressive collapse has a practical significance for long-span transmission tower-line system. Considering material damage effect, the Tian–Ma–Qu model is used to capture the nonlinear...

Effects of Bolt Slip on the Dynamic Characteristics of Transmission Tower-line System

Effects of Bolt Slip on the Dynamic Characteristics of Transmission Tower-line System

Wind-Induced Coupling Vibration Effects of High-Voltage Transmission Tower-Line Systems

A three-dimensional finite element model of a 500 kV high-voltage transmission tower-line coupling system is built using ANSYS software and verified with field-measured data. The dynamic responses of the tower-line system under different wind speeds and directions are analyzed and compared with the design code. The results indicate that wind speed plays an important role in the tower-line coupling effect. Under the low wind speed, the coupling effect is less obvious and can be neglected. With increased wind speed, the coupling effect on the responses of the tower gradually becomes prominent, possibly resulting in the risk of premature failure of the tower-line system. The designs based on the quasi-static method stipulated in the current design code are unsafe because of the ignorance of the adverse impacts of coupling vibration on the transmission towers. In practical engineering, when the quasi-static method is still used in design, the results for the design wind speed should be multiplied by the corresponding tower-line coupling effect amplifying coefficient δ.

Parameter Analysis on Wind-Induced Vibration of UHV Cross-Rope Suspension Tower-Line

This paper analyzes the influences of important structural design parameters on the wind-induced response of cross-rope suspension tower-line. A finite element model of cross-rope suspension tower-line system is established, and the dynamic time-history analysis with harmonic wave superposition method is conducted. The two important structural design parameters such as initial guy pretension and sag-span ratio of suspension-rope are studied, as well as their influences on the three wind-induced vibration responses such as tensile force on guys, the reaction force on mast supports, and the along-wind displacement of the mast top; the results show that the value of sag-span ratio of suspension-rope should not be less than 1/9 and the value of guy pretension should be less than 30% of its design bearing capacity. On this occasion, the tension in guys and compression in masts would be maintained in smaller values, which can lead to a much more reasonable structure.

Response control of a large transmission tower-line system under seismic excitations using friction dampers

The transmission tower-line system is widely used in electric infrastructures across the world and generally possesses a small stiffness and low structural damping. The excessive vibration of a transmission tower-line system subjected to seismic excitations may induce a structural damage or failure. To avoid the excessive vibration under strong earthquakes, a large transmission tower-line system requires some measures to abate their dynamic responses. Friction damper is a solution to realize the response control of a transmission tower-line system. In this regard, the response mitigation and performance assessment on a transmission tower-line system with friction dampers under strong earthquakes are actively carried out in this study. The analytical model of a transmission line is proposed based on Hamilton’s variational statement of dynamics and Lagrange’s formulation. A two-dimensional lumped mass model of a transmission tower is developed for the dynamic analysis by simplifying the three-dimensional finite element model. The mechanical model of a friction damper is established by considering the effect of damper axial stiffness. The equations of motion and dynamic analytical method of a transmission tower-line system without/with friction dampers subjected to seismic excitations are proposed. In addition, the approach for assessing energy responses of a transmission tower-line system without/with friction dampers subjected to seismic excitations is also developed. A real transmission tower-line system is taken as an example to examine the feasibility of the proposed control approach. The parametric study is conducted to investigate the effects of damper control force, damper stiffness, earthquake intensity, and damper location. The made observations demonstrate that the implementation of friction dampers in a transmission tower-line system can substantially suppress the seismic responses with optimal damper parameters.

Influence of spatial variation of ground motions on dynamic responses of supporting towers of overhead electricity transmission systems: An experimental study

An overhead electricity transmission system typically consists of a series of steel lattice towers supporting transmission lines (referred to herein as the tower-line system). Recent major earthquakes suggest that the tower-line system constructed based upon existing knowledge can be vulnerable. A tower-line system typically extends over a large region and it may be subjected to spatially varying ground motions during an earthquake event. The influence of spatial variation of ground motions is not explicitly considered in current design of the system and very limited research (particularly, experimental research) has been completed in this regard. A two-phase experimental program was conducted using an array of three shake tables to quantitatively assess the respective impact of three factors causing non-uniform excitations (namely, the wave passage effect, the ground motion coherency loss effect, and the local site effect) on dynamic response of the supporting towers. Test results show that neglecting the wave passage effect may result in underestimates of peak dynamic responses of the towers. Additionally, it is found that non-uniform ground motions with a higher degree of coherency loss tend to amplify tower dynamic responses. Furthermore, test results reveal that when the soil at the bases of adjacent towers becomes more flexible, the resulting spatially varying ground motions cause larger tower dynamic responses.

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.

Progressive Collapse of Power Transmission Tower-Line System Under Extremely Strong Earthquake Excitations

The simulation of progressive collapse of a power transmission tower-line system subjected to extremely strong earthquakes is studied in this paper. A three-dimensional finite element model is established for the coupled system that combines three towers and four span lines based on a practical project. The birth to death technique is adopted to simulate the progressive collapse of the system by using the user subroutine VUMAT in ABAQUS. The simulation of progressive collapse of the transmission tower-line system under either single-component or multi-component earthquake excitations is conducted. The collapse path, fracture position and collapse resistant capacity of the transmission tower are investigated. The result shows that the effect of multi-component seismic excitations should be taken into account in simulation of progressive collapse of the transmission tower, since the behavior of towers under multi-component excitations is different from that of single-component excitations. In addition, incremental dynamic analysis (IDA) is carried out to verify the results obtained herein. The present result should prove useful to the seismic design of power transmission towers.

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.

Wind-induced Response Suppression of Transmission Tower-Line System Using a Robust and Semi-active Controller

Wind-induced Response Suppression of Transmission Tower-Line System Using a Robust and Semi-active Controller