Transmission Tower Research Articles

Evaluation of the Ultimate Collapse Load of a High-Voltage Transmission Tower under Excessive Wind Loads

Several high-voltage transmission towers failed under excessive wind loads in a mountainous and exposed area. This study discusses the efficient and reliable modeling of lattice towers dominantly loaded by wind, a scenario which led to a collapse cascade in a high-voltage transmission line. The ultimate load-bearing capacity had to be estimated and the failure positions identified. Finite Element Analysis was employed through static analyses, Linear Buckling Analyses (LBA) and RIKS analyses (Arc-Length method) in Abaqus 2021. With the purpose of improving the accuracy in the simulation of structural instabilities of complex lattice structures, the model sensitivity to superimposed geometrical imperfections and the joint stiffness of the truss connections were investigated in brace and lattice structure sub-assemblies. Afterwards, linear analyses and non-linear analyses with imperfections were performed on the single tower model. The analysis proved that solely excessive wind can cause such failure on the lattice structures, and the critical structural elements have been correctly identified. The investigation proved that the towers had not been under-designed with respect to the standards valid at the time of erection. However, they were not designed for this exceptional storm event, and evidence was provided that wind alone could bring about the collapse. It is nevertheless not recommended to increase the safety factors in general for the design of such structures, but to base the assumed loading on actual and local wind and service load measurements.

Seismic response study of a steel lattice transmission tower considering the hysteresis characteristics of bolt joint slippage

Ignorance of the influences of bolt slippage effects on transmission towers will lead to the underestimation of the deformations of the transmission towers. Therefore, the responses of transmission towers under different load scenarios cannot be accurately predicted. This will result in an incorrect estimation of the ultimate load-bearing capacity and the failure mode of transmission towers. Recently, studies of the influences of bolt slippage effects on transmission towers have been limited to static analysis only. This paper presents a dynamic response study of transmission towers considering bolt slippage. This paper first presents the test results of the mechanical properties of typical bolt joints in transmission towers under cyclic and monotonic loads. The numerical models of typical joints and the hysteresis curves of each joint under cyclic loads are then proposed, and the numerical models of hysteresis curves are validated through laboratory tests. From the various simulation results on the different types of joints, the hysteretic curves of each joint are obtained, and the skeleton curves are extracted. The numerical models of the slippage effect of transmission tower joints are then integrated into the tower–line system model for seismic analysis. The numerical simulation results indicate that neglecting the dynamic effect of bolt slippage will underestimate the seismic response of transmission towers, which will directly lead to an overestimation of the dynamic resistance capacity of the transmission towers. Furthermore, the higher the earthquake magnitude is, the more serious the influence.

Detection of Bird Nests on Transmission Towers in Aerial Images Based on Improved YOLOv5s

To further improve the accuracy of bird nest model detection on transmission towers in aerial images without significantly increasing the model size and to make detection more suitable for edge-end applications, the lightweight model YOLOv5s is improved in this paper. First, the original backbone network is reconfigured using the OSA (One-Shot Aggregation) module in the VOVNet and the CBAM (Convolution Block Attention Module) is embedded into the feature extraction network, which improves the accuracy of the model for small target recognition. Then, the atrous rates and the number of atrous convolutions of the ASPP (Atrous Spatial Pyramid Pooling) module are reduced to effectively decrease the parameters of the ASPP. The ASPP is then embedded into the feature fusion network to enhance the detection of the targets in complex backgrounds, improving the model accuracy. The experiments show that the mAP (mean-Average Precision) of the fusion-improved YOLOv5s model improves from 91.84% to 95.18%, with only a 27.4% increase in model size. Finally, the improved YOLOv5s model is deployed into the Jeston Xavier NX, resulting in a model that runs well and has a substantial increase in accuracy and a speed of 10.2 FPS, which is only 0.7 FPS slower than the original YOLOv5s model.

Comparison of wind-induced responses of transmission tower in normal wind field and downburst wind field

To study the difference in the wind-induced response of the transmission tower caused by the downburst and the well-conditioned wind field, this paper uses the harmonic superposition method to simulate the well-conditioned wind field and the downburst wind field. The wind-induced responses of the transmission tower under the two wind farms are obtained and compared through the analysis. The wind-induced responses caused by the two wind fields on the transmission tower are quite different, and the downburst can cause a larger wind-induced response.

Capacity Assessment of a Transmission Tower Considering the Wind-Ice Probability Distributions

Extreme weather, such as wind and ice, threatens the safety and stability of transmission networks. In this paper, the joint probability distribution model of wind speed and ice thickness are established, based on which the bearing capacity of a transmission tower under combined wind and ice loads are evaluated. The results show that the developed probability distribution models can well characterize the dependence structure of wind speed and ice thickness, and the safety of the transmission tower under combined wind-ice loads can be guaranteed within its design life.

Analysis of the stability behavior of cross bracings in transmission towers based on experiments and numerical simulations

Angle steel towers are widely used in various transmission lines owing to their convenient connections, easy availability, simple production processes, and high efficiencies. Cross bracings play an important role in resisting wire tension, wind, and snow loads as the main support components ensuring the stability of an angled steel tower. Thus, an analysis of the buckling resistance of cross bracings is significant in improving the bearing capacity of transmission towers. In this study, full-scale tests of equal-leg and unequal-leg angles in planar tower sections were conducted. The influence of the axial force ratio on the stability of a cross bracing was studied based on numerical simulations and compared with the current codes. The results revealed that the failure mode of an equal-leg angle cross bracing was always out-of-plane buckling, whereas the final failure mode of an unequal-leg angle steel cross bracing could be out-of-plane buckling or both out-of-plane and in-plane co-buckling. With an increase in the axial force ratio, the buckling resistance of the cross bracing decreased rapidly, with over 40% decline in the amplitude. The buckling resistance of the unequal-leg angle was approximately 20% higher than that of the equal-leg angle at all axial force ratios. Compared with the current codes for tower structures, we discovered that the code values and finite-element results were considerably different. Notably, the calculation methods of ASCE 10-15 and EN1993-3-1 neglect the variation in the effective length with the axial force ratio. Although DL/T 5154-2012 considers the effect of the axial force ratio, the values are all greater than the finite-element results. The findings of this study can help elucidate the cross bracing stability in angle steel lattice towers.

Research on optimal coil configuration scheme of insulator relay WPT system

This paper presents the optimized structure of the multi-relay coils insulator of WPT system. With the rapid development of the smart grid, on-line monitoring devices in the transmission tower have been widely used. However, the power supply problem has become an important bottleneck in the development of transmission tower intelligent sensing technology. Hence, the multi-relay coils wireless power transfer technology has been proposed to supply for the tower monitoring equipment in this paper. Compared with traditional multi-relay coils, the effects of the number, arrangement position and turns of relay coils on the performance of WPT system are further explored. The simulation results show that the operation performance of WPT can be significantly improved by optimizing the coil arrangement position and turns. Moreover, there are multiple configuration schemes that the design indexes of the system could be achieved. The experiment results show that in the 110 kV high-voltage transmission with the insulator length of 1.015 m, the transmitting power and efficiency of the WPT system could be increased to 1.81 W and 60.11% respectively by parameters optimization, which ensures the continuous and stable work of the monitoring equipment.

Failure evaluation of transmission tower with asymmetrical legs by Scaled–Down pushover experiment

Power transmission towers are essential for the maintenance of daily living activities. Natural disasters such as wind storms, earthquakes, and landslides may damage these towers and cause considerable economic losses. To prevent these losses, transmission towers with asymmetrical legs, which have great flexibility on mountainous terrain, have been considered. Consequently, a scaled-down numerical model was first designed on the basis of a full-scale tower to understand the basic failure behavior of a transmission tower with asymmetrical legs. In addition, an experimental tower model was also conducted by pushover test to observe the failure mechanism and ductility. The failure mechanisms of the model were compared with the numerical simulations obtained from the finite element analysis. To accommodate the effects of asymmetrical legs, the component size should be increased appropriately for body extension. The results have demonstrated the feasibility of implementing transmission towers with asymmetrical legs at unique geographical locations.

Frost heave performance of a foundation at an overhead transmission line in the alpine seasonal frozen regions

The Manzhouli 500 kV electrical transmission line travels more than 218 km through seasonal frozen regions, which result in many freezing soil engineering problems with respect to the transmission tower foundations. Physical model tests of independent reinforced concrete foundations at various temperatures were conducted and verified by numerical simulation to investigate the frost-heaving characteristics of the reinforced concrete foundation in an alpine seasonally frozen region. The evolution of the temperature field, frost-heaving force, and water migration of frozen soil were studied in an open water refill environment with a dead load. The heave force in the foundation soil increases as temperature decreases. The horizontal heave force in the middle and upper parts of the foundation can reach 540 kPa. However, the maximum tangential frost-heaving force becomes 3.83 kN, and the maximum frozen depth of the frozen soil was 240 mm. During the freezing process, the frost heave of the foundation was significantly more noticeable. The correlation between experimental and simulated values is good, and each parameter’s variation error is less than 5 %. Finally, control measures of frost heave were proposed to guide engineering practice based on experimental and numerical studies.

Estimation of dynamic wind forces on a steel lattice tower based on generalized wind force spectra

This article presents a method for estimating dynamic wind forces on a steel lattice tower. The spectra of local wind forces are derived based on generalized wind force spectra, which have considered the coherence between different axial wind forces under the skewed wind. With the established cross-power spectral density (PSD) matrix of wind forces, the fluctuating wind forces can be simulated in the time domain using the harmony superposition method. The wind tunnel experiments on a typical transmission steel lattice tower are introduced. Using the test data, the coherence of wind forces on different body axes is analyzed, and the corresponding empirical function is fitted. With the empirical PSDs of the generalized forces obtained in the previous wind tunnel experiments, the dynamic wind forces on the transmission tower are simulated in target wind environments. The dynamic responses of the tower are calculated under the estimated wind forces and compared with the measurements in the aeroelastic wind tunnel experiments. Results reveal that the proposed approach to estimating distributed dynamic wind forces on a steel lattice tower performs effectively.

Application of convolutional neural networks based on Bayesian optimization to landslide susceptibility mapping of transmission tower foundation

The stability of tower foundation slopes is an important factor to maintain the operation of a power system. However, it is time-consuming and expensive to evaluate tower foundation slopes one by one due to the large area. The aim of this study is to investigate the performance of CNNs with different architectures and training options for transmission tower foundation landslide spatial prediction (LSP) by Bayesian optimization. Accordingly, fourteen influencing factors related to landslide evaluated by gain ratio technique are considered and 424 historical landslide locations in Luoding and Xinyi Counties (Guangdong Province, China) are randomly divided into 80% for training and 20% for testing the CNNs. The CNN performances are investigated by permutating and combining different numbers of convolutional layers, pooling layers and learning rate strategy. In 59 Bayesian optimized cases, three conclusions are drawn: (a) the CNNs yielded the best result with 3 convolution layers, (b) the CNN without a pooling layer performs best, and (c) a piece-wise decay learning rate strategy yields better performance. Meanwhile, the excellent performance of the CNN obtained by Bayesian optimization (CNNB) has also been validated by comparisons with gravitational search optimization algorithm and other landslide spatial models, which indicates that CNNB can be applied to generate the susceptibility maps for locating transmission tower foundations in high landslide susceptibility zones and reducing the impact of landslides on power supply by taking measures in advance.

Experimental Study on Vortex-Induced Vibration of Steel Tubes in Transmission Towers at Various Inflow Conditions

With the extensive construction of ultra-high voltage (UHV) transmission lines, the fatigue damage of steel tube members caused by vortex-induced vibration (VIV) in tubular towers has received growing attention. Although some progress has been made in the research of the VIV of steel tubes in uniform flow, there is still relatively scarce research on the VIV of steel tubes at various inflow conditions. In this paper, a series of wind tunnel tests are conducted to investigate the VIV of the steel tube subjected to uniform, turbulent, and oblique flows. Three turbulence intensities (Iu = 5.9%, 9.7%, and 12.6%), and four yaw angles (α = 10°, 20°, 30°, and 40°) are considered. The results show that the VIV response of the steel tube in the in-line (IL) direction is negligible compared to that in the cross-flow (CF) direction. The displacement amplitude gradually decreases as the turbulence intensity increases, accompanied by a more unstable response. For the inclined steel tube, the VIV maximum amplitude almost remains constant when α ≤ 20°, while it sharply decreased in the case of α = 30° and α = 40°. Furthermore, it was found that the so-called independent principle is applicable for α ≤ 10°.

Analytical Investigation of the Effects of Secondary Structural Members on the Structural Behaviors of Transmission Towers

High-voltage transmission towers consist of structures that are designed to avoid the risk of electric shock and prevent the risk of collapse. Hence, for efficiency, they are generally designed as high-rise towers. The main tower posts are the primary structural members that resist loads under various load conditions. Therefore, the contribution of the secondary members to securing the stiffness and strength of the main posts by reducing the effective buckling length is an important one. However, we lack detailed secondary member design criteria. In this study, we observed the structural effects of the horizontal members and braces on the torsional stiffness, elastic buckling strength, and load-carrying capacity of a transmission tower using various structural analysis methods, including linear elastic, eigenvalue, and geometric nonlinear and inelastic analyses, under governing load combinations. According to the analytical results, it is the brace spacing rather than the horizontal members that substantially affects the structural performance. Therefore, we can minimize the number of horizontal members if we erect sufficient brace members. If the brace spacing is wide, then the horizontal members should be erected to create K bracing, thereby enhancing the buckling resistance of the main posts.

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.

Dynamic simulation analysis and experimental verification of transmission tower climbing robot

In order to replace the climbing work of the first climbers of the transmission tower without safety ropes, a transmission tower climbing robot is designed in this paper. First of all, this paper designs the structure of the robot by imitating the silkworm crawling on the branches through the principle of bionics. On this basis, through the inverse kinetics solution method, under the premise of planning the gait of the robot first, the dynamic simulation analysis of the robot is carried out according to the gait, so as to obtain the torque required for each joint motion. At the same time, according to the simulation results, the experimental test of the robot is carried out. Experiments have shown that the robot can climb to the top of a 50 m high transmission tower in 70 min with a load of 10 kg. The research results show that the transmission tower robot can replace the manual climbing operation of the transmission tower, and the mechanization and intelligence of the high-altitude operation of the transmission tower is highly feasible.

Improving power transmission tower state recognition in remote sensing images using cooperative Adaboost-MobileNet

ABSTRACT Tower state recognition is of great importance in smart electric power management. Most previous efforts were devoted on the guyed towers and tower structures or materials to monitor the structural stability of towers through sensors fixed on them. Actually, identifying their states as a whole is also needed for remote management. This study addresses the task of tower state recognition in high-resolution remote-sensing images under the framework of deep learning. To achieve this goal, a new remote-sensing image dataset is constructed. Technically then, an ensemble learning strategy is developed to classify the states of the transmission towers. Specifically, MobileNetV3 is taken as the weak classifier as it is simple yet parameter-light in the family of convolutional networks. Along the line of ensemble learning with the principal of Adaboost in machine learning, an Adaboost-style network paradigm, named as Adaboost-MobileNetV3 in this paper, is finally proposed to recognize the states of towers. To evaluate its effectiveness, a series of deep convolutional networks are compared with the proposed network. The extensive comparative experiments indicate that the proposed Adaboost-MobileNetV3 network is suitable for practical tower state recognition, which achieves about 90% accuracy with at least about 4% higher than these compared models.

Logic motion algorithm and design of flexible limb of gecko-imitating robot

The tower climbing robot is supposed to climb up and down smoothly along the power transmission tower skeleton and stay firmly at the desired position, and install the safety cable at the appropriate position of the tower end, providing the basic life safety guarantee for the operator’s in climbing and operating for the maintenance of the tower connection of the high-voltage transmission line. Because of the non-uniform arrangement of the handles along the angular steel of the skeleton, the most critical problem to be solved in the climbing process is to find and eliminate pseudo targets and reliably grasp the real targets and move forward reliably. In this paper, we proposed and designed a set of searching and pseudo target elimination algorithms for robot flexible limbs with the chassis and intelligent control. The grasping climbing state sequence sets of robot flexible limbs were defined and constructed in Euclidean n-dimensional space with a real number, and a complete cycle map of the flexible limb behaviors was drawn. By using the norm sequence set of the distances between the centers of two adjacent handles on the same side of the skeleton, the machine vision and the specific W-type sensor layout, the pseudo target and real target can be discriminated effectively, so that the robot’s grasping and climbing can be established on a reliable mathematical basis. Flexible limbs consist of a built-in motor, screw expansion mechanism, flexible palm-fingers, and W type of sensor layout region. In the process of crawling, the screw mechanism makes macroscopically the limb approach the handle, meanwhile the palm-fingers justify microscopically to the center of the handle by the pressure-uniform algorithm, ensuring that the robot climbs, discriminates the pseudo target, and stays at any position of the skeleton. Simulation study and case analysis show that the proposed flexible limb and climbing-removing pseudo-target algorithm are of correctness, reliability, and practice.

Finite Element Analysis of K-node of Curved Arm of Transmission Tower

The stress on the key nodes of transmission towers is complex, which plays a vital role in the stress and stability of the whole structure of transmission towers. Due to the larger negative head of the link and the larger connecting plate at the K node of the curved arm of the transmission tower, the actual stress of some components is quite different from the theoretical calculation results. At the same time, the load value of the smaller part is not clear when the included Angle of the stressed material at the K node is less than 25°.In this paper, the difference between the stress of the bar at the K node of the curved arm and the ideal model is studied, and the stress status of the position with small Angle is analyzed, and the reasons for the difference and the suggested value of the position with small Angle are analyzed.

Research on Improving Denoising Performance of ROI Computer Vision Method for Transmission Tower Displacement Identification

The health monitoring technology of transmission towers based on vibration data had become a research hotspot. At present, vibration data mainly relied on sensors installed on the tower, which was time-consuming and laborious. Nevertheless, the ROI computer vision method could achieve long-distance, multi-point, and non-contact monitoring, which offers a new possibility for the structure-safety identification of power transmission towers. However, transmission towers are generally located in the field environment, and the background is complicated, resulting in the ROI key point method for vibration data acquisition encountering various types of noise. Thus, the key point in practice was clearing the noise and reducing the impact of noise on identification accuracy. The subpixel corner method was used to detect a minor error with the research object of pixel sets. The dilation + erosion method could reduce image noise. Under white noise with a variance of 0.05, the dilation + erosion could reduce average error (Emae) and mean square error (Emse) by 27% and 23% and increase percentages of data with absolute error less than 5 mm and 10 mm in the total number of data (σ5 and σ10) by 8% and 4.3%, respectively, which was compared to median filter + sharpen. The histogram equalization method was used to balance background lighting conditions and reduce identification errors from non-uniform illumination. Emae and Emse were reduced by 92% and 99%, and σ5 and σ10 were increased by 5 and 3 times, respectively, and the identification time was cut by 62% with the histogram equalization method. Under white noise with a variance of 0.15 or lower, the three methods combined increased the numerical stability of Emae, Emse, σ5, and σ10, which indicated that the combination of the three methods could improve the anti-noise performance, robustness, and identification accuracy of the ROI computer vision method for transmission tower displacement identification.

Eiffel Effect on Towers of UHV AC Transmission Lines

The principle of Eiffel Effect on transmission towers was analyzed, and the necessity of considering Eiffel Effect on transmission towers, especially multi-loop transmission towers, was proposed. A comparative analysis on calculation methods for Eiffel Effect on tower mast structures both at home and abroad was conducted and the applicability of various calculation methods to transmission towers and their advantages/disadvantages are proposed. On this basis, the analysis method for Eiffel Effect on transmission towers is proposed. The Eiffel Effect was calculated by taking four tower types of EHV/UHV AC multi-circuit transmission lines on the same tower as examples, during which the stress state of member bar of each tower type after considering the Eiffel Effect, the influence of the intersection angle between the main members of the tower on the Eiffel Effect, and the minimum bearing capacity requirement of diagonal members etc. were analyzed. The analysis shows that: It is simple, reasonable and convenient to consider the Eiffel Effect on the tower with the rigidity-reduction method for engineering application; both the diagonal member and the diaphragm member of the tower are influenced by Eiffel Effect, where its influence on the latter is higher; it may be unsafe if designing the minimum bearing capacity requirement for the diagonal member with the internal force not less than 5% of the main members to satisfy the Eiffel Effect on the tower for the UHV transmission towers, and especially for the transmission towers with EHV/UHV AC multi-circuit transmission lines on the same tower.