Transmission Tower Research Articles

The Spectral Approach of Love and Mindlin-Herrmann Theory in the Dynamical Simulations of the Tower-Cable Interactions under the Wind and Rain Loads

The paper presents the transmission line dynamic response considering tower-conductor cable coupling under wind and rain load is presented. The cable and the tower are modeled using the Spectral Element Method. The finite Element Method with different types of elements is used for verification. Excitations, such as wind and rain, are researched in the analysis and the results show the variation of the OTL displacements in each case. The tower modulates the dynamic cable response close to the coupling point and has a high influence in the response of the system. The application of the methodology based on spectral modeling, confirming good feasibility for the overhead transmission line, tower, and cable is the purpose of the study. The new approach of Love and Mindlin-Herrmann theory in the dynamical simulations and tower-cable interactions depending on the distance from the cable connection point is studied. Analysis of the wave number depending on the frequency is also shown.

Experimental and numerical study on the stable bearing capacity of steel tubular cross bracing of a transmission tower

Taking the 1000 kV ultra-high voltage (UHV) steel tube transmission tower as the engineering research subject, the ultimate bearing capacity of the X-cross bracing was experimentally studied. The main tube was manufactured together to add the end constraint on the cross bracing used in the design, with six types of X-cross bracing specimens under two horizontal loading cases to study its ultimate bearing capacity and failure mode in the steel tube transmission tower. Under two loading cases as described, the two inclined tubes of the cross bracing are simultaneously compressed. One is in compression, the other is in tension. The magnitude of the force applied to the tubes remain the same. And then, the results show that the bearing capacities of the common U-joint and C-joint cross bracing specimens are low, especially the bearing capacity of the C-joint with diaphragm is insufficient as the inclined tubes of cross bracing is compressed simultaneously, while the bearing capacities of the intersecting joint and the cross-insert joint are excellent under both cases. Moreover, the corresponding ABAQUS finite element model with imperfection was verified using the test results. As a result, the stress distribution, failure mode and ultimate bearing capacity of the numerical simulation are in good agreement with the experimental results, which shows that results obtained from the subsequent numerical analysis are reasonable. The simplified finite element model is used to analyze the bearing capacity of the intersecting joint cross bracing with the different cross positions and the slenderness ratios under two loading cases. For the calculation according to the Technical Specification for Design of Steel Tube Towers for Overhead Transmission Lines, combined with the calculation results from 60 finite element models, the calculation formula of the slenderness ratio correction factor under two loading cases is elaborated. Compared with the existing formula, the improved formula is closer to the finite element calculation results, which helps reduce material waste during the stage of design.

Two-dimensional full-field displacement reconstruction of lattice towers using data fusion method: Theoretical study and experimental validation

Full-field displacement measurement of lattice tower is very important for assessing its service conditions. However, most of the existing measurement techniques or reconstruction methods only can obtain the point-type displacement or not suitable for lattice tower. To fill this gap, this paper proposes a data fusion method to reconstruct two-dimensional full-field displacement of lattice tower via strain and acceleration. First, lattice tower was simplified to thin-walled variable-section cantilever beam, then full-field displacement is calculated from the strain based on strain decomposition and modal conversion principles, and a novel data fusion algorithm is developed to fuse the strain-derived displacement and acceleration to acquire more accurate results. The effectiveness of the proposed method is verified by the numerical simulation of the transmission tower structure under wind loads, the results show that the full-field displacement can be calculated, and the reconstructed error of the highest point is only 1%. Then the parametric analysis illustrates that the proposed method has excellent performance under the influence of high sampling ratio or strong noise. The field measurements of the full-scale lattice tower are conducted to further verify the feasibility, and the results show that the reconstructed displacement value of the highest point differs from the observation value of the total station by a maximum of 5.4 mm, accounting for only 6% of the measured value.

A machine learning‐based approach for dielectric strength prediction of long air gaps with engineering configurations

It is a long-term goal in external insulation studies to determine the discharge voltages of complicated engineering gaps by simulation methods. Based on the one-to-one correspondence between air gap structure and the static electric field (EF) distribution, this paper characterizes the transmission tower gap configuration by spatial EF features, which were used for machine learning to achieve switching impulse discharge voltage prediction. An interelectrode path and a conical zone between the energized sub-conductor and the crossarm or the tower window were considered as EF regions strongly associated with gap breakdown, where 73 parameters were extracted to construct a feature set. Taking 15 extra-high voltage (EHV) transmission tower gaps as training samples, with different gap distances and tower configurations, their EF features were input to a support vector machine (SVM) for model training to establish the relationships with discharge voltages. The trained SVM model was used to predict the impulse discharge voltages of 20 EHV and ultra-high voltage (UHV) transmission tower gaps. The prediction results with different feature dimensions and various sizes of conical zones were compared to the experimental values, which demonstrate similar variation trends and acceptable errors. This study contributes to realize insulation strength calculation of engineering gaps.

GPR-based prediction and uncertainty quantification for bearing capacity of steel tubular members considering semi-rigid connections in transmission towers

In this paper, the effect of semi-rigid connections on the bearing capacity of steel tubular members in transmission towers is investigated by the numerical analysis based on experimental validation and the metamodel-based prediction method. Especially, for the stability bearing capacity of steel tubular members considering semi-rigid connections (STM-SRC), a prediction method based on the Gaussian process regression (GPR) model is proposed to accurately predict its value and to efficiently quantify its uncertainty. Firstly, on the basis of the development of mechanical model of STM-SRC in transmission towers, the experimental and numerical studies on STM-SRC are conducted. Then, a dataset of 1125 samples generated by the validated finite element model is used to train and test the GPR model, and the accuracy of the proposed method based on the GPR model is evaluated. Finally, based on the proposed prediction method and the Monte Carlo simulation, the uncertainty for the stability bearing capacity of STM-SRC is quantified under the probabilistic framework. The results show that the proposed method has high accuracy in predicting the stability bearing capacity of STM-SRC. Meanwhile, the stability bearing capacity of steel tubular members is enhanced and their reliability exhibits the linear increase after considering semi-rigid connections.

Development of a monitoring system for disassembled towers with internal suspension poles

The traditional construction monitoring methods of suspended pole-mounted decomposed towers are mostly manual monitoring. The monitoring personnel has multiple blind spots, and the possibility of misjudgment based on personal experience is relatively large. It is difficult to ensure the construction safety of the suspended pole decomposing tower. For this reason, combined with the current power Internet of Things technology, this paper develops an intelligent monitoring system for suspended pole-mounted decomposing towers. According to the construction technology and its safety requirements of inner suspension derrick for transmission tower erection in sections, this system is classified into intellisense layer, wireless transport layer and information integration layer. According to the physical characteristics of the seven major risk points of the inner suspension pole group tower, the intellisense layer developed corresponding sensing equipment to obtain risk information. In the wireless transport layer, the ZigBee and 4G communication technologies are selected to interconnect self-constituted LAN and 4G wide area networks, to complete on-site data interaction and long-distance transmission. In the information integration layer, the force of cable, the inclination and height of derrick, and the distance between derrick and tower are determined. The system has been verified by the 500 kV delivery project of Fujian Zhouning Pumped Storage Power Station. The average error of critical monitoring point data is 4.14%, and the average data transmission delays in the far and near fields of the system are 18 ms and 176 ms.

Repair and Protection of Existing Steel-Reinforced Concrete Structures with High-Strength, Textile-Reinforced Mortars

Numerous concrete monuments built in the High Modern Era (turn of the 20th century until the 1970s) must now be repaired for preservation. Traditional concrete repair according to current guidelines involves considerable material removal, changing the appearance of the existing structure. With a combination of the material properties of high-/ultra-high-performance concrete (HPC/UHPC) with its dense microstructure and corrosion-free textile reinforcement (carbon and basalt), a high-performance mortar repair system can be developed. Such a system allows for concrete repairs with minimal material loss by using very thin layers that are durable and do not change the architectural character of the repaired monument. For the investigation of the load-bearing behaviour of a structural repair system using textile-reinforced, high-performance mortar, 20 mm thick slabs were produced and mechanically characterized. In the next step, the proposed repair system was applied to 70 mm thick old concrete slabs. The results show that a high surface tensile strength of 2.9 MPa was obtained. In a further step, the system will be applied to concrete pillars of transmission tower in Berus, adapted in terms of colour and structure and installed for long-term monitoring.

Experimental and numerical study on the ultimate bearing capacity of a K-type tube-gusset plate joint of a steel transmission tower

The ultimate bearing capacity of K-type tube-gusset plate joints was experimentally investigated in the engineering context of ultrahigh voltage (UHV) steel tube transmission towers. Three K-joint specimens were fabricated: ZK30, ZK50 and PK30, where the eccentricity e of the ZK and PK specimens was 0 and D/4, respectively. The branch and main load ratios λ are 29.41% and 50% for ZK30 and ZK50, respectively, and 29.41% for PK30. The experimental results show that increasing λ has a negative effect on the bearing capacity of the main tube. Compared with ZK30, ZK50 has 17% lower main tube axial force and 33% higher branch tube axial force when the specimen was failed. In contrast, the negative eccentricity is beneficial to the bearing capacity of the main tube. Compared with ZK30, PK30 has the same main tube axial force and 6.7% higher branch tube axial force when the specimen was failed. Local buckling occurs in both ZK30 and ZK50, while overall failure occurs in the PK specimen. The finite element model (FEM) in the ABAQUS platform with initial geometric defects was verified by the experimental results. The stress distribution, failure mode and ultimate bearing capacity of the FEM show agreement with the experimental results. The simplified FEM was employed to analyze the bending capacity of K-joints with different diameters of the main tube, different thicknesses of the main tube and different lengths of the gusset plate. The results show that for the K-joints analyzed in this paper, the bending bearing capacity only decreased by 16.41% as the diameter of the main pipe increased by 50.25%, increased by 48.99% as the length of the node plate increased by 37.50%, and increased by 145.33% as the wall of the main pipe increased by 71.43%. The formula for calculating the bending capacity of the K-type tube-gusset plate joint was fitted. Compared with the existing specifications, calculation results with the fitting formula are more similar to those of the FEM.

Seismic responses of a long-span transmission tower and tower-line system

The seismic responses of a long-span transmission tower (LTT) and tower-line system (TL) are presented in the paper. The mode decomposition response spectrum method (MDR) and time domain analysis method (TD) are both employed to obtain the seismic responses. The axial stress of the main member of the tower and TL obtained using these two methods are compared. Results show that the first six vibration frequencies of the tower and TL are quite close. The axial stresses of main members under the TL condition undertake greater values than those under the tower condition. Based on the time analysis method, the axial stresses of the main member under the TL condition are much larger than those under the tower condition, indicating that the mass effect of the transmission line has a similar effect as tuned mass dampers in reducing the seismic response. For the TL, the MDR presents much larger values than those of the TD which may partially contribute to the fact that the coupling effect of the line and the tower cannot be well addressed by the mode decomposition method.

Effect of Stacking Sequence on Long-Term Creep Performance of Pultruded GFRP Composites.

Pultruded glass-fibre reinforced polymer (pGFRP) composites are classified as lightweight material, which exhibit high strength-to-weight ratio for structural usage. This composite material has been applied as cross-arm members in transmission towers due to its ability in thermal and electrical insulation. However, the influence of the stacking sequence of pGFRP composite on its mechanical performance has not been fully covered in the literature to explain the long-term durability of the current cross-arm designs. The study expected to evaluate five fiber layers with various stacking sequences in terms of quasi-static and creep tests in a four-point bending mode. The creep test was performed for 1440 h (60 days). These composites were fabricated using the pultrusion process in the form of a square hollow structure. Later, it was cut into composite coupons with various sizes depending on the test conducted. The results showed that nine layers with 0°/45°/0°/−45°/0°/−45°/0°/45°/0° had the ultimate flexural strength. This stacking sequence configurations seemed to be optimally manufactured in continuous roving fibre by alternating between 0° and ±45° fiber orientations. Additionally, the S-9 pGFRP composite sample showed that it had a low-creep deflection with high elastic and apparent creep moduli in 1440 h. In terms of strength reduction factor, this configuration was recorded as the highest. The findings showed that the nine layers of pGFRP composites with alternation of 0° and ±45° fiber orientations were highly suitable for structural application at transmission towers for a long-term operation.

Power Tower Inspection Simultaneous Localization and Mapping: A Monocular Semantic Positioning Approach for UAV Transmission Tower Inspection.

Realizing autonomous unmanned aerial vehicle (UAV) inspection is of great significance for power line maintenance. This paper introduces a scheme of using the structure of a tower to realize visual geographical positioning of UAV for tower inspection and presents a monocular semantic simultaneous localization and mapping (SLAM) framework termed PTI-SLAM (power tower inspection SLAM) to cope with the challenge of a tower inspection scene. The proposed scheme utilizes prior knowledge of tower component geolocation and regards geographical positioning as the estimation of transformation between SLAM and the geographic coordinates. To accomplish the robust positioning and semi-dense semantic mapping with limited computing power, PTI-SLAM combines the feature-based SLAM method with a fusion-based direct method and conveys a loosely coupled architecture of a semantic task and a SLAM task. The fusion-based direct method is specially designed to overcome the fragility of the direct method against adverse conditions concerning the inspection scene. Experiment results show that PTI-SLAM inherits the robustness advantage of the feature-based method and the semi-dense mapping ability of the direct method and achieves decimeter-level real-time positioning in the airborne system. The experiment concerning geographical positioning indicates more competitive accuracy compared to the previous visual approach and artificial UAV operating, demonstrating the potential of PTI-SLAM.

A New Positioning Method for Climbing Robots Based on 3D Model of Transmission Tower and Visual Sensor.

With the development of robot technology and the extensive application of robots, the research on special robots for some complex working environments has gradually become a hot topic. As a special robot applied to transmission towers, the climbing robot can replace humans to work at high altitudes to complete bolt tightening, detection, and other tasks, which improves the efficiency of transmission tower maintenance and ensures personal safety. However, it is mostly the ability to autonomously locate in the complex environment of the transmission tower that limits the industrial applications of the transmission tower climbing robot. This paper proposes an intelligent positioning method that integrates the three-dimensional information model of transmission tower and visual sensor data, which can assist the robot in climbing and adjusting to the designated working area to guarantee the working accuracy of the climbing robots. The experimental results show that the positioning accuracy of the method is within 1 cm.

Fragility Analysis of Wind-Induced Collapse of a Transmission Tower Considering Corrosion

To investigate the variation law of the wind-resistant performance of transmission towers during their operation, this paper proposes an evaluation method for the wind resistance of the transmission tower considering corrosion, and a 220-kV transmission tower is analyzed as an example. Considering the uncertainty of the material and geometric parameters, the wind-induced collapse of the transmission tower was analyzed, and the collapse wind speeds were obtained via pushover and incremental dynamic analyses. In addition, the sensitivity of the transmission tower to various parameters was analyzed. Based on the existing meteorological and corrosion data, corrosion prediction models were established using a back-propagation (BP) artificial neural network, and the mean relative error between the predicted and measured values of the test samples was 8.91%. On this basis, the corrosion depth of the tower members in the four regions was predicted, and the fragility of the transmission tower was analyzed considering the effects of corrosion and strong winds. The results show that the collapse wind speed of the transmission tower is most significantly affected by the thickness of the angle steel, followed by the elastic modulus and yield strength, and is less affected by the width of the angle steel. When the exposure time was 25 years, the wind-resistant performance of transmission towers in regions with severe acid rain and coastal industrial regions decreased by 10% to 20%. With an increase in exposure time, the failure mode of the transmission tower tended to be brittle failure.

Multi‐hazard typhoon and earthquake collapse fragility models for transmission towers: An active learning reliability approach using gradient boosting classifiers

AbstractNatural hazards such as earthquakes and typhoons pose a considerable threat to the power transmission grid. In regions prone to both hazards, the overhead transmission infrastructure may experience multi‐hazard effects where two consecutive hazards can occur within an interval shorter than the time that would be needed to repair the system for damages occurred in the first event. This consequently increases the susceptibility to damage during the subsequent hazard. In this context, this paper presents the first set of multi‐hazard fragility models for typhoons and earthquakes. The computational cost of numerical simulations for multi‐hazard analyses is high due to the complex nonlinear behavior of transmission towers, numerous sources of material and geometric uncertainty, and the multifaceted effects of multi‐hazard events. To tackle this challenge, we introduce a novel active learning approach for the probabilistic classification of physics‐based collapse data. An initial pool of labeled collapse data is generated by performing a limited number of nonlinear time history analyses on random realizations of a high‐fidelity finite element model of a common double circuit tower. A machine learning‐based extreme gradient boosting (XGBoost) classification model is trained via the query by committee (QBC) for the task of predicting the probability of belonging to the class of collapse (i.e., probability of collapse). Active learning is established by leveraging the disagreement information between the learners and the query points are sequentially labeled and added to the initial pool of collapse/survival data. Using this approach, multi‐hazard typhoon and earthquake collapse fragility surfaces of transmission towers in different directions and sequences of hazards are developed. Results point to the significance of multi‐hazard effects on the fragility of transmission structures. They also reveal the efficacy of the introduced active learning approach in reducing the computational complexity of multi‐hazard fragility assessments. The fragility models developed in this study constitute a key step toward multi‐hazard resilience assessment and optimal management of the power transmission grid.

Wind Tunnel Tests of an Aeroelastic Model of a Long-Span Transmission Tower

The modal analysis of a long-span transmission tower was carried out using a finite element method, and then its aeroelastic model was established by the discrete stiffness method for wind tunnel tests. The displacement and acceleration of the aeroelastic model were measured by a vision-based displacement measuring instrument and accelerometer, respectively. Also, the wind-induced responses of the tower were conducted by finite element calculation, with which the results of the wind tunnel tests are compared. The gust response factor was calculated and compared with those from the specifications and other studies. The results show that the vision-based displacement instrument can record well the vibration of the model tower in the wind tunnel. The acceleration of the tower is dominated by the first-order resonant response, whereas the displacement is dominated by the background response. The displacement and acceleration in the longitudinal and transversal directions are almost equal, indicating that the crosswind and along-wind responses are of the same magnitude. The displacement atop the tower obtained from the test after considering the Reynolds number correction almost coincided with that from the numerical simulation. The gust response factor of the tower obtained via wind tunnel tests is smaller than that of the codes and close to that found via finite element calculations.

Required jacking force for deviation rectification of inclined structures supported with rigid piles

Light poles or transmission towers may become tilted over the design life, which needs rectifying considering safety and continued use. The jacking pushing method is an efficient way to rectify deviations of these inclined structures supported with rigid piles, but there is a lack of relevant engineering standards and research in this aspect. In this study, a numerical method using FLAC3Dis proposed to estimate the required jacking force at the pile top to plumb inclined piles in cohesive soils. Good agreements between the results obtained from the present numerical models and those taken from published experimental and numerical results suggest the reliability of the conclusion. Besides, elaborate parameter analyses including pile geometry, soil properties, and properties of the soil-pile interface are conducted to investigate their influences on the required jacking force. The results can contribute to a safer and more cost-efficient design for rectifying deviations of rigid inclined piles, especially in terms of the required jacking force.

Reliability assessment of guyed transmission towers through active learning metamodeling and progressive collapse simulation

This manuscript presents a novel approach to the reliability of guyed transmission line towers (TLTs) considering complete geometric and material non-linear analyses, bolt slippage effects, and progressive collapse simulation, using active learning Kriging to handle the computational burden. In the existing literature, such issues have been considered separately, with the main focus on self-supporting towers. Herein, novelty arises from the combined consideration of the above and the addressing of guyed TLTs. Yet, because the wind speed variability is much higher than those related to the mechanical model, a modified initial sampling plan strategy is successfully proposed to reduce the computational time required. The application case-study addressing long transmission lines in midwest Brazil is also relevant, considering the recent updating of design wind speeds, with increases of up to 25%. Failure probabilities obtained using code resistance models indicate the need for tower retrofitting. However, the more accurate assessment via collapse simulation shows that the support is still safe, even for the updated wind speeds. Results demonstrate the accuracy and efficiency of the proposed analysis framework and show the importance of using accurate numerical models in retrofit evaluations.

Estimation of first-passage probability under stochastic wind excitations by active-learning-based heteroscedastic Gaussian process

In the processes for designing and assessing structural systems, it is essential to evaluate their reliability against stochastic loads caused by natural or human-made hazards, e.g., wind loads, earthquakes, and collisions. The first-passage probability is a crucial measure of a system's reliability under such conditions. However, the first-passage probability estimation generally requires repetitive dynamic simulations and thus may result in high computational cost. This paper proposes a new active-learning-based surrogate method that efficiently estimates the first-passage probability under stochastic wind excitations to address the computational issue. The proposed method introduces an alternative formulation using the conditional distribution of the maximum response given time-invariant uncertain parameters to handle the high dimensionality of stochastic excitation sequences. The method employs the Gaussian-process-based surrogate model with heteroscedastic noises to fit the distribution parameter functions considering uncertainties arising from the structural system and the environmental loads. In addition, an adaptive training process of surrogates is introduced to identify the best experimental designs achieving efficient convergence. The numerical examples of an eight-story building and a transmission tower demonstrate that the proposed method can produce accurate estimation results with fewer structural simulations than existing methods.

Multi-Sensor Fusion-based Settlement Monitoring Method for Power Transmission Towers

Transmission lines are the main arteries of power systems, which inevitably pass-through geological areas such as coal mining areas, desert areas, soft soil areas, etc. Transmission towers are at risk of tilting and settling. Traditional tower monitoring methods such as GPS/Beidou method and static level have high price, inconvenient installation and risk of external breakage. In this paper, we propose a multi-sensor fusion method for tower settlement monitoring, using ultrasonic distance sensor and tilt sensor fusion to achieve the monitoring of tower settlement, and design a monitoring system and carry out a simulation of settlement experiments, the experimental results show that the average measurement error of the system is 5%, the system has the advantages of good economy, easy installation and good measurement accuracy.

Research on Fault Location Technology of Overhead Line Based on Non-Contact High Sensitivity Distributed Traveling Wave

Aiming at the characteristics of overhead transmission line faults and starting from the research of the fault transient current and features of traveling wave signals of the grounded transmission tower when fault occurs, this paper analyzes non-contact distributed methods of acquiring fault traveling wave signals and then puts forward one. The transient traveling wave signal designed at the earth potential terminal of the transmission line tower allows the quick and accurate acquisition of the fault signal, improving the reliability and accuracy of the fault signal. At the same time, a series of simulation and experimental analysis were carried out. The distributed non-contact fault location method is more flexible than the traditional method and can be used in the field application of overhead transmission lines to improve the fault location accuracy and search efficiency.