Transmission Tower Research Articles

Investigation on Combined Wind Load Factors of Lattice Transmission Tower Body under the Action of Skewed Wind

In the current standards, wind loads on lattice transmission tower (LTT) bodies only account for the action of horizontal winds, which may not be suitable for an LTT under the action of extreme winds. The wind load coefficients of LTT bodies subjected the skewed wind with both horizontal and vertical components were measured via several well-designed wind tunnel tests. The test results and standard calculations of the skewed wind load factors (SWLF) at a wind attack angle of 0° were compared and analyzed. A new parameter—combined wind load factor (CWLF) was introduced, and a suggested formula is proposed for it. The results showed that the standard-recommended formula was unable to accurately reflect the characteristics of SWLF, and its calculated results were significantly smaller than the test results, indicating that the actual wind loads were underestimated. The CWLF could correctly describe how wind load factors changed with the yaw angles or the attack angles. The CWLF effectively improved the calculation accuracy of the SWLF, and the absolute error between the calculations and test results under the critical yaw and attack angles was less than 7%.

Aspects of the Ecology of Urban-Nesting Bald Eagles (Haliaeetus leucocephalus) in South-Coastal British Columbia

Bald Eagle (Haliaeetus leucocephalus) populations throughout North America have increased considerably since the ban of DDT in 1972 and eagles now inhabit suburban areas in large numbers. To better understand the ecology of urban populations living in south-coastal British Columbia, we compared nest-site characteristics, reproductive rates, and diets of more than 150 breeding pairs of rural-, suburban- and urban-nesting eagles in the Greater Vancouver area. Three-quarters of the nests were located within 230 m of buildings and roads, or within 31 m of a potential source of disturbance. Urban eagles nested in live, taller trees that were close to the edges of patches, whereas rural eagles used shorter trees and occasionally human-made structures such as transmission towers. Eagles at nests located close to patch edges and in areas with greater human land use had higher reproductive rates than those at isolated nests or in remote rural habitat. Waterfowl and gulls (family Laridae) were common in the diet across the study area, but urban eagles also used alternative sources such as C-O sole (Pleuronichthys coenosus), Bufflehead (Bucephala albeola), and Band-tailed Pigeon (Patagioenas fasciata). Eagles in the Vancouver area have adapted to human-altered landscapes; management strategies should focus on maintaining edge habitat, monitoring population expansion in urban areas, and protecting nest sites.

A feasibility study on construction methods of high voltage transmission towers’ foundations

Civil engineering projects deal with different risks over their life-cycle. Generally, risk sources are categorized into three types of cost, time, and project quality. The Modified Advanced Programmatic Risk Analysis Model (MAPRAM) is one of the leading approaches in this field that can assess the risks of the project on its whole life cycle. Electricity transmission lines have always been one of the most costly and time-consuming infrastructure projects. The costs of these projects play a significant role in a country's development budget. Given the considerable time and cost of constructing the foundations for power transmission towers, providing an economical design will significantly help in reducing duration and budget of these projects. In this study, using MAPRAM, first, different types of foundations of power transmission lines were studied; then the optimal foundations were introduced for a specific place as a case study, shaping a general framework to appoint the optimal foundation for power transmission lines in different areas. The foundations studied in this study included: pad & chimney foundation, auger foundation, steel grillage foundation, concrete piles, and helical piles. Initially, different types of foundations were designed, and then, the costs of each foundation in a whole life-cycle were estimated. Next, the risks and probability of their occurrence were identified for each type of foundation. Finally, the appropriate foundation was determined for the studied soil samples by performing an optimization process.

Resistance Reduction Scheme for Tower Grounding with Conductive Cement

The construction conditions of transmission lines are becoming more and more difficult. It is necessary to find new ways to reduce the grounding resistance of poles and towers at high soil resistivity and small construction area. Conductive cement samples with graphite, stainless steel fibers, and their mixtures as conductive phases materials were prepared, the resistivity, flexural strength and compressive strength were tested, compared and analyzed. The graphite and stainless steel fiber conductive cement with better comprehensive performance was selected out for tower grounding. The application schemes of conductive cement for tower grounding were designed and compared, the partial wrapping scheme was selected and its application methods under different soil resistivity was analyzed. The analysis results can provide theoretical basis and guidance for the application of conductive cement in transmission tower grounding, the feasibility of scheme is proved by the field application.

Effect of Power Line Type on The Safety of Transmission Tower

The supply of electricity is directly affected by the structural safety of transmission tower. The unsuitable power line type can impose extra forces on transmission tower. The failure within transmission tower results in power outage because the designed power transmission tower cannot bear the extra force loading. In this paper, the mechanical responses in transmission tower with different power line types were calculated by means of finite element software. Commercial software Abaqus was employed for analyzing the structural safety of transmission tower. Ten kinds of power line were chosen to impose static forces on transmission tower. Based on the finite element results, the maximum stress and displacement were obtained. When the dimension of power line is less than a certain value, the transmission tower is safe; otherwise, the transmission tower may collapse.

Research and Application of Light Combined Composite Material Holding Pole

Suspension spanning frame is widely used in the construction of newly constructed overhead transmission lines, and plays an important role in protecting the safety of the objects being crossed. The temporary beam of the suspension cable-type span is installed on the transmission tower, and the impact load in the event of an accident will be transmitted to the transmission tower through the temporary beam.Therefore,the installation of temporary beams will have an important impact on the safety of transmission towers. This paper analyzes the typical installation method of the suspension cable spanning frame on the transmission tower, discusses the dynamic simulation method of the suspension cable spanning frame and the transmission tower under the impact of the conductor, selects a 500kV transmission line crossing project to carry out the wire breakage Analysis of the impact of the lower impact load on the transmission tower. The results show that the wrong installation method will have a significant adverse effect on the safety of the transmission tower. Based on the analysis results, suggestions for the installation of temporary beams were proposed, which provided a reference for the suspension construction of the suspension bridge.

Simulating the Safety of Power Transmission Tower Subjected to Strong Wind Loading

In recent years, with the increase of transmission line height and span, the risks accompanied by transmission towers are significantly increased during the usage of transmission tower. Most of collapsing accidents are caused by strong wind. Therefore, it is necessary to assess the safety of transmission tower. Transmission tower system is a tall building, which is sensitive to the tilt deformation. In order to analyze the mechanical response of transmission tower under strong wind loading, in this paper, the commercial ABAQUS software was employed to create a three-dimensional space model of transmission tower. Firstly, the wind force at different heights of the tower was calculated, and then the wind forces were imposed on each node. By means of finite element method, the deformation of the tower under the strong wind loading was simulated, and its stability was analyzed. Based on the simulated results, the stress field of transmission tower was obtained under strong wind loading. The maximum stress in transmission tower is 189.6 MPa, which is less than the yield strength of steel. The designed transmission power can bear the strong wind of level 10.

Analysis slope stability of transmission tower 150 kV on moderately-cemented-sand due to soil excavation

T.66, transmission tower of 150 kV line Cilegon Baru – Asahimas was in high light for the threaten of slope stability because of soil mine excavation around tower area. Massive Excavation soil were occurring next to tower foundation, which is the depth approximately 14 m (height) and the inclination almost 80°. Therefore, analysis was highly needed to ensure that tower stand on stable spot. The method used in this research were study literature, soil investigation (deep boring and hand boring) and laboratory test for undisturbed samples, geoelectric test, and topography mapping. The type of soil was ‘moderately cemented sand’ slope. It has a complete characteristics and tends more challenging in determine the slope stability. By considering that, the data parameters input were approached in conservative way, which was considering literature and soil investigation data. In this case, slope stability was modeled with Finite Element Method (FEM) by doing back analysis. The result shown that tensile stress was relative small (near 0).

Damage Detection of Transmission Tower Based on Stochastic Subspace and Statistic Model

During the long service period of the transmission tower, the severe environment, material aging and fatigue effects result in the damage accumulation and resistance fading of the transmission tower, which even lead to the structural failure. In this paper, a stochastic subspace-based damage detection algorithm combined with statistical model is proposed for the damage identification of transmission tower structures through processing and analysing its vibration signals. Based on the structural modal parameters identified from the structural vibration response, the nominal modal parameters are defined. Considering that the Hankel matrixes constructed by the system observability matrix and the system output covariance matrix have the same kernel space, the damage index sensitive to the modal parameters is constructed. In the manuscript, firstly, the damage index establishment method and process of the algorithm are presented; and then the vibration data of transmission tower structure simulation under different damage conditions are obtained through numerical simulations; finally, above data are analysed to obtain the damage identification results of transmission tower. The results show that the method proposed in this work can effectively identify the local damage of transmission tower structure.

Finite element analysis of stress and distortion for welding reinforced structure of angular steel used for power tower under load

Based on thermal-elastic-plastic theory, a three-dimensional numerical model of residual stress and distortion in L-shaped welding reinforced structure of angle steel used for power transmission tower is developed. The characteristics of residual stress distribution and deformation are numerically investigated, which are compared with the stress and deformation under the action of lateral compressive load. The research results show that, a large stress is generated in and near the weld zone. With enhancing the weld bead length, both equivalent stress and residual distortion have a growth, and the equivalent stress peak reaches 329Mpa, slightly lower than the yield stress of base metal, meanwhile the longitudinal residual stress peak is 399Mpa, higher than the yield stress of base metal. Under the action of 15000Pa lateral compressive load, the stress has no obvious change in the near weld zone of reinforce structure compared with that without load, and the distortion peak reaches 11mm.

Vibration Control of a High-Rise Slender Structure with a Spring Pendulum Pounding Tuned Mass Damper

High-rise structures are normally tall and slender with a large height-width ratio. Under the strong seismic action, such a structure may experience violent vibrations and large deformation. In this paper, a spring pendulum pounding tuned mass damper (SPPTMD) system is developed to reduce the seismic response of high-rise structures. This SPPTMD system consists of a barrel limiter with the built-in viscoelastic material and a spring pendulum (SP). This novel type of tuned mass damper (TMD) relies on the internal resonance feature of the spring pendulum and the collision between the added mass and barrel limiter to consume the energy of the main structure. Based on the Hertz-damper model, the motion equation of the structure-SPPTMD system is derived. Furthermore, a power transmission tower is selected to evaluate the vibration reduction performance of the SPPTMD system. Numerical results revealed that the SPPTMD system can effectively reduce structural vibrations; the reduction ratio is greater than that of the spring pendulum. Finally, the influence of the key parameters on the vibration control performance is conducted for future applications.

Influence of Additional Bracing Arms as Reinforcement Members in Wooden Timber Cross-Arms on Their Long-Term Creep Responses and Properties

Previously, numerous creep studies on wood materials have been conducted in various coupon-scale tests. None had conducted research on creep properties of full-scale wooden cross-arms under actual environment and working load conditions. Hence, this research established findings on effect of braced arms on the creep behaviors of Virgin Balau (Shorea dipterocarpaceae) wood timber cross-arm in 132 kV latticed tower. In this research, creep properties of the main members of both current and braced wooden cross-arm designs were evaluated under actual working load conditions at 1000 h. The wooden cross-arm was assembled on a custom-made creep test rig at an outdoor area to simulate its long-term mechanical behaviours under actual environment of tropical climate conditions. Further creep numerical analyses were also performed by using Findley and Burger models in order to elaborate the transient creep, elastic and viscoelastic moduli of both wooden cross-arm configurations. The findings display that the reinforcement of braced arms in cross-arm structure significantly reduced its creep strain. The inclusion of bracing system in cross-arm structure enhanced transient creep and stress independent material exponent of the wooden structure. The addition of braced arms also improved elastic and viscoelastic moduli of wooden cross-arm structure. Thus, the outcomes suggested that the installation of bracing system in wooden cross-arm could extend the structure’s service life. Subsequently, this effort would ease maintenance and reduce cost for long-term applications in transmission towers.

Vulnerability of transmission towers under intense wind loads

In this research, the response of high voltage transmission towers under wind load patterns is discussed from the point of view of structural reliability. The paper focuses the attention on the response of two existing tension towers that are part of the 400 kV circuit at the perimeter of Mexico City. Two hundred nonlinear pushover analyses were carried out in detailed models in order to study peak demands in the critical structural elements in tension, compression and in the critical support to establish the vulnerability as a function of the: i) variability of the lateral load pattern and ii) the material overstrength from commercial profiles available in the local market. Based on the results, the global buckling of the elements in the mid-height led to a fragile collapse mechanism, regardless of the applied loading profile. This observation represents a research opportunity in the design practice for the existing towers. The study identifies a dependency between the collapse mechanism and the structure height, which is not currently considered by the specialized codes.

Utilization of Bracing Arms as Additional Reinforcement in Pultruded Glass Fiber-Reinforced Polymer Composite Cross-Arms: Creep Experimental and Numerical Analyses.

The application of pultruded glass fiber-reinforced polymer composites (PGFRPCs) as a replacement for conventional wooden cross-arms in transmission towers is relatively new. Although numerous studies have conducted creep tests on coupon-scale PGFRPC cross-arms, none had performed creep analyses on full-scale PGFRPC cross-arms under actual working load conditions. Thus, this work proposed to study the influence of an additional bracing system on the creep responses of PGFRPC cross-arms in a 132 kV transmission tower. The creep behaviors and responses of the main members in current and braced PGFRPC cross-arm designs were compared and evaluated in a transmission tower under actual working conditions. These PGFRPC cross-arms were subjected to actual working loads mimicking the actual weight of electrical cables and insulators for a duration of 1000 h. The cross-arms were installed on a custom test rig in an open area to simulate the actual environment of tropical climate conditions. Further creep analysis was performed by using Findley and Burger models on the basis of experimental data to link instantaneous and extended (transient and viscoelastic) creep strains. The addition of braced arms to the structure reduced the total strain of a cross-arm’s main member beams and improved elastic and viscous moduli. The addition of bracing arms improved the structural integrity and stiffness of the cross-arm structure. The findings of this study suggested that the use of a bracing system in cross-arm structures could prolong the structures’ service life and subsequently reduce maintenance effort and cost for long-term applications in transmission towers.

The Effect of Nonlinear Behavior of Bolted Connections on Dynamic Analysis of Steel Transmission Towers

Transmission towers are kinds of complex lattice structures which affects their accurate modeling and analysis and brings about some problems in the prediction of their actual behavior. For this reason, full-scale experiments are usually applied for transmission towers to examine their resistance and control their behavior. In this paper, the displacements of a transmission tower in the full-scale test, including effective parameters such as geometric and material nonlinearity and joint slip effect are attained applying the developed nonlinear analysis software. These displacements for four cases of analysis: linear, geometric nonlinear, geometric and material nonlinear and lastly, geometric and material nonlinear along with joint slip effect are obtained and compared with the results of the full-scale test. In this comparison, the results of geometric and material nonlinear analysis along with joint slip effect coincide well with the results of the full-scale experiment which demonstrates the joint slip effect importance and the capability of developed software. Finally, the tower natural frequencies are obtained and it is obvious that taking the joint slip effect into account of the analysis reduces the natural frequencies of the tower as a significant parameter in the dynamic analysis of these kind of structures either individually or as coupled system along with conductors.

Prediction of surf-zone and open-ocean airborne sea-salt spatial distribution via computational fluid dynamics and statistical method

ABSTRACT The atmospheric corrosion of steel is a critical design and maintenance issue for structures such as electric transmission towers and bridges, which are generally widely dispersed. As airborne sea-salt particles are a major corrosion factor, the long-term cumulative spatial distributions of sea salt deposited on the structure surfaces are needed. In this study, we predict the long-term cumulative spatial distribution of sea-salt particles originating from the surf zone and from the open ocean, combining a computational fluid dynamics simulation and a statistical procedure. A new prediction method is introduced for sea-salt particle concentration originating from the surf zone and is validated based on comparisons with observed data. The predicted results indicate that surf-zone-originating particles increase remarkably the amount of airborne sea-salt particles near the coastline and can travel more than 5 km inland.

Symmetry Analysis of Oriental Polygonal Pagodas Using 3D Point Clouds for Cultural Heritage.

Ancient pagodas are usually parts of hot tourist spots in many oriental countries due to their unique historical backgrounds. They are usually polygonal structures comprised by multiple floors, which are separated by eaves. In this paper, we propose a new method to investigate both the rotational and reflectional symmetry of such polygonal pagodas through developing novel geometric models to fit to the 3D point clouds obtained from photogrammetric reconstruction. The geometric model consists of multiple polygonal pyramid/prism models but has a common central axis. The method was verified by four datasets collected by an unmanned aerial vehicle (UAV) and a hand-held digital camera. The results indicate that the models fit accurately to the pagodas’ point clouds. The symmetry was realized by rotating and reflecting the pagodas’ point clouds after a complete leveling of the point cloud was achieved using the estimated central axes. The results show that there are RMSEs of 5.04 cm and 5.20 cm deviated from the perfect (theoretical) rotational and reflectional symmetries, respectively. This concludes that the examined pagodas are highly symmetric, both rotationally and reflectionally. The concept presented in the paper not only work for polygonal pagodas, but it can also be readily transformed and implemented for other applications for other pagoda-like objects such as transmission towers.

Frost Jacking Characteristics of Transmission Tower Pile Foundations with and without Thermosyphons in Permafrost Regions of Qinghai–Tibet Plateau

Frost jacking of electricity transmission tower (ETT) pile foundations in permafrost regions of the Qinghai–Tibet Plateau is becoming increasingly serious. This study investigated the effects of thermosyphons on the frost jacking characteristics of such pile foundations. Field tests of pile foundations with and without thermosyphons were carried out in the Wonkhu–Budongquan section of the Qinghai–Tibet Plateau. A three-dimensional finite-element model was established to analyze the effectiveness of thermosyphons, ground temperature distributions, and jacking displacements and force characteristics of ETT pile foundations. The results showed that the power of thermosyphons decreases yearly within 30 years. The thermosyphons can effectively increase the cold reserves of the permafrost and reduce the soil temperature; the soil temperature around the pile and the depth of thaw is the lowest in the fifth year, and this will increase the top of permafrost by 48 cm in the thirtieth year. Thermosyphons can effectively increase the adfreezing force of the pile side below the active layer and reduce the frost jacking displacement, thus alleviating frost jacking damage to ETT pile foundations.

Analysis of the Synthetic Electric Field of an UHVDC Transmission Tower in a High-Altitude Area

The synthetic electric field of an ultrahigh voltage direct current (UHVDC) transmission tower in a high-altitude area is complex, which makes it difficult to protect the tower operators. Therefore, it is necessary to study the synthetic electric field. Firstly, this study establishes a mathematical model of the ion flow field and determines the solution process. Secondly, the relationship between the synthesis field of the transmission line and the ion mobility, wind speed, and the number of wire splits is analyzed using finite element simulations. Five typical operation positions are then selected for the simulation calculation of the composite field. Finally, the field measurement of the composite field is carried out, and the measurement results are compared with the simulation results. The accuracy of the simulation and theoretical analysis is verified by comparative analysis.

Surge analysis for lightning strike on overhead lines of wind farm

The overhead line in wind farm is vulnerable to lightning strikes at a high risk. The lightning surge would propagate along the line and damage the equipment in substation. In this work, the mathematical models for transmission tower, overhead lines, power transformer and wind farm substation have been developed in the environment of EMTP, especially the wind turbine converter and step up transformer models. The transients in the case of back flashover and shielding failure are analysed. The influences of radial and cross-shaped connections of wind turbine topology on the wave reflection and refraction have been investigated. The performance of surge arrester, not only the protection area but also the absorbed energy under lightning overvoltage is also computed. The wind farm substation is divided into multi zones and the transient response at different nodes is obtained. It indicates that the characteristics and propagation for surge under lightning strike on overhead line are completely different from direct lightning strike on wind turbine receptor. The capacitance between the high and low voltage side of step up transformer plays a key role in system transients. Compared with back flashover, the overvoltage caused by shielding failure is relatively small; the cross-shaped scheme is preferred and would benefit the lightning protection; the absorbed energy of arresters under a high lightning current is a major consideration.