Transmission Tower Research Articles

Comprehensive evaluation system of transmission tower foundation safety

With the expansion of power grid construction scale, the upgrading of transmission current level and the innovation of current transmission technology, we are forced to pay close attention to the safety management of transmission projects, which is very important for social security and development. As an important part of the power grid, the stability and security of the transmission tower are closely related to the safe operation of the whole power grid. Therefore, the construction and maintenance of transmission towers need a set of scientific, quantitative and systematic safety evaluation methods. This paper will sort out the influencing factors that affect the safety of transmission towers, and then introduce a variety of mathematical models and methods to establish a perfect safety evaluation system.

Effect of incident directionality on seismic responses and bearing capacity of OLF1000

As a typical and important supporting structure in ultra-high voltage substations, the 1000 kV outgoing line frame (OLF1000) bears the role of supporting electrical equipment and long-span transmission lines. The interaction between transmission towers, lines and OLF1000 makes it exhibit asymmetric stress and deformation states in normal use. For this kind of irregular coupling system (i.e., OLF1000-tower-line coupling system), the seismic incident directionality effect (SIDE) with high uncertainty may be a disadvantage. To investigate the effect of incident directionality on the seismic responses and ultimate bearing capacity of the OLF1000, and provide a reference for its seismic design, this study numerically evaluated the seismic responses of the OLF1000 by considering the dynamic coupling effect between a tower-line system and OLF1000 (DCE-TLS-OLF1000) under 40 multi-direction ground motions. According to our results, the seismic incident directionality significantly affects seismic responses, participation of vibration modes, plastic development law, failure modes, and ultimate bearing capacity of the OLF1000. In contrast, traditional approaches (i.e., 0° directional excitations) cannot ensure the seismic safety of the OLF1000 in arbitrary incident direction as the guarantee rate is less than 50%. Furthermore, the direction-to-direction (DTD) and record-to-record (RTR) uncertainties were theoretically derived; moreover, 95% guarantee models based on the two uncertainties and prediction models by considering the DCE-TLS-OLF1000 and SIDE were proposed to ensure the seismic safety of the OLF1000 under excitations exhibiting arbitrary incident direction and provide a helpful seismic design method for designers.

Comparative Analysis of Transmission Tower

Comparative Analysis of Transmission Tower

Experimental and numerical study on the aerodynamic characteristics of steel tubular transmission tower bodies under skew winds

A study of the aerodynamic characteristics of circular steel tubular lattice tower bodies in an ultrahigh-voltage direct-current transmission tower under skew winds is presented. The objective of the study, which was based on experimental and numerical methods, was to investigate the aerodynamic coefficients of tower bodies under both yaw and tilt angles. Scaled rigid models of tower bodies with a scale ratio of 1:30 were tested, and the influence of the wind velocity and turbulence intensity on the aerodynamic coefficient was examined. Furthermore, a modified formula for the skewed wind load factor is proposed and compared with different standards. The aerodynamic coefficients of tower bodies with different solidity ratios and tilt angles were obtained via numerical simulation. Additionally, a recommended calculation formula of tilted wind load factor is proposed. The results show that the drag coefficients calculated by standards for different yaw angles were significantly underestimated and that the wind direction corresponding to the predicted maximum drag coefficient was inconsistent with observed wind direction. The formulas proposed in this study accurately describe the characteristics of wind load factor under different yaw and tilt angles. In particular, the influence of the tilt angle on the drag coefficient cannot be ignored.

Integrated model of transmission tower surge impedance and multilayer grounding system based on full-wave approach

In this paper, a full-wave approach based on the method of moment (MoM) is proposed to investigate the harmonic impedance of a tower and its connected ground electrode in the frequency domain. The accuracy of the results is validated in comparison with NEC-4. The proposed numerical method is also employed for the evaluation of a full-sized HVDC tower harmonic impedance. The main contribution is the assessment of the harmonic impedance of a real tower with detailed geometrical information connected to the multi-layer grounding system. The validity of the transmission line method is evaluated through comparison with the results computed using the developed full-wave approach at the high frequency. In addition, the simulation results assure that a real tower’s harmonic impedance could be smaller than the value estimated for very simplified models at the high frequencies. When the full-wave method is applied and the precise model of the ground electrode is considered, the harmonic impedance of the tower in the frequency domain and consequently, the transient impedance in the time domain are different, while the grounding system is assumed to be a perfectly conducting plane. These differences can become very significant, especially close to the resonant frequencies. The harmonic impedance of power transmission towers is strongly influenced by the connected grounding system.

Wind-Resistant Capacity Modeling for Electric Transmission Line Towers Using Kriging Surrogates and Its Application to Structural Fragility

Wind loading on a transmission tower structure is jointly influenced by the wind field, structural parameters, and the geo-spatial configuration of the transmission line. Considering the multi-parametric effect, this paper aims at developing a limit capacity model for transmission towers under strong winds. To this end, the limit capacity of the tower is expressed via two equivalent means: one is the limit wind speed as a function of the wind angle of attack and the span of transmission line; the other is a limit capacity surface with three fundamental wind load components as the principal axes. An adaptive kriging surrogate modeling is constructed to approximate the function/surface with structural uncertainties considered. The performance of the surrogate model is improved by adding support points and then evaluated by the overall accuracy validation and local error check. A numerical example demonstrating the feasibility of the surrogate modeling for the limit capacity of the transmission tower under winds is presented. Finally, a fragility assessment concerning a practical transmission line and towers subjected to typhoons is accomplished using the established limit capacity model of the tower.

Seismic fragility analysis of transmission towers considering effects of soil-structure interaction and depth-varying ground motion inputs

Seismic fragility analysis of transmission towers considering effects of soil-structure interaction and depth-varying ground motion inputs

A novel series-parallel hybrid robot for climbing transmission tower

Purpose The purpose of this paper is to describe the design and development of a novel series-parallel robot, which aims to climb on the transmission tower. Design methodology approach This study introduces a hybrid robot, which consists of adsorption and two 3-degree of freedom (DOF) translation parallel legs connected by a body linkage. The DOF of the legs ensures that the robot can move on the climbing plane, also contribute to a compact design of the robot. An electromagnet is used to adsorb onto the transmission tower, simplifying the overall structure. Based on the robot design, this paper further defines its climbing gait and adopt the 6th B-spline curves for climbing trajectory planning under different working environments. Findings The developed prototype that implements the design of the robot, which was used in simulation and experiments, showing that the robot is capable of climbing in the test environments with the planned climbing gait. Originality value The hybrid robot is able to climb under varying degrees of inclinations and cross the obstacles, and the magnetic attraction can ensure stable climbing.

Studies on the damping mechanism of shape memory alloy-spring tuned vibration absorber attached to a multi-degree-of-freedom structure

To mitigate the adverse structural responses, an improved version of the traditional tuned vibration absorber has been proposed based on the shape memory alloy spring, referred as the shape memory alloy-spring tuned vibration absorber. The finite element numerical models of the multi-degree-of-freedom structure (e.g., transmission tower) and shape memory alloy-spring tuned vibration absorber are developed by using the commercial software ANSYS, and the nonlinear behavior of the shape memory alloy spring is validated based on a previous experimental study. The damping mechanism of the shape memory alloy-spring tuned vibration absorber attached to a multi-degree-of-freedom structure under seismic excitations is investigated, and the nonlinear hysteretic behavior of the shape memory alloy spring is also discussed. The results show that the proposed damper has a two-stage damping mechanism, and its control performance is remarkable. Because the coupled system response is sensitive to the amplitude level, the optimal configuration of the shape memory alloy-spring tuned vibration absorber can be obtained by parametric analysis. Particularly, because of the nonlinear target energy transfer and transient resonance capture mechanism, the shape memory alloy-spring tuned vibration absorber exhibits stable control ability under different seismic waves, indicating a good stability in vibration control of a multi-degree-of-freedom system.

Influence of tower modeling on the assessment of backflashover occurrence on transmission lines due to first negative lightning strokes

This paper assesses the influence of tower modeling on the calculation of voltages across insulator strings, critical currents and percentage of backflashover occurrence for typical 138-, 230- and 500-kV towers. Three different model types are considered: geometric, multistory and multiconductor models. The results are compared to those obtained with the Hybrid Electromagnetic Model (HEM), which is taken as reference. The extended Jordan model belonging to the multiconductor model type is responsible for the results closest to those provided by HEM. The geometric and multistory models also lead to consistent results but with some limitations. The former provides good results for tower-footing impedance above 20 Ω, for the 138-kV tower, and above 40 Ω for the 230- and 500-kV towers. The latter is more appropriate to represent towers with geometry close to the one adopted on the development of its formulation, such as double circuit transmission towers with heights above 60 m.

Evaluation of atmospheric galvanic aluminum corrosion in electrical transmission towers at different sites in the Valparaíso region, Chile. Wire‐on‐Bolt Test (CLIMAT)

AbstractThis study evaluates environmental aggressiveness and atmospheric galvanic corrosivity categories in Chile (Classification of Industrial and Marine ATmospheres test) by installing bolts in electrical transmission towers in the Valparaiso region across four exposure sites: Playa Ancha, San Sebastián, Las Vegas, and San Felipe. Classifications of marine corrosion index (MCI), industrial corrosion index (ICI), and atmospheric corrosion index (ACI) used different galvanic couples: aluminum/steel for MCI, aluminum/copper for ICI, and aluminum/polyethylene for ACI. Corrosion indices varied by season (summer, autumn, winter, and spring), for which couples were exchanged every 3 months. Intraseason variation depended mainly on the meteorochemical variables of the zone, the Cl−/SO2 ratio, and the presence of general and pitting corrosion in the aluminum. The results indicate that, regardless of environmental condition, the aluminum in Al/steel (MCI) and Al/copper (ICI) couples presented a higher corrosion rate than when not forming a galvanic couple (ACI). Moreover, under higher environmental chloride, these differences increase. The Playa Ancha station presented the highest ACI.

Geometric imperfections and ultimate capacity analysis of a steel lattice transmission tower

The effect of geometric imperfections on the decrease of the ultimate capacity of transmission towers has not been sufficiently studied. Despite bucking mode-shaped imperfections are commonly used in deterministic imperfection simulation methods, the current efforts still exist many limitations such as unknown worst buckling mode shape or indeterminate modal combination rules, participation coefficients and truncation order of buckling modes. Herein, a new method named eigenmode assembly method (EAM) is proposed based on linear buckling analysis (LBA). In this method, the first three order local buckling modes of each weak position predicted by LBA are assembled in their sequential order. Two full-scale test towers are employed to implement and validate the proposed approach in this study. The effect of discretized element numbers on the buckling mode shape is firstly discussed, then material and geometric nonlinear analysis is conducted for each case of the EAM-based imperfection assembly process. The results indicate that the EAM can obtain a stable reduction factor for the ultimate capacity of the ideal tower structure which benefited from the advantage of horizontal segment of the capacity curve and can accurately predict the failure positions of transmission towers. Finally, the minimum discretized element number, the minimum introduced buckling mode number and the simplified imperfection assembly formula are recommended by parametric analysis.

Effect of tsunami load induced by earthquake at Manila Trench on transmission tower

The Manila Trench subduction zone is an active convergent plate margin between the South China Sea and northern Philippines. This strongly indicates a high probability for larger earthquakes that could potentially trigger a tsunami in the future and anticipated to affect neighboring countries such as Malaysia which has power plants near the coastal areas. The potential disastrous impact of tsunami waves on a power plant causes loss of lives, damage to assets, and loss of electricity for the coastal communities similar to year 2011 Tohoku tsunami in Japan. Therefore, application of shallow water equation (SWE) in tsunami modelling namely generation and propagation phase and nonlinear shallow water equation (NSWE) for run-up and inundation phase of a tsunami event are pertinent in simulating various scenarios of tsunami. Results from tsunami simulation is used as tsunami lateral load. Linear Static Analysis is then utilized to analyze stability of 275-kV transmission tower.

Research on impulse impedance model and protection optimization of transmission tower grounding device in mountainous area

Research on impulse impedance model and protection optimization of transmission tower grounding device in mountainous area

A Passive Adaptive Suspended Mass Pendulum to Compensate Detuning Due to Large Swing Angle

The suspended mass pendulum (SMP) conventionally used is a type of frequency sensitive vibration control device. It is vulnerable to detuning due to large amplitude oscillations, which can lead to a significant loss in vibration control performance. Although active or semi-active control systems can solve the problem of frequency detuning, the reliability and stability of the sensors and actuators in the control system are difficult to guarantee for large-scale civil structures. To overcome this issue, this study proposes a passive adaptive suspended mass pendulum (PASMP) that uses a curved support. First, the mathematical equations describing the curved support are derived to show that it can keep the frequency of the pendulum constant at large swing angles. Then the kinematic equations of a single-degree-of-freedom (SDOF) structure installed with the PASMP are established. A parametric analysis is conducted to verify how the parameters of the control system, including the excitation period, pendulum length and mass ratio, affect the dynamic responses of the main structure. Furthermore, to verify the effectiveness of the PASMP and the validity of the theoretical analysis, a two-story frame structure is chosen as the model structure in shaking table tests. Also, the proposed PASMP is applied to a transmission tower to numerically verify its effectiveness of vibration suppression under different seismic excitations. The numerical and experimental results demonstrate that the PASMP can more effectively suppress the vibration of structures than the conventionally used SMP.

Structural optimization of transmission towers using a novel Genetic Algorithm approach with a variable length genome

This paper presents an approach to topology, shape, and size optimization of transmission towers. The key feature of the presented approach is the independent variation of the number and heights of tower panels. For that purpose, a modified version of a Genetic Algorithm with a variable length genome is utilized. A novel method of two-stage mutation is developed for handling a variable length genome. Structural optimization of a 110 kV transmission tower is performed as a demonstration with the key result of 10% cost reduction.

Experimental and numerical appraisal of steel joints integrated with single- and double-angles for transmission line towers

The transfer joint is the key structurally functioning part of the transmission tower. The reliability of the transfer joint directly affects the stress and deformation characteristics of the whole tower structure. This paper studies experimentally and numerically the performance of a novel steel transfer joints formed with the integration of single- and double-angles respectively at the upper and lower parts of the connection. Two specimens with different sizes of gusset plates have been designed and tested with tensile loading. Moreover, finite element models have been constructed and validated with experimental findings for a detailed behavior analysis of yielding. The mechanical behavior in terms of stress distribution contours, deformation, yield locations, and failure mode of the gusseted steel joint has been evaluated. Combining observations made from simulation and test results, existing theoretical models for the design of the gusseted plate are discussed and improved. For engineering design convenience, the existing theoretical model is then updated to be experimentally-complying.

Corrosion analysis of guyed rod used for 500 kV transmission tower

As an important part of the guyed device of cable stayed tower, guyed rod plays a key role of preventing transmission tower from tilting and toppling. In this paper, the corroded guyed rod of 500kV transmission tower was investigated by means of macro-morphology inspection, chemical composition analysis, scanning electron micrograph analysis, microstructure analysis and energy spectrum analysis. The result showed that high content of corrosive sulfate in the soil near the leg of transmission tower was the main cause of corrosion of the guyed rod.

Corossion failure analysis on cotter pins used for fittings of 500kV transmission tower

Transmission line is an important part of power system and plays a key role in the process of power transmission and distribution. As the skeleton of the transmission line, the reliability of the transmission tower is an important guarantee for the safe and stable operation of the power grid. In this paper, the corroded cotter pins of fittings used for 500kV transmission tower was investigated by means of macro-morphology inspection, chemical composition analysis, scanning electron micrograph analysis, microstructure analysis and energy spectrum analysis. The result showed that the misuse of material for cotter pins and sulfide discharged from industrial production were the main causes of corrosion of the cotter pins.

Artificial Neural Network Plan for Transmission Tower Structure Safety Assessment

The security of transmission tower structure is the foundation to ensure the safe operation of power grid. The research of fuzzy qualitative assessment method for the structural health of transmission towers is the basic work of large-scale digital power grid engineering. In this paper, artificial neural network (ANN) is used as a generalized tool for structural health assessment of transmission towers. The feasibility of using artificial neural network to qualitatively evaluate the structural health of transmission towers is verified by numerical simulation data. In order to train the artificial neural network, the displacement, stress and other signals generated by the finite element model are calculated and used as the training input of the artificial neural network. The detailed stress results of the finite element model are calculated as the qualitative evaluation basis of the structural health, and the training output of the artificial neural network is generated. By the same method, the test set is generated, and it is found that the artificial neural network is feasible for the fuzzy qualitative assessment of the structural health of transmission tower, and the misstatement rate is less than 5%.