Transmission Tower Research Articles

Anti-Wind Experiments and Damage Prediction of Transmission Tower under Typhoon Conditions in Coastal Areas

Typhoons are a serious threat to transmission towers and lines in coastal areas. The anti-wind performance of a transmission tower needs to be reinforced and optimized to avoid tower collapse. Here, an improved real-time wind-field mathematical model and a tower-line coupled simulation model were established to reproduce the wind field distribution, mechanical vibration, and interaction between the wind field and tower. The damage prediction of the transmission tower was analyzed. Furthermore, an actual scaled tower-line model was built, which was used to measure the acceleration and displacement responses in the anti-wind experiments. The research results show that the improved model is feasible and correct based on the verification of Typhoon Mujigae. The tower’s vibration response is mainly characterized by low frequencies, whereas the lines indicate a high frequency response. The transmission line has a remarkable impact on tower vibrations in high turbulence. A flow direction angle of 50° and a long span are dangerous conditions for transmission systems in coastal regions. The acceleration and displacement responses of the main bars show opposite trends to that of the auxiliary cross-bars. The contribution of this article is the possibility of tower collapse prediction and prevention.

High-Dimensional Reliability Analysis with Error-Guided Active-Learning Probabilistic Support Vector Machine: Application to Wind-Reliability Analysis of Transmission Towers

Adaptive reliability analysis methods based on surrogate models, especially kriging, have been successfully implemented in many problems. However, the application of kriging is limited to low-dimensional problems with noncategorical performance data. Support vector machine (SVM), by contrast, addresses these limitations, but its application in reliability analysis faces several challenges with regard to robustness, accuracy, and efficiency. This study proposed a new adaptive approach based on probabilistic support vector machine for reliability analysis (PSVM-RA). Different from existing methods that only select training points in the margin of the SVM, the proposed method adopts a new learning function that considers the wrong classification probability for each realization and maximizes the potential for new information offered by a candidate sample for the training set. Moreover, the upper bound of the error that is introduced by the SVM in estimating the failure probability is derived based on a Poisson binomial distribution model considering the likelihood of wrong classification for all the points in the margin of the SVM. This upper bound of error was used in the proposed framework as a stopping criterion to guarantee the desired accuracy. Three numerical examples and an engineering application regarding the wind-reliability analysis of transmission towers were investigated to demonstrate the performance of the proposed method. It was demonstrated that PSVM-RA can provide robust estimates of failure probability when other state-of-the-art methods fail. Moreover, it offers a balance between efficiency and accuracy.

Investigation on the Critical Wind Speed of Instability Failure of UHV Transmission Tower-line Coupling System under Typhoon

Wind is one of the most destructive external loads of transmission lines, and typhoon-caused severe damage or even destruction of electric power facilities occurred frequently. In order to research the critical wind speed of instability failure of UHV transmission tower-line coupling system under typhoon, the UHV transmission line in Zhejiang is chosen as the research subject and a finite element model of the UHV tower-line coupling system is established. By using the improved generalized force calculation method, the dynamic response of the transmission tower is converted to the static response. Then the LRC method is used to calculate the equivalent static wind load of the tower and obtains the wind response of the UHV transmission tower-line coupling system. The results show that under the typhoon wind field, the component at the junction of the tower head and the body first reaches the supercritical state. Specifically, when the wind speed at 10-meters height reaches 31m/s, the profile component of the tower head will be damaged. With the increase of wind speed, the damaged area of the tower head also expends. When the wind speed at 10-meters height reaches 37m/s, the main load-bearing component of the tower head-body junction will lose its stability, which will directly threaten the safety of the transmission tower.

Cyclone preparedness strategies for regional power transmission systems in data-scarce coastal regions of India

As frequency and intensity of tropical cyclones, and degree of urbanization increase, a systematic strengthening of power transmission networks in the coastal regions becomes imperative. An effective strategy for the same can be to strengthen select transmission towers, which requires consideration of network at a holistic scale and its orientation relative to coastline, towers' fragilities, and cyclones' properties. Since necessary information is often missing, actionable frameworks for the prioritization remain elusive. Based on publicly available data, a representative fragility curve for the towers in the state of Odisha, India was developed. The state has a 485 km long coastline, and is subjected to cyclones routinely. The power transmission network in the state serves over 40 million people. Performance of the network under cyclones was quantified in terms of population affected. The performance was found to depend significantly on landfall location, and path traversed prior to landfall. The results highlighted the importance of performing such studies at a regional scale. Further, efficacies of strategic interventions in the network were evaluated. These interventions (72 considered herein) differ from each other in selection of a geographical region, basis for prioritizing the towers, number of towers to strengthen and extent of strengthening. Strategies that consider rather simplistic properties of the network and its orientation with respect to the coastline work much better than those based purely on the network's properties, in spite of minor variations in towers' fragilities. This integrated approach opens avenues for actionable engineering and policy interventions in resource-constrained and data-deprived settings.

Performance Analysis of Full Assembly Glass Fiber-Reinforced Polymer Composite Cross-Arm in Transmission Tower.

The usage of glass fiber reinforced polymer (GFRP) composite cross-arms in transmission towers is relatively new compared to wood timber cross-arms. In this case, many research works conducted experiments on composite cross-arms, either in coupon or full-scale size. However, none performed finite element (FE) analyses on full-scale composite cross-arms under actual working load and broken wire conditions. Thus, this work evaluates the performance of glass fiber reinforced polymer (GFRP) composite cross-arm tubes in 275 kV transmission towers using FE analysis. In this study, the performance analysis was run mimicking actual normal and broken wire conditions with five and three times more than working loads (WL). The full-scale assembly load test experiment outcomes were used to validate the FE analysis. Furthermore, the mechanical properties values of the GFRP composite were incorporated in simulation analysis based on the previous experimental work on coupons samples of GFRP tubes. Additionally, parametric studies were performed to determine the ultimate applied load and factor of safety for both normal and broken wire loading conditions. This research discovered that the GFRP composite cross-arm could withstand the applied load of five times and three times working load (WL) for normal and broken wire conditions, respectively. In addition, the factor of safety of tubes was 1.08 and 1.1 for normal and broken wire conditions, respectively, which can be considered safe to use. Hence, the composite cross-arms can sustain load two times more than the design requirement, which is two times the working load for normal conditions. In future studies, it is recommended to analyze the fatigue properties of the composite due to wind loading, which may induce failure in long-term service.

Nonlinear damage identification method of transmission tower structure based on general expression for linear and nonlinear autoregressive model and Itakura distance

Fatigue cracks and bolt looseness are two kinds of common nonlinear damage in a transmission tower structure. However, due to the complexity of the transmission tower structure, it is difficult to identify the nonlinear damage accurately by using traditional damage identification methods. To solve this problem effectively, a time domain damage identification method based on general expression for linear and nonlinear autoregressive model (GNAR model) and Itakura distance is proposed. To describe the stochastic characteristics of time series more concisely and accurately, the optimized structure of GNAR model was selected by the stochastic pruning algorithm based on greedy strategy. And Itakura distance was used as a damage indicator for nonlinear damage identification. The nonlinear damage experiment of three-story frame model in Los Alamos laboratory was used to verify the effectiveness of the proposed method, and this method was applied to the nonlinear damage identification experiment of a transmission tower steel frame model. In the transmission tower model experiment, two kinds of nonlinear damage types are considered: component breathing cracks and joint bolt loosening. The results show that the proposed nonlinear damage identification method can easily identify the nonlinear damage of the frame model and the transmission tower model effectively. The change of floor mass barely has effects on the damage identification results. The damage probability of the damaged stories calculated by the proposed method is significantly higher than that of the undamaged stories, so that it is helpful to find the location of the nonlinear damage source efficiently. And the proposed method is a damage identification method based on sub-structure story, which can identify the transmission tower model with two nonlinear damage sources at the same time.

Study on the influence of restraint stiffness of main material on the compression stability bearing capacity of cross-bracing in transmission tower

Abstract In order to study the influence of restraint stiffness of main material on the compression stability bearing capacity of cross-bracing in transmission tower, in this paper, the load of cross-bracing under eccentric compression in transmission tower is simulated. The load test of 45 Q355 equilateral angle steel cross-bracing specimens with typical sections is completed, and an effective ANSYS finite element model is established for analysis. The effects of the restraint stiffness of main materials, slenderness ratio, material strength and the number of connecting bolts on the bearing capacity of cross-bracing are discussed, and the relevant laws are obtained, which provides a reference for engineering application.

Potential of Flax Fiber Reinforced Biopolymer Composites for Cross-Arm Application in Transmission Tower: A Review

Potential of Flax Fiber Reinforced Biopolymer Composites for Cross-Arm Application in Transmission Tower: A Review

Transmission Tower Earthing Design for Lightning Condition in Malaysia’s Power Grid

The transmission tower earthing design is installed under the ground to protect nearby personnel and equipment, as well as to improve the line lightning performance. The previous tower earthing design in Malaysia’s grid system was tailored for normal power frequency fault, which are low-frequency in nature. This tower earthing design was not suitable during lightning fault, which is of higher frequency. The previous earthing design practice involves installing radial counterpoises up to 120 meters horizontally from each tower legs to get the tower footing resistance (TFR) reading of 10 Ω or less. This practice is proven to be ineffective in lowering the resistance at higher frequency i.e. lightning strike. This paper discusses a new compact earthing design that has low impedance value at low and high-frequency. The performance of this new earthing design were simulated at various soil resistivity values over a frequency range, and were compared to the performance of previous tower earthing design. The new earthing design were also installed on a number 500kV, 275kV and 132kV towers and their TFR were measured using both low and high-frequency TFR meters. The proposed concentrated earthing design was shown to have low impedance value at both low and high-frequency domain.

Egyptian Vulture Nesting on Power Transmission Tower, Chhattisgarh, India

Egyptian Vulture Nesting on Power Transmission Tower, Chhattisgarh, India

Backflashover Performance Evaluation of the Partially Grounded Scheme of Overhead Lines With Fully Composite Pylons

A design of a fully composite pylon has been proposed for new-generation 400 kV transmission towers to save line corridors and to reduce visual impact. Correspondingly, a method of external down-leads is proposed to bring grounding potential to the shield wires, together with a plan that not all pylons are grounded called ‘partially grounded transmission lines’ (PGTLs). This paper investigates backflashover performance of a partial grounding scheme of overhead lines (OHLs) supported by composite pylons. The transient analysis was carried out in PSCAD based on Monte Carlo method. For OHLs with every pylon grounded, reducing footing resistance and soil resistivity can improve backflashover performance effectively, but for PGTLs, these two methods do not have obvious effect and increasing insulation distance has limited effect. When lightning strikes at PGTLs, overvoltage is mainly dependent on the distance to the nearest grounded pylon and a longer distance will cause overvoltage with larger amplitude and longer wave front duration. Therefore, backflashover rate also increases along with the distance to the nearest grounded pylon until reaching a value limited by the inceptive condition of flashover. A coefficient recommended by CIGRE TB 63 to estimate backflashover rate is discussed and modified when using in PGTLs.

Failure Analysis of Transmission Tower in Full-Scale Tests

With the rapid development of Ultra-High Voltage (UHV) transmission lines, it is necessary to study the performance of UHV transmission towers. First, we performed full-scale tests on a transmission tower under seven loading patterns. Then, the test results were compared with the calculation results of the Chinese tower design software Transmission Tower Analysis Program (TTA), and the failure location of the tower and the stress characteristics of the key parts were studied. Finally, we discuss the influence of bolt slippage and a new joint on the tower performance, and propose some design proposals for the current Chinese code, based on the test results. The results show that a bolt slip will significantly increase the displacement of the transmission tower, but the residual displacement can correct it. The new joint design has good mechanical performance. The bracing member at the bottom of the tower leg is located at the connection of the tower leg and the foundation, and there is a significant sudden change in stiffness, which we recommend designing according to 4% of the axial force of the main members.

Numerical and full-scale test case studies on post-elastic performance of transmission towers

Post-elastic capacity of transmission tower is critical for the realistic assessment of tower vulnerability under the extreme loading conditions. This paper first presented a series of numerical simulations of a lattice transmission tower section under torsional (longitudinal) or bending (transverse) loading in both static and dynamic scenarios. From the results of the numerical simulations, four prototypes of lattice transmission towers were constructed and tested for the investigation of the post-elastic performances of the towers under different loading conditions. The tests results showed that there existed significant post-elastic strength reserve of the tower under investigation. For the towers tested in this research, the post-elastic strength reserve was 1.22 for flexure-torsion (i.e. tower under longitudinal loading) governed by diagonals, and 1.37 for bending (i.e. tower in transverse loading) governed by inelastic buckling of the main legs. Diagonal members affected the failure modes of transmission towers and their connection design may be a weak link in the development of their post-elastic capacity.

Integrated wind turbines and power transmission line: A novel concept

New technologies for wind energy systems have received great attention globally in recent years. These technologies are trying to reduce the drawbacks of conventional wind systems. This paper introduces a novel concept for wind systems to improve efficiency, reduce costs, and reduce environmental damage. The proposed system is considered from two viewpoints in this paper. Firstly, the design of a novel structure of wind turbines and power transmission towers that combines power transmission lines and wind blades. Secondly, a new power delivery method for injecting the power generated by the wind turbines is proposed. In the proposed system, a common tower is used to hold both the conductors of the transmission line and vertical-axis wind turbines, which as a result, wind turbines are located in the Right Of Way (ROW) area of the transmission line. For injecting the power of wind turbines into the transmission line in a double-circuit transmission line, creating a specific phase difference between the two lines creates a suitable voltage difference between them for injecting wind turbine power to the transmission line without using large transformers. The power circuit of the proposed system and its performance have also been analyzed. Moreover, the created voltage equation between the two lines and each wind turbine's generated power according to the system parameters are obtained. Finally, the proposed system is simulated by MATLAB software and compared with the conventional wind farms.

Research on Lightning Overvoltage of Oil-Gas Pipeline Caused by Lightning Strikes on Adjacent Electrical Transmission Line

As natural lightning strikes on a transmission tower, lightning current will flow along grounding lines into the adjacent tower grounding grid. As lightning current is dispersed from the tower grounding grid into the soil, a lightning overvoltage may be produced on adjacent pipelines. In this paper, the lightning current shunt characteristics in multi-tower scenarios are calculated by simulation method under different soil resistivity conditions. Then, based on the lightning current shunt characteristics, the current dispersion process among multi-tower grounding grids and the pipeline is analyzed with different soil resistivities, gap distances, and lightning current amplitudes. Finally, the protective effect of “drain wire” and “forced commutation” on pipeline overvoltage are compared. Simulation results showed that with increasing soil resistivity, tower grounding resistance was increased and tower shunt coefficient decreased. Considering lightning current through the multi-tower grounding grids, pipeline overvoltage is much larger than that of a single tower. Pipeline overvoltage is increased with soil resistivity and lightning current amplitude, while it is decreased with “pipeline-line” distance. Both “drain wire” method and “forced commutation” method can effectively reduce pipeline potential.

Mechanical behavior of steel transmission tower legs reinforced with innovative clamp under eccentric compression

Most steel lattice towers have been in service for over 20 years in China. Many existing towers are now required to carry higher loads than those for which they were originally designed because of new heavier devices and revised wind design codes. An effective way of increasing the carrying capacity of a tower is to reinforce its core leg members by attaching additional elements with bolted connections. However, the reinforcing methods proposed in previous studies require drilling into the core leg members, which results in considerable construction inconvenience. Therefore, an innovative clamp-type (IC) method is proposed herein. To evaluate the effectiveness of the proposed IC method, this paper presents results from 90 new cases comprising 10 eccentric compression tests and 80 finite element (FE) analyses of the load capacity of starred compound members, by varying the interconnector arrangement, form, spacing and bolt row, and slenderness ratio of the compound members. The experimental results show that the compound members with the IC interconnector mainly exhibit buckling failure in the core member. However, in the case of instability about the imaginary axis, the bearing capacity of the compound members with the IC interconnector is approximately 41%–62% higher than that of the single angle member. A nonlinear FE model is developed, which considers the material, contact non-linearity, and geometric imperfections. The FE model is validated against the experimental test results, which show good agreement, both in terms of failure mode and load–displacement curve. The validated FE model is used to conduct a parametric analysis to investigate the effect of slenderness ratio on the bearing capacity of the compound member. Four width–thickness ratios of connected angles and five IC interconnector spacings are considered in the parametric study. The bearing capacity values obtained from the experimental tests and FE analyses are used to assess the performance of current design guidelines. The results show that the current DL/T 5154-2012 code is too conservative by an average value of 30%. Therefore, a kd coefficient method is proposed to improve the prediction accuracy of the bearing capacity, and the method is verified against the FE and test results of the compound member with the IC interconnector under eccentric compression tests.

ANALYTICAL STUDY ON VARIOUS BRACING SYSTEM FOR TRANSMISSION TOWER

Transmission line towers and monopoles. Transmission line towers and monopoles are often used for high steel structures used for electric transmission. The transmission line tower or monopole should be carefully planned so that they won't fail over their whole lifespan and should be followed both nationally and internationally. This paper describes the transmission tower for different spans, such as 3m, 5m, 7m, and 9m, and with 3 types of bracing systems (K, X, and K & X). Comparing each brace with each other and observing the displacement of each tower to bring out the best self-supporting and most economical transmission tower based on the displacement values. The results show that displacement was observed to be high in K-bracing and low in K & X bracing combined. Keywords. Transmission tower, K-bracing, X-bracing, K & X bracing.

A nodal‐based evolutionary optimization algorithm for frame structures

AbstractThis work proposes a nodal‐based evolutionary design optimization algorithm to design frame structures whose edges are the Delaunay triangulation of homogeneously distributed nodes in the design domain. The remaining nodes can freely sway in the design domain except for the loading nodes and boundary nodes. As a result, it can extend the space of admissible solutions to this optimization problem and reduce the number of design variables. Then, the sensitivity of the objective function, namely, the sum of compliance and its volume, is input into the method of moving asymptotes to update the nodal coordinates and member thickness. The most inefficient node is deleted in each iteration based on the average nodal strain energy until its number reaches a prescribed limit. 2D numerical examples for the Michell arch, L‐shaped bracket, and Messerschmidt–Bölkow–Blohm beam show that the proposed algorithm can get the optimal structure within a few iterations. Compared with initial configurations in 3D, the optimal crane arm, transmission tower, and aquatic dome have less strain energy and fewer materials, showing a great potential of the proposed method to design actual space frames.

The Estimate of Fault Location based on Transmission Tower Coordinates

This study was conducted to predict the fault location based on tower coordinates using the Artificial Neural Network (ANN). The electrical power system modeled made use of an actual system including 150 kV transmission line with KP bus to the GS bus and 64 km length while ANN technique was used to coordinate the points for the fault location on the electric power transmission line due to its ability to predict what will happen in the future based on the pattern of past events. The ANN was tested and trained at certain iterations with different data which were simulated for short circuit fault type at several locations to achieve the best value. The results obtained with fault location coordinates were in the form of latitude and longitude while the simulation results for the AG fault were at 0.0381 km distance starting from the KP bus to the GS bus at 8,246 kA. Moreover, the estimated error values were found in the 2-phase fault to the ground at 4.01×10- 3 % while the ANN structure performance showed the MSE value to be 2.08 - 4 % with a very small error value of 0.57 % and this means it is included in the existing standard tolerance category. The data validation of this system modeling was conducted on the short circuit current value between simulation and theoretical estimation.

An Optimization Framework for Power Infrastructure Planning

The ubiquitous expansion and transformation of the energy supply system involves large-scale power infrastructure construction projects. In view of investments of more than a million dollars per kilometre, planning authorities aim to minimize the resistances posed by multiple stakeholders. Mathematical optimization research offers efficient algorithms to compute globally optimal routes based on geographic input data. We propose a framework that utilizes a graph model where vertices represent possible locations of transmission towers, and edges are placed according to the feasible distance between neighbouring towers. In order to cope with the specific challenges arising in linear infrastructure layout, we first introduce a variant of the Bellman-Ford algorithm that efficiently computes the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">minimal-angle</i> shortest path. Secondly, an iterative procedure is proposed that yields a locally optimal path at considerably lower memory requirements and runtime. Third, we discuss and analyse methods to output <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$k$</tex-math></inline-formula> diverse path alternatives. Experiments on real data show that compared to previous work, our approach reduces the resistances by more than 10% in feasible time, while at the same time offering much more flexibility and functionality. Our methods are demonstrated in a simple and intuitive graphical user interface, and an open-source package (LION), available at <uri xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">https://pypi.org/project/lion-sp/</uri>