Transmission Line Tower Research Articles

Analysis of Collapse Accident of Transmission Line Tower Causing by Typhoon Attacking in the Coastal District of Guangdong Province

This paper is based on the background of towers collapsing accidents of overhead transmission lines during CaiHong typhoon. The criterion on design reviewing of existing towers is discussed, and the wind load acting on the damage towers of the 220 kV overhead transmission line from typhoon attacking is calculated, as well as the reason for the tower collapsing was analyzed. Finally, some conclusions and suggestions are proposed to enhance design standards and tower strength on the coastal zones where typhoons landing always recur.

In-situ monitoring the thermal regime of foundation backfill of a power transmission line tower in permafrost regions on the Qinghai–Tibet Plateau

The stability of tower foundations in permafrost regions is related to the thermal regime of the adjacent soils. The aim of this study is to investigate the ground temperature evolution in the foundation backfill of a tower, which is constructed by open excavation on the Qinghai–Tibet Plateau. Soil temperature and water content in the backfill were monitored continuously in the first three years after the tower's construction. Results demonstrated that the winter-time construction resulted in lower initial ground temperature around tower footings, and potential natural convection in the loose backfill, which facilitated the cooling in the first winter. In the following summer, the temperature in backfill was higher than that in a nearby natural field, due to the latent heat of infiltration water in the backfill and the heating of warmer undisturbed soils. The events of water infiltration led to a heating rate of 1 to 2 orders higher than that of thermal conduction in the backfill. Whereas, after one annual freeze–thaw cycle, the dominant heat transfer changed to heat conduction in the compacted backfill. The study provides valuable insights for evaluating the constructing technique and proposing mitigative measures for power transmission lines in permafrost regions.

Method for estimating backflashover rates on HV transmission lines based on EMTP-ATP and curve of limiting parameters

Abstract This paper presents a general method for estimating the backflashover rate (BFOR) on high voltage (HV) transmission lines. The method employs a state-of-the-art model of HV transmission line (TL) for backflashover (BFO) analysis, assembled within the EMTP-ATP software package and subsequently used—with EMTP running in batch mode—to construct a curve of limiting parameters (CLP). The CLP brings into relationship incident lightning currents with critical currents for the BFO occurrence and, furthermore, provides means for estimating the BFO probability. Namely, the probability of BFO occurrence at a particular TL tower is obtained by computing the volume under the surface of the probability density function of the bivariate log-normal statistical distribution of lightning current parameters, bounded by the CLP in the appropriate coordinate space. This probability in combination with the estimated number of direct lightning strikes to TL towers—obtained from the application of the electrogeometric model—provides the associated BFOR, assuming it is further normalised on the basis of 100 km-years. The usage of the proposed method is demonstrated on a typical HV transmission line. A sensitivity study for estimating the BFOR is provided, along with results comparison between different methods.

Quick calculation of the grounding resistance of a typical 110 kV transmission line tower grounding system

A general practical method, based on the Finite Element Method modelling and a numerical analysis of the obtained results, was applied for the calculation of the grounding resistance of a complex grounding system frequently used for typical 110kV transmission line towers. An approximate formula for a practical evaluation of such a grounding system resistance, valid for the ranges of input parameters used in the Serbian transmission power system, is proposed. A new, more accurate formula for calculating the square loop grounding resistance is also given. The proposed method for generating approximate formulas intended for fast grounding resistance calculations is general and, therefore, can be applied to any type of complex grounding systems.

Sensor Placement for Structural Monitoring of Transmission Line Towers

Transmission line towers are usually analyzed using linear elastic idealized truss models. Due to the assumptions used in the analysis, there are discrepancies between the actual results obtained from full scale prototype testing and the analytical results. Therefore, design engineers are interested in assessing the actual stress levels in transmission line towers. Since it is costly to place sensors on every member of a tower structure, the best locations for sensors need to be carefully selected. This study evaluates a methodology for sensor placement in transmission line towers. The objective is to find optimal locations for sensors such that the real behavior of the structure can be explained from measurements. The methodology is based on the concepts of entropy and model falsification. Sensor locations are selected based on maximum entropy such that there is maximum separation between model instances that represent different possible combinations of parameter values which have uncertainties. The performance of the proposed algorithm is compared to that of an intuitive method in which sensor locations are selected where the forces are maximum. A typical 220 kV transmission tower is taken as case study in this paper. It is shown that the intuitive method results in much higher number of non-separable models compared to the optimal sensor placement algorithm. Thus the intuitive method results in poor identification of the system.

An Algorithm for Estimating the Grounding Resistance of Complex Grounding Systems Including Contact Resistance

In cases where the grounding system is buried in soils characterized by poor contact with the electrodes (e.g., karst and sandy terrains), the contact resistance frequently represents a dominant component of the total grounding resistance. In such cases, estimation of the grounding resistance by conventional formulas given in the literature is useless, because they do not take into account the contact resistance. An algorithm for estimating the total grounding resistance of complex grounding systems, with the contact resistance included, was developed and presented in this paper. The algorithm is applied to a grounding system of a typical 110-kV transmission line tower used in the Serbian transmission power system. Simple formulas by which the total grounding resistance of the analyzed grounding system can easily be calculated are also derived. The obtained results are validated using 3-D finite-element method (FEM) modeling and a practical method from the literature. It was shown that the total grounding resistances determined by the proposed algorithm deviate less than 4% from those obtained by FEM calculations. Since the proposed algorithm is general and can be applied to any grounding system, it represents a powerful tool for estimating the grounding resistance in an early stage of the design process.

Comparison of Responses of Guyed and Freestanding Transmission Line Towers Under Conductor Breakage Loading

Cascades have been a prominent feature of many transmission line (TL) accidents around the world. During these events, a localized member failure changes the boundary conditions of the structural system, magnifying member loads over a considerable extension of the line. This results in the progressive failure of successive support structures. Phase conductor breakage is regarded as the most severe cascade triggering event, generating a shock wave that propagates through the conductor and induces large unbalanced longitudinal loads on the transmission line components. Under such an extreme loading event, nonlinear time-history dynamic analysis has to be employed to predict the response of the TL system. In the present work, an explicit dynamic analysis scheme is developed to predict the response of a multi-span TL section. The analysis includes all the main structural components of a TL section. This procedure was used to investigate the response of two types of suspension steel latticed towers, guyed and freestanding, subjected to conductor breakage loading. Results indicate the occurrence of peak dynamic loads (PDLs), that significantly increase the internal forces in system components, exceeding their design capacities, particularly in tower's members. The results also show that the guyed tower accommodates such a loading event more adequately than the freestanding tower.

Transient Lightning Impulse Performance Analysis for Composite Transmission Line Tower

In this paper, the transient impulse performances of a 330-kV composite transmission line tower under direct lightning strokes are comprehensively presented. An equivalent distributed parameter model combined with lumped capacitance elements for the tower is established. The wave impedances of the hybrid model are determined by using analytic equations. The lumped capacitances are calculated by 3-D finite element method (FEM). An accurate model for extended grounding structure (EGS) of the tower base considering the soil ionization is used to simulate its impulse performances. The wave process of the tower is analyzed by using the electromagnetic transient program (EMTP). The proper grounding conductor system is determined for the case of a superior lightning impulse performance considering three diverse grounding configurations. The influence of radius of the grounding conductor is assessed. The numerical electromagnetic field analysis, finite-difference time-domain (FDTD) simulation is applied to verify the validity of the presented hybrid model. Then, the influence of the wave-front time of the lightning current, the soil resistivity, the dimension of the EGS, and their combined effect on the transient impulse performances for the EGS are analyzed and discussed.

Wavelet-based Analysis of Impulse Grounding Resistance–Experimental Study of the “A”-type Grounding System

This article presents the results of experimental investigation concerned with the “A”-type grounding system's impulse characteristics, which are utilized for grounding of high-voltage transmission line towers. The investigation results point to the presence of high-frequency components in voltage and current signals that are not caused by tower footing response to the impulse current. Additionally, both surge generator coupling and measuring circuit remain their main source. High-frequency components of signals are extracted from voltage and current signals by means of the discrete wavelet transform. In addition to being external influence results, the extracted components have very low energy content as well as short duration. The discrete wavelet transform analysis application has validated the existence of external influences.

Analysis of a back flashover across insulator strings on a 115 kV transmission line tower by PSCAD

Lightning striking on a transmission tower induces high ground potential rise and high voltage at tower arms in which potential is normally at ground level, and subsequently causes overvoltage across an insulator string. If this overvoltage is higher than the withstanding voltage of the insulator string according to the v-t (voltage-time) curve, back flashover phenomena will occur and this event may cause outage. The main objective of this paper is to study the factors influencing the back flashover phenomena. The computer program PSCAD/EMTDC (Power System Computer Aided Design/Electromagnetic Transients including DC) is used to simulate lightning striking on a transmission tower 115kV. Lightning current, transmission towers, ground resistance, insulator strings and back flashover phenomena are modeled. Main simulations are lightning striking on different towers, different soil resistivity, different lightning current magnitudes and wave shapes, different locations, and different phase angles of source voltage. Simulation results show that the higher tower encounters higher induced voltage. A back flashover occurs at the top tower arm easier than at the middle and lower arms. The higher soil resistivity induces higher voltage. The larger lightning current magnitude impacts on higher induced voltage. The longer rise time of lightning current generates lower induced voltage. Lightning strikes directly on tower generate higher voltage than that of striking on overhead ground wires.

Static and Dynamic Analysis of Transmission Line Towers under Seismic Loads

Static and Dynamic Analysis of Transmission Line Towers under Seismic Loads

A Technique for Representing Coaxial Cables for FDTD-Based Surge Simulations

The finite-difference time-domain (FDTD) method is a very effective tool for predicting surge phenomena in 3-D structures such as buildings and transmission line towers and in grounding systems such as grounding grids. In this paper, we propose a new technique for representing a coaxial cable for FDTD-based surge simulations. In this technique, the metal sheath of the cable and the electromagnetic field outside the metal sheath are simulated in the FDTD method, while the surge phenomena inside the metal sheath are solved on the basis of transmission line theory. Therefore, this technique can take into account the effect of the metal sheath of the coaxial cable, the traveling wave inside the cable, and wires connected to the internal conductor of the cable at the same time. Using the proposed technique, we predicted the surge phenomena in a coaxial cable and compared them with measured results for the purpose of validation.

Simultaneous optimization of force and placement of friction dampers under seismic loading

It is known that the use of passive energy-dissipation devices, such as friction dampers, reduces considerably the dynamic response of a structure subjected to earthquake ground motions. Nevertheless, the parameters of each damper and the best placement of these devices remain difficult to determine. Some articles on optimum design of tuned mass dampers and viscous dampers have been published; however, there is a lack of studies on optimization of friction dampers. The main contribution of this article is to propose a methodology to simultaneously optimize the location of friction dampers and their friction forces in structures subjected to seismic loading, to achieve a desired level of reduction in the response. For this purpose, the recently developed backtracking search optimization algorithm (BSA) is employed, which can deal with optimization problems involving mixed discrete and continuous variables. For illustration purposes, two different structures are presented. The first is a six-storey shear building and the second is a transmission line tower. In both cases, the forces and positions of friction dampers are the design variables, while the objective functions are to minimize the interstorey drift for the first case and to minimize the maximum displacement at the top of the tower for the second example. The results show that the proposed method was able to reduce the interstorey drift of the shear building by more than 65% and the maximum displacement at the top of the tower by approximately 55%, with only three friction dampers. The proposed methodology is quite general and it could be recommended as an effective tool for optimum design of friction dampers for structural response control. Thus, this article shows that friction dampers can be designed in a safe and economic way.

Analysis and Design of Vertical and Horizontal Configurations of Cross-arms in A Transmission Line Tower.

Analysis and Design of Vertical and Horizontal Configurations of Cross-arms in A Transmission Line Tower.

Modeling and Insulation Performance Analysis of Composite Transmission Line Tower Under Lightning Overvoltage

In this paper, a new non-uniform multiconductor transmission line model combining with lumped circuit elements for a composite transmission line (TL) tower under lightning strokes is established. The metal ground-wire cross arms, the metal tower main body and its bracings are modeled as equivalent horizontal and vertical TLs, respectively. The two grounding ladders are regarded as two parallel-vertical TLs considering their mutual coupling. These distributed TL parameters are calculated by analytic equations. The composite arms are equivalent as lumped capacitances determined by employing 3-D finite-element method. The lightning overvoltage analysis for a 330-kV composite tower is performed by applying the hybrid model. The incident and reflected voltages are calculated. The insulation performance evaluation for the composite tower is discussed in detail.

输电线路大型铁塔组立专用塔式起重机的设计与优化

针对输电线路工程铁塔塔材重、塔身高、就位难度大、安装精度要求严、施工环境复杂、安全风险大的特点，综合考虑重量、可操控性、施工效率、场地占用等因素，开展专业化设计，研制成功输电线路组塔大型专用塔式起重机，采用单动臂上回转结构、装配式基础、平衡重系统、分片式标准节、下顶升机构、自拆卸施工等先进的技术方案，具有施工效率高、安全性好、场地和人员占用少等优点，满足了特高压工程铁塔的组立施工需要，已在特高压电网施工中得到广泛应用。 Transmission line tower has the features of tower material weight, tower height high, difficulty in installation, high accuracy, complicated installation, complex construction environment and grave risk. Comprehensive consideration of weight, maneuverability, construction efficiency, site occu-pancy and other factors, to carry out professional design, the large special tower crane used for the large tower of transmission line is successfully developed. The special tower crane adopts the advanced technological scheme such as single jib, the top rotary structure, the assembling founda-tion, the balanced weight system, the chip standard section, the under jacking mechanism and the self-removal function. The special tower crane has the advantages of high efficiency, good safety, small space and personnel, etc. The special tower crane meets the need of the construction of the special high pressure engineering tower, and has been widely used in the construction of UHV power network.

Grounding Impedance Measurement of High Speed Railway Integrated Grounding System

The high-speed railway integrated grounding system is the basic guarantee for the safe and stable operation of the railway. It is the world’s largest long-distance horizontally elongated joint grounding system, which stretches the length of hundreds to thousands of kilometers, and its structure is not only different from power station and substation grounding system, but also different from the transmission line tower, lightning rod and other small grounding devices. There is little research information on the grounding impedance of high-speed railway integrated grounding system. This paper adopted 0.618 compensation method and reverse away method respectively, measured a section of high-speed railway integrated grounding system grounding impedance by JD16 and CA6425. Measurement results are in good agreement using those two type instrument. By using 0.618 compensation method, the measurement result will be gradually converged at 0.3 Ω with the increasing of current electrode distance, which is the real grounding impedance of integrated grounding system. By using reverse away method, the maximum measurement result difference is less than 0.024 Ω with the lead of current electrode distance increasing. The measurement results will be rapidly converged 0.25 Ω. The results showed that the reverse away method is helpful to shorten the length of current electrode wiring. The measurement error will be small when the current electrode wiring is longer.

Monitoring and Analysis of Transmission Line Tower Base Deformation of some Coal Mine Goaf

On the basis of monitoring surface deformation in some area subject to large transmission line tower base hazard, monitoring method description, monitoring data sorting and calculation of characteristic parameters for surface deformation are conducted to obtain relevant conclusions of the transmission line tower base deformation by sorting and analysis of monitoring results in this paper. Calculation, analysis methods and conclusions of this paper lay a foundation for analysis on stability of the transmission line tower base and provide a basis for design of the transmission line.

Applications of the FDTD Method to Lightning Electromagnetic Pulse and Surge Simulations

Electromagnetic computation methods (ECMs) have been widely used in analyzing lightning electromagnetic pulses (LEMPs) and lightning-caused surges in various systems. One of the advantages of ECMs, in comparison with circuit simulation methods, is that they allow a self-consistent full-wave solution for both the transient current distribution in a 3-D conductor system and resultant electromagnetic fields, although they are computationally expensive. Among ECMs, the finite-difference time-domain (FDTD) method for solving Maxwell's equations has been most frequently used in LEMP and surge simulations. In this paper, we review applications of the FDTD method to LEMP and surge simulations, including 1) lightning electromagnetic fields at close and far distances, 2) lightning surges on overhead power transmission line conductors and towers, 3) lightning surges on overhead distribution and telecommunication lines, 4) lightning electromagnetic environment in power substations, 5) lightning surges in wind-turbine-generator towers, 6) lightning surges in photovoltaic (PV) arrays, 7) lightning electromagnetic environment in electric vehicles (EVs), 8) lightning electromagnetic environment in airborne vehicles, 9) lightning surges and electromagnetic environment in buildings, and 10) surges on grounding electrodes.

Soil corrosion of the AISI1020 steel buried near electrical power transmission line towers

Soil corrosion of carbon steel samples buried up to hundred days close to a high voltage power transmission line tower was examined by weight loss vs. time. A higher weight loss was observed if the samples were electrically connected to the tower than if they were not. This was attributed to the influence of alternating current (AC) signals induced in the soil by the transmission line. This field study showed for the first time the influence of the AC power line on the buried structure of the tower, while other studies so far were focused only on AC corrosion of cathodically protected coated pipelines, running parallel to the transmission line. An improved method was used to measure weight loss by descaling in Clark solution. The new method substitutes discontinuous measurements, proposed in the ASTM-G1-90 standard, by in situ measurements of the weight loss during descaling, using a computer controlled microbalance.