Overhead Transmission Conductors Research Articles

Study on current carrying capacity calculation model for dynamic capacity increase of carbon fiber reinforced composite core conductor

Abstract With the “dual-carbon” as the goal of the new power system construction gradually in-depth, transmission lines must have energy-saving capacity for the direction of development. A new type of large-capacity overhead transmission conductor is the carbon fiber reinforced composite core (CFCC) conductor. The conductor has high capacity, low loss, high-temperature resistance, low high-temperature sag, and other characteristics. It is one of the key technologies and equipment applied to the transformation of old overhead transmission lines to enhance its capacity. At the same time, it can also realize the dynamic transmission capacity regulation of the overhead line. The application of the prospect is very promising. The accurate assessment and calculation model for the conductor’s allowable current carrying capacity is the key core technical problem of the overhead transmission line dynamic capacity increase capability. The paper establishes a maximum allowable current capacity calculation model for carbon fiber-reinforced composite core conductors based on Morgan’s formula. The results of the load flow calculation are compared with the actual load flow test results to verify the calculation model, and the maximum error is 3.59%, which proves the reliability of the calculation model. On this basis, the influence of external environmental factors (ambient temperature, sunlight intensity, wind speed, and direction) on the maximum allowable current capacity of the conductor is discussed. The correlation coefficient of the model is analyzed.

Carbon fiber composite core conductor operation risk assessment model based on various types of monitoring data

Abstract As the national economy grows gradually and the scale of urbanization expands, the standard for power transmission is also continuously increasing. Currently, the existing transmission lines can no longer meet the rising power demand, thus urgently requiring the construction of power transmission capacity expansion. Although there are many strategies for increasing capacity, the development of enhanced conductor material is indeed its greatest advantage. However, among the various options for increasing capacity, the development of capacity-enhancing wires is also the most advantageous. Carbon fiber conductors, which are known as “black gold,” are the perfect material for this purpose. Given the inherent economic value, high brittleness, and complexity of the installation process of carbon fiber materials, this study proposes an operational risk assessment model for carbon fiber composite core conductors based on multiple monitoring data. For the first time, the influence between quarterly lightning strike probability and arc droop as well as the temperature drop effect on overhead transmission conductors by convective heat dissipation from natural wind are taken into account. The expected arc sag size of the conductor in the future period can be predicted according to the meteorological forecast, which can effectively prevent the impact of flashovers and wire breakage on the operation of the power grid. In addition, the practicality and functionality of the assessment model have been verified by real accident data.

Fabrication of hypoeutectic Al-4Si alloy with high electrical conductivity, high plasticity and medium strength by the dual treatment of Al matrix and eutectic Si microstructure

Hypoeutectic Al-Si alloys exhibit excellent mechanical properties and relatively good electrical conductivity (EC), and they are often used as overhead transmission conductors. But, due to the contradiction between EC and mechanical properties (especially EC and strength), high EC and good mechanical properties are hard to be obtained simultaneously, which limits their applications in the field of electrical engineering. Thus, it is necessary to improve the matching between EC and mechanical properties. In this study, composite boron treatment, Sr modification, homogenization heat treatment and hot extrusion deformation process were done to fabricate a kind of hypoeutectic Al-4Si alloy with high EC, high plasticity and medium strength. Through the process mentioned above, not only Al matrix was purified, but also eutectic Si exhibited good orientation consistent with α-Al. In addition, eutectic Si morphology was modified from large needle/plate-like to fine particles, and its distribution was changed from segregation along grain boundary to uniform distribution. The scattering probability of solid solution TM elements to electrons was significantly reduced, and the number of channels for electron migration in the eutectic Si region was also increased obviously. Meanwhile, the optimization of the microstructure enhanced the mechanical strength and elongation of Al-4Si alloy at the same time. The special extrusion texture also promoted improvement of the electrical and mechanical properties of Al-4Si alloy. Finally, the EC of Al-4Si alloy was improved from 41.8 %IACS to 59.2 %IACS, and the corresponding ultimate tensile strength (UTS) and elongation can reach 206 MPa and 26.7%, respectively. Compared with that as-cast condition, EC, UTS and elongation improved by 41.6%, 60.9% and 136.3%, respectively, which has a certain application prospect in the field of electrical engineering.

Solving the Overhead Transmission Conductor Heat Balance Equation Using the Newton Raphson Algorithm

This paper utilizes the Newton Raphson (NR) iterative algorithm to solve a detailed heat balance equation for overhead transmission conductors, for the purpose of calculating a Dynamic Line Rating or temperature-dependent impedance using real-time or forecasted weather data. Provided ambient weather conditions, conductor parameters and electrical current passing through the conductor, a starting guess is formed and the iterative solution method arrives upon a solution within a preset solution tolerance. A simple method to approximate the Rayleigh Number / Nusselt Number and Reynolds Number / Nusselt Number relationships is proposed to ensure successful convergence. The paper performs a thorough, numeric electrothermal conductor simulation to demonstrate proper solution convergence. This exercise identifies a minimum conductor temperature rise necessary for the solution method to converge successfully. Error related to the minimum starting conductor temperature rise, and error introduced by the approximated air property functions is illustrated. The temperature solution method is compared with several well-known thermal models.

A preliminary analysis on mechanical characteristics of transmission conductors in the vicinity of suspension clamps

Overhead transmission conductors are prone to wire strands breaking under the conditions of breeze vibration, and many broken strands occur in the vicinity of suspension clamps. In order to research the stress distribution characteristics of the conductor in the vicinity of suspension clamps, a relatively effective Finite Element (FE) model was proposed. Preliminary verification of model rationality through comparative analysis of theoretical calculation and simulation, and use this model to study the mechanical characteristics of the cross-section of the conductor in the key position of the conductor-clamp system. The research conclusions are as follows: a new concept of equivalent bending stiffness and equivalent diameter is proposed, which is used to calculate the alternating bending stress of conductors under breeze vibration conditions. The alternating bending stress of the wire strands follow the bending amplitude (Y b) increases with increasing. Under the complex load, the Equivalent (Von-Mises) stress of the aluminum wire strands at the Last Point of Contact (LPC) of the conductor and the clamp shows a decreasing trend from the outside to the inside, and the maximum Von-Mises stress occurs at the contact position between the outermost wire strands and the clamp.

Influence of CNTs addition on the mechanical, microstructural, and corrosion properties of Al alloy using spark plasma sintering technique

Monolithic aluminium 1000 alloy is used in overhead transmission conductors because of its light weight, high electrical conductivity and high passivation property. But its low strength is a very big challenge to this application. However, the strength can be improved by proper reinforcement in a way that will not compromise other properties. So, this work was focused on improving the strength and corrosion properties of Al alloy with carbon nanotubes (CNTs) using spark plasma sintering (SPS). The start-up powders were blended with tubular mixer and sintered with SPS technique. The densities, microhardness and corrosion characteristics of the sintered samples were determined accordingly. Results obtained showed that there was a homogeneous dispersion of CNTs in the Al matrix of all the samples except Al-8CNTs. Al-4CNTs gave the highest microhardness of 482.60 ± 12 MPa which represented 27% improvement in relation to monolithic Al alloy. Again, Al-4CNTs gave the least corrosion rate of 0.26723 mm/year in NaCl medium and 0.24188 mm/year in H2SO4 medium (46% and 47% improvements, respectively). These results indicate that Al-CNTs composite is a robust material for high transmission conductors.

Spectral model and experimental validation of hysteretic and aerodynamic damping in dynamic analysis of overhead transmission conductor

Abstract The paper treats a new approach of dynamic analysis of a conductor cable of an overhead transmission line under the theoretical background of spectral element method (SEM). The methodology relies on the analytical solution of the displacement wave equation in the frequency domain; moreover, it both enhances the accuracy of model predictions and reduces the computational efforts when compared to a finite element (FE) model. Two numerical models based on SEM are built for transmission lines taking into account hysteretic and aerodynamics damping and whose analyses consider dispersion diagrams and frequency response functions (FRFs). As SEM leads to a transcendental eigenvalue problem, to obtain the natural frequencies of the conductor, it is used the Wittrick–Williams algorithm. The results presented in the paper show the sensitivity of the response conductor changes according to the tensile load and damping parameters. Finally, the numerical models have compared with the analytical solution of the cable and experimental tests performed at CEPEL’s (Electric Power Research Center) laboratory with the overhead conductor Grosbeak cable. The results show outstanding accuracy in both experimental measurements and analytical analysis aspects.

Monitoring of Overhead Transmission Conductors Subjected to Static and Impact Loads Using Fiber Bragg Grating Sensors

It has previously been shown that the next-generation polymer core composite high-voltage transmission line conductors under severe transverse impact conditions develop complex failure modes strongly dependent on the type and magnitude of external multiaxial loads. In this paper, we greatly improve our understanding of the dynamic structural response of the conductor subjected to low-velocity impacts. We successfully demonstrate that fiber Bragg grating (FBG) sensors could be a viable technique for in-service monitoring of the conductors subjected to a variety of static and impact situations. It is shown that under static and low-energy/velocity conditions, the sensors can accurately measure strains both on the bare rods and inside the conductors. The accuracy of the sensors is independently verified by performing finite-element calculations of associated strains in the rods under axial tension and three- and four-point bend loading conditions. The tests on the full-scale conductors under low-energy impact also show that the sensors can identify the location and magnitude of impact with a very high degree of sensitivity. These results, combined with the intrinsic properties of optical sensors and fibers, indicate the FBG sensors could be especially useful in the monitoring of low- and high-energy impact events in service.

Corrosion Study of Galvanized Ultra High Strength Steel Reinforced Overhead Transmission Conductors

Overhead high voltage transmission conductors used worldwide are produced in several configurations. A multi-strand conductor of the type ACSR330 is typically used for 275 kV overhead transmission lines. The conductor is composed of 7 inner strands of Ultra High Strength Galvanized Steel for the mechanical support of the conductor and 26 strands of high conductivity Aluminum wires meant for power transfer over long distances. During the use, weather conditions and power fluctuations tend to degrade the properties of these conductors. In the present work, study of the state of galvanization and oxidation of an ACSR330 conductor is undertaken with a view to understand the effectiveness of the loss in corrosion protection and changes in the zinc coating on the galvanized steel strands after use for 25 to 30 years. The Scanning Electron Microscopy (SEM), X Ray Diffraction (XRD) and Energy Dispersive Analysis through X rays (EDAX) provide a very useful insight into the state of the conductor and gives important information to the strategic decision maker, whether or not to replace the conductor. It was observed in the present study that the zinc coating diffuses inside the steel strand under temperature and time effect. This unique study on the used conductors also reveals that the morphology of the coating and its interface structure changes significantly compared to an unused conductor of the same age.

Analysis of buffeting response of hinged overhead transmission conductor to nonstationary winds

Abstract This paper addresses analysis of dynamic buffeting response of a hinged transmission line (conductor) under nonstationary wind excitations. The nonstationary wind speed is characterized by deterministic time-varying mean and stochastic fluctuating components. The wind load on the conductor is quantified using quasi-steady theory. The wind-induced response of the conductor is decomposed into deterministic time-varying mean and stochastic dynamic components. The time-varying mean response is determined by nonlinear static analysis with an analytical solution. The stochastic dynamic response is determined through quasi-static analysis in terms of influence function around the time-varying mean equilibrium. A closed-form formulation is presented for calculating time-varying standard derivation of response. The cumulative distribution function of the extreme response over a given time duration is then calculate using mean upcrossing rate theory of nonstationary random process. The effectiveness and accuracy of the proposed analytical framework are verified through response time history analysis using a nonlinear finite element model. The response characteristics of conductor under various nonstationary winds are examined through a parametric study.

Fatigue and Fracture Behavior of a Cold-Drawn Commercially Pure Aluminum Wire.

Fatigue properties and cracking behavior of cold-drawn commercially pure aluminum wires (CPAWs) widely used as the overhead transmission conductors were investigated. It was found that the fracture surface of the CPAWs shows an obvious four-stage fracture characteristic, i.e., crack initiation, planar crack propagation, 45°-inclined crack propagation and final rapid fracture. The crack growth mechanisms for the CPAWs were found quite different from those for the conventional coarse-grained materials. The cracks in the CPAWs firstly grow along the grain boundaries (Stage I crack growth), and then grow along the plane of maximum shear stress during the last stage of cycling (Stage II crack growth), leading to the distinctive fracture surfaces, i.e., the granular surface in the planar crack propagation region and the coarse fatigue striations in the 45°-inclined crack propagation region. The grain boundary migration was observed in the fatigued CPAWs. The increase in fatigue load enhances the dislocation recovery, increases the grain boundary migration rate, and thus promotes the occurrence of softening and damage localization up to the final failure.

Microstructure and electrical conductivity of aluminium/steel bimetallic rods processed by severe plastic deformation

Equal-channel angular pressing (ECAP) was used to fabricate Al/steel bimetallic rod for potential application in overhead transmission conductors. Bimetallic rods consisted of an austenitic stainless steel 316L core and an Al alloy 6201 cladding layer. By means of ECAP processing at 175°C, increase of mechanical strength without loss of electrical conductivity was achieved for one particular rod geometry out of three geometries tested. X-ray diffraction and transmission electron microscopy were employed to analyse how the microstructure was influenced by the number of processing passes and the bimetallic rod geometry. The co-deformation mechanism of the bimetallic rod under ECAP and accelerated dynamic ageing of Al alloy 6201 were discussed based on the microstructure characterisation results.

Overhead Transmission Conductor Low Axial Tension and the Study of Linear

In view of the large cross-section wire overhead transmission lines, Starting from the conductor is flexible, By studying the shortage of the existing equation, The tension of conductor is low level is determined , Under the condition of the conductor is stable, Analyzed the lead in any little effect when the concentrated load lead the actual linear and sag.The analysis of comparing with existing practices.Get a new linear algorithm of computing function when a single concentrated load.After the calculation under the action of concentrated load transmission wire line has a certain reference value.

Spatial Analysis of Thermal Aging of Overhead Transmission Conductors

This paper introduces a new methodology for spatial analysis of conductor thermal aging that can be performed at three different levels: point, line, and area. The methodology uses known characteristics of transmission conductors, along with load and weather data, to determine time series of conductor temperatures and corresponding thermal aging. Weather conditions can be obtained with high resolution, providing environmental conditions virtually at every point of a transmission system. This novel approach provides a complete spatiotemporal view of the thermal state of the system, bringing a whole new dimension to the research of thermal aging. All described types of aging analysis are important for effective transmission asset management, for scheduling of line maintenance or inspections, and for planning future transmission systems.

가공송전선의 부하용량과 이도 특성에 관한 실험적 연구

Overhead transmission lines in domestic area have been built by several different design standards of dip and ground clearance. This paper describes an experimental study for evaluating load capacity and dip margin in overhead transmission lines. Such design standards for selection of overhead transmission conductors, dip and ground clearance, as well as electrical equipment technical standard are discussed. Based on daily load and weather data, several characteristics such as line utilization factor, load factor, conductor temperature and dip, etc. are analyzed, and compared with the specified levels of design standards. As a result, it is verified that DLR method can be a clue of the solving of the problem, for occurring in old transmission conductors which may be rarely operating below standards.

Numerical calculation of the negative onset corona voltage of high-voltage direct current bare overhead transmission conductors

The negative onset corona voltage of high-voltage direct current bare overhead transmission conductors has been studied by numerical calculations and gas discharge experiments. First, the charge simulation method, an accurate numerical method, is employed to calculate the distribution of the electrical fields in the vicinity of a bare conductor. Then, the electrical field values calculated and a criterion from the gas discharge theory are utilised to evaluate the onset voltage of the negative corona on the bare conductor. Furthermore, a formula for a high altitude correction factor is used to calculate the negative onset corona voltage of a bare conductor located at a high altitude. Finally, it is found that the calculated onset-voltage values agree satisfactorily with the data measured on laboratory models and full-scale test lines.

Fretting fatigue analysis of aluminium conductor wires near the suspension clamp: Metallurgical and fracture mechanics analysis

Fretting fatigue is the main phenomenon inducing reduction of fatigue strength in overhead transmission conductor lines which are subjected to aeolian vibrations. Using the Bersfort ACSR 48/7 conductor, fatigue tests were conducted under several traction forces and relative vibration amplitudes. By metallographic examinations it has been observed that fretting induces microcracks which are mainly located between the keeper edge (KE) and the last point of the contact (LPC) of the conductor at the mouth of the suspension clamp. Under the fatigue tests conditions, several cross-sections of wires in the external layer of the conductor were instrumented using strain gauges. Wire strains recorded near to the suspension clamp show that the alternating strains were predominantly traction strains near the KE and that bending alternating strains become significant near the LPC. On the basis of fatigue tests results and assuming some simplified hypothesis, stress intensity factors were computed at the tip of cracks. The computed stress intensity factors take into account the combined effect of fretting behaviour at the contact points and both traction and bending stresses. The computed stress intensity factor ranges for low fatigue bending vibration amplitudes show good agreement with the endurance limit of the conductor.

Overhead Transmission Conductor Sag: A Novel Measurement Technique and the Relation of Sag to Real Time Circuit Ratings

This article deals with overhead transmission conductor sag. The design, construction, instrumentation, and testing of a differential global positioning satellite (DGPS) system-based instrument for the measurement of conductor sag is proposed. Inherent and intentional errors in GPS technologies are discussed, and the DGPS method is described for accuracy enhancement. A DGPS-based overhead conductor-sag measuring instrument has been designed, constructed, and subjected to selected laboratory bench and power substation testing. A method to measure directly the physical sag of overhead conductors is described. The main advantage of the concept is the real-time direct measurement of a parameter (i.e., conductor sag) needed for the operation of the transmission system without intermediate measurement of conductor tension, temperature, and ambient weather conditions.

Development of an Overhead Transmission Conductor of Low Wind Noise and Low Drag Force

The new type of conductoreduced the drag coefficient (15%) and wind noise (10dBA) was developed. The authors carried out the water flow tunnel test, wind tunnel test and full-scale field test for confirming the reducing mechanism of drag coefficient and evaluating the reduction value of drag coefficient. This paper reports these test results and some evaluations.

Impedance of Nonmagnetic Overhead Power Transmission Conductors

A high-accuracy method of calculating skin-effect resistance and reactance of nonmagnetic stranded overhead power transmission conductors is described. This method uses an equivalent network approach and takes into account the effects due to wire spiraling, as well as the proximity effect between strands and the nonuniform current distribution in each strand. It produces results of greater accuracy than manufacturing tolerances usually warrant for overhead transmission conductors and requires a very small investment in computation cost. A table of skin-effect resistance factors that covers a wide range of standard aluminum conductors has been computed.