Overhead Transmission Line Conductors Research Articles

The Detecting System and Method of Quasi-Distributed Fiber Bragg Grating for Overhead Transmission Line Conductor Ice and Composite Insulator Icing Load

Transmission lines icing is destructive to the operation of the power grid. There is a lack of methods to monitor overhead transmission line conductors and insulators for icing load simultaneously. In this paper, we implanted six optical fibers with three quasi-distributed FBGs each into the interface of a 110kV composite insulator and built an icing detection system, and proposed three ways for measuring overhead transmission lines icing load. A method for quasi-distributed FBG to differentiate between the measurement of running insulator umbrella and conductor icing load was proposed and validated. The effect of the number of implanted optical fibers on the measurement accuracy was studied. The results show that the relative error of simulated insulator umbrella skirt icing load measurement is -7.3%∼-2.7%. The 200m-span running conductor insulator umbrella skirt icing load measurement relative error is -11.5%∼-3.8%; the relative error of conductor ice measurement is -16.5%∼9.0% and absolute error is -0.83∼1.5mm. The composite insulator with an optical fiber embedded can accurately warn of serious icing on the conductor, with two can achieve the conductor icing measuring absolute error of about ±1mm. As for accurately measuring both the umbrella skirt and the conductor icing, it is necessary to implant six optical fibers.

Operation Recommendations for Tension Joints and Clamps on a 63 kV Overhead Transmission Line Conductor Based on Experimental Tests

This study provides the operation recommendations for the tension fittings used on a 63 kV overhead transmission line conductor based on experimental tests. In this way, the tension fittings, including the dead-end clamp, the mid-span joint, and the repair sleeve, are assembled on the lynx conductor under different faulty and healthy assembly conditions in the laboratory. The lynx conductor is one of the widely used conductors in the 63 kV overhead power lines. The electric current injection test, along with thermal imaging and also tensile test, are conducted on the studied samples. The results show that the surface temperature of the lynx conductor is higher than the surface temperatures of the dead-end clamp and mid-span joint under normal and overload current conditions. Also, the crimping pressure of the aluminum and steel pipes less than the standard value, the crimping length of the steel cores of conductor less than the standard value, and the crimping length of the aluminum pipes more than the standard value can lead to a developmental defect which should be repaired or replaced at the first opportunity of the transmission line service outage. The repair sleeve is under more thermal stress than the dead-end clamp and mid-span joint, even in the standard assembly condition. A slight temperature difference of a repair sleeve compared with the same type fitting may be a severe operating condition. Also, the use of two consecutive repair sleeves to cover the conductor cut strands is not recommended. Furthermore, the loose connection of bolts at the junction of the jumper terminal to the dead-end clamp causes a very high temperature which should be repaired immediately. If the temperature difference between two defective and healthy dead-end clamp or mid-span joint is more than 13 °C, a critical defect is diagnosed; however, the temperature difference between two repair sleeve more than 7 °C indicates a critical operation condition for defective one.

Hourly wind data for aeolian vibration analysis of overhead transmission line conductors

Fretting fatigue of conductors due to aeolian vibrations is an important phenomenon for the design and maintenance of electric transmission networks. The evaluation of exposure and susceptibility of a given span to aeolian vibrations requires information on the distribution of hourly wind speed and direction. Interpolation has been used to obtain wind data at non-instrumented locations; however, their accuracy is not adequate at locations far from stations and at locations in mountainous regions. Numerical Weather Prediction data sets provide wind information on a regular grid covering equally all regions; however, the spatial resolution is not adequate. A procedure is proposed using a mass-conserving diagnostic model (WindNinja) that incorporates a detailed map of local topography to improve predictions of wind direction. A second correction is proposed to account for local surface roughness as a function of wind direction and average canopy height from high-resolution LiDAR data. The proposed procedure is applied to nine meteorological stations and two experiment sites over southern Quebec, Canada. WindNinja was found to provide good estimates for the effects of local topography in mountainous regions. Wind speed after correction provides good agreement with hourly observations as well as with Weibull distributions fitted to the actual observations.

Analysis on the crimping quality of overhead transmission line conductors considering equivalent cross-sectional stiffness

Approximately 58% of wire failures are caused by slippage and fracture of electrical connectors, and the crimping quality analysis of connectors is based on equivalent cross-sectional stiffness. First, a JL/GLA 400/35 steel cord aluminum strand and NY-400/35 strain clamp are selected to fabricate 26 groups of specimens with different pipe penetration depths, opposite edge distances, inner diameters of the aluminum tube, and die widths. Then, through crimping tests on the aluminum tube and conductor and the steel core and steel anchor, five main crimping failures, namely, the slip at the outlet of the clamp, the slip at the outlet of the clamp with some broken aluminum strands, fracture of the aluminum tube in the non-pressure area, wire fracture at the outlet of the clamp, and separation of steel anchors, are observed. Finally, a failure analysis method for conductor crimping is proposed based on equivalent cross-sectional stiffness. Through the analysis of grip force and crimping quality, four failure modes and simplified curves of the load–displacement curve are obtained, and the failure principle of the conductor crimping is further elaborated. The results show that the stress release caused by the steel core and steel anchor of the crimping wire and the crimping aluminum tube and wire is the main reason for the slippage and fracture of the transmission line conductors and that it is also the key to improve the installation quality of the transmission line.

Methodology for Minimizing Electric Field at Ground Level from Transmission Lines Using Sensitivity Analysis

In this paper, a new methodology is applied to optimize the geometry of conductors of overhead transmission lines (TL) with high precision and low computational cost. This methodology is based on the sensitivity analysis of the electrical charge of the transmission lines using the adjoint method. This information is used with the gradient method and the golden section algorithm to minimize the electric field at the ground level of three-phase TL with two cables per phase. The approximation using central finite differences to obtain sensitivity is adopted for validation and comparisons. The TL's with high surge impedance loading is obtained after the optimization process.

A structural health monitoring system of the overhead transmission line conductor

Transmission lines are affected by aeolian vibration, sandstorms and acid rain, which cause structural damage and eventually lead to line breaking accidents. In this paper, the structural health monitoring technology of conductors is researched, and a structural monitoring system for conductors is designed. First, based on the structure of the ACSR (Aluminum Conductor Steel Reinforced) conductor and the dynamic equation, the relation between the natural frequencies and the structure of the conductor is obtained. Then, an online health monitoring system of the conductor structure is proposed, and key issues, such as the power supply solution of sensors, data preprocessing technology, multiple-sensor synchronization method, are analyzed in detail. Finally, the structural health monitoring of overhead transmission lines designed in this paper is tested on 110-kV experimental transmission lines. The experimental results show that from the system proposed the operation parameters of the conductors can be well obtained.

Tribo-fatigue characteristics of braided wire rope for traction under low cycle bending fatigue

Braided wire rope as the traction tool is indispensable for stringing conductors in overhead transmission lines. However, rope body wear and fatigue fracture failure often lead to its premature scrap. In this paper, the bending fatigue test of YS 9-8 × 19 braided wire rope for traction was carried out by the test rig. The bending fatigue life of the braided wire rope was discussed by the number of broken wires. Furthermore, the fracture mechanism and wear morphology of the rope wires were analyzed by Ultra-depth three-dimensional microscope combined with the scanning electron microscope. The fatigue damage mechanism was discussed, and the tribo-fatigue characteristics of the wire rope were investigated. Results show that the failure of braided wire rope is the result of the interaction of cyclic bending stress and surface damage. Moreover, most broken wires occur at the place where the rope wires are severely worn. When the bending fatigue cycle is between 2.0 × 104–2.4 × 104, the number of broken wires reaches the scrap standard. Additionally, the bending tribo-fatigue damage of the wires between adjacent strands is the most serious. The primary wear mechanisms of the wires in contact with the pulley are fatigue wear and abrasive wear. In contrast, the wires between adjacent strands are affected by fatigue wear, adhesive wear, and tribo-oxidation.

Calculation of the overhead transmission line conductor temperature in real operating conditions

The integration of fluctuating renewable sources, load growth and aging of the current power system is the major reasons for the development of the electric power engineering. Transmission lines are recently facing new technical and economic challenges. The immediate utilization of advanced technologies and modern methods could solve these issues. This study deals with the transmission and distribution of electrical energy with orientation on the calculation of operating temperature on the conductor of transmission line, which is under actual current load. The load of the transmission line is limited with allowable operating temperature. The operating temperature should not exceed the allowable operating temperature because the conductors of the transmission line have mechanical limit from the standpoint of deflection of conductors. The operating temperature as well as operating conditions of the conductor is determined by the type and material of the ACSR conductor. This article aims to propose the suitable calculation methods of the operating temperature of the overhead transmission line conductor in real operating conditions (external weather influences, current loading and corona effect). The originality of this proposed method (by differential equation) lies in considering corona effect. This improves the accuracy of the calculation of the operating temperature of the conductor under real conditions. In this article, the calculations are compared according to methodology of differential equation and methodology described in CIGRE Technical Brochure 601—guide for thermal rating calculations of overhead lines. The methodology of differential equation counts with or without losses by corona. The article also compares these methods of operating temperature during days in various different weather conditions like environment temperature, solar irradiance, wind speed and direction. It was found that under the action of the corona, the temperature of the conductor increases to a small extent.

Analysis on the Mechanical Stability of the Leg Joints in UHV Transmission Tower

Transmission line pole tower, whose safety and reliability will directly affect the safe and stable operation of the entire transmission line, is a rod-shaped and tower-shaped structure that supports overhead transmission line conductors and ground lines and maintains a certain distance between them and the ground. Moreover, the stress stability of the leg structure joints in UHV transmission towers is mainly analyzed in the paper. With the help of the finite element analysis software, taking the arrangement of the long and short legs in the actual structure of the tower as an example, the influence of different angles of the tower on the bending moment is compared and analyzed under the condition that the main material slenderness ratio is the same. Meanwhile, in order to eliminate the influence of horizontal force on the height of different tower legs, only the bending moment generated by the structural system at the tower legs under axial pressure is considered to continuously improve the stability and reliability of the line pole tower structure, so that the power safety can be guaranteed to a large extent.

Numerical Analysis and Finite Element Simulation of Axial Stiffness of Overhead Transmission Line Conductor

Numerical Analysis and Finite Element Simulation of Axial Stiffness of Overhead Transmission Line Conductor

Optimal selection and positioning of conductors in multi-circuit overhead transmission lines using evolutionary computing

This paper presents a new approach for designing transmission lines to transmit more power in a narrower space. Multi-circuits lines are a good alternative to attain this objective. However, the optimum solution is not obtained by just positioning several regular single-circuit transmission lines in a single tower structure. Although double-circuit and multi-circuit transmission lines have been used over the last years, there are not many studies about non-conventional multi-circuit transmission lines. Thus, in this research a mathematical model to represent the problem related to increasing the surge impedance loading level of each circuit, and reducing the costs, the ROW and the height of the towers by optimizing their bundle geometry and conductor type by applying genetic algorithms is proposed. The overall transmission lines presented as examples have an improvement between 52% and 149% in the objective function.

Calibration of Dynamic Line Rating Model for Phasor Measurement Unit Based Wide Area Measurement System in Smart Grid Application

The inefficiency of power transmission lines always becoming an issue in power system analysis. One of the most applicable methods Dynamic Thermal Current Rating (DTCR) to measure the thermal line ratings of existing transmission lines. This DTCR system operated through Phasor Measurement Units (PMUs) in Wide Area Measurement (WAM) system of the Sarawak Energy. To calculate the line rating based on measured or predicted weather conditions of the overhead transmission lines. However, the existing DTCR system of Sarawak Energy facing several accuracy issues. Therefore, this paper intended to perform an extended study on the sensitivity analysis of conductors in overhead transmission lines using the dynamic thermal rating model. The parameters (wind speed, the density of air, solar radiation) that influence the thermal line ratings considered in measuring, assessing the conductors’ thermal effects and then these parameters were considered for the line rating models that dynamically will adjust the weather information of the conductor in overhead transmission lines on WAM systems. The performance of this study carried out using Matlab based simulation. The result shows that the proposed model that uses the dynamic factors brings the expected outcome in measuring the accurate ratings of the overhead transmission lines.

Optimal mechanical sag estimator for leveled span overhead transmission line conductor

Mechanical sag of the overhead transmission line (OTL) is a critical parameter for power system operation. However, remote locations of the conductor limit observability of sag. To monitor sag, distributed (DMS) or point measurement systems (PMS) are used. But, due to the limitation of DMS to use ruling span method, PMS is preferred. PMS requires sensors on every tower; as a result, sensor and data transmission requirements are high. This paper attempts to reduce the sensor requirement and estimate the sag in leveled span. To reduce the number of sensors and identify their location a linear integer programming based optimal sensor placement approach is proposed while keeping the redundancy intact. Using this, a reduced order, least-square based state estimator is proposed to estimate the sag in leveled span configuration. The estimator uses the conductor temperature and tension at one end of the span as input. Though, designed assuming ideal leveled span configuration, it is found to work for actual operating conditions. The performance of the proposed estimator is validated on the sag and tension data obtained with simulations on PLS-CADD™. Moreover, to eliminate the bad data, sensitivity based bad data elimination approach is presented. It allows replacement of bad data with almost exact values. The results show the robustness of the proposed approach.

The Impact of Water Droplet Vibration on Corona Inception on Conductors Under 50 Hz AC Fields

The relationship between the size of water droplets on the surface of ac high-voltage conductors, their vibration, and corona onset is investigated. Measurements have been carried out on individual droplets in high-voltage experiments, including high-speed photography, and discharge inception measurements. These have been correlated with acoustic emission from larger arrays of droplets on overhead transmission line conductors. A numerical model based on the finite element method has also been developed to simulate the vibration of the droplet enabling evaluation of the electric field and the characteristics of the droplet vibration. It is shown that the size of the water droplet is critical in its mechanical response to the field and that corona does not necessarily occur when the droplet is deformed into its most conical state as is the case under dc fields. For larger droplets the phase shift between the field and droplet vibration results in the maximum field occurring when the droplet is in a “flattened” profile rather than when it is “pointed.” The phase relationship between the droplet vibration and the electric field thus controls the onset of corona. It is argued that conductors which facilitate the development of small, uniform, stable droplets on their surface are the cause of abnormally high levels of low-frequency audible noise sometimes observed by transmission utilities. Moreover, the narrow resonant response of the droplet may lead to a difference in acoustic emissions experienced between power utilities with 50 and 60 Hz system frequencies.

A Finite-Element Approach for Electric Field Computation at the Surface of Overhead Transmission Line Conductors

The purpose of this paper is to introduce a modified approach for the electric field computation at the surface of overhead transmission line (TL) conductors through the finite-element method (FEM). The proposed strategy is based on a spatial transformation, well-known as Kelvin transformation, resulting in a special way to treat the unbounded domain. Unlike other applications of the FEM in TLs, the suggested procedure aims to reduce the computational domain and the solution time, allowing an efficient numerical evaluation of the electric potential gradients, without the need of geometric simplifications of the conductors. Comparative results show that a more realistic treatment offers a better understanding of how electric fields operate near real conductors and, in addition, that the proposed approach can be used to provide an accurate design for conductor systems in TLs.

Aerodynamic damping of nonlinear movement of conductor cables in wind tunnel tests, numerical simulations and full scale measurements

Aerodynamic damping is a decisive parameter influencing the dynamic response of overhead transmission line conductors. Methods of how to account for the effects of aerodynamic damping differ significantly and so might do the results. In this work, the source of aerodynamic damping being the result of the relative velocity between the structure and wind flow will be revised. Based on wind tunnel tests and validated by simulations, the differences of linear movement compared to a pendulum movement of a sagging cable are shown. The reasons for that deviation are the large deflections, resulting in a movement non-parallel to the acting wind flow. For analysis in frequency domain, it is not possible to incorporate aerodynamic damping implicitly by fluid structure interaction. If the dynamic movement can be linearized at a working point of the mean deflection, a modification to the linear approach is suggested. This approach is validated by simulation with a finite element model of an existing overhead transmission line, calibrated with full scale measurements. Aerodynamic damping is incorporated in time step analysis by Rayleigh damping and modal damping. The differences between both approaches are emphasized and modal damping is shown to be the most adequate.

Techno Economic Analysis of the Use of High Temperature Low Sag (HTLS) Conductors in the Sri Lanka’s Transmission System

High Temperature Low Sag (HTLS) conductors are introduced with the intention of mitigating some of the disadvantages of the conventional overhead conductors. When compared to conventional conductors, HTLS conductors have better electrical and mechanical characteristics and by using these conductors in overhead transmission lines, some of the complex issues related to power transmissions could be resolved. However, most of the utilities are still in a quandary about using these conductors in place of conventional overhead conductors which have provided a commendable service to them over a period of a century or so. It is because of their lack of experience in using them in the field as well as because of the novel appearance of the conductors. Almost the entire transmission system in Sri Lanka comprises of overhead lines constructed using conventional conductors, especially ACSR conductors. Utility engineers therefore do not have much knowledge on HTLS conductors and also have very little experience in using them. This paper discusses the possibility of adopting the HTLS conductor technology in the Sri Lanka’s transmission system. The properties, behavior and special characteristics as well as the technoeconomic feasibility of using HTLS conductors instead of the conventional conductors are discussed in depth. Lastly, the issues and challenges related to the application of HTLS conductors are discussed. The results of this research will provide valuable information on the possibility of using HTLS conductors in the Sri Lanka’s transmission system.

Overview of different overhead transmission line conductors

There is a nationwide need for upgradation and expansion of the nation’s electrical power grid in the forthcoming decades to reach the growing demand of transmission and distribution capacity. Insufficient current carrying capacity (ampacity) and sagging with increase in temperature leads to complete blackouts. In order to address these issues, new conductors are designed, calculated and developed. The new conductors developed to address these issues were Aluminum Conductor Steel Supported (ACSS), Aluminum Conductor Steel Reinforced (ACSR), Aluminum Conductor Composite Reinforced (ACCR), and Aluminum Conductor Composite Core/Trapezoidal wire (ACCC/TW). This research paper provides an overview of the existing conductors related to their behavior under different operating temperatures and load. This paper provides report on the issues with respect to pollution severity analysis, ampacity, sag and coefficient of thermal expansion (CTE) of conductor systems currently or traditionally in use. A comparative study of existing conductors reveals that composite ACCC/TW conductor has certain advantages related to pollution severity analysis, high temperature sag and increased ampacity.

国内外の架空送電線用電線及び電線付属品の技術動向

国内外の架空送電線用電線及び電線付属品の技術動向

Galvanic Corrosion of High Temperature Low Sag Aluminum Conductor Composite Core and Conventional Aluminum Conductor Steel Reinforced Overhead High Voltage Conductors

A High-Temperature Low-Sag Aluminum Conductor Composite Core (ACCC) bare overhead transmission line conductor utilizing a load bearing unidirectional carbon and glass fiber reinforced epoxy composite rod was evaluated for potential galvanic corrosion problems. A series of corrosion tests were performed in 0.5 M NaCl aqueous solution at room temperature, and at 85 $^{\circ}{\rm C}$ . The corrosion performance of the ACCC conductor was compared to a conventional Aluminum Conductor Steel Reinforced (ACSR) conductor. The bi-metallic ACSR design suffers inherently from galvanic corrosion, while the ACCC design does not develop galvanic corrosion unless its fiberglass composite galvanic corrosion barrier is compromised. Even with a severely compromised barrier in the ACCC conductor, the measured galvanic corrosion rate of the aluminum in the ACCC conductor was much lower than the galvanic corrosion rate measured in the ACSR conductor.