Overhead Line Conductors Research Articles

Studies on the Evolution of Fatigue Strength of Aluminium Wires for Overhead Line Conductors.

Traditional ACSR overhead wires, which consist of a high-strength steel core and several layers of aluminium wires, are currently the most popular overhead line conductor (OHL) design globally. Operating conditions, particularly operating under varying stresses from Karman vortices, lead to the fatigue cracking of wires of the outer layer, followed by wires of the inner layers. Karman vortices are formed by the detachment of a laminar wind stream flowing around the conductor, which causes vibrations in the conductor called wind or aeolian oscillations. Aluminium wires are manufactured using standard batch material drawing technology. Although the fatigue strength of such wires is not standardised, there are various criteria for evaluating this characteristic, as well as established limits on the number of cycles needed to break the first wires of the outer layer. Fatigue strength also strongly depends on the geometric structure of the wire and its operating conditions. The article analyses the influence of the mechanical condition of aluminium wires used in ACSR cables on their fatigue strength. We then present results from aluminium wire fatigue tests conducted on a specially constructed test rig. In addition, fatigue cracks were interpreted using scanning microscopy.

Degradation of superhydrophobic aluminium overhead line conductor surfaces

AbstractIt has been shown that noise emissions from HV overhead line conductors can be reduced under rain conditions by making their surfaces superhydrophobic. The working environment makes ensuring the longevity of any treatment a major challenge. The degradation of various superhydrophobic surfaces generated by applying a superhydrophobic coating and patterning microscale channels is assessed under an AC electric field (18 kV/cm) with continuous water spray. By examining the droplet distribution on the surfaces during the degradation and the surface roughness before and after degradation, the authors demonstrate that no water droplets were found on the microscale patterned surface, but droplets were formed on the coated surface after degradation. The surface roughness reduction of the coated surface and microscale patterned surface was 29.8% and 11.3%, respectively, indicating that the microscale patterned surface has better durability than the superhydrophobic coating under the AC electric stress.

Inception Characteristics of Surge Corona on Line Conductors

Knowledge on the characteristics of surge corona on overhead line conductors is of great importance for studies on attenuation and distortion of lightning overvoltage surges. Impulse corona may initiate and grow in various discharge modes, namely glow, intermittent or stable streamer corona. Its inception characteristics can be described by statistical distributions, with parameters dependent on the steepness of the electric field strength around the conductor and on the atmospheric conditions. Agreement between theory and experiment on impulse corona inception characteristics is achieved based on the critical volume theory. The impulse corona performance of line conductors may differ between laboratory and outdoor testing, due to differences in the background density of negative ions. An empirical procedure yielding probability distributions for the inception characteristics of surge corona on overhead line conductors is introduced.

Transient induced voltages on aboveground pipelines parallel to overhead transmission lines

Lightning strikes to conductors of overhead lines may cause high transient induced voltages at neighbouring pipelines. Thus, the computation of these voltages is important for the safe and reliable pipeline operation. This work investigates the effects of line parameters and soil modelling on the transient voltages induced at an aboveground pipeline due to lightning strikes to a phase conductor of a nearby overhead transmission line. Three different earth formulations are evaluated: the Carson, Wise, and the method of moments with surface operator combined with the extended transmission line approaches. Computations are performed using both frequency- and time-domain models, as well as constant and frequency-dependent soil electrical properties. CIGRE lightning current waveforms are employed in simulations derived on the basis of the statistical distributions of their parameters for negative first return-strokes. Transient induced voltage waveforms differ among the evaluated lightning currents, with higher peak values for shorter and steeper current wavefronts. Conservative results are obtained for the constant soil properties and Carson’s earth formulations, which neglect, respectively, the dispersion of soil electrical properties and displacement current.

Study on the Dynamic Characteristics of Tensional Force for Ice Accumulated Overhead Lines Considering Instantaneous Wind Speed

Icing is one of the key factors affecting the security and reliability of power system operation. Ice accumulation on the overhead line (OHL) conductors is often accompanied by strong winds, whose magnitude and direction are varied constantly, which imposes challenges to the on-line monitoring of OHL’s ice load. This paper analyzed the dynamic characteristics of the tensional force for ice accumulated OHLs through both the on-site experiment and the finite element method (FEM). The correlation between the instantaneous wind speed, the thickness of the accumulated ice and the dynamic tensional force, the aerodynamic resistance coefficient of the conductor, is investigated. It is found that the axial dynamic tension at the end of the iced conductor is approximately proportional to the square of the instantaneous wind speed. The higher the wind speed, the larger the difference between the static tension and the maximum dynamic tension calculated using the 10-min average wind speed. Under the conditions of the example in this article (crescent-shaped icing), when the average wind speed is 20 m/s, the ratio of the difference to static tension is 11.19%. These conclusions are verified with the computational fluid dynamic (CFD) simulation, the same correlation is identified in comparison with the experiments. Due to the fact that the magnitudes of tensional force and vibration are determined by the instantaneous wind speed, significant error exists within traditional calculation methods where average wind speed is used instead.

The Electric Field Evaluation for Vibrating Rain Droplets on the Overhead Line Conductors

The water droplets on the surface of the overhead line (OHL) conductors are subject to an intensive electric field, which induces electric force on the charged liquid surface. Under the combined action of the surface tension as well as the electric force, movement and deformation can be observed on those water droplets. These result in a re-distribution of charge density on the liquid surface and therefore a re-distribution of electric force. In this paper, in order to strengthen the understanding of this complex multi-physics problem of interaction and mutual coupling, the vibration characteristics of water droplets under alternating electric fields is studied using the finite element method (FEM). Parameters such as the volume size of the water droplet, static/dynamic contact angle between the water droplet and conductor surface and voltage level are studied in relation to the vibration characteristics. The reproducible correlation between the phase and amplitude of the water droplet vibration on the surface of the conductor and the applied voltage is established. According to the calculated instantaneous electric field strength, it is explained that protrusions such as water droplets are the starting point of corona discharge.

Advancing OHL Rating Calculations: Modeling Mixed-Convective Cooling and Conductor Geometry

The existing standard current-temperature calculations for overhead line (OHL) conductors have been adequate for conventional conductors and their operating temperatures. However, these calculations make assumptions and include simplifications about conductor geometry and aero-thermal-dynamics, introducing an error in the High-Temperature Low-Sag conductors operating temperatures. To quantify the error introduced by the shape of strands, the paper employs a Multi-Physics Finite Element Modeling approach that calculates the conjugate heat transfer for trapezoidal stranded OHL conductors. Furthermore, it proposes corrective equations to improve the accuracy of existing methods. The equations incorporate a new Nusselt number correlation for mixed convection and capture the surface area ignored by current calculations. The outer conductor geometry assumptions and the combined natural and forced convective cooling omission in the IEEE and CIGRE methods introduce an error at low (below 0.12 m/s) cross-flow wind speeds suggesting an underestimation of conductor temperature by up to 4%. In medium wind speeds, typically at 0.5 m/s–0.61 m/s, the standard methods overestimate the conductor temperature limiting its current-carrying capability. A 5% uprating for existing OHLs is potentially feasible, particularly for the trapezoidal stranded conductors, when removing the assumptions made in existing methods.

Application of Heat Treatment to Aluminum Alloy Wires and Comparison of Full Alloy AAAC Conductor Manufactured with These Wires and Conventional ACSR Stranded Conductors

Conventional ACSR conductors are formed by stranding aluminum wires over a steel core. The steel core does not contribute to current carrying and is used only for carrying purposes. The steel core has a great role in the shedding of the line weight. With the increase in line weight, longer poles are used at shorter distances, but it cannot be abandoned because it undertakes the transport task. Nowadays, the search for alternatives to the ACSR conventional conductor has accelerated. One of these alternatives is AAAC (Full aluminum alloy conductors). The wires in AAAC are hardened with special alloy production and eliminate the need for a steel core as a carrier in the center. While producing the aluminum overhead line conductor, after the aluminum ingots are melted in the melting furnaces and taken to the resting furnaces, after the addition of alloy elements such as Si, Mg in certain proportions, it is solidified by pouring it into a copper mold through refractory runners, and after the rolling process, 9.5 mm or 12 mm Aluminum Alloy rod (wire rod) semi-finished products are produced. While producing wire in the diameter determined in the standards for the overhead line conductor to be produced, 9.5 mm or 12 mm Aluminum rod (wire rod) is thinned with a certain reduction ratio in the semi-finished drawing process, and aluminum wire of the desired diameter is obtained. In the drawing process, the rod is rolled with a reduction ratio suitable for the machine and the final product to be produced. The wires produced are brought together with the step ratio in the standards to form a conductor. In order to gain the mechanical and electrical properties of the produced aluminum alloy wire, heat is applied at a certain time and temperature in heat treatment furnaces. Considering the heat treatment time and degree applied in this study, the properties before and after the heat treatment will be compared and the effect of the heat treatment process on the wire will be shown with experimental studies. Mechanical and electrical tests of AAAC 774 AL7 conductor made of alloy wires and ACSR Pheasant conductors made of aluminum wires knitted on steel cores will be carried out and the two conductors will be compared considering some parameters in line selection.

How statistical modeling and machine learning could help in the calibration of numerical simulation and fluid mechanics models? Application to the calibration of models reproducing the vibratory behavior of an overhead line conductor

The world of fluid mechanics is increasingly generating a large amount of data, thanks to the use of numerical simulation techniques. This offers interesting opportunities for incorporating machine learning methods to solve data-related problems such as model calibration. One of the applications that machine learning can offer to the world of Engineering and Fluid Mechanics in particular is the calibration of models making it possible to approximate a phenomenon. Indeed, the computational cost generated by some models of fluid mechanics pushes scientists to use other models close to the original models but less computationally intensive in order to facilitate their handling. Among the different approaches used: machine learning coupled with some optimization methods and algorithms in order to reduce the computation cost induced. In this paper, we propose a framework which is a new flexible, optimized and improved method, to calibrate a physical model, called the wake oscillator (WO), which simulates the vibratory behaviors of overhead line conductors. an approximation of a heavy and complex model called the strip theory (ST) model. OPTI-ENS is composed of an ensemble machine learning algorithm (ENS) and an optimization algorithm of the WO model so that the WO model can generate the adequate training data as input to the ENS model. ENS model will therefore take as input the data from the WO model and output the data from the ST model. As a benchmark, a series of Machine learning models have been implemented and tested. The OPTI-ENS algorithm was retained with a best Coefficient of determination (R2 Score) of almost 0.7 and a Root mean square error (RMSE) of 7.57e−09. In addition, this model is approximately 170 times faster (in terms of calculation time) than an ENS model without optimization of the generation of training data by the WO model. This type of approach therefore makes it possible to calibrate the WO model so that simulations of the behavior of overhead line conductors are carried out only with the WO model.

Influence degree of skin-effect for overhead line conductors

This paper analyzes the skin-effect influence on ACSR conductors for overhead lines. The analysis is based on numerical models: one cylinder, and two coaxial cylinders, and cylinders layers. The authors compare all models with each other, as well as with the well-known analytical solution, and direct current mode. All numerical models were verified by comparison with the analytical solution. The results show the one cylinder model get incorrect results for ACSR conductors. Moreover, the maximum error about 40% is given by conductors with a medium cross-sectional area, such as the ”AC 240/39” conductor by GOST 839-2019. The two coaxial cylinders model gives better results but about 10% less than the cylinders layers model, since it does not consider the electric field penetration between wires of a conductor. As a result, the authors conclude that the skin effect has a great influence for all ACSR conductors.

Electromagnetic Fields Due to an Electron Avalanche

In electric power and electronic systems, localized breakdown of air in the form of corona, partial discharge (PD), and electrostatic discharge (ESD) occurs frequently. These processes are known to be sources of electromagnetic fields. Corona on overhead line conductors produces electromagnetic noise over a wide frequency range leading to electromagnetic interference. The magnetic field due to PD can be employed to detect and possibly locate PD inside the apparatus. The fields due to ESD assume importance in designing suitable protection systems. Therefore, there is a need to relate the electromagnetic field produced by the discharge phenomenon to the physical ionization process, which constitutes them. The basic mechanism behind naturally initiated electrical discharges is the electron avalanche and an expression for its total electric field has been derived and validated in the literature. The next step in this direction is to obtain the magnetic field produced by it. An expression for the complete magnetic field, i.e., both near- and far-field components, is derived starting from Lienard–Wiechert potentials. The derived expression is validated with the numerical solution of Maxwell's equation. A simplified procedure to extend avalanche results for practical discharges is demonstrated. Close agreement is obtained between the estimated results and measured results reported in the literature.

Optimization of the Creation of a Training Set for the Calibration of a Model Reproducing the Vibration Behavior of an Overhead Line Conductor

One of the applications that machine learning can offer to the world of Engineering and Fluid Mechanics in particular is the calibration of models making it possible to approximate the representation of a particular phenomenon. Indeed, the computational cost generated by some fluid mechanics models pushes scientists to use other models close to the original models but less computationally intensive in order to facilitate their handling. Among the different approaches used: machine learning coupled with some optimization methods and algorithms in order to reduce the computation cost induced. This paper proposes a new framework called OPTI-ENS: a new flexible, optimized and improved method, to calibrate a physical model, called the wake oscillator (WO), which simulates the vibratory behaviors of overhead line conductors. An approximation of a heavy and complex model called the strip theory (ST) model. OPTI-ENS is composed of an ensemble machine learning algorithm (ENS) and an optimization algorithm of the WO model so that the WO model can generate the adequate training data as input to the ENS model. ENS model will therefore take as input the data from the WO model and output the data from the ST model. As a benchmark, a series of Machine learning models have been implemented and tested. The OPTI-ENS algorithm was retained with a best Coefficient of determination (R2 Score) of almost 0.7 and a Root mean square error (RMSE) of 7.57e-09. In addition, this model is approximately 170 times faster (in terms of calculation time) than an ENS model without optimization of the generation of training data by the WO model. This type of approach therefore makes it possible to calibrate the WO model so that simulations of the behavior of overhead line conductors are carried out only with the WO model.

Assessing the Superhydrophobic Performance of Laser Micropatterned Aluminium Overhead Line Conductor Material

Overhead electric supply lines are subject to water and ice accumulation, causing noise and weight increase, and leading to faults or failures. In this research, micro-textures were laser-ablated on aluminium substrates representative of overhead line conductors to achieve superhydrophobic properties. Samples were then subjected to a range of tests to measure the resilience and durability of such surfaces to conditions experienced by overhead line conductors. Tests to examine thermal ageing, thermal cycling, UV exposure, long term ambient outdoor environment exposure, and corona exposure testing were conducted and the evolution of surface superhydrophobicity was quantified. A high degree of resilience was observed for most of the testing. The feasibility of manufacturing upscale is discussed in addition to optimising test methods.

Experimental verification of the potential of superhydrophobic surfaces in reducing audible noise on HVAC overhead line conductors

Overhead line conductors can generate audible noise across a wide frequency spectrum as a result of elevated electric fields at the conductor surface. Such fields are enhanced by the presence of surface defects, insects, water drops and pollution. Within this paper, the impact of a superhydrophobic coating on the audible noise produced by an overhead line conductor is examined. Noise levels from a conductor coated with a superhydrophobic coating were compared to those from a bare conductor in a semi-anechoic chamber. The conductors were energised at voltages to provide surface electric fields ranging from 6 kV/cm to 21 kV/cm (rms). With a continuous water spray system depositing droplets on the conductor surface, the frequency domain sound pressure level, overall sound pressure levels and corona discharge magnitude were measured. It is demonstrated that the use of a superhydrophobic coating reduced audible noise levels and corona discharge magnitude, especially at electric fields above 14 kV/cm. The image analysis suggests that the water drop size distribution and the position of surface droplets on the conductor circumference play an important role in the magnitude of audible noise.

Resilient Operation of Electric Power Distribution Grids Under Progressive Wildfires

Wildfires have been growingly recognized as a prominent threat in regions with high temperatures during the summer. Power distribution systems, especially those passing through forest regions, are exposed and highly vulnerable to wildfires. This article provides a general formulation to enhance the operational resilience of power distribution networks equipped with renewable energy resources, e.g., wind and solar energy, micro turbines as well as energy storage systems when exposed to progressive wildfires. The wildfire incident is characterized comprehensively and the dynamic heat balance equations of power distribution branches are used to model the impacts of wildfires on overhead line conductors. A mixed-integer quadratic optimization formulation is applied to optimally operate and coordinate all local energy resources to reduce load outages and enhance the system resilience. The applied framework is evaluated on the IEEE 33-node test system. Comprehensive sensitivity analyses are conducted to assess the efficacy of the applied framework, where the numerical results reveal the resilient operation of power distribution networks in the face of wildfire emergencies.

Opti-Ens: A New Approach for the Calibration of an Overhead Line Conductors Behaviors’ Simulation Model

Opti-Ens: A New Approach for the Calibration of an Overhead Line Conductors Behaviors’ Simulation Model

STUDY OF THE INFLUENCE OF DISTANCE RELAY SETTING ON AIR LINE HIGH VOLTAGE 150 KV AGAINST HVCRC WIRE 1x310 mm² and ACCC 1x310 mm²

The faults Overhead line is generally caused by short circuit, overload, lightning surge, and tree. Distance relay is one of the protection equipments over the overhead line, and as the main protection by measuring fault impedance magnitude and comparing it to intended impedance. Distance relay setting has wide working area ranging from zone-1, zone-2, and zone-3. The setting must be adjusted when the equipment replacement exists. The replacement of overhead line conductor wire of ACSR 1 x 240 mm² into HVCRC 1 x 310 mm² and ACCC 1 x 310 mm² causing the necessity of re-setting adjustment in purpose of obtaining the appropriate one. This thesis is done by quantitative method which needs parameters in term of number. According to the calculation, the setting is obtained that zone-1 = 41,29257 Ω by t1 = instantaneous, zone-2 = 58,82457 Ω by t2 = 0,8 second, and zone-3 = 69,34377 Ω by t3 = 1,6 second.

Proof of Concept: Calibration of an Overhead Line Conductors’ Movements Simulation Model Using Ensemble-Based Machine Learning Model

Proof of Concept: Calibration of an Overhead Line Conductors’ Movements Simulation Model Using Ensemble-Based Machine Learning Model

Investigation of the dynamic rating of tubular busbars in substations

In recent years, Austrian Power Grid AG (APG) has successfully introduced dynamic line rating for the weather-dependent determination of the current-carrying capacity on various overhead lines. The higher current loading of overhead lines also increases the current loading in substations. In some cases busbars appear to be the new limiting element. As weather-dependent operation of tubular busbars is not yet in practice, a physical model working in a similar way as dynamic rating for overhead lines has been developed and evaluated. Due to the significantly larger surface area of tubular busbars compared to conductors of overhead lines, radiation as well as absorption and convection have a greater influence on the current-carrying capacity of tubular busbars than of conductors of overhead lines. Calculations of the current-carrying capacity of a tubular busbar based on the weather data over one year show that the current-carrying capacity can be regularly increased by several ten percentage points. In the near future, dynamic rating will be used for tubular busbars at APG in network operation to be able to significantly increase the current-carrying capacity of busbars in suitable ambient conditions.

Real-Time Dynamic Thermal Rating Method to Uprate the Ampacity of Overhead Transmission Lines: A Case Study

Traditionally, Static Thermal Rating (STR) calculates current carrying capacity based on “Worst case weather conditions”, which is used by most of the utilities around the world including Sri Lanka. Assumptions made in the STR calculations may reduce the actual line capacity whenever real weather conditions are less stressful. However, the smart-grid technology based Real Time dynamic Thermal Rating (RTTR) allows to utilize the overhead line conductors by increasing the current carrying capacity of the line based on real time weather data. The identification of critical span to ensure the minimum electrical clearance is the major consideration to ensure the safety of the people and equipment when applying RTTR method. This paper presents a method to introduce real time thermal rating to overhead transmission lines in Sri Lanka. Current rating of lines is calculated using real time weather data. In here, the selected line sections have been analysed using PLSCADD software with RTTR design. This novel methodology can be used by system operators to analyse weather based current ratings for the transmission network in future.