Overhead Conductors Research Articles

An Equivalent Heat Transfer Model Instead of Wind Speed Measuring for Dynamic Thermal Rating of Transmission Lines

With the increase in electricity demand, the ampacity calculation based on the dynamic thermal rating (DTR) technology is increasingly significant for assessing and improving the power transfer capacity of the existing overhead conductors. However, the DTR models now available present some inadequacies in measurement techniques related to wind speed. Therefore, it is essential to propose a new model instead of wind speed measuring in DTR technology. In this paper, the influence analysis of various weather parameters on the conductor ampacity is carried out by using the real weather data. Based on the analysis, it is confirmed that the impact of wind speed is significant, especially in the case of the low wind speed. Moreover, an equivalent heat transfer (EHT) model for DTR technology is proposed instead of wind speed measuring. For this EHT model, the calculation of conductor ampacity is realized through investigating the correlation of heat losses between the heating aluminum (Al) ball and conductor. Finally, combined with the finite element method (FEM), the EHT model proposed in this paper is verified by the Institute of Electrical and Electronic Engineers (IEEE) standard. The results indicate that the error of the EHT model is less than 6% when employing the steady thermal behavior of the Al ball to calculate the ampacity. The EHT model is useful in the real-time thermal rating of overhead conductors. It can increase the utilization of overhead conductors while also avoiding the limitation of the existing measurement techniques related to wind speed.

Model of own harmonic conductor oscillations for tasks of monitoring the status of airline power transmission lines

The article substantiates the relevance of the inspection of overhead power lines by determining the mechanical loads of the conductors. The conductor sways under the action of external loads and variable internal mechanical loads. The conductor behaves in span like a pendulum. Using the inclinometric method, it is possible to determine the deviations of the conductor in space from its equilibrium position. Having restored the geometry of the conductor in the span of an overhead power line, mechanical loads can be determined. A model of the harmonic oscillations of the conductor in flight is derived to assess the mechanical loads of the conductor overhead power lines. This mathematical model is based on mathematical models of a flexible thread and a model of a physical pendulum. A conductor is a physical pendulum, where the conductor acts as the body, and in the role of the fixed axis of rotation, a straight line passing through the suspension points of the conductor. The developed model allows you to determine the arrow of its sag from the period of oscillations of the conductor in the span. The article considers algorithms for calculating the conductor sag arrows for two cases: the conductor suspension points are at the same height; conductor suspension points are at different heights. A theoretical calculation is given for a model of a span overhead power line with an estimate of the sensitivity of the developed model and its error in determining the sag of the conductor. Using the arrow of the conductor sag, you can restore its geometry, and hence the mechanical load of the conductor. Therefore, knowing the initial geometric parameters of the span of the overhead power line and the current period of the conductor’s oscillations, it is possible to examine its current state.

Closed-Form Expressions for the Analysis of Wave Propagation in Overhead Distribution Lines

The calculation of the influence of the imperfect earth on overhead conductors is an important issue in power system analysis. Rigorous solutions contain infinite integrals; thus, due to their complex form, different simplified closed-form expressions have been proposed in the literature. This paper presents a detailed analysis of the effect of different closed-form expressions on the investigation of the wave propagation of distribution overhead lines (OHLs). A sensitivity analysis is applied to determine the most important properties influencing the calculation of the OHL parameters. The accuracy of several closed-form earth impedance models is evaluated as well as the influence of the displacement current and imperfect earth on the shunt admittance, which are further employed in the calculation of the propagation characteristics of OHLs. The frequency-dependence of the soil electrical properties, as well as the application of different modal decomposition algorithms, are also investigated. Finally, results on the basis of frequency-domain signal scans and time-domain electromagnetic transient responses are also discussed.

Experimental device for fretting fatigue tests in 6201 aluminum alloy wires from overhead conductors

– This article presents the design, production and testing of an experimental device that seeks to evaluate fretting fatigue of wires taken from conductors used in energy transmission lines. The fretting device has three independent actuators that allow tests to be carried out under controlled load (or displacement). Thus, the effect of relevant parameters to the fretting fatigue process (such as normal, tangential and bulk forces, wear level, and wear surface morphology) can be studied. To evaluate the device performance, tests were carried out on 6201 aluminum alloy wires, considering two different contact normal forces, P. Results showed that, for lives greater than 106 cycles, the increase of P from 250 to 500 N produced a substantial reduction on fatigue strength when compared to tests of smooth wire specimens. The SEM images and EDS analyses after the fretting fatigue test demonstrate that the wire-wire marks generated by the device show all the characteristics found in wires of internal layers of overhead conductors fractured by fatigue under fretting conditions.

Experimental investigation and modeling of temperature-dependent flexural strength of hybrid composite rods

The flexural behavior of hybrid composite rods used in high capacity low sag overhead conductors at elevated temperatures is experimentally investigated. Dynamic mechanical analysis (DMA) is carried out on pultruded carbon/glass/epoxy specimens, followed by three-point bending experiments at different elevated temperatures. The failure mechanisms are examined by using macro/micro images taken from the failed specimens. The results show that flexural properties such as strength and modulus decrease as temperature increases. The failure mode of hybrid composite rods is also found highly temperature-dependent. A new simple model is developed based on DMA data to predict the flexural strength of high-performance polymeric composites at different temperatures. The predictions are in good agreement with the experimental data.

Fatigue life estimation of an all aluminium alloy 1055 MCM conductor for different mean stresses using an artificial neural network

This study is aimed to employ artificial neural networks (ANNs) to predict the fatigue lives of the All Aluminium Alloy Conductor (AAAC) 1055 MCM overhead conductor, considering different values of stretching load (mean stress). For ANN training, three Wöhler (S-N) curves are generated for a conductor/suspension clamp assembly. Twenty-seven fatigue tests are carried out with stretching loads, related to everyday stress (EDS) of 17%, 20% and 25.6% of the conductor’s ultimate tensile strength (UTS), corresponding to mean stresses of 48 MPa, 54 MPa and 73 MPa, respectively. Constant life diagrams (at 105, 106, 107 number of loading cycles) for the AAAC 1055 MCM overhead conductor are built using the ANN. The results confirm that the ANN can accurately predict the fatigue lives of an overhead conductor for various levels of mean stress also when limited experimental data is used for training.

Development of controlled heating for fatigue test in overhead conductors at high temperature

The objective of this work was to evaluate the influence of elevated temperature on the fatigue resistance of an all aluminum conductor. A dispositive was developed to reach temperatures like those undergone by high-voltage electrical conductors during their useful life. This dispositive is based on the classical temperature control of proportional integral derivative. In this work, the dispositive used for heating the conductor/suspension clamp assembly and the methodology used to execute fatigue tests at 75 °C of one “All Aluminum Conductor” (Orchid) were presented in detail. There is a remarkable and sensible difference between S and N curves for tests carried out at room temperature and those accomplished at 75 °C, which may indicate degradation of all aluminum conductors when tested under fatigue conditions at higher temperatures.

Wind: generating power and cooling the power lines

Abstract. The electric power that can be transmitted via high-voltage transmission lines is limited by the Joule heating of the conductors. In the case of coastal wind farms, the wind that produces power simultaneously contributes to the cooling of high-voltage overhead conductors. Ideally this would allow for increased power transmission or decreased dimensions and cost of the conductor wires. In this study we investigate how well the wind speed in coastal wind farms is correlated with wind along a 75 km long 330 kW power line towards inland. It is found that correlations between wind speed in coastal wind farms at turbine height and conductor-level (10 m) are remarkably lower (R=0.39–0.64) than between wind farms at distances up to 100 km from each other (R=0.76–0.97). Dense mixed forest surrounding the power line reduces both local wind speed and the correlations with coastal higher-level wind, thus making the cooling effect less reliable.

Numerical Algorithms for Calculating Temperature, Layered Stress, and Critical Current of Overhead Conductors

Accurate calculation of temperature, stress, sag, and critical current (corresponding to critical temperature) of operational overhead conductors is important for ensuring the strength and sag safety of overhead lines. Based on 2D steady-state heat transfer equations, this article studies the temperature fields of the cross section of typical electrified conductors and establishes numerical simulation methods for calculating the layered stress, sag, and critical temperature. Using the algorithm, the relationship between the critical temperature and characteristics of conductors (e.g., the sag and tensile force) is studied. The results are verified by a comparison with the test results for heat-resistant aluminum alloy conductors JNRLH1/G1A-400/65 and JNRLH1/G1A-630/55. Finally, the paper studies the relationship between the critical temperature of the conductor and its most sensitive factors.

Preparation and Characterization of Polyurethane/Carbon/Organoclay Composite for Coating of Aluminum Conductor Overhead Lines

Preparation and Characterization of Polyurethane/Carbon/Organoclay Composite for Coating of Aluminum Conductor Overhead Lines

Life prediction in multiaxial high cycle fretting fatigue

The aim of this work is to show that multiaxial fatigue modeling can be successfully adapted to estimate crack initiation life of mechanical assemblies under fretting conditions. The paper is divided into two parts. In Part I, the focus is on the study of size and gradient effects but considering the influence of incorporating fretting wear on the life estimation procedure. New data for a Ti-6Al-4V cylindrical on plane contact configuration were produced to assess the analyses. It is shown that critical plane criteria, coupled with a critical distance which varies with life, are capable to provide accurate estimates of fretting fatigue life in the medium high cycle regime. The inclusion of wear in the modeling did not significantly improved the life estimates but increased a lot the computational cost. In Part II, the paper extended this life estimation approach to the contact of wires taken from overhead conductors. Fretting fatigue data of AA1350-H19 wires and new tests on the more resistant AA6201-T81 corroborated the successful use of the life methodology to other materials and applications.

Uncertainties in the Testing of the Coefficient of Thermal Expansion of Overhead Conductors

Overhead lines can be replaced by high temperature low sag (HTLS) conductors in order to increase their capacity. The coefficients of thermal expansion (CTE) of the HTLS conductors are lower than the CTE of conventional conductors. The utilities and conductor manufacturers usually carry out the verification of the CTE of the overhead conductors in an actual size span. The verification is based on the observation of the change of the conductor length as a result of the conductor temperature change. This process is influenced by the coefficient of thermal expansion to be verified. However, there are other factors that also affect it. This paper analyzes the effect of some of the uncertainty sources in the testing of the coefficient of thermal expansion of the overhead conductors. Firstly, the thermal expansion process is described and the uncertainty sources related to the conductor and the line section are identified. Then, the uncertainty sources and their effect on the CTE testing are quantified.

A Practical Health Index for Overhead Conductors: Experience From Australian Distribution Networks

Quantifying the health condition of bare overhead conductors is an enabler for an effective condition-based risk management of the power distribution network. This paper presents a health index calculation methodology derived for the bare overhead conductors in the Australian power distribution networks. Proposed methodology is based on a customizable weighted sum algorithm and uses a set of input parameters, which are readily available for the asset managers. Industry experts’ experience and conductor failure statistics are used for determining the most significant input parameters and corresponding numerical values. Finally, a methodology for correlating the conductor health index with the probability of failure is demonstrated on a set of copper and aluminum conductors. The methodologies developed in this paper could improve the accuracy and effectiveness of condition monitoring and asset management of bare overhead conductors in the power distribution networks.

Non-contact Dynamic Capacity-Increasing of Overhead Conductor Based on Cooling Tester (CT)

The traditional dynamic capacity-increasing technology of overhead conductors needs to monitor the operation state of conductors (temperature, sag, etc.), and the relevant sensors are usually installed directly on the surface of conductors. The installation cost is high, and the operating maintenance is complicated. In this paper, a non-contact dynamic capacity-increasing method for overhead conductors based on CT is proposed. Firstly, the theory of the non-contact dynamic capacity-increasing method for conductors is introduced, and a cooling testing device is designed according to the theory. Then, the cooling index is defined to represent the cooling capacity of the object, and the corresponding cooling indexes for the conductors and the CT are calculated based on the steady-state thermal balance equation. By establishing a cooling correlation model for the conductors and the CT, the calculation for the dynamic ampacity of the conductors can be obtained. Finally, the cooling conditions of cooling testing device at different ambient temperatures and wind speeds are calculated through the finite element simulation method. Combined with the dynamic capacityincreasing method proposed in this paper, the corresponding ampacity value are obtained, and the effect of capacity increase is analyzed. The results show that the non-contact dynamic capacity-increasing method based on the CT has obvious effect in capacity-increasing compared with the static ampacity.

Modeling Multi-Layer OHL Conductors Undergoing Wind-Induced Motion

Utilities aim to improve asset management strategies and enhance the utilization of their assets through low-risk reliable practices. Overhead lines and conductor designs have been evolving to increase systems' power capacity and mechanical integrity, which have also extended asset lifetimes. Nevertheless, it is still challenging to predict a conductor's fatigue stresses due to wind-induced vibrations that can help to estimate its useful life. A finite element model (FEM) has been established in COMSOL to study the free and forced wind-induced vibrations and the resultant fatigue on single multi-layer conductors considering their complex round and trapezoidal stranding patterns. The FEM analysis is based on multi-physics accounting for the conductor's thermal and mechanical aspects as well as material and geometry properties. Consequently, the fatigue is quantified for both inter-layer and inter-wire interactions. The simulations show that free conductor vibrations are dictated by the conductor materials and tension distribution between the core and aluminum strands. The bigger the difference between the material properties of the core and aluminum, the lesser the conductor vibrations, especially when the aluminum becomes slack. In fact, a conductor equipped with carbon core (ACCC), has the best vibration resistance among other conductors with steel core (ACSR) and homogeneous (AAACs). Forced vibration simulations identified non-linear fatigue stresses for round and trapezoidal designs, which is more pronounced in larger conductor sizes. Larger trapezoidal ACSRs exhibit better fatigue resistance compared to smaller and round stranded AAACs.

Fatigue Analysis of Hinged Support Structures for Overhead Conductor Rails based on Power Density Theory

Fatigue Analysis of Hinged Support Structures for Overhead Conductor Rails based on Power Density Theory

Fault Detection on Insulated Overhead Conductors Based on DWT-LSTM and Partial Discharge

Insulated conductors can improve the stability of power transmission and reduce the construction space compared with traditional bare conductors. Therefore, insulated conductors are used more and more in overhead power transmission. However, a major challenge of using insulated overhead conductors (IOC) is that the ordinary protection devices are not able to detect the phase-to-ground faults and something, such as tree branch, hitting conductor events. This may cause an accident such as power failure or electrical fire and result in serious damage. In this paper, a new approach, which is based on Discrete Wavelet Transform (DWT) and Long Short Term Memory network (LSTM) for detecting of IOC fault according to partial discharge, is presented. Firstly, the original signal is denoised by DWT. Secondly, the denoised signal is decomposed and extracted features on different layers by DWT. Finally, IOC fault is detected by LSTM. This method can improve the detection accuracy of IOC fault which is tested on the ENET public data set and compared with other classification methods.

Determination the conductor sag according to the period of own harmonic oscillations

The article substantiates the relevance of the inspection of overhead power lines by determining the mechanical loads of the conductors. The conductor sways under the action of external loads and variable internal mechanical loads. The conductor behaves in span like a pendulum. A model of the harmonic oscillations of the conductor in flight is derived to assess the mechanical loads of the conductor overhead power lines. This mathematical model is based on mathematical models of a flexible thread and a model of a physical pendulum. A conductor is a physical pendulum, where the conductor acts as the body, and in the role of the fixed axis of rotation, a straight line passing through the suspension points of the conductor. The article briefly describes an algorithm for calculating the conductor sag for the case when the conductor suspension points are at the same height. The results obtained using the developed model for calculating the sag of the conductor by its period are compared with the available experimental data. Experimental equipment is described. The error of the method is estimated.

Capacity assessment for wind power integration considering transmission line electro-thermal inertia

Considering differences in planning and construction period, there may exist a mismatch of between effective wind farms capacity and dedicated transmission line ampacity. Then, conflict appears while increasing wind power integrates into main system through limited transmission utilities. Once excessive wind power integration (WPI) causes transmission overload, wind power generation is preferably curtailed with certain scheme. However, transmission conductor electro-thermal characteristic in case of wind power fluctuation makes static thermal rating inaccurate for overload confirmation. Then this study centers on analyzing WPI considering wind power curtailment scheme which allows for overhead conductor dynamic electro-thermal inertia involving various time-varying ambient factors. Accordingly, this study presents a WPI capacity assessment method, which captures the dynamic features of WPI by synchronously simulating wind power generation as well as curtailment regulation, transmission line electro-thermal behaviors and ambient changes. The sequences of wind power and ambient factors with fixed time span given in advance are approximately treated as piecewise linear functions of time and incorporated into differential-algebra equations for WPI. Performances of power curtailment and network loss are explored by taking either static or dynamic thermal rating as transmission overload standard to adjust wind farm output.

A case study of rupture in 110 kV overhead conductor repaired by full-tension splice

Rupture accidents of overhead conductors may occur due to its complex operating environment. If wires rupture happens, the overhead conductors can be repaired by full-tension splice (FTS) in practical engineering to restore the mechanical strength and ampacity required. However, with time increases, ageing will occur on the overhead conductors. There may exist potential of rupture in the repaired segment of the conductor. Once the conductor is broken, the reliability of transmission line will be seriously destroyed. Therefore, it is of great importance to investigate the rupture reason and process of conductor repaired by FTS. In this paper, a rupture accident of 110 kV overhead conductor repaired by FTS is discussed. Firstly, the fractography analysis for the conductor sample is conducted, and the rupture reason is preliminarily inferred according to the rupture feature of the sample. Then, the current density distributions in the repaired segment of new conductor and aged conductor are compared by a finite element analysis (FEA) model of electromagnetic field. Also, the reason of high temperature produced in the conductor sample during rupture process is determined. Subsequently, to analyze the relationship between temperature and equivalent plastic strain, a FEA model of structure field for the steel core of conductor is established. Finally, combined with the fractography test results and simulation results, the rupture mechanism of conductor repaired by FTS is summarized in detail. The analytical method and conclusions proposed in this paper can provide references and suggestions for the study of similar conductor rupture accident and optimization of repaired process.