Overhead Lines Research Articles

Inspection Route Optimization of Unmanned Aerial Vehicle in the Presence of Electrical Field around the Overhead Line

Planning of unmanned aerial vehicle (UAV) route is vital for quality of the image acquisition and the safety of UAVs in the inspection of overhead lines (OHLs). However, the influence of the electrical field generated by OHLs on the UAV inspection route was not taken into consideration in previous efforts. In this paper, an optimal route planning method is proposed to avoid UAVs flying too close to OHLs. The results in simulation shows that the UAV keep safe distance with the OHLs.

Partial Discharge Detection Method for Distribution Network Based on Feature Engineering

Partial discharge phenomenon of overhead lines in distribution network is usually caused by the concentration of local electric field inside or on the surface of electrical equipment. According to partial discharge problem, based on the characteristics of the project the use of a machine learning is proposed for distribution network overhead line partial discharge detection model, first using the characteristics of engineering to extract the signal characteristics of different sides characterization, then respectively using K neighbor algorithm and back propagation algorithm, support vector machine (SVM) classification algorithm test. Experimental results show that when machine learning algorithm is used to classify time domain characteristic signals based on the feature engineering selected in this paper, k-nearest Neighbor algorithm has better classification and recognition effect than back propagation algorithm and support vector machine algorithm, with accuracy rate of 97.20%, recall rate of 96.30% and F value of 96.73%. In the frequency domain feature recognition and classification, the k-nearest Neighbor algorithm has 98.95% accuracy, 99.42% recall rate and 97.61% F value. Compared with the back propagation algorithm and support vector machine algorithm, the K-nearest Neighbor algorithm has the highest detection accuracy in the frequency domain feature detection of partial discharge on overhead lines of distribution network.

Effect of Overhead Line Broken Strand Fault on Axial Temperature Decay Distance Under Natural Convection

The broken strand fault of overhead transmission lines will cause a local temperature rise. The temperature extreme value point will decay to the normal area, affecting the operation of adjacent lines. In order to study the relationship between the temperature decay distance, the number of broken strands, and the load current of overhead lines under natural convection, a type LGJ-240/30 line is selected as the test object. Destructive thermal cycling tests are performed in the laboratory. The temperature distribution of the outer surface of the line at the fault area is obtained. Based on the theory of heat transfer, the definition of axial temperature decay distance is proposed, and the relationship between the defined distance and each factor is analyzed. The results indicate that axial temperature decay distance is only negatively related to the load current but not to the number of broken strands. This conclusion provides a theoretical reference for fault identification and maintenance of overhead lines.

Indirect weather‐based approaches for increasing power transfer capabilities of electrical transmission networks

AbstractDynamic line rating (DLR) systems are recognized as a cost‐effective and socially accepted asset for relieving network congestion and uprating existing transmission systems, based upon accessing additional weather‐dependent capacity of overhead lines. Although direct and indirect DLR methods are available, utilization of indirect weather‐based approaches, that is, sensors are not installed on the conductor, are of increasing interest due to fast installation times, that is, no requirement for line outages and lower capital costs, with achievable potential for wide‐area implementation. An extensive review is presented on the components and requirements of such systems, including weather stations, forecasting models, downscaling and DLR calculations, overhead line and conductor thermal models, and communication platforms. In addition, the features of practical instances of these systems are briefly reviewed. Moreover, a systematic approach is introduced for statistical evaluation of the high‐level DLR potential across an entire region, as well as an assessment of the line‐level DLR ampacities within an electrical grid, based on (weather forecasting) reanalysis data. The proposed methodology can disclose available additional capacity as part of early‐stage planning for wide‐area DLR systems. The island of Ireland and the 110 kV network of the Republic of Ireland (ROI) power system are considered as the study cases, with comparison made against seasonal static ratings and ambient temperature adjusted line rating methods.This article is categorized under: Energy and Power Systems > Energy Infrastructure Climate and Environment > Net Zero Planning and Decarbonization

Exact Expressions for Lightning Electromagnetic Fields: Application to the Rusck Field-to-Transmission Line Coupling Model

An exact analytical expression for the electric field of the return stroke as excited by a propagating step current source is derived in this paper. This expression could be advantageously used to evaluate the disturbances caused by lightning on overhead lines. There are three equivalent procedures to evaluate the voltages induced by lightning on power lines, namely, the Agrawal–Price–Gurbaxani model, the Taylor–Satterwhite–Harrison model, and the Rachidi model. In the case of a vertical return stroke channel, the coupling model developed by Rusck becomes identical to these three coupling models. Due to its simplicity, the Rusck model is frequently used by engineers to study the effects of lightning on power distribution and transmission lines. In order to reduce the time involved in the electromagnetic field calculation, the Rusck model is incorporated with an analytical expression for the electromagnetic fields of the return stroke excited by a propagating step current pulse. Our research work shows that the Rusck expression can be used to calculate the peak values of lightning induced voltages to an accuracy of about 10%. However, the use of this analytical expression to calculate the time derivatives of lightning induced voltages may result in errors as large as 50%. The derived expression in this paper can be used to correct for this inaccuracy. We also provide an exact expression for the electric field at any given point in space when the propagating current is an impulse function. This expression can be combined with the convolution integral to obtain the electric field corresponding to waveforms similar to measured return stroke currents.

Nonintrusive overhead‐line current detection using a vertical magnetic‐field sensor array

AbstractWith the growing infrastructure for overhead lines, the demand for overhead‐line condition‐monitoring technologies has become increasingly urgent. Traditional current transformers used to measure three‐phase currents are bulky and difficult to install, which further increases the cost of monitoring. In order to meet the current state assessment needs of transmission and distribution networks, this study uses a novel magnetic‐field sensor array to realize nonintrusive overhead‐line current detection. Based on the magnetic fields measured by magnetic‐field sensors placed on the ground under the overhead line, the proposed algorithm can be used to calculate the three‐phase current values. The proposed method does not require on‐site calibration before the field measurements are conducted. With partially known overhead‐line geometry specifications from utilities, the algorithm can optimize the overhead‐line geometry and finally achieve accurate current detection. The simulation and experimental results verify that the proposed current‐detection technique can accurately calculate the three‐phase currents of the overhead line with only three three‐axis magnetic‐field sensors.

Research on the Effect of an Air-Blown Interrupting Gap to Reduce the Rate of Lightning Tripping

The air-blown interrupting gap protection method is a self-energy interrupting method based on the concept of suppressing arc building by frequency continuation. In order to verify the effect of an air-blown interrupting gap to reduce the rate of line lightning tripping, in this paper, the protection principle of the air-blown interrupter gap is first described, and the action process simulated by COMSOL Multiphysics simulation software. Next, a frequency renewal test circuit is built for the test. Then, an arc-building rate calculation model and a lightning trip rate calculation model under the condition of an air-blown interrupting gap are established, and, finally, a 10 kV overhead line in Yunnan is selected for the verification of the calculation example. The results show the following: a gas blowing arc gap can be effectively extinguished in about 2.5 ms frequency arc and with no re-ignition phenomenon. Before and after the installation of the gas blowing arc gap line, the arc rate changed from 37.27% to 4.1%, respectively, and the lightning trip rate changed from 8.64 times/(40 thunderstorm days—100 km) to 0.337 times/(40 thunderstorm days—100 km), respectively. The decline rate was more than 95%, and in actual operation, it reduced the lightning trip rate enough to achieve good results.

On the Role of Shield Wires in Mitigating Lightning-Induced Overvoltages in Overhead Lines - Part II: Simulation Results for Practical Configurations

In the companion Part I, the theory relevant to the role of shield wires in mitigating lightning-induced overvoltages in overhead lines has been analyzed and clarified. A more consistent meaning has been assigned to the concept of Shielding Factor by introducing two innovations compared to the current literature: the first one concerning the distinction between <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">internal</i> and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">external</i> parameters, and the other one concerning the point along the line where to assess the mitigation effect. Thanks to this new approach, uncertainties seen in the literature have been sorted out, and the Shielding Factor has been shown to be a parameter which can be precisely quantified. However, our new contribution was applied to a schematic (unrealistic) configuration: a line with a shield wire grounded at only one point. This Part II is precisely devoted to confirming the results obtained in Part I, by applying the proposed approach to more realistic and practical line configurations, namely a line with multi-grounded shield wire, and a line equipped with laterals too.

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.

On the Role of Shield Wires in Mitigating Lightning-Induced Overvoltages in Overhead Lines - Part I: A Critical Review and a New Analysis

The ability of shield wires installed in overhead lines to mitigate lightning-induced overvoltages has been extensively investigated. Unfortunately, these studies came to different results, sometimes contradicting each other: some authors found that shield wires produce a significant overvoltage reduction, while others found the reduction negligible; conflicting results also pertain to the role played by the various parameters involved, such as the relative height of the shield wire(s) compared to the phase conductors. This paper aims to clarify this topic. The paper is organized in two parts: Part I, which starts from the analysis of the theory behind the mitigation effect, is devoted to establishing a more solid base to the topic. Two fundamental improvements are proposed. The first one is the distinction between <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">internal</i> and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">external</i> of the parameters involved: current literature makes an indiscriminate grouping of all of them; the second one is concerned with the point along the line where the mitigation effect needs to be assessed. Thanks to this new approach, we show that this effect can be precisely quantified. The analysis in this Part I is limited to the basic case of a single grounding point of the shield wire, which represents an unrealistic case. Part II is devoted to completing the study, by applying the proposed approach to more realistic and practical cases.

A Thévenin-Type Version of the Extended Modal-Domain Model for Lightning-Induced Voltage Calculations

In this paper, a new procedure is proposed for determining the external current sources required for evaluating lightning-induced voltages on overhead lines with the extended-modal domain (EMD) model. Unlike the original model, in which the calculation of the inducing current sources depends on the fitting of the characteristic admittance of the line, in the proposed procedure this calculation is performed using the characteristic impedance of the line. This significantly simplifies the use of the EMD model because now all parameters can be readily obtained from the built-in fitting tool that is usually available in electromagnetic transient programs to derive the parameters of Marti’s transmission line model. The validity of the proposed procedure is demonstrated through examples that indicate its accuracy in the calculation of lightning-induced voltages on overhead distribution lines terminated with different types of loads, including transformers and surge arresters, and multiple grounding points.

Lightning Protection With a Differentiated Configuration of Arresters in a Distribution Network

When concerning the installation and operation costs, it is always desirable to protect an overhead distribution network with a limited quantity of surge arresters (SAs). This paper presents a novel procedure for designing differentiated protection against lightning, by identifying appropriate positions for those SAs on the overhead line. Rather than the traditional flashover rate of a whole line, indices in terms of flashover numbers at individual poles and associated with possible stroke locations are introduced in this paper. Based on these flashover indices, a differentiated configuration of SAs can be identified using a selection strategy. After several rounds of selection, a differentiated SA protection scheme can be obtained, given by a pre-set quantity of SAs. In this procedure, a simplified probability-based approach is proposed to determine the flashover indices. By comparing the traditional Monte Carlo method, this approach can achieve a 10-fold increase in computational efficiency with reasonable accuracy. Two different selection strategies are introduced in this paper. Compared with the selection strategy using the flashover indices at individual poles, the selection strategy based on a group of poles is recommended because it yields a configuration with better lightning performance with the same quantity of SAs. This design procedure is applied to practical distribution networks with a shield wire and nearby structures. The influence of grounding impedance, a shield wire, and nearby structures is addressed. Finally, a generalized step-by-step procedure is provided to assist in a differentiated SA protection design.

Research on adaptive active power coordinated control strategy of Zhangbei Flexible DC Grid project

Zhangbei Flexible DC Grid project with grid characteristics is different from the previous multi-terminal flexible DC project. Zhangbei Flexible DC Grid project uses a DC breaker (DCB) to isolate DC line faults. Limited by the current domestic research and development level of high-voltage DCB, it does not have overload operation capacity. Against this problem that the overload of DCB endangers the safety of equipment and system after a permanent fault of the DC overhead line, the adaptive power coordination control strategy is proposed when the sending end converter station is connected to the new energy station and the AC grid respectively, The feasibility and rationality of this strategy are verified by the RTDS real-time simulation system of Zhangbei Flexible DC Grid project and provides technical reference for the long-term upgrading and transformation of Zhangbei Flexible DC Grid project.

On the Accuracy of Correlation Estimator Based Fault Location Methods in Transmission Lines via Polynomial Chaos and Regression Analysis

The electromagnetic time reversal (EMTR) method has recently shown a novel advantage in locating faults along transmission lines. Under the ideal condition for EMTR, the key parameters in the transmission line between the direct and reversed phases are assumed to be identical. Thus, the fault position can be pinpointed via the cross-correlation matching theory. However, due to natural and geographical causes, the parameters vary along the line; therefore, accurately obtaining the parameters is difficult. In this article, we first investigate the impact of uncertain parameters on the performance of EMTR-based fault location methods. It has been observed that the performance is insensitive to the variation of the parameters in the lossless case of transmission lines. But in the case of the overhead line above the lossy ground, a significant error in fault location is witnessed. So, under parameter uncertainty, a novel approach to finding the confidence fault interval is proposed, based on utilizing the polynomial chaos and regression analysis. A simulation case with uncertain parameters for different scenarios is presented to validate the performance of the proposed approach.

A Novel Energy Harvesting Method for Online Monitoring Sensors in HVdc Overhead Line

Due to the lack of alternating electric fields and alternating magnetic fields in HVdc transmission system, there has been no sustainable and stable energy harvesting method compatible with them up to now, hindering the application of HVdc sensors. In this letter, we proposed a novel dc energy harvesting method using corona current, and an energy harvesting circuit is constituted with space ion flow generated by dc corona. The feasibility of the proposed method is increased by adding an artificial corona electrode and placing the load before the corona electrode. In addition, it can flexibly operate at any position in an HVdc transmission system according to actual demand. Then the output power is further maximized by adopting a capacitor with high working voltages. The detailed measurement results based on the experimental system validate the effectiveness of the proposed method, with a stable output power as high as 10.15 mW in a dc system of 22 kV. A detailed discussion of the overall performance is finally carried out.

Prediction of Intra-Period Minimum Thermal Rating of Overhead Conductors

Regarding power system dispatch decisions, the current-carrying limits of transmission lines in each dispatch period in the look-ahead time horizon should be represented by the intra-period minimum thermal rating (IMTR) for the sake of security. In this paper, the IMTR prediction issue of the overhead conductor is raised, and the predictability of the IMTR is investigated. Specifically, for the overhead conductor, the distribution and correlation characteristics of the IMTR and its corresponding meteorological elements are analyzed based on the measured meteorological data around an overhead conductor. On this basis, the quantile regression neural network (QRNN) and copula model are employed to make probability predictions on IMTRs of multiple periods in the prediction time horizon considering the temporal correlation of the IMTR. Also, the influences of the time period length, prediction time horizon, and the consideration of the temporal correlation of the IMTR on prediction results are analyzed. The work presented in this paper reveals the predictability of the IMTR, which is of significance to guide the prediction of the IMTR of the overhead conductor. Thus, it can help operators safely exploit the current-carrying capability of the overhead line.

High Voltage Composite Line Post Insulators Combined Load Limits

Overhead line design utilizing composite line post insulators requires an understanding of the insulator mechanical load carrying capabilities in multiple simultaneous directions. This paper covers the development of combined loading curves and offers guidance on the presentation of such curves so that informed decisions regarding the selection of composite line posts can be made.

On the Transient Analysis of Towers: A Revised Theory Based on Sommerfeld-Goubau Wave

Accurate tower models for fast transients are essential for the insulation design of overhead lines, since lightning may produce temporary or even permanent faults. The aim of the work is to further investigate the nature of the electromagnetic modes supported by the tower, and on the applicability of the transmission line approaches, originally inspired by the model proposed by Jordan. The influence of a perfectly conducting ground plane and of losses distributed along the tower will be discussed. A new approach, based on the Sommerfeld-Goubau wave formalism, is proposed to give physical insights on the propagation phenomenon along transmission line towers.

Grounding fault location method of overhead line based on dual-axis magnetic field trajectory

To address the challenges in fault location in distribution networks, the distribution of magnetic field under overhead line and its relationship with three-phase currents are explored in this paper. At the same time, considering the influence of sensor installation position, line sag and galloping on magnetic field, a grounding fault location method of an overhead line based on dual-axis magnetic field trajectory is proposed. The analytical expressions of the magnetic field on the x-axis and y-axis under the overhead line are obtained by least squares fitting. The Lissajous figure synthesized by dual-axis is then compared with the general equation of an ellipse, and the characteristic quantity expression characterizing the magnetic field trajectory structure is obtained. Finally, a fault location criterion is constructed using the difference of the characteristic quantities of the ellipses synthesized by x-axis and y-axis magnetic fields upstream and downstream of the fault point, i.e., the difference of the length of the major axis and the minor axis, and the sign for the ratio of the cosine value of the inclination angle. Compared with other location methods based on electrical quantity, the principle of this method is simpler and it can locate faults more quickly and accurately. A large number of simulation results show that the proposed method is suitable for different types of fault conditions.

An Improved Phase-Disposition Pulse Width Modulation Method for Hybrid Modular Multilevel Converter

The hybrid modular multilevel converter (MMC) consisting of half-bridge submodules (HBSMs) and full-bridge submodules (FBSMs) is a promising solution for overhead lines high-voltage direct current systems (HVDC) due to the advantages of direct current short circuit fault ride-through (DC-FRT) capability. This paper proposes an improved phase-disposition pulse width modulation (PDPWM) method for the hybrid modular multilevel converter. The number of carriers can be reduced from 3N (N is the number of submodules in each arm) to 6. The theoretical harmonic analysis of the improved PDPWM method for hybrid MMC is performed by using double Fourier integral analysis. The influence of three carrier displacement angles between HBSMs and FBSMs in the upper and lower arms on harmonic characteristics is investigated. The output voltage harmonics minimization PDPWM scheme and circulating current harmonics cancellation PDPWM scheme can be achieved by selecting the optimum carrier displacement angles, respectively. The proposed method for hybrid MMC is verified by the simulation and experimental results.