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Maintenance of power transmission lines is essential for the safe and reliable operation of the power grid. The use of deep learning‐based networks to improve the performance of power line defect detection faces significant challenges, such as small target sizes, shape similarities, and occlusion issues. In response to these challenges, a transformer‐based end‐to‐end power line detection network called Power‐DETR is introduced. Initially, building upon Deformable DETR, a large pre‐trained model (Swin‐large) is utilized to increase the number of multi‐scale features, and activation checkpoint technology is applied to ensure effective training within limited memory capacity. Subsequently, a contrastive denoising training strategy is integrated to combat ambiguity and instability of the Hungarian matching algorithm during training, aiming to expedite model convergence. Additionally, a hybrid label assignment strategy combining OHEM and cost‐based ATSS is proposed to provide the model with high‐quality queries, ensuring adequate training for the decoder and enhancing encoder supervision. Experimental results substantiate the efficacy of the proposed Power‐DETR model as a novel end‐to‐end detection paradigm, surpassing both one‐stage and two‐stage detection models. Furthermore, the model demonstrates a significant 15.7% enhancement in mAP0.5 compared to the baseline. [ABSTRACT FROM AUTHOR]

Abstract Maintenance of power transmission lines is essential for the safe and reliable operation of the power grid. The use of deep learning‐based networks to improve the performance of power line defect detection faces significant challenges, such as small target sizes, shape similarities, and occlusion issues. In response to these challenges, a transformer‐based end‐to‐end power line detection network called Power‐DETR is introduced. Initially, building upon Deformable DETR, a large pre‐trained model (Swin‐large) is utilized to increase the number of multi‐scale features, and activation checkpoint technology is applied to ensure effective training within limited memory capacity. Subsequently, a contrastive denoising training strategy is integrated to combat ambiguity and instability of the Hungarian matching algorithm during training, aiming to expedite model convergence. Additionally, a hybrid label assignment strategy combining OHEM and cost‐based ATSS is proposed to provide the model with high‐quality queries, ensuring adequate training for the decoder and enhancing encoder supervision. Experimental results substantiate the efficacy of the proposed Power‐DETR model as a novel end‐to‐end detection paradigm, surpassing both one‐stage and two‐stage detection models. Furthermore, the model demonstrates a significant 15.7% enhancement in mAP0.5 compared to the baseline.

Abstract Given the complex form of distribution line faults, the accuracy of fault location using traditional artificial intelligence networks needs to be further improved. Here, a combined fault location method is proposed for a 110 kV distribution line based on the improved complete ensemble empirical mode decomposition with adaptive noise (ICEEMDAN), mantis search algorithm (MSA), and convolutional gate recurrent unit (ConvGRU). Firstly, the study used the ICEEMDAN algorithm to decompose the signals and discard the high‐frequency signals with low correlation so as to achieve the purpose of noise cancellation. Then, the study used the root mean square error (RMSE) of the ConvGRU model training as the adaptation value, optimized the internal parameters of the model using the MSA algorithm, and obtained a combined fault locating model. By using the proposed model, the effects of the fault form and transition impedance changes on the location accuracy were analysed, and the location accuracy was compared with other artificial intelligence methods. The location accuracy index showed that the proposed model had a better convergence speed of training error than the traditional model. Also, the RMSE of the localization results was reduced by 50%, with a higher fault location accuracy.

Given the complex form of distribution line faults, the accuracy of fault location using traditional artificial intelligence networks needs to be further improved. Here, a combined fault location method is proposed for a 110 kV distribution line based on the improved complete ensemble empirical mode decomposition with adaptive noise (ICEEMDAN), mantis search algorithm (MSA), and convolutional gate recurrent unit (ConvGRU). Firstly, the study used the ICEEMDAN algorithm to decompose the signals and discard the high‐frequency signals with low correlation so as to achieve the purpose of noise cancellation. Then, the study used the root mean square error (RMSE) of the ConvGRU model training as the adaptation value, optimized the internal parameters of the model using the MSA algorithm, and obtained a combined fault locating model. By using the proposed model, the effects of the fault form and transition impedance changes on the location accuracy were analysed, and the location accuracy was compared with other artificial intelligence methods. The location accuracy index showed that the proposed model had a better convergence speed of training error than the traditional model. Also, the RMSE of the localization results was reduced by 50%, with a higher fault location accuracy. [ABSTRACT FROM AUTHOR]

Abstract In this study, a long‐distance non‐contact current measurement method is proposed based on the non‐contact sensor array measurement technology, combined with a new current algorithm. The sensor array is a vertical array composed of three three‐axis magnetic field (MF) sensors that is placed on the ground plane below the measured overhead line. The proposed current algorithm can optimize the geometry of the overhead line using the spatial MF values measured by the sensor array and then the three‐phase currents can be calculated. To improve the accuracy of current measurement, the spatial MF model in the algorithm considers the influence of cable sag. It enables a more accurate coupling matrix between the measured overhead line and the sensor array to be established. Additionally, the current algorithm architecture is designed using a composite algorithm to more optimally obtain the best three‐phase current values. A scale‐down overhead‐line measurement system is developed to test the proposed current measurement method. The results show whether a cable sag exists when the three‐phase currents are approximately balanced, with errors less than 2.0%. Moreover, it can be determined whether cable sag exists when the three‐phase currents are unbalanced, with less than 3.4% errors.

In this study, a long‐distance non‐contact current measurement method is proposed based on the non‐contact sensor array measurement technology, combined with a new current algorithm. The sensor array is a vertical array composed of three three‐axis magnetic field (MF) sensors that is placed on the ground plane below the measured overhead line. The proposed current algorithm can optimize the geometry of the overhead line using the spatial MF values measured by the sensor array and then the three‐phase currents can be calculated. To improve the accuracy of current measurement, the spatial MF model in the algorithm considers the influence of cable sag. It enables a more accurate coupling matrix between the measured overhead line and the sensor array to be established. Additionally, the current algorithm architecture is designed using a composite algorithm to more optimally obtain the best three‐phase current values. A scale‐down overhead‐line measurement system is developed to test the proposed current measurement method. The results show whether a cable sag exists when the three‐phase currents are approximately balanced, with errors less than 2.0%. Moreover, it can be determined whether cable sag exists when the three‐phase currents are unbalanced, with less than 3.4% errors. [ABSTRACT FROM AUTHOR]

Abstract Existing fault localization methods for power lines are not applicable to the collector line in onshore wind farms due to the dense access of complex power supplies. Therefore, a fault localization method based on equivalent zero‐sequence injection current (ZIC) is proposed for asymmetric phase‐to‐ground faults on collector lines. Firstly, the idea of load shifting is adopted to generalize the theory of equivalent injection current (EIC) to multi‐terminal and meshed lines. Then, considering features of the zero‐sequence network of wind farms, the EIC theory on two‐terminal and multi‐terminal lines is applied to zero‐sequence networks, and thus faulty areas, faulty sub‐lines, and fault distance can be determined. Attractively, the element correlation in node impedance matrices of zero‐sequence networks is derived from the network branch‐addition process, and the numerical characteristic of matrix elements is further revealed from the particularity of wind farms, based on which root‐mean‐square (RMS) calculation of ZIC can be improved to enable the localization without phasor measurement. Verification results prove that this proposed method can accurately realize the fault localization independent of wind turbine generators with a few measurement points, and the applicability of collector lines with line branches is also considered; additionally, only voltage RMS needs to be measured.

Abstract A novel method is introduced to determine cost‐optimized active power curtailment (APC) of renewable energy sources (RES) considering weather‐dependent dynamic line rating (DLR). A new formulation of the security‐constrained optimal power flow (SC‐OPF) is developed and applied in a case study. The reduction of the required preventive APC in the (N-0) case for (N-1) secure grid operation due to the consideration of thermal inertia of overhead power lines is demonstrated. Considering thermal inertia allows relying on curative APC that is activated only after an (N-1) situation occurs. The overhead power line temperature, calculated with the temperature‐dependent power flow (TDPF), acts as a new limit for line loading and releases unused transmission reserves. The TDPF algorithm is integrated in the open‐source Python library pandapower, providing access to it to the broader community. The power system can be utilized to a greater extent, with a reduced demand for congestion management.

Existing fault localization methods for power lines are not applicable to the collector line in onshore wind farms due to the dense access of complex power supplies. Therefore, a fault localization method based on equivalent zero‐sequence injection current (ZIC) is proposed for asymmetric phase‐to‐ground faults on collector lines. Firstly, the idea of load shifting is adopted to generalize the theory of equivalent injection current (EIC) to multi‐terminal and meshed lines. Then, considering features of the zero‐sequence network of wind farms, the EIC theory on two‐terminal and multi‐terminal lines is applied to zero‐sequence networks, and thus faulty areas, faulty sub‐lines, and fault distance can be determined. Attractively, the element correlation in node impedance matrices of zero‐sequence networks is derived from the network branch‐addition process, and the numerical characteristic of matrix elements is further revealed from the particularity of wind farms, based on which root‐mean‐square (RMS) calculation of ZIC can be improved to enable the localization without phasor measurement. Verification results prove that this proposed method can accurately realize the fault localization independent of wind turbine generators with a few measurement points, and the applicability of collector lines with line branches is also considered; additionally, only voltage RMS needs to be measured. [ABSTRACT FROM AUTHOR]

A novel method is introduced to determine cost‐optimized active power curtailment (APC) of renewable energy sources (RES) considering weather‐dependent dynamic line rating (DLR). A new formulation of the security‐constrained optimal power flow (SC‐OPF) is developed and applied in a case study. The reduction of the required preventive APC in the (N-0)$(N\text{-}0)$ case for (N-1)$(N\text{-}1)$ secure grid operation due to the consideration of thermal inertia of overhead power lines is demonstrated. Considering thermal inertia allows relying on curative APC that is activated only after an (N-1)$(N\text{-}1)$ situation occurs. The overhead power line temperature, calculated with the temperature‐dependent power flow (TDPF), acts as a new limit for line loading and releases unused transmission reserves. The TDPF algorithm is integrated in the open‐source Python library pandapower, providing access to it to the broader community. The power system can be utilized to a greater extent, with a reduced demand for congestion management. [ABSTRACT FROM AUTHOR]

Abstract With 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.

With 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. [ABSTRACT FROM AUTHOR]

To locate the ground encroachments in transmission line corridor effectively, the application of a novel binocular stereo vision (BSV) for distance measurement is realized with improvement and adjustment in calibration and reconstruction process of BSV. Firstly, a calibration method using a 1‐D pole with spatial constraints to replace the 2‐D calibration object is proposed. The field experiment shows that this method improves the accuracy of the calibration in a large‐scale scene by expanding the calibration area. Then, a regulation algorithm to eliminate the difference between focal lengths for binocular cameras is designed to further improve accuracy of calibration. For practical utilization of BSV in the monitor system, the 3‐D reconstructions from world coordinate system (WCS) to ground‐based system is achieved by rotation and transformation of the reconstructed coordinate system and direct height measurement is realized consequently. Further, based on the calibration method being proposed, the partial calibration with a reduced calibration distribution area is studied considering the probable complex terrain. Height measurement calculations are carried out on both hypothetical and real obstacles to verify the validity of the calibration method and postprocessing algorithms. The results demonstrated that the calibration method algorithms successfully realized the practical application of BSV in large‐scale scene with high accuracy. By using this novel BSV technology, the total transmission line inspection cost is expected to be greatly reduced by comparing with manned helicopter and UAV inspections. [ABSTRACT FROM AUTHOR]

Abstract A bipolar short‐circuit transient fault identification method for overhead transmission lines in modular multi‐level converter‐based high voltage direct current (MMC‐HVDC) grid based on the hybrid HVDC breaker is proposed. The circuit breakers on both sides of the positive and negative overhead transmission lines will trip after a bipolar short‐circuit fault in the MMC‐HVDC grid. In order to identify whether the fault is a transient fault, the isolating switch of the DC breaker on one line side is reclosed first, and the voltage change on this line side in the case of transient and permanent faults is analysed. By comparing the electrical characteristics of the voltage on the line side under transient and permanent faults, a transient fault identification method is proposed, and the calculation method of the setting value of the criterion is obtained. Finally, by building the MMC‐HVDC system model for simulation in power systems computer aided design, the accuracy and effectiveness of the proposed method for transient fault identification are verified.

Abstract This paper presents an analysis of 64 lightning‐induced voltage waveforms recorded in an experimental system implemented in the campus of the University of São Paulo, Brazil. The voltages were measured on a 10 m high, 2.7 km long un‐energized overhead line consisting of two conductors installed on 6 m crossarms. One of the conductors had surge arresters, while the other one was left unprotected. Strictly speaking, all the recorded voltages on the unprotected conductor were bipolar, but in many cases only one semi‐cycle could be considered important for practical purposes. Different criteria are discussed for the determination of the waveshape parameters, which may differ significantly from those of the standard lightning impulse voltage (1.2/50 μs). Based on the proposed criterion for classifying the induced voltages, unipolar waveforms accounted for 67% of the total and, except for one case, all of them had positive polarity. The median values of the front time and time‐to‐half‐value were, respectively, 5.2 μs and 15.8 μs. Bipolar waveforms were 33% of the total and in approximately 62% of the cases the first semi‐cycle was of positive polarity. In 91% of the cases the voltage peak occurred either in the first or the second semi‐cycle.

With the conversion of the global power economy and energy structure, access to a large amount of renewable energy has led to a decrease in power system inertia. The slight abnormal disturbance in the distribution network may have a significant impact on social and economic development. Aim at enhancing power stability and system resiliency; this study focuses on the detection and location of multiple abnormal sources in the distribution network. Most traditional methods use models relying on precise line parameters, subject to poor adaptability to the distribution network with a large number of nodes, and rapidly changing topology. Therefore, this study proposes a novel random matrix model, driven by monitoring data from phasor measurement units distributed on the overhead transmission lines. In this model, linear shrinkage (LS) theory, and Marchenko–Pastur law are combined for noise reduction to ensure the dynamic character and anti-noise ability. Moreover, data dimensions and sample points may be at the same level in an extensive scale network. The LS and standard condition number rule (SCN) are used for estimating the number of abnormal sources. Finally, the effectiveness of this paper's model is verified in PSCAD. The results indicate that the method has specific dynamic performance and anti-noise ability. [ABSTRACT FROM AUTHOR]

Considering both environmental and commercial aspects, mixed three-terminal transmission lines are attractive. Mixed three-terminal lines consist of two sections of the overhead line and one section of underground cable. In this work, a selective auto-reclosing, fault location, and parameter estimation technique for mixed three-terminal lines using synchronised data from all three terminals are proposed. The proposed method uses the pre and during-fault data recorded at the three ends of the line. Using the recorded sampled data, pre-fault and during-fault phasors are estimated. Four functions are formulated from the pre-fault equivalent network of the system. Additionally, three sets of four functions each are formulated after assuming the fault to be on each of the three sections. Subsequently, the faulted section, fault location, and three sets of line parameters are simultaneously calculated by solving each set of equations. Finally, the correct faulted section, location, and parameters are identified based on the characteristics of obtained line parameters and fault location. Furthermore, the identified faulted section information is applied to enable or block the auto-reclosing function. The simulations and analysis are carried out using PSCAD/EMTDC and MATLAB scripts, respectively. The accuracy, capabilities, applications, and limitations are discussed for different fault scenarios. [ABSTRACT FROM AUTHOR]

The characteristic impedance of a transmission line, a wire or a conductor changes in a non‐uniform manner if the distance to the ground at all points longitudinally is not the same. Vertical conductors, transmission towers and sagging overhead lines are examples for the non‐uniform lines. In this study, lumped‐parameter‐based state variable representation of the single‐phase non‐uniform line is described. From the lumped‐parameter non‐uniform line model a linear set of first‐order differential equations is obtained in the form of state equations and this analytical expression is solved in closed form using MATLAB to obtain the transient response directly in the time domain. The closed‐form solution has the advantage of obtaining the response of the system at an instant without the need for data in the previous states except for the initial conditions. The method also allows attaining the voltage and current profile of the system for any instant. In the illustrative cases presented, the systems with different surge impedance variations are considered and the surge response of a vertical conductor, an exponential line, and a horizontal cone and a vertical cone with constant and also varying propagation velocity are computed. The results are verified by those obtained using s‐domain simulations of distributed‐parameter transmission line and inverse Laplace transform. [ABSTRACT FROM AUTHOR]

This study presents a non‐intrusive sensing method to obtain the phasor of system voltage of overhead lines for a mobile partial discharge diagnostics platform; with the phasor, partial discharges detected by the mobile platform can be characterised by statistical phase‐resolved patterns. Firstly, finite‐element analysis simulations were conducted to understand the relations between overhead lines of different configurations and the electric field underneath. With an electric field sensor, the phasor of system voltage can be derived with the aid of a second measurement unit for system frequency. The two measurement units are synchronised by two GPS receivers with 1 pulse per second (PPS) accuracy. The method is based on the wide area measurement principle and was verified by laboratory experiments. Then, the methodology has been deployed in the 132/275/400 kV substation and underneath single‐circuit overhead lines in the field. The phasor of system voltage on an overhead transmission line can be successfully derived, and phase‐resolved partial discharge information can be calculated. This non‐intrusive and mobile methodology is effective and efficient for practical field measurements. The method eliminated the needs of connecting to an on‐site system voltage, and this is of great importance for diagnostics research carried out by mobile platforms. [ABSTRACT FROM AUTHOR]

Many catastrophes may occur due to the interference between the metallic pipeline and the high voltage overhead transmission lines (HVOHTLs). These problems exist due to the neighbouring between the HVOHTLs and the other infrastructures. Many types of research cover cathodic protection points, detailed description for the production of the AC voltage, and preliminary mitigation ways. Mainly potassium hydroxide‐polarisation cells (KOH‐PCs) have been applied to discharge this voltage to the soil. Based on the KOH‐PCs electrical model introduced previously, this study investigates a novel mitigation technique, where the discharged AC voltage converts to DC voltage that is proper for the cathodic protection for the metallic pipelines. An integrated system consists of power electronic circuits and distributed intelligent controllers designed to discharge the AC induced voltage and use in the cathodic protection for the pipelines. Different controllers such as the artificial neural network, a fuzzy logic controller, and adaptive neuro‐fuzzy inference system controllers have been implemented. Two key performance indicators have been investigated to show the superiority of these controllers, where the total discharged energy per annum DEyear from the pipeline to the soil, and the total saved per year SEyear. [ABSTRACT FROM AUTHOR]

Based on a ±10 kV three-terminal MMC-MVDC (medium voltage DC distribution system based on modular multilevel converter) system, in this study, the authors mainly study on the influencing factors and protection schemes of the lightning intruding overvoltage (including direct lightning and back-flashover lightning). Firstly, a lightning intruding overvoltage simulation model of the MMC-MVDC distribution system using overhead lines is established based on the PSCAD/EMTDC program. The influence of steady-state operating voltage and the number of converter stations on the simulation results are simulated and analysed. Meanwhile, the proper simulation modelling method of the lightning intruding overvoltage for multi-terminal MMC-MVDC system is proposed. Secondly, the lightning intruding overvoltage is simulated when the line is struck by the lightning stroke current that occurs once in 20 years and the different lightning protection schemes are proposed. Finally, based on the lightning impulse withstand voltage, lightning trip-out rate and the cost of the protection schemes, the lightning protection schemes in different scenarios are proposed. The simulation results show that if the cost of the system is prioritised, the protection scheme of increasing the number of parallel stacks of the DL arresters can be selected, and if the power supply reliability of the system is prioritised, the protection scheme of installing the overhead ground wire as well as reducing grounding resistance can be selected.

With an impetuous growth of DC links and future grids that will be often hybrid, providing AC and DC supply to nearby or the same customer, an important element is often neglected, that is, electrical insulation. There are no doubts that overhead lines will step back compared to insulated cables, for known reasons of environmental impact, right of way and reliability, especially in an urban or harsh environment. On the other hand, while AC insulation systems have been investigated and used for decades, there is no analogue experience for DC polymeric insulation, nor for insulation systems subjected to power electronics supply. This study aims at enhancing the attention on this topic, focusing on insulation ageing mechanisms and models of relevance for hybrid AC/DC assets and grids. Ageing and life models for AC, DC and power electronics supply are discussed and compared to experimental data, focusing on partial discharge and space charge. It is shown how these two phenomena affect lifetime for different AC, DC and transient operating conditions. The main drivers for insulation design and material selection are discussed, showing that insulation reliability can be achieved only if operating stresses, ageing mechanisms and life models are known and accounted for properly by insulation designers.

High-impact low-probability weather hazards threaten the power network operation. One of the existing solutions is to reinforce the network with further investment, while the network hardening is restricted by environmental policies and financial conditions. Flexibility methods become increasingly important to enhance network reliability and resilience at low costs. Emergency loadings and probabilistic thermal ratings for overhead lines (OHLs) are the common flexibility options to the network operators. So far, the reliability and resilience impacts of such operations of OHLs and their associated ageing risks are not thoroughly investigated in the up-to-date literature. This study presents a novel resilience enhancement method against windstorms using available emergency demand response in the network and emergency loading of OHLs. The proposed methodology framework can capture the enhancement of network resilience from emergency loading and emergency demand response to provide extra flexibility and minimise network ageing. It is a novel optimisation approach to quantify the trade-off between enhanced network resilience and ageing accounting for operators' preferences regarding the criticality of an individual line's ageing. The proposed method is applied on the IEEE 24 bus reliability test system with having network resilience improvements up to 39% in the conditional value at risk of the energy not supplied and ageing minimisation up to 44%. [ABSTRACT FROM AUTHOR]

Phase‐to‐phase air gap is a type of external insulation in power transmission and transformation projects. The dielectric strength of phase‐to‐phase air gaps affects the safety and reliability of power systems. Currently, in the external insulation design of power transmission and transformation projects, discharge tests are mainly used to obtain the dielectric strength of air gaps. Due to the lack of reasonable prediction model of dielectric strength, the design of the tests is not reasonable enough, which are time consuming and costly. In order to solve the problem, an engineering model of dielectric strength in phase‐to‐phase air gaps was proposed in this study. The engineering model could predict the dielectric strength in phase‐to‐phase air gaps by finite‐element method simulation and numerical calculation. In this study, the engineering model was applied in ultra high voltage (UHV) substations and UHV compact transmission lines to predict the dielectric strength of tubular busbar phase‐to‐phase air gaps and conductor phase‐to‐phase air gaps. The predicted results were in good agreement with discharge test results, and the errors were <6%, which proved the engineering model has certain applicability in power transmission and transformation projects. [ABSTRACT FROM AUTHOR]

Measurement of electric fields is crucial for the evaluation of the electromagnetic environment in electric power transmission system. Due to limited transmission corridor resources, the hybrid transmission lines including high‐voltage alternating current and high‐voltage direct current (HVAC/HVDC) are more common nowadays. However, commonly used field‐mill direct current electric field sensors (DC EFSs) can only be used beneath HVDC lines and the emergence of alternating current (AC) electric fields has adversely affected measurement results recorded by DC EFS. In this work, a DC EFS was designed that is capable of measuring ground‐level DC electric fields generated by overhead HVAC/HVDC transmission lines in a hybrid corridor. A field‐mill structure was used to modulate the DC and AC hybrid electric field and then a narrow band‐pass filter was used to realise suppression of the AC electric field signal. Subsequently, the phase‐sensitive detection method was used to realise amplitude demodulation and phase discrimination of the DC electric field. Sensor prototypes based on the foregoing method were experimentally tested in the China national high‐voltage base. These DC EFSs could be mass‐produced conveniently from current field‐mill for hybrid corridors application. [ABSTRACT FROM AUTHOR]

This study proposes a three‐dimensional (3D) quasi‐static modelling of the electric field produced by high voltage (HV) overhead power lines using charge simulation method combined with intelligent optimisation algorithms, such as particle swarm optimisation, genetic algorithm and grey Wolf optimiser (GWO), to find the optimal values of parameters for an accurate calculation. Results show that the GWO works better than other algorithms. Several parameters affecting the electric field have been studied; it is observed that taking into account the effect of the exact catenary curve of the power line conductors is much more interesting particularly at the mid‐span level where the electric field becomes very significant. According to these values, the limits set by the International Commission on Non‐Ionising Radiation Protection guidelines for electric field strength are met for occupational and public exposure. The simulation results are compared with those obtained by the 3D Integration method, a fairly good agreement is found. To confirm the performance and effectiveness of the proposed method, the results obtained are also verified with measurement values available in the literature, a good similarity is achieved. [ABSTRACT FROM AUTHOR]

This study investigates the overall and local vibration characteristics of disk-type windings in power transformers. The influence of clamping pressure relaxation and pressboard aging on windings' overall modal characteristics is studied. Individual conductors in a winding can vibrate independently and have the local vibration from that of overall windings. The local vibration characteristics of conductors under hoop tension, axial bending and the loss of clamping pressure are investigated. It is found that the clamping pressure relaxation and pressboard aging lead to the decrease of natural frequencies but the faulty conductors result in the increasing number of natural frequencies. [ABSTRACT FROM AUTHOR]

This study proposes an alternative method to calculate the transient responses of multi‐conductor overhead transmission lines based on ABCD representation, recursive convolutions and numerical method for rational approximation in the frequency‐dependent curves. In the classical universal line model, the characteristic admittance matrix Yc(ω) and propagation matrix H(ω) are represented by rational functions. In H(ω), previous and correct identification of the modal travelling times is required. However, these modal travelling times are estimated numerically, which do not offer good accuracy in some cases. This fact has a considerable effect on the rational representation of H(ω) itself and consequently on the transient responses. In the alternative method, a previous estimation of the modal travel times is unnecessary because when using the ABCD representation for each propagation mode, a direct relation exists between the currents and tensions of the receiving and sending ends. These relationships are fitted by smooth rational functions, and then, using recursive convolution methods, the authors obtain the explicit equations of the currents and voltages to calculate the transient responses. The results demonstrate that the alternative method is accurate when compared with the frequency‐domain solution of the transmission line transformed to the time domain using the numeric Laplace transform and with the Bergeron method. [ABSTRACT FROM AUTHOR]

With the increasing application of OPGW (optical fibre composite overhead ground wire) in power systems, the strands in OPGW are frequently broken due to lightning strikes. In this study, ten kinds of OPGW lightning‐strike tolerance was tested according to the IEC standards. The influences of the following factors, such as transfer charge, tensile force, the diameter and material of OPGW outer layer strands, were analysed. The transfer charge and tensile force are positively proportional to the degree of lightning strike damage to OPGW. The diameters of OPGW outer layer strands are positively related to the lightning strike tolerance of OPGW. Compared with OPGW with aluminium alloy outer layer strands, lightning strikes tolerance of OPGW with aluminium clad steel (AS) outer layer strands is better. It suggested that the OPGW outer layer strands diameter >3.2 mm and with AS outer‐layer strands shows good lightning strike tolerance. The mechanism of OPGW strands breaking was also analysed by the infrared detection, micro‐morphology detection and energy spectrum. The experimental results of this study provide significant data support for OPGW type selection for lightning protection. [ABSTRACT FROM AUTHOR]

Grounding electrodes have an important role in electric power transmission and distribution systems. They are used to prevent excessive hazardous voltages due to ground potential rise in the case of system faults or lightning surges. The electrical properties of soil, which vary substantially with geographical location and time of year, affect the process considerably along with the properties of the grounding electrode itself, such as its dimensions. To have an accurate estimation of the induced overvoltages due to lightning strike, one has to take into account the effect of the value of the soil electrical parameters, such as the electrical conductivity and dielectric constant. This study investigates the high frequency behaviour of the grounding electrodes by solving a full‐wave electromagnetic problem using the finite element method. The focus of this paper is on the effect of the variation of soil relative permittivity on the induced transient voltage in grounding electrodes. This allows an evaluation of the response of grounding systems due to seasonal changes, which would cause its electrical properties to vary significantly. This study demonstrates the importance of considering the variation of relative permittivity of the soil especially in the modelling of electrodes buried in highly resistive soil. [ABSTRACT FROM AUTHOR]

This study does research on resonance and harmonic transmission problems in a new continuous cable traction power supply system (CCTPSS), CCTPSS can realise long-distance co-phase power supply and effectively reduce phase separation and is applicable for extended power supply in areas with the weak power grid. Firstly, the system structure is introduced, a cable traction network is divided into three kinds of subnets for its complicated topology and huge system scale. The equivalent circuit model and mathematical model of each subnet are established with distribution parameters, especially the cable capacitance effect be considered. Then, according to the two-port network analysis theory, the system equivalent circuit is constructed by considering the electrical connection relationship, system harmonic impedance expression is calculated. Resonance influence factors and harmonic transmission mechanisms are analysed. Finally, theoretical analysis validity is verified in simulation; harmonic transmission characteristics CCTPSS including traction cable and overhead catenary, are studied. The new system shows better resonance performance compared with the existing AT traction power supply system. [ABSTRACT FROM AUTHOR]

Service unavailability of transmission lines, particularly in mountain areas due to the direct and indirect lightning strikes, is considered as a challenging issue within electric companies. Therefore, the efforts to mitigate the power outages caused by this phenomenon have been introduced. In this study, an attempt has been made to study the different types of externally gapped line arresters (EGLAs) considering the Pinceti model and discharge voltage curve. Based on the best selected EGLA, the installation effect of EGLA on the possibility of instance back‐flashover in different phases of the transmission line is investigated in the presence of downstream shield wire. For assessment, a double‐circuit 400 kV transmission line in a mountainous area is modelled in EMTP‐RV software. Then, an extensive analysis is carried out to verify the effectiveness of this method. The obtained results show the acceptable transmission line direct lightning protection can be achieved by four EGLAs in upper and middle phases with downstream shield wire. Although employing the downstream shield wires in the transmission line imposes more costs, but by using them, the scale and capability of EGLAs can be reduced. [ABSTRACT FROM AUTHOR]

Atmospheric snow accretion along the insulators can eventually bridge adjacent shed spacing, which pose severe risks to the security of power networks. Aiming to investigate the influence of snow accumulation on the electrical performance of various types of insulators, the flashover tests of snow‐accreted insulators were conducted. The effects of various factors on the electrical characteristics of insulators were analysed based on the experimental data. Results show that AC arc flashover gradient of the insulator covered with nonuniform snow accumulation is lower than that of the uniform snow‐covered insulator. The former is as low as 22.5% lower than the latter. Moreover, the AC arc flashover gradient of the porcelain and glass insulators is 0.27–6.27% higher than that of the DC. For a silicone rubber insulator, this gap is greater than 20%. The flashover gradient of the glass insulator is the minimum at the snow thickness of 10 mm. The flashover process of snow‐covered insulator is neither similar to that of the contaminated insulator nor different from that of the iced insulator but a combination of the two. The presented work helps to better understand the flashover mechanism of snow‐covered insulators, and take efforts to mitigate its effects. [ABSTRACT FROM AUTHOR]

Power system automation is an effective tool from both economical and technical aspects to improve the optimal operation of power generators. In this regard, Security Constrained Unit Commitment (SCUC) incorporating Dynamic Thermal Line Rating (DTLR) of overhead transmission lines can boost the system security effectively. Using Transmission Switching (TS) tool in SCUC problems leads to cost reduction. Still, one of the main challenges arisen in TS problems is the excessive number of switching in lines, which decreases the lifespan of power switches. In this paper, an Improved Linear AC Optimal Power Flow (ILACOPF) is proposed by using TS and considering Heat Balance Equation (HBE) as a security constraint. Merging dynamic thermal line rating (considering the weather conditions) in SCUC with TS, besides decreasing the number of switching and increasing the lifespan of power switches, causes a remarkable reduction in operating costs. In this power flow, system losses are modeled by linear formulations. Moreover, a linear approximation of the heat losses due to power flow through lines is proposed. To solve the proposed model, Benders' decomposition approach is applied. The performance of the proposed framework has been evaluated on 6‐bus and 118‐bus IEEE test systems. [ABSTRACT FROM AUTHOR]

Dynamic line rating (DLR) technologies are fast becoming a key instrument in power systems with high penetration of wind farms, because power companies can reduce the value of wind power spillage and also can postpone the investments of transmission lines by using DLR equipment. However, what the authors know about DLR is largely based on empirical studies that investigate how to change the capacity of transmission lines with changing the weather data. Therefore, lack of a mathematical model for estimating the capacity of lines by considering the weather conditions across the line and wind farm generations can be accounted as a research gap of DLR problems. This study proposes a solution for transmission expansion planning considering DLR technologies. Also, this study seeks to develop a model, which will help to address the research gap of DLR problems. The geostatistical analysis is used to develop a mathematical model, which can provide the relationship between wind farms as well as the capacity of lines calculated based on the weather conditions across the line. The efficiency of the proposed model is examined on a modified IEEE 118‐bus test system. [ABSTRACT FROM AUTHOR]

Distribution overhead line network faults with the potential threats to public safety are of extreme importance. High‐impedance faults (HIFs) occur on distribution feeders with close proximity to the population. Advanced technology has enabled power distribution utilities to detect a high percentage of HIFs. However, the application of HIF detectors (HIFDs) should meet both operational and economic requirements due to expense and a large number of distribution feeders. Installation of these devices on overhead feeders among several candidate feeders seems to be a challenging issue. Therefore, ranking of feeders is essential for equipping them with HIFDs. This study proposes a practical approach which is an improved fuzzy analytic hierarchy process (AHP), accompanied by a constrained non‐linear optimisation model to extract optimal crisp priorities from fuzzified inputs, considering various criteria with a degree of inconsistency in their real data. This improved integrated model is also able to adequately evaluate both qualitative and subjective parts of the location‐allocation problems. In this study, enhanced particle swarm optimisation (EPSO) is used to deal with the optimisation problem for criteria weight ratio and also finding the individual feeder preference weighting to optimally locate HIFDs in distribution feeders. The proposed model is applied on a real network and then sensitivity analysis is performed in the optimal solution. [ABSTRACT FROM AUTHOR]

An essential requirement to improve the lightning performance of transmission line is the achievement of low impulse impedance of grounding system, which diminishes the occurrence of the external overvoltages. In this study, for the first time, a multi‐cross structure used as transmission line tower‐footing grounding system is investigated by means of hybrid continuous circuit‐trapezoidal integration method (HCCTIM). It is discovered that the angle of minimum impulse impedance or the optimal structure of multi‐cross grounding system is mainly dependent on the branch length compared to the effective length of a single horizontal conductor. Furthermore, in the current work, the trapezoidal integration method is used to solve the continuous circuit equations which elements are extracted from electromagnetic integral method, called HCCTIM. Coupling elements and soil ionisation are considered in this model. This method is an accurate, simple, and less time‐consuming computational method. The comparison of the results with measurements, other recent simulations and CDEGS software, satisfactorily validate the proposed method. [ABSTRACT FROM AUTHOR]

Air gap discharge voltage is the key parameter to determine the minimum approach distance for live working. In this study, a mathematical–physical model for predicting 50% discharge voltage of the transmission line air gaps considering the effect of live line worker is developed based on the continuous leader inception criterion. Also, the tower structure coefficient ST is proposed to represent the influence of various tower structures and ST is calculated by finite element method. Finally, the switching impulse discharge tests of the equipotential worker‐tower structure gaps are carried out on 750 kV transmission lines to verify the proposed model. The research results show that the errors between the calculation and experimental data are within ±4.03% which demonstrates the feasibility of discharge voltage prediction for complicated live working gaps. This model offers a possible way to determine the safety air gap distance for live working by analytical and numerical calculation rather than costly and time‐consuming experiments. [ABSTRACT FROM AUTHOR]

During the current transformer (CT) saturation, the secondary current waveform of a CT is notably different from the primary current's waveform. When the discrete Fourier transform (DFT) is applied to such a distorted secondary current of a CT, the obtained root mean square (RMS) value is significantly lower than it actually is, which can lead to the malfunctioning of the relay protection devices. The operation of some relay protection algorithms (such as certain algorithms for electric arc detection on overhead lines) is conditioned by higher fault current harmonics. Obviously, due to the secondary current's distortion, the higher current harmonics cannot be accurately estimated. On the other hand, even when there is no CT saturation, the RMS value can be incorrectly estimated under DFT due to the fault current's direct component. This study presents a new algorithm which enables an accurate RMS value estimation regardless of the CT saturation and/or presence of the direct fault current component. What is more, the algorithm also enables the estimation of higher fault current harmonics under CT saturation. Various tests have indicated a high precision and robustness of the proposed algorithm and the possibility of combining this algorithm with the algorithm for electric arc detection on overhead lines. [ABSTRACT FROM AUTHOR]

The study generalises the calculation method described by Lucca, devoted to the evaluation of induced voltage and current on a pipeline due to a nearby overhead power line in a fault condition, from the case of homogeneous soil to the case of a two‐layer soil. By means of some examples of calculation, it is put in evidence that the homogeneous soil hypothesis can lead, in some cases, to excessively precautionary results and, in other cases, to underestimated results. Therefore, a calculation method based on the two‐layer soil model seems a better approach. [ABSTRACT FROM AUTHOR]

With the development of high‐voltage direct current (HVDC), modular multilevel converter (MMC) is seeking its application in onshore wind power integration. AC and DC faults are important issues for the wind power integration system, during which the wind generation system continuously provides wind power and the surplus power may cause overvoltage to sub‐modules of MMC. This study focuses on the energy dissipation during AC and DC faults for the overhead‐line MMC‐HVDC system integrating large‐scale wind power. A two‐terminal MMC‐HVDC system with permanent magnet synchronous generator based wind farm is studied. Hybrid DC circuit breakers (DCCBs) are employed to interrupt DC fault current and the method based on measuring the rate of change of DC line voltage is adopted to trip DCCBs. Also a full‐bridge sub‐module based dynamic braking system (FB‐DBS) is implemented at the DC link to absorb the surplus wind power in case of AC or DC faults in the HVDC grid. To ride‐through AC and DC faults without blocking IGBTs, the control of hybrid DCCB and the system fault ride‐through strategies are properly designed. PSCAD/EMTDC simulations are shown to demonstrate theoretical analysis. [ABSTRACT FROM AUTHOR]

This study presents a dynamic arc model of a polluted insulator based on the formulation of the Obenaus model and the Hampton criterion for discharge propagation. An experiment was conducted on a practical glass insulator installed in the Algerian network for the purpose of measuring the flashover voltage and estimating the arc parameters (A and N) using a genetic optimisation algorithm. The parameters used in the dynamic model were the arc current, arc length, and arc resistance calculated using MATLAB. Moreover, an attempt was made with finite element software to calculate the voltage and electric‐field throughout the insulator surface with and without the presence of contaminants. Finally, the obtained simulation and experimental results showed high performances under operational conditions and respect IEC 60060‐1 standard recommendations. [ABSTRACT FROM AUTHOR]

Despite the good operating results of passive anti‐icing devices installed by the Italian transmission system operator (TSO) on high‐voltage overhead lines (OHLs), the increasing number and consequences of wet snow events have prompted consideration of other anti‐icing measures. In particular, attention focuses on the thermal approach, which is intended to achieve – before, or in the early stage of wet snow events – the anti‐icing current in OHL phase conductors where snow sleeve formation is foreseen. The authors carried out a specific anti‐icing study with reference to a 132 kV critical path in an area of the Apennines, with simulation results illustrated in this study. Anti‐icing measures investigated were (i) load shifting actions and (ii) insertion of shunt reactors used as ballast loads. The results show that shunt reactors are the most effective anti‐icing measure. The main disadvantage of this innovative solution is the degradation of voltage regulation in the area. However, this downside can be limited by combining the insertion of reactors with control of autotransformers under load tap changers. Similar results are obtained from analyses of other critical areas. As a result of these findings, the Italian TSO is now undertaking the installation of the first ballast reactors. [ABSTRACT FROM AUTHOR]

This paper describes the use of new methods of detecting faults in medium-voltage overhead lines built of covered conductors. The methods mainly address such faults as falling of a conductor, contacting a conductor with a tree branch, or falling a tree branch across three phases of a medium-voltage conductor. These faults cannot be detected by current digital relay protection systems. Therefore, a new system that can detect the above mentioned faults was developed. After having tested its operation, the system has already been implemented to protect mediumvoltage overhead lines built of covered conductors.

Flashover of ice-covered insulators seriously affects the safe operation of transmission lines. It is necessary to study the electric field distribution for flashover analysis of ice-covered insulators. The electric field of ice-covered insulators was mostly calculated by a two-dimensional (2D) axisymmetric model that cannot be well corresponded to actual icing situations. In this study, a 3D electric field simulation model of ice-covered suspension insulators under moderate icing condition with applied DC voltage was established. Two characteristic parameters, E(av) and E(max) were proposed to measure electric field distortion degree. Based on the simulation results, the effects of water film conductivity, icicle length, icicle deviation angle, and icicle distribution on E(av) and E(max) were studied. The results showed that icicles have a significant influence on the electric field distribution of insulators. E(av) increases with the increase of icicle length and decreases with the increase of icicle deviation angle. E(max) increases with the increase of the icicle length, icicle spacing and adjacent icicle length difference. When the icicle deviation angle is 45°, E(max) is the largest. Lastly, the possible flashover paths were analysed based on the simulation results, which would provide a theoretical basis for building a flashover model of ice-covered insulators.

Here, using the probabilistic evaluation based on the Monte Carlo method, back-flashover rate and shielding failure flashover rate of 230 kV overhead transmission lines in the western regions of Iran are evaluated. To such an aim, first, the number of thunderstorm days per year is collected from the reported weather information in order to determine the ground flash density. Then, using MRU-200 equipment, the tower-footing resistance of several towers is measured. Matlab® software is used in order to produce lightning surges considering its probabilistic nature and randomly distribution on the ground to evaluate striking distance based on the geometric model. Then, calculated parameters are transferred to EMTP-RV software by establishing a link to perform the transient simulation and report the results for modelled 230 kV transmission line. Finally, considering IEEE-1243 standard, it is shown that due to high ground flash density, using 230 kV tower with one shield wire is not sufficient to protect the line against lightning phenomena.

An approach is demonstrated to visualise overhead line failure rates and estimated wind power output during extreme wind events on transmission networks. Reanalysis data is combined with network data and line failure models to illustrate spatially resolved line failure probability with data corrected for asset altitude and exposure. Wind output is estimated using a corrected power curve to account for high speed shutdown with wind speed corrected for altitude. Case studies demonstrate these methods' application on representations of real networks of different scales. The proposed methods allow users to determine at-risk regions of overhead line networks and to estimate the impact on wind power output. Such techniques could equally be applied to forecasted weather conditions to aid in resilience planning. The methods are shown to be particularly sensitive to the weather data used, especially when modelling risk on overhead lines, but are still shown to be useful as an indicative representation of system risk. The techniques also provide a more robust method of representing weather-related failure rates on lines considerate of the altitude, voltage level, and their varying exposure to weather conditions than current techniques typically provide, which can be used to usefully represent failure probability of lines during storms.

Condition monitoring of outdoor insulation systems is crucial to the integrity of distribution and transmission overhead lines and substations. The objective of this study is to use a commercial acoustic sensor along with artificial neural network (ANN), to classify different typical types of discharges in outdoor insulation systems. First, ANN was used to distinguish between five common electrical discharges that were generated under controlled conditions. Next, this approach was extended to include outdoor ceramic insulators. Three types of defects were tested under laboratory conditions, i.e. a crack in the ceramic disc, surface pollution discharge, and corona near the insulator surface. Both a single disc, and three discs connected in an insulator string were tested with respect to these defects. For both controlled samples and full insulators, a recognition rate of more than 85% was achieved.

Recently, there has been significant interest in developing the modular multilevel converter (MMC) based DC grids in the power industry. However, the immature DC circuit breaker (DCCB) technology hampers the development of DC grids in overhead lines transmission field. The full controlled power electronic devices based hybrid DCCB has been proposed and researched substantially. But the hybrid type DCCB suffers from the drawback of high cost and low reliability, leading to high capital cost for DC grids that require numerous DCCBs. In this paper, a mechanical type DCCB, consisting of a mechanical switch, a circuit and an oscillation circuit, is proposed. Then, a four-terminal bipolar MMC-HVDC system implementing the mechanical DCCBs is studied. Extensive simulations have been conducted to analyse the transient performance under different fault conditions. The simulation results verify the technical feasibility of this mechanical DCCB in DC grid.

When a DC line fault happens, the converter will be blocked instantly. This leads to an interruption of power transmission and influences the stability of DC and AC systems. To avoid the blocking of converters, this paper presents a novel protection scheme for VSC-HVDC system, which consists fault isolation and auto-reclosing of DC circuit breaker (DCCB). First, this paper coordinates the protective actions of converters and DCCB. The DC line fault is cut immediately by DCCB while the blocking signal of converter is isolated during the fault. Second, since the faults of long overhead transmission DC lines are mostly transient, an auto-reclosing strategy is developed. The emphasise of this part, which includes fault discrimination and time sequences, between DCCB and converter is elaborated, and the value of reclosing delay is derived by analysing the charging and discharging characteristics of capacitor paralleled with converter. Finally, the protection scheme is evaluated by overcurrent, overvoltage, and recovery time of DC system, and simulation results of a point-to-point VSC-HVDC transmission system proves its validity.