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This paper analyses the innovatory development of key technologies of global intelligent transmission operation and maintenance by mining the global patent data. Patent information analysis method and DDA patent analysis tool are used to analyze patent application situation, technology life cycle, technology distribution, dominant countries and institutions, and the latest development trend of technology This study draws the following conclusions: (1)technological innovation in the field of intelligent transmission operation and maintenance is very active, and patent applications are increasing significantly, which is still in the stage of rapid development; (2)patent technology mainly concentrates on the detection of faults in cables/transmission lines or power grids, circuit devices providing remote control of power grids, data processing systems or methods of power departments, etc.; (3)in recent years, technology fields such as manipulator, resource/workflow/ personnel or project management, dielectric strength testing or breakdown voltage testing are the hotspots of technological innovation; (4)the number of patents in China is much larger than that in developed countries such as Japan, the United States, South Korea, etc.; (5) the new patented technologies emerging in recent years are mainly focuses on the calculation based on neural network model calculation, image analysis and processing, satellite radio beacon positioning system, and in particular the neural network model calculation is the most significant growth.

To study how the flashover voltage of silicone rubber depends on surface roughness, we prepared samples of silicone rubber of varying surface roughness to explore the relationship between surface roughness and the hydrophobicity of silicone rubber. We investigate the surface-flashover voltage of these samples. The results show that an increase in surface roughness leads to a decrease in the hydrophobicity of silicone rubber. The-dry flashover voltage of a sample with high surface roughness increases with surface roughness, and the wet-flashover voltage is reversed. The flashover characteristics for a attached water droplet depend mainly on the length of the water droplet.

A single-station-based lighting mapping system comprising a microphone array, which detects electromagnetic (EM) and thunder signals, has recently been developed and deployed for lightning observations. Using one microphone array consisting of 19 electret microphones installed on a 3-D steel frame, this system receives and processes the EM and thunder signals to determine the location of lightning thunder sources. We implement a new broadband direction-of-arrival estimation technique, namely, the maximum power beamforming algorithm and derive the 3-D location results based on the time difference between the acoustic signal and the EM signal. In this paper, four cloud-to-ground flashes with different branch channels recorded by the system are analyzed and presented in which the located thunder sources of two lightning flashes are compared with the photograph of the high-speed camera. The details of the system implementation along with the successful reconstruction of the lightning channel in 2-D and 3-D space are discussed. The results indicate that the location system could effectively map the lightning thunder sources, and the result is highly consistent with the high-speed video camera images. Moreover, the acoustic mapping system is capable of locating the main channel produced by the return stroke process; it also depicts the branching channels. It is shown that the system is capable of distinguish different branches of the same lightning; it also obtains different lightning channels occurring almost simultaneously.

Atmospheric electric field instrument is often used for lightning warning. The lightning alert is issued by setting the threshold of electric field. Because the threshold value directly affects the accuracy of the warning, the optimal threshold can be determined by evaluating the effectiveness of lightning early warning. But the conventional evaluation method is to match the alarm information with the lightning activity information. The method does not consider the operation state and network communication of the electric field instrument itself. There is a certain deviation in the evaluation accuracy, which affecting the optimal threshold. In this paper, the effectiveness evaluation method of the conventional lightning early warning is optimized. The evaluation method based on the abnormal operation state and data reception rate of the instrument is proposed. The original evaluation results are modified. The electric field data of Jiangsu in 2017 are analyzed. The results show that the evaluation method proposed in this paper can not only evaluate the early-warning effect of the electric field instrument more accurately, but also the efficiency of the lightning early-warning algorithm based on the atmospheric electric field instrument is improved.

According to the typical tower structure of ±800 kV UHV DC transmission line, considering the influence of several factors including the tower, bundle conductor, grading ring, and dielectric as well as conductivity of ZnO varistor, the calculation of the impact of ±800 kV DC line arrester and its novel installation method on the composite insulator string, grading ring electric potential and field strength distribution have been done comparatively via the three-dimensional finite element method of the electrostatic field. Research indicates that the arrester slightly increases the maximum value of the potential and electric field strength of the composite insulator string. The arrester also makes the uniformity of the distribution of the electric potential and field strength along the composite insulator slightly reduced, but the impact is rather small. On the other hand, the arrester reduces the surface field strength of the grading ring on the side of the cross arm and increases the surface field strength of the grading ring on the conductor side, but the maximum electric field strength is far below the limit. Analysis indicates that the impact of the arrester on the electric field distribution of the insulator string can be neglected.

UHV DC line arrester long length, there is a significant electric field distribution uniformity. This paper establishes a simulation analysis model for the electric field distribution of the UHV DC line arrester, and systematically studies the influence of measures such as adjusting the structure and the dielectric constant of the arrester valve disc on the electric field distribution of the arrester. It shows that the combination of different dielectric constants of arrester valves can significantly improve the electric field distribution of the arresters in UHV DC lines.

A compact electric field change meter combined the fast and slow electric field change measurement was developed. This paper presented the structure, the features and the calibration method of the instrument as well as the collected typical lightning discharges, including the return stroke and preliminary breakdown pulse train of cloud-to-ground lightning, the compact intracloud discharge, the conventional intracloud discharge and the continuing current. The application of the instrument for fault analysis of transmission lines, especially those caused by lightning return stroke and continuing current, and other non-contact measurement of transients were discussed and expected.

When the Ultra High Voltage Direct Current (UHV DC) line is struck by lightning, it may cause the protection action of the DC system. In this paper, a simulation analysis model of the lightning transient process of UHV DC line is established, and the influence of the line arrester and its installation position and quantity on the protection action is systematically studied. The research results show that line arresters can reduce the impact of lightning overvoltage on UHV DC system protection and prevent lightning strikes from causing DC system protection under certain conditions. The more line arresters are installed along the line, the more significant the effect.

A systematic evaluation of the performance of the World Wide Lightning Location Network (WWLLN) over the Tibetan Plateau is conducted using data from the Cloud-to-Ground Lightning Location System (CGLLS) developed by the State Grid Corporation of China for 2013–15 and lightning data from the satellite-based Tropical Rainfall Measuring Mission (TRMM) Lightning Imaging Sensor (LIS) for 2014–15. The average spatial location separation magnitudes in the midsouthern Tibetan Plateau (MSTP) region between matched WWLLN and CGLLS strokes and over the whole Tibetan Plateau between matched WWLLN and LIS flashes were 9.97 and 10.93 km, respectively. The detection efficiency (DE) of the WWLLN rose markedly with increasing stroke peak current, and the mean stroke peak currents of positive and negative cloud-to-ground (CG) lightning detected by the WWLLN in the MSTP region were 62.43 and −56.74 kA, respectively. The duration, area, and radiance of the LIS flashes that were also detected by the WWLLN were 1.27, 2.65, and 4.38 times those not detected by the WWLLN. The DE of the WWLLN in the MSTP region was 9.37% for CG lightning and 2.58% for total lightning. Over the Tibetan Plateau, the DE of the WWLLN for total lightning was 2.03%. In the MSTP region, the CG flash data made up 71.98% of all WWLLN flash data. Based on the abovementioned results, the ratio of intracloud (IC) lightning to CG lightning in the MSTP region was estimated to be 4.05.

In order to solve the frequently occurring lightning flashover problems on ±500 kV dc transmission lines in China, the authors have conducted the research on the dc line arrester since 2011. In this paper, the structure and installation, technical parameters, and protection performances, as well as their deterministic processes of the arrester are presented and analyzed in detail. In 2013, the authors successfully developed the arrester products, and the type tests show that they have excellent performance parameters and can act effectively against the lightning impulse and cutoff the dc follow current. By now more than 500 dc line arresters have been installed and used on seven ±500 kV dc transmission lines in eight provinces of China. About four years of operating experience shows that the arresters work safely and reliably over a long period of time, and have been effectively reducing the lightning flashover rate of the ±500 kV dc lines.

We studied the effects of indium doping on the microstructure and electrical properties of ZnO varistors co-doped with Al 2 O 3 and Ga 2 O 3 . Scanning electron microscopy, current–voltage testing, capacitance–voltage testing, and X-ray diffraction were performed. The results showed that the leakage current of sintered varistors decreased as the indium dopant concentration was increased. The average grain size decreased slightly with increasing indium content, which improved the voltage gradient. A certain amount of the doped In 3+ dissolved into the grains causing the grain resistance to decrease, which resulted in a low level residual voltage. The sintered samples with 0.024 mol% indium, 0.2 mol% aluminum, and 0.42 mol% gallium showed excellent overall performance, exhibiting a nonlinear coefficient of 58.8, a leakage current of 1.82 µA/cm 2 , a 1-mA residual voltage of 433.9 V/mm, and a residual voltage ratio of 1.53. The obtained co-doped ZnO varistors will provide better protection and stability in applications as metal oxide arresters for power systems.

The traditional method of conducting regular inspections for high-voltage transmission towers is mainly based on manual inspection. Workers need to board the tower for visual inspection during operation, which is not only unsafe, but also inefficient. With the gradual popularization of drones in the use of power industry, automated inspections based on artificial intelligence and image processing technology have become possible. In the complex background of aerial images, doing defect detection for key equipment components of high-voltage transmission lines is a challenging problem, and achieving the goal of target recognition of transmission line equipment is the basis of defect detection. Based on the deep learning technology, this paper researches the target recognition of transmission line equipment by using aerial image, focusing on insulator and anti-vibration hammer. The process is as follows: Firstly, the image data should be preprocessed. Secondly, the data should be marked and the data set should be divided. Then the two networks of Faster R-CNN and YOLOv3 are used for training. Finally, the trained model is evaluated.

Cloud-to-Ground (CG) lightning in Guangdong Province, South China has been observed over decades by the Lightning Location System (LLS) operated by power sector in China. In this paper, we present the characteristics of CG lightning based on the data collected during 2004–2017 when the LLS performance was relatively steady from year to year. To the best of our knowledge, it is the first time to investigate CG lightning from such a long period in this area. Over 30 (67) million CG lightning flashes (strokes) were recorded during this 14-year period. Various characteristics, including flash density, peak current, multiplicity, ratio of positive CG lightning, lightning day, etc, are investigated. Interesting spatiotemporal patterns of the CG lightning parameters are obtained and the potential causes are discussed.

With the rapid expansion of the power grid, lightning strikes are still the main cause of line failures. In order to further reduce the lightning risks, a lightning proximity warning system for power transmission channel with integrated multi-sensor is studied and developed. The system adopts a three-part structure consisting of the base station, central station, and application terminal. The lightning proximity warning system combines multi-sensor data including the atmospheric electric fields, lightning detection data, radar echoes, and satellite cloud images. The corresponding methods including the dynamic self-adapting threshold values, density-based spatial clustering of applications with noise algorithm, thunderstorm identification, cloud movement curve predict with cubic spline interpolation function are used and combined to realizing the lightning proximity warning. The system has covered 16 power companies at provincial level with more than 300 base stations, and formed a lightning proximity warning network covering the main UHV DC transmission channels of SGCC. The system has been running for some years and has issued thousands of warning messages, which plays an important role in ensuring the safe operation of the power grid. The specific case is given and shows that the early warning effect is very good.

In order to study the pressure release capability of $\pm 500 \ \mathbf{kV}$ DC transmission line surge arrester after short-circuit fault, $\pm 500 \ \mathbf{kV}$ Yichang-Shanghai line was taken as the engineering background to calculate the short-circuit current that may occur in the whole line. The surge arrester short-circuit current test device was built. At the same time, pressure release structure and mechanical performance of surge arrester were analyzed. Finally, the high and low short-circuit current performance tests were carried out. The results show that the maximum and minimum short-circuit currents along the $\pm 500 \ \mathbf{kV}$ DC transmission line are about 18 kA and 5 kA. According to the short-circuit current series specified in IEC 60099–4, the surge arrester needs to withstand short-circuit currents are 50 kA and 800 A, respectively. The designed pressure release structure with a waist groove type can release the short-circuit fault energy effectively. It is verified that the short-circuit current performance of the surge arrester can meet the technical requirements of $\pm 500 \ \mathbf{kV}$ DC transmission project.

In order to solve the operation problems of traditional lightning protection equipment (for example, line arrester and parallel gap) for 220 kV AC transmission line, a novel lightning protection equipment – lightning flashover limited equipment for 220 kV AC transmission line – has been developed successfully, which owns the advantages of line arrester and parallel gap. Technical parameters, and electrical and mechanical performances are researched through theoretical calculation and experimental verification, and an installation structure of new split type is designed. The results show that the lightning flashover limited equipment has good electrical and mechanical performance and meets insulation, tensile, and bending requirements. By now, more than 200 sets of lightning flashover limited equipment for 220 kV AC transmission line have been applied on lines in four provinces of China. About 2 years of operating experience show that all the sets of lightning flashover limited equipment work safely and reliably.

In order to improve the lightning withstand level of ±660 kV DC transmission line in China, the authors had begun to develop the ±660 kV DC line arrester since 2014, which was developed successfully in 2016. The structure, technical parameters, protection performance, and installation of line arrester are analysed in detail. The arrester adopts the structure of polymer housing with an external series air gap and a four-section body. The technical parameters and protection performance are designed and calculated according to the relevant standards. The results show that the arrester has good electrical and mechanical performances, and it meets the requirement of insulation coordination. Pillar insulator supporting installation is used in the arrester application. Up to now, the ±660 kV DC line arrester has been used in the ±660 kV DC transmission line in China, which works safely and reliably over a long time. The successful operation can accumulate operating experience and provide a basis for the large-scale application of the line arrester on the ±660 kV DC transmission line in the future.

Lightning is the main cause of transmission line failure, and it is important to improve the lightning protection level of the transmission line for the stability of the power system. Traditional solutions for the shielding failure of transmission lines is to use the electrical geometric model method. However, with the improvement of the voltage level, the physical size increases, and the calculation of lightning protection for ultrahigh-voltage dc lines has a greater difference with operating experience. Based on the Ningxia-Shandong dc transmission lines in China, this study utilised the lead development model to describe the flashover of insulators and the breakdown of the gaps. A comprehensive calculation method of shielding failure trip-out rate considering terrain, earth resistance and weather was proposed. The accuracy was much higher when compared with the traditional calculation and the result can be a reference for other similar calculation for dc lines.

In this paper, a thunder signal detection method is proposed based on the deep learning framework. The recorded thunder signal is segment-wise acquired, stored and pre-processed. In each frame, we use Mel Frequency Cepstrum Coefficient (MFCC) to extract the features of the thunder signal, which is consistent with the frequency characteristics of human perception. We then use the MFCC features derived in each frame to form a 3-channel tensor data, which is used as the further input to the designed convolutional neural network (CNN). The goal of CNN is to classify the existence of thunder for a single data frame. To improve the robustness of CNN, we included other confusing signals that are similar to thunder signals in the training and testing datasets. On the testing dataset, our proposed method outperforms the state-of-art methods in terms of accuracy, sensitivity, and specificity. Our proposed deep-learning-based thunder detection method not only increases the real-time performance of the lighting location system with thunder signals but also further improves the accuracy of other sound alarm systems.

The overhead catenary system of high-speed railway, usually supported by viaducts, attracts more direct strikes than the conventional railway. However, there are ten thousands of slender steel rods in the reinforced concrete structure of viaducts. Therefore, it takes a lot of time to calculate the model of a long series of viaducts by the conventional electromagnetic field modeling method. An electromagnetic transient model for high-speed railway viaducts struck by lightning based on the decoupling method is proposed in this paper, in which the railway viaducts are divided into the box girder unit and viaduct pier unit. The viaducts model based on decoupling method (VMDM) is established by a series of box units supported by viaduct pier units at equal intervals. The equivalent circuit model of each unit was obtained by employing the vector fitting method based on the frequency-domain response. Experimental results of a newly built railway viaduct pier under lightning impulse current were presented to validate the equivalent circuit model of viaduct pier unit, which show high consistency with simulation results. In particular, the typical VMDM model of Beijing-Tianjin intercity railway viaducts was established with the proposed method. The result obtained from the VMDM model are compared with the simplified model.

In order to avoid the lightning insulation flashover and ensure the safe operation under lightning for EHV/ HV DC transmission lines, this paper studied and analyzed the basic structures and technical parameters of the corresponding line surge arresters. Some key performances were discussed comparatively, such as energy absorption capacity, protection characteristics and insulation coordination characteristics. The results show that the designed arresters can meet the requirements of energy absorption for the lightning protection of EHV/UHV DC lines, and have protection characteristics coefficients of more than 1.25 and insulation coordination coefficients of less than 0.85. The developed arresters have been applied with a large deal on EHV/UHV DC transmission lines in China, and the installed amounts and images of the arresters were given in this paper.

Smart substations are an integral part of a smart grid. There are different new smart devices and components in the key systems of the substations. In order to study the impact of lightning to smart substations, simulation modeling will be used to analyze the damages caused by lightning and the lightning protection level. According to the analysis, the impact of lightning to smart substations differs from that to conventional substations in the following three aspects: the number of cables is reduced; there are short cables; and there are smart devices at the outdoor switching station. According to the calculation for an 110kV smart substation, high-amplitude lightning directly striking lightning rods is the main cause of disruption to the devices of smart substations; the impact of low amplitude lightning to smart substations will be considered only when it strikes smart substations of 500kV or higher; where there are line arresters and intact metal shells, the lightning intruding surge and inductive lightning will not affect the equipment of the station.

Based on the idea of risk evaluation, the existing lightning damage risk assessment methods are reviewed and summarized in this paper. And the power grid lightning damage risk assessment system is established on the basis of lightning flashover risk evaluation methodology for transmission lines, and adopts the improved Analytic Hierarchy Process as the core algorithm. It can comprehensively evaluate the risk for transmission lines of regional grid, various sections of a line and each tower of the section, considering much more impact factors, including the running time of line, importance of grades, equipment damage, and the success rate of lightning stroke reclosing and so on. According to the calculation results of the risk assessment of the analytic hierarchy process and lightning flashover risk evaluation, the principles and methods of grade classification for power grid lightning damage risk map are studied, and give typical examples in the paper. It can describe the lightning withstanding ability much more scientifically and provide important references for the manage department of power system.

Based on the research of lightning stroke fault character discrimination method and lightning protection calculation method for transmission lines, the analysis method of transmission line lightning stroke trip-out fault is proposed in this paper. It includes 4 parts: collection and sorting of operation materials, information inquiry of lightning activities, judgment and analysis of lightning stroke accident character, and lightning protection performance calculation. The value of fault analysis is looking for the potential law of lightning faults, through many times of lightning failure analysis. The conclusion will provide specific guidance and advice for lightning protection measure implementation. An example of lightning stroke fault analysis for once lightning trip-out fault of 750kV transmission line in the year of 2009 is given in this paper. According to the line and fault data provided by operating units, compared with the detection information of LLS, the lightning withstanding level of shielding failure and back flashover were calculated. This trip-out fault was caused by lightning shielding failure, and the lightning currents which might cause this fault were found out. Because of the high height and complex topographical feature of tower, the transmission lines in this area were easily to be stroke by shielding failure. And the outside line located on the slope need to be paid much more attention to the shielding failure protection.

In view of the shortcomings of traditional lightning protection measures in the initiative defense, it is necessary to research lightning warning technology, which can provide decision support for avoiding the lightning strike risks of infrastructures. This paper adopted atmospheric electric field and time-differencial calculation, combined with prediction of lightning moving trend based on Lightning Location System, achieved the technology of small-scale and short-time lightning warning for targeted areas. Finally, its effectiveness and practicality are verified by applying this method to transmission line in power grid.

Aiming at the shortcomings of traditional lightning protection measures in active defense for lightning accident, it is necessary to carry out studies on lightning warning method. On the basis of lightning warning information, measures can be taken to avoid lightning risk in advance. This paper makes comparative analysis between fair-weather electric field and thunderstorm-weather electric field by using Hilbert-Huang Transform, and analyses their intrinsic oscillation characteristics for lightning warning. Combining the amplitude of atmospheric electric field with its proportion of energy on high frequency band, a lightning warning method is proposed. Then typical thunderstorm-weather is utilized to verify this lightning warning method workable and accurate.

Based on the method of moment (MOM) and marching on-in-time method (MOT), a new method to solve the time domain integral equation (TDIE) was put forward, which can be used to investigate the transient response of the complex electrical networks and those with lumped parameters electrical element effectively. With the axial currents on the metal conductors taken as unknown variables, and the piecewise linear function selected as basis function, the time invariant matrix is set up by applying subdomain match method. As the matrix inversion is removed from calculation process, the efficiency is improved significantly. Comparison of the results and those obtained by using the method of multi-conductor transmission lines (MTL) displays little difference. Finally, the proposed method, which is applicable to far field, is used to analyze the effect of a simplified reinforced concrete building on the lightning radiation magnetic field, and some useful results are obtained.

The relationship between the cloud-to-ground lightning characteristics and the air quality data over Guangzhou megacity, South China was investigated in this report. A simple method was proposed to cluster lightning location data into two types of thunderstorms: the traverse thunderstorms and the local ones. It was found that the AQI (air quality index), PM10 concentration, PM2.5 concentration, NO 2 concentration and O 3 concentration were positively correlated to the number of cloud-to-ground lightning flashes for the local thunderstorms. It was also found that the ratio of the positive cloud-to-ground flashes showed decreasing trend and the duration of the local thunderstorm showed increasing trend as the PM10 concentration increased. No obvious correlation was observed for the cloud-to-ground lightning count and the SO2 concentration.

This paper analyses the lightning striking smart substation earth wire, due to the insulator flashover, after lightning current phase conduction into the substation, passing through transformer and surge arrester action influence on smart components. The influence of the lightning arrester action on the smart components of the switching field is analyzed.

This paper analyzes the surge interference of the port of smart subassembly for potential difference of the grid while lightning strike on the metal framework of smart substation. The difference between the smart substation with conventional substations while direct lightning stroke is compared, and the influences are summarized

This paper presents an evaluation method for the low voltage system in the smart substation while lightning striking. This method has three steps. First, calculate the maximum value of lightning current that can be tolerate by the low voltage system in the smart substation; second, according to the geographic information of the smart substation, t the current value and the probability distribution of lightning current amplitude can be obtained in the database of the lightning location system; third, according to the maximum allowable lightning current value, the value of current and the change index, the lightning current amplitude is not less than the maximum allowable lightning current value.

In order to investigate the different features of the positive leader propagation in the rod-plane and inverted rod-plane gaps, the discharge experiments in a 3-m rod-plane gap and a 3-m inverted rod-plane gap were carried out under switching impulse voltage. The positive leader propagation process was recorded by using a high-speed CCD camera. Some aspects to describe the positive leader propagation characteristics of the rod-plane and inverted rod-plane gaps are obtained and compared in this paper, including the critical corona radius, the average continuous leader inception voltage, the axial leader velocity, and the final jump length. The possible reason resulting in those differences is also discussed here.

Flashovers due to lightning, pollution and other factors frequently generate long ac arcs along the surfaces of insulator strings on overhead transmission lines; they cause great damage to insulators. Based on the motion characteristics of long ac arcs obtained from experiments, this paper presents the propagation models of the motion processes of long ac arcs, these simulations are important to design suitable parallel arc horns to protect insulator strings. The simulation models include the spatial model, the temporal model of a long ac arc, and the motion simulation models of an arc root and an arc column. The spatial model discretizes a long arc to current elements; the temporal model is proposed to consider the motion mode of a current element; and the motion simulation models of an arc root and an arc column describe the motion processes of an arc root and a column, respectively. At last, numerical simulations and corresponding experiments of long ac arcs along the surfaces of insulator strings of overhead transmission lines are compared. Both of them show a similar motion trend.

The breakage of overhead covered conductors on distribution lines resulting from the short-circuit arcs caused by lightning flash becomes a challenge as the application of covered conductors increases on distribution lines. Based on various methodologies and devices developed to avoid the covered conductor breakage in the world, novel arc-guided devices, including arcing protection hardware with barbs, clamping post composite insulator, and barb electrode clamping post porcelain/composite insulator are presented in this paper. Experimental results are also presented to validate these new developed devices. Devices based on the developed technologies have been widely applied on the power grids in China successfully.

This paper presents the study on the potential distribution of the ac 1000-kV ultra-high voltage metal-oxide arrester (MOA). Based on the idea of field-circuit combination, the 3-D finite-element method (FEM) and circuit-analytic method are applied to analyze and improve the potential distribution of the 1000-kV MOA. The 3-D FEM is used to obtain the 1000-kV MOA's potential distribution and stray capacitances to build the equivalent circuit of the MOA. With the equivalent circuit, the method to improve the potential distribution of the MOA by adding parallel capacitors is analyzed. A scheme to obtain the recommended values of parallel capacitors is achieved to improve the potential distribution coefficient within plusmn 5%. In addition, the influences of the grading ring and mounting height of the MOA on the potential distribution are also discussed. The potential distribution of the developed 1000-kV surge arrester was tested by the photoelectricity measurement method, which is close to the analysis results.

Covered conductors have been widely used on overhead distribution lines, and are very easily broken by short-circuit arcs caused by direct lightning strokes or lightning induced overvoltages. The analysis and comparison of all measures and devices to prevent breakage of covered conductors applied in different countries are presented. All of these methods are classified into three categories according to their operation principles, and according to their functions, these methods are summarized into the arc-blocked method and the arc-guided method.

Three-phase short-circuit arcs often cause the breakage of covered conductors on distribution lines, and their movement processes have become an important problem in power-distribution systems. This paper presents the studies on the movement simulation of the three-phase short-circuit arcs. Based on the latest electric arc model and the coupling of magnetic field and motion, this paper develops the procedure to simulate the movement processes of the arcs. Simulation results show that the arcs have different movement directions and behaviors, which are in agreement with the experimental phenomena. This paper is very helpful to design an effective device that prevents the arcs from causing the breakage of the conductor and the damage of the insulator.

For the problem of lightning breakage of covered conductors on overhead distribution lines, two kinds of 10-kV surge arresters, namely a metal-oxide arrester with a ring-shaped series gap and stab electrode metal-oxide arrester with series gap were developed in this paper. Their structure, installing mode, and experiments were presented. Large amounts of lightning impulse flashover tests validate that these arresters have good effects. Based on these developed arresters, the protection measure for a 10-kV feeding line in substations was proposed. Now these arresters have been applied in China and have the potential for wide applications prospect.

The electric fields under high-voltage direct current (HVdc) transmission lines and the ions produced by corona affect each other greatly. This paper presents an iterative method to calculate ion flow fields under HVdc bipolar transmission lines in the presence of wind. Both the electric fields and the ion densities are calculated by integral equation method. The method is fast and stable. The results are in good agreement with the experimental data. The ion flow fields under a plusmn 800-kV bipolar direct current (dc) transmission line are analyzed