The Proceedings of 2023 4th International Symposium on Insulation and Discharge Computation for Power Equipment (IDCOMPU2023)

The breakdown characteristics of the metallized film significantly affect the reliability of self-healing capacitors. Traditional two-parameter Weibull distribution can be well described breakdown distribution of metallized film, but it is difficult to describe its early failure intuitively. Metallized film breakdown under low field strength has important influence on the reliability of the capacitor. In this paper, a mixed three-parameter Weibull distribution model is established to describe the breakdown characteristics and to analyze the mechanisms of metallized film. Metallized polypropylene films with different electrode thicknesses are chosen as the object to study the breakdown characteristics and mechanisms. The paper has shown there are three apparent breakdown peaks in the breakdown field strength of 400–500, 500–600 and 600–700 V/μm, which correspond early failure breakdown, low-field defects breakdown, near-intrinsic breakdown. The metallized film with electrode thickness d1 has been used as an example to state that three-parameter Weibull model can well describe different breakdown mechanisms. Moreover, the paper has shown that near-intrinsic breakdown is the main breakdown mechanism for metallized films.

With the continuous expansion of the power grid, large-scale AC/DC hybrid transmission systems are currently facing greater pressure on DC exceeding the standard. By collecting historical operating data of various DC grounding electrodes in Central China, this paper determines the possible operating conditions of multiple DC grounding electrodes, proposes equivalent models for substations and transmission lines, and establishes a DC current model for Central China power grid. Based on the developed DC bias simulation software, the ground potential, grounding current, and DC bias current of substations near the grounding electrode under different operating conditions are calculated. The study found that the impact of the combined action of multiple DC projects on DC bias in substations can be equivalent to the vector superposition of the respective effects of a single DC ground electrode. When multiple DC ground electrodes with the same polarity operate in a relatively close monopolar earth loop, it may further exacerbate the DC bias risk in nearby substations. The research conclusions can provide a reference for DC bias risk assessment and management in areas where multiple DC projects are located.

The gas mixture of C4F7N/CO2 is considered as a leading choice and environmentally conscious solution for gas insulation. To maintain the stability of gas insulating equipment and ensure the safety of operation and maintenance personnel, it is crucial to choose suitable materials for treating C4F7N mixture and its decomposition products. One potential material for adsorption is ZnBDC, which belongs to the metal organic frameworks. Therefore, studying the interaction mechanism between ZnBDC and C4F7N mixture and its decomposition products can provide a theoretical basis for selecting suitable adsorbents for C4F7N/CO2 gas insulating equipment. In this study, we utilized GCMC simulation to investigate the adsorption process of C4F7N/CO2 gas mixture and its nine decomposition products in ZnBDC. By conducting a simulation of competitive adsorption with equal proportions, we derived the distribution of adsorption density, adsorption isotherm, and isosteric heats. Furthermore, a schematic diagram of CO molecules adsorbed inside the ZnBDC cage was demonstrated. The results suggest that ZnBDC has good adsorption performance for decomposition products with little effect on C4F7N. Therefore, it is a potential candidate for an adsorbent in C4F7N/CO2 gas insulating equipment.

High voltage cables are key factors that determine the quality and capacity of power transmission. Polyimide has been widely concerned for its excellent thermal stability and electrical insulation properties, and has been used in the development of cable insulation materials. The surface charge of insulating material has an important influence on the performance of the material. It can not only distort the electric field around itself, but also provide a discharge channel for surface discharge, which affects the safe and stable operation of power system. In this paper, the surface of polyimide for new cables is subjected to voltage treatment by needle-plate electrode, the surface potential is measured by electrostatic probe method, and the surface charge is calculated by inverse mathematical method. The surface charge accumulation distribution characteristics of the polyimide under different applied voltage times and amplitudes and the surface charge dissipation distribution characteristics under different dissipation time under DC high voltage are obtained. The experimental results show that increasing the time and amplitude of voltage applied to the polyimide can promote the accumulation of electric charges. The surface electric charges take on the form of charge patterns and are unevenly distributed. On the whole, compared to the edge position of the material, the charge density at the center position is greater, and in this case, the surface electric charge distribution does not have similarity. In the decay process, the surface potential of the center of the material decays faster than the surrounding, forming a bell shape. Under the action of the electric field, the surface charge pattern presents a positive and negative alternating phenomenon.

Insulation materials are widely used in various fields such as high voltage insulation, power electronics and aerospace. However, as the voltage level increases and the application area expands, the surface of the insulation material will have the phenomenon of flashover along the surface, which will lead to the aging of the insulation and thus reduce the stability of the power system. The current methods to enhance the flashover voltage along the surface of insulating materials generally have the disadvantages of high cost and environmental pollution. However, most of the existing plasma-modified devices focus on small-area materials. In this paper, we proposed a dielectric barrier discharge device for large-area insulating materials, which uses a water-net electrode structure to solve the problem of large-area discharge uniformity while limiting the temperature rise of the electrode so that it can operate stably for a long time. A 30 cm × 40 cm epoxy resin plate is used as the target, and the surface modification of the designed electrode is used to enhance the flashover voltage along the surface. The results show that the surface of the sample modified by the device with water repellent deposited a silica-like film, which increased the surface conductivity by an order of magnitude and increased the flashover voltage uniformly from 8.4 to 9.2 kV. The results of this paper are a guide to the deposition of thin films on large-area flat materials by DBD.

With the gradual increase of the national economy's demand for electric power, power transformers are also gradually developing in the direction of high voltage level and large capacity. According to incomplete statistics, the damage of insulation structure is one of the main factors leading to the failure of transformers. Therefore, the research on the main insulation of transformers will become a top priority. In this paper, we use COMSOL finite element simulation software to simulate the electric field of the main insulation of power transformers with burr defects. The locations where the maximum field strength appears in the transformer main insulation are analyzed to investigate the effects of different sizes and locations of burr defects on the electric field distribution of the transformer main insulation. This study is of general significance to focus on detecting the main insulation devices of power transformers, avoiding partial discharges that may be caused by burrs and ensuring safe and reliable operation of power transformers.

To solve the problem of atmospheric pollution caused by dust generated in the coal transportation and coal-fired processes of power plants, this article compares two common dust removal technologies, electrostatic precipitator and Venturi dust collector, and simulates electrostatic precipitators under different wind speeds using COMSOL. Simulation study of the flow characteristics of a double rotating Venturi dust collector using a k-ε turbulence model. The results show that as the inlet air velocity increases, the velocity of the flow field inside the electrostatic precipitator also increases. The maximum velocity occurs near the discharge electrode, and the particle collection efficiency is highest when the inlet wind speed is 15 m/s, but the dust removal efficiency is below 50%. The flow field inside the Venturi can be exactly simulated by the k-ε turbulence modeling. As the inlet air velocity increases, the outlet air velocity of the double rotating Venturi dust collector also increases. When the inlet liquid velocity is 0.35 m/s, the maximum flow rate of liquid inside the venturi is 40.26 m/s.

With the rapid development of economy, modern power industry demands more and more transformer capacity. The increase of transformer capacity leads to the increase of heat production during operation and the corresponding increase of operating temperature. It is very important to analyze and calculate winding temperature rise for transformer product development and operation maintenance. In this paper, based on the heat generation and heat dissipation conditions of transformer windings, the finite element equations of temperature field and flow field are established by applying the principles of heat transfer and fluid mechanics, and the distribution of temperature field of windings is further obtained.

Cable injection rejuvenation technology is a means to improve the insulation performance of aging cables and extend their service life. The permeability characteristics and rejuvenation effect evaluation of rejuvenation fluids are key research areas in the application of cable rejuvenation technology. The present work compares and analyzes existing cable rejuvenation fluids, and proposes a method for analyzing the infiltration characteristics that can be used in the selection of rejuvenation fluids. Molecular dynamics simulations were conducted on the main components of three rejuvenation fluids, Phenyl-methyl-dimethoxy-silane, Trimethyl-methoxy-silane, and Diphenyl-dimethoxy-silane, to obtain their diffusion coefficients in polyethylene. Furthermore, finite element simulations of chemical substance transfer were conducted to compare the infiltration characteristics of the rejuvenation fluid components in polyethylene. The results indicate that the diffusion coefficient ratios of the three organosilicon compounds in polyethylene are 1.49:5.62:1, and the concentration ratios at the same observation point on the seventh day after infiltration are 6.7:160:1. The diffusion coefficient can be used to evaluate infiltration characteristics.

The rubber-impregnated fiber high-voltage bushing boasts properties such as fire, explosion and moisture resistance, which have been widely promoted over recent years. The capacitor core is one of the core components of the Ultra-high voltage (UHV) AC rubber-impregnated fiber bushing, which is accident-prone as a result of its complex working conditions. On the basis of the initial structural parameters of 1100 kV AC transformer rubber-impregnated fiber bushing, this paper constructs a finite element model of 1100 kV AC transformer rubber-impregnated fiber bushing, which mainly focuses on the analysis of the electric field distribution of the capacitor core, analyzes the influence law of the length, thickness and spacing of the pole plate of the capacitor core on the maximum electric field strength, thereby proposing a bushing capacitor core design scheme. The results show that, in comparison with the initial scheme, the maximum Electric field strength at the end of the capacitor core pole plate is 16.886 kV/mm, which is 17.8% lower than that of the initial scheme, while the maximum electric field strength in the radial direction is 5.420 kV/mm, which is 7.6% lower than that of the initial scheme. The results can give references to the structural design of the 1100 kV AC transformer rubber-impregnated fiber bushing.

Metallized film capacitors are widely used as low-voltage reactive power compensation devices in power systems. However, frequent self-healing breakdown seriously affects the insulation performance and life of capacitors. In order to study the self-healing characteristics of metallized film capacitors, an experimental platform was established to study the effects of voltage, temperature, shunt capacitance, film thickness, and interlayer pressure on the self-healing energy of metallized film capacitors. The results show that, the self-healing energy increases by 58.59% with increasing voltage in the range of 950–1150 V; in the range of 30–90 °C, the self-healing energy decreases by 36.08% with increasing temperature; in the range of 10–160 μF, the parallel capacitance has little effect on the self-healing energy; in the range of 6–10 μm, the self-healing energy increases by 246% with increasing film thickness and in the range of 20–800 kPa, the self-healing energy decreases by 47.11% with the increase of interlayer pressure. The results of the study can provide guidance for the optimal design of metalized film capacitors.

The continuous rapid growth of national economy keeps improving the requirement of our electric power infrastructure. The cross-linked polyethylene (XLPE) cable with good insulation and transmission performance has become the mainstream configuration of urban electric power equipment. Based on the existing research on the causes of cable insulation aging, this paper determines the evaluation parameters reflecting the influence factors of aging, aiming at establishing a novel XLPE cable insulation evaluation model system. According to the linear regression equation, the factors that have little influence on the cable insulation are excluded, the weight vector of the main influencing factors is determined based on the entropy weight method, the weight is tested by the principal component analysis method, and the weight of the parameters affecting the insulation state of XLPE cable is calculated by the TOPSIS method. Finally, the evaluation system is formulated and the suggestions for cable stability maintenance are given.

The normal operation of the grounding grid is related to the safety of transmission lines and even the power grid. Due to its buried underground location, wide distribution, and harsh operating environment, the grounding body is prone to corrosion. Therefore, the corrosion problem of the grounding grid has always been a problem that troubles the power sector. Therefore, in-depth research on the methods of grounding grid corrosion diagnosis is of great significance for ensuring the safe operation of transmission lines. To effectively improve the accuracy of detecting the location and type of corrosion faults in substation grounding grids, a grounding grid fault diagnosis method based on Naive Bayes Classifier (NBC) impulse impedance feature spectrum is proposed. First, CDEGS software simulation is used to obtain the corresponding spectrum maps under various fault conditions, and then the waveform fitting degree and amplitude difference between each frequency band and the standard spectrum map are input into the Naive Bayes Classifier as characteristic parameters, and the expected results are obtained. The test results show that the identification accuracy of the model for fault types is as high as 93.33%, and can accurately distinguish Single point of failure and regional fault.

The temperature rise of gas insulated switch-gear (GIS) bus bar is an important factor affecting its safe and stable operation. Based on the finite element method of electric-thermal-fluid multi-physical field coupling, the finite element simulation model of 252 kV GIS was established by considering the vortex loss of GIS bus bar, skin effect, heat conduction, heat convection, heat radiation and other complex heat transfer processes. The temperature distribution of GIS was calculated. The results show that when the ambient temperature is 293 K and 4 kA power frequency current is passed into the central conductor, the internal temperature of GIS distributes symmetrically along the central axis. The highest temperature in GIS is 324 K and the lowest temperature is 297 K. At the same height, the temperature of GIS decreases gradually along the radial direction from the conductor center, and the temperature difference between the top and the inside and outside is slightly larger than that at the bottom. The lower surface temperature of the basin insulator is greater than that of the upper surface, and the radial temperature difference between inside and outside is 23.5 K. Chamber height has great influence on gas temperature. The multi-physical field coupling simulation can effectively simulate the temperature rise of GIS under actual working conditions and provide theoretical support for GIS condition monitoring and maintenance.

The heating of mid-joints is one of the common hidden dangers in cable systems, and temperature monitoring at the mid-joint is of significant importance for assessing cable operation status. In this paper, a method for inversely calculating the core temperature at the mid-joint of a 110 kV cable is proposed, based on the thermal circuit method for cable body from the standards IEC-60287 and GB/T-10181, as well as the temperature measurement method of distributed temperature sensing devices installed on the inner side of the outer sheath. This method aims to improve the accuracy of temperature calculations by considering the effect of contact resistance loss on core heating and comparing the results with simulation data to validate the accuracy of the proposed approach. The results show that when the cable operates under steady-state conditions and for different temperature conditions on the inner side of the outer sheath, the absolute errors between the calculated current and core temperature using the modified inversion method and the simulation results are within 5%, which basically meets the requirements for field application.

SF6/N2 gas mixture applied in gas insulated equipment can reduce the greenhouse effect of pure SF6 gas. This paper investigates the partial discharge decomposition of SF6/N2 gas mixtures under metal fouling on insulator surfaces. The results show that the decomposition products are SO2F2, SOF2, SO2, NO2, NF3 and CF4, the generation of which increases with the increase of the discharge time, but the generation of SOF2 is much higher than that of SO2F2. the generation of SO2F2, SO2, NO2 and NF3 shows a linear saturation trend with the increase of the discharge volume. the generation of CF4 increases with the increase of the PD intensity. The generation of CF4 shows a linear trend with the increase of PD intensity, which can be used as a characteristic product to characterize the fault severity of insulator metal surface fouling defects.

Conventional lightning protection measures are inadequate because the lightning type is not considered, and the current flow amplitude is uncontrollable. Channel devices cannot completely overcome these drawbacks. Therefore, impact channel-arc suppression-power frequency blocking was proposed in the semi-closed space. In this study, a two-dimensional geometric model was established to develop a high-speed explosive airflow arc-extinguishing device and a self-compression multi-break arc-extinguishing device. COMSOL simulation software was used to investigate the high-speed explosive airflow arc-extinguishing device and arc physical characteristics. The simulation results revealed that the explosive high-speed airflow can quickly extinguish the flash arc and suppress the power frequency arc; the self-compression multi-break device uses the heat of the arc to form a high-speed airflow in the power frequency arc. The combination of the explosive high-speed airflow device and self-compression multi-break device can extinguish the power frequency arc with large current values. The combined device can be applied on overhead transmission lines with high-voltage grades.

SF6 gas has many disadvantages such as extremely high greenhouse effect and easy to liquefy in low temperature environment. Using SF6/N2 gas mixture to replace pure SF6 gas can improve the liquefaction temperature and environmental characteristics of pure SF6 gas. In this paper, the needle-plate electrode is used to simulate the metal protrusion defects and carry out the 96 h partial discharge (PD) decomposition experiment of 50% SF6/50% N2 gas mixture. The results show that the content of five characteristic components, SO2F2, SOF2, SO2, NO2 and NF3, all increase with the increase of discharge time and external applied voltage, and the content of SOF2 is always higher than SO2F2 at the same external applied voltage, and the effective gas production rate of SO2F2 and SOF2 basically shows a linear growth trend with the increase of magnitude of PD, SO2F2 and SOF2 can be used as the characteristic products to characterize the severity of defective metal protrusions in SF6/N2 gas mixture insulated equipment.

Insulators primarily support transmission lines as a shielding control in the electric power system, which exposes them to the elements over an extended period of time and forces them to contend with their severe effects, making them prone to failure. When the insulator fails, it will significantly increase regular energy use and result in significant losses in output and life. In order to safeguard the regular and steady functioning of transmission lines, insulator defect issues must be identified early on during the power inspection process. This study uses insulator images captured during the inspection process and the PP-YOLOv2 deep learning algorithm to explore insulator defect detection in the context of UAV power inspection. The PP-YOLO algorithm is found to be more accurate than the YOLOv3 algorithm while guaranteeing real-time detection and can better extract the data features of insulators in the inspection images, which has better practicability, according to simulation tests on the data set.

Mixing N2 into SF6 can effectively reduce the amount of SF6 used in electrical equipment. Micro-water is a common operating condition in electrical equipment, so the effect of micro-water on SF6/N2 needs to be considered before it is put into use. In this paper, the AC voltage breakdown experiments were performed on 0.5 MPa 30% SF6/70% N2 gas mixture at different concentrations and the decomposition products and breakdown voltage were quantitative analyzed. The experimental results show that when the water content exceeds 331 ppm, the content and gas production rate of SOF2 and SO2F2 increase significantly, which can affect the safety of people and equipment. There is a linear relationship between the content of H2S and the content of water inside the equipment, which can be used as a characteristic quantity to monitor the water content inside the equipment. When the water content exceeds 549 ppm, the insulation strength of the gas mixture is significantly reduced. Overall, the micro water content inside the equipment should not exceed 300 ppm.

At the moment when the contacts are separated, a metal vapor arc is generated in the gap. During the formation process, there are strong material transfer, arc root accumulation and stagnation, which causes the surface of the contact to be ablated and form a crater, resulting in the surface of the contact being broken after many times. The damage is aggravated, affecting the breaking performance. A method of contact rotation and separation is proposed to change the microscopic ionization conditions at the initial stage of arc formation, thereby affecting the motion behavior of vacuum metal vapor arc. In this paper, the influence of contact rotation on the arc characteristics is studied, and it is shown that the contact rotation promotes the transition time point of the limited arc movement in the initial stage, and the limited arc changes from bridge columnar diffusion to radial until the arc splits. The contact rotation will provide a favorable supplement to the research on the improvement of the breaking capacity of the vacuum interrupter.

Using spiral tube damping busbar is a promising method for VFTO suppression due to its effectiveness and ease of installation. To optimize the suppression effect, it is crucial to deeply understand the suppression mechanism and related factors. Thus, a complete circuit model of the damping busbar is established, including all stray parameters and impedance. The method to calculate stray inductance and capacitance between the shell and busbar under high frequency VFTO is introduced. The completely circuit model is established based on SF6 breakdown criterion. The model is applied to a 550 kV GIS platform, and the effect of circuit parameters on suppression is analyzed. Results indicate that the stray capacitance between the busbar and shell also significantly affects VFTO rejection, in addition to coil inductance and shunt capacitance.

Daily sampling inspection is crucial for identifying and eliminating hidden dangers in power grid materials. However, traditional sampling inspection methods that rely on experience often lead to a wastage of resources and manpower. Hence, there is a need to find a suitable method for sampling inspection of power grid materials. This paper proposes a mathematical model to evaluate the quality level of power grid materials in the sampling inspection process. The model involves data cleaning of the original data of power grid materials to obtain the standard data of operational quality. The analytic hierarchy process is then used to analyze the standard data of material quality, enabling the determination of the quality level of each supplier’s materials. Based on the theory of Acceptance Quality Limit, the foundation of the sampling inspection method for each supplier’s materials is established.

With the rapid development of modern industry, the demand for stable operation of high-power AC motors is increasing. The insulation performance of the stator end winding of the motor directly affects whether the motor can operate reliably. There is a multi-physical field environment inside the high-power AC motor, and the complex physical environment affects the insulation failure of the stator end winding. In this paper, the finite element analysis of the non-destructive stator end winding insulation layer is carried out by coupling electromagnetic power and mechanical force. The analysis results show that the insulation layer at the slot outlet and the nose end is most vulnerable to damage, and then three-dimensional arbitrary cracks are added to analyze the insulation damage. Finally, the stress strength factor theory is used to analyze the propagation law of insulation cracks. Through the analysis results, it is found that the crack at the notch is easier to expand than the nose crack in the multi-physical field environment. In this paper, the failure behavior of insulation damage of high power AC motor is studied, which provides a reliable theory for the production of AC motor in the early stage and the fault maintenance and prediction in the later stage.

ZnO varistors have excellent nonlinear voltage-current characteristics, are widely used in overvoltage protection of electrical equipment. The nonlinear behavior of ZnO varistors is attributed to the double Schottky barrier structure of their grain boundaries. However, few studies have investigated the influence of micro grain-boundary structure parameters on the macroscopic electrical properties of ZnO varistors. In this paper, we utilized the Voronoi network and an improved grain boundary partitioning model to simulate and calculate the impact of micro grain-boundary parameters, such as double Schottky barrier and grain boundary partitioning parameters, on the macroscopic electrical properties of ZnO varistors. By classifying and optimizing grain boundary characteristics based on their effects on classification variables and targets, we effectively simplified the complex multivariate and multi-objective problem. These findings provide insight into improving the performance of ZnO varistors, and are of significant importance for the production of high-performance ZnO varistors.

A succession of ultrahigh-voltage (UHV) converter transformer interturn arcing faults have recently emerged, eventually giving rise to catastrophic fire accidents. For a long time, modeling and analyzing transformer interturn faults have been well-known challenges in both academia and industry, while such a dilemma turns out to be intractable in the face of those in UHV converter transformers. In this study, a coupled field-circuit model is presented for numerically investigating converter transformer interturn faults. In the circuit domain, a black box model is chosen for a quantitative description of the nonlinear conductance of the fault arc. As study cases, representative line-side winding (LSW) interturn arcing fault scenarios within a typical single-phase converter transformer are analyzed. The specific results reveal that an interturn fault causes the internal flux distribution to be seriously distorted and leakage flux lines to concentrate around the faulty turns. The LSW interturn fault witnesses a high-amplitude circulating current flowing in the fault loop, and a certain increase in the LSW current, while no apparent fault features can be observed on the valve side. This investigation sheds light on the complex characteristics of interturn arcing faults inside a converter transformer and is expected to offer an alternative to dangerous and costly short-circuit experiments in the field.

Oil pressure rise caused by internal faults in converter transformers and the possible resulting tank rupture have long been a serious concern for the power industry. This paper presents a numerical method to study overpressures inside a converter transformer tank during an arcing fault. Specifically, an arc-driven bubble dynamics model is established to quantitatively describe the gas bubble behavior with the release of arc energy and the overall variations in oil pressure. Meanwhile, a fluid model and the bubble-fluid interaction model are utilized to simulate the complex fault effects within the converter transformer. In addition, a simulation model of a full-scale 415 MVA/500 kV converter transformer is established, and representative results of the dynamic evolution of the gas bubble and oil pressure fluctuations under internal faults with arc energy of 1.2 MJ are obtained and analyzed. The simulation results show that the oil pressure rise inside the faulty converter transformer tank depends on the gas bubble, and exhibits an obvious uneven spatial distribution.

In order to study the impact of crimping defects caused by excessive contact resistance on the temperature distribution of cable joints, based on the contact resistance theory of equivalent conductivity, a multi-physical field coupling simulation model of 10 kV high-voltage cable joints with crimping defects was established using finite element software, and the variation of thermal stress characteristics under the condition of crimping defects in cable joints was studied. The results show that, taking k = 5 as an example, the temperature at the conductor junction of the cable joint with crimping defects is the highest, reaching 58.5 °C, which is 19.9% higher than without defects. As the contact coefficient k increases, the temperature of the connector increases, but the influence of the change in k on the cable core temperature at 2500 mm from the center of the connector can be ignored. The research results of this paper can provide theoretical support for monitoring heating faults caused by crimping defects in 10 kV cable joints.

The contact group is the core component of the on-load tap changer, which has a crucial impact on the mechanical life of the tap changer. In this section, the dynamic and static simulation models of the transition contact of the on load tap changer are established, and the static and dynamic simulation analysis of the contact process of the contact is carried out using the COMSOL finite element software, and the motion characteristics of the dynamic contact bridge of the transition contact are analyzed. Through the simulation analysis, the mechanical characteristics of the Contact process of the transition contact of the on load tap changer are obtained. The greater the stiffness coefficient of the spring behind the static contact, the greater the contact pressure on the contact surface, and the greater the degree of spring bounce; The curvature radius of the moving contact is different, and the degree of spring bounce is different, which needs to be selected and analyzed according to the actual situation; The higher the initial speed of the moving contact, the longer the bounce time, and the more intense the bounce.

Power transmission towers are the support point of transmission lines in power system. With the increase of voltage level and the development of UHV transmission, the stability and safety of power transmission towers has been paid more attention. At present, it is an effective method to design and verify power transmission towers by analyzing structural and mechanical characteristics of power transmission towers with finite element analysis software. The characteristic analysis of power transmission towers is mainly divided into static analysis and dynamic analysis. The two bases are buckling analysis and modal analysis respectively. In this paper, aiming at drum-type self-supporting power transmission towers, finite element simulation model of power transmission towers is established by using finite element software ANSYS. Further more, Modal analysis and buckling analysis of strong wind load under different wind directions are carried out. The results show that the first-order natural frequency of power transmission towers is 2.02, which is close to the result of empirical formula 2.05. The low-order vibration modes of power transmission towers are mainly flat bending, while the high-order vibration modes are mainly local torsion. The main materials and adjacent auxiliary materials in the lower section of the tower body are weak parts, so reinforcement and improvement are required. Eigenvalue buckling analysis and nonlinear buckling analysis both show that the tower structure is most likely to destabilize when the wind direction angle is 90°, and the results of Eigenvalue buckling analysis are more conservative, which must be based on the results of nonlinear buckling analysis.

The construction defects of 10 kV cable intermediate joint is easy to cause insulation fault. In order to detect and identify the construction defects of cable intermediate joint quickly and accurately, an edge detection method of Canny operator is proposed. Firstly, the Canny algorithm is used to remove the false edge and highlight the edge information, and the edge information of different parts of the intermediate joint is obtained. The experimental results show that the stains and scratches in the cable main insulation surface defect image detected by the Canny edge detection algorithm have high purity and integrity, and the accuracy of the defect algorithm is more than 90%. The Canny edge detection algorithm improves the intelligence of defect detection and can effectively control the construction quality.

The uneven cutting of the main insulation and the outer semi-conductive layer and the burr of the pressure pipe are easy to lead to insulation failure. The image recognition technology can be used to intelligently control the construction defects. Aiming at the construction defects of cable intermediate joint, an edge detection method based on Canny operator is proposed. Firstly, the image of segmented cable joint is spliced by using Scale-in-Variant Feature Transform (SIFT) algorithm, and then the false edge can be removed and the edge information can be highlighted by using Canny operator, and the edge information of different parts of the intermediate joint can be obtained. The experimental results show that the cable detected by the algorithm in this paper can also accurately detect the defects of uneven peeling of semi-conductor and burr, and the accuracy of defect algorithm can reach more than 90%, which verifies the effectiveness of the algorithm.

Based on the monitoring data from the 3-D lightning monitoring network (LMN) in the Kingdom of Cambodia (Cambodia), we analyzed the spatial and temporal distribution of lightning activity in 2021. The results show that the transitions between the dry and rainy seasons are periods with a high incidence of lightning activity, and there are very few lightning activities in the middle of the dry season. The predominant feature of diurnal lightning activity is the occurrence of lightning during the afternoon and early evening. The distribution of lightning activity is predominantly concentrated over mountainous regions and over the plateau areas, with less lightning activity over the Tonle Sap and Tonle Sap River basins.

The conductor and shell of an enclosed isolated phase bus will be subjected to alternating electromagnetic forces, bring by alternating magnetic field environment, which causes a long time vibration. The insulator that supports these two parts may become damaged or loose under this vibration environment, which can cause some faults. In this paper, the insulator failure into air gap fault and crack defect, to reveal the mechanism of insulator failure caused by bus vibration. Through theoretical analysis and finite element simulation, the different stress and deformation manifestations of insulators under normal state, air gap and crack faults are analyzed. Thus, the influence of internal electric force on faulty insulators in isolated phase enclosed bus is revealed. The impact of air gap and crack faults on insulators should receive more attentions.

At present, only the deterioration effect of electric field on insulating oil under oil-sulfur corrosion has been studied, but the deterioration of insulating paper has not been studied. Therefore, two sulfides, dibenzyl disulfide and dodecyl mercaptan, were selected in this paper. The effect of electric field on insulating paper under oil corrosion was studied by measuring elastic modulus and molecular chain motion of cellulose using reaction molecular dynamics simulation technique. Then the ball plate electrode was used to apply 2 times the initial discharge voltage, and aged in a 150 °C electrothermal aging chamber for 24 h. Another group of control group was set up without electric field. The final results showed that the breakdown voltage, polymerization degree and moisture mass fraction of insulating paper decreased. This verifies the correctness of the simulation from macroscopic experiment. The results show that the addition of electric field will accelerate the process of oil sulfur corrosion, resulting in the deterioration of the performance of the oil paper insulation system.

Aiming at improving material utilization and performance quality of electrical equipment, this paper investigates the level set method (LSM) assisted topology optimization to obtain new electromagnetic structure. The performance of LSM is validated by the magnetic actuator. Finally, the LSM topology optimization combined with size optimization is applied to improve torque properties of an interior permanent magnet synchronous machine (IPMSM). The no-load back EMF, torque ripple, and average torque of optimal design are compared with the initial design, which shows better improvement.

The high voltage rating of the battery pack requires that it has good insulation properties. Once an insulation fault occurs, it will not only cause a fire, but also poses a threat to equipment and personal safety, therefore, the study of insulation fault diagnosis methods for power storage systems is of great importance. This paper firstly proposes an equivalent model for battery pack insulation fault diagnosis based on the signal injection method; then uses a double Kalman filter algorithm to identify the model parameters to improve the identification accuracy, and at the same time makes an estimate of the end voltage and charge state; finally, the lithium battery pack is tested and verified using the hybrid power pulse characteristics experiment, and the results show that the maximum absolute error of the output voltage of the battery pack is 3.48 mV, and the maximum absolute value of the error in the prediction of the charge state is 0.0005 which improves the recognition accuracy and prediction accuracy of the parameters effectively.

As a kind of passive monitoring DC short circuit protection device, propellant-assisted interrupting and arc triggered hybrid current limiting fuse is widely used in the integrated power system of ships. The closed environment temperature of warship is higher, and the temperature rise generated by rated current of device makes the propellant in high temperature environment. High temperature will accelerate the reaction of the propellant itself, weaken the power after excitation, and affect the interrupting performance of the interrupter. In this paper, the thermoelectric coupling model of the device is established to reduce the temperature rise of the propellant, and the temperature rise distribution of the propellant-assisted interrupter is analyzed. Based on the thermal resistance model, the optimal structure design of the interrupter is proposed, and the relevant temperature rise test is carried out. The test and simulation results verify that the optimized structure can reduce the temperature rise of the propellant.

In this paper, based on the theory of multi-physical field coupling, the coupled calculation model of fluid-temperature field is established. The data of dry reactor temperature field in normal operation are calculated by means of finite element modeling, and the transient temperature change law of reactor in normal operation is obtained. On this basis, the microcosmic COMSOL simulation model of the encapsulation material is established and the thermal conductivity of the composite material is calculated. Simulation models of epoxy reactors with different thermal conductivity are established to analyze the influence of thermal conductivity on hot spot temperature rise of dry bridge arm reactors. The results show that there are obvious differences in temperature rise of hot spots between different thermal conductivity. Compared with conventional epoxy materials, the temperature of hot spots of high thermal conductivity materials is reduced by 9.5 °C, which can achieve the goal of reducing the temperature rise of hot spots by 5 K.

Power transformer is one of the most important electrical equipment in power system operation. Therefore, the calibration of the transformer helps to prevent the abnormal operation of the transformer system timely. A method to consider the cumulative effect of short circuit windings deformation and its deformation prediction is proposed in the paper. Firstly, the mathematical expressions and influencing factors between the accumulated number of short circuit shocks and transformer windings deformation are determined. Secondly, based on COMSOL finite element analysis method, by the actual transformer basic parameters, a three-dimensional finite element simulation model of magnetic and structural coupling field of transformer core and winding is established. The accumulated winding deformation renderings under different short-circuit shock are simulated, and the law between the accumulated number of short circuits and the transformer winding deformation is obtained. Simulation and experimental results prove the feasibility of the theoretical analysis, which provides a reliable method for transformer calibration.

The use of plasma technology to assist scramjet ignition and combustion has been a research hotspot in the field of supersonic propulsion technology. This paper summarizes the main mechanisms of plasma aerodynamic, thermal, and activity effects and their roles in enhanced fuel mixing, ignition, and combustion in scramjets, before reviewing the main research results of plasma technology applied to the above three scramjet stages, focusing on research progress related to different discharge forms of plasma ignition and combustion technologies. Research shows that plasma based on the triggering of aerodynamic disturbances and thermal effects, through interaction with shock waves, control the flow structure to promote the generation of a vortex structure, improve the thickness of the mixing layer, enhance jet instability, to achieve mixing efficiency. The plasma ignition field has matured, with short ignition time delays, flameout limits, and improved ignition efficiency. However, different conditions—such as the nature of the plasma jet working gas and ignition location—can have a considerable impact on the ignition success. Limited by the complexity of the plasma-enhanced combustion research results focused on the description of phenomena and changes in the law, the research mechanism is relatively constrained, but it has been shown to enhance the flame propagation speed, increase flame intensity, suppress combustion oscillations, and improve combustion efficiency. Finally, the difficulties and problems associated with the current research on plasma ignition and enhanced combustion are analyzed.

To address the problem of low efficiency of real-time data transmission in areas without signals in the process of transmission lines inspection, the drone-mounted mobile operation platform is investigated. A power supply scheme for the platform is developed. A communication system based on 5G plus BeiDou satellite and its deployment scheme are proposed, which turns from single communication method to dual communication method. When the 5G signal is good, the data transmission is achieved through the 5G network; when the 5G network link fails, the satellite communication system starts to work. The autonomous flight performance of drone on the mobile operating platform is tested. The results show that the drone has good take-off performance. The high-precision positioning of drone for transmission line inspection can be met using the real time kinematic (RTK) positioning technique. The landing accuracy of drone based on image recognition is high, and the flight stability of drone is good.

In the modern power grid, the accuracy of power measurement and relay protection devices is critical for all parties involved in power supply, transmission, and utilization. The accuracy of the secondary current of the current transformer is of utmost importance in reflecting the primary current. To achieve this objective, we propose a fault diagnosis method for voltage transformers based on the ResNet50 network. This involves training the residual network with voltage fault signals to obtain an optimal fault diagnosis model with high recognition performance. By utilizing this model, we can accurately detect voltage transformer faults.

The critical role of insulation system quality in the proper functioning of solid-state transformers (SST) is very important. To ensure that the SST is maintained properly and estimate its lifespan, certain parameters must be measured, reflecting the degradation rate of the transformer dielectric insulation. However, the complexity of the insulation structure and degradation process can make this task difficult. To address this issue, the paper proposes a new approach using fuzzy logic to create a reliable insulation life model that predicts the life of an SST based on experimental tests. The validity of this fuzzy logic model is confirmed by experimental data collected under various parameters, including voltage magnitude, frequency, and temperature. The results show that the proposed model is effective and can assist in making timely decisions to protect equipment.

For the problem of insulation deterioration under ultra-fast pulsed electric field, we study the charge characteristics of organic insulating materials from the quantum point of view. It is found that due to the strong interaction between the electrons and the nucleus in organic molecules, the electrons exist in the trap energy level in the form of local states when there are defects in the material. Based on Marcus’ theory, the local space charge transition is different from the free electrons, and it will be not only related to trap distance, trap depth, temperature, and other factors, but also closely related to the soft properties of polymer materials. Therefore, the relative speed between the space charge relaxation time and the mutation time of ultra-fast pulsed electric field is the premise to reveal the insulation failure caused by trapping and detrapping.

In order to solve the problem that the performance parameters of permanent magnet actuators are difficult to be identified and by computers and the multi-objective optimization problem, this paper proposes a multi-objective optimization method based on the surrogate model. Firstly, a surrogate model based on orthogonal least squares radial basis functions (OLS-RBF) is proposed to solve the problem of identifying the performance parameters of permanent magnet actuators. Then, for the multi-objective optimization problem, a novel elimination mechanism is proposed for NSGA-III to take the place of the original selection mechanism, which improves the diversity of the Pareto solution sets and reduces the running time of the algorithm. And combine it with the fitted surrogate model for multi-objective optimization. Finally, taking the electromagnetic needle selector with permanent magnets as an example, the feasibility of the method and the accuracy of the improved NSGA-III algorithm are verified by simulation, which lays the foundation for the general optimization design scheme of permanent magnet actuators.

At present, there is no effective ways to estimate the contact status and maximum load capacity of the double-fracture disconnect switchgear (DDS), which cause the contact defects cannot be excavated when the load is low. To this end, the heat transfer process inside the DDS is analyzed using a thermal network, and a varying-parameters state-space model is established, which takes the load current and ambient temperature as input variables, and key nodes temperature as state variables. On this basis, a real-time least square system estimation method for contact resistance is proposed, whose input are the on-line measurement results of contact temperature, shell temperature and load current. Then, an estimation method for maximum load capacity is proposed according to the estimated contact resistance and rated temperature rise. A DDS temperature rise experiment plat-form which takes a switchgear cabinet as an example is set up to verify the accuracy of the state-space model and the effectiveness of the contact resistance estimation under different contact resistance. The proposed method can diagnose the contact defect of the two contacts of DDS and estimate its maximum load capacity without any additional hardware, which provides timely guide for substation operation personnel and builds the physical layer, model layer and application layer of DDS digital twin.

In order to improve the fuel mixing efficiency of scramjet, combined with the research progress at home and abroad, the effect of surface dielectric barrier discharge plasma on the mixing of detached combustors was numerically simulated, and the impact of different positions and The results show that: positively excited plasma can increase fuel mixing length and reduce fuel penetration depth; and the effect of excitation forms on the fuel penetration depth and effect of blend length. The results show that: positively excited plasma can increase fuel mixing length and reduce fuel penetration depth; the effect of reversely excited plasma on fuel is related to the application position.

With the aim of researching the braking characteristics of the electromagnetic eddy current brake and the influence of various factors on the braking performance, in this paper, a 3D transient field simulation model is established based on the finite element method with the DS-50 eddy current brake as an object, and verifies the reasonableness of the model by analyzing the change of the rotation angle of the rotor of the eddy current brake with time, so that this model to be used to simulate the electromagnetic characteristics of the eddy current brake as well as the influencing factors of the braking torque. The results show that when the speed is less than 50 rpm, the braking torque increases rapidly with the increase of speed, and after the speed reaches 75 rpm, the braking torque gradually shows a slow increase; as the excitation current is increased, the braking torque exhibits a gradually increasing trend and the peak torque increases according to a linear function.

Compensated pulsed alternator (CPA) uses the flux compression effect of compensation elements to reduce transient inductance and release large current, and is used in the field of pulsed power with the advantages of high energy and power density. However, the traditional compensation elements are integral structures, such as compensation shield and short-circuit compensating winding. During the discharge process, especially at the highest current moment, the compensating potential directions are different under different poles, so the compensating eddy currents or compensating currents will be affected and weakened, which decreases the local compensation effect. To improve this disadvantage, this paper proposes a new air-core permanent magnet (PM) CPA with segmental squirrel-cage, which has the advantages of the PM excitation and air-core, small volume, light weight, compact structure and large output current. And at the highest current moment, the compensating current in each segment of the squirrel-cage will not be influenced by the compensating potential under different poles, thus the compensating effect is better. The simulation results verify that segmental squirrel-cage has more advantages than the conventional compensating elements. The research results are an important guide to the optimal design of compensating elements, and also provide a basis for the selection of the number of segments of the segmental squirrel-cage.

Insulating cylinders are important components in dry-type transformers. Placing an insulating cylinder in the main air channel can effectively reduce insulation distance between LV and HV winding. Therefore, to study the influence of insulating cylinders on the distribution of electric field in transformers is necessary. This paper built a CRDT cross-sectional model and the electric field was calculated by using finite element software COMSOL. This paper focused on the influence of the position, quantity, and relative permittivity of insulating cylinders on the electric field of transformers, especially on the electric field of HV winding. In addition, this paper also studied the influence of insulating cylinders on the electric field of the main air channel. The results show that, the insulating cylinders will increase the electric field strength of the transformer. The results also show that reducing the relative permittivity of the insulating cylinders can reduce the above impact.

Transformer fault will cause great harm to the grid reliability, but the current condition evaluation guidelines can only make threshold judgment on the current condition quantity, lacking early warning criteria. In addition, it is difficult to analyze the degradation process and the dispersion of the late degradation using the commonly used prediction methods because there are few transformer fault cases. For this reason, this paper collects a large amount of field fault data, proposes the analysis method of transformer deterioration development law based on degradation track, and lays the foundation for determining the early warning criterion of transformer condition evaluation. Firstly, the degradation-based reliability modeling method and analysis process are summarized, and the most suitable modeling method is selected by balancing the advantages and disadvantages of each aspect. Then the application of each degradation model is analyzed from the theoretical level, and the degradation track model is determined to describe the transformer degradation development law. Finally, according to the statistical distribution of the field data to determine the state quantity note value, combined with the collected fault data to establish the transformer degradation track model and estimate the model parameters, and describe the application methods of degradation track model.

The dry-type bridge arm reactor is an indispensable apparatus in flexible DC transmission systems, and it holds significant importance in promoting the intelligent development of power grids. This article focuses on the dry-type bridge arm reactor and establishes a numerical model for the coupling of fluid and temperature fields. It thoroughly investigates the impact of multiple typical structural parameters on the hotspot temperature rise of the reactor. Initially, a two-dimensional axisymmetric model for the dry-type bridge arm reactor is established, and the finite element simulation method is adopted to calculate the distribution of the temperature and flow fields within the reactor. Subsequently, the impact mechanism of structural parameters, such as encapsulation thickness, air duct width, and air duct height, on the temperature distribution and temperature rise of the reactor were investigated. Finally, a structural optimization design scheme for the reactor is proposed by comprehensively considering various factors. The results demonstrate that the optimized reactor’s hotspot temperature rise is reduced from 83.33 °C to 76.07 °C, indicating a notable decrease in temperature rise. The optimization method is of significant guidance in improving the heat dissipation capacity of the reactor.

The temperature distribution of submarine cables is an important parameter reflecting its operation status. The acquisition of temperature distribution trends for submarine cables under varying seawater flow rates holds important engineering significance. In this paper, the geometric model is constructed using a 220 kV three-core AC armored submarine cable laid on the seabed. The simulation model of AC three-core submarine cable temperature field is proposed based on the coupling of electro-thermal-flow multi-physics field. Finally, the study investigates how the steady-state temperature distribution of submarine cables varies with different seawater flow velocities. The results show that the temperature is radially distributed at the seawater velocity of 0m/s, and the temperatures of different phase conductors are different by the relative position, which are 89.9 °C, 89.6 °C and 89.08 °C, respectively. As the seawater flow velocity increases, the heat taken away from the cable surface by convection increases. When the seawater flow velocity is 1 × 10−6m/s, 0.0001 m/s, 0.001 m/s, 0.001 m/s and 0.001 m/s, the maximum conductor temperatures are 69.5 °C, 44.6 °C, 38.5 °C, 33.6 °C and 32.7 °C, and the ampacity is 871.7 A, 1216 A, 1382.8 A, 1590.7 A and 1640.9 A, respectively. The simulation results can provide reference for submarine cable transmission engineering design.

This paper proposes a real-time voltage compensation method based on dq transformation by simulating three-phase voltage. With A, B and C phases as reference, the phase locking method of second order generalized integrator is used to measure the three-phase voltage phase. The three phase alternating current is established respectively, and the corresponding Ud and Uq are obtained by abc-dq transformation. When the voltage dropping, the Ud corresponding to the single phase voltage will drop, so that keeping the Ud value at the rated value (Ud at the rated voltage of the grid), and the voltage drop can be quickly recovered. The energy of the DC unit of the inverter is rectified by the auxiliary winding of the transformer. When the voltage sag occurring, the corresponding voltage compensation is given by the single-phase inverter, which can keep the original amplitude of the grid voltage. The simulation model of the circuit is established by MATLAB/SIMULINK. The three-phase voltage drop is simulated in the simulation circuit, and the load voltage waveform and the output voltage waveform of the inverter are simulated in the case of the drop. The effectiveness of the proposed method is verified by observing the load voltage waveform after compensation.

In the field of power metering, automatic monitoring and analysis of equipment alarm events are essential for stable operation of the metering system. To address the problem of fault diagnosis for metering equipment, a mixed-expert model based on deep neural networks is proposed. The proposed model combines the advantages of mixture-of-experts (MoE) and Deep feature fitting networks (DFFN). The MoE system can divide the measurement warning problem into several sub-problems for processing, which greatly improves the system's ability to recognize and predict warning problems. On the other hand, the DFFNs can be used to analyze measurement data, fit complex features, and better analyze fault problems.

As the scale of offshore wind power continues to expand, more and more three-core AC submarine cables have been put into construction. Submarine cables are the only way of offshore wind power transmission. The accurate acquisition of their sequence parameters is an important basis for planning, designing and analyzing offshore wind power systems. In view of the fact that the existing IEC standards do not have a formula corresponding to the parameters of submarine cables with semi-conductive sheaths, this paper uses a simulation method to calculate the sequence parameters of a 220 kV three-core AC semi-conductive submarine cable. Considering the semi-conductive layer of the cable and its more structures and laying environment, the sequence parameters are deduced and calculated taking into account the semi-conductive sheaths through the multi-conductor system modeling of cables and the application of the symmetrical component principle, and compared with the measured values. The results show that the sequence parameters can reflect the unknown material parameters and the submarine environment, and the simulation results are more accurate, which can provide reference for engineering designers.

In order to reduce the complexity of calculating the temperature field of a transformer by finite elements analysis software, this paper establishes a method for predicting the winding heat transfer coefficient based on the asymptotic homogenization theory, writes a solution code by matlab, and calculates the equivalent heat transfer coefficient of the winding with temperature. The winding model is simplified by this coefficient, and the temperature field simulation is carried out for the original complex model and the simplified model. The simulation results of the simplified model match with the simulation results of the complex model, which proves that the method can be used for transformer winding finite element model simplification.

Before the breakdown of the insulation material, the growth and aging of electrical trees is an important factor leading to the material’s final breakdown. The morphology and growth law of electrical trees in insulating materials are the theoretical basis for diagnosing the severity of defects in power equipment and timely warning. Therefore, the study of the method of observing the morphology of electrical trees is of great engineering significance for improving the long-term operation of electrical equipment. However, due to the opacity of the pressboard material, there is no effective observation method for the electrical trees generating inside it. In this paper, it is proposed to model the measurement system, establish a mathematical model for solving inverse problem in the electrostatic field, and combine PSO (particle swarm optimization) to solve the inverse problem to achieve partial discharge location. In addition, the objective function of the optimization algorithm is analyzed, and the methods to improve the accuracy of partial discharge location are explored. On the basis of the previous one-dimensional measurement system, a two-dimensional measurement system is proposed to improve the positioning accuracy in the y direction.

Aiming at the problem that the hot spot temperature of oil-immersed power transformer with natural oil cooling is affected by oil temperature and oil time constant, a prediction model of hot spot temperature of transformer winding based on thermoelectric analogy principle is proposed in this paper. Firstly, based on the principle of thermoelectric analogy, considering the change of time constant of top oil affected by oil temperature, the Susa thermal model is improved, and the thermal model of power transformer with natural cooling of internal oil is established. Secondly, based on the top oil temperature, the fourth-order Runge–Kutta method is used to calculate the winding hot spot temperature. Then, the research group used the model SFSZ7-31500/110 transformer for temperature rise test. Finally, the proposed algorithm is verified by simulation experiment and compared with Susa’s temperature rise algorithm. The results show that the proposed algorithm has less error, which verifies the effectiveness of the proposed method.

In order to study the thermal stability and its influencing factors of OPGW under power frequency short circuit fault and lightning fault, a three-dimensional transient temperature finite element simulation model is established in this paper, and the temperature simulation of 8 different types of OPGW is carried out. The results show that the temperature rise of OPGW is low when the single-phase power frequency short-circuit fault occurs in the transmission line. When the two-phase power frequency short-circuit fault occurs in the transmission line, the OPGW produces a higher temperature rise. When the fault time is 100 ms, the aluminum layer temperature reaches 380.39 °C, which exceeds the maximum tolerated temperature of aluminum in OPGW, which may cause the aluminum layer to overheat and melt and fall off, affecting the mechanical and electrical properties of OPGW. When OPGW is subjected to a single lightning stroke, its temperature rise rate is less than that of the two-phase power frequency short circuit fault.

Humidity affects the microscopic process of negative streamer discharge in air gap. Considering the influence of humidity on ionization, attachment and recombination in the discharge process, a fluid model of negative streamer discharge in rod-plane air gap is established. The initiation, development and breakdown process of negative streamer discharge in air gap are simulated under the conditions of relative air humidity of 0, 30, 60 and 90%. In this study, humidity promotes negative streamer discharge. It is found that humidity promotes negative streamer discharge, and humidity is positively correlated with the average development speed of negative streamer discharge, the electric field intensity of streamer head and the peak value of electron concentration.

Aiming at the problem of electrocution casualties of personnel in emergency repair after water flooding in underground distribution room caused by rainstorm weather, finite element simulation software was used to establish the water dispersion model in underground distribution room, calculate and analyze the influence of water medium and other factors on potential distribution, and obtain the potential distribution rule under the condition of water accumulation. The simulation results show that when connecting zones are installed around the distribution room, the water potential changes from 285.76 V without connecting zones to 48.14 V. With the water depth changing from 0.1 to 0.8 m, the water potential increased by 10.8%. The research results are of great significance for reducing electric shock casualty rate and ensuring underground production safety.

In order to study the temperature rise characteristics of tower grounding under lightning strike and power frequency short circuit conditions, this paper first calculates the current flowing into the tower grounding device under lightning strike and power frequency short circuit conditions. The calculated current flowing into the underground is taken as the terminal condition of the finite element simulation model of the tower grounding electrode. Low carbon steel and graphite wire and graphite belt are used as simulation grounding materials to analyze the temperature rise characteristics and influencing factors of the grounding electrode under lightning strike and power frequency short circuit conditions. The results show that when the lightning current and power frequency short circuit current flow into the grounding electrode, the temperature rise at the down lead of the grounding electrode is significantly higher than that at other positions of the grounding electrode, and the temperature rise of the down lead exposed to the air is the highest. The temperature rise of grounding electrode increases with the increase of current amplitude. The temperature rise of flexible graphite grounding material under power frequency short-circuit current may exceed its temperature tolerance limit, while the temperature rise of grounding electrode caused by lightning current is small.

Substation grounding network in the substation to ensure the reliable operation of substation and personnel safety plays a vital role, flexible graphite composite grounding material as a non-metallic anti-corrosion grounding material has been good performance in transmission line tower grounding applications, but there are certain problems in the application of substations. In this paper, the effects of current amplitude, soil characteristics and ground position on the ground dispersion and temperature rise characteristics of flexible graphite grounding grid and traditional metal grounding grid are compared and analyzed by COMSOL Multiphysics simulation software. The simulation results show that under the action of intrusion lightning, the scattering effect of flexible graphite grounding grid and metal grounding grid is similar, the surface potential is mainly concentrated near the entry point, and the temperature rise of the grounding grid is low and there is no fusing risk. Under the action of power frequency short circuit, the maximum temperature rise of flexible graphite grounding grid is very high, which does not meet the thermal stability requirements of flexible graphite materials, and the influence of soil characteristics on the temperature rise of flexible graphite grounding grid is not obvious, and the closer the entry point is to the edge of the grounding grid, the higher the temperature rise, so in order to ensure the safe and stable operation of the grounding grid, it is necessary to improve the down conductor. The research conclusion of this paper can provide a theoretical reference for the application of non-metallic flexible graphite composite grounding materials in substation grounding networks.

With the continuous construction of social integrated energy lines, the intersection and proximity of power overhead lines and natural gas pipelines are becoming more and more frequent. The problem of lightning overvoltage in the case of adjacent crossing has attracted wide attention. Aiming at the problem of lightning overvoltage protection of anticorrosive coating of natural gas pipeline near high voltage line, firstly, ATP-EMTP software is used to calculate the characteristics of lightning current into the ground of tower near natural gas pipeline. Combined with COMSOL Multiphysics finite element software, the calculation model of lightning overvoltage of natural gas pipeline and its anticorrosive coating is established to clarify the output mechanism of pipeline body potential and anticorrosive coating potential difference. Secondly, the influence of lightning current amplitude, soil resistivity and “pipeline-line” spacing on pipeline overvoltage is analyzed by simulation. Finally, the lightning breakdown protection method of pipeline anticorrosive coating under the action of grounding current dispersion is proposed. The voltage limiting effect is verified by simulation examples and the construction suggestions of actual reconstruction project are put forward. The conclusion of this paper can provide reference for the design, construction and safe operation and maintenance of oil and gas pipelines.

In order to research the problems of grounding dispersion characteristics and resistance reduction efficiency of concrete foundation for wind turbine, this study uses COMSOL Multiphysics simulation software to build a model of concrete foundation for wind turbine, to study the effects of concrete resistivity and soil conditions on the dispersion characteristics of concrete foundation and spark breakdown characteristics of soil, and to propose structural optimization measures for external application of flexible graphite composite electrical grounding material. The results show that: the concrete foundation grounding resistance increases with the increase of concrete (soil) resistivity; the influence of soil resistivity on the concrete foundation dispersion characteristics is more obvious than that of concrete resistivity; the spark breakdown volume of the soil around the concrete foundation increases with the increase of concrete (soil) resistivity, while the soil resistivity has a greater effect on it; the external flexible graphite composite electrical grounding material can influence the concrete foundation dissipation characteristics and increase the spark breakdown volume of the soil around it. The results of the study can provide a reference for the design of concrete pile foundations for actual wind turbines.

At present, the cross-adjacent conditions of oil and gas pipelines and power lines are more and more frequent. The lightning overvoltage problem under the condition of “two lines—one ground” cross-adjacent to each other has attracted the attention of different industries. Aiming at the lightning overvoltage protection problem of oil and gas pipelines near power lines, firstly, COMSOL Multiphysics software was used to establish the calculation model of lightning overvoltage under the condition of “two lines—one ground” cross adjacent to each other, to clarify the production mechanism of pipeline potential and potential difference of anticorrosive layer. Secondly, the influence law of soil resistivity and soil stratification on the amplitude of pipeline overvoltage is analyzed by simulation calculation, and the method of pipe-line overvoltage protection considering the scatter flow of tower grounding grid is proposed. Finally, the pipeline pressure limiting effect of the optimized transformation scheme is verified by a simulation example and its engineering application value is demonstrated. The conclusions of this paper can provide a reference for the design, construction and safety operation and maintenance of oil and gas pipelines.