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

The usually used grounding mode of submarine cables, e.g., the two-ends grounding mode or the multi-spots grounding mode, can often generates significant circulating currents in the metal sheaths and armors, limiting the allowable ampacity of submarine cables. As a solution, this paper proposes a new grounding mode that mitigates the circulating currents and upgrades the allowable ampacity. The detailed structure and requirements of the proposed grounding mode for single-circuit, double-circuit and triple-circuit transmission lines (TL) are firstly described. The numerical calculation model is then constructed to compare the ampacities and circulating currents in different grounding modes. The numerical results show that the proposed grounding mode can dramatically suppress the circulating currents and upgrade the ampacity by approximate 20%, compared with the traditional grounding method. Further research reveals a high terminal voltage performance of this new method. Therefore, the proposed new method can only be used within the certain laying length which is dependent on the insulation grade. This new grounding mode is a promising solution to upgrade the ampacity of submarine cables.

Ice coating on overhead transmission lines will cause line disconnection, towers falling or other accidents, which will seriously threaten the safe and steady operation of the power grid. The present anti-icing measures have disadvantages such as passive response, poor effect, and huge energy consumption. In this paper, a superhydrophobic aluminum surface was prepared by chemical etching. The surface contact angle reached 152°, and the rolling angle was 3°. There are mountain-valley rough structures on the surface, which is in Cassie contact state and makes the surface achieve superhydrophobicity status. The effects of solution concentration and etching time on the micro-morphology and hydrophobicity of aluminum surface were investigated, and the anti-icing performance of superhydrophobic aluminum surface was studied. The results show that the contact angle first increases and then decreases with the increase of solution concentration when the etching time is the same. With the increase of etching time, the contact angle first increases and then decreases, and the rolling angle first decreases and then increases. With the etching time of 1 min, the surface reached the superhydrophobic state. Under the same cold surface temperature, with the increase of surface contact angle, the solidification time of water droplets increases, and the superhydrophobic aluminum surface is in Cassie contact state, which has good anti-icing performance.

Ice covering of transmission lines may cause mechanical damage to equipment, including fixtures, conductors, poles and towers, and even lead to serious accidents such as tripping of lines, power failure, burning of wires, and collapse of poles and towers. This paper presents a high voltage pulse ice-breaking technique. The high voltage pulse acts on the ice accumulation covering on transmission lines, breaking down the ice from the inside, forming a high pressure, high temperature plasma channel, and finally breaking the whole ice. In this paper, a high voltage pulse ice-breaking model is constructed based on the structural characteristics of typical transmission line glaze ice and the three-dimensional transient electric field simulation is carried out. The results show that under certain pulse excitation conditions, the bubbles in the ice will be broken down, and the closer the bubbles are to the ice surface, the easier the bubbles will be broken down. The electric field inside the bubbles has the same trend with time, and the electric field intensity increases uniformly with the increase of excitation intensity. This study can provide a reference for the research of power line energy saving and ice breaking.

High-voltage transmission line online monitoring device can effectively promote the safety and stability of the power system, thus acting as an important part of the smart grid. However, for practical applications, the power supply problem is always the key limitation that restricts the development of online monitoring device. To provide stable and reliable power supply to the online monitoring devices, a space energy harvesting system based on the electric field induction is proposed to pick up power from the high voltage (HV) electric field around the transmission lines. Firstly, the system structure is demonstrated, with the analysis of the system’s working principles. Then, the coupling plates for space energy harvesting is optimized, with the use of frame-shaped plates to seek a balance between the power level and the system sizes. Furthermore, based on the system’s quasi-current source characteristics, a DC/DC converter is designed to notably improve the output power level. Finally, with respect to the discontinuous power demand of the on-line monitoring device, a hysteresis discharge mechanism is designed. Both the theoretical and the experimental results show that the system is able to output more than 25mW power stably. With the use of energy storage module, the on-line monitoring device is able to upload the picture information every two hours.

Bushing is an important component of transformers, mainly serving as insulation and mechanical support. Its operating status is of great significance for the normal operation of transformers. This paper judges whether the defect identification method based on the temperature change inside the bushing is feasible by analyzing the temperature change inside the transformer oil paper bushing, the temperature field distribution of the bushing, the influence of the temperature distribution of the bushing conductive rod, and the temperature field distribution of the insulating oil under different defects. The analysis result has reference significance for the safe operation of the oil-paper capacitor bushing.

In this paper, the plasma ion and electron density in the post-arc stage of vacuum circuit breakers and the influence of the main shield voltage distribution configuration on this article are simulated by a 2-D particle-in-cell model and probe diagnosis experiments. In the simulation of the distribution of charged particles and the rate of development of the sheath, there is no applied magnetic field. The main shielding voltage distribution in the post-arc stage is the main cause of the asymmetric distribution of charged particles, which also slows down the attenuation process of the plasma. The main shield voltage distribution configuration in the post-arc phase not only accelerates the media recovery of the post-arc phase of the vacuum circuit breaker, but also reduces the risk of the vacuum circuit breaker breaking down when the large fault current is disconnected in the post-arc phase. In addition, the main shield voltage distribution configuration can accelerate the ions and electrons decay and the development of the post-arc sheath layer, as well as make the post-arc potential distribution more uniform and enhance the internal insulation of the vacuum interrupter. The probe diagnosis results show that the attenuation of residual plasma is the fastest when the main shield voltage distribution configuration is 50%TRV, and the distribution of cathode spots is more uniform in arc extinguishing, which is more favorable to the diffusion of the remaining plasma.

The power transformer plays a critical role in power grid. In the case of extra-high and ultra-high voltage transformers, an indirect central outlet device is commonly employed. This device, however, poses a vulnerability to transformer insulation due to concentrated field strength. Consequently, it becomes imperative to investigate the detection of partial discharges (PD) in the outlet device. The ultra-high frequency (UHF) method is widely utilized for monitoring PD in electrical equipment due to its high sensitivity. This study focuses on accurately modeling the indirect outlet device and employs the time-domain finite difference simulation method to study signals characteristics associated with PD in the outlet device. The simulation results provide evidence that when PD takes place in the outlet device, the UHF signal effectively propagates into the external space through the oil channel between the casing and bushing. The location and magnitude of the PD have a significant influence on the time-domain waveform of the UHF signal.

The three-layers extrusion was used in grafted polypropylene (PP) cables producing, and there occurred a color difference in insulating layer due to the temperature characteristics of materials and big section. In this paper, the temperature field simulation of three-layer extrusion was studied in 110 kV grafted PP power cables. Firstly, the thermal conductivity of insulating and shielding materials were tested. Then, the COMSOL Multiphysics was used to calculated the temperature field distribution by importing the measured data. Finally, the simulation results were obtained and analyzed. The conclusion is that the conductor temperature has a great influence on the temperature field distribution, while the atmosphere temperature on the temperature field distribution. It will guide the production and manufacturing of grafted PP insulated power cables in 110 kV and higher voltage levels in the future.

Under direct current (DC) operation conditions, local electric field in insulation layer will be distorted, leading to insulation failure. Since the conductivity of insulating materials generally corresponds positively with temperature, a temperature gradient will form inside the insulating material during cable operation, making the conductivity distribution uneven and causing the “electric field reversal” phenomenon in the cable insulation layer. The distribution of the electric field and temperature field of the polypropylene grafted as the cable insulation under the electric heating-coupling field is yet to be studied. Studies have proved that by grafting modification the insulating properties of materials can be improved. This paper studied the and conductivity characteristics of grafted polypropylene materials, and selected one type for more experiments to obtain the material's conductivity-temperature-electric field strength characteristic equation through data fitting. A model of a 100 kV DC cable was established in COMSOL, and simulation of the cable section’s electric heating-coupling field was performed, revealing the temperature and electric field distribution inside the insulation layer when the cable is rated, overloaded, or short-circuited. This paper can provide some reference for operational analysis of polypropylene-insulated HVDC cables.

Since the electromagnetic torque of hybrid stepper motor (HSM) is generated by the cogging effect, the change of tooth geometric parameters has a great influence on its performance. When the finite element software is used for optimization, the modeling workload is large. In this paper, the HSM parametric simulation model is established based on ANSYS software, and the geometric parameters of the tooth can be adjusted to improve the efficiency of the optimization design. Based on the parametric simulation model, the influence of the tooth width angle pitch angle ratio of the rotor and stator and the change of the stator pitch angle on the cogging torque and the holding torque is analyzed, and the tooth geometry parameters that take into account the waveform and amplitude of the holding torque are obtained.

This paper presents several technologies for the development of a power analyzer based on FPGA high-speed synchronous acquisition and real-time transmission strategy in order to meet the requirements for the power analyzer’s accuracy, sampling rate, real-time, and synchronization in measuring high-frequency harmonic signals. The method of synchronous sampling of two ad9226 processors can simultaneously sample four analog signals at a sampling rate of 10MSPS per channel, followed by a ping-pong operation for alternate caching. The system uses Xilinx’s Tri-Mode Ethernet IP core based on the AXI bus for UDP communication between the FPGA and PC. The PC calculates and analyses the user's signal. In the meantime, the optical transceiver module is added to replace the cable with an optical cable in order to accomplish electrical isolation via photoelectric conversion, thereby preventing potential ground faults during the measurement process and ensuring reliable data transmission. After experimental analysis, the synchronous sampling rate and real-time performance meet expectations, the data transmission rate reaches 640 Mbit/s, and the accuracy of signal measurement reaches 0.095%.

This paper studies how metal impurities in alumina fillers affect the electrical properties of epoxy/alumina composites, which are used for gas-insulated transmission line insulators. The paper prepares samples with aluminum, copper and iron particles, and measures their glass transition temperature, dielectric spectrum and temperature spectrum, power frequency breakdown strength and volume resistivity. It also uses COMSOL Multiphysics software and Latin hypercube sampling technique to model and simulate the dielectric constant and electric field distribution of the samples. The results show that metal impurities lower the volume resistivity and breakdown strength, increase the dielectric constant and loss, and distort the electric field of the composites. The simulation results match well with the experimental data. The paper offers theoretical and experimental guidance for improving the electrical properties of epoxy/alumina composites.

Power cables are important power equipment in high-voltage power transmission systems. Compared with cross-linked polyethylene (XLPE), polypropylene (PP) is environmentally friendly and has better insulation properties. As a result, PP-insulated cables are gaining traction rapidly. In this paper, the simulation research of 10 kV PP-insulated cable terminal accessories is carried out. The effects of different materials, including conventional semi-conductive materials and various nonlinear materials, on voltage equalization are examined using accessories with a stress cone structure. The results show that appropriate nonlinear materials outperform semi-conductive materials. A novel structure of the accessories with a field grading layer based on nonlinear materials is proposed and the uniformed electric field distribution is obtained. The novel scheme, as compared to the conventional semi-conductive stress cone, considerably simplifies the geometric structure of the accessories while successfully controlling the concentration of internal electrical stress.

The study of charge regulation mechanism in C4F7N/CO2 is of significant importance for advancing the applications of C4F7N/CO2. In this study, coating samples with varying SiC content were fabricated using conventional brush coating method, and the surface charge distribution of these samples under negative voltage was measured using a surface potential measurement system. The results revealed that in the absence of coating, the surface charge in C4F7N/CO2 exhibited bipolar distribution, with a large number of negative charges concentrated near the high voltage electrode and a small number of positive charges concentrated near the ground electrode. When coatings existed, the pattern of surface charge distribution changed. Under the same voltage, with the increase of SiC content, the maximum potential along the electrode centerline first increased and then decreased, reaching a decrease of 70.7% at 30% wt of SiC content, and charges on both sides of the electrode continuously increased. Through the measurement of coating material's conductivity and trap distribution characteristics, it was found that the coating material reduced the surface trap energy level, increased the trap density, and exhibited nonlinear conductivity characteristics. It is suggested that nonlinear conductivity played a role in equalizing the electric field, reducing the gas ionization in C4F7N/CO2. Lower trap energy level and higher conductivity will promote charge gas neutralization and accelerate surface conduction. The combined effect of both factors effectively suppresses the charge accumulation at the electrode front origin. However, the increased conductivity and trap density also promotes charge injection and charge-captured possibility, as a result of the lack of dissipation channels, the charges at both sides of the electrode increase with the increase of SiC content.

Strong electromagnetic effects imperil the safety of shipboard electronic systems and components. To ensure their safety, it is necessary to predict strong electromagnetic effect phenomena. However, the acquisition and simulation of strong electromagnetic effect data are troublesome, resulting in the problem of small sample sizes and sample imbalance when predicting phenomena involving strong electromagnetic effects. To resolve the aforementioned issues, this paper proposes a prediction model based on the CNB classifier. The model selects the features, concatenates the discrete features prior to data processing, and then uses the term frequency–inverse document frequency (TF-IDF) algorithm to encode the feature word weights. The vectors are finally fed to a CNB classifier calibrated with an isotonic probability for prediction. In experiments with traditional plain Bayes, the Isotonic probabilistic calibrated CNB classifier achieves an accuracy score of 0.94 on the strong EM effect dataset. This result demonstrates the model's superior performance. The model avoids the problems of small sample size influencing model performance and the tendency of the classifier to favor large categories while ignoring small ones, safeguarding against the prediction of the strong EM effect phenomenon.

Compared with the traditional alternating current (AC) transmission system, High-voltage direct current (HVDC) transmission technology plays an essential role in the long distance, large capacity, and regional power grid interconnection, for its characteristics of higher economy, reliability, and stability. As the key power equipment in the HVDC transmission system, the converter trans-former cooperates with the converter valve to achieve AC and DC conversion. Due to the large capacity, high impedance, harmonics, DC bias, and other working conditions for the converter transformer, the eddy current loss of the structural components induced by leakage magnetic flux, will be increased significantly and result in the efficiency reduction and local overheating problem, endangering the operational reliability of itself and the power system. In a flexible HVDC transmission system, regarding the convert-er transformer as the research object, the optimal composite shielding scheme is proposed and determined by the optimization design and finite element analysis (FEA) calculation, which are based on the values and distribution of leakage flux and loss density. Furthermore, the experimental results verify the proposed overall leakage magnetic flux control scheme.

Wildfires have become an important factor threatening the safe and stable operation of transmission lines, and large-scale wildfires can significantly reduce the air gap insulation level of transmission lines and cause line tripping. Therefore, based on the principle of cellular automata and Wang Zhengfei's model of wildfire spread, this paper analyzes in detail the effects of factors such as slope, wind speed, wind direction, and fuel type on the speed of wildfire spread and the area of the fire site, and predicts the time when the wildfire arrives below the transmission line. The results indicate that the established model can preliminarily reflect the spread law of wildfires, and has a certain guiding role for the safe and stable operation of the power grid.

During the rapid current falling phase of DC breaking, due to the current drops quickly, resulting in a strong eddy current effect, which makes that the variation of the axial magnetic field (AMF) produced by AMF contact obviously lags behind that of current. Therefore, when the current approaches zero, the strength of AMF in the electrode gap is still strong. According to previous research, when the current density of high-current vacuum arc is less than 500 A/cm2 or the strength of the AMF is greater than 10 mT/kA, the vacuum arc (VA) is a multi -cathode vacuum arc. This article aims to study the dynamic properties of VA in DC breaking process based on artificial current zero when the current approaches zero. The dynamic characteristics of single-cathode spot jet are simulated by 2D transient MHD model. The simulation results indicate that the ion density, axial current density, ion pressure, ion temperature and electron temperature of plasma decrease with the decrease of arc current, and the diffusion degree of arc shape decreases with the decrease of current.

Aiming at the disadvantages of rotating generators' low electrical energy conversion efficiency and poor system stability in eddy vibration sea current energy generation systems, this paper proposes a radially magnetized cylindrical permanent magnet linear generator, which simplifies the intermediate transmission device and improves the stability of system operation. The Ansys program was used to investigate the relationship between the magnetization technique, pole arc coefficient, permanent magnet thickness, back iron thickness, and the linear motor. The air gap magnetic density and no-load-induced electric potential waveform curves were also provided. The results demonstrate that the maximum generating power can be reached by analyzing the load characteristics when the polar arc coefficient is 0.75, the amplitude of the no-load induced electromotive force generated by the radial magnetization drum permanent magnet linear motor is the largest, and the waveform sinusoidal is the best.

Straight curved contact is a vacuum interrupter contact structure with excellent interrupting performance. The process of post arc dielectric recovery during the disconnection process is not yet clear. However, one-dimensional and two-dimensional Particle-In-Cell/Monte Carlo (Pic-Mcc) models cannot accurately describe this process. This article establishes a three-dimensional Pic-Mcc model for the dielectric recovery process after vacuum arc of curved contacts. Taking the butt contact as a reference, the particle diffusion process and particle characteristics of curved contact in the post-arc phase were compared and analyzed. The results indicate that the curved electrode structure and larger electrode surface area are the main factors affecting the post arc particle diffusion process.

As the key electrical equipment of substation, it is necessary to study the electric heating characteristics of RIP bushing in order to ensure its safe and stable operation. In this paper, the multi-layer structure of the capacitor board is established by the calculation method of equal capacitance, and the distribution characteristics of the electric heating field of RIP bushing are determined by the finite element simulation software. The results show that at rated voltage, the internal electric field intensity of the capacitor core exhibits a U-shaped distribution. The surface field strength of the capacitor core near the guide bar is the highest, which is 1.69 kV/mm. Along the axial direction, the overall temperature of RIP bushing is high in the middle and lower parts and low at both ends. High in the middle and low at both ends along the radial direction. The highest temperature is 98℃, which appears in the middle and lower part of the central current-carrying guide rod. The design of air gap between the inner and outer guide bars can effectively reduce the temperature distribution. The research results can provide theoretical and practical basis for the optimal design of high voltage AC RIP bushing.

Polypropylene (PP) is an excellent environmental-friendly cable insulation material with a high melting point, low density, excellent electrical insulation properties, and recyclability. The mechanical properties of PP have an essential influence on its application in cable insulation and play an important role in determining the use of cable. The mechanical properties of the material are usually evaluated using film samples, but they are significantly different from those of actual cable. This paper simulated and analyzed the mechanical properties of pure PP and grafted PP cable insulation materials to compare the mechanical properties of the two insulation materials in cable use. The simulation results showed that the stress and strain of different parts of the cable were different in the force process, and the stress distribution of cable insulation in different radial positions was uneven. The simulation has given a good indication of the stress on the various parts of the cable during deformation, with the surface layer requiring higher mechanical properties due to the more significant deformation. Considering the maximum deformation of the cable during manufacture and use, the stress on the cable was calculated for both insulation materials, and the distribution was analyzed. This study provides a good basis for the development and application of grafted PP cable.

The surge generated by lightning strike blade will impact the electrical system of wind turbine. When the traditional voltage limiting surge protective device (SPD) is used in PWM wave instability and long cable effect, the frequent repeated temporary overvoltage will lead to the phenomenon of sharp reduction in the life of SPD. Therefore, the MW wind turbine is used as the simulation model to analyze the expected surge characteristics at the converter position of the fan electrical system under the condition of lightning strike fan blade. Based on ATP-EMTP simulation, the operation characteristics of the traditional voltage limited SPD selection scheme and the optimized selection scheme under the condition of harmonic oscillation are verified and compared. It is proved that the optimized scheme is feasible to realize fine protection and high tolerance in the case of repetitive transient.

When high voltage XLPE cables are cross-linked with dicumyl peroxide (DCP), the by-products generated by the decomposition of DCP can significantly reduce the intrinsic breakdown performance of XLPE dielectrics. To investigate the effect of crosslinking by-products on the breakdown performance of XLPE, the band gap of three typical crosslinking by-products, α-methylstyrene, acetophenone and benzenemethanol, was calculated based on the first-principles and band gap theory, and the resulting data were fitted and analyzed. The results show that in the calculated field strength range, the band gap of all three decreases with increasing electric field strength, but at different rates; and the threshold values of electric field strength when the band gap of acetophenone, α-methylstyrene, and benzenemethanol decreases to zero are 0.048, 0.065 and 0.068 a.u., respectively; at any electric field strength the band gap values of acetophenone are lower than the other two when the band gap decreases to zero, which has the greatest impact on breakdown and should be removed as a priority in the production process.

To reveal the mechanism of the directional transport of dust particles in the traveling wave electric field. In this paper, by establishing the mathematical model of the spatial electric field distribution above the electric curtain surface, giving the mathematical description of the spatial electric field distribution, studying the electric field distribution law of the traveling wave electric curtain, using COMSOL Multiphysics multi-physics field simulation software, coupling the results calculated in the AC/DC module to the fluid flow particle tracking module, using numerical simulation to track the particle motion, studying the effect of external applied voltage and particle diameter on particle motion is investigated. The trajectory of single particle motion at different starting positions and different electric field frequencies is studied, the conditions required for directional transport of dust particles are proposed, and the transport mechanism of traveling wave electric curtain is explained.

In order to explore the influence of wildfire on the streamer discharge of transmission line gap, combined with the characteristics of the high temperature environment and the change of air gas composition ratio caused by wildfire, based on the theory of plasma hydrodynamics, this paper establishes a streamer discharge model with a rod-plane gap of 5 mm under wildfire conditions, and conducts two-dimensional numerical simulation of the streamer discharge process. Air is regarded as a mixture of N2, O2 and CO2, and different CO2 concentrations and temperature are set to simulate the transmission line environment under wildfire conditions. The simulation results show that under standard atmospheric pressure, the development rate of streamer increases with the increase of temperature and the increase of CO2 concentration. Compared with the influence of the two on the gap streamer discharge, temperature plays a decisive role.

The high frequency of harmonic voltage is more likely to cause partial discharge and insulation failure. The partial discharge experimental platform is built to study the partial discharge characteristics of oil-pressboard insulation under different frequency voltages. Based on the analysis of the obtained partial discharge information, it can be found that the spectrum changes with frequency. As the voltage frequency increases, the discharge quantity increases more steeply with the phase. The higher the voltage frequency, the larger the discharge quantity and discharge repetition rate, and the more serious the partial discharge. The accumulation and dissipation of residual charge have an important influence on the development of partial discharge. The higher the voltage frequency is, the slower the residual charge dissipation is, forming a residual electric field to promote partial discharge.

Currently, testing of epoxy resin insulation parameters yields good results; however, existing research results primarily focus on the influence of epoxy resin degradation on insulation characteristics, and there is a lack of research on the discharge characteristics of epoxy resin under condensation conditions with varying environmental factors and aging degrees. The electrical properties of epoxy resin are investigated in this work from two perspectives: environmental influences and corona aging effects. The results show that both environmental factors and hygrothermal corona aging can affect the condensation state and condensation discharge characteristics of an epoxy resin surface, but in different ways, with the former primarily changing the surface medium and the latter changing the material structure itself.

Existing transformer condition assessment methods cover too few condition indicators and the assessment process relies on expert experience, making it difficult to guide field maintenance work. To address these problems, this paper proposes a transformer health condition assessment method based on full life cycle data. The method uses multi-dimensional, multi-structured, full life cycle data such as transformer operation information, online monitoring data, offline test data and operations and maintenance records as feature quantities, analyses the correlation between different condition indicators and transformer health status, constructs a fuzzy inference-based transformer health index calculation method, realises the quantitative rating of transformer health status, and verifies the method with field example analysis The feasibility and validity of the method were verified by combining with field cases. The results of the field application show that the method can effectively reflect the transformer operation status and has certain guiding significance for the field operation and maintenance decision.

In operation, the negative temperature coefficient (NTC) electrical resistivity characteristics of polymeric insulating materials causes DC electric field distortion within power equipment insulation and lead to the failure. The doping of positive temperature coefficient (PTC) ceramic particles can suppress the NTC characteristics of the composites, but the electrical properties under AC voltages are unrevealed. In this paper, epoxy composites (0–20 wt%) doped with polydopamine-coated PTC particles were prepared, whose AC breakdown strength and dielectric properties were tested. The results shows that the decrease of AC dielectric strength is smaller than that under DC voltages after the doping PTC particles, and the coating of polydopamine can enhance the AC dielectric strength. As the doping content increases, the dielectric constant and tanδ of the epoxy composites increases, and the maximum increase of dielectric loss power is about 2% of the loss power caused by the current-carrying conductor. The research provides a theoretical basis for the optimization of the insulating performance of the equipment under the AC-DC composite voltages.

The stage recognition of surface discharge in oil-impregnated paper is of great significance to the safe and reliable operating of power transformer and the construction of digital twin system. Therefore, a convolutional neural network (CNN) method is proposed in this paper to identify the development stages of surface discharge. Firstly, the surface discharge experiment of oil-paper insulation was carried out by step-up voltage method. Then, according to the difference of phase-resolved partial discharge (PRPD), the surface discharge process could be divided into various stages. Finally, CNN was adopted to identify different stages of surface discharge, compared with support vector machine (SVM) and back propagation neural network (BPNN) based on 24-dimensional feature extraction. The results show that after 100 iterations, the recognition accuracy of CNN on surface discharge stage reaches 99.17%, while the overall accuracy of SVM and BPNN is only 91.04% and 87.29%, respectively. The CNN model proposed in this paper can automatically and effectively identify the PRPD patterns of different stages of surface discharge, with a higher recognition accuracy than the traditional methods such as SVM and BPNN.

In recent years, arcing faults inside large oil-immersed power transformers have been frequent. Suspended bubbles, as the main product of high temperature, high humidity, material aging and cracking gas production inside transformers, are one of the main causes of arcing inside transformers. However, due to the complex structure of the oil channel and the large fluctuation of the internal flow field distribution, the resulting bubble morphology evolution and movement law is not clear. In this paper, the influence of the initial position of bubbles and the relative position between bubbles on the flow field distribution is fully considered, and the dynamic behavior of suspended bubbles in oil under two fluid forms of natural oil circulation and forced oil circulation is simulated and studied by combining laminar and turbulent flow models and bubble force control equations, and the correlation mechanism between suspended bubbles and flow field distribution characteristics is analyzed. The simulation results show that the flow field in the laminar state affects the bubble aggregation and trajectory, while the turbulent state affects the bubble distortion and motion time, and a reasonable model in the simulation of bubble dynamic behavior is more beneficial to improve the simulation accuracy.

Epoxy resin has the characteristics of high adhesion and insulation, excellent dielectric properties, mechanical properties and heat resistance, good chemical stability and easy processing. However, in hygrothermal, epoxy resin generally has insulation aging phenomenon, which seriously affects the reliability and service life of equipment operation. In this paper, a hydrothermal corona aging platform was first built, and then the samples were subjected to artificial accelerated aging for up to 5 days under different hydrothermal environments, and the leakage current and flash-over voltage of the samples after aging were tested. The results show that the wet flash-over voltage of the epoxy resin aged samples affected by different temperatures is larger than that of the aged samples affected by different humidity, and the flash-over voltage is smaller. The higher the relative humidity of the aging sample, the greater the effective value of the leakage current, and the stronger the waveform periodicity. However, compared with the influence of different temperatures, the insulation performance of low humidity aging samples is less damaged.

For high-voltage SiC MOSFET power devices, the breakdown voltage is a key parameter in device design, but the cylindrical junction can affect the withstand voltage capability of the device. Aiming at the problem of uneven electric field distribution and high electric field intensity on the surface of SiC MOSFET devices, a new 6.5 kV SiC terminal structure of field limiting rings is designed in this paper. The termination is optimized by adjusting the field limiting ring spacing and adding field plates, acheveing the goal of 8.9 kV breakdown voltage. The termination reduces the junction surface effect to a certain extent, and greatly improves the electric field distribution on the chip surface.

To address the growing public concern over the issue of audible noise from overhead transmission lines, this paper focuses on the 500 kV AC double-circuit transmission line on the same tower. Using a controlled variable method under rated conditions, the paper analyzes the factors that affect audible noise, including different subconductor radii, minimum ground clearances, and phase-to-phase distances. The primary methods used in the study are the COMSOL finite element simulation software and MATLAB formula calculation, combined with the calculation of audible noise levels 1.5 m above the ground directly beneath the transmission line. The goal of the study is to identify the main factors affecting audible noise and provide feasible suggestions and measures to reduce audible noise levels from transmission lines.

The improvement of the transmission capacity of the line of EHV submarine cable has become urgent issues that need to be addressed. The transmission capacity of the EHV submarine cable is mainly determined by the operating temperature of the submarine cable. Therefore, several cooling schemes are compared to analyze their cooling effect on the cable core temperature in this paper. For the water pipe cooling scheme, the cooling effect is the most significant when the velocity of the cooling water is slower than 0.1 m/s, increasing the number of cooling water pipes can effectively reduce the cable core temperature. For the wind cooling scheme, the cooling effect is the most significant when the velocity of the air is slower than 0.1 m/s, and the cooling effect is more significant with the air velocity. For the backfill soil cooling scheme, the cooling effect is more significant with the thermal conductivity of the backfill soil.

The thermal faults of GIS (Gas Insulated Switchgear) disconnect switch can lead to serious electrical accidents, and the temperature of the contacts is an important indicator for effectively detecting thermal faults. Therefore, conducting temperature field calculations for GIS is of great significance. In this paper, a multi-physics simulation calculation model is established for a 110 kV GIS disconnect switch. Firstly, electromagnetic simulation calculations are carried out to obtain the distribution of losses. Then, the calculated losses are coupled as heat sources to the temperature fluid field to obtain the temperature and flow field distribution. Based on this, temperature field analysis is further carried out for different contact resistance values in abnormal contact conditions. The results show that the temperature hotspots of the GIS disconnect switch are concentrated on the upper contacts of the disconnect switch. In the case of poor contact, the highest temperature point is 42.06% higher than that under normal working conditions.

Power transformer is the core equipment which transmits and distributes electric energy in power system. Power grid performance is directly influenced by the performance of the transformer, and the transformer core losses account for the vast majority of the total losses. As a result, the choice of transformer core materials has a significant impact on the overall efficiency of the grid. The objective of this paper was to develop a three-dimensional model of a three-coherent transformer using ANSYS Electronics Desktop software, with PC95 as the core material and a multi-physical field coupling calculation simulation using the finite element mesh method for obtaining the physical parameters of the dynamic change characteristics, thereby enabling the visualization of transformer parameters. The magnetic field distribution and core loss of the transformer were simulated and compared with those of different core materials (PC44). According to the results of the study, the permeability of PC95 material is much greater, the loss of transformer core is much lower, and the temperature adaptability is greater than that of PC44 material. And it is more adaptable to the effects of temperature change, the optimization design of transformer in the environment of large temperature difference provides theoretical basis, so as to improve the efficiency of the transformer more effectively.

The problem of short-circuit fault limitation and protection is a big challenge in the development of medium voltage DC integrated power system. The traditional current–time protection principle cannot limit the fast rising short-circuit current, which will have a serious impact on the system. It is an effective protection idea to install fault current limiter in the power system. In this paper, the network structure and basic parameters of a medium voltage DC integrated power system are given, and the short-circuit fault characteristics and protection requirements are analyzed. Then, a protection strategy based on a new liquid metal current limiter is proposed, and the optimal configuration scheme and characteristics of the current limiter are analyzed, thereby achieving fast limitation of short circuit faults and rapid support of bus voltage, significantly reducing the system’s requirements for circuit breaker breaking capacity and speed.

Polycrystalline ceramics of Bi6La3Ti3Fe5O27 (BLTF) were prepared by a sol–gel method. Structural, magnetic, relaxor ferroelectric and magnetoelectric coupling properties were investigated. Studies indicate that the prepared sample has a plate-like shape structure with a thickness of 160–170 nm and a diameter of 2 µm. La substitution has been shown to effectively induce the room temperature combining of ferroelectricity and ferromagnetism, thus indicating a promising way for improving multiferroic properties of antiferromagnetic Bi9Ti3Fe5O27. Two dielectric relaxations were observed in the temperature ranges of 500–590 and 600–650 K in BLTF ceramics. In addition, the magnetoelectric coupling effect between charge and spin ordering was determined by measuring the relative change of the ferroelectric polarization and dielectric constant in external magnetic field.

Optical fiber is widely used in power systems, and partial discharge of optical fiber occasionally occurs during normal operation, resulting in signal transmission interruption and insulation performance degradation. In this paper, the electric field simulation analysis is carried out for the structure of the end flange of the optical fiber insulator, indicates that the electrical strength inside the flange reaches 0.48 kV/mm, higher than the average electrical field strength of 0.15 kV/mm. The electric field distribution in the flange of materials with different resistivity and size is studied, and the electric field strength of the interface between the materials inside the flange is taken as the optimization goal. By using Random Focus Search Algorithm, electrical field strength is reduced to 0.12 kV/mm, and the optimal resistivity material parameters and flange size structure of the optical fiber insulator are obtained.

Metallized film capacitors are widely applied in power electronics devices due to their large capacitance and high power density, such as support capacitors for flexible DC converter valves. In this paper, thermal resistance of the T-shaped safety film and the diamond-shaped safety film are simulated and calculated, and the power density of the film is calculated according to the equivalent resistance. The overall temperature rise of the capacitor is simulated and analyzed. Simulation results show that the ordinary metallized film has the lowest thermal resistance; the thermal resistance and equivalent resistance of the safety film mainly depend on the effective cross-sectional area of fuse. When the effective cross-sectional area is increased, the thermal resistance will become smaller, improving the heat dissipation capacity of the capacitor. The temperature rise of T-type safety film capacitors is the most serious, which is 15 K higher than that of ordinary metallized films.

Due to the proposal of China's the goals of carbon peaking and carbon neutrality, vacuum circuit breakers have become the best choice for SF6 replacement due to their advantages of zero carbon emissions and strong breaking capacity. However, there are only 126 kV and below single-break vacuum interrupters for high-voltage transmission levels, and 252 kV vacuum interrupters have not yet been put into use for commercial products. The 252 kV level vacuum switch has the characteristics of high withstand voltage level and long contact gap distance, and its breaking capacity is closely related to the recovery process of the back-arc medium. In this paper, the Continuous Transition Model (CTM) model of the back-arc sheath is adopted, and the transient recovery voltage of the 220 kV transmission line model is input as a parameter. Parameters, the curves of the length of the sheath, the surface electric field intensity of the new cathode, and the power density with time are obtained, and the time spent in the recovery phase of the back-arc sheath, the maximum value of the surface electric field intensity, and the maximum power density are obtained, which is high voltage level, long gap vacuum circuit breaker design provides theoretical support.

This paper quantitatively analyzes the impact of induced current and leakage current on GIL equipment by establishing a GIL shell circulating current calculation model. In addition, the GIL grounding system and shell circulation model were established. When the grounding spacing is less than 2000 m, the shell circulation and shell potential will increase significantly with the increase of grounding spacing, and the GIL shell potential shows a “U”-shaped distribution with low middle and high end. The potential can be reduced to a single digit to ensure the safety of staff.

As an important part of HVDC transmission engineering, DC grounding electrode leads the fault current into the ground when the HVDC transmission fault occurs. DC grounding electrode will cause the ground electric field exceeding the standard, which will affect the normal operation of the power system and pipeline system nearby. This paper presents a digital twinning technology of ground electric field near DC grounding electrode, and deduces the basic theory and algorithm of horizontal layered ground space potential and electric field under the condition of unlimited layers. The paper presents a digital twinning algorithm of ground potential analysis based on 45-point linear filtering method, and a digital twinning algorithm of space electric field based on 47-point linear filtering method. The effectiveness of this method is proved by case analysis, and the results are compared with the complex image method, which proves the accuracy of this algorithm. The work of this paper can provide reference for the analysis of potential and electric field near DC grounding electrode Analytical work.

In this paper, the finite element model of the spike defect of the high-voltage conductor in the 10 kV cable joint is built, the propagation characteristics of the acoustic signal during the insulation air gap partial discharge are simulated, and the coupling function between the partial discharge acoustic wave of the cable joint and the external sensing fiber is established. The results indicate that for this type cable joint air gap partial discharge, it is most suitable to choose an external sensing fiber winding width of about 30 mm; When the external voltage of the cable joint is 19 kV and the partial discharge of the air gap defect is 250 pC, the maximum phase change of the corresponding sensing fiber is about 0.3 rad; The main component of sound waves received on optical fibers is within 2 kHz, and high-frequency signals rapidly decay. And a high-voltage testing system was built, and the phase change of the external optical fiber during partial discharge of the corresponding cable joint was measured using a coherent optical time-domain reflectometer. The correctness of the simulation results was verified through experiments. This analysis can provide basis for acoustic partial discharge detection of cable joints.

As an emerging method of substation inspection, when unmanned aerial vehicle (UAV) is too close to the substation during the inspection process, it can cause interference to its normal operation, causing damage to the internal electrical structure of the drones or discharges. In order to analyze the safety of UAV substation inspection, we construct a simplified electric field simulation model for UAV and 220 kV substation, and use finite element method to simulate and analyze the changes in their electric field. The UAV inspection methods are divided into three types: UAV traverse insulation intervals for inspection, UAV conduct inspections near wires, and UAV patrol above insulation intervals, the variation of maximum surface field strength of unmanned aerial vehicles under three inspection methods is simulated and calculated separately. The maximum surface electric field strength of the UAV during the UAV conduct inspections near wires is 768 kV/m, less than air breakdown field strength (3000 kV/m). As a result, under the condition of only considering the influence of electric field, UAV is safe under these three inspection methods.

UAVs have the advantages of close observation, eliminating visual dead space, improving inspection speed and carrying a variety of inspection equipment in substation equipment inspection, which meet the needs of intelligent substation construction. But the complex electromagnetic environment in the substation, it is easy to cause electromagnetic interference to the UAV, while the UAV into the strong electric field environment there is also the possibility of triggering discharge. In this paper, we take the Genie 4 UAV commonly used for substation inspection as the research object, and study the safety distance when the UAV inspects the high-voltage equipment in the substation. By constructing the simulation model of the UAV and 220 kV substation, we simulate and calculate the electric field distribution when the UAV inspects different high-voltage equipment. Finally, the safety distance of the UAV inspection of high-voltage equipment in substations is analyzed by the simulation results, and provides data support for the subsequent research.

The complex distribution network has an obviously various lightning performance with that of the straight periodic lines, due to the uneven pole spans and feeder structure in the distribution network. In this paper, the lightning-induced flashover (FO) performance in a distribution network is investigated via a Monte Carlo method, based on the numerical PEEC-MTL method for line modeling and transient simulation. Different from the traditional indicator, i.e., the flashover rate of a total line, the annual FO number at individual poles is defined and concerned to reflect the distribution of the FO risk due to indirect lightning strikes. It is found that the in a part of an existing rural distribution network of concern if the terminal poles with distribution transformers located protected by surge arresters by default, the poles where the open area is around are more likely to have a higher annual FO number. The soil conductivity significantly affects the values of the annual FO number of individual poles, while there is no obvious change in its overall distribution characteristic of the distribution network, which is mainly determined by the line topology. Compared with the case without surge arresters besides the distribution transformers, it indicated the great significance of the protection for terminal poles with distribution transformers. The present work could provide a theoretical basis for differentiated protection against indirect lightning and more factors and conditions would be of concern in the following work.

The optical fiber composite overhead ground wire (OPGW) has been widely used in power transmission lines. It can not only serve as an overhead ground wire for lightning protection but also be used for information communication for power system as well as achieving functions such as online monitoring. There are two common grounding methods for OPGW: all-tower grounding and single-point grounding. Adopting a single-point grounding method can effectively reduce induction current and energy loss by 50 Hz power transmission, but may generate a larger induction voltage. This paper studied the induced voltage of insulated OPGW by single-point grounding on 35 kV single-circuit distribution lines. The conditions of segmented insulation and mid-point grounding are adopted for numerical simulation, and the influence of tower height and wire displacement on induction voltage was discussed. The results showed that tower height and wire displacement have almost no effect on the induced voltage.

Tropical islands frequently face energy supply shortages due to limitations imposed by their natural environment. The utilization of a single microgrid structure often leads to power instability and even network-wide failures. Interconnecting multiple microgrids and operating them in a clustered manner can effectively enhance the reliability of power supply. However, during the process of integrating a specific microgrid into the cluster, voltage magnitude and phase imbalances at the common connection points can give rise to transient stability issues. To address the aforementioned challenges, a microgrid cluster synchronization and integration strategy based on pre-synchronization control is proposed. The voltage magnitude of inverter outputs and the voltage vector of the microgrid cluster are transformed into the rotational coordinate system using Clark and Park transformations, thereby obtaining the phase angle and magnitude deviations of the voltages. With PI control employed, compensatory values for grid frequency and grid voltage are individually determined to ensure consistent voltage phase and magnitude between the pre-synchronization side and the microgrid cluster side. This approach effectively resolves voltage and frequency fluctuations during mode transitions, enabling smooth switching between the islanded and grid-connected modes of microgrid operation. Finally, the effectiveness of the proposed control strategy is verified through simulation to be a feasible solution for the smooth integration of a microgrid into microgrid clusters.

Metal oxide arrester (MOA), as an important device for limiting overvoltage in transmission lines, can ensure the safe and stable operation of the power system. The technology of using infrared instruments for troubleshooting arrester is relatively mature, but environmental factors can cause significant interference in infrared detection, and its accuracy is not high through visual observation. This article proposes an improved U-Net MOA segmentation algorithm to segment arresters in infrared images, and obtains temperature information from the images through operations such as dataset preprocessing, image segmentation, grayscale conversion, and temperature extraction. By combining the surface temperature method, the arrester in the infrared image can be diagnosed and the fault level and related treatment suggestions can be given.

Image feature matching and image recognition are two important branches of image processing. In recent years, with the rapid development of artificial intelligence, big data and other information technology, as well as the technological breakthrough of computer computing ability, image analysis technology has been widely used in various industries. Daily inspection and defect detection of substation equipment is an important work of equipment operation and maintenance. Relying on image intelligent processing technology, it can greatly improve the efficiency of operation and maintenance, reduce the workload of operation and maintenance personnel, improve the detection probability of equipment defects and abnormalities, and ensure the safe and stable operation of power grid. Aiming at the complex defect scene of substation equipment, it has good research significance and application prospect to carry out the research of intelligent defect image detection technology. This paper described the basic principles and development of image feature matching technology and artificial intelligence image recognition technology, discussed the key problems and technical difficulties in the practical application of image processing technology, introduced the solutions and technical characteristics of key technologies, and put forward the image intelligent detection algorithm and multi-dimensional image comprehensive analysis method suitable for complex scenes. The verification results indicated that the method described in the article can effectively solve the problem of device multi scene defect detection.

This article mainly describes a rapid motorized spanning device for transmission line erection development process. First of all, the article analyses the characteristics and difficulties of crossing power lines, kilometres, railways and other crossing constructions when erecting transmission lines and puts forward the functional requirements of the crossing frame. The structural form of the fast motorised crossing device is designed in combination with the functional requirements of the crossing frame. Finally, the focus of this paper is to use ANSYS structural analysis software to simulate the structure of the rapid motorized crossing device for various load conditions and analyse whether its load bearing capacity is satisfied.

The arc sag is the key point of quality control in the erection of transmission lines, and the accuracy of its observation directly affects the operation safety of the line. The research status of arc sag observation of transmission lines is introduced, the theoretical and practical basis and structural and functional parameters of the arc sag observer on the convenient tower are analyzed, and the good results obtained by the arc sag observation of Anhui Shuangling-Transformer-Anqing 3500 kV transmission line project are introduced, which provides reference for similar projects.

Accurately identifying the fault type of transmission lines is of great significance to the safe operation of transmission lines. In this paper, the distributed detection method is adopted to collect and classify transmission line fault data, while 15 time-domain features and 12 frequency-domain features are extracted from each fault waveform to build a transmission line fault database. Then, based on this database, study on classification and identification of faults by Deep Forest t algorithm, and eliminate the imbalance of data by SMOTE, finally achieve intelligent diagnosis of fault types of transmission lines. The correctness rate of the proposed method is 92% in the binary diagnosis of lightning and non-lightning strike, and 79% in the full classification diagnosis. Compared with the traditional classification algorithm, the proposed method has higher accuracy and better generalization performance. The research has reference significance for the digital construction of transmission lines and the intelligent upgrading of power grid.

Polypropylene (PP) is regarded as a rather potential insulation material alternative for the next generation HVDC cable system. Grafting styrene is proved to be an effective method to further enhance the DC insulation properties especially under high temperature. The trap introduced by grafting modification is believed to be the key issue on such enhancement. In this paper, the quantum chemistry analysis based on DFT method is adopted to computationally investigate the chemical trap originating from grafting modification. The results indicate that grafting styrene introduces new trap orbitals within the HOMO–LUMO gap of PP, and the grafted aromatic ring, especially the delocalized Pi bond is responsible for it. Besides, the delocalized Pi bond can also lead to the local high negative electrostatic potential area on the PP chain, thus affecting the microscopic charge transportation in PP. This work is expected to provide a reference for investigating the mechanisms of charge transportation and macroscopic electrical properties enhancement of PP-based insulation for HVDC cables.

Vehicle-mounted mobile transformers are installed on mobile platforms, characterized by their compact structure and convenient transportation. It can be used as a temporary transformer when the capacity of the main transformer in a substation is insufficient or the power planning and construction do not meet the requirements. In order to analyze the temperature distribution in the compacted 110 kV/40 MVA mobile transformer at this voltage and capacity level, a single-phase axisymmetric 2-D finite element model of the mobile transformer was established, and transient temperature rise of the transformer was simulated using the short-circuit method. The results show that the maximum hotspot temperature reached 87.9 ℃ when the total losses were applied, while it reached 85.2 ℃ when the rated current was applied. The temperature rise satisfies the conditions for safe operation, indicating that the transformer’s structural design is reasonable and has good heat dissipation performance.

If the scale of distributed photovoltaic exceeds the hosting capacity of the distribution network, the safe and stable operation of the distribution network will be seriously affected. To solve this problem, DIgSILENT/PowerFactory is used to calculate the hosting capacity of distributed photovoltaic in the distribution network. Firstly, a simulation model of low-voltage distribution network was established, and the influence mechanism and simulation analysis were used to explain the influence of distributed photovoltaic capacity and location on voltage, current, losses and harmonics. On this basis, the corresponding constraint conditions are constructed, and the hosting capacity of distributed photovoltaic in the distribution network is calculated to obtain the photovoltaic hosting capacity of each nodes, as well as the limiting factors and limiting elements.

In recent years, the use of optical fiber composite overhead ground wires (OPGW), which are a combination of optical fibers and overhead ground wires, has become increasingly common due to the growing demand for reliable and secure communication links in power transmission and distribution systems. In high-voltage transmission lines, the all grounding method is commonly used for OPGW. Due to electromagnetic induction, there is an induced electromotive force on the ground wire, creating a loop between the towers and generating induced currents. These induced currents result in power losses. This study establishes a single-circuit model of a 750 kV transmission line using typical towers, with two OPGW cables employed and an all grounding configuration. The distribution of induced currents and ground currents along the line is investigated. Additionally, the effects of three operational parameters, namely, ground resistance, span distance, and conductor transposition, on induced currents are discussed. The results indicate that span and ground resistance have a relatively small impact on ground-induced currents, while ground resistance has a more significant influence on ground currents. On the other hand, conductor transposition has a substantial effect on both induced currents along the ground wire and currents into the earth.

The common lightning strikes in nature can threaten the flight safety of aircraft directly. In order to investigate the lightning environment of aircrafts and improve the lightning protection ability, a three-dimensional, full-size electromagnetic calculation model is established here. According to the static charge distribution, the lightning attachment points are determined, and several lightning paths are designed. Calculation results of the electromagnetic field on the aircraft surface under different paths show that the electric field distribution is uniform, but the magnetic field distribution is significantly different. Inside the aircraft, however, the variation characteristics of the electromagnetic field is related to the lightning path. The electromagnetic field tends to show the highest value in the area close to the lightning current flow. This study can determine the intensity of lightning current in each area, and help to find the weak point, which has important reference significance for the lightning protection design of the aircraft.

The side overlap rate and heading overlap rate of the oblique photographic route are an important factor affecting the 3D reconstruction. The heading overlap rate and the side overlap rate determine the number of images and thus affect the model accuracy and modeling time. In this paper, in order to investigate the influence of oblique photographic route overlap rate on 3D reconstruction, oblique photographic images of substations with different combinations of overlap rates were acquired by using DJI Mavic 2 Enterprise for oblique photography at 40 m height, and then 3D reconstruction was performed to obtain 3D models of substations. The final experimental results proved that as the overlap rate increased, the number of acquired images increased, and the 3D model obtained by the three reconstructions had higher accuracy, but the data acquisition time and modeling time also increased greatly. Considering the model accuracy and modeling work efficiency, it is more appropriate to use about 80% of the heading overlap rate and the side overlap rate for the 3D reconstruction of general substations.

According to the requirements of the fixed-wing UAV’s ejection acceleration take-off index, based on the T-type equivalent circuit model of the linear induction motor, the electromagnetic thrust output value of the linear induction motor required for acceleration and driving is deduced and analyzed. Design a long primary unilateral linear induction motor for take-off of fixed-wing UAV to meet the electromagnetic ejection acceleration requirements of UAV. The equivalent circuit of the motor considering the side effect is established, and the mathematical model of the linear induction motor is established according to the design parameters of the linear induction motor. Simulation and analysis of the influence of the slip frequency on the electromagnetic thrust output of the linear induction motor under different operating speeds and different influencing factors. The constant current-slip frequency control method is used to control the electromagnetic thrust output of the linear motor, seek the optimal slip frequency of the linear induction motor, and optimize the design parameters and control methods to meet the accelerated take-off requirements of the fixed-wing UAV.

Modular Multilevel Converter (MMC) is a common multilevel topology for medium voltage motor drives. However, the voltage fluctuation of the sub-module (SM) capacitor is the main obstacle when motor runs at low speed. A variable frequency voltage injection method is recommended in this paper, in which the frequency of the injection voltage changes synchronously with the speed (output frequency) and is permanently guaranteed to be K times of the frequency. The optimal voltage suppression can be achieved at low frequency operation and overmodulation can be effectively avoided. Finally, the availability of the recommended variable frequency voltage injection method is checked with simulation and experimental results.

In order to suppress input current harmonics and output voltage ripple and simplify the configuration of linear aero AC-DC converters, this paper proposes a 24-pulse rectifier based on an auto-fed half-bridge auxiliary circuit. It consists of a 12-pulse transformer, a rectifier bridge and an auxiliary circuit. The auxiliary circuit is simple in structure and its output is connected in parallel with the load. It injects AC voltage ripple into the DC bus, which is six times the frequency of the power supply. Thus, a 24-pulse DC output is obtained, and pulse multiplication is achieved. In this paper, the circuit structure, operating mode and harmonic suppression principle of the proposed 24-pulse rectifier are analyzed. The output current and output current ripple functions are derived, the parameter optimization study of the autotransformer is carried out, and the KVA rating of the autotransformer is discussed. The simulation and experimental results verify the correctness of the theoretical analysis and the feasibility of the proposed method.

The operation experience shows that the zinc oxide line arrester fracture is a common fault due to instantaneous large current. In view of the difficulties in the fracture analysis of zinc oxide line arresters, a highly reliable, objective, scientific and practical fracture prediction method for zinc oxide line arresters is proposed. Calculate that maximum pulse power of the zinc oxide valve plate by operate a nonlinear time domain method according to the waveform data of the obtained lightning current and the nonlinear resistance model of the lightning arrester; According to the internal crack defect data of the zinc oxide varistor and the calculated maximum pulse power, the fracture of the zinc oxide line arrester is predicted. Finally, a case study is given to illustrate the effectiveness of the proposed method. The work of this paper can provide an effective reference for the operation and maintenance of line arrester.

In this paper, a 1100 kV GIL thermal–mechanical-electrical multi-physics coupling simulation model was established, the evolution characteristics of the internal temperature field of the tri-post insulator GIL with external factors were investigated. The results show that the temperature of the GIL tri-post insulator gradually decreases from the conductor to the enclosure, and the internal temperature is slightly lower than the surface; the maximum thermal stress occurs at the edge of the insulator wrapped around the conduct. Under rated conditions, the maximum stress inside the insulator can be up to 180 MPa, and the thermal expansion difference between the upper and lower surfaces of the enclosure hardly changes with temperature. This study provides an important guarantee for the safe operation of GIL.

Metallized film capacitors are key power equipment in flexible direct transmission systems, pulse power systems and electric vehicles, and their application performance directly affects the stability and reliability of power grid systems and users. This article investigates the effects of hot-press setting time and winding tension control on capacitor performance during the manufacturing process of capacitor elements in durability tests. At a certain temperature, the setting of the hot-press setting time of the capacitor element and the winding tension setting of the element can eliminate the residual stress inside the metallized film element, make the dielectric film produce irreversible heat shrinkage, eliminate the moisture and air in the metallized film element through the film shrinkage and physical compression force to compress the element, reduce the probability of air discharge inside the metallized film, and improve the internal breakdown strength and partial discharge starting voltage of the element. Therefore, according to different performance requirements, choosing a certain hot-press setting time and winding tension is conducive to improving the service life of metallized film capacitor.

In order to improve the efficiency of photovoltaic (PV) grid-connected response and reduce the total harmonic distortion rate, a multivariate model predictive control (MPC) strategy for PV inverter grid-connected system is proposed. Firstly, the maximum power point tracking (MPPT) of DC/DC converter is designed according to the output power curve of PV. Then, based on the mathematical model of the inverter in rotating coordinate system, MPC method is used to determine the predicted value of the output current at k + 2 time. The current error and DC bus voltage error are taken as the control factors of the value function. The aim is to minimize the value function and achieve optimal control. Finally, MATLAB/Simulink simulation verifies the effectiveness of this strategy in improving the voltage stability of DC bus and reducing the total harmonic distortion of current on the grid side.