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Abstract The micro‐defects in epoxy‐based insulation materials generate a local high electric field which results in continuous degradation, seriously endangering the insulation system of gas‐insulated switchgears. A highly sensitive detection technique is reported for micro‐defects of insulation pull rods based on the photon counting (PC) technique. The results demonstrated that for an epoxy‐based insulation pull rod, the photons released during electroluminescence and ionisation at 2 kV, which is less than the partial discharge inception voltage, can be clearly detected. The findings presented a strong correlation between photon counts and defect severity. Discourse has been conducted to elucidate the mechanism behind defect‐induced PC, employing the amplification of ionising luminescence through electric field distortion induced by micro defects and the augmentation of electroluminescence through the aggregation of trap charge. In this regard, the authors verified that PC can serve as a potential tool in the detection of micro‐insulation defects, which also has huge potential in online insulation condition monitoring.

Aircraft electrification poses new challenges to the safe design of the insulation system under harsh operating conditions. This study focuses on the investigation of electrical treeing, a precursor to electrical breakdown in the bulk of electric wires and cables, under emulated low pressure and high temperature for high density electrification at high altitude. It was found in a model insulation of cross-linked polyethylene (XLPE) that low pressure and high temperature significantly decreased the treeing initiation voltage and increased tree growth propagation rate. Moreover, the presence and size of artificial air gaps affected tree morphology, growth rate, and fractal dimension in a way that decreases insulation durability. The effect of pressure on treeing growth was studied by using the partial discharge (PD) measurements, which suggested lower pressure increased PD activities, with respect to the rate and magnitude of PDs during both stages of treeing initiation and propagation. This work could be used as a baseline for studying electrical treeing phenomenon at high altitudes with coupled high temperature-low pressure, to pave the way for the reliable design of insulation systems on the path towards aircraft electrification.

PCB layouts with different polygon shapes and insulation distances were prepared and their surface flashover voltage subjected to different ramping rates were measured at different temperatures and different low gas pressures for emulated high-altitude conditions. The dependence of the surface flashover voltage on effects of gas pressure, surface insulation distance, temperature, and polygon shape was studied. Modulation efforts which include tailoring the local surface conductivity and local topography modification were performed to increase the flashover of PCB, and the related mechanism was studied. The results showed that the voltage ramping rate plays an important role in determining flashover voltage. The flashover voltage is lower when the sample is subjected to a rapid voltage ramping rate than with a slow ramping rate. This phenomenon is more prominent towards ambient pressure. The increase in temperature results in a decrease in flashover voltage at 100 kPa, while at 20 kPa and 10 kPa, the influence of temperature on flashover becomes less significant. Through-holes designed in the PCB have a positive role in increasing flashover voltage at lower pressures. However, at 100 kPa, the holes no longer contribute to any higher flashover voltage. Modification of local surface conductivity has no contribution in increasing the flashover voltage, while a surface coating with a surface conductivity of $10^{-10}$ S dramatically decreases the flashover voltage. The work presented in this paper provides a reference for the design and modification of PCB layouts for use in future aerospace hybrid propulsion systems.

Biometric authentication prevents losses from identity misuse in the artificial intelligence (AI) era. The fusion method integrates palmprint and palm vein features, leveraging their stability and security and enhances counterfeiting prevention and overall system efficiency through multimodal correlations. However, most of the existing multi-modal palmprint and palm vein feature extraction methods extract only feature information independently from different modalities, ignoring the importance of the correlation between different modal samples in the class to the improvement of recognition performance. In this study, we addressed the aforementioned issues by proposing a feature-level joint learning fusion approach for palmprint and palm vein recognition based on modal correlations. The method employs a sparse unsupervised projection algorithm with a "purification matrix" constraint to enhance consistency in intra-modal features. This minimizes data reconstruction errors, eliminating noise and extracting compact, and discriminative representations. Subsequently, the partial least squares algorithm extracts high grayscale variance and category correlation subspaces from each modality. A weighted sum is then utilized to dynamically optimize the contribution of each modality for effective classification recognition. Experimental evaluations conducted for five multimodal databases, composed of six unimodal databases including the Chinese Academy of Sciences multispectral palmprint and palm vein databases, yielded equal error rates (EER) of 0.0173%, 0.0192%, 0.0059%, 0.0010%, and 0.0008%. Compared to some classical methods for palmprint and palm vein fusion recognition, the algorithm significantly improves recognition performance. The algorithm is suitable for identity recognition in scenarios with high security requirements and holds practical value.

The requirements for the construction of a new power system inevitably pose significant challenges and changes to the operation and maintenance of the power grid. To ensure the safe and stable operation of ultra-high voltage (UHV) transmission equipment, this work reports on the principles and preliminary results of using electroluminescence (EL)-based photon counting (PC) methods for early detection of micro-defects in GIS/GIL insulation spacer. In this study, the impact of voltage, gas pressure, and gas composition on the photon response of insulation is examined. Furthermore, the corresponding relationship between defect status and photon response characteristics is explored, along with the discussion of the EL mechanism and its evolution induced by defects. The research results demonstrate that PC measurement exhibits high sensitivity to variations in millimeter-scale defect size, position, and morphology at lower electric fields before partial discharge (PD) initiation. With this regard, this paper reveals promising prospects for the early detection of micro-defects in UHV transmission equipment using PC measurement-based methods.

This paper proposes a deep learning-based intelligent detection device for insulation pull rod defects, addressing the issues of low detection accuracy, poor timeliness of intelligent analysis, and the difficulty in preserving detection results. Firstly, by constructing the pull rod defects dataset and training the YOLOv5s network, along with commonly used object detection algorithms in industrial defect detection, the feasibility of deep learning networks for insulation pull rod defects detection is explored. Secondly, the trained model is combined to build an intelligent detection device for pull rod defects, integrating insulation pull rod image acquisition and defect detection into a unified system. The research results demonstrate that the YOLOv5s network can quickly and accurately detect pull rod defects. On the test set constructed in this paper, the detection performance metric mAP@0.5:0.95 of the trained model reached 54.7%. Specifically, the mAP@0.5 score was 86.9% at a threshold of 0.5. The detection speed FPS reached 169.5, significantly improving the detection efficiency and accuracy compared to traditional object detection algorithms. By establishing an organic connection between the image hardware acquisition device and the deep learning network, the existing problems of inefficient detection and difficult storage of detection results in pull rod defects detection methods are effectively addressed. This research provides new insights for detecting insulation pull rod defects.

The reliability of GIS (gas-insulated switchgear) circuit breakers significantly depends on the condition of the insulated pull rods, with micro-defects on their surface posing a potential risk for micro-discharges and breakdown incidents. Experimentally investigating these micro-discharges is challenging due to their minute nature. This study introduces a framework to examine the linkage between micro-defects and micro-discharges, coupled with numerical simulations of the micro-discharge process in insulated pull rods afflicted by surface infiltration flaws under operational conditions. Initially, samples containing micro-defects were sectioned via water jet cutting for microstructural analysis through white light interferometry. Subsequently, a two-dimensional axisymmetric model simulating positive corona discharge from a needle to a plate electrode was employed to derive the relationship between charged particle density and the electric field in SF6 and air. Building on these observations, a micro-discharge model specific to micro-defects was developed. Comparative analysis of micro-discharge behaviors in SF6 and air for identical defect types was conducted. This research framework elucidates the discharge dynamics of charged particles in SF6 and air during micro-discharge events, shedding light on the mechanisms underpinning micro-discharges triggered by insulation rod defects.

Abstract To meet the requirements of power grid operation control, constructing an extensive sensor network in the power grid is a future development trend. However, due to the high cost, the difficulty of continuous power supply for a long time, the large amount of energy consumption, and the environmental problems caused by abandoned batteries, the traditional power supply mode based on batteries for sensors is inconsistent with China's goal of carbon peak and carbon neutrality. It cannot meet the needs of the future grid. Therefore, it is significant to solve the energy supply problem of numerous sensors to promote the construction of new power grid and improve the utilization rate of renewable energy. As an emerging energy harvesting device, triboelectric nanogenerators (TENG) are suitable for developing self‐powered sensors and powering low‐power sensors due to their mall size, high efficiency, low cost, and environmental friendliness. At the same time, due to the abundant, stable, and widely distributed magnetic field around the equipment in the grid, it can provide continuous excitation for the TENG. Therefore, applying magnetic field energy‐harvesting TENG in the future power grid has a broad development prospect. This paper analyzes the development trend and the crucial problems facing the power grid in the future. We review the research and application of TENG based on the magnetic field in recent years and explain the mechanism of TENG in detail. Finally, the application prospect of TENG in the future power grid has been prospected. This paper can provide a reference for applying magnetic field energy harvesting triboelectric nanogenerators in future power grids.

The construction of the future energy structure of China under the 2050 carbon-neutral vision requires compact direct current (DC) gas-insulation equipment as important nodes and solutions to support electric power transmission and distribution of long-distance and large-capacity. This paper reviews China's 10-year progress in DC gas-insulated equipment. Important progresses in basic research and industry perspective are presented, with related scientific issues and technical bottlenecks being discussed. The progress in DC gas-insulated equipment worldwide (Europe, Japan, America) is also reported briefly.

Abstract Triboelectric nanogenerators (TENGs) represent a promising next‐generation renewable energy technology. TENGs have become increasingly popular for harvesting vibration energy in the environment due to their advantages of lightweight, broad range of material choices, low cost, and no pollution. However, issues such as input force irregularity, working bandwidth, efficiency calculation, and dynamic modeling hinder the use of TENGs in industrial or practical applications. In this paper, the modeling process of the dynamical system of a TENG is reviewed from the perspective of energy flow. In addition, this paper reviews the main contributions made in recent years to achieve optimized output based on springs, magnetic forces, and pendulums, and introduces different ways to increase the bandwidth of TENGs. Finally, the main problems of TENGs in the process of harvesting vibration energy are discussed. This review may serve as a practical reference for methods to convert irregular mechanical input sources into optimized output performance toward the commercialization of TENGs.

Electromagnetic radiation at higher harmonics of the plasma frequency ( ω ∼ n ω _pe , n > 2) has been occasionally observed in type II and type III solar radio bursts, yet the underlying mechanism remains undetermined. Here we present two-dimensional fully kinetic electromagnetic particle-in-cell simulations with high spectral resolution to investigate the beam-driven plasma emission process in weakly magnetized plasmas of typical coronal conditions. We focused on the generation mechanisms of high-harmonic emission. We found that a larger beam velocity ( u _d ) favors the generation of the higher-harmonic emission. The emissions grow later for higher harmonics and decrease in intensity by ∼2 orders of magnitude for each jump of the harmonic number. The second and third harmonic (H _2 and H _3 ) emissions get closer in intensity with larger u _d . We also show that (1) the H _3 emission is mainly generated via the coalescence of the H _2 emission with the Langmuir waves, i.e., H _2 + L → H _3 , wherein the coalescence with the forward-propagating beam-Langmuir wave leads to the forward-propagating H _3 , and coalescence with the backward-propagating Langmuir wave leads to the backward-propagating H _3 ; and (2) the H _4 emission mainly arises from the coalescence of the H _3 emission with the forward- (backward-)propagating Langmuir wave, in terms of H _3 + L → H _4 .

Abstract The 2050 carbon‐neutral vision spawns a novel energy structure revolution, and the construction of the future energy structure is based on equipment innovation. Insulating material, as the core of electrical power equipment and electrified transportation asset, faces unprecedented challenges and opportunities. The goal of carbon neutral and the urgent need for innovation in electric power equipment and electrification assets are first discussed. The engineering challenges constrained by the insulation system in future electric power equipment/devices and electrified transportation assets are investigated. Insulating materials, including intelligent insulating material, high thermal conductivity insulating material, high energy storage density insulating material, extreme environment resistant insulating material, and environmental‐friendly insulating material, are categorised with their scientific issues, opportunities and challenges under the goal of carbon neutrality being discussed. In the context of carbon neutrality, not only improves the understanding of the insulation problems from a macro level, that is, electrical power equipment and electrified transportation asset, but also offers opportunities, remaining issues and challenges from the insulating material level. It is hoped that this paper envisions the challenges regarding design and reliability of insulations in electrical equipment and electric vehicles in the context of policies towards carbon neutrality rules. The authors also hope that this paper can be helpful in future development and research of novel insulating materials, which promote the realisation of the carbon‐neutral vision.

Abstract To suppress the charge accumulation on the spacer surface in direct current (DC) gas insulated transmission line (GIL) is an important and emergent issue for the development of a clean, safe and economic smart grid. A design method of the DC spacer is proposed, and a spacer prototype is prepared and evaluated both by simulation and type test. The DC withstand voltage test and polarity reversal test are performed using the new DC spacer compared with a commercialised 220 kV AC spacer. The simulation results indicate that the surface electric field and surface charge of the DC spacer are lower than those of the alternating current (AC) spacer under DC voltage. The test results verify that the surface flashover voltage of this DC spacer is higher than that of the AC spacer. The potential feasibility of the spacer design for HVDC is discussed. It is hoped that the content of this paper can bring new ideas in the development of HVDC gas insulated equipment.

A narrow resonance bandwidth of an energy harvesters limits its response to the wide frequency spectrum in ambient environments. This work proposes an addition of a nonlinear restoring force applied to a triboelectric nanogenerator (TENG) to tune and broaden the resonance bandwidth. This restoring force is applied by permanent magnets at both sides of the slider and two external magnets. The noncontact strategy is adopted between the slider and the grating electrodes to avoid the wear of electrodes and energy loss caused by friction. The results show that compared with the linear system, the nonlinear noncontact TENG (NN-TENG) can increase the peak current from 6.3 μA to 7.89 μA, with an increment of about 25%, increase the peak power from 650 μW to 977 μW, increasing by about 50%, and increase the bandwidth from 0.5 Hz to 7.75 Hz, increasing by about1400%. This work may enable a new strategy to boost the bandwidth and output power of TENG through nonlinear oscillators.

Abstract The gas‐insulated switchgear (GIS) has been widely used in modern ultra‐high voltage systems. However, once it fails, its fully enclosed feature brings challenges in its diagnosis and maintenance. As the failure rate of GIS due to insulator failure has been increasing in recent years, it is necessary and important to understand the commonly existing defects presented in the insulator. First, the manufacturing process of GIS insulators is introduced here. The defect types commonly existing in the insulator are categorised. The failure of GIS due to insulator defects that occurred in recent years are reviewed and discussed. The content in this study is useful for engineers and scientists to study on the GIS solid insulation defects and their failure mechanisms.

As a state of matter, liquids exist in an extremely wide range, including water such as that in oceans and rivers, as well as various solutions, oils, liquid metals, etc. Due to the fluidity of liquids, the triboelectric effect based on them often shows unexpected results and can be used in complex environments. Herein, the latest research on working principles of the triboelectric effect at liquid–solid, liquid–liquid, and liquid–gas interfaces are reviewed. The factors affecting triboelectric charge generation and the output performance of liquid‐interfaces‐based TENGs (LI‐TENG) in terms of material, environment, and structure are systematically discussed. Besides, to harvest the ubiquitously existing energy in various forms, studies about the hybridization of LI‐TENG with other energy harvesters for syngeneic single‐source and multisource energy harvesting are also reviewed. Moreover, the performances of LI‐TENGs as energy harvesters and as novel sensors with various applications are reviewed. Finally, opportunities and challenges in the future development of LI‐TENG are discussed.

Abstract The safe and reliable operation of insulation material used in key high voltage components under extreme environmental conditions represents the major concerns for manufacturers and operators of More Electric Aircrafts (MEA). Surface discharge occurring in high current carrying components in DC power system diminishes the insulation material’s performance and life, especially at high‐temperature conditions. Here, the surface discharge behaviour of two commonly used high‐temperature insulation materials, ethylene‐tetrafluoroethylene (ETFE) and polyetheretherketone (PEEK) is studied at different temperatures under ramp and DC voltages. Extracted partial discharge (PD) features are presented and the impact of voltage polarity on surface discharge propagation is discussed. Our studies reveal that, while both materials exhibit non‐linear PD behaviour with respect to their electrical conductivity, ETFE generally shows PDs with higher intensity at high temperature above 100°C with a higher possibility of surface discharge due to its lower permittivity. Overall, the PD mechanism in high‐temperature, DC voltage applications is explored, and a basis for the selection of high‐temperature PD suppressing materials is developed.

Abstract To study the effect of nano‐silica particles on the conductivity characteristics of ethylene propylene diene monomer (EPDM) insulation, EPDM nanocomposites with different mass fractions of nano silica were prepared via the melt‐blending method. Scanning electron microscopy was used to analyze the dispersion of nanoparticles in EPDM. Based on the Fourier‐transform infrared spectrum, the bonding properties between the nanoparticles and EPDM were analyzed. The steady‐state current at 30–100 °C and 1–20 kV/mm was measured. Moreover, the conductivity characteristic was analyzed. The experimental results show that as the content of nano‐silica increases, the electrical conductivity of EPDM nanocomposite as well as the threshold field strength gradually decreases. Samples with a small number of nanoparticles will increase the activation energy of the carrier conductivity, and the interface region effect introduced by nanoparticles will reduce the carrier mobility and concentration, resulting in a lower conductivity. Comparing the calculated value of the dielectric constant with the measured value can conclude that the high‐field conductance process is a combination of the electrode effect and the body effect, which in this case, Schottky effect dominates.

Air gap defects inside a spacer reduce its insulation performance, resulting in stress concentration, partial discharge, and even flashover. If such gap defects are located at the interface between the insulation and conductor, a decrease in mechanical stress may occur. In this work, a finite element method-based simulation model is developed to analyze the influence of gap defects on the electrical and mechanical properties of a ±320 kV direct current gas insulated line (DC GIL) spacer. Present findings reveal that a radially distributed air gap produces a more significant effect on the electric field distribution, and an electric field strength 1.7 times greater than that of the maximum surface value is observed at the air gap. The axial distribution dominates the distortion of the surface stress by generating a stress concentration region in which the maximum stress of the air gap is twice the pressure in the surrounding area.

Partial discharge (PD) as one of well-known signatures of defects in the insulation system of high voltage equipment has been studied over eight decades. It is of a great interest to power grid operators and owners to identify and distinguish local weak spots in insulation system of the key components of power system by using the obtained PD information to make timely decision thus to avoid any unexpected failures in the system. This article reviews the research progress of PD in high voltage apparatus, including motors and generators, cables, transformers and gas insulated equipment, with attempts to assess the severity of different types of PD initiating defects as well as key PD features that can be selected for classifying defects. Experimental and on-site test results for each type of discharge and defect associated are summarized and discussed. Also, development of these defects during operation of equipment caused by changes in physical and chemical parameters of defect and/or insulation, and its impact on phase-resolved PD pattern variation are thoroughly explained. It is expected that this paper can provide a comprehensive guideline for PD data analysis of available PD information extracted by conventional PD acquisition instruments for both engineers and asset managers of high voltage apparatus.

DC cross-linked polyethylene (XLPE) power cables are being used recently for HV/EHV applications, the reliability of which is claimed to be significantly affected by space charge accumulation in the insulating material. Many methods have been provided for limiting the injection and accumulation of space charge. In the paper, three kinds of specimens with graphene coating applied on a sandwich composed of XLPE and semiconductive layer were made. Space charge distribution of specimens was measured at 10 kV/mm and 40 kV/mm under room temperature and 60 °C. The measurement results show that positive charges are injected and accumulate in reference XLPE specimen. Negative charge accumulates in XLPE, and the quantity of positive charge injected from anode is significantly reduced, when graphene is coated on the semiconductive side. Little space charge is injected into XLPE coated with graphene, and positive charge accumulates near the interface between XLPE and electrode, which lowers electric field near the anode. Graphene layer introduced deeper trap distribution, thus making difficult negative charge injection from the cathode into XLPE.

High temperature vulcanized silicone rubber (HTV SIR) is important insulation for high voltage direct current (HVDC) cable accessories. The pulse voltage in the HVDC system may initiate an electrical tree in SIR insulation. During the operation, there is a temperature gradient in SIR caused by the different temperatures of conductor and external environment. So it is necessary to research the electrical tree initiated by pulse voltage under the temperature gradient. In this paper, electrical trees in SIR with different temperature gradients were recorded. The inception voltage, tree length, and accumulated damage (AD) distribution were analyzed. The experiment results indicate that tree inception voltage decreases with the increase of temperature of the ground electrode when the needle temperature is 90 °C, it also decreases with the increase of needle temperature when the ground temperature is 90 °C. All the trees are in bush structure when the ground temperature is 90 °C, the structure changes from branch to bush with the increase of ground temperature when the needle temperature is 90 °C. When the needle temperature is 90 °C, AD distribution changes obviously with the increase of ground temperature. The conductivity of SIR under different temperatures and electric fields was tested. The effect of changing conductivity on tree inception was discussed. Surface potential decay (SPD) at different temperatures was tested. The trap characteristics and charge kinetic properties influenced by temperature may be the main reasons for the change of tree structures in the growth process.

Perfluorinated isobutyronitrile (C4F7N) is favored in electrical engineering because it is an environmentally friendly gas-insulating medium with a low greenhouse effect. Unfortunately, under the influence of electricity and over-heating, its decomposition results in the deterioration of its insulating properties, which potentially leads to partial discharge or even gas breakdown. In this paper, the adsorption behavior of C4F7N gas and its toxic decomposition product, acetonitrile (C2N2), on MoS2 surfaces doped with small copper clusters was investigated by calculating the adsorption energy and density of states, etc. The effects of multiple initial adsorption positions as well as externally applied electric fields were also taken into account. The results depict that the maximum adsorption energy of C4F7N on the Cuγ (γ = 1–3)-MoS2 surface gradually decreases with the increase in γ. The Cu3-modified MoS2 is most suitable for use as a resistive-based gas-sensitive sensor substrate. This paper provides the theoretical foundation for the maintenance of future power equipment with environmentally friendly insulating gas.

A mathematical model is established using the space coordinates of nodes and vector matrix of components to study the construction method and lightweight nature of single-layer tensegrity structures on the basis of their geometric parameters. Connection matrix and configuration of the single-layer tensegrity structures are built using MATLAB software. The force balance equations of nodes of a three-bar tensegrity structure are established by introducing the force–density method, and the force–density relationship amongst the components is analysed. Thus, the configuration principle of single-layer tensegrity structure is verified. The force–density relationship between the components in the single-layer tensegrity structure is obtained. The change rule of the force–density relationship in different single-layer tensegrity structures is also analysed. Notably, p-1 stable configurations are present in the p-bar tensegrity structure. The force–density relationships of these p-1 configurations are in symmetrical distribution, that is, the j-th and (p-j)th configurations have the same force–density relationship. The lightweight nature of the structure is studied using the force–density relationship between the components, and the optimal structural parameter relationship is obtained when the structure has the lightest mass.

With the rise of renewable energy resources, especially offshore wind power plant, the DC transmission concept has attracted more and more attention. The selection of eco-friendly insulating gas, as most critical insulating part of gas-insulated equipment is top priority for developing highly reliable system. Moreover, it is acknowledged that eco-friendly C(3)F(7)CN/CO(2) gas mixtures have become a potential alternative to SF(6) gas due to its excellent performance. This study reviews the basic physical properties of C(3)F(7)CN gas/gas mixtures and insulation properties including the gas gap breakdown and surface flashover performance at DC, as well as lightning impulse voltage. Investigation about the gas stability is presented, including the compatibility of gas with solid materials in gas-insulated transmission line (GIL), and the decomposition characteristics under long-term electrical and thermal stresses. The important progress on the charge accumulation characteristics of gas–solid interface in the novel gas environment under DC voltage stress is analysed. Finally, the key issues that need to be paid attention to and further followed through regarding the application of this novel gas in GIL are summarised and put forward. This study hopefully can provide a complete reference for the development of eco-friendly DC gas insulation equipment with C(3)F(7)CN/CO(2) gas mixtures.

Surface charge accumulation on the spacers is one of the key issues restraining the development of HVDC GIS/GIL. The precise measurement of surface charge properties provides the basis for further study of the surface charge transport mechanism as well as the charge-induced flashover mechanism under DC voltage. In this study, the authors discuss their perspective on the current status, development needs and potential developing orientation of surface charge characterisation techniques. Different surface potential measurement methods and charge inversion algorithms are reviewed regarding the previous studies and future research needs. Drawbacks and outlooks of surface charge measurement techniques are also discussed with the background of laboratory experiment results and on-site measurements. It is hopefully that this study can serve as a useful guide reference for researchers within the same research field. More importantly, it is authors’ hope that this study can inspire some novel ideas for readers into developing of more accurate and scientific interface charge characterisation techniques.

During operation of high voltage (HV) motors, different types of discharges, e.g. surface discharge, corona discharge and bar-to-bar discharge can occur at the same time, increasing the difficulty of partial discharge (PD) sources determination and PDs pattern identification. In this study, the end-winding of a 10 kV motor coil was artificially aged and the related PD was measured. The initiation and variation of different PDs under multi-factor stresses were studied. The localised fingerprints coexisting with multiple PDs were identified and analysed. The results confirm that the end-winding discharge process was significantly influenced by the experiment relative humidity (RH) and temperature. The bar-to-bar discharge was easily recognised at a lower voltage since the identification of bar-to-bar discharge pattern would be affected by the corona discharge pattern at a higher voltage. It is shown that it is more difficult for the corona discharge to be detected when RH exceeded 80%, while the surface discharge dominated at the higher RH. In addition, the PDs were more easily identified with the rise of the temperature. This study can provide a reference in PD identification test and be useful for the PD online monitoring of HV motors.

This work presents the development, validation, and sensitivity analyses of a portable device capable of performing high-frequency dielectric spectroscopy tests on site. After a brief introduction on the operation principle and the description of the impact of frequency on dielectric spectroscopy, the article presents the results of tests on reference samples confirming good agreement with expected values. The frequency region in which the device operates, 1–200 kHz, was chosen because of its correlation with oxidative species of polymeric compound. The sensitivity analyses were performed measuring the dielectric response of low voltage cables with different aged lengths. The outcome of these tests is twofold. On the one hand, they confirm the suitability of the technique for aging evaluation, and, on the other hand, they allow the assessment of the minimum aged length (damage ratio) which causes appreciable variations on the obtained dielectric spectrum. This quantity was found to be ~35% of the total cable length.

A rotary driving component is the power output unit of a lunar sampler. A planetary gear system is used as the transmission system. The lunar sampler is subjected to an extremely rigorous mechanical environment during transportation. In this paper, the time-varying meshing stiffness curves of planetary gears are calculated by the Shi Chuan method. A translational torsional dynamic model of a two-stage planetary gear system is established. Based on the Runge-Kutta method, a solution program is used to obtain the inherent characteristics of the transmission, and corresponding verification tests are performed. With respect to the transportation process (i.e., the stage between launch and landing), the dynamic response of the transmission is examined. With respect to adverse geological conditions, the load sharing characteristics of the transmission are calculated. The aforementioned investigations provide a theoretical basis for parameter setting and structural design of a lunar exploration project.

Dielectric nanocomposites with high energy storage density (Ue) have a strong attraction to high-pulse film energy-storage capacitors. Nevertheless, low breakdown strengths (Eb) and electric displacement difference (Dmax-Drem) values of nanocomposites with incorporating the randomly distributed high dielectric constant additions, give rise to low Ue, thereby hindering the development of energy-storage capacitors. In this study, we report on newly designed SrTiO3@SiO2 platelets/PVDF textured composites with excellent capacitive energy storage performance. SrTiO3@SiO2 platelets are well oriented in the PVDF when perpendicular to the electric field with the assistance of shear force in the flow drawing process to establish microscopic barriers in an inorganic–polymer composite that is able to substantially improve the Eb of composites and enhance the Ue accordingly. Finite element simulation demonstrates that the introduction of the highly insulating SiO2 coating onto the SrTiO3 platelets effectively alleviates the interface dielectric mismatch between filler and PVDF matrix, resulting in a reduction in the interface electric field distortion. The obtained composite film with optimized paraelectric SrTiO3@SiO2 platelets (1 vol%) exhibited a maximum Dmax-Drem value of 9.14 μC cm−2 and a maximum Ue value of 14.4 J cm−3 at enhanced Eb of 402 MV m−1, which are significantly superior to neat PVDF and existing dielectric nanocomposites.

Abstract This report intends to reveal the role of electron migration and its effects in triggering direct current (DC) surface flashover under temperature gradient conditions when using epoxy-based insulating composites. The surface potential and the surface flashover voltage are both measured using insulators that are bridged between two thermo-regulated electrodes. The space charge injection and migration properties under different temperature are detected. The results show that the surface potential rises significantly because of electron migration near the high voltage (HV) electrode under high temperature conditions, thus creating an “analogous ineffective region”. The expansion of this “analogous ineffective region” results in most of the voltage drop occurring near the ground electrode, which serves as an important factor triggering positive streamers across the insulation surface. This work is helpful in understanding of DC surface flashover mechanism from a new perspective and also has important significance in design of a suitable DC insulator to avoid surface flashover problem.

To investigate the effect of fluorination on surface electrical performance of ethylene propylene rubber (EPR), four pieces of EPR specimens are prepared and fluorinated for different duration ranging from 120 min to 480 min. The surface morphology and element compositions of experimental specimens are tested. The surface potential decay and complex permittivity are measured. The tracking discharge property and the erosion properties after tracking test are investigated. The surface charge transport and electrical property tailoring mechanism are discussed. The results show that when the fluorination duration is from 120 min to 360 min, the surface morphology gradually becomes flat and compact with time, and the surface resistance to electrical tracking is improved. While an excessive fluorination with the duration of 480 min leads to a significant increase in surface conductivity and a weakening in the resistance to electrical tracking, which is mainly due to a change in surface morphology. The recommended fluorination duration for an optimised surface property is between 240 and 360 min for EPR specimen.

Silicone rubber (SIR) is widely used as an insulation material in high voltage cable accessories. Electrical tree is a typical electrical degradation and is easily initiated because of the distorted electric field. In this study, graphene nanoplatelets at contents of 0.001−0.010 wt % (0.00044−0.00436 vol %) were added into SIR to improve the electrical tree inhibiting ability. Scanning electron microscopy, conductivity and surface potential decay tests were conducted to analyze the characteristics of graphene/SIR nanocomposites. The typical electrical treeing experiment was employed to observe the electrical tree inhibition of graphene in SIR. The results show that graphene nanoplatelets were well dispersed in SIR. The conductivity was higher after the addition of graphene nanoplatelets, and the trap distribution was affected by graphene nanoplatelets. The tree was changed from a bush-branch structure to a bush structure after the addition of graphene. Tree inception voltage improved and reached the highest mean value at 0.003 wt %. The tree length was inhibited at 0.001 to 0.007 wt % and the lowest tree length occurred at 0.005 wt %.

Epoxy resins blended with micro-sized alumina show more compact surface condition and exhibit lower light emission after modified in fluorinated atmosphere. Surface morphology reflected by atomic force microscope shows that the fluorinated surface layer can overlap alumina particles inlayed in the original surface and a smoother and more compact surface condition is generated. Thermally stimulated current test exhibits that surface fluorination is able to bring more shallow traps to surface states, and the trap amount increases with the extension of fluorinating time. The photon counting technique illustrates that the fluorinated surface has lower light emission which indicates better aging inhibition properties. Therefore, we believe that the surface fluorination technique may have potential significance in modifying epoxy based insulators used in high voltage applications.

Surface charge accumulation on insulators under high dc voltage is a major factor that may lead to the reduction of insulation levels in gas insulated devices. In this paper, disc insulators made of Al2O3-filled epoxy resin were surface fluorinated using a F2/N2 mixture (12.5% F2) at 50 °C and 0.1 MPa for different durations of 15 min, 30 min and 60 min. A dc voltage was applied to the insulator for 30 min and the charge density on its surface was measured by an electrostatic probe. The results revealed significant lower surface charge densities on the fluorinated insulators in comparison with the original one. Surface conductivity measurements indicated a higher surface conductivity by over three orders of magnitude after fluorination, which would allow the charges to transfer along the surface and thus may suppress their accumulation. Further, attenuated total reflection infrared analysis and surface morphology observations of the samples revealed that the introduction of fluoride groups altered the surface physicochemical properties. These structure changes, especially the physical defects reduced the depth of charge traps in the surface layer, which was verified by the measurement of energy distributions of the electron and hole traps based on the isothermal current theory. The results in this paper demonstrate that fluorination can be a promising and effective method to suppress surface charge accumulation on epoxy insulators in gas insulated devices.

Fusing hand-based features in multi-modal biometric recognition enhances anti-spoofing capabilities. Additionally, it leverages inter-modal correlation to enhance recognition performance. Concurrently, the robustness and recognition performance of the system can be enhanced through judiciously leveraging the correlation among multimodal features. Nevertheless, two issues persist in multi-modal feature fusion recognition: Firstly, the enhancement of recognition performance in fusion recognition has not comprehensively considered the inter-modality correlations among distinct modalities. Secondly, during modal fusion, improper weight selection diminishes the salience of crucial modal features, thereby diminishing the overall recognition performance. To address these two issues, we introduce an enhanced DenseNet multimodal recognition network founded on feature-level fusion. The information from the three modalities is fused akin to RGB, and the input network augments the correlation between modes through channel correlation. Within the enhanced DenseNet network, the Efficient Channel Attention Network (ECA-Net) dynamically adjusts the weight of each channel to amplify the salience of crucial information in each modal feature. Depthwise separable convolution markedly reduces the training parameters and further enhances the feature correlation. Experimental evaluations were conducted on four multimodal databases, comprising six unimodal databases, including multispectral palmprint and palm vein databases from the Chinese Academy of Sciences. The Equal Error Rates (EER) values were 0.0149%, 0.0150%, 0.0099%, and 0.0050%, correspondingly. In comparison to other network methods for palmprint, palm vein, and finger vein fusion recognition, this approach substantially enhances recognition performance, rendering it suitable for high-security environments with practical applicability. The experiments in this article utilized amodest sample database comprising 200 individuals. The subsequent phase involves preparing for the extension of the method to larger databases. [ABSTRACT FROM AUTHOR]