A Hand Features Based Fusion Recognition Network with Enhancing Multi-Modal Correlation

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.

Photon counting technique as a potential tool in micro-defect detection of epoxy insulation pull rod in gas-insulated switchgears

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 re-sults 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.

Isolation and application of predatory Bdellovibrio-and-like organisms for municipal waste sludge biolysis and dewaterability enhancement

Bdellovibrio-and-like organisms （BALOs） are a group of ubiquitous and obligate predatory bacteria and conmlonly used as biocontrol agents. In this study, an efficient, environmental-friendly, and convenient BALOs encouraged municipal waste sludge biolysis pretreatment technique was developed and investigated for dewaterability enhancement of excess waste sludge. The indigenous predatory BALOs were successfully isolated from the sludge for biolysis treatment. Without any chemical addition or pH adjustment, the sludge specific resistance （SRF） and capillary suction time （CST） were significantly reduced by as high as 53.4% and 23.8%, respectively within 24 h＇s treatment, which would further be lowered with the increase of BALOs input dosage. However, the continuous extension of reaction time would women the sludge dewaterability. The decreases of SRF and CST accompanied with the increases of sludge disintegration degree and soluble chemical oxygen demand, nitrogen, and phosphorus concentrations all emphasized the contributions of BALOs＇ predation activities to sludge disturbance, cell lysis, and consequently the release of sludge intracellular water to finally effectively improve the sludge dewaterability and disposal efficiency.

Insulating materials for realising carbon neutrality:Opportunities,remaining issues and challenges

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 cat-egorised 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 en-visions 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.

Defects and failure types of solid insulation in gas‐insulated switchgear:In situ study and case analysis

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 intro-duced 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.

Gas–solid interface charge characterisation techniques for HVDC GIS/GIL insulators

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.

Environment-friendly Insulating Gases for HVDC Gas-insulated Transmission Lines

Environment-friendly gas insulating mediums adapted to a DC gas-insulated transmission line(GIL)electric field condition is the key to the next generation of Environment-friendly HVDC GILs.In this paper,we review the literature on sulfur hexafluoride(SF6)alternatives including the scientific understanding,control,and implementation of gas-solid systems in this type of power transmission.First,the structure-activity relationship between the molecular structure and physico-chemical properties of Environment-friendly insulating gases is presented.Then,the search and prediction of important physicochemical properties of gases are summarized.Subsequently,in view of the potential of environmental friendly insulating gases,the swarm parameters of gas discharge and breakdown properties in a quasi-uniform field,inhomogeneous field,and at the gas-solid interface,that need to be taken into account with industrialized DC GILs are discussed.The latest research progress on insulation characteristics,especially the polarity effect in DC gas-solid insulation systems,the sensitivity to the electrode surface state,and the non-uniformity of the electric field,and the influence of metal particles and their variation with air pressure,is highlighted.In addition,the heat transfer characteristics of insulating gases,related to DC GIL transmission with a large current-carrying capacity and the influence of alternative gases on the heat transfer characteristics are described.Finally,aiming at solving the contradiction of low environmental impact,high dielectric strength and low liquefaction temperatures in the selection of alternative gases,an coordinated regulation model for Environment-friendly gases in DC GILs is established.Considerations for future work on this topic are also presented.

Metal Particle Contamination in Gas-insulated Switchgears/Gas-insulated Transmission Lines

Metal particle contamination in a gas-insulated switchgear(GIS)or a gas-insulated transmission line(GIL)is an important factor leading to the decline of insulation performance.Exploring the deterioration mechanism and suppression measures of metal particles on insulation is a key technical problem in enhancing the dielectric strength of GIS/GIL equipment.In this paper,the charge and motion characteristics of metal particles are first introduced.The gas gap breakdown caused by free metal particles and the surface flashover caused by metal particles near or adsorbed on the insulator are then analyzed according to different particle motion patterns and spatial locations.Subsequently in terms of operation managements,the existing methods of particle detection are analyzed.In addition,the main inhibition methods of metal particles are introduced from three aspects:particle trap,insulator surface treatment and electrode coating.Finally,the prospects in the future research on particle pollution in GIS/GIL are also pointed out.

Feasibility of C_(3)F_(7)CN/CO_(2)gas mixtures in high-voltage DC GIL:a review on recent advances

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.

Advanced insulating materials contributing to“carbon neutrality”:Opportunities,issues and challenges

The vision of 2050 worldwide carbon-neutral ignites a revo-lution in all industries.Enormous innovations in both electrical power equipment and electrified transportation assets are shaping our future energy structure.Insulating materials,as the core element of energy infrastructure,are facing unprece-dented challenges that stand in the pathways to global carbon neutrality.However,researchers from both academic in-stitutions and industrial sections are working to turn the challenges into opportunities.

Surface Charging Phenomena on HVDC Spacers for Compressed SF_(6) Insulation and Charge Tailoring Strategies

Surface flashover of spacers is a key factor limiting the application of HVDC GIS/GIL,while the charge accumula-tion on the surface of the spacer could have a potential adverse effect on the surface flashover voltage.This paper discusses the laws regarding distribution patterns of surface charges and the related mechanisms.The field-dependent property is discussed in detail to comprehensively illustrate the charge transport mecha-nism and explain the research differences regarding different surface charge patterns obtained by previous researchers.In addition,the main surface charge control methods for epoxy resin are summarized and discussed.The potential research directions of charge control methods and key points in manufacturing of spacers used in HVDC GIS/GIL are also explored.

Understanding DC Partial Discharge:Recent Progress,Challenges,and Outlooks

As a non-destructive local gas breakdown phenomenon within a surface or bulk cavity surrounded by insulation,partial discharge(PD)contains important information which can be used to evaluate and diagnose electrical insulation systems.In this paper,distinctive characteristics of PD for DC versus AC are reviewed.A summary of experimental studies on DC PD in different insulation coordinations is presented,including PD in gaseous insulating media,PD in solid insulating media and PD in liquid insulating media.Conclusions and some thoughts based on existing studies are provided,and challenges and suggestions for future studies are given.This paper can serve as a guide reference for readers to learn the background and state-of-the-art of DC PD studies.More importantly,it is hopeful that this study can inspire novel ideas for further advancing fundamental research of DC PD mechanisms and PD mitigation methods.

Significant enhancement in the electrical conductance properties of ethylene propylene diene monomer using the nano‐SiO_(2) particles

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.

Designing HVDC GIS/GIL spacer to suppress charge accumulation

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 kVAC 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.

Temperature-dependent partial discharge characteristics of high temperature materials at DC voltage for hybrid propulsion systems

The safe and reliable operation of insulation material used in key high voltage compo-nents under extreme environmental conditions represents the major concerns for man-ufacturers 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 in-tensity 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.

Effect of long-term fluorination on surface electrical performance of ethylene propylene rubber

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.

Guest editorial:Partial discharge at DC voltage

With the development of DC power transmission and dis-tribution technology,power equipment such as converter transformers,DC cables,and DC gas-insulated equipment has been widely used in the power grid.In addition,with the growing attention of hybrid and all-electric vehicles including electric aircraft and electric ship in commercial transportation and military industry,the stability of the propulsion system driven by DC voltage has become a great concern in recent years and will continue drawing much more attention in the near future.

Development and pattern identification of end-winding discharge under effect of relative humidity and temperature for HV motors

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.

Guest Editorial:Interface Charging Phenomena for Dielectric Materials

Interface charge accumulation,leading to unpredictable insulation breakdown,restricts the development and industrialisation of high voltage direct current(HVDC)power equipment.Understanding the mechanism of interface charge transport and interface charge triggered dielectric breakdown is,therefore,of particularly high interest and vital importance.For example,the surface charging of aircraft in space brings damage to board electronic instruments as well as interference to sensing systems.Moreover,the randomly distributed charge clusters on the spacer surface,as shown in the cover page of this Special Issue,is considered as a potential threat to the surface flashover,while the accumulation of space charge within the insulating material poses a threat to the reliability of DC power cables.However,currently we still know very little about the development of charge dynamics in different interfaces,and the related breakdown mechanism of dielectrics induced by charge accumulation is also not very clear.

Dynamics of triboelectric nanogenerators: A review

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.