The corona onset voltage gradient(COG)of conductors is a key parameter in the design of overhead transmission lines.The commonly used semi-empirical calculation formula proposed by Peek(1910s)at present can roughly es...The corona onset voltage gradient(COG)of conductors is a key parameter in the design of overhead transmission lines.The commonly used semi-empirical calculation formula proposed by Peek(1910s)at present can roughly estimate the COG of single conductors and is not applicable to large cross-section bundle conductors.In this paper,experiments are conducted to investigate the corona characteristics of a whole series of bundle conductors at different altitudes,and a prediction formula is proposed for the COG of large cross-section bundle conductors on AC transmission lines considering the altitude correction.The calculated values using the proposed prediction formula are compared with the experimental values of the COG in two cases:UHV eight-bundle conductors at an altitude of 19 m;500 kV UHV four-bundle conductors in Wuhan,Xining,Geermu,and Nachitai at four different altitudes.The results show that the use of the formula can predict the COG of bundle conductors with the radius of 1.34 cm to 1.995 cm and the number of subconductors of 4 to 12 at altitudes of 19 m to 4000 m above the mean sea level.The research findings can provide a reference for the design of EHV and UHV overhead transmission lines and even those in higher voltage levels.展开更多
A high voltage gradient(V_(g))of ZnO-based varistor ceramics is critical for realizing miniaturized and lightweight overvoltage protection devices.However,improving V_(g) of ZnObased varistor ceramics through conventi...A high voltage gradient(V_(g))of ZnO-based varistor ceramics is critical for realizing miniaturized and lightweight overvoltage protection devices.However,improving V_(g) of ZnObased varistor ceramics through conventional high-temperature sintering process remains a significant challenge.Here,we present a strategy to fabricate ultrahigh voltage-gradient ZnO-based varistor ceramics by combining cold sintering process/spark plasma sintering(CSP–SPS)with post-annealing process.Employing CSP–SPS,the ZnO-based varistor ceramics were initially densified at 300℃ and subsequently annealed at a low temperature of 700–900℃.CSP–SPS technique combined with a low annealing temperature enables the production of ZnO-based varistor ceramics with fine and homogeneous microstructures,while suppressing the volatilization of Bi-rich phases at grain boundaries.This approach achieves the ultrahigh V_(g) of~1832.71 V/mm,high nonlinear coefficient(α)of~106.69,and low leakage current density(J_(L))of less than 0.2μA/cm^(2).This work shows that the integration of CSP–SPS and post-annealing provides a promising way to design ZnO-based varistor ceramics with ultrahigh V_(g).展开更多
Electrokinetic remediation is a promising method to decontamination of the heavy metals from soils.In this paper,the remediation of a contaminated calcareous soil with Zn,Cd and Pb sampled from around Zanjan province ...Electrokinetic remediation is a promising method to decontamination of the heavy metals from soils.In this paper,the remediation of a contaminated calcareous soil with Zn,Cd and Pb sampled from around Zanjan province of Iran,was investigated using electrokinetic method.In this paper,the soil contain a high concentration of Zn(1400 mg·kg^(-1)),Cd(15 mg·kg^(-1))and Pb(250 mg·kg^(-1)).Electrokinetic decontamination consists of two series of experiments as follows:(1)the effect of five treatments including the use of distilled water,acetic acid and EDTA electrolyte solutions,and approaching anodes systems,and the circulation flow of electrolyte at two different voltage gradient(i.e.1.33 and 2.66 V·cm^(-1)),and(2)the effect of moisture content(saturated,FC and 0.7 FC,FC indicated soil moisture at "Field Capacity")with a voltage gradient of 1.33 V·cm^(-1).After applying electric current for 5 days,the results of experiments indicated that the removal efficiency of heavy metals can be increased by raising the voltage gradient.In this matter,the highest remediation can be observed among different treatments in EDTA(Ethylene diamine tetra acetic acid)treatment(40.11%,43.10%and 24.7%for Zn,Cd and Pb,respectively).Moreover,the heavy metals removal at the saturated moisture was at the highest level so that 32.62%cadmium,31.33%zinc and 18.82%lead being removed after 120 h of electric current application.By decreasing moisture to 0.7 FC,the removal percentage for the three heavy metals obtained 20.97%,18.44%and 12.25%,respectively.Furthermore,Cd had the highest removal,and Zn and Pb were next among the three heavy metals in question.展开更多
Dielectric elastomers(DE),renowned for their lightweight,rapid response,high energy density,and efficient conversion,have garnered significant attention in the realm of avian flight bionics.However,a lack of understan...Dielectric elastomers(DE),renowned for their lightweight,rapid response,high energy density,and efficient conversion,have garnered significant attention in the realm of avian flight bionics.However,a lack of understanding of the mechanical principles underlying flapping wing biomimetics has hindered accurate simulations of actual bird flight postures.To address this,a stiffness-variable DE-based wing(DEW)has been designed,inspired by the characteristics of seagulls,to mimic the wing deformations across different bird flight phases.The evolution of the DEW’s deformation is modeled based on the differential equation describing the bending curve of a DE cantilever beam.By applying different voltage cycles,three continuous avian flight postures have been replicated:takeoff,cruising,and hovering.The simulation results demonstrate that the stiffness-variable DEW effectively mimics the wing deformations observed in birds during different flight postures,closely resembling real-world flight conditions.This study has the potential to serve as an important reference for exploring changes in bird flight behavior,thereby advancing the application of DE materials in the field of soft robotics.展开更多
基金This work was supported by the National Natural Science Foundation of China(51577069,51277073)National Basic Research Programme of China(2011CB209401)+2 种基金the Science and Technology Project of State Grid Corporation of China(SGTYHT/15-JS-191)the Science and Technology Program of EPPEI(K201909-D)the Fundamental Research Funds for the Central Universities(2020MS092).
文摘The corona onset voltage gradient(COG)of conductors is a key parameter in the design of overhead transmission lines.The commonly used semi-empirical calculation formula proposed by Peek(1910s)at present can roughly estimate the COG of single conductors and is not applicable to large cross-section bundle conductors.In this paper,experiments are conducted to investigate the corona characteristics of a whole series of bundle conductors at different altitudes,and a prediction formula is proposed for the COG of large cross-section bundle conductors on AC transmission lines considering the altitude correction.The calculated values using the proposed prediction formula are compared with the experimental values of the COG in two cases:UHV eight-bundle conductors at an altitude of 19 m;500 kV UHV four-bundle conductors in Wuhan,Xining,Geermu,and Nachitai at four different altitudes.The results show that the use of the formula can predict the COG of bundle conductors with the radius of 1.34 cm to 1.995 cm and the number of subconductors of 4 to 12 at altitudes of 19 m to 4000 m above the mean sea level.The research findings can provide a reference for the design of EHV and UHV overhead transmission lines and even those in higher voltage levels.
基金supported by the Joint Funds of the National Natural Science Foundation of China(No.U23B20115)the Fok Ying-Tong Education Foundation,China(No.171050)。
文摘A high voltage gradient(V_(g))of ZnO-based varistor ceramics is critical for realizing miniaturized and lightweight overvoltage protection devices.However,improving V_(g) of ZnObased varistor ceramics through conventional high-temperature sintering process remains a significant challenge.Here,we present a strategy to fabricate ultrahigh voltage-gradient ZnO-based varistor ceramics by combining cold sintering process/spark plasma sintering(CSP–SPS)with post-annealing process.Employing CSP–SPS,the ZnO-based varistor ceramics were initially densified at 300℃ and subsequently annealed at a low temperature of 700–900℃.CSP–SPS technique combined with a low annealing temperature enables the production of ZnO-based varistor ceramics with fine and homogeneous microstructures,while suppressing the volatilization of Bi-rich phases at grain boundaries.This approach achieves the ultrahigh V_(g) of~1832.71 V/mm,high nonlinear coefficient(α)of~106.69,and low leakage current density(J_(L))of less than 0.2μA/cm^(2).This work shows that the integration of CSP–SPS and post-annealing provides a promising way to design ZnO-based varistor ceramics with ultrahigh V_(g).
文摘Electrokinetic remediation is a promising method to decontamination of the heavy metals from soils.In this paper,the remediation of a contaminated calcareous soil with Zn,Cd and Pb sampled from around Zanjan province of Iran,was investigated using electrokinetic method.In this paper,the soil contain a high concentration of Zn(1400 mg·kg^(-1)),Cd(15 mg·kg^(-1))and Pb(250 mg·kg^(-1)).Electrokinetic decontamination consists of two series of experiments as follows:(1)the effect of five treatments including the use of distilled water,acetic acid and EDTA electrolyte solutions,and approaching anodes systems,and the circulation flow of electrolyte at two different voltage gradient(i.e.1.33 and 2.66 V·cm^(-1)),and(2)the effect of moisture content(saturated,FC and 0.7 FC,FC indicated soil moisture at "Field Capacity")with a voltage gradient of 1.33 V·cm^(-1).After applying electric current for 5 days,the results of experiments indicated that the removal efficiency of heavy metals can be increased by raising the voltage gradient.In this matter,the highest remediation can be observed among different treatments in EDTA(Ethylene diamine tetra acetic acid)treatment(40.11%,43.10%and 24.7%for Zn,Cd and Pb,respectively).Moreover,the heavy metals removal at the saturated moisture was at the highest level so that 32.62%cadmium,31.33%zinc and 18.82%lead being removed after 120 h of electric current application.By decreasing moisture to 0.7 FC,the removal percentage for the three heavy metals obtained 20.97%,18.44%and 12.25%,respectively.Furthermore,Cd had the highest removal,and Zn and Pb were next among the three heavy metals in question.
基金the financial support of the National Natural Science Foundation of China(Nos.12172206 and 11972218).
文摘Dielectric elastomers(DE),renowned for their lightweight,rapid response,high energy density,and efficient conversion,have garnered significant attention in the realm of avian flight bionics.However,a lack of understanding of the mechanical principles underlying flapping wing biomimetics has hindered accurate simulations of actual bird flight postures.To address this,a stiffness-variable DE-based wing(DEW)has been designed,inspired by the characteristics of seagulls,to mimic the wing deformations across different bird flight phases.The evolution of the DEW’s deformation is modeled based on the differential equation describing the bending curve of a DE cantilever beam.By applying different voltage cycles,three continuous avian flight postures have been replicated:takeoff,cruising,and hovering.The simulation results demonstrate that the stiffness-variable DEW effectively mimics the wing deformations observed in birds during different flight postures,closely resembling real-world flight conditions.This study has the potential to serve as an important reference for exploring changes in bird flight behavior,thereby advancing the application of DE materials in the field of soft robotics.
