It is necessary to find an efficient selection method to pre-analyze the gas electric strength from the perspective of molecule structure and the properties for finding the alternative gases to sulphur hexafluoride (...It is necessary to find an efficient selection method to pre-analyze the gas electric strength from the perspective of molecule structure and the properties for finding the alternative gases to sulphur hexafluoride (SF6). As the properties of gas are determined by the gas molecule structure, the research on the relationship between the gas molecule structure and the electric strength can contribute to the gas pre-screening and new gas development. In this paper, we calculated the vertical electron affinity, molecule orbits distribution and orbits energy of gas molecules by the means of density functional theory (DFT) for the typical structures of organic gases and compared their electric strengths. By this method, we find part of the key properties of the molecule which are related to the electric strength, including the vertical electron affinity, the lowest unoccupied molecule orbit (LUMO) energy, molecule orbits distribution and negativeion system energy. We also listed some molecule groups such as unsaturated carbons double bonds (C=C) and carbonitrile bonds (C=N) which have high electric strength theoretically by this method.展开更多
The characterization of the performances of a PV cell is linked to intrinsic factors of this cell. It is therefore important for us to identify the favorable or unfavorable conditions that affect the performance of PV...The characterization of the performances of a PV cell is linked to intrinsic factors of this cell. It is therefore important for us to identify the favorable or unfavorable conditions that affect the performance of PV cells. It is from this perspective that it seems judicious to us to study the simultaneous influence of the heating of the base and an external electric field on the performance of a PV cell under intense illumination of 50 suns. Two phenomena contribute to the heating of the base of a PV cell which is heating due to the transfer by conduction of solar radiation energy received by the surface of the PV cell and the heat generated inside the PV cell by various phenomena linked to the movement of photogenerated charged carriers. In this study, we take into account the heating linked to the movement of the charged carriers in the base. After a mathematical modeling of the PV cell considered, some hypotheses are formulated and the expressions of the electrical parameters are established as a function of the electric field and base temperature. Subsequently, we use numerical simulation to highlight the behavior of theses parameters as a function of temperature and of the intensity of the electric field. The results show that for any given temperature, the orientation of the electric field as considered in our work improves the performance of the PV cell while high temperatures degrade these performances. Furthermore, the analysis of the curves shows that the harmful effect of temperature on the performance of a PV cell is more accentuated at large values of electric field.展开更多
Based on the concepts of fast polarization, effective electric field and electron impact ionization criterion, the effect of polymer type on electric breakdown strength (EBD) on a nanosecond time scale is investigat...Based on the concepts of fast polarization, effective electric field and electron impact ionization criterion, the effect of polymer type on electric breakdown strength (EBD) on a nanosecond time scale is investigated, and a formula that qualitatively characterizes the relation between the electric breakdown strength and the polymer type is derived. According to this formula, it is found that the electric breakdown strength decreases with an increase in the effective relative dielectric constants of the polymers. By calculating the effective relative dielectric constants for different types of polymers, the theoretical relation for the electric breakdown strengths of common polymers is predicted. To verify the prediction, the polymers of PE (polyethylene), PTFE (polytetrafluoroethelene), PMMA (organic glass) and Nylon are tested with a nanosecond-pulse generator. The experimental result shows EBD (PTFE) 〉 EBD (PMMA) 〉 EBD (Nylon) 〉 EBD (PE). This result is consistent with the theoretical prediction.展开更多
Lead borate glasses xB2O3+(99–x)PbO+0.5Eu2O3(x=70,60,...,10) were prepared by melt-quenching method.The luminescent properties were characterized with excitation and emission spectra.The emission intensities for 5D0-...Lead borate glasses xB2O3+(99–x)PbO+0.5Eu2O3(x=70,60,...,10) were prepared by melt-quenching method.The luminescent properties were characterized with excitation and emission spectra.The emission intensities for 5D0-7FJ(J=0–4) were analyzed to give variation of the relative electric dipole line strengths with the composition of glasses so as to examine the crucial implicit assumption of independent electric dipole line strength on the composition of glass in the Phys.Rev.Lett.2003,91,203903 paper studying l...展开更多
The geometry effect of a vapor cell on the metrology of a microwave electric field is investigated. Based on the splitting of the electromagnetically induced transparency spectra of cesium Rydberg atoms in a vapor cel...The geometry effect of a vapor cell on the metrology of a microwave electric field is investigated. Based on the splitting of the electromagnetically induced transparency spectra of cesium Rydberg atoms in a vapor cell, high-resolution spatial distribution of the microwave electric field strength is achieved for both a cubic cell and a cylinder cell. The spatial distribution of the microwave field strength in two dimensions is measured with sub-wavelength resolution. The experimental results show that the shape of a vapor cell has a significant influence on the abnormal spatial distribution because of the Fabry-P6rot effect inside a vapor cell. A theoretical simulation is obtained for different vapor cell wall thicknesses and shows that a restricted wall thickness results in a measurement fluctuation smaller than 3% at the center of the vapor cell.展开更多
We calculated the uniform dielectric breakdown field strength of residual 30% CF3I/CO2 gas mixtures during the arc extinction process over the temperature range 300-3500 K at 0.1 MPa. The limiting reduced field streng...We calculated the uniform dielectric breakdown field strength of residual 30% CF3I/CO2 gas mixtures during the arc extinction process over the temperature range 300-3500 K at 0.1 MPa. The limiting reduced field strengths are decided by a balance of electron generation and loss based on chemical reactions estimated by the electron energy distribution function (EEDF), which employs the Boltzmann equation method with two-term expanding approximation in the steady-state Townsend (SST) condition. During the insulation recovery phase, the hot CF3I/CO2 gas mixtures have maximum dielectric strength at a temperature of about 1500 K. At room temperature 300 K, the electric strength after arc extinction (90.3 Td, 1 Td=10-21 V.m2) is only 38% of the original value before arc (234.9 Td). The adverse insulation recovery ability of CF3I/CO2 gas mixtures in arc extinction hinders its application in electric circuit breakers and other switchgears as an arc quenching and insulating medium.展开更多
Influence of the gassing materials, such as PA6, PMMA, and POM on the dielectric properties of air are investigated. In this work, the fundamental electron collision cross section data were carefully selected and vali...Influence of the gassing materials, such as PA6, PMMA, and POM on the dielectric properties of air are investigated. In this work, the fundamental electron collision cross section data were carefully selected and validated. Then the species compositions of the air–organic vapor mixtures were calculated based on the Gibbs free energy minimization. Finally, the Townsend ionization coefficient, the Townsend electron attachment coefficient and the critical reduced electric field strength were derived from the calculated electron energy distribution function by solving the Boltzmann transport equation. The calculation results indicated that H;O with large attachment cross sections has a great impact on the critical reduced electric field strength of the air–organic vapor mixtures. On the other hand, the vaporization of gassing materials can help to increase the dielectric properties of air circuit breakers to some degree.展开更多
Poly(methyl methacrylate) (PMMA) was used to wrap alumina siloxane sol through emulsion polymerization. A kind of suspensions with notable ER effect was produced by fully mixing the prepared microcapsule with silicon...Poly(methyl methacrylate) (PMMA) was used to wrap alumina siloxane sol through emulsion polymerization. A kind of suspensions with notable ER effect was produced by fully mixing the prepared microcapsule with silicon oil. Meanwhile a series of PMMA wrapped alumina-siloxane gel doped with rare earths was obtained and its ER effect was tested, like viscosity of different rare earth ion doped samples in different powder concentrations and at different temperatures, at the same time, leak current density and dielectric constant were measured. Results show that the ER effect of this suspension is remarkable, and its stability is much better. The condition of emulsion polymerization and the mechanism of effect are discussed.展开更多
A 4H-SiC power MOSFET with specific on-resistance of 3.4 mΩ·cm^2 and breakdown voltage exceeding 1.5 kV is designed and fabricated.Numerical simulations are carried out to optimize the electric field strength in...A 4H-SiC power MOSFET with specific on-resistance of 3.4 mΩ·cm^2 and breakdown voltage exceeding 1.5 kV is designed and fabricated.Numerical simulations are carried out to optimize the electric field strength in gate oxide and at the surface of the semiconductor material in the edge termination region.Additional n-type implantation in JFET region is implemented to reduce the specific on-resistance.The typical leakage current is less than 1μA at VDS=1.4 kV.Drain–source current reaches 50 A at VDS=0.75 V and VGS=20 V corresponding to an on-resistance of 15 mΩ.The typical gate threshold voltage is 2.6 V.展开更多
Electrostatic energy storage technology based on dielectrics is the basis of advanced electronics and high-power electrical systems.High polarization(P)and high electric breakdown strength(Eb)are the key parameters fo...Electrostatic energy storage technology based on dielectrics is the basis of advanced electronics and high-power electrical systems.High polarization(P)and high electric breakdown strength(Eb)are the key parameters for dielectric materials to achieve superior energy storage performance.In this work,a composite strategy based on antiferroelectric dielectrics(AFEs)has been proposed to improve the energy storage performance.Here,AlN is selected as the second phase for the(Pb_(0.915)Ba_(0.04)La_(0.03))(Zr_(0.65)Sn_(0.3)Ti_(0.05))O_(3)(PBLZST)AFEs,which is embedded in the grain boundaries to construct insulating networks and regulate the local electric field,improving the Eb.Meanwhile,it is emphasized that AFEs have the AFE–FE and FE–AFE phase transitions,and the increase of the phase transition electric fields can further improve the recoverable energy density(Wrec).As a result,the Eb increases from 180 to 290 kV·cm−1 with a simultaneous increase of the phase transition electric fields,magnifying the Wrec to~144%of the pristine PBLZST.The mechanism for enhanced Eb and the phase transition electric fields is revealed by the finite element simulation method.Moreover,the PBLZST:1.0 wt%AlN composite ceramics exhibit favorable temperature stability,frequency stability,and charge–discharge ability,making the composite ceramics a promising candidate for energy storage applications.展开更多
Polyparapheneylene (PPP) was doped by CeCl 4 and FeCl 3, and then electrorheological (ER) suspensions were prepared by polymer powder with high dielectric constants and silicone oil. Under electric field, the change...Polyparapheneylene (PPP) was doped by CeCl 4 and FeCl 3, and then electrorheological (ER) suspensions were prepared by polymer powder with high dielectric constants and silicone oil. Under electric field, the change of viscosity, leakage current density and relative physical constants were measured. The relationships among electric field strength, particle concentration, viscosity and leakage current density were discussed. The speed of electrorheological response and the recovery time were studied and corresponding mechanisms were investigated.展开更多
Based on Darcy's Law and the Helmholta-Smoluchowski equation, an imbibition velocity formula for the water phase with an electric field was deduced, showing that the imbibition velocity with an electric field is to v...Based on Darcy's Law and the Helmholta-Smoluchowski equation, an imbibition velocity formula for the water phase with an electric field was deduced, showing that the imbibition velocity with an electric field is to various extents not only related to the rock permeability and characteristic length, the fluid viscosity, the oil-water interface tension and the gravity of the imbibing brine, but also to the fluid dielectric permittivity, zeta potential, applied electric field direction, and strength. Imbibition experiments with electric fields that are different in direction and strength were conducted, showing that application of a positive electric field enhances the imbibition velocity and increases the imbibition recovery ratio, while application of a negative electric field reduces the imbibition velocity and decreases the imbibition recovery ratio. The imbibition recovery ratio with a positive electric field increases with the strength of the electric field, and the imbibition recovery ratio with a negative electric field is lower than that without an electric field.展开更多
A recurring challenge of a DC SF_(6)/N_(2)-filled GIS/GIL apparatus is the charge accumulation at DC stress.The conventional design rules and knowledge of AC spacers may not be applicable for this new type of apparatu...A recurring challenge of a DC SF_(6)/N_(2)-filled GIS/GIL apparatus is the charge accumulation at DC stress.The conventional design rules and knowledge of AC spacers may not be applicable for this new type of apparatus.A novel design rule is proposed considering the effect of accumulated charge on the threshold of electric field strength being resistant to the superposed voltage.A surface charge accumulation simulation model is introduced,and the key parameters in the simulation model are measured.In addition,an experimental platform for a 100 kV spacer flashover test is established.Spacer flashover tests under superimposed voltage with opposing polarities are carried out,and the withstanding voltage of the spacer is obtained.Finally,based on the proposed model,the threshold of the surface electric field strength(tangential component)on the DC spacer in SF_(6)/N_(2) mixed gases is discussed.For a reliable insulation design of a DC GIS/GIL apparatus filled with 0.7 MPa SF_(6)/N_(2),the threshold of surface electric field strength on the DC spacer is 12 kV/mm.The insulation design rule can be referenced in the design of a high-voltage DC SF_(6)/N_(2)-filled GIS/GIL apparatus.展开更多
Polypropylene(PP) sheets are cast with various chill roll temperatures and rates, which are studied with differential scanning calorimetry, wide angel X-ray diffraction, scanning electronic microscopy and dielectric w...Polypropylene(PP) sheets are cast with various chill roll temperatures and rates, which are studied with differential scanning calorimetry, wide angel X-ray diffraction, scanning electronic microscopy and dielectric withstand voltage test system. The results show that increasing the chill roll temperature and cast rate can promote the increase of crystallinity and the growth of β-form. The PP sheets have asymmetric skin layer structures. The lower the chill roll temperature, the thicker the skin layer, the smaller the spherulite size. The electric breakdown strength(Eb) of PP sheets is mainly affected by the crystallinity but not the morphology. The PP sheets are further stretched to prepare bi-axially oriented PP(BOPP) films with various heat setting time. Our results indicate that the structure of PP sheets affects the properties of BOPP films. The as prepared BOPP films from the sheets cast at high chill roll temperature and rate have the highest crystallinity and Eb. Heat setting time has profound effect on the crystallinity and Eb, which increase first and then decrease with the heat setting time. It is expected that our study can provide guidance for optimizing process parameters.展开更多
Cu-0.45 Cr-0.2 Zr-xLa(x = 0-0.48) alloys were prepared by vacuum casting. The effects of La addition and orientation on the microstructure and properties of the as-cast alloy were investigated by an optical microsco...Cu-0.45 Cr-0.2 Zr-xLa(x = 0-0.48) alloys were prepared by vacuum casting. The effects of La addition and orientation on the microstructure and properties of the as-cast alloy were investigated by an optical microscope, a scanning electron microscope with an energy dispersive X-ray spectrometer, a tensile testing machine and an electrical conductivity tester. The result shows that the addition of La significantly refines the columnar grainsize and decreases the secondary dendrite arm spacing. Trace addition of La improves the room temperature ultimate tensile strength,elongation and electrical conductivity mainly by purifying during melting and casting. The ultimate tensile strength, elongation and electrical conductivity significantly decrease with the increase of La content due to formation of coarse particles and oxides, which severely harm the performance of the Cu-0.45 Cr-0.2 Zr-xLa alloys. The Cu-0.45 Cr-0.2 Zr-0.13 La alloy possesses a good combination of room temperature ultimate tensile strength, elongation and electrical conductivity. In addition, room temperature ultimate tensile strength and electrical conductivity along transverse direction of the ingot are higher than that along longitudinal direction,which is mainly ascribed to different distribution of grain boundary and grain orientation.展开更多
基金supported by National Natural Science Foundation of China(Nos.51177101 and 51337006)
文摘It is necessary to find an efficient selection method to pre-analyze the gas electric strength from the perspective of molecule structure and the properties for finding the alternative gases to sulphur hexafluoride (SF6). As the properties of gas are determined by the gas molecule structure, the research on the relationship between the gas molecule structure and the electric strength can contribute to the gas pre-screening and new gas development. In this paper, we calculated the vertical electron affinity, molecule orbits distribution and orbits energy of gas molecules by the means of density functional theory (DFT) for the typical structures of organic gases and compared their electric strengths. By this method, we find part of the key properties of the molecule which are related to the electric strength, including the vertical electron affinity, the lowest unoccupied molecule orbit (LUMO) energy, molecule orbits distribution and negativeion system energy. We also listed some molecule groups such as unsaturated carbons double bonds (C=C) and carbonitrile bonds (C=N) which have high electric strength theoretically by this method.
文摘The characterization of the performances of a PV cell is linked to intrinsic factors of this cell. It is therefore important for us to identify the favorable or unfavorable conditions that affect the performance of PV cells. It is from this perspective that it seems judicious to us to study the simultaneous influence of the heating of the base and an external electric field on the performance of a PV cell under intense illumination of 50 suns. Two phenomena contribute to the heating of the base of a PV cell which is heating due to the transfer by conduction of solar radiation energy received by the surface of the PV cell and the heat generated inside the PV cell by various phenomena linked to the movement of photogenerated charged carriers. In this study, we take into account the heating linked to the movement of the charged carriers in the base. After a mathematical modeling of the PV cell considered, some hypotheses are formulated and the expressions of the electrical parameters are established as a function of the electric field and base temperature. Subsequently, we use numerical simulation to highlight the behavior of theses parameters as a function of temperature and of the intensity of the electric field. The results show that for any given temperature, the orientation of the electric field as considered in our work improves the performance of the PV cell while high temperatures degrade these performances. Furthermore, the analysis of the curves shows that the harmful effect of temperature on the performance of a PV cell is more accentuated at large values of electric field.
文摘Based on the concepts of fast polarization, effective electric field and electron impact ionization criterion, the effect of polymer type on electric breakdown strength (EBD) on a nanosecond time scale is investigated, and a formula that qualitatively characterizes the relation between the electric breakdown strength and the polymer type is derived. According to this formula, it is found that the electric breakdown strength decreases with an increase in the effective relative dielectric constants of the polymers. By calculating the effective relative dielectric constants for different types of polymers, the theoretical relation for the electric breakdown strengths of common polymers is predicted. To verify the prediction, the polymers of PE (polyethylene), PTFE (polytetrafluoroethelene), PMMA (organic glass) and Nylon are tested with a nanosecond-pulse generator. The experimental result shows EBD (PTFE) 〉 EBD (PMMA) 〉 EBD (Nylon) 〉 EBD (PE). This result is consistent with the theoretical prediction.
基金supported by the National Natural Science Foundation of China (10874253 and 10874173)
文摘Lead borate glasses xB2O3+(99–x)PbO+0.5Eu2O3(x=70,60,...,10) were prepared by melt-quenching method.The luminescent properties were characterized with excitation and emission spectra.The emission intensities for 5D0-7FJ(J=0–4) were analyzed to give variation of the relative electric dipole line strengths with the composition of glasses so as to examine the crucial implicit assumption of independent electric dipole line strength on the composition of glass in the Phys.Rev.Lett.2003,91,203903 paper studying l...
基金Project supported by the National Key Research and Development Program of China(Grant Nos.2017YFA03044200 and 2016YFF0200104)the National Natural Science Foundation of China(Grant Nos.91536110,61505099,and 61378013)the Fund for Shanxi“331 Project”Key Subjects Construction,China
文摘The geometry effect of a vapor cell on the metrology of a microwave electric field is investigated. Based on the splitting of the electromagnetically induced transparency spectra of cesium Rydberg atoms in a vapor cell, high-resolution spatial distribution of the microwave electric field strength is achieved for both a cubic cell and a cylinder cell. The spatial distribution of the microwave field strength in two dimensions is measured with sub-wavelength resolution. The experimental results show that the shape of a vapor cell has a significant influence on the abnormal spatial distribution because of the Fabry-P6rot effect inside a vapor cell. A theoretical simulation is obtained for different vapor cell wall thicknesses and shows that a restricted wall thickness results in a measurement fluctuation smaller than 3% at the center of the vapor cell.
基金supported by National Natural Science Foundation of China(No.10875093)
文摘We calculated the uniform dielectric breakdown field strength of residual 30% CF3I/CO2 gas mixtures during the arc extinction process over the temperature range 300-3500 K at 0.1 MPa. The limiting reduced field strengths are decided by a balance of electron generation and loss based on chemical reactions estimated by the electron energy distribution function (EEDF), which employs the Boltzmann equation method with two-term expanding approximation in the steady-state Townsend (SST) condition. During the insulation recovery phase, the hot CF3I/CO2 gas mixtures have maximum dielectric strength at a temperature of about 1500 K. At room temperature 300 K, the electric strength after arc extinction (90.3 Td, 1 Td=10-21 V.m2) is only 38% of the original value before arc (234.9 Td). The adverse insulation recovery ability of CF3I/CO2 gas mixtures in arc extinction hinders its application in electric circuit breakers and other switchgears as an arc quenching and insulating medium.
基金supported by the National Key Basic Research Program of China(973 Program)2015CB251002National Natural Science Foundation of China under Grant 51521065,51577145+1 种基金the Fundamental Research Funds for the Central UniversitiesShaanxi Province Natural Science Foundation 2013JM-7010
文摘Influence of the gassing materials, such as PA6, PMMA, and POM on the dielectric properties of air are investigated. In this work, the fundamental electron collision cross section data were carefully selected and validated. Then the species compositions of the air–organic vapor mixtures were calculated based on the Gibbs free energy minimization. Finally, the Townsend ionization coefficient, the Townsend electron attachment coefficient and the critical reduced electric field strength were derived from the calculated electron energy distribution function by solving the Boltzmann transport equation. The calculation results indicated that H;O with large attachment cross sections has a great impact on the critical reduced electric field strength of the air–organic vapor mixtures. On the other hand, the vaporization of gassing materials can help to increase the dielectric properties of air circuit breakers to some degree.
文摘Poly(methyl methacrylate) (PMMA) was used to wrap alumina siloxane sol through emulsion polymerization. A kind of suspensions with notable ER effect was produced by fully mixing the prepared microcapsule with silicon oil. Meanwhile a series of PMMA wrapped alumina-siloxane gel doped with rare earths was obtained and its ER effect was tested, like viscosity of different rare earth ion doped samples in different powder concentrations and at different temperatures, at the same time, leak current density and dielectric constant were measured. Results show that the ER effect of this suspension is remarkable, and its stability is much better. The condition of emulsion polymerization and the mechanism of effect are discussed.
基金supported by the National Science and Technology Major Project(No.2017YFB0102302)。
文摘A 4H-SiC power MOSFET with specific on-resistance of 3.4 mΩ·cm^2 and breakdown voltage exceeding 1.5 kV is designed and fabricated.Numerical simulations are carried out to optimize the electric field strength in gate oxide and at the surface of the semiconductor material in the edge termination region.Additional n-type implantation in JFET region is implemented to reduce the specific on-resistance.The typical leakage current is less than 1μA at VDS=1.4 kV.Drain–source current reaches 50 A at VDS=0.75 V and VGS=20 V corresponding to an on-resistance of 15 mΩ.The typical gate threshold voltage is 2.6 V.
基金supported by the National Natural Science Foundation of China(51972126,51972125,and 52172114)the Key Research and Development Project of Hubei Province(2020BAB067)+2 种基金HUST International Cooperation and Exchange Project,Double First Class Program of China(5001182055)the Innovation Research Fund of Huazhong University of Science and Technology(2019KFYRCPY126 and 2018KFYYXJJ052)the Innovation Fund of WNLO.We also would like to acknowledge the Analytical and Testing Center of Huazhong University of Science and Technology.
文摘Electrostatic energy storage technology based on dielectrics is the basis of advanced electronics and high-power electrical systems.High polarization(P)and high electric breakdown strength(Eb)are the key parameters for dielectric materials to achieve superior energy storage performance.In this work,a composite strategy based on antiferroelectric dielectrics(AFEs)has been proposed to improve the energy storage performance.Here,AlN is selected as the second phase for the(Pb_(0.915)Ba_(0.04)La_(0.03))(Zr_(0.65)Sn_(0.3)Ti_(0.05))O_(3)(PBLZST)AFEs,which is embedded in the grain boundaries to construct insulating networks and regulate the local electric field,improving the Eb.Meanwhile,it is emphasized that AFEs have the AFE–FE and FE–AFE phase transitions,and the increase of the phase transition electric fields can further improve the recoverable energy density(Wrec).As a result,the Eb increases from 180 to 290 kV·cm−1 with a simultaneous increase of the phase transition electric fields,magnifying the Wrec to~144%of the pristine PBLZST.The mechanism for enhanced Eb and the phase transition electric fields is revealed by the finite element simulation method.Moreover,the PBLZST:1.0 wt%AlN composite ceramics exhibit favorable temperature stability,frequency stability,and charge–discharge ability,making the composite ceramics a promising candidate for energy storage applications.
文摘Polyparapheneylene (PPP) was doped by CeCl 4 and FeCl 3, and then electrorheological (ER) suspensions were prepared by polymer powder with high dielectric constants and silicone oil. Under electric field, the change of viscosity, leakage current density and relative physical constants were measured. The relationships among electric field strength, particle concentration, viscosity and leakage current density were discussed. The speed of electrorheological response and the recovery time were studied and corresponding mechanisms were investigated.
基金supported by the National Key Basic Research Development Program of China (Grant No. 2002CCA00700)
文摘Based on Darcy's Law and the Helmholta-Smoluchowski equation, an imbibition velocity formula for the water phase with an electric field was deduced, showing that the imbibition velocity with an electric field is to various extents not only related to the rock permeability and characteristic length, the fluid viscosity, the oil-water interface tension and the gravity of the imbibing brine, but also to the fluid dielectric permittivity, zeta potential, applied electric field direction, and strength. Imbibition experiments with electric fields that are different in direction and strength were conducted, showing that application of a positive electric field enhances the imbibition velocity and increases the imbibition recovery ratio, while application of a negative electric field reduces the imbibition velocity and decreases the imbibition recovery ratio. The imbibition recovery ratio with a positive electric field increases with the strength of the electric field, and the imbibition recovery ratio with a negative electric field is lower than that without an electric field.
基金supported in part by the National Basic Research Program of China(973 Program)(2014CB239500)Young Elite Scientists Sponsorship Program by CAST YESS20160004the Fundamental Research Funds for the Central Universities(2019MS006).
文摘A recurring challenge of a DC SF_(6)/N_(2)-filled GIS/GIL apparatus is the charge accumulation at DC stress.The conventional design rules and knowledge of AC spacers may not be applicable for this new type of apparatus.A novel design rule is proposed considering the effect of accumulated charge on the threshold of electric field strength being resistant to the superposed voltage.A surface charge accumulation simulation model is introduced,and the key parameters in the simulation model are measured.In addition,an experimental platform for a 100 kV spacer flashover test is established.Spacer flashover tests under superimposed voltage with opposing polarities are carried out,and the withstanding voltage of the spacer is obtained.Finally,based on the proposed model,the threshold of the surface electric field strength(tangential component)on the DC spacer in SF_(6)/N_(2) mixed gases is discussed.For a reliable insulation design of a DC GIS/GIL apparatus filled with 0.7 MPa SF_(6)/N_(2),the threshold of surface electric field strength on the DC spacer is 12 kV/mm.The insulation design rule can be referenced in the design of a high-voltage DC SF_(6)/N_(2)-filled GIS/GIL apparatus.
基金financially supported by the State Key Laboratory of Advanced Power Transmission Technology (No.GEIRI-SKL2020-009)。
文摘Polypropylene(PP) sheets are cast with various chill roll temperatures and rates, which are studied with differential scanning calorimetry, wide angel X-ray diffraction, scanning electronic microscopy and dielectric withstand voltage test system. The results show that increasing the chill roll temperature and cast rate can promote the increase of crystallinity and the growth of β-form. The PP sheets have asymmetric skin layer structures. The lower the chill roll temperature, the thicker the skin layer, the smaller the spherulite size. The electric breakdown strength(Eb) of PP sheets is mainly affected by the crystallinity but not the morphology. The PP sheets are further stretched to prepare bi-axially oriented PP(BOPP) films with various heat setting time. Our results indicate that the structure of PP sheets affects the properties of BOPP films. The as prepared BOPP films from the sheets cast at high chill roll temperature and rate have the highest crystallinity and Eb. Heat setting time has profound effect on the crystallinity and Eb, which increase first and then decrease with the heat setting time. It is expected that our study can provide guidance for optimizing process parameters.
基金Project supported by the Fund of Independent Innovation in Shandong Province(2013CXB60201)the Science and Technology Development Project of Shandong Province(2014GGX102003)+1 种基金the Independent Innovation and Achievements Transformation Special Project of Shandong Province(2014CGZH0102)the Fundamental Research Funds of Shandong University(2016JC016)
文摘Cu-0.45 Cr-0.2 Zr-xLa(x = 0-0.48) alloys were prepared by vacuum casting. The effects of La addition and orientation on the microstructure and properties of the as-cast alloy were investigated by an optical microscope, a scanning electron microscope with an energy dispersive X-ray spectrometer, a tensile testing machine and an electrical conductivity tester. The result shows that the addition of La significantly refines the columnar grainsize and decreases the secondary dendrite arm spacing. Trace addition of La improves the room temperature ultimate tensile strength,elongation and electrical conductivity mainly by purifying during melting and casting. The ultimate tensile strength, elongation and electrical conductivity significantly decrease with the increase of La content due to formation of coarse particles and oxides, which severely harm the performance of the Cu-0.45 Cr-0.2 Zr-xLa alloys. The Cu-0.45 Cr-0.2 Zr-0.13 La alloy possesses a good combination of room temperature ultimate tensile strength, elongation and electrical conductivity. In addition, room temperature ultimate tensile strength and electrical conductivity along transverse direction of the ingot are higher than that along longitudinal direction,which is mainly ascribed to different distribution of grain boundary and grain orientation.