One commonly used strategy to enhance polymers specific properties such as the resistance to partial discharges erosion is the incorporation into the polymeric matrix of inorganic micro or nanoparticles. This study fo...One commonly used strategy to enhance polymers specific properties such as the resistance to partial discharges erosion is the incorporation into the polymeric matrix of inorganic micro or nanoparticles. This study focused on the dielectric properties of Low-Density Polyethylene (LDPE) filled with nano-sized Magnesium Oxide (MgO) particles compounded by thermo-mechanical process and one of the purposes was to establish appropriate processing parameters in order to reach the desired dielectric properties. LDPE was used as a matrix and was reinforced by MgO particles having a nominal average size of 30 nm. The MgO nanoparticles were treated with a silane coupling agent (3-Glycidyloxypropyl Trimethoxysilane). The samples were initially prepared in a melt-mixing chamber with a MgO content of 1% wt. These pre-mixed samples were further treated by the means of thermo-mechanical mixing in a conical co-rotating twin-screw extruder in order to improve the dispersion and distribution of the MgO particles. In this report, both lifetime under a PD activity and AC dielectric strength of pure and nano-filled LDPE samples have been measured and compared. Nano-filled LDPE samples were found to exhibit an improve lifetime, without any detrimental impact on their short-term dielectric strength. This suggests that nano-filled LDPE may be for electric applications for which the dielectric materials may be exposed to partial discharge activities. This is significant result for the use of MgO-reinforced PE as an insulating material for HV cables since the resistance to PD is closely related to treeing resistance which is the main electrical degradation mechanism that leads to failure for shielded extruded power cables.展开更多
The inductively coupled plasma chemical vapor deposition(ICP-CVD) deposited silicon nitride(SiN_(x)) thin film was evaluated for its application as the electrical insulating film for a capacitor device.In order to ach...The inductively coupled plasma chemical vapor deposition(ICP-CVD) deposited silicon nitride(SiN_(x)) thin film was evaluated for its application as the electrical insulating film for a capacitor device.In order to achieve highest possible dielectric strength of SiN_(x),the process parameters of ICP-CVD were carefully tuned to control hydrogen in SiN_(x) films by means of tuning N_(2)/SiH_(4) ratio and radio frequency(RF) power.Besides electrical measurements,the hydrogen content in the films was measured by dynamic secondary ion mass spectrometry(D-SIMS).Fourier transform infrared spectroscopy(FTIR) and micro Raman spectroscopy were used to characterize the SiN_(x) films by measuring Si-H and N-H bonds’ intensities.It was found that the more Si-H bonds lead to the higher dielectric strength.展开更多
Nanoparticles succeeded to enhance the dielectric properties of industrial insulation but the presence of voids inside the power cable insulation still leads to formation high electrical stress inside power cable insu...Nanoparticles succeeded to enhance the dielectric properties of industrial insulation but the presence of voids inside the power cable insulation still leads to formation high electrical stress inside power cable insulation material and collapse.In this paper,the dielectric strength of new design nanocomposites has been deduced as experimental work done to clarify the benefit of filling nanoparticles with different patterns inside dielectrics.Also,it has been studied the effect of electrical stress distribution in presence of air,water and copper impurities with different shapes(cylinder,sphere and ellipse)inside insulation of single core.In simulation model,it has been used finite element method(FEM)for estimating the electrostatic field distribution in power cable insulation.It has been applied new strategies of nanotechnology techniques for designing innovative polyvinyl chloride insula-tion materials by using nanocomposites and multi-nanocomposites.Finally,this research succeeded to remedy different partial discharges(PD)patterns according to using certain types and concentrations of nanoparticles.展开更多
CuCr25W1Ni2 alloy was prepared by means of vacuum induction melting (VIM). A series of Cu/Cr alloys with different compositions (mass fraction, 25%～75%) and Cr grain sizes (up to 150 μm) were investigated for their ...CuCr25W1Ni2 alloy was prepared by means of vacuum induction melting (VIM). A series of Cu/Cr alloys with different compositions (mass fraction, 25%～75%) and Cr grain sizes (up to 150 μm) were investigated for their differences in physical properties and breakdown voltage. The influence of alloy elements and microstructure on the performance of CuCr25W1Ni2 alloy was also discussed. Experimental results show that the chromium phase is strengthened and its size is minimized by the addition of tungsten powder. After electrical breakdown, very fine tungsten particles in the melt layer form the external nuclei in the solidification process. The microstructure of surface melt layer of CuCr25W1Ni2 alloy is much flatter. It can notably improve the dielectric strength. On the other hand, the nickel can enhance the mutual solubility of copper and chromium, and the whole alloy is strengthened. [展开更多
High voltage power modules are used in numerous applications to build high power converters. Technically, these modules are made of different materials and among them, dielectric materials are organic and inorganic. O...High voltage power modules are used in numerous applications to build high power converters. Technically, these modules are made of different materials and among them, dielectric materials are organic and inorganic. Organic insulators (gels) are used to avoid corona discharges in the vicinity of connecting wires and high voltage dies (diodes and transistors) and to protect them from moisture and contaminants. Inorganic insulators (ceramic substrates) are used to insulate the high voltage which dies from the grounded elements and to transfer heat to the heat sink. Despite being used since the late 90s, there is a lack of fundamental knowledge about the electrical properties of these substrates. Consequently, manufacturers tend to assure the reliability by over sizing them. As there are no clear rules for how to do that, failures occur, leading to the converter shutdown. The aim of this study is to bring new information about the understanding of the dielectric strength of ceramic materials used in these modules. We have focused our work on the correlation between the mechanical and the dielectric properties of ceramics by using relevant experiments. We provide new information about the impact of existing cracks on the ceramic dielectric failure, according to the electromechanical breakdown model. Our conclusions bring crucial information about the precautions to be taken during manufacturing and implementation of these substrates in power modules to reduce the likelihood of the particular causes of failure.展开更多
Annealing and firing in wet hydrogen are widely used steps in the processing alumina.ceramic insulators that may affect their dielectric breakdown strengths(DBS).In this study,the effects of annealing(at 1300℃for 7 h...Annealing and firing in wet hydrogen are widely used steps in the processing alumina.ceramic insulators that may affect their dielectric breakdown strengths(DBS).In this study,the effects of annealing(at 1300℃for 7 h)and firing in wet hydrogen on the DBS of alumina ceramics(all sintered at 1650℃)were studied,and the underlying mechanisms were analyzed by material characterizations.Annealing reduced the DBS of the 95%alumina ceramics due to the inter-granular phase crystallization,and the reduction in the DBS could be correlated to the reduction in mechanical strength.In contrast,annealing improved the DBS of the 99%alumina ceramic without intergranular phase transformation.Firing in wet hydrogen at 1500℃caused the DBS increment,which can be ascribed to the reduction in the concentrations of point defects and electrical carriers.展开更多
Dielectric elastomers are widely investigated as soft electromechanically active polymers(EAPs)for actuators,stretch/force sensors,and mechanical energy harvesters to generate electricity.Although the performance of s...Dielectric elastomers are widely investigated as soft electromechanically active polymers(EAPs)for actuators,stretch/force sensors,and mechanical energy harvesters to generate electricity.Although the performance of such devices is limited by the dielectric strength of the constitutive material,the electrical breakdown of soft elastomers for electromechanical transduction is still scarcely studied.Here,we describe a custom-made setup to measure electrical breakdown of soft EAPs,and we present data for a widely studied acrylic elastomer(VHB 4905 from 3M).The elastomer was electrically stimulated via a planar and a hemispherical metal electrode.The breakdown was characterized under different conditions to investigate the effects of the radius of curvature and applied force of the hemispherical electrode.With a given radius of curvature,the breakdown field increased by about 50% for a nearly 10-fold increase of the applied mechanical stress,while with a given mechanical stress the breakdown field increased by about 20% for an approximately two fold increase of the radius of curvature.These results indicate that the breakdown field is highly dependent on the boundary conditions,suggesting the need for reporting breakdown data always in close association with the measurement conditions.These findings might help future investigations in elucidating the ultimate breakdown mechanism/s of soft elastomers.展开更多
A large number of insulation/dielectric failures in power systems are related to thermally-induced dielectrical breakdown,also known as‘thermal breakdown’,at higher operating temperatures.In this work,the thermal br...A large number of insulation/dielectric failures in power systems are related to thermally-induced dielectrical breakdown,also known as‘thermal breakdown’,at higher operating temperatures.In this work,the thermal breakdown behavior of typical silicone formulations,used as dielectrics in stretchable electronic devices,is analyzed at practically relevant operating temperatures ranging from 20℃ to 80℃.An effective way of delaying the thermal breakdown of insulating materials is to blend micro-or nano-sized inorganic particles with high thermal conductivity,to dissipate better any losses generated during energy transduction.Therefore,two types of commercial silicone formulations,blended with two types of rutile hydrophobic,high-dielectric TiO_(2) fillers,are investigated in relation to their dielectric properties,namely,relative permittivity,the dissipation factor,and electrical breakdown strength.The breakdown strengths of these silicone composites are subsequently evaluated using Weibull analysis,which indicates a negative correlation between temperature and shape parameter for all compositions,thus illustrating that the homogeneity of the samples decreases in line with temperature,but the breakdown strengths nevertheless increase initially due to the trapping effect from the high-permittivity fillers.展开更多
Ordered domain engineering has been further developed for modifying and improving physical prop-erties in complex perovskite ceramics. In the present work, Ba(Ni_(1/3)Nb_(2/3))O_(3) ceramic is taken as a typicalexampl...Ordered domain engineering has been further developed for modifying and improving physical prop-erties in complex perovskite ceramics. In the present work, Ba(Ni_(1/3)Nb_(2/3))O_(3) ceramic is taken as a typicalexample for ordered domain engineering, in which the sintering temperature lies above the order-disorder transition temperature. Though the well-ordered structure could not be obtained in as-sintered samples, high ordering degree could be achieved together with preferred ordered domainstructures in Ba(Ni_(1/3)Nb_(2/3))O_(3) ceramics through long-time annealing, and subsequently the physicalproperties such as electrical resistivity, thermal conductivity, dielectric strength and energy storagedensity are significantly enhanced, where the ordering degree, ordered domain structure and ordereddomain boundary play the critical rules. The present work provides an effective approach for developingcomplex perovskite dielectric ceramics with superior physical properties.展开更多
文摘One commonly used strategy to enhance polymers specific properties such as the resistance to partial discharges erosion is the incorporation into the polymeric matrix of inorganic micro or nanoparticles. This study focused on the dielectric properties of Low-Density Polyethylene (LDPE) filled with nano-sized Magnesium Oxide (MgO) particles compounded by thermo-mechanical process and one of the purposes was to establish appropriate processing parameters in order to reach the desired dielectric properties. LDPE was used as a matrix and was reinforced by MgO particles having a nominal average size of 30 nm. The MgO nanoparticles were treated with a silane coupling agent (3-Glycidyloxypropyl Trimethoxysilane). The samples were initially prepared in a melt-mixing chamber with a MgO content of 1% wt. These pre-mixed samples were further treated by the means of thermo-mechanical mixing in a conical co-rotating twin-screw extruder in order to improve the dispersion and distribution of the MgO particles. In this report, both lifetime under a PD activity and AC dielectric strength of pure and nano-filled LDPE samples have been measured and compared. Nano-filled LDPE samples were found to exhibit an improve lifetime, without any detrimental impact on their short-term dielectric strength. This suggests that nano-filled LDPE may be for electric applications for which the dielectric materials may be exposed to partial discharge activities. This is significant result for the use of MgO-reinforced PE as an insulating material for HV cables since the resistance to PD is closely related to treeing resistance which is the main electrical degradation mechanism that leads to failure for shielded extruded power cables.
基金Project supported by the Natural Science Foundation of Jiangsu Higher Education Institutions of China(Grant Nos.19KJD140002 and 19KJB140008)the Key Projects of Ministry of Science and Technology of China(Grant No.SQ2020YFF0407077)+3 种基金Postgraduate Research&Practice Innovation Program of Jiangsu Province,China(Grant Nos.2020XKT786 and KYCX202337)the National Foreign Experts Bureau High-end Foreign Experts Project,China(Grant No.G20190114003)the Key Research and Development Program of Jiangsu Province,China(Grant No.BE2018063)the Scientific Research Program for Doctoral Teachers of JSNU(Grant No.9212218113)。
文摘The inductively coupled plasma chemical vapor deposition(ICP-CVD) deposited silicon nitride(SiN_(x)) thin film was evaluated for its application as the electrical insulating film for a capacitor device.In order to achieve highest possible dielectric strength of SiN_(x),the process parameters of ICP-CVD were carefully tuned to control hydrogen in SiN_(x) films by means of tuning N_(2)/SiH_(4) ratio and radio frequency(RF) power.Besides electrical measurements,the hydrogen content in the films was measured by dynamic secondary ion mass spectrometry(D-SIMS).Fourier transform infrared spectroscopy(FTIR) and micro Raman spectroscopy were used to characterize the SiN_(x) films by measuring Si-H and N-H bonds’ intensities.It was found that the more Si-H bonds lead to the higher dielectric strength.
基金The present work was supported by the Nanotechnology Research Center at Aswan University that is established by aiding the Science and Technology Development Fund(STDF),Egypt,Grant No:Project ID 505,2009-2011.
文摘Nanoparticles succeeded to enhance the dielectric properties of industrial insulation but the presence of voids inside the power cable insulation still leads to formation high electrical stress inside power cable insulation material and collapse.In this paper,the dielectric strength of new design nanocomposites has been deduced as experimental work done to clarify the benefit of filling nanoparticles with different patterns inside dielectrics.Also,it has been studied the effect of electrical stress distribution in presence of air,water and copper impurities with different shapes(cylinder,sphere and ellipse)inside insulation of single core.In simulation model,it has been used finite element method(FEM)for estimating the electrostatic field distribution in power cable insulation.It has been applied new strategies of nanotechnology techniques for designing innovative polyvinyl chloride insula-tion materials by using nanocomposites and multi-nanocomposites.Finally,this research succeeded to remedy different partial discharges(PD)patterns according to using certain types and concentrations of nanoparticles.
文摘CuCr25W1Ni2 alloy was prepared by means of vacuum induction melting (VIM). A series of Cu/Cr alloys with different compositions (mass fraction, 25%～75%) and Cr grain sizes (up to 150 μm) were investigated for their differences in physical properties and breakdown voltage. The influence of alloy elements and microstructure on the performance of CuCr25W1Ni2 alloy was also discussed. Experimental results show that the chromium phase is strengthened and its size is minimized by the addition of tungsten powder. After electrical breakdown, very fine tungsten particles in the melt layer form the external nuclei in the solidification process. The microstructure of surface melt layer of CuCr25W1Ni2 alloy is much flatter. It can notably improve the dielectric strength. On the other hand, the nickel can enhance the mutual solubility of copper and chromium, and the whole alloy is strengthened. [
文摘High voltage power modules are used in numerous applications to build high power converters. Technically, these modules are made of different materials and among them, dielectric materials are organic and inorganic. Organic insulators (gels) are used to avoid corona discharges in the vicinity of connecting wires and high voltage dies (diodes and transistors) and to protect them from moisture and contaminants. Inorganic insulators (ceramic substrates) are used to insulate the high voltage which dies from the grounded elements and to transfer heat to the heat sink. Despite being used since the late 90s, there is a lack of fundamental knowledge about the electrical properties of these substrates. Consequently, manufacturers tend to assure the reliability by over sizing them. As there are no clear rules for how to do that, failures occur, leading to the converter shutdown. The aim of this study is to bring new information about the understanding of the dielectric strength of ceramic materials used in these modules. We have focused our work on the correlation between the mechanical and the dielectric properties of ceramics by using relevant experiments. We provide new information about the impact of existing cracks on the ceramic dielectric failure, according to the electromechanical breakdown model. Our conclusions bring crucial information about the precautions to be taken during manufacturing and implementation of these substrates in power modules to reduce the likelihood of the particular causes of failure.
基金The study was financially supported by the Science Development Foundation of China Academy of Engineering Physics(2014A0302012)the Funding Support by Laboratory of Precision Manufacturing Technology,CAEP(ZD18001).
文摘Annealing and firing in wet hydrogen are widely used steps in the processing alumina.ceramic insulators that may affect their dielectric breakdown strengths(DBS).In this study,the effects of annealing(at 1300℃for 7 h)and firing in wet hydrogen on the DBS of alumina ceramics(all sintered at 1650℃)were studied,and the underlying mechanisms were analyzed by material characterizations.Annealing reduced the DBS of the 95%alumina ceramics due to the inter-granular phase crystallization,and the reduction in the DBS could be correlated to the reduction in mechanical strength.In contrast,annealing improved the DBS of the 99%alumina ceramic without intergranular phase transformation.Firing in wet hydrogen at 1500℃caused the DBS increment,which can be ascribed to the reduction in the concentrations of point defects and electrical carriers.
基金B.Chen would like to acknowledge sponsorship from the UK National Physical Laboratory,the China Scholarship Council and the European Scientific Network for Artificial Muscles-ESNAM(COST Action MP1003).
文摘Dielectric elastomers are widely investigated as soft electromechanically active polymers(EAPs)for actuators,stretch/force sensors,and mechanical energy harvesters to generate electricity.Although the performance of such devices is limited by the dielectric strength of the constitutive material,the electrical breakdown of soft elastomers for electromechanical transduction is still scarcely studied.Here,we describe a custom-made setup to measure electrical breakdown of soft EAPs,and we present data for a widely studied acrylic elastomer(VHB 4905 from 3M).The elastomer was electrically stimulated via a planar and a hemispherical metal electrode.The breakdown was characterized under different conditions to investigate the effects of the radius of curvature and applied force of the hemispherical electrode.With a given radius of curvature,the breakdown field increased by about 50% for a nearly 10-fold increase of the applied mechanical stress,while with a given mechanical stress the breakdown field increased by about 20% for an approximately two fold increase of the radius of curvature.These results indicate that the breakdown field is highly dependent on the boundary conditions,suggesting the need for reporting breakdown data always in close association with the measurement conditions.These findings might help future investigations in elucidating the ultimate breakdown mechanism/s of soft elastomers.
基金supported by the Independent Research Fund Denmark.
文摘A large number of insulation/dielectric failures in power systems are related to thermally-induced dielectrical breakdown,also known as‘thermal breakdown’,at higher operating temperatures.In this work,the thermal breakdown behavior of typical silicone formulations,used as dielectrics in stretchable electronic devices,is analyzed at practically relevant operating temperatures ranging from 20℃ to 80℃.An effective way of delaying the thermal breakdown of insulating materials is to blend micro-or nano-sized inorganic particles with high thermal conductivity,to dissipate better any losses generated during energy transduction.Therefore,two types of commercial silicone formulations,blended with two types of rutile hydrophobic,high-dielectric TiO_(2) fillers,are investigated in relation to their dielectric properties,namely,relative permittivity,the dissipation factor,and electrical breakdown strength.The breakdown strengths of these silicone composites are subsequently evaluated using Weibull analysis,which indicates a negative correlation between temperature and shape parameter for all compositions,thus illustrating that the homogeneity of the samples decreases in line with temperature,but the breakdown strengths nevertheless increase initially due to the trapping effect from the high-permittivity fillers.
基金The present work was financially supported by National Natural Foundation of China under grant No.U20A20243.
文摘Ordered domain engineering has been further developed for modifying and improving physical prop-erties in complex perovskite ceramics. In the present work, Ba(Ni_(1/3)Nb_(2/3))O_(3) ceramic is taken as a typicalexample for ordered domain engineering, in which the sintering temperature lies above the order-disorder transition temperature. Though the well-ordered structure could not be obtained in as-sintered samples, high ordering degree could be achieved together with preferred ordered domainstructures in Ba(Ni_(1/3)Nb_(2/3))O_(3) ceramics through long-time annealing, and subsequently the physicalproperties such as electrical resistivity, thermal conductivity, dielectric strength and energy storagedensity are significantly enhanced, where the ordering degree, ordered domain structure and ordereddomain boundary play the critical rules. The present work provides an effective approach for developingcomplex perovskite dielectric ceramics with superior physical properties.
