Commercial biaxially oriented polypropylene(BOPP)film capacitors have been widely applied in the fields of electrical and electronic engineering.However,due to the sharp increase in electrical conduction loss as the t...Commercial biaxially oriented polypropylene(BOPP)film capacitors have been widely applied in the fields of electrical and electronic engineering.However,due to the sharp increase in electrical conduction loss as the temperature rises,the energy storage performance of BOPP films seriously degrades at elevated temperatures.In this study,the grafting modification method is facile and suitable for large-scale industrial manufacturing and has been proposed to increase the high-temperature energy storage performance of com-mercial BOPP films for the first time.Specifically,acrylic acid(AA)as a polar organic molecular is used to graft onto the surface of commercial BOPP films by using ultraviolet irradiation(abbreviated as BOPP-AA).The results demonstrate that the AA grafting modification not only slightly increases the dielectric constant,but also significantly reduces the leakage current density at high-temperature,greatly improving the high-temperature energy storage performance.The modified BOPP-AA films display a discharged energy density of 1.32 J/cm3 with an efficiency of>90%at 370 kV/mm and 125℃℃,which is 474%higher than that of the pristine BOPP films.This work manifests that utilizing ultraviolet grafting modification is a very efficient way to improve the high-temperature energy storage performance of commercial BOPP films as well as provides a hitherto unexplored opportunity for large-scalable production applications.展开更多
As an indispensable part of high-voltage direct current(HVDC)cable,the semiconductive shielding layer plays the role of uniforming electric field in the cable.However,cable shielding materials>35 kV mainly rely on ...As an indispensable part of high-voltage direct current(HVDC)cable,the semiconductive shielding layer plays the role of uniforming electric field in the cable.However,cable shielding materials>35 kV mainly rely on foreign imports in China,which belongs to the technical weak issues in the field of electrical materials.At present,there are few systematic reports on semiconductive shielding material of HVDC cable.In the work,the mechanisms of charge conduction and thermal conduction of semiconductive material have been introduced.Effect of raw material,carbon black content and the second conductive filler on the resistance characteristics of the semiconductive layer,the charge accumulation characteristics of the insulating layer and the interface characteristics have been studied.A kind of semiconductive layer as a high voltage terminal charge emission method has been proposed to study charge emission from the semiconducting layer to the insulation layer.This work can provide theoretical guidance for the research of semiconductive shielding materials.展开更多
Dielectric capacitors have a high power density,and are widely used in military and civilian life.The main problem lies in the serious deterioration of dielectric insulation performance at high temperatures.In this st...Dielectric capacitors have a high power density,and are widely used in military and civilian life.The main problem lies in the serious deterioration of dielectric insulation performance at high temperatures.In this study,a polycarbonate(PC)-based energy storage dielectric was designed with BN/SiO_(2)heterojunctions on its surface.Based on this structural design,a synergistic suppression of the carrier injection and transport was achieved,significantly improving the insulating properties of the polymer film.In particular,the composite film achieves optimal high-temperature energy-storage properties.The composite film can withstand an electric field intensity of 760 MV m^(-1)at 100℃and obtain an energy storage density of 8.32 J cm^(-3),while achieving a breakthrough energy storage performance even at 150℃(610 MV m^(-1),5.22 J cm^(-3)).Through adjustment of the heterojunction structure,free adjustment of the insulation performance of the material can be realized;this is of great significance for the optimization of the material properties.展开更多
A semi‐conductive shielding layer plays an important role in the uniform electric field for a high‐voltage cable.The electric‐thermal properties of the semi‐conductive layer and insulation layer directly affect th...A semi‐conductive shielding layer plays an important role in the uniform electric field for a high‐voltage cable.The electric‐thermal properties of the semi‐conductive layer and insulation layer directly affect the overall insulation performance of the cable.The physicochemical performances of semi‐conductive composites are firstly analysed herein.Furthermore,electric‐thermal properties of the semi‐conductive layer and insulation layer are discussed.The experimental results show that the thermal conductivity of the commercial semi‐conductive layer is about twice that of the insulation layer,owing to the effect of carbon black.The thermal expansion coefficient of the insulation layer rises from 1.86×10^(−4)/K at 25℃ to 3.20×10^(−4)/K at 90℃.By contrast,the semi‐conductive layer begins to slowly decline at a certain temperature,and decreases signif-icantly to 2.25×10^(−4)/K at 80℃,owing to the effect of ethylene‐vinyl acetate copolymer(EVA).The electrical experiments show that the resistivity of semi‐conductive composite gradually rises with an increase in temperature,and gradually declines with an increase in the carbon black content.The dc breakdown strength of the composite structure of the semi‐conductive layer/insulation layer decreases significantly with an increase in tem-perature,decreasing from 307 kV/mm at 25℃ to 203 kV/mm at 90℃.At four typical temperatures,the breakdown strength reaches the maximum value when the carbon black content is 25 phr.It is about 15%and 19%higher than carbon black contents of 20 and 30 phr.These findings have reference significance for high‐voltage cable breakdown fault analysis and material selection in cable design.展开更多
Space charge accumulation in the insulation layer of high-voltage direct current(HVDC)cable is one of the key factors restricting the development of HVDC cable.The inner semi-conductive layer as an important structure...Space charge accumulation in the insulation layer of high-voltage direct current(HVDC)cable is one of the key factors restricting the development of HVDC cable.The inner semi-conductive layer as an important structure of cable will affect the charge accumu-lation characteristics in the insulation layer.This work intends to explore the method of modifying the semi-conductive layer with graphene,to suppress charge accumulation in the insulation layer.First,the semi-conductive layer with different contents of Graphene(G)and carbon black(CB)are prepared.Second,the morphology and surface roughness of the cross section are analysed.Further,the effects of the semi-conductive layer on space charge accumulation of the insulation layer are studied by pulsed electro-acoustic method and thermal stimulation depolarisation current method.The experimental re-sults show that a moderate amount of graphene replacing CB can effectively reduce charge accumulation in the insulation layer and inhibit positive temperature coefficient(PTC)effect at the same time.The surface roughness of specimens decreases with the increase of G content from 0 to 3 phr(parts per hundreds of resin),when the CB content decreases from 25 to 10 phr,the surface roughness of specimen increases.The resistivity test shows that doping G can significantly inhibit the PTC effect of the semi-conductive layer.The volume resistivity of the semi-conductive layer decreases with the increase of G content and CB content.In addition,charge accumulation of the insulation layer rises and then drops under the action of the semi-conductive layer.展开更多
Breakdown failure in insulation material is one of the key problems that threaten the safe operation of high-voltage direct current cable.In this work,the effect of boron nitride nanosheets(BNNSs)concentration,space c...Breakdown failure in insulation material is one of the key problems that threaten the safe operation of high-voltage direct current cable.In this work,the effect of boron nitride nanosheets(BNNSs)concentration,space charge and temperature on DC breakdown strength have been explored.Cross-linked polyethylene(XLPE)/BNNS nanocomposites were prepared by the melt blending method,and the basic characteristics of nanoparticles and composite were characterised.The experimental results indicate that DC breakdown strength of nanocomposite can be effectively improved when a small amount of BN nanosheet is doped into the matrix.The breakdown strength of the sample reaches the maximum value of 407.52 kV/mm when BNNS content is 0.5 wt%,which is about 33%higher than that of pure XLPE.Further,the effect of space charge on the breakdown of nanocomposites has been studied by pre-injecting charges.For the samples with different BNNS contents,all the breakdown strength present ascending trend when the polarity of the applied voltage is the same as that of the pre-injected charges.Besides,it can be found that the breakdown strength of the XLPE/BNNSs composite decreases significantly at 50°C,which is due to more charge accumulation at 50°C.It reaches 2.06×10^(−8)C which increases by about 2.2 times than the room temperature.展开更多
Owing to the formation of interface and new feature of which, the properties of nanodielectrics can be improved. ‘Hard/soft interface’ and its trap distribution can be tailored by functionalised groups. Molecular si...Owing to the formation of interface and new feature of which, the properties of nanodielectrics can be improved. ‘Hard/soft interface’ and its trap distribution can be tailored by functionalised groups. Molecular simulation results show that the interaction energy and electrostatic potential are larger for the soft interface, which indicates the greater bonding strength with the polymer matrix and electrostatic force on charge carriers. Charge transport simulation indicates that the accumulation of homo-charges would form a reverse electric field and distort electric field distribution. The injection depth would be restricted at the vicinity of sample/electrodes due to the greater trapping effect of deep traps, thus weakening the distortion in the sample bulk, thereby decreasing carrier energy and delaying the formation of impact ionisation. Based on the accumulation of carrier energy Φ = Eeλ, the idea of suppressing electron free path and carrier energy to enhance the insulation breakdown is confirmed. The classified effects of nanofillers during dc breakdown and corona-resistant are further understood from carrier energy. The introduced interfacial trap is effective in trapping carriers due to the low carrier energy under dc voltage, while ineffective in blocking the energetic charges during corona-discharge, but nanoparticles exert blocking and scattering effect against the energetic charges.展开更多
Film dielectric capacitors have been widely used in high‐power electronic equipment.The design of microstructure and the choice of fillers play an important role in nano-composites'energy storage density.Machine ...Film dielectric capacitors have been widely used in high‐power electronic equipment.The design of microstructure and the choice of fillers play an important role in nano-composites'energy storage density.Machine learning methods can classify and summarise the limited data and then explore the promising composite structure.In this work,a dataset has been established,which contained a large amount of data on the maximum energy storage density of nanocomposites.Though using processed visual image infor-mation to express the internal information of composite,the prediction accuracy of the prediction models built by three machine learning algorithms increase from 84.1%to 91.9%,80.9%to 68.9%,70.6%to 81.6%,respectively.By calculating the branch weight in the random forest prediction model,the influence degree of different descriptors on the energy storage performance of nanocomposites is analysed.A total of 10 groups of composites with different structure and filler amount were prepared in the laboratory,which were used to verify the reliability of prediction models.Finally,the effective filler's structure is explored by three prediction models and some suggestions for the interface design of filler are given.展开更多
The high‐voltage isolated energy supply transformer(HIET)is the key component of the HVDC breaker,which is used for energy transmission and the potential isolation.There is a lack of research results that can meet en...The high‐voltage isolated energy supply transformer(HIET)is the key component of the HVDC breaker,which is used for energy transmission and the potential isolation.There is a lack of research results that can meet engineering applications at home and abroad.The design of a 500 kV HIET with dry‐type insulation is proposed,using 10 cascade connected 50 kV sub‐transformers(STs),which uses silicon rubber suitable for DC voltage as the main insulation material.High‐voltage(HV)winding of ST adopts double‐shielding structure of coil semi‐conductive shielding and inner semi‐conductive shielding to improve electric field distribution.The simulation analysis of an electric field at different insulation thicknesses and temperatures shows that the electric field decreases with an increase in thickness of insulation.When the thickness is greater than 25 mm,the electric field reduction effect is significantly weakened.The electric field is closely related to temperature,when at 20℃,the electric field between double‐shielding is relatively uniform.When at 70℃,the inner shielding electric field is much higher than coil shielding,and undergoes obvious reversal.In addition,the 500 kV HIET's electric field has been analysed.The 500kV HIET prototype has been manufactured and passed the type test,and successfully applied to the 500 kV Zhangbei DC grid project.展开更多
The semiconductive shield layer is between the conductive core and the insulation layer of high voltage direct current transmission cables and plays an important role in suppressing the accumulation of space charge in...The semiconductive shield layer is between the conductive core and the insulation layer of high voltage direct current transmission cables and plays an important role in suppressing the accumulation of space charge in the insulation layer.Since the prevalent positive temperature coefficient effect(PTC)of the semiconducting layer leads to cable ageing and failure,this paper proposes the use of lithium cobaltate to modify the semiconducting shield to suppress its PTC effect and improve its ability to inhibit space charge injection.The ionic conductor LiCoO_(2)was prepared by the sol–gel method.LiCoO_(2)particles with particle sizes ranging from tens to hundreds of nanometres were obtained by ball milling.The prepared LiCoO_(2)was used as a filler to modify the carbon black(CB)/ethylene vinyl acetate copolymer(EVA)/low density polyethylene(LDPE)composites.After melt blending and moulding cross-linking,LiCoO_(2)/CB/EVA/LDPE semiconductive shielding specimens were successfully fabricated.Resistivity,Thermally Stimulated Depolarisation Currents(TSDC),and pulsed electroacoustic measurements were conducted for the prepared specimens.The PTC effect,which is common in polymer composites,was successfully suppressed,and the PTC strength was reduced by 17%.The resistivity of the semiconductive shielding layer was significantly reduced.The ability of the semiconducting shield to inhibit space charge injection from the conductive core to the insulation layer was significantly improved.When LiCoO_(2)content is 0.5 wt%,the semiconductive shielding layer has the best performance,and the space charge in the insulation layer was reduced by 70%compared to the undoped semiconducting shield.展开更多
In this study,conductive polyaniline(PANI)ribbons were introduced to a semi-conductive layer to improve the conductivity stability of the layer during thermal expansion and enhance its ability to inhibit charge inject...In this study,conductive polyaniline(PANI)ribbons were introduced to a semi-conductive layer to improve the conductivity stability of the layer during thermal expansion and enhance its ability to inhibit charge injection into the insulating layer.To maximise the effect of PANI,PANI and carbon black(CB)were preformed into a uniformly dispersed composite,which was then added to the polymer matrix of the semiconductive layer.The experimental results show that the resistivity of the semi-conductive layer containing the PANI/CB composite is more stable during thermal expansion than that of the semiconductive layer only doped with CB.This is attributed to the conductive CB network being enhanced by the PANI ribbons.In addition,due to the unique conductivity mechanism and high dielectric constant of PANI,the semiconductive layer has a strong ability to inhibit space charge injection into the insulating layer.展开更多
基金supported by the National Natural Science Foundation of China(Nos.U20A20308,51977050)Heilongjiang Provincial Natural Science Foundation of China(No.ZD2020E009)+1 种基金China Postdoctoral Science Foundation(Nos.2021T140166,2018M640303)University Nursing Program for Young Scholars with Creative Talents in Heilongjiang(Nos.UNPYSCT-2020178,UNPYSCT-2020180).
文摘Commercial biaxially oriented polypropylene(BOPP)film capacitors have been widely applied in the fields of electrical and electronic engineering.However,due to the sharp increase in electrical conduction loss as the temperature rises,the energy storage performance of BOPP films seriously degrades at elevated temperatures.In this study,the grafting modification method is facile and suitable for large-scale industrial manufacturing and has been proposed to increase the high-temperature energy storage performance of com-mercial BOPP films for the first time.Specifically,acrylic acid(AA)as a polar organic molecular is used to graft onto the surface of commercial BOPP films by using ultraviolet irradiation(abbreviated as BOPP-AA).The results demonstrate that the AA grafting modification not only slightly increases the dielectric constant,but also significantly reduces the leakage current density at high-temperature,greatly improving the high-temperature energy storage performance.The modified BOPP-AA films display a discharged energy density of 1.32 J/cm3 with an efficiency of>90%at 370 kV/mm and 125℃℃,which is 474%higher than that of the pristine BOPP films.This work manifests that utilizing ultraviolet grafting modification is a very efficient way to improve the high-temperature energy storage performance of commercial BOPP films as well as provides a hitherto unexplored opportunity for large-scalable production applications.
基金supported by the China Postdoctoral Science Foundation(Grant No.2018M642627)the National Natural Science Foundation of China(Grant No.51907095)+1 种基金the Shandong Provincial Natural Science Foundation,China(Grant No.ZR2019BEE036)the National Engineering Laboratory for Ultra High Voltage Engineering Technology(Grant No.NEL201802).
文摘As an indispensable part of high-voltage direct current(HVDC)cable,the semiconductive shielding layer plays the role of uniforming electric field in the cable.However,cable shielding materials>35 kV mainly rely on foreign imports in China,which belongs to the technical weak issues in the field of electrical materials.At present,there are few systematic reports on semiconductive shielding material of HVDC cable.In the work,the mechanisms of charge conduction and thermal conduction of semiconductive material have been introduced.Effect of raw material,carbon black content and the second conductive filler on the resistance characteristics of the semiconductive layer,the charge accumulation characteristics of the insulating layer and the interface characteristics have been studied.A kind of semiconductive layer as a high voltage terminal charge emission method has been proposed to study charge emission from the semiconducting layer to the insulation layer.This work can provide theoretical guidance for the research of semiconductive shielding materials.
基金This research was funded by the National Natural Science Foundation of China(No.U20A20308,52177017,and 51977050)Natural Science Foundation of Heilongjiang Province of China(No.YQ2021E036 and ZD2020E009)+3 种基金China Postdoctoral Science Foundation(No.2020T130156)Heilongjiang Postdoctoral Financial Assistance(No.LBHZ18098)Fundamental Research Foundation for Universities of Heilongjiang Province(No.2019-KYYWF-0207 and 2018-KYYWF-1624)University Nursing Program for Young Scholars with Creative Talents in Heilongjiang Province(UNPYSCT-2020177).
文摘Dielectric capacitors have a high power density,and are widely used in military and civilian life.The main problem lies in the serious deterioration of dielectric insulation performance at high temperatures.In this study,a polycarbonate(PC)-based energy storage dielectric was designed with BN/SiO_(2)heterojunctions on its surface.Based on this structural design,a synergistic suppression of the carrier injection and transport was achieved,significantly improving the insulating properties of the polymer film.In particular,the composite film achieves optimal high-temperature energy-storage properties.The composite film can withstand an electric field intensity of 760 MV m^(-1)at 100℃and obtain an energy storage density of 8.32 J cm^(-3),while achieving a breakthrough energy storage performance even at 150℃(610 MV m^(-1),5.22 J cm^(-3)).Through adjustment of the heterojunction structure,free adjustment of the insulation performance of the material can be realized;this is of great significance for the optimization of the material properties.
文摘A semi‐conductive shielding layer plays an important role in the uniform electric field for a high‐voltage cable.The electric‐thermal properties of the semi‐conductive layer and insulation layer directly affect the overall insulation performance of the cable.The physicochemical performances of semi‐conductive composites are firstly analysed herein.Furthermore,electric‐thermal properties of the semi‐conductive layer and insulation layer are discussed.The experimental results show that the thermal conductivity of the commercial semi‐conductive layer is about twice that of the insulation layer,owing to the effect of carbon black.The thermal expansion coefficient of the insulation layer rises from 1.86×10^(−4)/K at 25℃ to 3.20×10^(−4)/K at 90℃.By contrast,the semi‐conductive layer begins to slowly decline at a certain temperature,and decreases signif-icantly to 2.25×10^(−4)/K at 80℃,owing to the effect of ethylene‐vinyl acetate copolymer(EVA).The electrical experiments show that the resistivity of semi‐conductive composite gradually rises with an increase in temperature,and gradually declines with an increase in the carbon black content.The dc breakdown strength of the composite structure of the semi‐conductive layer/insulation layer decreases significantly with an increase in tem-perature,decreasing from 307 kV/mm at 25℃ to 203 kV/mm at 90℃.At four typical temperatures,the breakdown strength reaches the maximum value when the carbon black content is 25 phr.It is about 15%and 19%higher than carbon black contents of 20 and 30 phr.These findings have reference significance for high‐voltage cable breakdown fault analysis and material selection in cable design.
基金National Natural Science Foundation of China,Grant/Award Number:51907095State Key Laboratory of Electrical Insulation and Power Equipment,Grant/Award Number:EIPE21213。
文摘Space charge accumulation in the insulation layer of high-voltage direct current(HVDC)cable is one of the key factors restricting the development of HVDC cable.The inner semi-conductive layer as an important structure of cable will affect the charge accumu-lation characteristics in the insulation layer.This work intends to explore the method of modifying the semi-conductive layer with graphene,to suppress charge accumulation in the insulation layer.First,the semi-conductive layer with different contents of Graphene(G)and carbon black(CB)are prepared.Second,the morphology and surface roughness of the cross section are analysed.Further,the effects of the semi-conductive layer on space charge accumulation of the insulation layer are studied by pulsed electro-acoustic method and thermal stimulation depolarisation current method.The experimental re-sults show that a moderate amount of graphene replacing CB can effectively reduce charge accumulation in the insulation layer and inhibit positive temperature coefficient(PTC)effect at the same time.The surface roughness of specimens decreases with the increase of G content from 0 to 3 phr(parts per hundreds of resin),when the CB content decreases from 25 to 10 phr,the surface roughness of specimen increases.The resistivity test shows that doping G can significantly inhibit the PTC effect of the semi-conductive layer.The volume resistivity of the semi-conductive layer decreases with the increase of G content and CB content.In addition,charge accumulation of the insulation layer rises and then drops under the action of the semi-conductive layer.
基金the Shandong Provincial Natural Science Foundation,China(grant no.ZR2019BEE036)the National Natural Science Foundation of China(grant no.51907095)the China Postdoctoral Science Foundation(grant no.2019M653629).
文摘Breakdown failure in insulation material is one of the key problems that threaten the safe operation of high-voltage direct current cable.In this work,the effect of boron nitride nanosheets(BNNSs)concentration,space charge and temperature on DC breakdown strength have been explored.Cross-linked polyethylene(XLPE)/BNNS nanocomposites were prepared by the melt blending method,and the basic characteristics of nanoparticles and composite were characterised.The experimental results indicate that DC breakdown strength of nanocomposite can be effectively improved when a small amount of BN nanosheet is doped into the matrix.The breakdown strength of the sample reaches the maximum value of 407.52 kV/mm when BNNS content is 0.5 wt%,which is about 33%higher than that of pure XLPE.Further,the effect of space charge on the breakdown of nanocomposites has been studied by pre-injecting charges.For the samples with different BNNS contents,all the breakdown strength present ascending trend when the polarity of the applied voltage is the same as that of the pre-injected charges.Besides,it can be found that the breakdown strength of the XLPE/BNNSs composite decreases significantly at 50°C,which is due to more charge accumulation at 50°C.It reaches 2.06×10^(−8)C which increases by about 2.2 times than the room temperature.
基金the National Basic Research Program of China(973 Program)under Project with NO.2015CB251003the National Key Research and Development Program of China under Project with NO.2017YFB0902702the National Natural Science Foundation of China(NSFC)under Project with NO.51337008.
文摘Owing to the formation of interface and new feature of which, the properties of nanodielectrics can be improved. ‘Hard/soft interface’ and its trap distribution can be tailored by functionalised groups. Molecular simulation results show that the interaction energy and electrostatic potential are larger for the soft interface, which indicates the greater bonding strength with the polymer matrix and electrostatic force on charge carriers. Charge transport simulation indicates that the accumulation of homo-charges would form a reverse electric field and distort electric field distribution. The injection depth would be restricted at the vicinity of sample/electrodes due to the greater trapping effect of deep traps, thus weakening the distortion in the sample bulk, thereby decreasing carrier energy and delaying the formation of impact ionisation. Based on the accumulation of carrier energy Φ = Eeλ, the idea of suppressing electron free path and carrier energy to enhance the insulation breakdown is confirmed. The classified effects of nanofillers during dc breakdown and corona-resistant are further understood from carrier energy. The introduced interfacial trap is effective in trapping carriers due to the low carrier energy under dc voltage, while ineffective in blocking the energetic charges during corona-discharge, but nanoparticles exert blocking and scattering effect against the energetic charges.
基金Foundation of China,Grant/Award Number:51807041,U20A20308 and 51977050the Natural Science Foundation of Heilongjiang Province of China,Grant/Award Number:ZD2020E009+3 种基金the China Postdoctoral Science Foundation,Grant/Award Number:2020T130156Heilongjiang Postdoctoral Financial Assistance,Grant/Award Number:LBH‐Z18098the Fundamental Research Foundation for Universities of Heilongjiang Prov-ince,Grant/Award Number:2019‐KYYWF‐0207 and 2018‐KYYWF‐1624the State Key Laboratory of Power System and Generation Equipment,Grant/Award Number:SKLD20M13.
文摘Film dielectric capacitors have been widely used in high‐power electronic equipment.The design of microstructure and the choice of fillers play an important role in nano-composites'energy storage density.Machine learning methods can classify and summarise the limited data and then explore the promising composite structure.In this work,a dataset has been established,which contained a large amount of data on the maximum energy storage density of nanocomposites.Though using processed visual image infor-mation to express the internal information of composite,the prediction accuracy of the prediction models built by three machine learning algorithms increase from 84.1%to 91.9%,80.9%to 68.9%,70.6%to 81.6%,respectively.By calculating the branch weight in the random forest prediction model,the influence degree of different descriptors on the energy storage performance of nanocomposites is analysed.A total of 10 groups of composites with different structure and filler amount were prepared in the laboratory,which were used to verify the reliability of prediction models.Finally,the effective filler's structure is explored by three prediction models and some suggestions for the interface design of filler are given.
文摘The high‐voltage isolated energy supply transformer(HIET)is the key component of the HVDC breaker,which is used for energy transmission and the potential isolation.There is a lack of research results that can meet engineering applications at home and abroad.The design of a 500 kV HIET with dry‐type insulation is proposed,using 10 cascade connected 50 kV sub‐transformers(STs),which uses silicon rubber suitable for DC voltage as the main insulation material.High‐voltage(HV)winding of ST adopts double‐shielding structure of coil semi‐conductive shielding and inner semi‐conductive shielding to improve electric field distribution.The simulation analysis of an electric field at different insulation thicknesses and temperatures shows that the electric field decreases with an increase in thickness of insulation.When the thickness is greater than 25 mm,the electric field reduction effect is significantly weakened.The electric field is closely related to temperature,when at 20℃,the electric field between double‐shielding is relatively uniform.When at 70℃,the inner shielding electric field is much higher than coil shielding,and undergoes obvious reversal.In addition,the 500 kV HIET's electric field has been analysed.The 500kV HIET prototype has been manufactured and passed the type test,and successfully applied to the 500 kV Zhangbei DC grid project.
基金State Key Laboratory of Advanced Power Transmission Technology,Grant/Award Number:GEIRI-SKL-2021-005。
文摘The semiconductive shield layer is between the conductive core and the insulation layer of high voltage direct current transmission cables and plays an important role in suppressing the accumulation of space charge in the insulation layer.Since the prevalent positive temperature coefficient effect(PTC)of the semiconducting layer leads to cable ageing and failure,this paper proposes the use of lithium cobaltate to modify the semiconducting shield to suppress its PTC effect and improve its ability to inhibit space charge injection.The ionic conductor LiCoO_(2)was prepared by the sol–gel method.LiCoO_(2)particles with particle sizes ranging from tens to hundreds of nanometres were obtained by ball milling.The prepared LiCoO_(2)was used as a filler to modify the carbon black(CB)/ethylene vinyl acetate copolymer(EVA)/low density polyethylene(LDPE)composites.After melt blending and moulding cross-linking,LiCoO_(2)/CB/EVA/LDPE semiconductive shielding specimens were successfully fabricated.Resistivity,Thermally Stimulated Depolarisation Currents(TSDC),and pulsed electroacoustic measurements were conducted for the prepared specimens.The PTC effect,which is common in polymer composites,was successfully suppressed,and the PTC strength was reduced by 17%.The resistivity of the semiconductive shielding layer was significantly reduced.The ability of the semiconducting shield to inhibit space charge injection from the conductive core to the insulation layer was significantly improved.When LiCoO_(2)content is 0.5 wt%,the semiconductive shielding layer has the best performance,and the space charge in the insulation layer was reduced by 70%compared to the undoped semiconducting shield.
基金supported by the State Key Laboratory of Advanced Power Transmission Technology(Grant No.GEIRI‐SKL‐2021‐005).
文摘In this study,conductive polyaniline(PANI)ribbons were introduced to a semi-conductive layer to improve the conductivity stability of the layer during thermal expansion and enhance its ability to inhibit charge injection into the insulating layer.To maximise the effect of PANI,PANI and carbon black(CB)were preformed into a uniformly dispersed composite,which was then added to the polymer matrix of the semiconductive layer.The experimental results show that the resistivity of the semi-conductive layer containing the PANI/CB composite is more stable during thermal expansion than that of the semiconductive layer only doped with CB.This is attributed to the conductive CB network being enhanced by the PANI ribbons.In addition,due to the unique conductivity mechanism and high dielectric constant of PANI,the semiconductive layer has a strong ability to inhibit space charge injection into the insulating layer.
