Research on the mechanical–electrical properties is crucial for designing and preparing high-temperature superconducting(HTS)cables.Various winding core structures can influence the mechanical–electrical behavior of...Research on the mechanical–electrical properties is crucial for designing and preparing high-temperature superconducting(HTS)cables.Various winding core structures can influence the mechanical–electrical behavior of cables,but the impact of alterations in the winding core structure on the mechanical–electrical behavior of superconducting cables remains unclear.This paper presents a 3D finite element model to predict the performance of three cables with different core structures when subjected to transverse compression and axial tension.The three cables analyzed are CORC(conductor-on-round-core),CORT(conductor-on-round-tube),and HFRC(conductor-on-spiral-tube).A parametric analysis is carried out by varying the core diameter and inner-to-outer diameter ratio.Results indicate that the CORT cable demonstrates better performance in transverse compression compared to the CORC cable,aligning with experimental data.Among the three cables,the HFRC cables exhibit the weakest resistance to transverse deformation.However,the HFRC cable demonstrates superior tensile deformation resistance compared to the CORT cable,provided that the transverse compression properties are maintained.Finite element results also show that the optimum inner-to-outer diameter ratios for achieving the best transverse compression performance are approximately 0.8 for CORT cables and 0.6 for HFRC cables.Meanwhile,the study explores the effect of structural changes in HTS cable winding cores on their electromagnetic properties.It recommends utilizing small tape gaps,lower frequencies,and spiral core construction to minimize eddy losses.The findings presented in this paper offer valuable insights for the commercialization and practical manufacturing of HTS cables.展开更多
High-voltage direct current(HVDC)cables are growing rapidly all over the world due to the development of offshore wind power interconnections,cross-island power interconnections,etc.Extensive research has been conduct...High-voltage direct current(HVDC)cables are growing rapidly all over the world due to the development of offshore wind power interconnections,cross-island power interconnections,etc.Extensive research has been conducted and many achievements have been made in the study of theoretical issues of HVDC insulation,structural design and manufacture of HVDC cables with the corresponding accessories,as well as in condition monitoring technology.展开更多
This study focuses on the electrical properties and microstructure of polypropylene(PP)-based blends used for cable insulation in nuclear power plants(NPPs).The PP-based blend,comprising isotactic PP and propylene-bas...This study focuses on the electrical properties and microstructure of polypropylene(PP)-based blends used for cable insulation in nuclear power plants(NPPs).The PP-based blend,comprising isotactic PP and propylene-based elastomer(PBE)at concentrations ranging from 0 to 50 wt%,underwent a melt blending process and subsequent cobalt-60 gamma-ray irradiation with doses ranging from 0 to 250 kGy.Electrical conductivity,trap distribution,and alternating(AC)breakdown strength were chosen to assess the insulation performance.These results indicate that the addition of PBE significantly improves the electrical properties of PP under irradiation.For PP,the electrical conductivity increased with irradiation,whereas the trap depth and breakdown strength decreased sharply.Conversely,for the blend,these changes initially exhibit opposite trends.When the irradiation was increased to 250 kGy,the AC breakdown strength of the blend improved by more than 21%compared to that of PP.The physical and chemical structures of the samples were investigated to explore the improvement mechanisms.The results offer insights into the design of new cable-insulation materials suitable for NPPs.展开更多
Frost heave and thaw settlement in cold regions pose a significant threat to engineering construction.Optical frequency domain reflectometry(OFDR)based on Rayleigh scattering can be applied to monitor ground deformati...Frost heave and thaw settlement in cold regions pose a significant threat to engineering construction.Optical frequency domain reflectometry(OFDR)based on Rayleigh scattering can be applied to monitor ground deformation in frozen soil areas,where the interface behavior of soil-embedded fiber optic sensors governs the monitoring accuracy.In this paper,a series of pullout tests were conducted on fiber optic(FO)cables embedded in the frozen soil to investigate the cable‒soil interface behavior.An experimental study was performed on interaction effects,particularly focused on the water content of unfrozen soil,freezing duration,and differential distribution of water content in frozen soil.The highresolution axial strains of FO cables were obtained using a sensing interrogator,and were used to calculate the interface shear stress.The interfacial mechanical response was analytically modeled using the ideal elasto‒plastic and softening constitutive models.Three freezing periods,correlating with the phase change process between ice and water,were analyzed.The results shows that the freezing effect can amplify the peak shear stress at the cable-soil interface by eight times.A criterion for the interface coupling states was proposed by normalizing the pullout force‒displacement information.Additionally,the applicability of existing theoretical models was discussed by comparing the results of theoretical back‒calculations with experimental measurements.This study provides new insights into the progressive interfacial failure behavior between strain sensing cable and frozen soil,which can be used to assist the interpretation of FO monitoring results of frozen soil deformation.展开更多
This paper focuses on the energisation of high voltage DC(HVDC)and medium voltage DC(MVDC)insulation systems,referring mainly to cables for both theoretical development and validation testing.Cable system energisation...This paper focuses on the energisation of high voltage DC(HVDC)and medium voltage DC(MVDC)insulation systems,referring mainly to cables for both theoretical development and validation testing.Cable system energisation can be frequent during its lifetime,and it can possibly be affected by partial discharges(PD),because of manufacturing,laying,ageing,interfaces or structural cavities(as butt gaps).A theory-driven and measurement-based procedure is presented in this paper,having the purpose to minimise PD inception risk.This procedure is based on stepwise voltage application during cable energisation.The fundamental idea behind the proposed approach stems from considering that the jump voltage is the trigger of PD occurrence.Indeed,the jump voltage,and the consequent electric field variation,directly relates to AC PD inception voltage(PDIVAC).In addition,the electric field distribution in an insulation system is driven by insulation permittivity(capacitance)during voltage transients,and by conductivity in DC,thus the PDIVAC is generally smaller than DC PD inception voltage(PDIVDC).Hence,energising a DC cable by an initial step lower than PDIVAC,and then increasing the voltage in steps smaller than PDIVAC,would minimise the risk of PD inception during transients and the relevant degradation rate.However,this does not change,the risk of occurrence(if any)of low-repetition partial discharges at DC steady state.Effectiveness of the proposed technique is proved by the help of tests performed on cables with artificial surface and internal defects.It is shown that compared with the conventional energisation consisting of rapidly increasing voltage,the stepwise approach can reduce the risk of PD inception and related extrinsic ageing,even for the steady state voltages larger than PDIVDC.展开更多
This paper investigates elastomer-toughened polypropylene(PP)insulation to meet the application requirements for green noncrosslinked PP cables in high-voltage direct current(HVDC)transmission.It focuses on the format...This paper investigates elastomer-toughened polypropylene(PP)insulation to meet the application requirements for green noncrosslinked PP cables in high-voltage direct current(HVDC)transmission.It focuses on the formation ofβ-crystals in isotactic polypropylene(iPP)by adding aβ-nucleator.It examines how varying concentrations ofβ-nucleator and elastomer(POE)impact the aggregation structure of PP insulation and its conductivity and breakdown characteristics in the DC field.The results indicated that at aβ-nucleator agent content of 0.1 wt%,the samples with various POE contents achieved the highest crystallinity,the maximum proportion ofβ-crystals and the most uniform elastomer distribution.The nucleating agent facilitates the formation ofβ-crystals in PP and enhances the order degree of the elastomer molecular chains,thereby improving their crystallization capabilities.Evaluations of DC performances and trap characteristics reveal that when the amount of theβ-nucleator is set at 0.1 wt%,the sample demonstrates the lowest trap density,an exceptional and lower electric field coefficient of conductivity at elevated electric fields and a superior DC field breakdown strength at 90°C.Compared to samples withoutβ-nucleator,the reduction of DC field breakdown strength for PPBx-0.1 from 25°C to 90°C is approximately 4.86%lower.This improvement is attributed to the ability of theβ-nucleator to improve the aggregation structure between PP and POE while optimising the stability of the two-phase interface.Thus,although DC electrical characteristics are maintained at normal temperatures,the DC characteristics are significantly improved at elevated temperatures.展开更多
Cross-linking byproducts in the cross-linked polyethylene(XLPE)cable insulation material significantly affect the insulation properties of XLPE,and the non-destructive detection method for cross-linking byproducts dur...Cross-linking byproducts in the cross-linked polyethylene(XLPE)cable insulation material significantly affect the insulation properties of XLPE,and the non-destructive detection method for cross-linking byproducts during cable degassing process still faces great challenges.This work develops an extra-low frequency(ELF)dielectric analysis method based on time-dependent polarisation current for non-destructive detection of byproducts in XLPE.The effects of single byproduct of acetophenone and cumyl alcohol on the ELF dielectric properties of XLPE are studied separately.The ELF associated static permittivity and the dielectric loss of XLPE rise as the content of the single byproduct increases,and theαrelaxation(10−4-10−3 Hz)andβrelaxation(10−3-10−2 Hz)of XLPE are observed.Ionisation of acetophenone occurs above electric field strength of 20 kV,whereas ionisation tends to saturate above 50 kV.The optimal field strength for ELF dielectric testing of XLPE is determined to be 20-50 kV.Furthermore,the degassing factor is proposed to accurately determine the removal of byproducts.Based on these,the non-destructive detection of degassing of XLPE cable is achieved.The proposed ELF dielectric analysis method enables the non-destructive detection of byproducts in cables,opening a new avenue for cable degassing effect evaluation.展开更多
This study proposes a nondestructive optical imaging-based three-dimensional(3D)reconstruction method to analyse electrical tree propagation in polypropylene(PP)cable insulation under mechanical bending.The technique ...This study proposes a nondestructive optical imaging-based three-dimensional(3D)reconstruction method to analyse electrical tree propagation in polypropylene(PP)cable insulation under mechanical bending.The technique combines focus-stacked optical imaging with a feature fusion algorithm to segment in-focus regions across depth layers,enabling 3D reconstruction of electrical trees in PP homopolymer(PPH),block copolymer(PPB)and elastomer-blended(PP/TPE)samples.The results demonstrate that mechanical bending accelerates electrical tree propagation in PPH,and that degradation channels transition from a branch-like to a straight-stick morphology,tending to grow directionally towards stretched regions.With a bending radius of 10 mm,the breakdown time drops from 297.0 min for the undeformed samples to 6.3 min.PPB and PP/TPE delay the time to breakdown by 70.6%and 171.2%,respectively,highlighting their superior resistance under bending stress,which is attributed to maintaining elasticity rather than yield deformation under bending stresses.This study provides a novel tool for evaluating the electrical tree resistance of PP composites under the mechanical stress,guiding the development of recyclable high-voltage direct current cable insulation.展开更多
基金supported by the National Natural Science Foundation of China(12072136).
文摘Research on the mechanical–electrical properties is crucial for designing and preparing high-temperature superconducting(HTS)cables.Various winding core structures can influence the mechanical–electrical behavior of cables,but the impact of alterations in the winding core structure on the mechanical–electrical behavior of superconducting cables remains unclear.This paper presents a 3D finite element model to predict the performance of three cables with different core structures when subjected to transverse compression and axial tension.The three cables analyzed are CORC(conductor-on-round-core),CORT(conductor-on-round-tube),and HFRC(conductor-on-spiral-tube).A parametric analysis is carried out by varying the core diameter and inner-to-outer diameter ratio.Results indicate that the CORT cable demonstrates better performance in transverse compression compared to the CORC cable,aligning with experimental data.Among the three cables,the HFRC cables exhibit the weakest resistance to transverse deformation.However,the HFRC cable demonstrates superior tensile deformation resistance compared to the CORT cable,provided that the transverse compression properties are maintained.Finite element results also show that the optimum inner-to-outer diameter ratios for achieving the best transverse compression performance are approximately 0.8 for CORT cables and 0.6 for HFRC cables.Meanwhile,the study explores the effect of structural changes in HTS cable winding cores on their electromagnetic properties.It recommends utilizing small tape gaps,lower frequencies,and spiral core construction to minimize eddy losses.The findings presented in this paper offer valuable insights for the commercialization and practical manufacturing of HTS cables.
文摘High-voltage direct current(HVDC)cables are growing rapidly all over the world due to the development of offshore wind power interconnections,cross-island power interconnections,etc.Extensive research has been conducted and many achievements have been made in the study of theoretical issues of HVDC insulation,structural design and manufacture of HVDC cables with the corresponding accessories,as well as in condition monitoring technology.
基金supported by the National Natural Science Foundation of China(No.52077151)the State Key Laboratory of Electrical Insulation and Power Equipment(No.EIPE23208)the Key Laboratory of Engineering Dielectrics and Its Application,Ministry of Education(No.KFM202203).
文摘This study focuses on the electrical properties and microstructure of polypropylene(PP)-based blends used for cable insulation in nuclear power plants(NPPs).The PP-based blend,comprising isotactic PP and propylene-based elastomer(PBE)at concentrations ranging from 0 to 50 wt%,underwent a melt blending process and subsequent cobalt-60 gamma-ray irradiation with doses ranging from 0 to 250 kGy.Electrical conductivity,trap distribution,and alternating(AC)breakdown strength were chosen to assess the insulation performance.These results indicate that the addition of PBE significantly improves the electrical properties of PP under irradiation.For PP,the electrical conductivity increased with irradiation,whereas the trap depth and breakdown strength decreased sharply.Conversely,for the blend,these changes initially exhibit opposite trends.When the irradiation was increased to 250 kGy,the AC breakdown strength of the blend improved by more than 21%compared to that of PP.The physical and chemical structures of the samples were investigated to explore the improvement mechanisms.The results offer insights into the design of new cable-insulation materials suitable for NPPs.
基金the National Key Research and Development Program of China(Grant No.2023YFF1303501)the National Science Fund for Distinguished Young Scholars of China(Grant No.42225702)the Open Fund of State Key Laboratory of Frozen Soil Engineering(Grant No.SKLFSE201814).
文摘Frost heave and thaw settlement in cold regions pose a significant threat to engineering construction.Optical frequency domain reflectometry(OFDR)based on Rayleigh scattering can be applied to monitor ground deformation in frozen soil areas,where the interface behavior of soil-embedded fiber optic sensors governs the monitoring accuracy.In this paper,a series of pullout tests were conducted on fiber optic(FO)cables embedded in the frozen soil to investigate the cable‒soil interface behavior.An experimental study was performed on interaction effects,particularly focused on the water content of unfrozen soil,freezing duration,and differential distribution of water content in frozen soil.The highresolution axial strains of FO cables were obtained using a sensing interrogator,and were used to calculate the interface shear stress.The interfacial mechanical response was analytically modeled using the ideal elasto‒plastic and softening constitutive models.Three freezing periods,correlating with the phase change process between ice and water,were analyzed.The results shows that the freezing effect can amplify the peak shear stress at the cable-soil interface by eight times.A criterion for the interface coupling states was proposed by normalizing the pullout force‒displacement information.Additionally,the applicability of existing theoretical models was discussed by comparing the results of theoretical back‒calculations with experimental measurements.This study provides new insights into the progressive interfacial failure behavior between strain sensing cable and frozen soil,which can be used to assist the interpretation of FO monitoring results of frozen soil deformation.
文摘This paper focuses on the energisation of high voltage DC(HVDC)and medium voltage DC(MVDC)insulation systems,referring mainly to cables for both theoretical development and validation testing.Cable system energisation can be frequent during its lifetime,and it can possibly be affected by partial discharges(PD),because of manufacturing,laying,ageing,interfaces or structural cavities(as butt gaps).A theory-driven and measurement-based procedure is presented in this paper,having the purpose to minimise PD inception risk.This procedure is based on stepwise voltage application during cable energisation.The fundamental idea behind the proposed approach stems from considering that the jump voltage is the trigger of PD occurrence.Indeed,the jump voltage,and the consequent electric field variation,directly relates to AC PD inception voltage(PDIVAC).In addition,the electric field distribution in an insulation system is driven by insulation permittivity(capacitance)during voltage transients,and by conductivity in DC,thus the PDIVAC is generally smaller than DC PD inception voltage(PDIVDC).Hence,energising a DC cable by an initial step lower than PDIVAC,and then increasing the voltage in steps smaller than PDIVAC,would minimise the risk of PD inception during transients and the relevant degradation rate.However,this does not change,the risk of occurrence(if any)of low-repetition partial discharges at DC steady state.Effectiveness of the proposed technique is proved by the help of tests performed on cables with artificial surface and internal defects.It is shown that compared with the conventional energisation consisting of rapidly increasing voltage,the stepwise approach can reduce the risk of PD inception and related extrinsic ageing,even for the steady state voltages larger than PDIVDC.
基金supported by China Southern Power Grid Company Limited(Grant GDKJXM20222136).
文摘This paper investigates elastomer-toughened polypropylene(PP)insulation to meet the application requirements for green noncrosslinked PP cables in high-voltage direct current(HVDC)transmission.It focuses on the formation ofβ-crystals in isotactic polypropylene(iPP)by adding aβ-nucleator.It examines how varying concentrations ofβ-nucleator and elastomer(POE)impact the aggregation structure of PP insulation and its conductivity and breakdown characteristics in the DC field.The results indicated that at aβ-nucleator agent content of 0.1 wt%,the samples with various POE contents achieved the highest crystallinity,the maximum proportion ofβ-crystals and the most uniform elastomer distribution.The nucleating agent facilitates the formation ofβ-crystals in PP and enhances the order degree of the elastomer molecular chains,thereby improving their crystallization capabilities.Evaluations of DC performances and trap characteristics reveal that when the amount of theβ-nucleator is set at 0.1 wt%,the sample demonstrates the lowest trap density,an exceptional and lower electric field coefficient of conductivity at elevated electric fields and a superior DC field breakdown strength at 90°C.Compared to samples withoutβ-nucleator,the reduction of DC field breakdown strength for PPBx-0.1 from 25°C to 90°C is approximately 4.86%lower.This improvement is attributed to the ability of theβ-nucleator to improve the aggregation structure between PP and POE while optimising the stability of the two-phase interface.Thus,although DC electrical characteristics are maintained at normal temperatures,the DC characteristics are significantly improved at elevated temperatures.
基金supported by Project of Science and Technology of State Grid Corporation of China(Grant 5500-202458116A-1-1-ZN).
文摘Cross-linking byproducts in the cross-linked polyethylene(XLPE)cable insulation material significantly affect the insulation properties of XLPE,and the non-destructive detection method for cross-linking byproducts during cable degassing process still faces great challenges.This work develops an extra-low frequency(ELF)dielectric analysis method based on time-dependent polarisation current for non-destructive detection of byproducts in XLPE.The effects of single byproduct of acetophenone and cumyl alcohol on the ELF dielectric properties of XLPE are studied separately.The ELF associated static permittivity and the dielectric loss of XLPE rise as the content of the single byproduct increases,and theαrelaxation(10−4-10−3 Hz)andβrelaxation(10−3-10−2 Hz)of XLPE are observed.Ionisation of acetophenone occurs above electric field strength of 20 kV,whereas ionisation tends to saturate above 50 kV.The optimal field strength for ELF dielectric testing of XLPE is determined to be 20-50 kV.Furthermore,the degassing factor is proposed to accurately determine the removal of byproducts.Based on these,the non-destructive detection of degassing of XLPE cable is achieved.The proposed ELF dielectric analysis method enables the non-destructive detection of byproducts in cables,opening a new avenue for cable degassing effect evaluation.
基金supported by National Natural Science Foundation of China(Grants 52477151 and 52522702).
文摘This study proposes a nondestructive optical imaging-based three-dimensional(3D)reconstruction method to analyse electrical tree propagation in polypropylene(PP)cable insulation under mechanical bending.The technique combines focus-stacked optical imaging with a feature fusion algorithm to segment in-focus regions across depth layers,enabling 3D reconstruction of electrical trees in PP homopolymer(PPH),block copolymer(PPB)and elastomer-blended(PP/TPE)samples.The results demonstrate that mechanical bending accelerates electrical tree propagation in PPH,and that degradation channels transition from a branch-like to a straight-stick morphology,tending to grow directionally towards stretched regions.With a bending radius of 10 mm,the breakdown time drops from 297.0 min for the undeformed samples to 6.3 min.PPB and PP/TPE delay the time to breakdown by 70.6%and 171.2%,respectively,highlighting their superior resistance under bending stress,which is attributed to maintaining elasticity rather than yield deformation under bending stresses.This study provides a novel tool for evaluating the electrical tree resistance of PP composites under the mechanical stress,guiding the development of recyclable high-voltage direct current cable insulation.
