<div style="text-align:justify;"> Generalized S-transform is a time-frequency analysis method which has higher resolution than S-transform. It can precisely extract the time-amplitude characteristics o...<div style="text-align:justify;"> Generalized S-transform is a time-frequency analysis method which has higher resolution than S-transform. It can precisely extract the time-amplitude characteristics of different frequency components in the signal. In this paper, a novel protection method for VSC-HVDC (Voltage source converter based high voltage DC) based on Generalized S-transform is proposed. Firstly, extracting frequency component of fault current by Generalized S-transform and using mutation point of high frequency to determine the fault time. Secondly, using the zero-frequency component of fault current to eliminate disturbances. Finally, the polarity of sudden change currents in the two terminals is employed to discriminate the internal and external faults. Simulations in PSCAD/EMTDC and MATLAB show that the proposed method can distinguish faults accurately and effectively. </div>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
In high-voltage direct current cable systems,the factory joint of cross-linked polyethylene(XLPE)-insulated cables presents significant electrical breakdown risk.The charge accumulation mechanism at the XLPE-XLPE inte...In high-voltage direct current cable systems,the factory joint of cross-linked polyethylene(XLPE)-insulated cables presents significant electrical breakdown risk.The charge accumulation mechanism at the XLPE-XLPE interface involves the accumulation of opposite charges on both sides of the interface,thereby complicating the comprehension of the interfacial charging phenomenon.This study investigates the fundamental mechanisms of charge accumulation and the associated homo-junction effect in homo-bilayer XLPE(H-XLPE).Space charge analysis,model calculations based on Maxwell's equations,and thermal stimulation depolarisation current(TSDC)measurements were performed.Space charge results show that the homo-junctioninduced charge accumulation causes greater electric field distortion,leading to lower breakdown strength of H-XLPE compared to single-layer XLPE.Model calculations indicate that the density of opposite charges on the interface is attributed to the local gradient of reciprocal conductivity in the H-XLPE interface region.TSDC measurements on XLPE and H-XLPE enabled extraction of trap parameters and analysis of the charge transport process.The findings provide experimental evidence and theoretical clue for elucidating the role of the interface area on the charge accumulation that affects reliability and stability of submarine cable systems.展开更多
This paper reviews the existing testing techniques for high voltage direct current(HVDC)cable systems,following as a backbone the structure of CIGRE Technical Brochure(TB)852:2021‘Recommendations for testing DC extru...This paper reviews the existing testing techniques for high voltage direct current(HVDC)cable systems,following as a backbone the structure of CIGRE Technical Brochure(TB)852:2021‘Recommendations for testing DC extruded cable systems for power transmission at a rated voltage up to 800 kV’because it has a fairly similar structure to CIGRE TB 853:2021 for lapped DC cables,and especially because of the impressive spread of HVDC extruded cables experienced worldwide in the last 25 years.The review considers development tests,pre-qualification tests,extension of qualification test,type tests(with hints at IEEE 1732-2017 for space charge measurements in the qualification of HVDC extruded cables),routine tests(with hints at IEEE 2862-2020 for routine tests of HVDC extruded cable system joints),sample tests and after installation tests.The review also analyses CIGRE TB 853 for lapped HVDC cable systems,as these cables remain unbeaten for submarine applications at the highest sea depths.The main novelties of CIGRE TB 852 and 853 with respect to previous standards for HVDC cable systems(mainly CIGRE TB 496 and IEC 62895 for extruded cables and CIGRE Electra 189:2000 for lapped cables)are put under the spotlight-with focus on the so-called temporary over-voltage tests-together with the limits and gaps of CIGRE TB 852.The main HVDC cable system testing equipment that is usually employed for electro-thermal tests is also treated.Emphasis is given to CIGRE TB 490 to treat the peculiarities of submarine cable systems,as well as to mechanical tests,having CIGRE TB 623 as a reference,with particular focus on the special sea trial tests.An example of an innovative sea trial testing procedure is shown,which is the outcome of a fruitful partnership between a cable manufacturer and the national Transmission System Operator in Italy.展开更多
Increased renewable energy integration and international power trades have led to the construction and development of new HVDC transmission systems.HVDC cables,in particular,play an important role in undersea power tr...Increased renewable energy integration and international power trades have led to the construction and development of new HVDC transmission systems.HVDC cables,in particular,play an important role in undersea power transmission and offshore renewable energy integration having lower losses and higher reliability.In this paper,the current commercial feasibility of HVDC cables and the development of different types of HVDC cables and accessories are reviewed.The non-uniform electric field distribution caused by the applied voltage,temperature dependent conductivity,and space charge accumulation is briefly discussed.Current research in HVDC cable for higher operation voltage level and larger power capacity is also reviewed with specific focus on the methodologies of space charge suppression for XLPE extruded cables.展开更多
Purpose For improving a beam quality of the linear accelerator and decreasing the influence of failure recovery on the accelerator available time,a high-voltage pulse modulator system is required to enhance the stabil...Purpose For improving a beam quality of the linear accelerator and decreasing the influence of failure recovery on the accelerator available time,a high-voltage pulse modulator system is required to enhance the stability of high-voltage pulses and maintain a low failure rate as well as a low failure recovery time,in order to implement a high-performance and stable operation.Methods This paper systematically analyzes the current status and operating conditions of the modulator equipment of BEPCII linear accelerator and simulates the typical parameters of the modulator considering the high-voltage DC charging power supply,DC charging cables and components and pulsed hydrogen thyratron.The technical route and retrofit scheme are proposed to decrease the failure rate and its recovery time.Results The stability of the high-voltage pulse modulator has increased by 1000 ppm,the failure rate has been decreased by two orders of magnitude,and the averaged recovery time from failures has been reduced by 94%as compared to the last operation period via implementing technical transformation with repeated exploration and experimental verification.展开更多
文摘<div style="text-align:justify;"> Generalized S-transform is a time-frequency analysis method which has higher resolution than S-transform. It can precisely extract the time-amplitude characteristics of different frequency components in the signal. In this paper, a novel protection method for VSC-HVDC (Voltage source converter based high voltage DC) based on Generalized S-transform is proposed. Firstly, extracting frequency component of fault current by Generalized S-transform and using mutation point of high frequency to determine the fault time. Secondly, using the zero-frequency component of fault current to eliminate disturbances. Finally, the polarity of sudden change currents in the two terminals is employed to discriminate the internal and external faults. Simulations in PSCAD/EMTDC and MATLAB show that the proposed method can distinguish faults accurately and effectively. </div>
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 Program of Beijing Huairou Laboratory(Grant ZD2022003A).
文摘In high-voltage direct current cable systems,the factory joint of cross-linked polyethylene(XLPE)-insulated cables presents significant electrical breakdown risk.The charge accumulation mechanism at the XLPE-XLPE interface involves the accumulation of opposite charges on both sides of the interface,thereby complicating the comprehension of the interfacial charging phenomenon.This study investigates the fundamental mechanisms of charge accumulation and the associated homo-junction effect in homo-bilayer XLPE(H-XLPE).Space charge analysis,model calculations based on Maxwell's equations,and thermal stimulation depolarisation current(TSDC)measurements were performed.Space charge results show that the homo-junctioninduced charge accumulation causes greater electric field distortion,leading to lower breakdown strength of H-XLPE compared to single-layer XLPE.Model calculations indicate that the density of opposite charges on the interface is attributed to the local gradient of reciprocal conductivity in the H-XLPE interface region.TSDC measurements on XLPE and H-XLPE enabled extraction of trap parameters and analysis of the charge transport process.The findings provide experimental evidence and theoretical clue for elucidating the role of the interface area on the charge accumulation that affects reliability and stability of submarine cable systems.
文摘This paper reviews the existing testing techniques for high voltage direct current(HVDC)cable systems,following as a backbone the structure of CIGRE Technical Brochure(TB)852:2021‘Recommendations for testing DC extruded cable systems for power transmission at a rated voltage up to 800 kV’because it has a fairly similar structure to CIGRE TB 853:2021 for lapped DC cables,and especially because of the impressive spread of HVDC extruded cables experienced worldwide in the last 25 years.The review considers development tests,pre-qualification tests,extension of qualification test,type tests(with hints at IEEE 1732-2017 for space charge measurements in the qualification of HVDC extruded cables),routine tests(with hints at IEEE 2862-2020 for routine tests of HVDC extruded cable system joints),sample tests and after installation tests.The review also analyses CIGRE TB 853 for lapped HVDC cable systems,as these cables remain unbeaten for submarine applications at the highest sea depths.The main novelties of CIGRE TB 852 and 853 with respect to previous standards for HVDC cable systems(mainly CIGRE TB 496 and IEC 62895 for extruded cables and CIGRE Electra 189:2000 for lapped cables)are put under the spotlight-with focus on the so-called temporary over-voltage tests-together with the limits and gaps of CIGRE TB 852.The main HVDC cable system testing equipment that is usually employed for electro-thermal tests is also treated.Emphasis is given to CIGRE TB 490 to treat the peculiarities of submarine cable systems,as well as to mechanical tests,having CIGRE TB 623 as a reference,with particular focus on the special sea trial tests.An example of an innovative sea trial testing procedure is shown,which is the outcome of a fruitful partnership between a cable manufacturer and the national Transmission System Operator in Italy.
基金supported by the State Grid Corporation of China:Research on Key Technologies of Insulation Material and Accessories for 320 kV HVDC XLPE Cable System(SGRIZLJS(2014)888).
文摘Increased renewable energy integration and international power trades have led to the construction and development of new HVDC transmission systems.HVDC cables,in particular,play an important role in undersea power transmission and offshore renewable energy integration having lower losses and higher reliability.In this paper,the current commercial feasibility of HVDC cables and the development of different types of HVDC cables and accessories are reviewed.The non-uniform electric field distribution caused by the applied voltage,temperature dependent conductivity,and space charge accumulation is briefly discussed.Current research in HVDC cable for higher operation voltage level and larger power capacity is also reviewed with specific focus on the methodologies of space charge suppression for XLPE extruded cables.
文摘Purpose For improving a beam quality of the linear accelerator and decreasing the influence of failure recovery on the accelerator available time,a high-voltage pulse modulator system is required to enhance the stability of high-voltage pulses and maintain a low failure rate as well as a low failure recovery time,in order to implement a high-performance and stable operation.Methods This paper systematically analyzes the current status and operating conditions of the modulator equipment of BEPCII linear accelerator and simulates the typical parameters of the modulator considering the high-voltage DC charging power supply,DC charging cables and components and pulsed hydrogen thyratron.The technical route and retrofit scheme are proposed to decrease the failure rate and its recovery time.Results The stability of the high-voltage pulse modulator has increased by 1000 ppm,the failure rate has been decreased by two orders of magnitude,and the averaged recovery time from failures has been reduced by 94%as compared to the last operation period via implementing technical transformation with repeated exploration and experimental verification.
