Synchrophasors are time-synchronized electrical measurements that represent both the magnitude and phase angle of the electrical sinusoids. Synchrophasors are measured by fast time-stamped devices called phasor measur...Synchrophasors are time-synchronized electrical measurements that represent both the magnitude and phase angle of the electrical sinusoids. Synchrophasors are measured by fast time-stamped devices called phasor measurement units(PMUs) to constitute the basis of realtime monitoring and control actions in the electric grid.Due to its enhanced situational awareness capabilities,many applications of PMUs are presented in the literature in the past decades. This paper presents a comprehensive summary of synchrophasor technology, its architecture,optimal placement techniques and its applications in electric power transmission and distribution systems. These applications include wide-area situational awareness and monitoring, state estimation, fault location and protective relaying, islanding detection etc. This review also covers some of the existing challenges in its implementation and its potential applications.展开更多
Modular multilevel converters(MMCs)have been one of the most broadly used multilevel converter topologies in industrial applications,particularly in medium-voltage motor drives and high-voltage dc power conversion sys...Modular multilevel converters(MMCs)have been one of the most broadly used multilevel converter topologies in industrial applications,particularly in medium-voltage motor drives and high-voltage dc power conversion systems.However,due to the utilization of large amount of semiconductor devices,the reliability of MMCs becomes one of the severe challenges constraining their further development and applications.In this paper,common electrical faults of the MMC have been summarized and analyzed,including open-circuit switching faults,short-circuit switching faults,dc-bus short-circuit faults,and single line-to-ground faults on the ac side.A thorough and comprehensive review of the existing online fault diagnostic methods has been conducted.In addition,fault-tolerant operation strategies for such various fault scenarios in MMCs have been presented.All the fault diagnosis and fault-tolerant operation strategies are comparatively evaluated,which aims to provide a state-of-the-art reference on the MMC reliability for future research and industrial applications.展开更多
The design of high voltage and medium voltage AC and DC standoff insulators,and,in general,of insulation systems where surface and interface properties are predominant factors,is based on specifications and standards ...The design of high voltage and medium voltage AC and DC standoff insulators,and,in general,of insulation systems where surface and interface properties are predominant factors,is based on specifications and standards that rely upon long-term experiences and lab testing.Surface insulating properties depend on electrical and thermal stresses,besides environmental factors,and the inception of extrinsic ageing phenomena,such as partial discharges,can be already a cause of reduced reliability and premature failure(for organic insulating materials).An innovative approach,based on field simulation,discharge modelling,and partial discharge inception measurements is presented by the authors,which can establish a solid basis to optimise insulation design for any type of supply voltage waveform.This method,the three-leg approach,is applied here to a cable system under AC sinusoidal voltage,but it can work for any type of insulation system,such as bushings,switch gears,transformers,rotating machines,and power electronics boards.展开更多
Aspects of terrestrial microgrids and ship power systems are examined.The work exposes a variety of technical synergies from these two power systems to effectively advance their technologies.Understanding their overla...Aspects of terrestrial microgrids and ship power systems are examined.The work exposes a variety of technical synergies from these two power systems to effectively advance their technologies.Understanding their overlap allows congruent efforts to target both systems;understanding their differences hinders conflict and redundancy in early-stage design.The paper concludes by highlighting how an understanding of both systems can reduce the investment in research resources.展开更多
Careful analysis of transients in shipboard power systems is important to achieve long life times of the components in future all-electric ships.In order to accomplish results with high accuracy,it is recommended to v...Careful analysis of transients in shipboard power systems is important to achieve long life times of the components in future all-electric ships.In order to accomplish results with high accuracy,it is recommended to validate cable models as they have significant influence on the amplitude and frequency spectrum of voltage transients.The authors propose comparison of model and measurement using scattering parameters.They can be easily obtained from measurement and simulation and deliver broadband information about the accuracy of the model.The measurement can be performed using a vector network analyzer.The process to extract scattering parameters from simulation models is explained in detail.Three different simulation models of a 5 kV XLPE power cable have been validated.The chosen approach delivers an efficient tool to quickly estimate the quality of a model.展开更多
Despite having very high solar irradiance,Pakistan still does not have any installed concentrated solar power(CSP)plant.Several studies have shown that multiple locations within the country are suitable for CSP plants...Despite having very high solar irradiance,Pakistan still does not have any installed concentrated solar power(CSP)plant.Several studies have shown that multiple locations within the country are suitable for CSP plants,but there is limited availability of comprehensive comparative studies.Therefore,this article presents a comparative analysis of different CSP technologies in Pakistan,focusing on their potential to address the country’s energy crisis.The study evaluates the pros and cons of different CSP technologies at various locations through site assessment,modelling,optimization and economic analysis using the System Advisor Model.Quetta and Nawabshah were selected as the locations for modelling multiple scenarios of 100-MW plants,using central receiver systems,parabolic trough collectors and linear Fresnel reflectors.The plants were integrated with thermal energy storage and the storage capacity was optimized using parametric analysis.The results showed that a central receiver system for the location of Quetta was the most favourable option,with an annual energy yield of 622 GWh at 7.44 cents/kWh,followed by a central receiver system for Nawabshah(608 GWh,9.03 cents/kWh).This study is the first to show that switching between line-concentrated and point-concentrated CSP technologies can open new opportunities for sites in Pakistan with relatively high solar resources,resulting in a 21.3%reduction in the levelized cost.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
Measuring partial discharges in DC insulation systems is an issue due to the lack of a reference relating the voltage waveform to the physics of discharge phenomena.Also,DC is not always steady state,due to voltage an...Measuring partial discharges in DC insulation systems is an issue due to the lack of a reference relating the voltage waveform to the physics of discharge phenomena.Also,DC is not always steady state,due to voltage and load transients that generate electric field profile variations inside an insulation system,which can affect partial discharge inception likelihood and characteristics.Partial discharge measurement technology must be able to separate discharge pulses from noise and identify the type of sources generating partial discharge,which is related to condition assessment and maintenance.Eventually,measurement and analysis should be automatic and unsupervised,in order to get rid,partially or totally,of expert support.This study addresses a new approach to partial discharge measurements in DC insulation systems,presenting algorithms for separation,recognition and identification,which are effective both in DC steady state and during voltage(and load)transients.These algorithms are automatic and do not require expert support.Various cases of algorithm application on test objects consisting of multilayer polymeric specimens with an internal cavity and defective cable models are presented and discussed.Their effectiveness is proved,at least at a laboratory level,with effective noise separation and identification of discharge typology.展开更多
Silicone rubber composite is a priority electrical insulating material used in high-voltage outdoor insulation applications.Low electrical tracking/erosion and poor flame resistance performance of silicone rubber once...Silicone rubber composite is a priority electrical insulating material used in high-voltage outdoor insulation applications.Low electrical tracking/erosion and poor flame resistance performance of silicone rubber once ignited,substantially reduce its working life.This paper attempts to investigate tracking/erosion performance of room temperature vulcanized(RTV)silicone rubber along with flame retardant parameters using aluminum trihydrate(ATH),graphene nanosheets(GN)and milled glass fiber(GF)additives.The inclined plane test(IPT)was performed in line with criteria defined in IEC 60587 using step-up tracking voltage method while flame retardancy is evaluated according to ASTM E 1354.0 using a cone calorimeter.Results suggest 30% of ATH assists in improving physical tracking/erosion resistance of pristine silicone elastomer rubber by impeding development of leakage current and a great reduction in maximum average temperatures on the surface of RTV2.Further improvement in performance of RTV2 is achieved through introduction of 1%of GN and 5% of GF as seen in RTV4.Moreover,30% of ATH reduces heat release rate and smoke production rate,and this trend is improved with the introduction of GN/GF.RTV4 has pop up as the most promising silicone rubber composite with excellent electrical tracking,erosion,and flame resistance performance relative to its counterparts in this study.展开更多
This paper analyses the impact of square wave pulse voltage deadtime on the partial discharge(PD)and the lifetime of turn-to-turn insulation.A bipolar repetitive pulse voltage with a deadtime of 0–10μs is produced u...This paper analyses the impact of square wave pulse voltage deadtime on the partial discharge(PD)and the lifetime of turn-to-turn insulation.A bipolar repetitive pulse voltage with a deadtime of 0–10μs is produced using double half-bridge solid-state switches having push–pull technology controlled by a field-programmable gate array.The mechanism of the discharge process at rising and falling edges of the pulse voltage before and after deadtime is analysed in detail.The discharge amplitude and PD probability at the rising/falling edges of the voltage waveform increase as the deadtime increases from 0 to 10μs due to the remanent charges.The number of PD and their intensity is higher at the first rising/falling edges of pulse voltage as compared to the second rising/falling edges for all deadtimes 0–10μs.As the deadtime increases beyond 2μs,the number of PDs increases and concentrates at a specific phase angle of rising/falling edges.These localise discharges degrade the insulation material and reduce its lifetime.This study helps to identify the inverter-fed motor insulation faults due to deadtime.It can provide guidelines to motor insulation designers to determine the limit value of deadtime to compensate PD and ensure the safer operation of such motors.展开更多
Diagnosing insulation intrinsic ageing is essential for preventing insulation failure of submarine cables,and in case of failure,helping in any decision about maintenance actions.In this study,a novel aged cable diagn...Diagnosing insulation intrinsic ageing is essential for preventing insulation failure of submarine cables,and in case of failure,helping in any decision about maintenance actions.In this study,a novel aged cable diagnosis approach based on high-voltage frequency domain spectroscopy(HV-FDS)with broader frequency width is proposed to analyse the high-field polarisation characteristics and conductivity behaviour of 500 kV submarine polymeric cables insulation,aiming to support the evaluation of overall insulation ageing.The measurement principle of HV-FDS and relaxation mechanism are stated,and then focus is on studying the extent of change of polarisation and conduction properties of submarine cables insulation as a function of ageing stress and time.Moreover,the high-field polarisation characteristics and conductivity behaviour are discussed in-depth based on the carrier transport and trap properties.Finally,the novel diagnostic indicator based on the high-field characteristics is extracted to quantify the thermal ageing state of submarine cables insulation.Results show that the high-field polarisation characteristics and conductivity behaviour seem to become sensitive diagnostic quantities if measured at reasonably high voltage,which are able to reveal mechanisms associated with thermo-oxidative ageing as that generated in the testing procedure considered in this paper.Sensitivity is considerably higher than that experienced in typical dielectric spectroscopy approaches.展开更多
With the increasing penetration of DC systems into the high voltage and medium voltage power industry,DC voltage is becoming common for distribution/transmission and to supply different typologies of loads.The allowab...With the increasing penetration of DC systems into the high voltage and medium voltage power industry,DC voltage is becoming common for distribution/transmission and to supply different typologies of loads.The allowable extent of AC ripple superimposed to DC,and its effect on insulation ageing,is a long-term discussed topic.The most harmful phenomenon causing extrinsic ageing acceleration and insulation system premature failure is partial discharges(PD);thus,the risk of incepting PD due to AC ripple could become a primary issue for electrical asset equipment reliability.In this work,the impact of AC sinusoidal ripple on insulation system life and reliability is dealt with,considering both intrinsic and extrinsic ageing but focusing on the latter,that is,the PD aspect.Experiments are performed to assess how the jump voltage(due to AC ripple)and the DC component impact on PD activity in terms of amplitude and repetition rate.For the first time,the correlation between the magnitude of jump voltage associated with ripple and PD inception is established,shedding a light on the allowable ripple extent which does not impact significantly on ageing and premature insulation failure.This approach can provide straightforward tools for design specification and ageing inference of insulation systems.展开更多
Quality control,commissioning and diagnostic tests on insulation systems of electrical apparatus are necessary to reduce the failure risk under operation,eliminate infant mortality failures and reduce the impact of ag...Quality control,commissioning and diagnostic tests on insulation systems of electrical apparatus are necessary to reduce the failure risk under operation,eliminate infant mortality failures and reduce the impact of ageing on insulation system reliability.This study tries to establish a path which,based on the statistical-phenomenological modelling of the hazard rate,or bathtub curve,drives in the choice of test overvoltage and procedures.The choice of the test voltage and its waveform should be made carefully to improve reliability(reduce failure hazard)in any section of the bathtub curve.This may require,however,different choices depending on the section which corresponds to the planned test.For example,large overvoltages could be acceptable to remove the infant mortality to ensure the highest reliability of newly commissioned apparatus,but they can incept highly energetic,and,thus,fast degradation mechanisms on apparatus operating on the field for a period of time,that can worsen,rather than improving,the insulation system reliability.Resorting to partial discharge measurement during any overvoltage test seems to be the optimal solution to find the most appropriate overvoltage for any type of testing need,leveraging the Latin concept that‘in medio stat virtus’.展开更多
Polymer dielectrics are widely used in electrical and electronic apparatus and devices because of their capability to insulate conductors,withstand high fields and suffer negligible conductive losses.Their near-to-zer...Polymer dielectrics are widely used in electrical and electronic apparatus and devices because of their capability to insulate conductors,withstand high fields and suffer negligible conductive losses.Their near-to-zero conductivity has been explained in terms of long-accepted theories of electronic and ionic transport that lead to the accumulation of local net charge regions at high electric fields.Here the authors describe a previously unknown conduction mechanism consisting of small bipolar ultra-fast charge pulses crossing the polymer with the mobility,as large as,4 to 5 orders of magnitude greater than that of the previously known.The authors show that this motion is a consequence of molecular relaxation processes triggered by the electric field locally enhanced by the pulses themselves.Pulse accumulation at the electrodes increases interface field and thus contributes substantially towards premature failure in insulating dielectrics in DC fields.展开更多
文摘Synchrophasors are time-synchronized electrical measurements that represent both the magnitude and phase angle of the electrical sinusoids. Synchrophasors are measured by fast time-stamped devices called phasor measurement units(PMUs) to constitute the basis of realtime monitoring and control actions in the electric grid.Due to its enhanced situational awareness capabilities,many applications of PMUs are presented in the literature in the past decades. This paper presents a comprehensive summary of synchrophasor technology, its architecture,optimal placement techniques and its applications in electric power transmission and distribution systems. These applications include wide-area situational awareness and monitoring, state estimation, fault location and protective relaying, islanding detection etc. This review also covers some of the existing challenges in its implementation and its potential applications.
文摘Modular multilevel converters(MMCs)have been one of the most broadly used multilevel converter topologies in industrial applications,particularly in medium-voltage motor drives and high-voltage dc power conversion systems.However,due to the utilization of large amount of semiconductor devices,the reliability of MMCs becomes one of the severe challenges constraining their further development and applications.In this paper,common electrical faults of the MMC have been summarized and analyzed,including open-circuit switching faults,short-circuit switching faults,dc-bus short-circuit faults,and single line-to-ground faults on the ac side.A thorough and comprehensive review of the existing online fault diagnostic methods has been conducted.In addition,fault-tolerant operation strategies for such various fault scenarios in MMCs have been presented.All the fault diagnosis and fault-tolerant operation strategies are comparatively evaluated,which aims to provide a state-of-the-art reference on the MMC reliability for future research and industrial applications.
基金U.S.Department of Energy,Grant/Award Numbers:DE-AC36-08GO28308,ZGJ-9-92284。
文摘The design of high voltage and medium voltage AC and DC standoff insulators,and,in general,of insulation systems where surface and interface properties are predominant factors,is based on specifications and standards that rely upon long-term experiences and lab testing.Surface insulating properties depend on electrical and thermal stresses,besides environmental factors,and the inception of extrinsic ageing phenomena,such as partial discharges,can be already a cause of reduced reliability and premature failure(for organic insulating materials).An innovative approach,based on field simulation,discharge modelling,and partial discharge inception measurements is presented by the authors,which can establish a solid basis to optimise insulation design for any type of supply voltage waveform.This method,the three-leg approach,is applied here to a cable system under AC sinusoidal voltage,but it can work for any type of insulation system,such as bushings,switch gears,transformers,rotating machines,and power electronics boards.
基金supported by a Grant from the Office of Naval Research(ONR)
文摘Aspects of terrestrial microgrids and ship power systems are examined.The work exposes a variety of technical synergies from these two power systems to effectively advance their technologies.Understanding their overlap allows congruent efforts to target both systems;understanding their differences hinders conflict and redundancy in early-stage design.The paper concludes by highlighting how an understanding of both systems can reduce the investment in research resources.
基金Supported by the US Office of Naval Research Under Grant(N00014-04-1-0664)NSF Cooperative Agreement and the State of Florida(DMR-0084173)
文摘Careful analysis of transients in shipboard power systems is important to achieve long life times of the components in future all-electric ships.In order to accomplish results with high accuracy,it is recommended to validate cable models as they have significant influence on the amplitude and frequency spectrum of voltage transients.The authors propose comparison of model and measurement using scattering parameters.They can be easily obtained from measurement and simulation and deliver broadband information about the accuracy of the model.The measurement can be performed using a vector network analyzer.The process to extract scattering parameters from simulation models is explained in detail.Three different simulation models of a 5 kV XLPE power cable have been validated.The chosen approach delivers an efficient tool to quickly estimate the quality of a model.
文摘Despite having very high solar irradiance,Pakistan still does not have any installed concentrated solar power(CSP)plant.Several studies have shown that multiple locations within the country are suitable for CSP plants,but there is limited availability of comprehensive comparative studies.Therefore,this article presents a comparative analysis of different CSP technologies in Pakistan,focusing on their potential to address the country’s energy crisis.The study evaluates the pros and cons of different CSP technologies at various locations through site assessment,modelling,optimization and economic analysis using the System Advisor Model.Quetta and Nawabshah were selected as the locations for modelling multiple scenarios of 100-MW plants,using central receiver systems,parabolic trough collectors and linear Fresnel reflectors.The plants were integrated with thermal energy storage and the storage capacity was optimized using parametric analysis.The results showed that a central receiver system for the location of Quetta was the most favourable option,with an annual energy yield of 622 GWh at 7.44 cents/kWh,followed by a central receiver system for Nawabshah(608 GWh,9.03 cents/kWh).This study is the first to show that switching between line-concentrated and point-concentrated CSP technologies can open new opportunities for sites in Pakistan with relatively high solar resources,resulting in a 21.3%reduction in the levelized cost.
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.
文摘Measuring partial discharges in DC insulation systems is an issue due to the lack of a reference relating the voltage waveform to the physics of discharge phenomena.Also,DC is not always steady state,due to voltage and load transients that generate electric field profile variations inside an insulation system,which can affect partial discharge inception likelihood and characteristics.Partial discharge measurement technology must be able to separate discharge pulses from noise and identify the type of sources generating partial discharge,which is related to condition assessment and maintenance.Eventually,measurement and analysis should be automatic and unsupervised,in order to get rid,partially or totally,of expert support.This study addresses a new approach to partial discharge measurements in DC insulation systems,presenting algorithms for separation,recognition and identification,which are effective both in DC steady state and during voltage(and load)transients.These algorithms are automatic and do not require expert support.Various cases of algorithm application on test objects consisting of multilayer polymeric specimens with an internal cavity and defective cable models are presented and discussed.Their effectiveness is proved,at least at a laboratory level,with effective noise separation and identification of discharge typology.
基金financially through the Fulbright Postdoctoral-Vice Chancellor’s Postdoctoral Research Fellowship.
文摘Silicone rubber composite is a priority electrical insulating material used in high-voltage outdoor insulation applications.Low electrical tracking/erosion and poor flame resistance performance of silicone rubber once ignited,substantially reduce its working life.This paper attempts to investigate tracking/erosion performance of room temperature vulcanized(RTV)silicone rubber along with flame retardant parameters using aluminum trihydrate(ATH),graphene nanosheets(GN)and milled glass fiber(GF)additives.The inclined plane test(IPT)was performed in line with criteria defined in IEC 60587 using step-up tracking voltage method while flame retardancy is evaluated according to ASTM E 1354.0 using a cone calorimeter.Results suggest 30% of ATH assists in improving physical tracking/erosion resistance of pristine silicone elastomer rubber by impeding development of leakage current and a great reduction in maximum average temperatures on the surface of RTV2.Further improvement in performance of RTV2 is achieved through introduction of 1%of GN and 5% of GF as seen in RTV4.Moreover,30% of ATH reduces heat release rate and smoke production rate,and this trend is improved with the introduction of GN/GF.RTV4 has pop up as the most promising silicone rubber composite with excellent electrical tracking,erosion,and flame resistance performance relative to its counterparts in this study.
基金National Natural Science Foundation of China,Grant/Award Number:51977134。
文摘This paper analyses the impact of square wave pulse voltage deadtime on the partial discharge(PD)and the lifetime of turn-to-turn insulation.A bipolar repetitive pulse voltage with a deadtime of 0–10μs is produced using double half-bridge solid-state switches having push–pull technology controlled by a field-programmable gate array.The mechanism of the discharge process at rising and falling edges of the pulse voltage before and after deadtime is analysed in detail.The discharge amplitude and PD probability at the rising/falling edges of the voltage waveform increase as the deadtime increases from 0 to 10μs due to the remanent charges.The number of PD and their intensity is higher at the first rising/falling edges of pulse voltage as compared to the second rising/falling edges for all deadtimes 0–10μs.As the deadtime increases beyond 2μs,the number of PDs increases and concentrates at a specific phase angle of rising/falling edges.These localise discharges degrade the insulation material and reduce its lifetime.This study helps to identify the inverter-fed motor insulation faults due to deadtime.It can provide guidelines to motor insulation designers to determine the limit value of deadtime to compensate PD and ensure the safer operation of such motors.
基金Project of Chongqing Human Resources and Social Security Bureau,Grant/Award Number:2020LY19Innovative Research Groups of the National Natural Science Foundation of China,Grant/Award Number:51321063111 Project,Grant/Award Number:BP0020005。
文摘Diagnosing insulation intrinsic ageing is essential for preventing insulation failure of submarine cables,and in case of failure,helping in any decision about maintenance actions.In this study,a novel aged cable diagnosis approach based on high-voltage frequency domain spectroscopy(HV-FDS)with broader frequency width is proposed to analyse the high-field polarisation characteristics and conductivity behaviour of 500 kV submarine polymeric cables insulation,aiming to support the evaluation of overall insulation ageing.The measurement principle of HV-FDS and relaxation mechanism are stated,and then focus is on studying the extent of change of polarisation and conduction properties of submarine cables insulation as a function of ageing stress and time.Moreover,the high-field polarisation characteristics and conductivity behaviour are discussed in-depth based on the carrier transport and trap properties.Finally,the novel diagnostic indicator based on the high-field characteristics is extracted to quantify the thermal ageing state of submarine cables insulation.Results show that the high-field polarisation characteristics and conductivity behaviour seem to become sensitive diagnostic quantities if measured at reasonably high voltage,which are able to reveal mechanisms associated with thermo-oxidative ageing as that generated in the testing procedure considered in this paper.Sensitivity is considerably higher than that experienced in typical dielectric spectroscopy approaches.
基金Office of Naval Research,Grant/Award Number:N00014-21-1-2124。
文摘With the increasing penetration of DC systems into the high voltage and medium voltage power industry,DC voltage is becoming common for distribution/transmission and to supply different typologies of loads.The allowable extent of AC ripple superimposed to DC,and its effect on insulation ageing,is a long-term discussed topic.The most harmful phenomenon causing extrinsic ageing acceleration and insulation system premature failure is partial discharges(PD);thus,the risk of incepting PD due to AC ripple could become a primary issue for electrical asset equipment reliability.In this work,the impact of AC sinusoidal ripple on insulation system life and reliability is dealt with,considering both intrinsic and extrinsic ageing but focusing on the latter,that is,the PD aspect.Experiments are performed to assess how the jump voltage(due to AC ripple)and the DC component impact on PD activity in terms of amplitude and repetition rate.For the first time,the correlation between the magnitude of jump voltage associated with ripple and PD inception is established,shedding a light on the allowable ripple extent which does not impact significantly on ageing and premature insulation failure.This approach can provide straightforward tools for design specification and ageing inference of insulation systems.
文摘Quality control,commissioning and diagnostic tests on insulation systems of electrical apparatus are necessary to reduce the failure risk under operation,eliminate infant mortality failures and reduce the impact of ageing on insulation system reliability.This study tries to establish a path which,based on the statistical-phenomenological modelling of the hazard rate,or bathtub curve,drives in the choice of test overvoltage and procedures.The choice of the test voltage and its waveform should be made carefully to improve reliability(reduce failure hazard)in any section of the bathtub curve.This may require,however,different choices depending on the section which corresponds to the planned test.For example,large overvoltages could be acceptable to remove the infant mortality to ensure the highest reliability of newly commissioned apparatus,but they can incept highly energetic,and,thus,fast degradation mechanisms on apparatus operating on the field for a period of time,that can worsen,rather than improving,the insulation system reliability.Resorting to partial discharge measurement during any overvoltage test seems to be the optimal solution to find the most appropriate overvoltage for any type of testing need,leveraging the Latin concept that‘in medio stat virtus’.
文摘Polymer dielectrics are widely used in electrical and electronic apparatus and devices because of their capability to insulate conductors,withstand high fields and suffer negligible conductive losses.Their near-to-zero conductivity has been explained in terms of long-accepted theories of electronic and ionic transport that lead to the accumulation of local net charge regions at high electric fields.Here the authors describe a previously unknown conduction mechanism consisting of small bipolar ultra-fast charge pulses crossing the polymer with the mobility,as large as,4 to 5 orders of magnitude greater than that of the previously known.The authors show that this motion is a consequence of molecular relaxation processes triggered by the electric field locally enhanced by the pulses themselves.Pulse accumulation at the electrodes increases interface field and thus contributes substantially towards premature failure in insulating dielectrics in DC fields.
