Traditional mineral oil has long served as a liquid insulating medium in power transformers.However,its low fire resistance,poor biodegradability and dependence on finite fossil fuel resources,along with its low flash...Traditional mineral oil has long served as a liquid insulating medium in power transformers.However,its low fire resistance,poor biodegradability and dependence on finite fossil fuel resources,along with its low flash point,contribute to transformer explosions and fires.To overcome these limitations,developing insulating liquids with high flash points and self-extinguishing properties is essential.Although natural ester-based insulating oils and silicone oils have been proposed as alternatives,their performance requires further optimisation,and their application in transformers remains challenging.This study examines the combustion characteristics of three novel self-extinguishing fluorinated silicone oils using combustion experiments and reactive molecular dynamics simulations.The results demonstrate that methylfluorinated and hydrofluorinated silicone oils exhibit superior self-extinguishing performance compared to mineral oil and natural ester-based insulating oils.Simulation analyses indicate that fluorinated silicone oils generate silicon-oxygen polymers upon ignition,which influence subsequent chain reactions.However,hydroxyfluorinated silicone oil releases a higher concentration of key free radicals,intensifying chain reactions and diminishing its self-extinguishing capability.As a result,its self-extinguishing performance is significantly weaker than that of methylfluorinated and hydrofluorinated silicone oils.These findings provide valuable insights for the development of advanced liquid insulating media as potential replacements for mineral oil.展开更多
Among the rubber sealing materials for power equipment, nitrile rubber has poor resistance to vegetable insulating oil. In this paper, the effects of the changes of raw rubber system, vulcanizing system, reinforcing s...Among the rubber sealing materials for power equipment, nitrile rubber has poor resistance to vegetable insulating oil. In this paper, the effects of the changes of raw rubber system, vulcanizing system, reinforcing system, plasticizing system and anti-aging system of NBR on the properties of several vegetable insulating oils are systematically studied, and the key points of blending system of NBR with vegetable insulating oil are analyzed.展开更多
The adhesion of carbon particles on the surface of epoxy resin in insulating oil is a significant factor contributing to surface flashover.However,there is currently a lack of a dynamic model that can reasonably expla...The adhesion of carbon particles on the surface of epoxy resin in insulating oil is a significant factor contributing to surface flashover.However,there is currently a lack of a dynamic model that can reasonably explain the adhesion process of impurity particles,and the characteristics of particle adhesion are not yet clear,making it difficult to assess the risks of insulation contamination and surface flashover of valve-side bushing capacitance core.In this study,based on the Johnson-Kendall-Roberts(JKR)theory and the normal distribution characteristics of particle charges,the adhesion probability model of conductive particles in insulating oil on the surface of epoxy resin under DC electric fields was established,and carbon particle adhesion experiments were conducted to verify the accuracy of the model.The impact of electric field intensity,particle size,particle charge,and surface energy of the insulation material on the adhesion characteristics of carbon particles was investigated using the proposed model.The results can be utilised for the assessment of insulation contamination risks of valve-side bushing capacitance core and serves as a vital theoretical foundation for guiding the optimisation of anticontamination structures in internal insulation and the development of advanced pollution-resistant and flashover-resistant insulation materials.展开更多
Traditional mineral insulating oils have problems such as environmental pollution and low fire resistance.Vegetable insulating oils are prepared from vegetable oils through refining and modification processes and have...Traditional mineral insulating oils have problems such as environmental pollution and low fire resistance.Vegetable insulating oils are prepared from vegetable oils through refining and modification processes and have high fire resistance and renewability.However,vegetable insulating oils have high viscosity and poor heat dissipation performance.Hybrid insulating oils can complement single insulating oils by mixing mineral and vegetable insulating oils.This paper investigates the compatibility between palm oil and mineral oil.COSMO calculations of triglyceride and mineral oil alkane molecules were performed using molecular simulations and the COSMO-RS model.We have carried out separate calculations of the molecular surface charge densities(σ-spectra)for four major triglycerides within the palm oil as well as for three major carbon 20 alkane molecules within the naphthenic mineral oil.We illustrate the polarity relationship between the glyceride molecules and alkane molecules of mineral oils and derive the principle of similar intercalation of the glyceride molecules with the alkane molecules of mineral oils from the microscopic point of view of the molecules.The findings suggest that palm oil and the mineral oil possess comparable forces between the molecules,which allows for stable blending.展开更多
The criticality of transformers and reactors in the power transmission network and the paramount importance of ensuring their reliability through maintenance of the insulating oil is known. This paper presents a compr...The criticality of transformers and reactors in the power transmission network and the paramount importance of ensuring their reliability through maintenance of the insulating oil is known. This paper presents a comprehensive examination of the efficacy and economic viability of a dielectric oil regeneration system, as implemented by the Transmission System Maintenance Department (TSMD) of the Independent Power Transmission Operator (IPTO), Greece’s sole transmission operator. Through a detailed chemical analysis and performance evaluation, we assess the impact of the regeneration system on treated insulating oil quality over multiple cycles. The study reveals that the electrical properties of the insulating oil are fully restored after regeneration, negating the need to fully replace it, while the investment becomes cost-neutral within weeks from the commissioning of the regeneration system. This economic analysis, coupled with the system’s environmental benefits of reducing waste oil generation, positions the dielectric oil regeneration system as a compelling solution for the maintenance of power transmission assets.展开更多
The interfacial electrification properties play an important role in the electrochemical corrosion reaction which leads the electrostatic charge to generate and accumulate on the metal surface when the insulating oil ...The interfacial electrification properties play an important role in the electrochemical corrosion reaction which leads the electrostatic charge to generate and accumulate on the metal surface when the insulating oil flows through a metal pipe. In this paper, the interfacial electrification properties resulted by the oil flow rate and the action of electric charge trapper are investigated by measuring the current and potential on the surface of the test metal pipe. The measured results showed that the current and potential between the metal pipe and the earth increased with the rise of flow rate; and as the flow rate increased, the growth trends of the current and potential difference between two close flow rates increased and decreased, respectively, while there was an electric charge trapper set in the radial direction of the pipe, the measured current and potential decreased compared with that of without electric charge trapper, which was because it captured and caught part of charge in the oil flow bulk to neutralize the opposite charge on the surface of the metal pipe.展开更多
Oil reclamation with Fuller＇s earth is known to have an improved effect on conditioning aged oil. In this paper it is shown that aged oil reclamation effectiveness can be monitored with turbidity and spectrophotometr...Oil reclamation with Fuller＇s earth is known to have an improved effect on conditioning aged oil. In this paper it is shown that aged oil reclamation effectiveness can be monitored with turbidity and spectrophotometry measurements. These low cost testing techniques offer a useful tool to quantify the effect of Fuller＇s earth. Experimental investigations performed in laboratory conditions have shown that the quality of properly reclaimed aged oil can compete with that of new oils. Thus, in addition to extending the life cycle of this non-renewable resource, on-line reclamation of liquid might also prevent the premature ageing of paper insulation. Studying the stability of reclaimed service aged oil samples emphasized the important role played by Fuller＇s earth absorption capability.展开更多
In this work,experimental and theoretical studies were carried out on arc-induced bubble dynamic behaviors in insulation oil.Direct experimental evidence indicated that the arc-induced bubble experiences pulsating gro...In this work,experimental and theoretical studies were carried out on arc-induced bubble dynamic behaviors in insulation oil.Direct experimental evidence indicated that the arc-induced bubble experiences pulsating growth rather than a continuous expansion.Furthermore,a theoretical model and numerical calculation method were proposed,which revealed the dynamic mechanism of bubble growth.Good agreement between the theoretical results and experimental observations verified the general correctness and feasibility of the proposed method.展开更多
The purpose of this work is to determine the impact of thermal aging on the dielectric and physicochemical properties of the oil/paper mixed insulation. We performed a comparative analysis of dielectric paper dipped i...The purpose of this work is to determine the impact of thermal aging on the dielectric and physicochemical properties of the oil/paper mixed insulation. We performed a comparative analysis of dielectric paper dipped in two cooling fluids: palm kernel oil methyl ester (MEPKO) and mineral oil (MO). Two types of dielectric paper were used: Thermally Upgraded Kraft paper (TUK) and Nomex-910 paper (NP-910). An accelerated aging test was realized at 110<span style="white-space:nowrap;">°</span>C during a total of 96 hours. Samples of oil and paper were collected after 0, 48, 72 and 96 hours for analyses purposes. The analyses performed included the measurement of the Breakdown voltage (BDV) of the dielectric papers, the Total Acid Number (TAN) and the Decay Dissolved Products (DDP) of the liquid dielectrics. The BDV of NP-910 is greater than the BDV of TUK. Concerning the type of oil, the BDV of dielectric papers impregnated with MEPKO is greater than the BDV of similar papers impregnated with MO, indicating a better preservation of paper when dipped in methyl esters. The analyses of TAN and DDP revealed that Nomex-910 improves the oxidation stability of MO, but reduces the oxidation stability of MEPKO. These results prove that methyl esters can be used as a substitute to replace mineral oils in power transformers. Furthermore, they show that NP can be used mainly in areas of transformer where solid insulation is subjected to high thermal and electrical stress, and TUK other places where solid insulation is required. Such combination could assure money savings and a better preservation of the oil viscosity.展开更多
Natural esters exhibit excellent flame retardant and biodegradability,which help minimize power accidents and reduce environmental impact.These qualities make natural esters a promising alternative to conventional tra...Natural esters exhibit excellent flame retardant and biodegradability,which help minimize power accidents and reduce environmental impact.These qualities make natural esters a promising alternative to conventional transformer insulating oils.However,the practical applications of natural esters in power equipment have been significantly restricted by their inherent limitations,including elevated viscosity,high dielectric loss,and poor oxidative stability.Nano-modification technologies present a novel methodological approach to solve these inherent constraints.A systematic analysis of the latest research developments in nano-modified natural ester transformer oils is provided in this review.The properties of various natural esters are examined,and their suitability as base fluids is evaluated,while the modification effects and mechanisms of typical nano-additives are comprehensively reviewed.The key role of nano-modification technology in improving the overall performance of natural esters is elucidated through detailed analysis of how nanoparticles influence physical properties,dielectric properties,and oxidative stability.In addition,the practical challenges facing nano-modification technology are addressed,providing valuable theoretical guidance for future developments in this field.展开更多
Currently,the design of transformers insulation predominantly depends on the allowable alternating current(AC)field values for insulating oil established by Weidmann in the 1980s,lacking the research under direct curr...Currently,the design of transformers insulation predominantly depends on the allowable alternating current(AC)field values for insulating oil established by Weidmann in the 1980s,lacking the research under direct current(DC)voltage for converter transformers.This study selects naphthenic oils and paraffin-based oil transformer oil as research subjects,establishing a practical measurement platform to ascertain the oil breakdown characteristics under DC voltage.Furthermore,it statistically analyses the allowable DC field values of the oil.The findings elucidate that(1)the three-parameter Weibull dis-tribution is more suitable to conduct a statistical analysis for oil breakdown probability,yielding a fitting degree up to 99.95%.(2)For a constant electrode spacing,a 14.81%voltage increment escalates the breakdown probability of the oil gap from 3.33%to 73.33%.Concurrently,an increase in electrode spacing leads to a substantial decrement in the breakdown field strength of transformer oil,with KI25X experiencing a 54.51%reduction as electrode spacing extends from 5 to 25 mm.(3)The constant terms of the allowable DC field strength for S4,KI50X,and KI25X are found to be 19.728,17.221,and 19.281,respectively.(4)A thorough analysis for differences in physicochemical properties and electrical parameters elucidates the variations in insulation properties across different transformer oils.The findings presented in this study offer essential theoretical and technical foundations for the design,evaluation,and enhancement of insulation structures in converter transformers.展开更多
Moisture ingression accelerates the ageing and degradation of the oil-paper insulation.Rapid and accurate moisture assessment of power apparatus in the field is thus essential.In this paper,an innovative design of a m...Moisture ingression accelerates the ageing and degradation of the oil-paper insulation.Rapid and accurate moisture assessment of power apparatus in the field is thus essential.In this paper,an innovative design of a microstrip petal-like complementary split ring resonator(MPCSRR)is proposed for the moisture assessment of the oil-paper insulation in the GHz range.The MPCSRR has advantages in concentrating the electromagnetic field,significantly increasing the number of resonance peaks,and achieving a sensitivity of approximately 3-4 times higher than the traditional microstrip ring resonators(MRRs).A mathematical model for analysing the dielectric response is established,combining the theoretical analysis and equivalent circuit model.The effects of microstrip width and substrate thickness on impedance matching,as well as the incidence depth and test sensitivity of the resonator,are explored using simulation.The experimental results demonstrate that the MPCSRR achieves rapid moisture detection within tens of seconds and accurately characterises the wetness of the oil-paper insulation.A moisture assess-ment model based on Lasso regression achieves an accuracy of 4%,confirming the reliability and validity of the proposed method.The results also verify that the sensitivity of the MPCSRR is also higher than that of the traditional MRR,showing its potential for precise and efficient moisture detection in oil-paper insulation.展开更多
Frequency domain spectroscopy(FDS)is widely used for assessing the condition of oil-paper insulated electrical equipment.However,in low temperatures,measurement results often deviate from expected values.This study in...Frequency domain spectroscopy(FDS)is widely used for assessing the condition of oil-paper insulated electrical equipment.However,in low temperatures,measurement results often deviate from expected values.This study investigates the low-temperature dielectric response characteristics of oil-paper insulation under large temperature differences(-60℃ to 30℃),wide frequency ranges(1 mHz-5 kHz)and varying moisture contents(0.41%-3.91%).The mechanisms of low-temperature effects on oil-paper insulation relaxation polarisation are revealed.Further,a novel low-temperature normalisation method and a moisture evaluation method are proposed based on the improved Havriliak-Negami model.Compared to traditional methods,the new approach signifi-cantly enhances the accuracy.The goodness of fit R2 for temperature normalisation improves from 0.9526 to 0.9757,and the error in moisture content evaluation has reached 0.498%.Finally,the novel approach is applied to diagnose the condition of a damped bushing model,demonstrating high potential for practical applications.This study enables condition diagnosis of oil-impregnated electrical equipment in extremely cold environ-ments,filling a critical gap in the field.展开更多
During the operation of power transformer,its oil-paper insulation is continuously subjected to various stresses,c.g.,the thermal,electrical,mechanical,and chemical stresses,which cause insulation aging gradually.It h...During the operation of power transformer,its oil-paper insulation is continuously subjected to various stresses,c.g.,the thermal,electrical,mechanical,and chemical stresses,which cause insulation aging gradually.It has been considered that the combined thermal and electrical stresses are the most important and unavoidable factors that induce insulation materials aging.In this work,accelerated aging experiments of oil-impregnated pressboards under combined thermal(130℃) and electrical stresses(4 kV/mm) are performed,while the aging experiments under single thermal stress are also carried out at the corresponding temperature(130℃).The electrical and physic-chemical properties of oil,including dielectric losses factor tanδ,resistivity,acid value and pH value etc.,are measured during the aging process.Dissolved gasses in oil and polymerization degree of cellulose are also measured.The relationship between these properties of oil-paper insulation and aging time is investigated.The results show that dissolved gases in oil,resistivity,tanδof oil under combined thermal and electrical stresses are obviously different from that tinder thermal stress during aging process while some other properties show similar changing trend.For cellulose, compared with the single thermal aging results,it even shows a slower degradation rate in the presence of electrical stress.展开更多
Use of traditional mineral oil(MO)as a liquid insulation in transformers has spanned more than 130 years.However,MO has poor heat resistance,a low ignition point,and is a non-renewable resource,which does not meet dev...Use of traditional mineral oil(MO)as a liquid insulation in transformers has spanned more than 130 years.However,MO has poor heat resistance,a low ignition point,and is a non-renewable resource,which does not meet development requirements for high-performance and environmentally friendly insulation oil.Consequently,researchers have explored alternatives such as natural ester(NE)and synthetic ester(SE)oils,as well as mixed insulation oils.Mixed insulating oil is a blend of diverse insulating oil types,with optimal performance achieved by adjusting proportions of base oils.This article summarizes the innovative achievements and development of mixed insulation oil in terms of development of mixed ratio,basic physical chemical properties,electrical properties,thermal stability,and application including operation and maintenance technology.Through these efforts,this article aims to provide recommendations for future development of mixed insulating oils to advance liquid dielectric research based on enhancement mechanisms.展开更多
Charge transport in oil impregnated paper impacts the insulation performance of a transformer.This paper proposes a simulation method for the charge transport in oil impregnated paper insulation.The transient upstream...Charge transport in oil impregnated paper impacts the insulation performance of a transformer.This paper proposes a simulation method for the charge transport in oil impregnated paper insulation.The transient upstream finite element method(FEM)is applied to the transport equations of bipolar charges for establishing a numerical simulation model of charge transport in oil impregnated paper insulation.The method is validated by experimental results.The charge transport and electric field distribution in single-layer oil impregnated paper insulation under different temperature gradients is simulated.The trends of the simulation results are seen to agree with the corresponding experimental results.This paper conducts exploratory research into the simulation of charge transportation phenomenon in oil impregnated paper,and is of importance to the design of oil impregnated paper insulation.展开更多
基金supported by the National Natural Science Foundation of China(52407170)the Natural Science Foundation of Hubei Province(2024AFB306).
文摘Traditional mineral oil has long served as a liquid insulating medium in power transformers.However,its low fire resistance,poor biodegradability and dependence on finite fossil fuel resources,along with its low flash point,contribute to transformer explosions and fires.To overcome these limitations,developing insulating liquids with high flash points and self-extinguishing properties is essential.Although natural ester-based insulating oils and silicone oils have been proposed as alternatives,their performance requires further optimisation,and their application in transformers remains challenging.This study examines the combustion characteristics of three novel self-extinguishing fluorinated silicone oils using combustion experiments and reactive molecular dynamics simulations.The results demonstrate that methylfluorinated and hydrofluorinated silicone oils exhibit superior self-extinguishing performance compared to mineral oil and natural ester-based insulating oils.Simulation analyses indicate that fluorinated silicone oils generate silicon-oxygen polymers upon ignition,which influence subsequent chain reactions.However,hydroxyfluorinated silicone oil releases a higher concentration of key free radicals,intensifying chain reactions and diminishing its self-extinguishing capability.As a result,its self-extinguishing performance is significantly weaker than that of methylfluorinated and hydrofluorinated silicone oils.These findings provide valuable insights for the development of advanced liquid insulating media as potential replacements for mineral oil.
文摘Among the rubber sealing materials for power equipment, nitrile rubber has poor resistance to vegetable insulating oil. In this paper, the effects of the changes of raw rubber system, vulcanizing system, reinforcing system, plasticizing system and anti-aging system of NBR on the properties of several vegetable insulating oils are systematically studied, and the key points of blending system of NBR with vegetable insulating oil are analyzed.
基金National Natural Science Foundation of China,Grant/Award Number:52077012。
文摘The adhesion of carbon particles on the surface of epoxy resin in insulating oil is a significant factor contributing to surface flashover.However,there is currently a lack of a dynamic model that can reasonably explain the adhesion process of impurity particles,and the characteristics of particle adhesion are not yet clear,making it difficult to assess the risks of insulation contamination and surface flashover of valve-side bushing capacitance core.In this study,based on the Johnson-Kendall-Roberts(JKR)theory and the normal distribution characteristics of particle charges,the adhesion probability model of conductive particles in insulating oil on the surface of epoxy resin under DC electric fields was established,and carbon particle adhesion experiments were conducted to verify the accuracy of the model.The impact of electric field intensity,particle size,particle charge,and surface energy of the insulation material on the adhesion characteristics of carbon particles was investigated using the proposed model.The results can be utilised for the assessment of insulation contamination risks of valve-side bushing capacitance core and serves as a vital theoretical foundation for guiding the optimisation of anticontamination structures in internal insulation and the development of advanced pollution-resistant and flashover-resistant insulation materials.
基金supported in part by the National Natural Science Foundation of China under Grant 52277139 and 52367014in part by the Specific Research Project of Guangxi for Research Bases and Talents under Grant 2020AC19010.
文摘Traditional mineral insulating oils have problems such as environmental pollution and low fire resistance.Vegetable insulating oils are prepared from vegetable oils through refining and modification processes and have high fire resistance and renewability.However,vegetable insulating oils have high viscosity and poor heat dissipation performance.Hybrid insulating oils can complement single insulating oils by mixing mineral and vegetable insulating oils.This paper investigates the compatibility between palm oil and mineral oil.COSMO calculations of triglyceride and mineral oil alkane molecules were performed using molecular simulations and the COSMO-RS model.We have carried out separate calculations of the molecular surface charge densities(σ-spectra)for four major triglycerides within the palm oil as well as for three major carbon 20 alkane molecules within the naphthenic mineral oil.We illustrate the polarity relationship between the glyceride molecules and alkane molecules of mineral oils and derive the principle of similar intercalation of the glyceride molecules with the alkane molecules of mineral oils from the microscopic point of view of the molecules.The findings suggest that palm oil and the mineral oil possess comparable forces between the molecules,which allows for stable blending.
文摘The criticality of transformers and reactors in the power transmission network and the paramount importance of ensuring their reliability through maintenance of the insulating oil is known. This paper presents a comprehensive examination of the efficacy and economic viability of a dielectric oil regeneration system, as implemented by the Transmission System Maintenance Department (TSMD) of the Independent Power Transmission Operator (IPTO), Greece’s sole transmission operator. Through a detailed chemical analysis and performance evaluation, we assess the impact of the regeneration system on treated insulating oil quality over multiple cycles. The study reveals that the electrical properties of the insulating oil are fully restored after regeneration, negating the need to fully replace it, while the investment becomes cost-neutral within weeks from the commissioning of the regeneration system. This economic analysis, coupled with the system’s environmental benefits of reducing waste oil generation, positions the dielectric oil regeneration system as a compelling solution for the maintenance of power transmission assets.
文摘The interfacial electrification properties play an important role in the electrochemical corrosion reaction which leads the electrostatic charge to generate and accumulate on the metal surface when the insulating oil flows through a metal pipe. In this paper, the interfacial electrification properties resulted by the oil flow rate and the action of electric charge trapper are investigated by measuring the current and potential on the surface of the test metal pipe. The measured results showed that the current and potential between the metal pipe and the earth increased with the rise of flow rate; and as the flow rate increased, the growth trends of the current and potential difference between two close flow rates increased and decreased, respectively, while there was an electric charge trapper set in the radial direction of the pipe, the measured current and potential decreased compared with that of without electric charge trapper, which was because it captured and caught part of charge in the oil flow bulk to neutralize the opposite charge on the surface of the metal pipe.
文摘Oil reclamation with Fuller＇s earth is known to have an improved effect on conditioning aged oil. In this paper it is shown that aged oil reclamation effectiveness can be monitored with turbidity and spectrophotometry measurements. These low cost testing techniques offer a useful tool to quantify the effect of Fuller＇s earth. Experimental investigations performed in laboratory conditions have shown that the quality of properly reclaimed aged oil can compete with that of new oils. Thus, in addition to extending the life cycle of this non-renewable resource, on-line reclamation of liquid might also prevent the premature ageing of paper insulation. Studying the stability of reclaimed service aged oil samples emphasized the important role played by Fuller＇s earth absorption capability.
基金supported by National Natural Science Foundation of China(No.51807151)。
文摘In this work,experimental and theoretical studies were carried out on arc-induced bubble dynamic behaviors in insulation oil.Direct experimental evidence indicated that the arc-induced bubble experiences pulsating growth rather than a continuous expansion.Furthermore,a theoretical model and numerical calculation method were proposed,which revealed the dynamic mechanism of bubble growth.Good agreement between the theoretical results and experimental observations verified the general correctness and feasibility of the proposed method.
文摘The purpose of this work is to determine the impact of thermal aging on the dielectric and physicochemical properties of the oil/paper mixed insulation. We performed a comparative analysis of dielectric paper dipped in two cooling fluids: palm kernel oil methyl ester (MEPKO) and mineral oil (MO). Two types of dielectric paper were used: Thermally Upgraded Kraft paper (TUK) and Nomex-910 paper (NP-910). An accelerated aging test was realized at 110<span style="white-space:nowrap;">°</span>C during a total of 96 hours. Samples of oil and paper were collected after 0, 48, 72 and 96 hours for analyses purposes. The analyses performed included the measurement of the Breakdown voltage (BDV) of the dielectric papers, the Total Acid Number (TAN) and the Decay Dissolved Products (DDP) of the liquid dielectrics. The BDV of NP-910 is greater than the BDV of TUK. Concerning the type of oil, the BDV of dielectric papers impregnated with MEPKO is greater than the BDV of similar papers impregnated with MO, indicating a better preservation of paper when dipped in methyl esters. The analyses of TAN and DDP revealed that Nomex-910 improves the oxidation stability of MO, but reduces the oxidation stability of MEPKO. These results prove that methyl esters can be used as a substitute to replace mineral oils in power transformers. Furthermore, they show that NP can be used mainly in areas of transformer where solid insulation is subjected to high thermal and electrical stress, and TUK other places where solid insulation is required. Such combination could assure money savings and a better preservation of the oil viscosity.
基金supported by the Shanghai Sailing Program(Grant No.24YF2744900)Research and Innovation Project of Shanghai Municipal Education Commission(Grant No.2023ZKZD54)+1 种基金Industrial Collaborative Innovation Project of Shanghai(Grant Nos.2021-cyxt1-kj37 and XTCX-KJ-2022-70)Technical Standard Project of Shanghai(Grant No.23DZ2201100).
文摘Natural esters exhibit excellent flame retardant and biodegradability,which help minimize power accidents and reduce environmental impact.These qualities make natural esters a promising alternative to conventional transformer insulating oils.However,the practical applications of natural esters in power equipment have been significantly restricted by their inherent limitations,including elevated viscosity,high dielectric loss,and poor oxidative stability.Nano-modification technologies present a novel methodological approach to solve these inherent constraints.A systematic analysis of the latest research developments in nano-modified natural ester transformer oils is provided in this review.The properties of various natural esters are examined,and their suitability as base fluids is evaluated,while the modification effects and mechanisms of typical nano-additives are comprehensively reviewed.The key role of nano-modification technology in improving the overall performance of natural esters is elucidated through detailed analysis of how nanoparticles influence physical properties,dielectric properties,and oxidative stability.In addition,the practical challenges facing nano-modification technology are addressed,providing valuable theoretical guidance for future developments in this field.
基金National Natural Science Foundation of China,Grant/Award Number:52107148China Postdoctoral Science Foundation,Grant/Award Number:2020M680485Fundamental Research Funds for the Central-Universities,Grant/Award Number:2021MS004。
文摘Currently,the design of transformers insulation predominantly depends on the allowable alternating current(AC)field values for insulating oil established by Weidmann in the 1980s,lacking the research under direct current(DC)voltage for converter transformers.This study selects naphthenic oils and paraffin-based oil transformer oil as research subjects,establishing a practical measurement platform to ascertain the oil breakdown characteristics under DC voltage.Furthermore,it statistically analyses the allowable DC field values of the oil.The findings elucidate that(1)the three-parameter Weibull dis-tribution is more suitable to conduct a statistical analysis for oil breakdown probability,yielding a fitting degree up to 99.95%.(2)For a constant electrode spacing,a 14.81%voltage increment escalates the breakdown probability of the oil gap from 3.33%to 73.33%.Concurrently,an increase in electrode spacing leads to a substantial decrement in the breakdown field strength of transformer oil,with KI25X experiencing a 54.51%reduction as electrode spacing extends from 5 to 25 mm.(3)The constant terms of the allowable DC field strength for S4,KI50X,and KI25X are found to be 19.728,17.221,and 19.281,respectively.(4)A thorough analysis for differences in physicochemical properties and electrical parameters elucidates the variations in insulation properties across different transformer oils.The findings presented in this study offer essential theoretical and technical foundations for the design,evaluation,and enhancement of insulation structures in converter transformers.
基金Ningbo Power Supply Company Science and Technology Program,Grant/Award Number:KJKY20230393。
文摘Moisture ingression accelerates the ageing and degradation of the oil-paper insulation.Rapid and accurate moisture assessment of power apparatus in the field is thus essential.In this paper,an innovative design of a microstrip petal-like complementary split ring resonator(MPCSRR)is proposed for the moisture assessment of the oil-paper insulation in the GHz range.The MPCSRR has advantages in concentrating the electromagnetic field,significantly increasing the number of resonance peaks,and achieving a sensitivity of approximately 3-4 times higher than the traditional microstrip ring resonators(MRRs).A mathematical model for analysing the dielectric response is established,combining the theoretical analysis and equivalent circuit model.The effects of microstrip width and substrate thickness on impedance matching,as well as the incidence depth and test sensitivity of the resonator,are explored using simulation.The experimental results demonstrate that the MPCSRR achieves rapid moisture detection within tens of seconds and accurately characterises the wetness of the oil-paper insulation.A moisture assess-ment model based on Lasso regression achieves an accuracy of 4%,confirming the reliability and validity of the proposed method.The results also verify that the sensitivity of the MPCSRR is also higher than that of the traditional MRR,showing its potential for precise and efficient moisture detection in oil-paper insulation.
基金National Natural Science Foundation of China,Grant/Award Number:52477027。
文摘Frequency domain spectroscopy(FDS)is widely used for assessing the condition of oil-paper insulated electrical equipment.However,in low temperatures,measurement results often deviate from expected values.This study investigates the low-temperature dielectric response characteristics of oil-paper insulation under large temperature differences(-60℃ to 30℃),wide frequency ranges(1 mHz-5 kHz)and varying moisture contents(0.41%-3.91%).The mechanisms of low-temperature effects on oil-paper insulation relaxation polarisation are revealed.Further,a novel low-temperature normalisation method and a moisture evaluation method are proposed based on the improved Havriliak-Negami model.Compared to traditional methods,the new approach signifi-cantly enhances the accuracy.The goodness of fit R2 for temperature normalisation improves from 0.9526 to 0.9757,and the error in moisture content evaluation has reached 0.498%.Finally,the novel approach is applied to diagnose the condition of a damped bushing model,demonstrating high potential for practical applications.This study enables condition diagnosis of oil-impregnated electrical equipment in extremely cold environ-ments,filling a critical gap in the field.
基金Supported by National High Technology Research and Development Program of China(2007AA04Z411)National Basic Research Program of China(2009CB724505-1)Open Fund of State Key Laboratory of Power Transmission Equipment & System Security and New Technology(2007DA10512709405)
文摘During the operation of power transformer,its oil-paper insulation is continuously subjected to various stresses,c.g.,the thermal,electrical,mechanical,and chemical stresses,which cause insulation aging gradually.It has been considered that the combined thermal and electrical stresses are the most important and unavoidable factors that induce insulation materials aging.In this work,accelerated aging experiments of oil-impregnated pressboards under combined thermal(130℃) and electrical stresses(4 kV/mm) are performed,while the aging experiments under single thermal stress are also carried out at the corresponding temperature(130℃).The electrical and physic-chemical properties of oil,including dielectric losses factor tanδ,resistivity,acid value and pH value etc.,are measured during the aging process.Dissolved gasses in oil and polymerization degree of cellulose are also measured.The relationship between these properties of oil-paper insulation and aging time is investigated.The results show that dissolved gases in oil,resistivity,tanδof oil under combined thermal and electrical stresses are obviously different from that tinder thermal stress during aging process while some other properties show similar changing trend.For cellulose, compared with the single thermal aging results,it even shows a slower degradation rate in the presence of electrical stress.
基金supported in part by the National Natural Science Foundation of China under Grant 52077015the National Natural Science Foundation of China under Grant HWQB2023001the Graduate Research and Innovation Foundation of Chongqing,China under Grant CYB23025.
文摘Use of traditional mineral oil(MO)as a liquid insulation in transformers has spanned more than 130 years.However,MO has poor heat resistance,a low ignition point,and is a non-renewable resource,which does not meet development requirements for high-performance and environmentally friendly insulation oil.Consequently,researchers have explored alternatives such as natural ester(NE)and synthetic ester(SE)oils,as well as mixed insulation oils.Mixed insulating oil is a blend of diverse insulating oil types,with optimal performance achieved by adjusting proportions of base oils.This article summarizes the innovative achievements and development of mixed insulation oil in terms of development of mixed ratio,basic physical chemical properties,electrical properties,thermal stability,and application including operation and maintenance technology.Through these efforts,this article aims to provide recommendations for future development of mixed insulating oils to advance liquid dielectric research based on enhancement mechanisms.
基金supported by the National Basic Research Program(973 Program)(2011CB209404)National Natural Science Foundation of China(51477120).
文摘Charge transport in oil impregnated paper impacts the insulation performance of a transformer.This paper proposes a simulation method for the charge transport in oil impregnated paper insulation.The transient upstream finite element method(FEM)is applied to the transport equations of bipolar charges for establishing a numerical simulation model of charge transport in oil impregnated paper insulation.The method is validated by experimental results.The charge transport and electric field distribution in single-layer oil impregnated paper insulation under different temperature gradients is simulated.The trends of the simulation results are seen to agree with the corresponding experimental results.This paper conducts exploratory research into the simulation of charge transportation phenomenon in oil impregnated paper,and is of importance to the design of oil impregnated paper insulation.
