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
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
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
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
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 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.
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.
