Poor electrical strength of the ceramic-vacuum interface restricts the development of various electrical/electronic devices.Limitations of solutions based on conventional ceramics fabrication procedures are becoming p...Poor electrical strength of the ceramic-vacuum interface restricts the development of various electrical/electronic devices.Limitations of solutions based on conventional ceramics fabrication procedures are becoming prominent with the further demand for compactness and performance improvement.In this study,a fabrication method utilising 3D printing technology is proposed to construct ceramic insulation with designed structures.The processing characteristics,dielectric properties and morphologies of 3D-printed ceramics fabricated under different processing parameters were analysed.The results indicated that fillers'particle size,sintering temperature and sintering aids have significant influence on the dielectric properties and the internal defects.Finally,with optimised processing parameters,Al_(2)O_(3)ceramics with low dielectric loss and complex structures were fabricated to inhibit vacuum flashover from the perspectives of electric field optimisation and secondary electron emission suppression.Compared with traditional ceramic insulator fabrication methods,the proposed construction strategy has an accurate and efficient fabrication process and high insulation performance,making it promising for industrial applications.展开更多
For converter transformer, AC-DC combined electric field can trigger space charge accumulation on oil-impregnated pressboard interface. The accumulation of space charge on oil-pressboard interface can result in electr...For converter transformer, AC-DC combined electric field can trigger space charge accumulation on oil-impregnated pressboard interface. The accumulation of space charge on oil-pressboard interface can result in electric field distortion, trend to trigger surface discharge of barriers. This paper studied the influence of surface charge on flashover voltage of oil-impregnated pressboard under AC-DC combined electric field. The study finds that the flashover voltage of oil-pressboard interface under negative polarity DC superimposed AC electric field is higher than that.of positive DC superimposed AC voltage to form composite electric field. It was found that homopolar surface charge has been accumulated on the interface of oil-pressboard with positive or negative DC voltage through measuring surface potential by the electrostatic capacitive probe. The surface charge produced electric field in the opposite direction, which weakening the synthetic electric field strength. What＇s more, under the same conditions, the negative surface charge density oil-pressboard is much larger than the positive.展开更多
Surface charge accumulation on insulator surface can have great influence on surface flashover performance.An experimental system is established to investigate surface charge accumulation and decay characteristics of ...Surface charge accumulation on insulator surface can have great influence on surface flashover performance.An experimental system is established to investigate surface charge accumulation and decay characteristics of Al2O3-filled epoxy resin insulators in 0.1 MPa SF6 under DC voltages.Surface potential is recorded by a Kelvin vibrating probe connected to an electrostatic voltmeter.By pre-depositing charges on insulator surface,the influence of surface charges on surface flashover performance is studied.The results reveal that surface charge distribution appearance is the combined effect of electrode injection,back discharge and gas ionization.Surface charge distribution has obvious polarity effect.It is concentrated near the HV electrode under positive voltages and dispersed under negative voltages.The difference in positive and negative surface flashover voltage is attributed to the difference in surface charge distribution under DC voltages of different polarities.Surface charge decay contains two stages,which satisfies the law of double exponential function.At first stage,surface charge decays fast,which corresponds to charges escaping from shallower traps.While it decays slowly at the second stage,which corresponds to charge escaping from deeper traps.Surface charge decay process is dominated by surface conductivity mechanism.The pre-deposited charges on insulation surface have great influence on surface flashover performance.The deposited positive charges can increase positive flashover voltage but decrease negative flashover voltage.展开更多
Research on the pulsed flashover characteristics of vacuum insulation material is significant for the design and manufacture of pulse power devices. In view of the voltage increase rate of the fast pulse （pulse steep...Research on the pulsed flashover characteristics of vacuum insulation material is significant for the design and manufacture of pulse power devices. In view of the voltage increase rate of the fast pulse （pulse steepness）, the vacuum fiashover characteristics of pure epoxy under different steepnesses is investigated by using a pulse generator with parameters of a rise time of 40 ns and a full width at half maximum of 2.5 μs. Pulses with six levels of steepness were achieved by changing the charging voltage of the generator. Based on the linear equation and electron emission equation, the relationship between the flashover voltage and pulse steepness was fitted. By virtue of the fitted formula, it was possible to predict the flashover voltage under near DC or higher steepness conditions. Based on the electron emission equation, the relationship between the time delay and flashover field was also fitted. Result shows that F-N electron emission dominates the flashover process.展开更多
The surface trap parameter can significantly affect the development of surface flashover in vacuum,but the effective mode and mechanism are not very clear yet.The trap parameters of three polymeric materials were test...The surface trap parameter can significantly affect the development of surface flashover in vacuum,but the effective mode and mechanism are not very clear yet.The trap parameters of three polymeric materials were tested and calculated by means of isothermal surface potential decay.The flashover experiment was developed under different applied voltages.The results show a positive correlation between the withstand voltage and the deep trap,i.e.,the deeper trap energy level is,the higher flashover voltage is.The dynamics process of charge trapping and detrapping was analyzed based on the charge transport model in dielectrics with a single trap level and two discrete trap levels.The time of charge trapping was compared with that of the discharge development.The results show that the charge trapping time is longer than the flashover development time.The way to influence flashover for a trap is not to decrease the secondary electrons in single discharge development,but to change the electric field distribution on the dielectric surface by charge capture.展开更多
Lightning stroke is one of the important causes of the accidents that occur on transmission lines.With the development of power system,the proportion of outages on transmission lines because of lightning stroke also i...Lightning stroke is one of the important causes of the accidents that occur on transmission lines.With the development of power system,the proportion of outages on transmission lines because of lightning stroke also increases.And according to the lightning accidents results,the lightning stroke characteristics is related to the time factors tightly.In order to analyze the correlativity between the lightning flashover amount and the time factors,about 425 times lightning flashover on 187 lines in 10 power supply companies of 220 kV and 500 kV transmission lines during 2000-2007 are investigated in this paper.The correlativity between the lightning flashover amount and the time factors is analyzed.According to the lightning stroke accidents investigation records,the lightning flashover amount of transmission line increases from the year of 2000 to 2007.In each year lightning flashovers mostly happen in the month of June,July and August.Similarly in each day the flashover amount also varies with the time of day obviously.These lightning flashovers mainly occur during 14:00-21:00 in the afternoon.The analysis results in this paper have a good agreement with the meteorological observations and lightning detection data of lightning location system(LLS).And these results provide good reference for the lightning protection work in power system.展开更多
基金supported by the National Natural Science Foundation of China(Grants 52407156,12475253,52207147).
文摘Poor electrical strength of the ceramic-vacuum interface restricts the development of various electrical/electronic devices.Limitations of solutions based on conventional ceramics fabrication procedures are becoming prominent with the further demand for compactness and performance improvement.In this study,a fabrication method utilising 3D printing technology is proposed to construct ceramic insulation with designed structures.The processing characteristics,dielectric properties and morphologies of 3D-printed ceramics fabricated under different processing parameters were analysed.The results indicated that fillers'particle size,sintering temperature and sintering aids have significant influence on the dielectric properties and the internal defects.Finally,with optimised processing parameters,Al_(2)O_(3)ceramics with low dielectric loss and complex structures were fabricated to inhibit vacuum flashover from the perspectives of electric field optimisation and secondary electron emission suppression.Compared with traditional ceramic insulator fabrication methods,the proposed construction strategy has an accurate and efficient fabrication process and high insulation performance,making it promising for industrial applications.
文摘For converter transformer, AC-DC combined electric field can trigger space charge accumulation on oil-impregnated pressboard interface. The accumulation of space charge on oil-pressboard interface can result in electric field distortion, trend to trigger surface discharge of barriers. This paper studied the influence of surface charge on flashover voltage of oil-impregnated pressboard under AC-DC combined electric field. The study finds that the flashover voltage of oil-pressboard interface under negative polarity DC superimposed AC electric field is higher than that.of positive DC superimposed AC voltage to form composite electric field. It was found that homopolar surface charge has been accumulated on the interface of oil-pressboard with positive or negative DC voltage through measuring surface potential by the electrostatic capacitive probe. The surface charge produced electric field in the opposite direction, which weakening the synthetic electric field strength. What＇s more, under the same conditions, the negative surface charge density oil-pressboard is much larger than the positive.
文摘Surface charge accumulation on insulator surface can have great influence on surface flashover performance.An experimental system is established to investigate surface charge accumulation and decay characteristics of Al2O3-filled epoxy resin insulators in 0.1 MPa SF6 under DC voltages.Surface potential is recorded by a Kelvin vibrating probe connected to an electrostatic voltmeter.By pre-depositing charges on insulator surface,the influence of surface charges on surface flashover performance is studied.The results reveal that surface charge distribution appearance is the combined effect of electrode injection,back discharge and gas ionization.Surface charge distribution has obvious polarity effect.It is concentrated near the HV electrode under positive voltages and dispersed under negative voltages.The difference in positive and negative surface flashover voltage is attributed to the difference in surface charge distribution under DC voltages of different polarities.Surface charge decay contains two stages,which satisfies the law of double exponential function.At first stage,surface charge decays fast,which corresponds to charges escaping from shallower traps.While it decays slowly at the second stage,which corresponds to charge escaping from deeper traps.Surface charge decay process is dominated by surface conductivity mechanism.The pre-deposited charges on insulation surface have great influence on surface flashover performance.The deposited positive charges can increase positive flashover voltage but decrease negative flashover voltage.
基金supported by National Natural Science Foundation of China(No.50437030)
文摘Research on the pulsed flashover characteristics of vacuum insulation material is significant for the design and manufacture of pulse power devices. In view of the voltage increase rate of the fast pulse （pulse steepness）, the vacuum fiashover characteristics of pure epoxy under different steepnesses is investigated by using a pulse generator with parameters of a rise time of 40 ns and a full width at half maximum of 2.5 μs. Pulses with six levels of steepness were achieved by changing the charging voltage of the generator. Based on the linear equation and electron emission equation, the relationship between the flashover voltage and pulse steepness was fitted. By virtue of the fitted formula, it was possible to predict the flashover voltage under near DC or higher steepness conditions. Based on the electron emission equation, the relationship between the time delay and flashover field was also fitted. Result shows that F-N electron emission dominates the flashover process.
基金supported by National Natural Science Foundation of China(Nos.51977202,U1830135,51807189)the Scientific Instrument Developing Project of the Chinese Academy of Sciences(No.YJKYYQ20170004).
文摘The surface trap parameter can significantly affect the development of surface flashover in vacuum,but the effective mode and mechanism are not very clear yet.The trap parameters of three polymeric materials were tested and calculated by means of isothermal surface potential decay.The flashover experiment was developed under different applied voltages.The results show a positive correlation between the withstand voltage and the deep trap,i.e.,the deeper trap energy level is,the higher flashover voltage is.The dynamics process of charge trapping and detrapping was analyzed based on the charge transport model in dielectrics with a single trap level and two discrete trap levels.The time of charge trapping was compared with that of the discharge development.The results show that the charge trapping time is longer than the flashover development time.The way to influence flashover for a trap is not to decrease the secondary electrons in single discharge development,but to change the electric field distribution on the dielectric surface by charge capture.
基金Supported by Eleventh—five Year Science and Teehnology Program of SGCC(SGKJ[2007]787).
文摘Lightning stroke is one of the important causes of the accidents that occur on transmission lines.With the development of power system,the proportion of outages on transmission lines because of lightning stroke also increases.And according to the lightning accidents results,the lightning stroke characteristics is related to the time factors tightly.In order to analyze the correlativity between the lightning flashover amount and the time factors,about 425 times lightning flashover on 187 lines in 10 power supply companies of 220 kV and 500 kV transmission lines during 2000-2007 are investigated in this paper.The correlativity between the lightning flashover amount and the time factors is analyzed.According to the lightning stroke accidents investigation records,the lightning flashover amount of transmission line increases from the year of 2000 to 2007.In each year lightning flashovers mostly happen in the month of June,July and August.Similarly in each day the flashover amount also varies with the time of day obviously.These lightning flashovers mainly occur during 14:00-21:00 in the afternoon.The analysis results in this paper have a good agreement with the meteorological observations and lightning detection data of lightning location system(LLS).And these results provide good reference for the lightning protection work in power system.
