Single zinc oxide nanowires(ZnO NWs)are promising for nanogenerators because of their excellent semiconducting and piezoelectric properties,but characterizing the latter efficiently is challenging.As reported here,an ...Single zinc oxide nanowires(ZnO NWs)are promising for nanogenerators because of their excellent semiconducting and piezoelectric properties,but characterizing the latter efficiently is challenging.As reported here,an electrical breakdown strategy was used to construct single ZnO NWs with a specific length.With the high operability of a nanomanipulator in a scanning electron microscope,ZnO-NW-based twoprobe and three-probe structures were constructed for fabricating AC/DC nanogenerators,respectively.For a ZnO NW,an AC output of between−15.31 mV and 5.82 mV was achieved,while for a DC nanogenerator,an output of24.3 mV was realized.Also,the three-probe structure’s output method was changed to verify the distribution of piezoelectric charges when a single ZnO NW is bent by a probe,and DC outputs of different amplitudes were achieved.This study provides a low-cost,highly convenient,and operational method for studying the AC/DC output characteristics of single NWs,which is beneficial for the further development of nanogenerators.展开更多
The valve side windings of converter transformers bear AC, DC, impulse, and reversal-polarity voltages during operation, which could result in serious insulation problems of the equipment. By performing experiments wi...The valve side windings of converter transformers bear AC, DC, impulse, and reversal-polarity voltages during operation, which could result in serious insulation problems of the equipment. By performing experiments with surface discharge model of oil-paper insula- tion at 80 ℃ under combined AC-DC voltage for 200 h, we studied the spectrums and statistical parameters of partial discharges at different discharge stages. Furthermore, some fingerprint parameters were calculated in order to estimate the development situation of par- tial discharge, while the characteristic gases dissolved in the transformer oil were measured by gas chromatography. The surface discharges in the experiments were observed using a high speed camera, and a full discharge process could be marked off into four stages as follows. ①The elementary stage. When a partial discharge occurs near electrodes, electrical charges are injected into the region near electrodes and causing bubble generation. ②Due to their high resistivity and low dielectric constant, the bubbles would bare the major part of the voltage applied to samples. Therefore, discharge happens inside the small bubbles, and it emits a lot of light. ③Micromolecules of gas are produced in discharge, and further ionization in the transformer oil takes place simultaneously when high-energy electrons collide with oil molecules. ④The carrier charge moves forward to electrodes driven by the applied electric field, till they neutralize with the charge from electrodes, and hence discharge channels are formed subsequently.展开更多
The influence of sand dust on discharge of external insulation has caused widespread concern.At present,the research results show wind-sand electricity has a remarkable effect on the discharge characteristics of insul...The influence of sand dust on discharge of external insulation has caused widespread concern.At present,the research results show wind-sand electricity has a remarkable effect on the discharge characteristics of insulator and has little influence on the discharge characteristics of air gap.The flashover of insulator strings occurs along the insulator surface and air gaps,and the sand dust deposited on the insulator surface may affect the flashover characteristics of insulator strings.This paper studies the flashover characteristics of flat plate model under DC voltage in wind-sand condition.The experimental results show that under positive polarity voltage,the flashover voltage of the flat plate model has a maximum value,while under negative polarity voltage,the flashover voltage of the flat plate model has a minimum value with a certain degree of sand dust deposition.The wind or sand in sand-dust weather has an important effect on the flashover characteristics of the flat plate model.In certain variation range of electric charge,electric charge of sand dust has little effect on the flashover voltage of flat plate model under DC voltage.The deposition of sand has significant influence on the flashover process of flat plate model,which is related to the deposition density and moisture content of sand particle.展开更多
Due to the complexity of the valve side winding voltage of the converter transformer,the insulation characteristics of the oil-impregnated pressboard(OIP)of the converter transformer are different from those of the tr...Due to the complexity of the valve side winding voltage of the converter transformer,the insulation characteristics of the oil-impregnated pressboard(OIP)of the converter transformer are different from those of the traditional AC transformer.The study on effect of temperature on the creeping discharge characteristics of OIP under combined AC-DC voltage is seriously inadequate.Therefore,this paper investigates the characteristics of OIP creepage discharge under combined AC-DC voltage and discusses the influence of temperature on creepage discharge characteristics under different temperatures from 70℃to 110℃.The experimental results show that the partial discharge inception voltage and flashover voltage decrease with increasing temperature.The times of low amplitude discharge(LAD)decrease and amplitude of LAD increases.Simultaneously,the times of high amplitude discharge(HAD)gradually in crease at each stage of creepage discharge with higher temperature.The analysis indicates that the charge carriers easily accumulate and quickly migrate directional movement along the electric field ahead of discharging.The residual charge carriers are more easily dissipated after discharging.The'hump'region of LAD moves to the direction of higher discharge magnitude.The interval time between two continuous discharges is shortened obviously.The concentration of HAD accelerates the development of OIP insulation creepage discharge.The temperature had an accelerating effect on the development of discharge in the OIP under applying voltage.展开更多
This paper describes an experimental and theoretical study on an extraction phenomenon of liquids occurring at an air gap between the liquid surface and the electrode by applying a direct current (DC) or low-frequency...This paper describes an experimental and theoretical study on an extraction phenomenon of liquids occurring at an air gap between the liquid surface and the electrode by applying a direct current (DC) or low-frequency alternating current (AC) voltage. Three liquids with a different physical property;2,3-dihydrodecafluoropenten, palm fatty acid ester oil and crude rapeseed oil are used as working liquids. The electrode configuration is the sphere or plane (high voltage electrode) to grounded plane electrode. The grounded plane electrode is fixed to the bottom of the test vessel with working liquid and the high voltage electrode is installed in an air above the liquid surface against the grounded plane electrode. The liquid surface swells towards the high voltage electrode by the increase of voltage and the liquid is extracted in a short time, thereafter the air gap between the liquid surface and the high voltage electrode is bridged at a thick liquid column. Such the liquid behavior displays unique features with voltage polarity effect for each working liquid. The relationship between the applied voltage, current variation, height of swollen liquid, force pulling liquid and dynamic feature of liquid is examined experimentally. The liquid behavior is considered theoretically based on experimental observations.展开更多
针对电动汽车充电电源额外热量产生影响电池使用寿命的问题,提出一种无电解电容隔离式单级双向AC/DC变换器。该变换器能有效阻止低频功率纹波注入电池单元,减少了额外热量的产生;同时电解电容的消除也大大提高了系统的可靠性。控制策略...针对电动汽车充电电源额外热量产生影响电池使用寿命的问题,提出一种无电解电容隔离式单级双向AC/DC变换器。该变换器能有效阻止低频功率纹波注入电池单元,减少了额外热量的产生;同时电解电容的消除也大大提高了系统的可靠性。控制策略方面,提出的一种四相控制器,不仅能使所有开关管实现零电压开关(Zero Voltage Switch,ZVS),并在导通损耗进行了性能优化。最后,通过PSIM仿真软件和实验样机,验证了理论分析的正确性和可行性。展开更多
基金supported by the Research Fund Program of the Guangdong Provincial Key Laboratory of Fuel Cell Technology (Grant No.FC202204).
文摘Single zinc oxide nanowires(ZnO NWs)are promising for nanogenerators because of their excellent semiconducting and piezoelectric properties,but characterizing the latter efficiently is challenging.As reported here,an electrical breakdown strategy was used to construct single ZnO NWs with a specific length.With the high operability of a nanomanipulator in a scanning electron microscope,ZnO-NW-based twoprobe and three-probe structures were constructed for fabricating AC/DC nanogenerators,respectively.For a ZnO NW,an AC output of between−15.31 mV and 5.82 mV was achieved,while for a DC nanogenerator,an output of24.3 mV was realized.Also,the three-probe structure’s output method was changed to verify the distribution of piezoelectric charges when a single ZnO NW is bent by a probe,and DC outputs of different amplitudes were achieved.This study provides a low-cost,highly convenient,and operational method for studying the AC/DC output characteristics of single NWs,which is beneficial for the further development of nanogenerators.
基金Project supported by National Basic Research Program of China(973 Program) (2011CB 209400)Program of State Key Laboratory of Power Systems for ±1 100 kV UHVDC Technology(SKLD10M09)
文摘The valve side windings of converter transformers bear AC, DC, impulse, and reversal-polarity voltages during operation, which could result in serious insulation problems of the equipment. By performing experiments with surface discharge model of oil-paper insula- tion at 80 ℃ under combined AC-DC voltage for 200 h, we studied the spectrums and statistical parameters of partial discharges at different discharge stages. Furthermore, some fingerprint parameters were calculated in order to estimate the development situation of par- tial discharge, while the characteristic gases dissolved in the transformer oil were measured by gas chromatography. The surface discharges in the experiments were observed using a high speed camera, and a full discharge process could be marked off into four stages as follows. ①The elementary stage. When a partial discharge occurs near electrodes, electrical charges are injected into the region near electrodes and causing bubble generation. ②Due to their high resistivity and low dielectric constant, the bubbles would bare the major part of the voltage applied to samples. Therefore, discharge happens inside the small bubbles, and it emits a lot of light. ③Micromolecules of gas are produced in discharge, and further ionization in the transformer oil takes place simultaneously when high-energy electrons collide with oil molecules. ④The carrier charge moves forward to electrodes driven by the applied electric field, till they neutralize with the charge from electrodes, and hence discharge channels are formed subsequently.
基金supported by National High-tech Research and Development Program of China(863 Program)(2009AA04Z416) National Science Foundation of China(51021005) Scientific Innovation of Colleges and Universities(Project v-200704)
基金supported by National High-tech Research and Development Program of China(863 Program)(2009AA04Z416) National Science Foundation of China(51021005) Scientific Innovation of Colleges and Universities(200704)
基金Project Supported by National Natural Science Foundation of China(90510014 ).
文摘The influence of sand dust on discharge of external insulation has caused widespread concern.At present,the research results show wind-sand electricity has a remarkable effect on the discharge characteristics of insulator and has little influence on the discharge characteristics of air gap.The flashover of insulator strings occurs along the insulator surface and air gaps,and the sand dust deposited on the insulator surface may affect the flashover characteristics of insulator strings.This paper studies the flashover characteristics of flat plate model under DC voltage in wind-sand condition.The experimental results show that under positive polarity voltage,the flashover voltage of the flat plate model has a maximum value,while under negative polarity voltage,the flashover voltage of the flat plate model has a minimum value with a certain degree of sand dust deposition.The wind or sand in sand-dust weather has an important effect on the flashover characteristics of the flat plate model.In certain variation range of electric charge,electric charge of sand dust has little effect on the flashover voltage of flat plate model under DC voltage.The deposition of sand has significant influence on the flashover process of flat plate model,which is related to the deposition density and moisture content of sand particle.
基金supported by the Natural Science Foundation of Qinghai Province(No.2016-ZJ-925Q)Chinese National Programs for Fundamental Research(No.2011CB209400)
文摘Due to the complexity of the valve side winding voltage of the converter transformer,the insulation characteristics of the oil-impregnated pressboard(OIP)of the converter transformer are different from those of the traditional AC transformer.The study on effect of temperature on the creeping discharge characteristics of OIP under combined AC-DC voltage is seriously inadequate.Therefore,this paper investigates the characteristics of OIP creepage discharge under combined AC-DC voltage and discusses the influence of temperature on creepage discharge characteristics under different temperatures from 70℃to 110℃.The experimental results show that the partial discharge inception voltage and flashover voltage decrease with increasing temperature.The times of low amplitude discharge(LAD)decrease and amplitude of LAD increases.Simultaneously,the times of high amplitude discharge(HAD)gradually in crease at each stage of creepage discharge with higher temperature.The analysis indicates that the charge carriers easily accumulate and quickly migrate directional movement along the electric field ahead of discharging.The residual charge carriers are more easily dissipated after discharging.The'hump'region of LAD moves to the direction of higher discharge magnitude.The interval time between two continuous discharges is shortened obviously.The concentration of HAD accelerates the development of OIP insulation creepage discharge.The temperature had an accelerating effect on the development of discharge in the OIP under applying voltage.
文摘This paper describes an experimental and theoretical study on an extraction phenomenon of liquids occurring at an air gap between the liquid surface and the electrode by applying a direct current (DC) or low-frequency alternating current (AC) voltage. Three liquids with a different physical property;2,3-dihydrodecafluoropenten, palm fatty acid ester oil and crude rapeseed oil are used as working liquids. The electrode configuration is the sphere or plane (high voltage electrode) to grounded plane electrode. The grounded plane electrode is fixed to the bottom of the test vessel with working liquid and the high voltage electrode is installed in an air above the liquid surface against the grounded plane electrode. The liquid surface swells towards the high voltage electrode by the increase of voltage and the liquid is extracted in a short time, thereafter the air gap between the liquid surface and the high voltage electrode is bridged at a thick liquid column. Such the liquid behavior displays unique features with voltage polarity effect for each working liquid. The relationship between the applied voltage, current variation, height of swollen liquid, force pulling liquid and dynamic feature of liquid is examined experimentally. The liquid behavior is considered theoretically based on experimental observations.
文摘针对电动汽车充电电源额外热量产生影响电池使用寿命的问题,提出一种无电解电容隔离式单级双向AC/DC变换器。该变换器能有效阻止低频功率纹波注入电池单元,减少了额外热量的产生;同时电解电容的消除也大大提高了系统的可靠性。控制策略方面,提出的一种四相控制器,不仅能使所有开关管实现零电压开关(Zero Voltage Switch,ZVS),并在导通损耗进行了性能优化。最后,通过PSIM仿真软件和实验样机,验证了理论分析的正确性和可行性。