A crowbar impulse current circuit for testing the switch-type surge protective device (SPD) is presented. The crowbar circuit consists of a computer control circuit, a trigger voltage pulse generator, a main dischar...A crowbar impulse current circuit for testing the switch-type surge protective device (SPD) is presented. The crowbar circuit consists of a computer control circuit, a trigger voltage pulse generator, a main discharging switch, and a crowbar pseudospark switch. The active trigger technology was studied in the crowbar impulse current circuit. The circuit monitors the main discharging current and generates a trigger signal at a proper time for the crowbar pseudospark switch operation. The trigger characteristics of the main discharge switch and the crowbar pseu- dospark switch were investigated. By monitoring the preset applied capacitor voltage, the gap distance of the main discharging switch could be adjusted to ensure a discharging delay time less than 2 μs. Equipped with a surface ttashover trigger device made of high relative perimittivity dielectric material BaTiO3 (εr = 3460), the discharge delay time of the crowbar pseudospark switch is less than 85 ns, and the minimum operating voltage is less than 1% of its self-breakdown voltage. With a storage capacitor of 9 μF , an inductor of 18 μH and a crowbar pseudospark switch, a load of 30 mΩ and an applied capacitor voltage of 40 kV, an impulse current waveform of maximum 25 kA was generated with a rise time and time to half peak value of 17.2 μs and 336μs respectively.展开更多
Generally,the flow of a lightning impulse current from a grounding electrode into ground is a very complicated process determined by many factors.In order to analyze the mechanism of the impulse current dissipating in...Generally,the flow of a lightning impulse current from a grounding electrode into ground is a very complicated process determined by many factors.In order to analyze the mechanism of the impulse current dissipating in the earth from grounding electrode,the experiments that had been carried out by other authors almost used a single horizontal grounding wire or vertical grounding rod for sake of simplicity.However,in practical conditions,most of the grounding systems are constructed of grounding electrodes with branches in different directions.In this study,basing on the principle of dimensional similarity,impulse simulation experiments are performed on the common ground electrodes with conductor branches.This paper focuses on analyzing the impulse current dispersal regularity of different branches when injecting at one point.Comparing with the leakage current distribution of a single ground electrode,it is found that the leakage currents along the branches increase with the distance to the current feed point,and the more conductors near the injection point,the more uneven the leakage current distribution is.This work indicates that shielding effect should be taken into account when analyzing the impulse characteristics of grounding electrodes.展开更多
Based on the method of controlling welding stress with trailing, the electromagnetic force in coil-sheet system was simulated with finite element software ANSYS. The effect of parameters of coil on the electromagnetic...Based on the method of controlling welding stress with trailing, the electromagnetic force in coil-sheet system was simulated with finite element software ANSYS. The effect of parameters of coil on the electromagnetic force density fy was analyzed. The results show that the maximum electromagnetic force density fy, max in sheet appears in the position near the inner radius of single-turn coil. The position is independent of section shape of coil. fy, max for flat coil is larger than that for long coil and the coil with wedge shape section, while section areas of all coils are equal to each other. The effect of turn number of multiple-turn coil on fy is dependent on the loop resistance in circuit. The kind of coil with more turns and larger inductance is commended while there is larger loop resistance in circuit. fy increases in a certain magnitude while a magnetic core is located in coil. However, the magnitude of fy is limited by saturating magnetic flux of the core.展开更多
The ablation tests on coated and uncoated Q235 B steel sheets were conducted under 30/80 μs impulse current simulating the lightning first return stroke current, aimed at further understanding the ablation characteri...The ablation tests on coated and uncoated Q235 B steel sheets were conducted under 30/80 μs impulse current simulating the lightning first return stroke current, aimed at further understanding the ablation characteristics of steel and investigating the impact of anti-corrosion coating on these characteristics. Ablation characteristics were investigated through the macroscopic morphology and x-ray diffraction patterns on the surface of damaged zones, the microstructure and micro Vickers hardness on the cross-section of damaged zones, and the maximum rear-face temperature of sample sheets. It can be concluded that the ablation areas of uncoated sheet consist of the melted layer and the heat-affect layer. These ablation areas include not only the area ablated directly by the arc root, of which the depth is deeper, but also the area forming due to the splashing of molten steel, of which the depth is shallower and decreases when the area’s distance from the arc attachment point increases. For coated sheet, coating materials have decomposed and evaporated forming an ablation pit on the sheet surface, in which the steel surface is exposed, and zinc filler of coating primer has infused into the exposed surface. The ablation diameter of uncoated sheet relates to the amplitude of the 30/80 μs impulse current in quadratic function, while for coated sheet, the relation is linear. In general, under the 30/80 μs impulse current, the coating can decrease the energy injected from the arc to the steel sheet and reduce the melting and splashing of steel. As a result, the ablation severity of uncoated sheet is severer than that of coated sheet.展开更多
A non-sputtering discharge is utilized to verify the effect of replacement of gas ions by metallic ions and consequent decrease in the secondary electron emission coefficient in the discharge current curves in high-po...A non-sputtering discharge is utilized to verify the effect of replacement of gas ions by metallic ions and consequent decrease in the secondary electron emission coefficient in the discharge current curves in high-power impulse magnetron sputtering (HiPIMS). In the non-sputtering discharge involving hydrogen, replacement of ions is avoided while the rarefaction still contributes. The initial peak and ensuing decay disappear and all the discharge current curves show a similar feature as the HiPIMS discharge of materials with low sputtering yields such as carbon. The results demonstrate the key effect of ion replacement during sputtering.展开更多
More and more applications of ZnO arrester in electrical system experienced more problems.One thing,that is still under some investigation,is the effect of multiple lightning strike to the performance of ZnO arrester....More and more applications of ZnO arrester in electrical system experienced more problems.One thing,that is still under some investigation,is the effect of multiple lightning strike to the performance of ZnO arrester.As we know,the design of ZnO arrester for transmission system and for distribution system differs in the point of view of the number of ZnO blocks.Transmission system,due to its higher nominal voltage than distribution system,has more numbers of ZnO blocks inside an arrester tube.In term of the current rating of an arrester,it is found that there is some different value of the current rating.The current rating of an arrester installed closer to electrical substation is higher than that of some further away from the substation.To the respond of a lightning impulse strike,the arrester will let a high value of impulse current flowing.It tends to heat the ZnO material of the arrester.If the number of impulse strike is quite high then it may give the effect to the change of the arrester performance.This condition will endanger the equipment that is protected by the arrester from lightning strikes.During this research,the scope of work is limited to making an impulse current generator toward to one having 8/20 μs wave-shape.This kind of impulse current wave-shape is the one that is used for studying the performance of ZnO block.The effect of the inductance and capacitance of the impulse current generator were also studied.A 10 fused cut out was blown by an impulse having 10321 A of 17.8/37.8 μs.A ZnO arrester block brokendown/allowed large value of current :10982 A flowing under the voltage of 10.5展开更多
The properties and structure of electrodeposited RE (CeO2)-Ni-W-P-SiC composite coating were investigated. The results show that the hardness and electrodepositing speed of composite coatings obtained at an impulse cu...The properties and structure of electrodeposited RE (CeO2)-Ni-W-P-SiC composite coating were investigated. The results show that the hardness and electrodepositing speed of composite coatings obtained at an impulse current are higher than those at a direct current. The hardness and wear resistance of the coating are obviously increased by adding RE and SiC. The hardness of the coating increases with the increase of treatment temperature and current density, and reaches the optimum value at 400 ℃ and at 10 A/dm2, respectively. The optimum operation parameters of electrodeposition of the composite coating are as follows: pH value is 4.5, bath temperature is 65 ℃ , and current density is 10 A/dm2.展开更多
With the widespread application of power electronic equipment in the power grid,the harmonic problem of the power grid becomes more pronounced,reducing the efficiency of power production,transmission,and utilization,a...With the widespread application of power electronic equipment in the power grid,the harmonic problem of the power grid becomes more pronounced,reducing the efficiency of power production,transmission,and utilization,and interfering with the normal operation of the power grid.Based on the requirements of harmonic suppression and power system protection,a shunt active power filter(SAPF)is proposed as an effective harmonic suppression method.However,there are problems with impulse current and impulse voltage in the starting process of SAPF.Impulse current and impulse voltage cause the power grid and switchgear to bear greater current stress and voltage stress,which seriously affect the security and reliability of the power grid and may damage the switchgear.To effectively solve the problem of impulse current and impulse voltage,the starting process of SAPF is divided into the uncontrolled rectification stage and the transition stage.The mathematical model of the DC side of APF is established.The causes of impulse current and impulse voltage in the uncontrolled rectifier and transition phases are analyzed.By introducing voltage square,a new starting impulse suppression strategy of active power filter based on the slow rising curve is proposed,fundamentally solving the problems of impulse current and impulse voltage.Simulation results verify the effectiveness and feasibility of this method.展开更多
针对极端灾害天气下配电网的故障恢复问题,计及极端灾害的时空演变特性,提出了一种利用移动储能(mobile energy storage system,MESS)的灵活性主动参与抑制合环冲击电流,辅助配电网故障恢复的策略。首先,建立了暴风雨等不同气象灾害条...针对极端灾害天气下配电网的故障恢复问题,计及极端灾害的时空演变特性,提出了一种利用移动储能(mobile energy storage system,MESS)的灵活性主动参与抑制合环冲击电流,辅助配电网故障恢复的策略。首先,建立了暴风雨等不同气象灾害条件下配电线路的故障率统计模型。其次,将复杂交通网与配电网进行耦合,建立了以最小化MESS调度时空成本的上层预布局模型。然后,分析了MESS出力对冲击电流的影响,以抑制合环冲击电流、最大化负荷恢复率和最小化MESS调度成本为目标,构建了MESS参与网络重构的下层调度模型。最后,在改进的IEEE 123节点系统中进行测试,验证了MESS对配网故障恢复安全性的提升效果。结果表明,采用MESS主动参与调控能够有效应对移动的极端气象灾害引发的配电网动态故障恢复问题,并抑制合解环过程中电流的波动,提升网络重构方案的可行性和增强配电网的韧性。展开更多
目的探究踝关节跖背屈疲劳任务中高精度经颅直流电刺激(high-definition transcranial direct current stimulation,HD-tDCS)对H-反射和M-波的调控效果,为HD-tDCS减轻神经肌肉疲劳的实际应用提供方向。方法招募20名健康青年男性受试者,...目的探究踝关节跖背屈疲劳任务中高精度经颅直流电刺激(high-definition transcranial direct current stimulation,HD-tDCS)对H-反射和M-波的调控效果,为HD-tDCS减轻神经肌肉疲劳的实际应用提供方向。方法招募20名健康青年男性受试者,随机分为真刺激组和假刺激组各10名。对受试者采取连续5 d的单盲HD-tDCS干预(时间20 min;强度2 mA;靶点Cz),干预前1天采集受试者安静条件下的H-反射和M-波,跖屈肌最大自主收缩(maximal voluntary isometric contraction,MVIC)时的M-波,跖屈肌和背屈肌MVIC力矩,并进行一次踝关节跖背屈运动性疲劳任务,以确定受试者达到该任务疲劳的时间。干预后1天进行与第1次疲劳任务相同的运动时间,并进行后测的数据采集。采用重复测量双因素(刺激方案×疲劳前后)方差分析其自变量对受试者肌肉力学特性、α运动神经元传导特性各指标的影响。结果相较于疲劳前,两组疲劳后的自主激活值(voluntary activation,VA)、H-反射最大值(maximal H-reflex,H_(max))、M-波最大值(maximal M-wave,Mmax)、跖屈肌和背屈肌MVIC力矩均显著降低(P<0.05),但相比于真刺激组,假刺激组的VA和背屈肌MVIC力矩下降更为显著(P<0.05)。结论连续5 d的HD-tDCS干预有助于提高脊髓节段α运动神经元的活性,且能抑制跖背屈疲劳诱发的外周“神经-肌肉”接头处信息传递能力的下降。展开更多
文摘A crowbar impulse current circuit for testing the switch-type surge protective device (SPD) is presented. The crowbar circuit consists of a computer control circuit, a trigger voltage pulse generator, a main discharging switch, and a crowbar pseudospark switch. The active trigger technology was studied in the crowbar impulse current circuit. The circuit monitors the main discharging current and generates a trigger signal at a proper time for the crowbar pseudospark switch operation. The trigger characteristics of the main discharge switch and the crowbar pseu- dospark switch were investigated. By monitoring the preset applied capacitor voltage, the gap distance of the main discharging switch could be adjusted to ensure a discharging delay time less than 2 μs. Equipped with a surface ttashover trigger device made of high relative perimittivity dielectric material BaTiO3 (εr = 3460), the discharge delay time of the crowbar pseudospark switch is less than 85 ns, and the minimum operating voltage is less than 1% of its self-breakdown voltage. With a storage capacitor of 9 μF , an inductor of 18 μH and a crowbar pseudospark switch, a load of 30 mΩ and an applied capacitor voltage of 40 kV, an impulse current waveform of maximum 25 kA was generated with a rise time and time to half peak value of 17.2 μs and 336μs respectively.
基金Project Supported by National Natural Science Foundation of China(50707036), Key Project of the National Eleventh-five Year Research Program of China ( 2006BAA02A18).
文摘Generally,the flow of a lightning impulse current from a grounding electrode into ground is a very complicated process determined by many factors.In order to analyze the mechanism of the impulse current dissipating in the earth from grounding electrode,the experiments that had been carried out by other authors almost used a single horizontal grounding wire or vertical grounding rod for sake of simplicity.However,in practical conditions,most of the grounding systems are constructed of grounding electrodes with branches in different directions.In this study,basing on the principle of dimensional similarity,impulse simulation experiments are performed on the common ground electrodes with conductor branches.This paper focuses on analyzing the impulse current dispersal regularity of different branches when injecting at one point.Comparing with the leakage current distribution of a single ground electrode,it is found that the leakage currents along the branches increase with the distance to the current feed point,and the more conductors near the injection point,the more uneven the leakage current distribution is.This work indicates that shielding effect should be taken into account when analyzing the impulse characteristics of grounding electrodes.
基金Project(56605011) supported by the National Natural Science Foundation of China
文摘Based on the method of controlling welding stress with trailing, the electromagnetic force in coil-sheet system was simulated with finite element software ANSYS. The effect of parameters of coil on the electromagnetic force density fy was analyzed. The results show that the maximum electromagnetic force density fy, max in sheet appears in the position near the inner radius of single-turn coil. The position is independent of section shape of coil. fy, max for flat coil is larger than that for long coil and the coil with wedge shape section, while section areas of all coils are equal to each other. The effect of turn number of multiple-turn coil on fy is dependent on the loop resistance in circuit. The kind of coil with more turns and larger inductance is commended while there is larger loop resistance in circuit. fy increases in a certain magnitude while a magnetic core is located in coil. However, the magnitude of fy is limited by saturating magnetic flux of the core.
基金supported by National Natural Science Foundation of China (No. 51577117)
文摘The ablation tests on coated and uncoated Q235 B steel sheets were conducted under 30/80 μs impulse current simulating the lightning first return stroke current, aimed at further understanding the ablation characteristics of steel and investigating the impact of anti-corrosion coating on these characteristics. Ablation characteristics were investigated through the macroscopic morphology and x-ray diffraction patterns on the surface of damaged zones, the microstructure and micro Vickers hardness on the cross-section of damaged zones, and the maximum rear-face temperature of sample sheets. It can be concluded that the ablation areas of uncoated sheet consist of the melted layer and the heat-affect layer. These ablation areas include not only the area ablated directly by the arc root, of which the depth is deeper, but also the area forming due to the splashing of molten steel, of which the depth is shallower and decreases when the area’s distance from the arc attachment point increases. For coated sheet, coating materials have decomposed and evaporated forming an ablation pit on the sheet surface, in which the steel surface is exposed, and zinc filler of coating primer has infused into the exposed surface. The ablation diameter of uncoated sheet relates to the amplitude of the 30/80 μs impulse current in quadratic function, while for coated sheet, the relation is linear. In general, under the 30/80 μs impulse current, the coating can decrease the energy injected from the arc to the steel sheet and reduce the melting and splashing of steel. As a result, the ablation severity of uncoated sheet is severer than that of coated sheet.
基金Supported by the National Natural Science Foundation of China under Grant Nos 51301004 and U1330110the Guangdong Innovative and Entrepreneurial Research Team Program under Grant No 2013N080+1 种基金the Shenzhen Science and Technology Research Grant under Grant Nos JCYJ20140903102215536 and JCYJ20150828093127698the City University of Hong Kong Applied Research Grant under Grant No 9667104
文摘A non-sputtering discharge is utilized to verify the effect of replacement of gas ions by metallic ions and consequent decrease in the secondary electron emission coefficient in the discharge current curves in high-power impulse magnetron sputtering (HiPIMS). In the non-sputtering discharge involving hydrogen, replacement of ions is avoided while the rarefaction still contributes. The initial peak and ensuing decay disappear and all the discharge current curves show a similar feature as the HiPIMS discharge of materials with low sputtering yields such as carbon. The results demonstrate the key effect of ion replacement during sputtering.
文摘More and more applications of ZnO arrester in electrical system experienced more problems.One thing,that is still under some investigation,is the effect of multiple lightning strike to the performance of ZnO arrester.As we know,the design of ZnO arrester for transmission system and for distribution system differs in the point of view of the number of ZnO blocks.Transmission system,due to its higher nominal voltage than distribution system,has more numbers of ZnO blocks inside an arrester tube.In term of the current rating of an arrester,it is found that there is some different value of the current rating.The current rating of an arrester installed closer to electrical substation is higher than that of some further away from the substation.To the respond of a lightning impulse strike,the arrester will let a high value of impulse current flowing.It tends to heat the ZnO material of the arrester.If the number of impulse strike is quite high then it may give the effect to the change of the arrester performance.This condition will endanger the equipment that is protected by the arrester from lightning strikes.During this research,the scope of work is limited to making an impulse current generator toward to one having 8/20 μs wave-shape.This kind of impulse current wave-shape is the one that is used for studying the performance of ZnO block.The effect of the inductance and capacitance of the impulse current generator were also studied.A 10 fused cut out was blown by an impulse having 10321 A of 17.8/37.8 μs.A ZnO arrester block brokendown/allowed large value of current :10982 A flowing under the voltage of 10.5
文摘The properties and structure of electrodeposited RE (CeO2)-Ni-W-P-SiC composite coating were investigated. The results show that the hardness and electrodepositing speed of composite coatings obtained at an impulse current are higher than those at a direct current. The hardness and wear resistance of the coating are obviously increased by adding RE and SiC. The hardness of the coating increases with the increase of treatment temperature and current density, and reaches the optimum value at 400 ℃ and at 10 A/dm2, respectively. The optimum operation parameters of electrodeposition of the composite coating are as follows: pH value is 4.5, bath temperature is 65 ℃ , and current density is 10 A/dm2.
基金supported by the National Natural Science Foundation of China under Grant 61863023.
文摘With the widespread application of power electronic equipment in the power grid,the harmonic problem of the power grid becomes more pronounced,reducing the efficiency of power production,transmission,and utilization,and interfering with the normal operation of the power grid.Based on the requirements of harmonic suppression and power system protection,a shunt active power filter(SAPF)is proposed as an effective harmonic suppression method.However,there are problems with impulse current and impulse voltage in the starting process of SAPF.Impulse current and impulse voltage cause the power grid and switchgear to bear greater current stress and voltage stress,which seriously affect the security and reliability of the power grid and may damage the switchgear.To effectively solve the problem of impulse current and impulse voltage,the starting process of SAPF is divided into the uncontrolled rectification stage and the transition stage.The mathematical model of the DC side of APF is established.The causes of impulse current and impulse voltage in the uncontrolled rectifier and transition phases are analyzed.By introducing voltage square,a new starting impulse suppression strategy of active power filter based on the slow rising curve is proposed,fundamentally solving the problems of impulse current and impulse voltage.Simulation results verify the effectiveness and feasibility of this method.
文摘针对极端灾害天气下配电网的故障恢复问题,计及极端灾害的时空演变特性,提出了一种利用移动储能(mobile energy storage system,MESS)的灵活性主动参与抑制合环冲击电流,辅助配电网故障恢复的策略。首先,建立了暴风雨等不同气象灾害条件下配电线路的故障率统计模型。其次,将复杂交通网与配电网进行耦合,建立了以最小化MESS调度时空成本的上层预布局模型。然后,分析了MESS出力对冲击电流的影响,以抑制合环冲击电流、最大化负荷恢复率和最小化MESS调度成本为目标,构建了MESS参与网络重构的下层调度模型。最后,在改进的IEEE 123节点系统中进行测试,验证了MESS对配网故障恢复安全性的提升效果。结果表明,采用MESS主动参与调控能够有效应对移动的极端气象灾害引发的配电网动态故障恢复问题,并抑制合解环过程中电流的波动,提升网络重构方案的可行性和增强配电网的韧性。