In urban power networks,a common practice is to bond numerous high-voltage cable circuits to a single grounding grid located in underground tunnels,primarily for reasons of installation convenience.In these situations...In urban power networks,a common practice is to bond numerous high-voltage cable circuits to a single grounding grid located in underground tunnels,primarily for reasons of installation convenience.In these situations,excessively high levels of sheath currents were often detected during routine inspections,but no electrical faults were found to be responsible.Previous publications ignored the currents flowing through the shared grounding points into the closed sheath loops of different circuits.In this paper,a mathematical model is established for the current circulating among sheath loops of different circuits,and the factors influencing the circulating current were analysed.The abnormal excessive sheath current is demonstrated to be an increase in the circulating current due to the combined effect of electromagnetic coupling and the shared grounding grid.The circulating current depends on the induced voltages which,in turn,depends on the cable layouts and load currents.The effects of these factors are evaluated in various scenarios.The increase of the circulating current is verified in a field case where four electrically healthy cable circuits sharing the same grounding points were found to have abnormal excessive sheath currents.展开更多
The current sheath velocity in 0.25 Torr gas pressure of Filippov type plasma focus is studied experimentally. By using two tridimensional magnetic probes on top of the anode surface, the current sheath velocity is me...The current sheath velocity in 0.25 Torr gas pressure of Filippov type plasma focus is studied experimentally. By using two tridimensional magnetic probes on top of the anode surface, the current sheath velocity is measured for argon, oxygen and nitrogen. Additionally, the effect of charging voltage on the current sheath velocity is studied in both axial and radial phases. We found that, the maximum current sheath velocities at both radial and axial phases are respectively 4.33 ± 0.28 （cm/μs） and 3.92 ± 0.75 （cm/μs） with argon as the working gas at 17 kV. Also, the minimum values of current sheath velocity are 1.48 ± 0.15 （cm/μs） at the radial phase and 1.14 ± 0.09 （cm/μs） at the axial phase with oxygen at 12 kV. The current sheath velocity at the radial phase is higher than that at the axial phase for all gases and voltages. In this study, variation of the full width half maximum （FWHM） of magnetic probe signals with voltage is investigated for different gases at radial and axial phases.展开更多
In this paper experiments and theoretical treatments [1] on 1.5 KJ coaxial plasma discharge device have been carried out to show, plasma current sheath, PCS, motion in coaxial plasma discharge by studying: the effect ...In this paper experiments and theoretical treatments [1] on 1.5 KJ coaxial plasma discharge device have been carried out to show, plasma current sheath, PCS, motion in coaxial plasma discharge by studying: the effect of nitrogen gas pressure in the range from 1 to 2.2 Torr and the axial position of PCS along the coaxial electrodes on the modification factor, actual drive parameter, PCS curvature and shape (thickness). Also the dynamics of PCS along the coaxial electrodes due to the combination effect of induced azimuthal and axial magnetic fields induction has been detected experimentally by using a magnetic probe technique.展开更多
In this paper, we adopt the modified Morozov secondary electron emission model to investigate the influence of the characteristic of a space-charge-saturated sheath near the insulated wall of the Hall thruster on the ...In this paper, we adopt the modified Morozov secondary electron emission model to investigate the influence of the characteristic of a space-charge-saturated sheath near the insulated wall of the Hall thruster on the near-wall conductivity, by the method of two-dimensional （2D） particle simulation （2Dq-3V）. The results show that due to the sharp increase of collision frequency between the electrons and the wall under the space-charge-saturated sheath, the near-wall transport current under this sheath is remarkably higher than that under a classical sheath, and equals the near-wall transport current under a spatially oscillating sheath in order of magnitude. However, the transport currents under a space-charge-saturated sheath and a spatially oscillating sheath are different in mechanism, causing different current density distributions under the above two sheaths, and a great influence of channel width on the near-wall transport current under a space-charge-saturated sheath.展开更多
The process to obtain high T(110K)phase quickly,the microstructure and properties of Ag-sheathed Bi(Pb)-Sr-Ca-Cu-O superconductor tapes have been studied.It was found that the formation time of the high T_c phase was ...The process to obtain high T(110K)phase quickly,the microstructure and properties of Ag-sheathed Bi(Pb)-Sr-Ca-Cu-O superconductor tapes have been studied.It was found that the formation time of the high T_c phase was greatly shortened by the addition of more Ca and Cu to the nominal composition of Bi(Pb):Sr :Ca:Cu=2:2:2:3 and the adoption of appropriate sintering temperature and cooling rate. Superconductor powder with predominant high T,phase was prepared after a 840 C/50 h treatment.The J of the Ag-sheathed tapes and the magnetic field dependence of Jwere obviously improved by repeatedly pres- sing and sintering.The maximum transport current density at 77K in a zero magnetic field was 12,200 A/cm^2. The magnetic dependence of Jwas summarized as follows:6.450 A/cm^(2)(B⊥1.B∥S.0.1T)1,810 A/cm^2 (B⊥1.B∥S,1T),390 A/cm^2(B⊥1.B∥S,2T)(B:magnetic field.1:electric current.S:surface of tapes).The improvement of Jwas attributed to the formation of the plate-like structure with homogeneous composition distribution and the strong c-axis texture.展开更多
通过监测护层电流可及早发现高压电力电缆线路的潜在故障,有效避免非计划性停电。为此,提出了1种可用于诊断故障与非故障情况下3相交叉互联高压电力电缆中护层电流的研究方案。通过建立数学模型详细分析了2种典型的电缆故障,并基于1条...通过监测护层电流可及早发现高压电力电缆线路的潜在故障,有效避免非计划性停电。为此,提出了1种可用于诊断故障与非故障情况下3相交叉互联高压电力电缆中护层电流的研究方案。通过建立数学模型详细分析了2种典型的电缆故障,并基于1条线路长度为1.5 km、电压等级为110 k V的隧道电缆的仿真计算,提出了1套适用于12种电缆故障的诊断及定位标准。仿真分析结果显示:当电缆接地系统中存在开路故障时,故障回路中的护层电流会降低;而当电缆交叉互联箱进水或电缆接头内环氧预制件击穿时,故障护层回路中将产生高于正常水平的护层电流值。基于故障仿真,所提出的故障诊断标准可准确识别并定位指定的3种电缆故障:接头松动导致护层开路、交叉互联箱进水和接头内环氧预制件击穿。仿真表明地电阻的大幅度变化会导致诊断标准发生变化。展开更多
基金Project of State Grid Corporation of China,Grant/Award Number:5700-202118195A-0-0-00。
文摘In urban power networks,a common practice is to bond numerous high-voltage cable circuits to a single grounding grid located in underground tunnels,primarily for reasons of installation convenience.In these situations,excessively high levels of sheath currents were often detected during routine inspections,but no electrical faults were found to be responsible.Previous publications ignored the currents flowing through the shared grounding points into the closed sheath loops of different circuits.In this paper,a mathematical model is established for the current circulating among sheath loops of different circuits,and the factors influencing the circulating current were analysed.The abnormal excessive sheath current is demonstrated to be an increase in the circulating current due to the combined effect of electromagnetic coupling and the shared grounding grid.The circulating current depends on the induced voltages which,in turn,depends on the cable layouts and load currents.The effects of these factors are evaluated in various scenarios.The increase of the circulating current is verified in a field case where four electrically healthy cable circuits sharing the same grounding points were found to have abnormal excessive sheath currents.
文摘The current sheath velocity in 0.25 Torr gas pressure of Filippov type plasma focus is studied experimentally. By using two tridimensional magnetic probes on top of the anode surface, the current sheath velocity is measured for argon, oxygen and nitrogen. Additionally, the effect of charging voltage on the current sheath velocity is studied in both axial and radial phases. We found that, the maximum current sheath velocities at both radial and axial phases are respectively 4.33 ± 0.28 （cm/μs） and 3.92 ± 0.75 （cm/μs） with argon as the working gas at 17 kV. Also, the minimum values of current sheath velocity are 1.48 ± 0.15 （cm/μs） at the radial phase and 1.14 ± 0.09 （cm/μs） at the axial phase with oxygen at 12 kV. The current sheath velocity at the radial phase is higher than that at the axial phase for all gases and voltages. In this study, variation of the full width half maximum （FWHM） of magnetic probe signals with voltage is investigated for different gases at radial and axial phases.
文摘In this paper experiments and theoretical treatments [1] on 1.5 KJ coaxial plasma discharge device have been carried out to show, plasma current sheath, PCS, motion in coaxial plasma discharge by studying: the effect of nitrogen gas pressure in the range from 1 to 2.2 Torr and the axial position of PCS along the coaxial electrodes on the modification factor, actual drive parameter, PCS curvature and shape (thickness). Also the dynamics of PCS along the coaxial electrodes due to the combination effect of induced azimuthal and axial magnetic fields induction has been detected experimentally by using a magnetic probe technique.
基金supported by the Fundamental Research Funds for the Central Universities (Grant No. HEUCF100212)the National Natural Science Foundation of China (Grant Nos. 51007013,10875024,and 10975026)
文摘In this paper, we adopt the modified Morozov secondary electron emission model to investigate the influence of the characteristic of a space-charge-saturated sheath near the insulated wall of the Hall thruster on the near-wall conductivity, by the method of two-dimensional （2D） particle simulation （2Dq-3V）. The results show that due to the sharp increase of collision frequency between the electrons and the wall under the space-charge-saturated sheath, the near-wall transport current under this sheath is remarkably higher than that under a classical sheath, and equals the near-wall transport current under a spatially oscillating sheath in order of magnitude. However, the transport currents under a space-charge-saturated sheath and a spatially oscillating sheath are different in mechanism, causing different current density distributions under the above two sheaths, and a great influence of channel width on the near-wall transport current under a space-charge-saturated sheath.
文摘The process to obtain high T(110K)phase quickly,the microstructure and properties of Ag-sheathed Bi(Pb)-Sr-Ca-Cu-O superconductor tapes have been studied.It was found that the formation time of the high T_c phase was greatly shortened by the addition of more Ca and Cu to the nominal composition of Bi(Pb):Sr :Ca:Cu=2:2:2:3 and the adoption of appropriate sintering temperature and cooling rate. Superconductor powder with predominant high T,phase was prepared after a 840 C/50 h treatment.The J of the Ag-sheathed tapes and the magnetic field dependence of Jwere obviously improved by repeatedly pres- sing and sintering.The maximum transport current density at 77K in a zero magnetic field was 12,200 A/cm^2. The magnetic dependence of Jwas summarized as follows:6.450 A/cm^(2)(B⊥1.B∥S.0.1T)1,810 A/cm^2 (B⊥1.B∥S,1T),390 A/cm^2(B⊥1.B∥S,2T)(B:magnetic field.1:electric current.S:surface of tapes).The improvement of Jwas attributed to the formation of the plate-like structure with homogeneous composition distribution and the strong c-axis texture.
文摘通过监测护层电流可及早发现高压电力电缆线路的潜在故障,有效避免非计划性停电。为此,提出了1种可用于诊断故障与非故障情况下3相交叉互联高压电力电缆中护层电流的研究方案。通过建立数学模型详细分析了2种典型的电缆故障,并基于1条线路长度为1.5 km、电压等级为110 k V的隧道电缆的仿真计算,提出了1套适用于12种电缆故障的诊断及定位标准。仿真分析结果显示:当电缆接地系统中存在开路故障时,故障回路中的护层电流会降低;而当电缆交叉互联箱进水或电缆接头内环氧预制件击穿时,故障护层回路中将产生高于正常水平的护层电流值。基于故障仿真,所提出的故障诊断标准可准确识别并定位指定的3种电缆故障:接头松动导致护层开路、交叉互联箱进水和接头内环氧预制件击穿。仿真表明地电阻的大幅度变化会导致诊断标准发生变化。
