Hugoniot relations of a two-dimensional axial shock with current and magnetic field in a cylindrical shock tube were investigated by a numerical method. The radial profiles of the magnetic field, electric current, pre...Hugoniot relations of a two-dimensional axial shock with current and magnetic field in a cylindrical shock tube were investigated by a numerical method. The radial profiles of the magnetic field, electric current, pressures, flow velocities and temperatures between the up- and down-stream radial force-balanced plasma of the shock were revealed by numerical analysis. It is clearly found that the axial shock can lead to two effects： one is an inverse skin effect （i.e., the current density rises towards the center of the conductor）, the another is a reversed current effect which occurs near the edge and about a half radius. It is also found that the radial gradient of pressure, density and temperature all become very large near the center due to the axial shock.展开更多
Interplanetary shocks or solar wind pressure pulses have prompted impacts on Earth's magnetospheric and ionospheric environment, especially in causing dynamic changes to the bright aurora in the polar ionosphere. ...Interplanetary shocks or solar wind pressure pulses have prompted impacts on Earth's magnetospheric and ionospheric environment, especially in causing dynamic changes to the bright aurora in the polar ionosphere. The auroral phenomenon associated with shock impingements, referred to as shock aurora, exhibits distinct signatures differing from other geophysical features on the dayside polar ionosphere. Shock aurora provides a direct manifestation of the solar wind–magnetosphere–ionosphere interaction. Imagers onboard satellites can obtain the associated large-scale auroral characteristics during shock impingement on the magnetopause. Therefore, auroral data from satellites are very useful for surveying the comprehensive features of shock aurora and their general evolution. Nonetheless, the ground-based high temporal-spatial resolution all-sky imagers installed at scientific stations play an essential role in revealing medium-and small-scale characteristics of shock aurora. Here, we focus on shock aurora imaging signatures measured by imagers onboard satellites and ground-based all-sky imagers.展开更多
全桥L-LLC谐振变换器在启动时存在谐振电流冲击大的现象,通常采用降频方式限制电流尖峰,从特定的高频逐渐降低到谐振频率,而由于谐振变换器的复杂动态特性,很难确定关键参数。因此,基于状态平面分析,提出了适用于全桥L-LLC谐振变换器的...全桥L-LLC谐振变换器在启动时存在谐振电流冲击大的现象,通常采用降频方式限制电流尖峰,从特定的高频逐渐降低到谐振频率,而由于谐振变换器的复杂动态特性,很难确定关键参数。因此,基于状态平面分析,提出了适用于全桥L-LLC谐振变换器的软启动策略。通过设计限流带确定最佳启动频率以及合理的降频策略,分三阶段将谐振电流限制在限流带内完成软启动。为了验证所提出的软启动策略的可行性,通过MATLAB/Simulink仿真验证,仿真结果表明,所提出的软启动策略不仅有效降低谐振电流过冲,还明显提高了启动速度,并能够保持原边侧开关管的零电压开通(zero voltage switching,ZVS)以及副边侧整流二极管的零电流关断(zero current switching,ZCS)特性。展开更多
文中介绍了一起停电试验发现的220 k V变压器低压绕组变形缺陷,为变压器累积效应的理论研究和变压器故障检测的试验研究提供现场数据诊断案例。试验检修人员首先根据变压器短路阻抗试验和绕组变形试验结果,推断出低压绕组发生不同程度变...文中介绍了一起停电试验发现的220 k V变压器低压绕组变形缺陷,为变压器累积效应的理论研究和变压器故障检测的试验研究提供现场数据诊断案例。试验检修人员首先根据变压器短路阻抗试验和绕组变形试验结果,推断出低压绕组发生不同程度变形;并结合该变压器历年遭受短路冲击后的色谱分析试验结果,综合分析、诊断发生变形的原因,主要由于低压侧短路电流冲击及绕组变形的累积效应。通过返厂解体发现,其低压绕组发生不同程度的变形,并存在过热现象,验证了试验和诊断结果。通过变压器绕组变形试验诊断,有效避免了一起设备潜伏性故障的发生,并给出变压器日常维护检修的注意事项及相关建议。展开更多
基金supported by National Natural Science Foundation of China (No. 10175025)in part by the JSPS-CAS Core-University Program on Plasma and Nuclear Fusion
文摘Hugoniot relations of a two-dimensional axial shock with current and magnetic field in a cylindrical shock tube were investigated by a numerical method. The radial profiles of the magnetic field, electric current, pressures, flow velocities and temperatures between the up- and down-stream radial force-balanced plasma of the shock were revealed by numerical analysis. It is clearly found that the axial shock can lead to two effects： one is an inverse skin effect （i.e., the current density rises towards the center of the conductor）, the another is a reversed current effect which occurs near the edge and about a half radius. It is also found that the radial gradient of pressure, density and temperature all become very large near the center due to the axial shock.
基金supported by the NSFC (Grant nos. 41431072, 41674169, 41474146, and 41831072)the International Collaboration Supporting Project by the Chinese Arctic and Antarctic Administration (Grant no. IC201608)+1 种基金the National Key R&D Program of China (Grant no. 2018YFC1407304)the Chinese Meridian Project
文摘Interplanetary shocks or solar wind pressure pulses have prompted impacts on Earth's magnetospheric and ionospheric environment, especially in causing dynamic changes to the bright aurora in the polar ionosphere. The auroral phenomenon associated with shock impingements, referred to as shock aurora, exhibits distinct signatures differing from other geophysical features on the dayside polar ionosphere. Shock aurora provides a direct manifestation of the solar wind–magnetosphere–ionosphere interaction. Imagers onboard satellites can obtain the associated large-scale auroral characteristics during shock impingement on the magnetopause. Therefore, auroral data from satellites are very useful for surveying the comprehensive features of shock aurora and their general evolution. Nonetheless, the ground-based high temporal-spatial resolution all-sky imagers installed at scientific stations play an essential role in revealing medium-and small-scale characteristics of shock aurora. Here, we focus on shock aurora imaging signatures measured by imagers onboard satellites and ground-based all-sky imagers.
文摘全桥L-LLC谐振变换器在启动时存在谐振电流冲击大的现象,通常采用降频方式限制电流尖峰,从特定的高频逐渐降低到谐振频率,而由于谐振变换器的复杂动态特性,很难确定关键参数。因此,基于状态平面分析,提出了适用于全桥L-LLC谐振变换器的软启动策略。通过设计限流带确定最佳启动频率以及合理的降频策略,分三阶段将谐振电流限制在限流带内完成软启动。为了验证所提出的软启动策略的可行性,通过MATLAB/Simulink仿真验证,仿真结果表明,所提出的软启动策略不仅有效降低谐振电流过冲,还明显提高了启动速度,并能够保持原边侧开关管的零电压开通(zero voltage switching,ZVS)以及副边侧整流二极管的零电流关断(zero current switching,ZCS)特性。
文摘文中介绍了一起停电试验发现的220 k V变压器低压绕组变形缺陷,为变压器累积效应的理论研究和变压器故障检测的试验研究提供现场数据诊断案例。试验检修人员首先根据变压器短路阻抗试验和绕组变形试验结果,推断出低压绕组发生不同程度变形;并结合该变压器历年遭受短路冲击后的色谱分析试验结果,综合分析、诊断发生变形的原因,主要由于低压侧短路电流冲击及绕组变形的累积效应。通过返厂解体发现,其低压绕组发生不同程度的变形,并存在过热现象,验证了试验和诊断结果。通过变压器绕组变形试验诊断,有效避免了一起设备潜伏性故障的发生,并给出变压器日常维护检修的注意事项及相关建议。
