In this paper, a computational model is constructed to investigate the phenomenon of the initial plasma formation and current transfer in the single-wire electrical explosion in a vacuum. The process of the single-wir...In this paper, a computational model is constructed to investigate the phenomenon of the initial plasma formation and current transfer in the single-wire electrical explosion in a vacuum. The process of the single-wire electrical explosion is divided into four stages. Stage Ⅰ： the wire is in solid state. Stage Ⅱ： the melting stage. Stage Ⅲ： the wire melts completely and the initial plasma forms. Stage IV： the core and corona expand separately. The thermodynamic calculation is applied before the wire melts completely in stages Ⅰ and Ⅱ. In stage Ⅲ, a one-dimensional magnetohydrodynamics model comes into play until the instant when the voltage collapse occurs. The temperature, density, and velocity, which are derived from the magnetohydrodynamics calculation, are averaged over the distribution area. The averaged parameters are taken as the initial conditions for stage Ⅳ in which a simplified magnetohydrodynamics model is applied. A wide-range semi-empirical equation of state, which is established based on the Thomas-Fermi-Kirzhnits model, is constructed to describe the phase transition from solid state to plasma state. The initial plasma formation and the phenomenon of current transfer in the electrical explosion of aluminum wire are investigated using the computational model. Experiments of electrical explosion of aluminum wires are carried out to verify this model. Simulation results are also compared with experimental results of the electrical explosion of copper wire.展开更多
The rate and cycling performances of the electrode materials are affected by many factors in a practical complicated electrode process. Learning about the limiting step in a practical electrochemical reaction is very ...The rate and cycling performances of the electrode materials are affected by many factors in a practical complicated electrode process. Learning about the limiting step in a practical electrochemical reaction is very important to effectively improve the electrochemical performances of the electrode materials. Li4Ti5O12, as a zero-strain material, has been considered as a promising anode material for long life Li-ion batteries. In this study, our results show that the Li4Ti5O12 pasted on Cu or graphite felt current collector exhibits unexpectedly higher rate performance than on A1 current collector. For Li4Ti5O12, the electron transfer between current collector and active material is the critical factor that affects its rate and cycling performances.展开更多
A mathematical model is presented to describe transient behavior of heat transfer and fluid flow in stationary pulsed current tungsten inert gas (PC-TIG) weld pool, which considers three kinds of driving, forces for w...A mathematical model is presented to describe transient behavior of heat transfer and fluid flow in stationary pulsed current tungsten inert gas (PC-TIG) weld pool, which considers three kinds of driving, forces for weld pool convection, i,e. buoyancyforce, electromagnetic force and surface tension force. furthermore. the effect of vaporization heat flux at the free surface of weld pool and the temperature coefficient of surface tenston which is a function of temperatuer and composition are considered in the model In order to accelerate the convergence of iteration the AST(additive source term)method which concerns with the thermal energv boundary conditions is extended successfully to deal with the momentum boundary conditions by which the transient momentum equation and energy equation are mutually coupled. At the same time. ADI (Alternating direction implicit) method and DBC (double blocks correction) technque are employed to solve the finite difference equations. The results of numerical simulation demonstrate the transient behavior of PC-TIG weld pool, as well as the periodic variation of fluid flow and heat transfer with the periodic variation of welding current in stationary PC-TIG weld pool. The theoretical predictions based on this model are, shown to be in good accordance with the experimental measurements.展开更多
Direct-current transfer characteristics of （InGaN）/A1GaN/A1N/GaN heterojunction field effect transistors （HFETs） are presented. A drain current plateau （IDs = 32.0 mA/mm） for Vcs swept from ＋0.7 V to -0. 6 V is...Direct-current transfer characteristics of （InGaN）/A1GaN/A1N/GaN heterojunction field effect transistors （HFETs） are presented. A drain current plateau （IDs = 32.0 mA/mm） for Vcs swept from ＋0.7 V to -0. 6 V is present in the transfer characteristics of InGaN/AIGaN/AIN/GaN HFETs. The theoretical calculation shows the coexistence of two-dimensional electron gas （2DEG） and two-dimensional hole gas （2DHG） in InGaN/AIGaN/A1N/GaN heterostructures, and the screening effect of 2DHG to the 2DEG in the conduction channel can explain this current plateau. Moreover, the current plateau shows the time-dependent behavior when IDs Vcs scans repeated are conducted. The obtained insight provides indication for the design in the fabrication of GaN-based super HFETs.展开更多
A simulation system used in the arc welding short circuit transfer process and current waveform control process was developed in this paper. The simulation results are basically consistent with welding technical exper...A simulation system used in the arc welding short circuit transfer process and current waveform control process was developed in this paper. The simulation results are basically consistent with welding technical experiments. The simulation system can be used to simulate and test the current waveform control parameters with welding variables. By this simulation system, the influence regularities of the current waveform control parameters in the CO 2 arc welding droplet short circuit transfer process can be got. Moreover, the basic mode of real time current waveform control can be also established by the simulation testing.展开更多
Effects of Hall current on heat transfer and magnetohydrodynamic (MHD) boundary layer flow induced by a continuous surface in a parallel free stream of a second-order viscoelastic fluid are studied for uniform suction...Effects of Hall current on heat transfer and magnetohydrodynamic (MHD) boundary layer flow induced by a continuous surface in a parallel free stream of a second-order viscoelastic fluid are studied for uniform suction/injection by taking viscous dissipation into account. Complex nonsimilar solutions to the stream function and temperature are developed by means of an elegant technique, known as homotopy analysis method (HAM). Convergence of the solutions is ensured with the help of -curves. Graphical and tabular results for the effects of Hall current reveal that it has a significant influence on: complex velocity, complex temperature, magnitude of the shear stress at the surface, magnitude of the rate of heat transfer at the surface and on boundary layer thickness.展开更多
A visible rectification effect on the current-voltage curves of metal/porous silicon/p-silicon has been observed by current-sensing atomic force microscopy. The current-voltage curves of porous silicon membranes with ...A visible rectification effect on the current-voltage curves of metal/porous silicon/p-silicon has been observed by current-sensing atomic force microscopy. The current-voltage curves of porous silicon membranes with different porosities, prepared through variation of etching current density for a constant time, indicate that a higher porosity results in a higher resistance and thus a lower rectification, until the current reaches a threshold at a porosity 〉55%. We propose that the conductance mode in the porous silicon membrane with porosities 〉55% is mainly a hopping mechanism between nano-crystallites and an inverse static electric field between the porous silicon and p-Si interface blocks the electron injection from porous silicon to p-Si, but with porosities ≤55%, electron flows through a direct continuous channel between nano-crystallites.展开更多
The aim of the paper is to investigate the effect of heat and mass transfer on the unsteady magnetohydrodynamic free convective flow with Hall current, heat source, and viscous dissipation. The problem is governed by ...The aim of the paper is to investigate the effect of heat and mass transfer on the unsteady magnetohydrodynamic free convective flow with Hall current, heat source, and viscous dissipation. The problem is governed by the system of coupled non-linear partial differential equations whose exact solution is difficult to obtain. Therefore, the problem is solved by using the Galerkin finite element method. The effects of the various parameters like Hall current, Eckert number, heat source parameter, Prandtl number, and Schmidt number on the velocity components, the temperature, and the concentration are also examined through graphs.展开更多
This paper systematically analyzes the transfer characteristics of the Rogowski-coil Current Transformer and its effect on protective relaying through theoretical analysis, experiments and simulations. The frequency c...This paper systematically analyzes the transfer characteristics of the Rogowski-coil Current Transformer and its effect on protective relaying through theoretical analysis, experiments and simulations. The frequency characteristics and transient characteristics of Rogowski transducer and Rogowski-coil Current Transformer are deeply analyzed based on the physical structure of the transformer.?It is revealed that broad bandwidth of the transformer can improve the performance of protective relaying, and the bandwidth is determined mainly by the parameters of the Rogowski transducer and signal processing circuits. It is also discovered that the measurement errors of transient current mainly depend on the abilities for the current transformer to reproduce an accurate replica of the decaying dc components, which is mainly decided by the decay time constant of the aperiodic component of transient current and the parameters of the integral unit. Finally, some measures are proposed for the performance improvement of Rogowski-coil Current Transformer to meet the requirements of protective relaying system in terms of structural design and testing standards.展开更多
The present numerically study investigates the influence of the Hall current and constant heat flux on the Magneto hydrodynamic (MHD) natural convection boundary layer viscous incompressible fluid flow in the manifest...The present numerically study investigates the influence of the Hall current and constant heat flux on the Magneto hydrodynamic (MHD) natural convection boundary layer viscous incompressible fluid flow in the manifestation of transverse magnetic field near an inclined vertical permeable flat plate. It is assumed that the induced magnetic field is negligible compared with the imposed magnetic field. The governing boundary layer equations have been transferred into non-similar model by implementing similarity approaches. The physical dimensionless parameter has been set up into the model as Prandtl number, Eckert number, Magnetic parameter, Schmidt number, local Grashof number and local modified Grashof number. The numerical method of Nactsheim-Swigert shooting iteration technique together with Runge-Kutta six order iteration scheme has been used to solve the system of governing non-similar equations. The physical effects of the various parameters on dimensionless primary velocity profile, secondary velocity profile, and temperature and concentration profile are discussed graphically. Moreover, the local skin friction coefficient, the local Nusselt number and Sherwood number are shown in tabular form for various values of the parameters.展开更多
The variation in arc characteristics and behavior of metal transfer with the change in pulse parameters has been studied by high speed video camera during pulse current flux-cored arc weld deposition.A comparative stu...The variation in arc characteristics and behavior of metal transfer with the change in pulse parameters has been studied by high speed video camera during pulse current flux-cored arc weld deposition.A comparative study of similar nature has also been carried out during flux-cored arc weld deposition in globular and spray transfer modes.The effect of pulse parameters has been studied by considering their mean current and arc voltage.The arc characteristics studied by its root diameter,projected diameter and length,and the behavior of metal transfer noted by the metal transfer model and the droplet diameter have been found to vary significantly with the pulse parameters.The observation may help in understanding the arc characteristics with respect to the variation in pulse parameters which may be beneficial in using pulse current FCAW to produce desired weld quality.展开更多
To investigate the affect of direct current electric field (DCEF) on the interfacial phase,in this paper,a hydrophobic ionic liquid (HIL)/water as liquid-liquid two-phase binary system is established by using the deio...To investigate the affect of direct current electric field (DCEF) on the interfacial phase,in this paper,a hydrophobic ionic liquid (HIL)/water as liquid-liquid two-phase binary system is established by using the deioned water and l-butyl-3-methyl imidazolium hexafluorophosphate,and the topographies of the HIL nanodroplets and nanolayers in ambient water are observed by atomic force microscope (AFM).The results show the AFM exerting the DCEF can enhance the intersolubility of the HIL/water binary system and induce their interfacial phase transfer.展开更多
Due to its significant attributes,the liquid metal current limiter(LMCL)is considered a new strategy for limiting short-circuit current in the power grid.A resistive wall liquid metal current limiter(RWLMCL)is designe...Due to its significant attributes,the liquid metal current limiter(LMCL)is considered a new strategy for limiting short-circuit current in the power grid.A resistive wall liquid metal current limiter(RWLMCL)is designed to advance the starting current-limiting time.Experiments are performed to investigate the dynamic behaviors of liquid metal,and the influence of different currents on the liquid metal self-shrinkage effect is compared and analyzed.Furthermore,the liquid metal self-shrinkage effect is mathematically modeled,and the reason for the formation of arc plasma is obtained by simulation.The laws of arc plasma formation and the current transfer in the cavity are revealed,and the motion mechanisms are explained by physical principles.The simulations are in accordance with the test data.It is demonstrated that the sudden change of the current density at both ends of the wall causes the liquid metal to shrink and depress under the electromagnetic force,and the current starts to transfer from the liquid metal path to the wall resistance path.The RWLMCL can effectively advance the starting current-limiting time.展开更多
Circuits with switched current are described by an admittance matrix and seeking current transfers then means calculating the ratio of algebraic supplements of this matrix. As there are also graph methods of circuit a...Circuits with switched current are described by an admittance matrix and seeking current transfers then means calculating the ratio of algebraic supplements of this matrix. As there are also graph methods of circuit analysis in addition to algebraic methods, it is clearly possible in theory to carry out an analysis of the whole switched circuit in two-phase switching exclusively by the graph method as well. For this purpose it is possible to plot a Mason graph of a circuit, use transformation graphs to reduce Mason graphs for all the four phases of switching, and then plot a summary graph from the transformed graphs obtained this way. First the author draws nodes and possible branches, obtained by transformation graphs for transfers of EE （even-even） and OO （odd-odd） phases. In the next step, branches obtained by transformation graphs for EO and OE phase are drawn between these nodes, while their resulting transfer is 1 multiplied by z^1/2. This summary graph is extended by two branches from input node and to output node, the extended graph can then be interpreted by the Mason＇s relation to provide transparent current transfers. Therefore it is not necessary to compose a sum admittance matrix and to express this consequently in numbers, and so it is possible to reach the final result in a graphical way.展开更多
随着电网换相型高压直流输电(line commutated converter based high voltage direct current,LCC-HVDC)技术的广泛应用,交直流混联电网的谐波交互问题愈加复杂,建立LCC-HVDC小信号模型是分析换流器交直流谐波耦合特性的重要手段。为此...随着电网换相型高压直流输电(line commutated converter based high voltage direct current,LCC-HVDC)技术的广泛应用,交直流混联电网的谐波交互问题愈加复杂,建立LCC-HVDC小信号模型是分析换流器交直流谐波耦合特性的重要手段。为此,基于谐波状态空间理论(harmonic state space, HSS)建立双端12脉动LCC-HVDC小信号模型,不仅考虑了LCC谐波传递特性,还考虑了换流变压器联结方式、控制链路延时等因素的影响。采用模块化思想分别建立各子系统谐波状态空间模型,通过接口矩阵连接为整体,使得LCC的谐波状态空间建模在易于扩展的同时,提高了精确度。最后,给出交直流谐波传递的具体表达式,并通过PSCAD仿真验证模型的准确性。所建模型不仅为后续扩展或接入更为复杂的系统奠定了基础,还可应用于双端LCC系统谐波交互稳定性评估和系统参数优化设计。展开更多
基金Project supported by the National Science Foundation of China(Grant Nos.51322706,51237006,and 51325705)the Program for New Century Excellent Talents in University,China(Grant No.NCET-11-0428)the Fundamental Research Funds for the Central Universities,China
文摘In this paper, a computational model is constructed to investigate the phenomenon of the initial plasma formation and current transfer in the single-wire electrical explosion in a vacuum. The process of the single-wire electrical explosion is divided into four stages. Stage Ⅰ： the wire is in solid state. Stage Ⅱ： the melting stage. Stage Ⅲ： the wire melts completely and the initial plasma forms. Stage IV： the core and corona expand separately. The thermodynamic calculation is applied before the wire melts completely in stages Ⅰ and Ⅱ. In stage Ⅲ, a one-dimensional magnetohydrodynamics model comes into play until the instant when the voltage collapse occurs. The temperature, density, and velocity, which are derived from the magnetohydrodynamics calculation, are averaged over the distribution area. The averaged parameters are taken as the initial conditions for stage Ⅳ in which a simplified magnetohydrodynamics model is applied. A wide-range semi-empirical equation of state, which is established based on the Thomas-Fermi-Kirzhnits model, is constructed to describe the phase transition from solid state to plasma state. The initial plasma formation and the phenomenon of current transfer in the electrical explosion of aluminum wire are investigated using the computational model. Experiments of electrical explosion of aluminum wires are carried out to verify this model. Simulation results are also compared with experimental results of the electrical explosion of copper wire.
基金supported by the "Hundred Talent Project" of the Chinese Academy of Sciencesthe National High Technology Research and Development Program of China(Grant No.2009AA033101)+3 种基金the National Basic Research Program of China(Grant Nos.2007CB936500 and 2010CB833102)the National Natural Science Foundation of China(Grant No.50972164)the Science and Technology Planning Project of Guangdong Province,China(Grant No.2010A090602001)the Knowledge Innovation Program of the Chinese Academy of Sciences(Grant No.KJCX2-YW-W26)
文摘The rate and cycling performances of the electrode materials are affected by many factors in a practical complicated electrode process. Learning about the limiting step in a practical electrochemical reaction is very important to effectively improve the electrochemical performances of the electrode materials. Li4Ti5O12, as a zero-strain material, has been considered as a promising anode material for long life Li-ion batteries. In this study, our results show that the Li4Ti5O12 pasted on Cu or graphite felt current collector exhibits unexpectedly higher rate performance than on A1 current collector. For Li4Ti5O12, the electron transfer between current collector and active material is the critical factor that affects its rate and cycling performances.
文摘A mathematical model is presented to describe transient behavior of heat transfer and fluid flow in stationary pulsed current tungsten inert gas (PC-TIG) weld pool, which considers three kinds of driving, forces for weld pool convection, i,e. buoyancyforce, electromagnetic force and surface tension force. furthermore. the effect of vaporization heat flux at the free surface of weld pool and the temperature coefficient of surface tenston which is a function of temperatuer and composition are considered in the model In order to accelerate the convergence of iteration the AST(additive source term)method which concerns with the thermal energv boundary conditions is extended successfully to deal with the momentum boundary conditions by which the transient momentum equation and energy equation are mutually coupled. At the same time. ADI (Alternating direction implicit) method and DBC (double blocks correction) technque are employed to solve the finite difference equations. The results of numerical simulation demonstrate the transient behavior of PC-TIG weld pool, as well as the periodic variation of fluid flow and heat transfer with the periodic variation of welding current in stationary PC-TIG weld pool. The theoretical predictions based on this model are, shown to be in good accordance with the experimental measurements.
基金Supported by the Knowledge Innovation Project of the Chinese Academy of Sciencesthe National Natural Science Foundation of China under Grant Nos 61204017 and 61334002+1 种基金the National Basic Research Program of Chinathe National Science and Technology Major Project of China
文摘Direct-current transfer characteristics of （InGaN）/A1GaN/A1N/GaN heterojunction field effect transistors （HFETs） are presented. A drain current plateau （IDs = 32.0 mA/mm） for Vcs swept from ＋0.7 V to -0. 6 V is present in the transfer characteristics of InGaN/AIGaN/AIN/GaN HFETs. The theoretical calculation shows the coexistence of two-dimensional electron gas （2DEG） and two-dimensional hole gas （2DHG） in InGaN/AIGaN/A1N/GaN heterostructures, and the screening effect of 2DHG to the 2DEG in the conduction channel can explain this current plateau. Moreover, the current plateau shows the time-dependent behavior when IDs Vcs scans repeated are conducted. The obtained insight provides indication for the design in the fabrication of GaN-based super HFETs.
文摘A simulation system used in the arc welding short circuit transfer process and current waveform control process was developed in this paper. The simulation results are basically consistent with welding technical experiments. The simulation system can be used to simulate and test the current waveform control parameters with welding variables. By this simulation system, the influence regularities of the current waveform control parameters in the CO 2 arc welding droplet short circuit transfer process can be got. Moreover, the basic mode of real time current waveform control can be also established by the simulation testing.
文摘Effects of Hall current on heat transfer and magnetohydrodynamic (MHD) boundary layer flow induced by a continuous surface in a parallel free stream of a second-order viscoelastic fluid are studied for uniform suction/injection by taking viscous dissipation into account. Complex nonsimilar solutions to the stream function and temperature are developed by means of an elegant technique, known as homotopy analysis method (HAM). Convergence of the solutions is ensured with the help of -curves. Graphical and tabular results for the effects of Hall current reveal that it has a significant influence on: complex velocity, complex temperature, magnitude of the shear stress at the surface, magnitude of the rate of heat transfer at the surface and on boundary layer thickness.
文摘A visible rectification effect on the current-voltage curves of metal/porous silicon/p-silicon has been observed by current-sensing atomic force microscopy. The current-voltage curves of porous silicon membranes with different porosities, prepared through variation of etching current density for a constant time, indicate that a higher porosity results in a higher resistance and thus a lower rectification, until the current reaches a threshold at a porosity 〉55%. We propose that the conductance mode in the porous silicon membrane with porosities 〉55% is mainly a hopping mechanism between nano-crystallites and an inverse static electric field between the porous silicon and p-Si interface blocks the electron injection from porous silicon to p-Si, but with porosities ≤55%, electron flows through a direct continuous channel between nano-crystallites.
基金supported by the University Grants Commission,New Delhi,India
文摘The aim of the paper is to investigate the effect of heat and mass transfer on the unsteady magnetohydrodynamic free convective flow with Hall current, heat source, and viscous dissipation. The problem is governed by the system of coupled non-linear partial differential equations whose exact solution is difficult to obtain. Therefore, the problem is solved by using the Galerkin finite element method. The effects of the various parameters like Hall current, Eckert number, heat source parameter, Prandtl number, and Schmidt number on the velocity components, the temperature, and the concentration are also examined through graphs.
文摘This paper systematically analyzes the transfer characteristics of the Rogowski-coil Current Transformer and its effect on protective relaying through theoretical analysis, experiments and simulations. The frequency characteristics and transient characteristics of Rogowski transducer and Rogowski-coil Current Transformer are deeply analyzed based on the physical structure of the transformer.?It is revealed that broad bandwidth of the transformer can improve the performance of protective relaying, and the bandwidth is determined mainly by the parameters of the Rogowski transducer and signal processing circuits. It is also discovered that the measurement errors of transient current mainly depend on the abilities for the current transformer to reproduce an accurate replica of the decaying dc components, which is mainly decided by the decay time constant of the aperiodic component of transient current and the parameters of the integral unit. Finally, some measures are proposed for the performance improvement of Rogowski-coil Current Transformer to meet the requirements of protective relaying system in terms of structural design and testing standards.
文摘The present numerically study investigates the influence of the Hall current and constant heat flux on the Magneto hydrodynamic (MHD) natural convection boundary layer viscous incompressible fluid flow in the manifestation of transverse magnetic field near an inclined vertical permeable flat plate. It is assumed that the induced magnetic field is negligible compared with the imposed magnetic field. The governing boundary layer equations have been transferred into non-similar model by implementing similarity approaches. The physical dimensionless parameter has been set up into the model as Prandtl number, Eckert number, Magnetic parameter, Schmidt number, local Grashof number and local modified Grashof number. The numerical method of Nactsheim-Swigert shooting iteration technique together with Runge-Kutta six order iteration scheme has been used to solve the system of governing non-similar equations. The physical effects of the various parameters on dimensionless primary velocity profile, secondary velocity profile, and temperature and concentration profile are discussed graphically. Moreover, the local skin friction coefficient, the local Nusselt number and Sherwood number are shown in tabular form for various values of the parameters.
文摘The variation in arc characteristics and behavior of metal transfer with the change in pulse parameters has been studied by high speed video camera during pulse current flux-cored arc weld deposition.A comparative study of similar nature has also been carried out during flux-cored arc weld deposition in globular and spray transfer modes.The effect of pulse parameters has been studied by considering their mean current and arc voltage.The arc characteristics studied by its root diameter,projected diameter and length,and the behavior of metal transfer noted by the metal transfer model and the droplet diameter have been found to vary significantly with the pulse parameters.The observation may help in understanding the arc characteristics with respect to the variation in pulse parameters which may be beneficial in using pulse current FCAW to produce desired weld quality.
基金Supported by the National Basic Research Program of China (973 Program No. 2007CB936000)the National Natural Science Foundation of China(No.10874198,90923002,21073222 and 10975175,No. 10874030)the Chinese Academy of Sciences (No. KJCX2-EW-N03)
文摘To investigate the affect of direct current electric field (DCEF) on the interfacial phase,in this paper,a hydrophobic ionic liquid (HIL)/water as liquid-liquid two-phase binary system is established by using the deioned water and l-butyl-3-methyl imidazolium hexafluorophosphate,and the topographies of the HIL nanodroplets and nanolayers in ambient water are observed by atomic force microscope (AFM).The results show the AFM exerting the DCEF can enhance the intersolubility of the HIL/water binary system and induce their interfacial phase transfer.
基金supported by National Natural Science Foundation of China(No.52177131)the Interdisciplinary Program of Wuhan National High Magnetic Field Center(No.WHMFC202130)Huazhong University of Science and Technology。
文摘Due to its significant attributes,the liquid metal current limiter(LMCL)is considered a new strategy for limiting short-circuit current in the power grid.A resistive wall liquid metal current limiter(RWLMCL)is designed to advance the starting current-limiting time.Experiments are performed to investigate the dynamic behaviors of liquid metal,and the influence of different currents on the liquid metal self-shrinkage effect is compared and analyzed.Furthermore,the liquid metal self-shrinkage effect is mathematically modeled,and the reason for the formation of arc plasma is obtained by simulation.The laws of arc plasma formation and the current transfer in the cavity are revealed,and the motion mechanisms are explained by physical principles.The simulations are in accordance with the test data.It is demonstrated that the sudden change of the current density at both ends of the wall causes the liquid metal to shrink and depress under the electromagnetic force,and the current starts to transfer from the liquid metal path to the wall resistance path.The RWLMCL can effectively advance the starting current-limiting time.
文摘Circuits with switched current are described by an admittance matrix and seeking current transfers then means calculating the ratio of algebraic supplements of this matrix. As there are also graph methods of circuit analysis in addition to algebraic methods, it is clearly possible in theory to carry out an analysis of the whole switched circuit in two-phase switching exclusively by the graph method as well. For this purpose it is possible to plot a Mason graph of a circuit, use transformation graphs to reduce Mason graphs for all the four phases of switching, and then plot a summary graph from the transformed graphs obtained this way. First the author draws nodes and possible branches, obtained by transformation graphs for transfers of EE （even-even） and OO （odd-odd） phases. In the next step, branches obtained by transformation graphs for EO and OE phase are drawn between these nodes, while their resulting transfer is 1 multiplied by z^1/2. This summary graph is extended by two branches from input node and to output node, the extended graph can then be interpreted by the Mason＇s relation to provide transparent current transfers. Therefore it is not necessary to compose a sum admittance matrix and to express this consequently in numbers, and so it is possible to reach the final result in a graphical way.
文摘随着电网换相型高压直流输电(line commutated converter based high voltage direct current,LCC-HVDC)技术的广泛应用,交直流混联电网的谐波交互问题愈加复杂,建立LCC-HVDC小信号模型是分析换流器交直流谐波耦合特性的重要手段。为此,基于谐波状态空间理论(harmonic state space, HSS)建立双端12脉动LCC-HVDC小信号模型,不仅考虑了LCC谐波传递特性,还考虑了换流变压器联结方式、控制链路延时等因素的影响。采用模块化思想分别建立各子系统谐波状态空间模型,通过接口矩阵连接为整体,使得LCC的谐波状态空间建模在易于扩展的同时,提高了精确度。最后,给出交直流谐波传递的具体表达式,并通过PSCAD仿真验证模型的准确性。所建模型不仅为后续扩展或接入更为复杂的系统奠定了基础,还可应用于双端LCC系统谐波交互稳定性评估和系统参数优化设计。
