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In this article, we proposed a discrete-time sliding mode load thrust observer to reduce the influence of load thrust mutation on the linear motor and improve the antiinterference ability and speed tracking performance of the system. First, the electrical and dynamic models of linear motor are established, and the limitation of conventional double-closed-loop control based on proportional integral (PI) algorithm is analyzed. Second, the extended state equation of velocity and load thrust is given and an improved sliding mode reaching law is designed to establish the discrete-time load thrust observer. Based on Lyapunov theory, the stability of the observer is proved. The observed load thrust is compensated to the controller in the form of feedforward. Finally, a series of comparative experiments were carried out. The experimental results show that compared with the PI control, the maximum speed fluctuation of this method is reduced by about 18.1% when the load changes between no-load and rated load. This means that the method in this article can effectively improve the antidisturbance ability of the system. [ABSTRACT FROM AUTHOR]

This work investigates the dynamic characteristics of vacuum arc in the initial expansion process of a direct current (dc) circuit breaker. Based on the commercial cup-type axial magnetic field (AMF) contact, a 3-D transient magnetohydrodynamic (MHD) model is established. In the model, transient equations are used to study the transient characteristics of the vacuum arc. The effect of magnetic field hysteresis is also considered in the method. The dynamic mesh technique is adopted to simulate the electrode separation, which can make the simulation results more accurate. The simulation results show that, during the initial expansion process, with the increase in the current, the arc gradually expands in the electrode gap. The ion pressure, ion number density, axial current density, and energy flux density to the anode gradually decrease. Ion rotation can be observed under the influence of the magnetic field, and the rotation speed will increase with the increase in the current. Two different arc ignition positions are also compared. The result shows that igniting the arc at the contact center is more helpful to the success of the interruption of the dc circuit breaker. The appearance of the arc predicted by the model is consistent with the experimental results. [ABSTRACT FROM AUTHOR]

This work investigates the effect of oxygen (O2) as gas admixture on hydrodynamic characteristics of a coaxial double-ring electrode helium plasma jet by a “Z-type” shadowgraphy system. The shadowgraphy images and visual optical photographs show that the addition of O2 will slow down the transition of gas flow from the laminar region to the turbulent region regardless of the plasma is ignited or not. The hydrodynamic behaviors of the plasma jet at the impact region for epoxy resin (EP) and aluminum substrates are also researched. The addition of oxygen reduces the vortex on the surface of both EP and aluminum surface. As a result, with the increase of O2, the decrease of gas temperature caused by reduction of electrons and the reduction of the density difference between the mixed gas and the ambient air weaken the gas velocity and results in a weaker collision between the gas and the substrate, which is the main factor for less vortex on the substrate surface. [ABSTRACT FROM AUTHOR]

To realize the demagnetization fault diagnosis and degree estimation of permanent-magnet synchronous linear motors in linear motion applications with high precision and multiple working conditions, a novel double closed-loop control with an adaptive linear neuron (ALN) model reference adaptive system (MRAS) flux linkage observer is proposed in this article. First, a sliding-mode control (SMC) is introduced to design the velocity loop to obtain good speed adaptability. Then, the MRAS flux observer is established, and the ALN algorithm for modifying the MRAS adaptive law online is designed combining with MRAS flux observer. In addition, the finite element models of normal, weak (F1), mild (F2), moderate (F3), and severe (F4) demagnetization faults are established, and the accurate values of flux linkage under different demagnetization degrees are simulated. Furthermore, the demagnetization fault diagnosis algorithm is introduced with an SMC-ALN-MRAS flux observer. Finally, a prototype motor experimental platform is built, and comparative experiments are designed to confirm the correctness and effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

A three-dimensional (3-D) model for multispecies vacuum arc considering ionization and recombination process has been built in this article. With the model, the arc behaviors and species characteristics subjected to actual spatial magnetic fields of cup-shaped axial magnetic field (AMF) contact and transverse magnetic field-axial magnetic field (TMF-AMF) contact are investigated and compared. Furthermore, the validity of the model is verified by comparing with the experiments. Simulation results show that contact structures affect the species distributions of the arc by changing magnetic field and current density distributions. More triple charged ions are generated through ionization under higher electron temperature so that the triple charged ions gather where current constricts. The heat flux density is large in the current contraction region, where the contribution from triple charged ions is large as well. Spatial magnetic field distribution affects the Lorentz force acting on ion components. The force distribution is relatively uniform and the species are subject to inward force on the arc edge under cup-shaped AMF contact. For TMF-AMF contact, the double charged ions are subject to the force pointing to the TMF contact arms, whereas the triple charged ions are subject to the force pointing to the arc center. In addition, the consideration of arc species can improve the accuracy of the simulation results of the heat flux distribution, leading to a good agreement of the erosion condition between experiments and simulation. [ABSTRACT FROM AUTHOR]

Battery energy storage system (BESS) plays an important role in solving problems in which the intermittency has to be considered while operating distribution network (DN) penetrated with renewable energy. Aiming at this problem, this paper proposes a global centralized dispatch model that applies BESS technology to DN with renewable energy source (RES). The method proposed in this paper aims to minimize the power purchase cost considering network active loss cost as well as voltage deviation penalty cost. Later, second-order cone programming (SOCP) method as well as big M method are applied to make the problem tractable. Last, the method illustrated in this paper is applied and validated on a modified IEEE 33-bus benchmark system to verify the effectiveness of the proposed scheduling model. [ABSTRACT FROM AUTHOR]

As a special phenomenon under transverse magnetic field (TMF) contacts, vacuum arc rotation deserves more attention. In this article, rotation characteristics of three typical TMF contacts, i.e., swastika-type, cup-shaped, and double-TMF contacts, are systematically studied. According to arc images, recorded by a high-speed camera, physical terms related to arc rotation such as rotation duration and rotation speed are clearly defined. The magnetic field and Lorentz force are calculated and the force balance of the moving arc is analyzed. On this basis, the effects of arc ignition mode, peak current, and contact type on arc rotation are investigated. Arc voltage noise as well as arc splashing outside caused by rotation is also discussed. The results show that the duration from ignition to rotation in two-point arc ignition (TPAI) mode is usually the shortest because of the rapidest constructed column formation. As the peak current increases, arc rotation becomes easier. Due to stronger TMF, the arc under double-TMF contacts has the longest rotation duration and the highest rotation speed. [ABSTRACT FROM AUTHOR]

The modeling and reconstruction of radar sea clutter (RSC) based on fractal theory is studied in this article. With theoretical derivation and quantitative analysis, the radar clutter reconstruction model based on singularity power spectrum (SPS) and instantaneous singularity exponent (ISE) distribution is proposed. The proposed ISE–SPS model consists of two coupling channels: power measure channel and dimension measure channel. The former is controlled by SPS to characterize the power distribution of signals in the SE domain, while the latter is determined by ISE function to characterize the statistical distribution of ISE. The multiscale wavelet coefficients are estimated based on the coupling of the two channels to reconstruct the RSC. The proposed ISE–SPS method is tested on RSC data in different sea state, from the ice multiparameter imaging X-band (IPIX) radar. Experimental and simulation based on the IPIX radar data set indicates that the proposed method performs better than the N-partitioned random multiplicative model (NRMM) method and SPS-multifractal spectrum (MFS) method, and exceeds the traditional methods by nearly 35% in terms of correlation coefficient and normalized mean square error of MFS and SPS. [ABSTRACT FROM AUTHOR]

In this article, the model including cathode spot process and deuterium desorption process on zirconium deuterium cathode is developed. Five kinds of particle fluxes on cathode surface and three mechanisms affecting deuterium diffusion in cathode are considered. The model not only describes the deformation of cathode metal, but also describes the variation of deuterium concentration with time. On pure zirconium cathode, the mean charge state is larger but on zirconium deuterium cathode, the total ion number density is larger since there are additional deuterium ions, and simulation results show the discharge currents are very close on the two cathodes, the energy flux density on ZrD0.66 cathode is larger so cathode spot crater develops faster on ZrD0.66 cathode. Ablation rates caused by different mechanisms are calculated and the results show in cathode spot development process, mass loss caused by evaporation is ignored, most of the liquid metal will resolidify on cathode surface, and droplets are the main reason for cathode ablation. The ablation rates due to the ejection of droplets are close to experimental results. The ratios of deuterium ion from different mechanisms in this process are also calculated and it is 93.5% in simulation. Simulation results are in agreement with the other researchers’ works. [ABSTRACT FROM AUTHOR]

In this article, the plasma decay in the postarc stage of vacuum circuit breakers and the influence of the transverse magnetic field (TMF) on this process are investigated with a 2-D particle-in-cell model. In this model, distributions of electric field and plasma are solved by Poisson’s equation and Newton’s law, respectively, in 2-D Cartesian coordinate system. The distributions of charged particles and the velocity of the sheath development in the simulation without magnetic field in this article agree well with those in the simulation solved in cylindrical coordinate system in the published work. The TMF in the postarc phase leads to asymmetric distributions of charged particles, which slows down the plasma decay process in the postarc phase. In addition, the TMF results density fluctuations in the plasma and makes the plasma discontinuous and cluster, which can disturb the ion sheath near the postarc anode and result the local electric fields in the plasma. Electrons can be accelerated and gain high velocities in these local fields. These effects of TMF will slow down the dielectric recovery in the postarc stage of vacuum circuit breakers and may increase the risk of rebreakdown in the postarc stage when the vacuum circuit breaker interrupts large fault currents. [ABSTRACT FROM AUTHOR]

The objective of this article is to investigate the effect of contact material on the formation and transition of high-current anode spots and anode plumes. A series of experiments are carried out in a demountable vacuum chamber at three current levels of 3, 4, and 6.5 kA. Plate contacts made of CuCr30 and CuCr40 with a diameter of 10 mm are adopted. Arc images are captured by a high-speed camera and synchronized with measurements of the arc current and voltage. The experimental results show that the three typical anode discharge modes, namely footpoint, anode spot type 1, and anode spot type 2, are formed at a smaller gap distance as the experimental current increases, and this tendency is independent of the contact material. The arc voltage is higher and the anode spot appears earlier and lasts longer under the CuCr40 contact than under the CuCr30 contact. As a result, the footpoint is formed at a smaller gap distance, whereas anode spot type 2 is formed at a larger gap distance. As a special anode discharge mode, an anode plume usually occurs between anode spot type 2 and arc current zero in various shapes at different locations on the anode surface. The anode plume of the CuCr40 contact appears at a larger gap distance and the corresponding threshold current and accumulated arc energy are also larger. Due to a stronger anode activity, the anode plume lasts a longer time under the CuCr40 contact than under the CuCr30 contact. [ABSTRACT FROM AUTHOR]

This paper proposes a high-performance current regulation scheme to enhance the current bandwidth and robustness of the permanent magnet synchronous linear motor (PMSLM). First, the disturbance caused by parameter variations and thrust ripple is considered in the modeling of PMSLM. Based on the model, a two-degree-of-freedom (2-DOF) controller consisting of improved predictive current control (PCC) and adaptive internal model control is derived. The improved PCC is used to overcome time delay and increase current control bandwidth, whilst the adaptive internal model is utilized to estimate the disturbance caused by parameter variations to compensate PCC. Second, a new discrete-time Jacobian linearization observer is designed to estimate the thrust ripple. The actual thrust ripple can be suppressed by injecting the estimated value into the control system. Subsequently, a comparatively smoother output thrust and higher precision position tracking is obtained. Finally, the precise test platform based on semiphysical system AD5435 is established. The experimental results verify the validity of the proposed approach. [ABSTRACT FROM AUTHOR]

SF6 has good insulation performance and is widely used in power equipment. But as climate change intensifies, the need for substitute gases is growing. While a lot of research focusing on the insulation performance of substitute gases has been done, little has been focused on their effects on temperature rise, though temperature rise is important for the safe operation of the power equipment. In this article, a 40.5-kV medium-voltage cubic gas-insulator switchgear (C-GIS) is modeled and simulated by the electromagnetic-fluid-temperature multiphysical coupled method. By implementing CFX Expression Language (CEL), the influence of temperature on thermal conductivity, density, viscosity, and specific heat capacity of gas is able to be coupled into the simulations, thus improving the accuracy of the simulations. The airflow and temperature distribution of the C-GIS with SF6 are obtained, and the temperature rise distribution is verified by experimental results. On this basis, simulation studies are conducted to analyze the influence of different filling gases on the temperature rise of the C-GIS. First, the influence of single filling gases including N2, CO2, and pressurized air is analyzed by the simulations. Second, the temperature rise distributions of the C-GIS when filled with a mixture of SF6 and N2 with different proportions of mole fraction are also obtained. By analyzing the changes in temperature rise distribution under different situations, it can be found that the temperature rise with N2, CO2, or pressurized air is relatively high. When the gas mixture is used, the maximum temperature tends to decrease with the increase of SF6 usage. According to the results of this article, it can provide a reference for selecting suitable substitute gas of SF6. [ABSTRACT FROM AUTHOR]

Modeling and numerical simulation is an important tool for the research of the physical mechanisms of the vacuum arc (VA). Compared with the experiments of the VA, numerical simulation is more efficient and economical. Axial magnetic fields (AMFs) are also the most popular control technology in vacuum interrupters and other application fields. First, the model of VA was reviewed from a relatively simple zero-order one to 2-D one, and then a 3-D one, which gives us a more comprehensive understanding of VA. Second, the influence of spatial distribution of magnetic fields on VA behavior is also studied. VA behavior under different commercial AMF contacts was simulated and compared based on 3-D magnetohydro-dynamic model. Influence of the radial slots and magnetic field generated by adjacent phase and bus bar on arc characteristics has been reviewed. Third, the VA modeling with active anode is reviewed and discussed. Anode vapor can cool arc plasma, and leads to changed distribution of current density and plasma parameters. Model and simulation technology of anode activity have also been reviewed in this paper, from 1-D, 2-D, to 3-D, and then the deformation of anode melting pool is considered. Deformation of anode melting pool will make anode temperature more reasonable. Finally, the challenge and research direction of VA modeling is also given and discussed. [ABSTRACT FROM AUTHOR]

Deep networks have been proved to encode high-level features with semantic meaning and delivered superior performance in salient object detection. In this paper, we take one step further by developing a new saliency detection method based on recurrent fully convolutional networks (RFCNs). Compared with existing deep network based methods, the proposed network is able to incorpor- ate saliency prior knowledge for more accurate inference. In addition, the recurrent architecture enables our method to automatically learn to refine the saliency map by iteratively correcting its previous errors, yielding more reliable final predictions. To train such a netw- ork with numerous parameters, we propose a pre-training strategy using semantic segmentation data, which simultaneously leverages the strong supervision of segmentation tasks for effective training and enables the network to capture generic representations to chara- cterize category-agnostic objects for saliency detection. Extensive experimental evaluations demonstrate that the proposed method compares favorably against state-of-the-art saliency detection approaches. Additional validations are also performed to study the impact of the recurrent architecture and pre-training strategy on both saliency detection and semantic segmentation, which provides important knowledge for network design and training in the future research. [ABSTRACT FROM AUTHOR]

Vacuum interrupter is widely used in the medium-voltage power system. Controlling the arc by the magnetic field is an effective method to improve the breaking capacity. The transverse magnetic field (TMF) forces the constricted arc to rotate to reduce local overheating. In this paper, three kinds of TMF contacts, which are Swastika-type contact, cup-shaped contact, and double-TMF contact that combines Swastika-type and cup-shaped contacts coaxially, are investigated in a demountable vacuum chamber with a high-speed camera. The arc voltage and current are also recorded. The experiments were conducted with circuit currents from 5 to 20 kA (root mean square) with a frequency of 50 Hz. There are four current levels in the experiment, which are 5, 10, 15, and 20 kA, and at least three tests are taken for each current level. The results showed that under low current (I = 10 kA), the arc of the three TMF contacts did not rotate. Under high current (I = 20 kA), it was observed that the arc of Swastika-type and double-TMF contacts rotated in the gap. The arc speed of double-TMF contacts is higher than that of Swastika-type contacts. The cup-shaped contacts have the highest arc voltage and noise among the three TMF contacts. The Swastika-type contacts were eroded most seriously. The simulation results show the force distribution of the arc on different locations. The resultant force makes the arc rotate counterclockwise. [ABSTRACT FROM AUTHOR]

Using magnetic fields to control the vacuum arc is a major way to improve the breaking capacity of vacuum interrupters. Besides the single transverse magnetic field (TMF) and single axial magnetic field (AMF), new type of TMF-AMF contact and TMF-TMF contact structures have been put forward to control the vacuum arc in recent years. In this paper, three different structural contacts are used in the experiments. The arc evolution was captured by an high-speed digital video camera, and at the same time, the arc current and arc voltage wave were recorded. The experiment was conducted under current ranging from 5 to 20 kA (root mean square) and 10 mm of gap distance. There are 12 current shots performed on one contact design. There are four current levels in the experiment which are 5, 10, 15, and 20 kA, and three tests are taken for each current level. The results showed that for TMF-AMF contacts, under low current (I = 5 or 10 kA), the arcs of the two kinds of contacts both kept diffused and rotating. Under high current (I = 20 kA), the arc of the TMF-AMF contact with six slots was constricted and rotated on the plate, and the melting was uniform and slight. As for the eight-slot contacts, the arc was constricted but did not rotate which resulted in significant melting in the local region. As for TMF-TMF contacts, the result is similar under low current, while the arc was constricted and rotated quickly on the inner plate under high current. The simulation results show that when the arc core is located on the outer plate; the total Lorentz force is near zero. When the arc core is located on the inner plate, the direction of total force is counterclockwise. [ABSTRACT FROM AUTHOR]

In order to improve the breaking capacity of contacts, it is very important to find a better contact material. In this paper, the triggering experiments of plate contact with different materials are studied to investigate the characteristics of vacuum arc. The current range is from 1 to 9 kA (rms). The gap distance is selected as 3 and 5 mm. The arc appearance and the behavior of cathode spots are captured by high-speed camera with an exposure time of $2~\mu \text{s}$. The surface topography of contacts after experiments is evaluated by scanning electron microscope. The arc current and arc voltage are measured at the same time by Rogowski coil and high-voltage probe. The diameter of the contact is 25 mm. There are seven kinds of materials (CuCr10, CuCr25, CuCr30, CuCr40, WCu10, WCu30, and CuW–WC) conducted in this paper. Compared with the experimental results, the arc of WCu alloy distributes more evenly on the contact plane with many bright cathode spots. The small gap distance makes the burning point more fixed. The arc of CuW–WC is unstable. During the arc trigger moment to the arc stable burning stage, the radial diffusion velocity of WCu10 cathode spot is the lowest with about 25% of CuCr10. CuCr10 alloy has the worst melting resistance. WCu alloy has good melting resistance and bad toughness. The toughness of CuW–WC is even worse. Under the low current, CuCr30 might be preferred for vacuum interrupters from the cathode spots’ radial diffusion speed, arc appearance, and erosion result. When the current increasing, the arc can easily spread to the entire surface of WCu contact, and WCu10 would be the prefer material with the diffusion arc and good erosion resistance. [ABSTRACT FROM AUTHOR]

Switchgear is an important power system protection equipment. Internal overheating of high-current switchgear has become the most common problem in the power system. In this paper, two different methods of simulation model are adopted to study the temperature rise issues of the 12-kV medium voltage switchgear. First, the electromagnetic field is calculated by using ANSYS APDL, then coupling with fluid dynamics software CFX to give the temperature and flow field distribution of the switchgear. Second, FLUENT and Maxwell 3-D are used to get the temperature and flow field distribution. It can be proven that CFX simulation of flow field is more suitable for the complex models. In the meantime, it has huge differences with FLUENT software when the temperature rise of the switchgear is calculated. In this paper, the influences of inlet velocity, the number of ventilation holes, and their positions are further studied, which could provide theoretical guidance for reducing temperature rise of the switchgear. [ABSTRACT FROM PUBLISHER]

In the interrupting process of a three-phase vacuum interrupter, there exists a transverse magnetic field (TMF) in the interelectrode region, which is produced by adjacent phases. The deflection of the vacuum arc caused by TMF will affect the interrupting process of vacuum circuit breakers. In this paper, the vacuum arc characteristics considering the action of TMF produced by adjacent phases is simulated based on a steady 2-D asymmetrical magnetohydrodynamic model. The simulation results show that the vacuum arc will swing around and is especially obvious at the smaller current moments near current-zero during one ac half-cycle, because of the changed direction of TMF produced by adjacent phases. This kind of swing phenomena can also be observed in the electrode erosion of unsuccessful interruption. At the moments near current-zero, axial magnetic field is relatively weaker, while TMF generated by adjacent phases is relatively stronger, therefore, the offset phenomenon of plasma parameters is more significant. Compared with smaller diameter electrode arc, larger diameter electrode has larger arc deflection distance, while its value of plasma parameters is much smaller. [ABSTRACT FROM AUTHOR]

Long-term heating and excessive temperature rise will significantly affect the electrical and insulation performance of electric power equipment, causing the potential security risk. In this paper, the temperature rise situation under normal operation of a 12-kV medium voltage switchgear is studied through modeling and simulation method. First, in the simulation analysis of the whole switchgear, based on the theory of eddy-current field, gas flow field, and temperature field, the temperature rise distribution of the switchgear under the condition of natural convection and forced convection is simulated and analyzed. Then, several improvement methods are taken to reduce the temperature rise that emerges in the switchgear, including using spring contact finger structure to replace flexible connection structure, and also the optimization scheme of vacuum circuit breaker (VCB) pole and current transformer (CT). Then, simulation and research of different improvement schemes are conducted based on the electromagnetic-thermal-flow field coupling method. The simulation results of whole switchgear show that the above coupling method is very useful for the calculation of temperature rise. The simulation results also show that the spring contact structure is beneficial to reduce the temperature rise of vacuum interrupter and mechanical connection part. After the modification of design, the temperature rise conditions of the VCB pole and CT are significantly improved. [ABSTRACT FROM PUBLISHER]

Anode material seriously influences the characteristics of vacuum arc and further affects the performance of medium-voltage vacuum switches when the interruption current is high. There are many materials used for electrode manufacture, and different materials are selected for different switches. For a pure metal, its performance usually cannot satisfy the actual requirement. To improve switch’s performance, an alloy is usually used as an electrode material. In this paper, thermal processes of six kinds of metal anodes (including pure metal and alloy anodes) are simulated and researched. The physical parameters of the pure metals all come from experiment results directly or are fitted by the experimental data. The physical parameters of the CuCr alloys are derived from Cu and Cr parameters. Two kinds of temperature calculation methods are used, which are called melting and solidification model and equivalent specific heat method, respectively. Simulation results show that W and Mo anodes have the higher temperature than Cu, Cr, CuCr25, and CuCr50 anodes. A pure Cr anode has the largest melting width and highest saturated vapor pressure and evaporation energy. A Cu anode has the biggest melting depth. A W anode has the smallest melting width and depth. Axial temperature gradient is related to the thermal conductivity, and the Cr anode has the largest axial temperature gradient. The thermal characteristics of CuCr25 and CuCr50 anodes are located between the pure Cu and Cr anodes. There are two melting points appearing in the results of CuCr alloys, and between the two melting points, the alloy anodes are in solid–liquid mixture state. [ABSTRACT FROM PUBLISHER]

Based on a steady-state 3-D magnetohydrodynamic (MHD) model, the high-current vacuum arc (HCVA) under combined effect of actual magnetic field (MF) and external transverse MF (ETMF) is simulated. The actual MF is generated by cup-type axial magnetic field contact system commonly used in commercial vacuum circuit breakers. The ETMF may cause the deflection of arc column, which is the main reason of the contact deflected erosion. According to some experimental results, the electron temperature in HCVA is assumed to be uniform and equal to 3 eV. Therefore, the MHD model is simplified by neglecting the electron energy equation to improve the simulation efficiency. With the three conservation equations (mass, momentum, and energy) of ion flow coupling solved, the spatial distributions of some flow parameters can be obtained. The influence of all three components of the MF is inserted by solving the magnetic transport equations sequentially. Proper boundary conditions are set on the cathode and anode side, which separated the cathode spots mixing region and anode sheath region from computation domain, respectively. Under the influence of the ETMF, the deflection of the plasma flow can be predicted, which may be helpful to understand the mechanism of the contact deflected erosion. [ABSTRACT FROM PUBLISHER]

In this paper, high-current vacuum arc (VA) breaking experiments in vacuum interrupters were conducted using two kinds of high-capacity (larger diameter) axial magnetic field (AMF) electrodes with contact gap distance changing from 10 to 40 mm. Triggering arc mode and fixed gap distance were adopted. Experimental results showed that during the initial diffusion stage, the arc voltage of high-current VA got a peak value. The change in high-current VA appearance would also affect the curve of arc voltage. With the increase of contact gap distance, the voltage of high-current VA increased and the VA near the anode appeared contracted, and its shape was changed from cylinder to cone. In the shorter gap distance, for cup electrodes, the plasma jets mix with each other and the arc column appears like a bright cone, whereas for coil electrodes, the plasma jets are clear and the column appears like a cylinder, and the transfer of arc appearance affects arc voltage distribution. Moreover, arc twist and rotation often occur under longer gap and higher current, which is due to the larger radial magnetic field component generated by AMF coils, and arc voltage appeared high-frequency and high-amplitude noise, and ultimately resulted in the distortion of the arc current in the current experimental conditions (lower charging voltage of capacitor). [ABSTRACT FROM PUBLISHER]

Trigatrons have been widely used in many fields. However, the performance of trigatrons typically degrades as operational time increases. Among many influence factors, electrode erosion is a primary cause of trigatrons failure. In this paper, the peak current and pulsewidth of trigatrons are in the order of kiloampere (kA) and microsecond (\mus) , respectively, with an electrode size in the order of millimeters (mm). The discharge images show that the arc appearance looks filamentary in shape during the early period of the discharge. As the discharge process progresses, the arc expands and moves radially to the side surface of the anode. Simultaneously, electrode erosion experiments are conducted on the trigatrons in an atmospheric environment. Experimental results show that the erosion level becomes more serious with an increase of gap distance and discharge current. The weight loss of Mo and W electrodes with erosion times are very close to a linear distribution, however, weight loss rate of W-Cu electrodes increases more dramatically with an increase of erosion times. The erosion of WCu electrode is more pronounced than Mo and W electrodes the volume erosion rate of W is smaller than Mo, but the mass erosion rate of W is higher than Mo. Many cracks always appear on the W and Mo electrode surfaces, which are due to frequent and intensive interaction between the expansion and shrinkage of the electrode material. [ABSTRACT FROM PUBLISHER]

In this paper, the fluid–solid interaction model of the impact process of internal pressure in arc chamber on housing structure of low-voltage circuit breaker is established, including the computational fluid dynamic (CFD) module that can assess 3-D pressure distribution of internal gas flow in the arcing chamber and finite element module (FEM) to calculate the impact of high-pressure gas flow on the housing. Based on the CFD module, the internal pressure distribution under different breaking currents and venting conditions is simulated, in which the simulation results agree well with the experimental results. Then, based on the 3-D pressure distribution, through the 3-D FEM of housing impact, the dynamic stress and deformation of chamber housing are simulated and analyzed. By this method, the stress concentration region of arc chamber housing can be predicted, which can provide reference for structure optimization design of arc chamber. For the region where stress is concentrated, structural strength needs to be enhanced, which can effectively avoid rupture problems due to local excessive stress on the housing. [ABSTRACT FROM PUBLISHER]

With a quasi-steady 3-D MHD model, time-dependent axial magnetic field vacuum arcs (AMFVAs) characteristics in commercial vacuum interrupters for half-wave interruption of power-frequency (50 Hz) current are simulated. In a current time-dependent simulation, the influence of AMF lagged from arc current is considered in the arc model. 3-D spatial distributions of many important plasma parameters and electrical characteristics in AMFVAs can be obtained, such as ion number density, ion temperature, electron temperature, plasma pressure, current densities along different directions (x, y, and z), electric fields strength along different directions, and so on. Simulation results show that there exists a significant spiral-shaped rotational phenomena in the AMFVAs and the rotational velocity at the moments (9, 8, 7, and 6 ms) after 5 ms (the current peak value moment) is always larger than that before 5 ms (1, 2, 3, and 4 ms) because of the lagged AMF. This kind of plasma rotational phenomena also can be observed by high-speed arc photographs. In the future, the asymmetric appearance in high-current vacuum arc will be simulated based on a 3-D model. [ABSTRACT FROM AUTHOR]

With the increase of interruption frequency of high-current vacuum arc (HCVA), the relaxation time of arc plasma is close to characteristic time of arc current and transient characteristics of vacuum arc plasma become more obvious. In this paper, based on a 2-D transient magneto-hydrodynamic model, HCVA under different interruption processes is simulated and analyzed. The simulation results of power-frequency (50 Hz) current show that transient simulation results are the same as those of the steady-state model, as characteristic time of current is much longer than relaxation time of plasma. For fast current drop stage in dc interruption process, simulation results show that higher frequency makes current drops faster and ion number density larger; besides, residual plasma density between electrodes at current-zero moment is higher, and interruption becomes more difficult. Finally, transient characteristics of high-frequency HCVA is also simulated and analyzed. Simulation results show that change curve of ion number density lagged behind current curve; higher ion number density in the second 1/4 cycle can lead to reignition more easily. [ABSTRACT FROM AUTHOR]

In this paper, a transient 3-D model of the anode activity in a high-current vacuum arc (HCVA) was established. The melting, flow, evaporation, and solidification of the anode material were included in this model. Based on this model, the thermal and flow process of the anode in an HCVA under axial magnetic fields was simulated and analyzed. Simulation results showed that the maximum anode temperature appeared near 7 ms. The maximum rotational velocity and melting radius appeared near 9 ms. This meant that the anode was still in the melting, flow, and evaporation status near current zero moment, which was easier to cause reignition of vacuum interruption. Through 3-D modeling and simulation, a more visualized anode process can be understood. In the future, unsymmetrical anode phenomena will be researched and analyzed by this 3-D model. [ABSTRACT FROM PUBLISHER]

To improve the thrust performance of permanent magnet synchronous linear motor (PMSLM), novel deep adaptive ridge regression with embedded analytical mapping function (EAMF-RR) is proposed to calculate the thrust performance of PMSLM quickly and accurately, and combined with the EAMF-RR, a whale optimization algorithm (WOA) is introduced to optimize the PMSLM structure. First, the PMSLM's thrust is analyzed by the analytical modeling (AM) to determine the variation range of structural design parameters. Based on the variation range, a finite-element sample database is established for the EAMF-RR. Then, EAMF derived from AM, k-nearest neighbor algorithm, and WOA are integrated into RR to establish deep adaptive EAMF-RR model. Comparative simulation experiments conducted by using another two machine learning methods, i.e., extreme learning machine and weighted random forest, confirm the superiority of the EAMF-RR. Finally, WOA is reused to optimize the thrust performance of PMSLM, and prototype experiments prove the effectiveness of the proposed optimization method. [ABSTRACT FROM AUTHOR]

Existing self-supervised methods pose one-shot video object segmentation (O-VOS) as pixel-level matching to enable segmentation mask propagation across frames. However, the two tasks are not fully equivalent since O-VOS is more reliant on semantic correspondence rather than accurate pixel matching. To remedy this issue, we explore a new self-supervised framework that integrates pixel-level correspondence learning with semantic-level adaptation. The pixel-level correspondence learning is performed through photometric reconstruction of adjacent RGB frames during offline training, while semantic-level adaption operates at test-time by enforcing a bi-directional agreement of the predicted segmentation masks. In addition, we further propose a new network architecture with multi-perspective feature mining mechanism which can not only enhance reliable features but also suppress noisy ones to facilitate more robust image matching. By training the network using the proposed self-supervised framework, we achieve state-of-the-art performance on widely adopted datasets, further closing up the gap between self-supervised learning methods and their fully supervised counterparts. [ABSTRACT FROM AUTHOR]

To solve the problem that both analytical model (AM) and finite element model are difficult to give consideration to the calculation accuracy and efficiency at the same time in motor optimization work, a novel Lasso regression with the embedded AM, called EAM-LR, is proposed to quickly and accurately calculate the thrust performance of the permanent magnet synchronous linear motor (PMSLM) in this article. First, the thrust performances of PMSLM are analyzed by the AM to determine the variation range of structural design parameters. Based on the variation range, a finite-element sample database is established. Then, combined with the finite-element sample database, the analytical mapping functions derived from AM, are integrated into Lasso regression to establish EAM-LR. The accuracy of EAM-LR was verified by comparison with AM, traditional lasso regression, and well-known extreme learning machine. Finally, combined with the EAM-LR, the chaotic golden section algorithm is introduced to search the optimal structure parameters of PMSLM, and the control simulation and prototype experiment prove the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Based on a 3-D steady magnetohydrodynamic model, the high current vacuum arc subjected to a realistic spatial magnetic field generated by the cup-type contacts was simulated. The influence of the realistic spatial magnetic field profile on plasma's rotation behavior was analyzed. The distribution of the azimuthal velocity on anode side under realistic spatial magnetic field profile was quite different from that under uniform axial magnetic field. [ABSTRACT FROM PUBLISHER]

Trace of oxygen adding to the helium atmospheric pressure plasma jet can make the jet behave differently, such as dimming the plume and changing the jet length as well as the discharge current. Moreover, with certain specific ratio of oxygen/helium, double-bullet phenomenon could be captured by intensified charge couple device. The speeds of the bullets are estimated to be several kilometers per second. [ABSTRACT FROM PUBLISHER]

In real power system, when the three-phase short-circuit fault occurs, the vacuum arc in one phase will be influenced by the transverse magnetic field generated by neighbor phases and bus bars. This kind of effect is the main cause of the unstable arc and deflected erosion of contact plates, which leads to the failure of vacuum circuit breakers interruption. The objective of this paper is to get more insight into the influence of external transverse magnetic field (ETMF) on vacuum arc’s behavior. The experiments were conducted in a demountable vacuum chamber with pressure about 10^-4 Pa. The cup-type axial magnetic field contacts were used, whose material was pure copper and the diameter is 35 mm. The uniform ETMF in the arc region was generated by two parallel bulk permanent magnets. The experiments were conducted under different ETMFs (0, 15, and 25 mT) and current levels (1-, 2.5-, and 4-kA rms) with different gap distances (6, 8.5, and 11 mm). The videos of arc column were recorded by a high-speed charge-coupled device camera. Under the action of ETMF, the vacuum arc got deflected. Due to the retrograde motion of cathode spots and Ampere force acting on arc column, the deflection behaviors during three typical periods (that is, initial, peak value, and close-to-current-zero period) were different. Moreover, the deflection level of vacuum arc at current peak value moment was greatly impacted by ETMF and gap distance. Larger the ETMF and gap distance were, higher the deflection level at current peak value moment was. The simulation results of arc deflection based on magnetic-hydrodynamic model were in agreement with experimental results in trends. [ABSTRACT FROM AUTHOR]

Ubiquitous information service converged by different types of heterogeneous networks is one of fundamental functions for smart cities. Considering the deployment of 5G ultra-dense wireless networks, 5G converged cell-less communication networks are proposed to support mobile terminals in smart cities. To break obstacles of heterogeneous wireless networks, the 5G converged cell-less communication network is vertically converged in different tiers of heterogeneous wireless networks and horizontally converged in celled architectures of base stations/ access points. Moreover, the software defined network controllers are configured to manage the traffic scheduling and resource allocation in 5G converged cell-less communication networks. Simulation results indicate the coverage probability and the energy saving at both base stations and mobile terminals are improved by the cooperative grouping scheme in 5G converged cell-less communication networks. [ABSTRACT FROM PUBLISHER]

Traditional clustering techniques are inapplicable to problems where the relationships between data points evolve over time. Not only is it important for the clustering algorithm to adapt to the recent changes in the evolving data, but it also needs to take the historical relationship between the data points into consideration. In this paper, we propose ECKF, a general framework for evolutionary clustering large-scale data based on low-rank kernel matrix factorization. To the best of our knowledge, this is the first work that clusters large evolutionary data sets by the amalgamation of low-rank matrix approximation methods and matrix factorization-based clustering. Since the low-rank approximation provides a compact representation of the original matrix, and especially, the near-optimal low-rank approximation can preserve the sparsity of the original data, ECKF gains computational efficiency and hence is applicable to large evolutionary data sets. Moreover, matrix factorization-based methods have been shown to effectively cluster high-dimensional data in text mining and multimedia data analysis. From a theoretical standpoint, we mathematically prove the convergence and correctness of ECKF, and provide detailed analysis of its computational efficiency (both time and space). Through extensive experiments performed on synthetic and real data sets, we show that ECKF outperforms the existing methods in evolutionary clustering. [ABSTRACT FROM PUBLISHER]

Multi-tenant data management is a major application of Software as a Service (SaaS). For example, many companies want to outsource their data to a third party that hosts a multi-tenant database system to provide data management services. The multi-tenant database system needs to have high performance, low space requirement, and excellent scalability. One big challenge is devising a high-quality database schema. Independent Tables Shared Instances (ITSI) and Shared Tables Shared instances (STSI) are two state-of-the-art approaches to designing the schema. However, they suffer from some limitations. ITSI has poor scalability since it needs to maintain large numbers of tables. STSI achieves good scalability at the expense of poor performance and high space overhead. Thus, an effective schema design method that addresses these problems is needed. In this paper, we propose an adaptive database schema design method for multi-tenant applications. We trade-off ITSI and STSI and find a balance between them to achieve good scalability and high performance with low space requirement. To this end, we identify the important attributes and use them to generate an appropriate number of base tables. For the remaining attributes, we construct supplementary tables. We discuss how to use the kernel matrix to determine the number of the base tables, apply graph-partitioning algorithms to construct the base tables, and evaluate the importance of attributes using the well-known PageRank algorithm. We propose a cost-based model to adaptively generate the base tables and supplementary tables. Our method has the following advantages. First, our method achieves high scalability. Second, our method achieves high performance and can trade-off the performance and space requirement. Third, our method can be easily applied to existing databases (e.g., MySQL) with minor revisions. Fourth, our method can adapt to any schemas and query workloads including both OLAP and OLTP applications. Experimental results on both real and synthetic datasets show that our method achieves high performance and good scalability with low space requirement and outperforms state-of-the-art methods. [ABSTRACT FROM AUTHOR]

Based on a 2-D magnetohydrodynamic model, high-current vacuum arcs (HCVAs) under axial magnetic fields (AMFs) with consideration of current density distribution at the cathode are simulated and analyzed. The current density distribution at the cathode used in the simulation is obtained by processing the image of cathode spots from experiments. In order to study the influence of current density distribution at the cathode on vacuum arc characteristics, HCVA is simulated under two kinds of current density distribution at the cathode. Then, for HCVA simulation in a half-sinusoidal period, the current density distribution at the cathode and the AMF delay are both taken into account. The simulation results show that the nonuniform current density at the cathode makes the values of the arc plasma parameters in the interelectrode region larger and their radial distribution more nonuniform than the uniform current density at the cathode. The more uniform current density at the cathode and the stronger AMF at the moments in the second 1/4 cycle make the values of the arc plasma parameters in the central region smaller and their radial distribution broader than those in the first 1/4 cycle. In addition, the simulation results will also be compared with the experimental results. [ABSTRACT FROM AUTHOR]

Accurate absolute gravimeters are important instruments in applications, such as metrology, geophysics, and geological exploration. Vibration is one of the limiting factors that cause deterioration in measurement accuracy, which includes trueness and precision. The vibration correction method, in which a seismometer is used to record the vibration, provides an effective method to deal with the disturbances. The theoretical analysis shows that the ultimate correction accuracy is limited by the inherent frequency performance of the seismometer. The correction algorithm is an optimization problem to achieve this ultimate accuracy. The selection of the optimization objectives affects the correction accuracy dramatically. Although the real gravitational acceleration is unknown before the measurement is taken, minimization of the standard deviation of the fitting residual for a single drop (SDFRSD) is proven to realize better trueness. Enhanced precision is achieved through minimization of the Type A uncertainty of gravitational accelerations for all drops (UGAAD). Simulations and experimental measurements with the T-1 absolute gravimeter verify the theoretical analysis results. In addition, the results also show that the SDFRSD correction contains the real gravitational acceleration value, while the UGAAD correction exceeds the valid range. Therefore, the SDFRSD correction approach provides better comprehensive accuracy than the UGAAD correction method. [ABSTRACT FROM AUTHOR]

Accurate observations of the gravitational acceleration ($g$ , about 9.8 m/s2) provide important geophysical data for use in geophysics, metrology, and geodesy. At present, the most widely used absolute gravimeter determines the value of $g$ by tracking a falling retroreflector in a vacuum using a laser interferometer. The precision and accuracy of the measurement are mainly affected by ground vibration noise. When compared with a vibration isolator, vibration correction offers a simple and convenient way to reduce the influence of ground vibrations. Previous correction methods have used a low-noise seismometer as a detector. However, their performance is limited by the seismometer’s bandwidth (which usually ranges from 0.01 to 60 Hz). An optimized correction method combined with digital filtering is proposed here to increase the seismometer’s bandwidth numerically. Experimental results show that the accuracy and precision of the corrected results using the optimized method are improved in both relatively quiet and complex vibration environments. And better improvement is shown in complex vibration environment. Therefore, both the feasibility and the superiority of the proposed method have been verified. Further improvements can be achieved by using a higher-order digital filter. [ABSTRACT FROM AUTHOR]

The absolute gravimeter plays an important role in metrology, geophysics, and geological exploration. Seismic and environmental vibration has been one of the most serious factors limiting its performance. Consequently, an ultralow-frequency vertical vibration isolator is required to significantly improve its measurement precision. A novel active vertical vibration isolator employing geometric antispring (GAS) structure is proposed in this paper. The payload is supported by a GAS structure fixed on an inner frame, and the inner frame is hung by coil springs from the base. The relative movement of the payload with respect to the inner frame is detected, and the inner frame is driven by a voice coil actuator controlled by a feedback circuit to track the payload’s motion. The new isolator has a compact size, and it can be used for different load ranges by tuning the GAS structure. The practical closed-loop system has a resonant period of 19.2 s, compared with the period of 0.74 s in an open-loop system. Experiments showed that the new isolator has great performance in a homemade T-1 absolute gravimeter, reducing the measurement deviation by a factor of 32. It is expected to be used in both free-falling and atomic-interference absolute gravimeters. Future improvements may include optimizing the mechanical structure and integrating a temperature control subsystem. [ABSTRACT FROM AUTHOR]

A quench protection switch (QPS) is indispensable to protect the magnet coils from the damage of quench in a superconducting Tokamak. In this paper, a QPS based on artificial current zero is involved. The vacuum circuit breaker (VCB), which is driven by a high-speed electromagnetic repulsion mechanism, is used as the main circuit breaker (MCB). Two kinds of commercial vacuum interrupters (VIs), which have contacts generating axial magnetic field (AMF) and transverse magnetic field (TMF), respectively, are applied. The breaking current with an amplitude of 10~25 kA is generated by an LC oscillating circuit. The countercurrent with frequency in the range of 500–3000 Hz is provided by a commutation branch. The interruption performance of the two kinds of VIs under different breaking current and countercurrent frequencies is investigated. The experimental results indicate that the differences in interruption performance under the two types of contacts are increasing with larger frequencies of countercurrents. [ABSTRACT FROM AUTHOR]

The Robson drift phenomenon is a macroscopic reflection of the movement of a cathode spot (CS) in oblique magnetic field (OMF). Although it was discovered many years ago, its physical mechanism remains unclear. In this paper, the influence of OMF on the Robson drift of CS motion is simulated. A 2-D stepwise model of the movement of a single CS in OMF is established. It is assumed that the probability of generating a new spot in directions of Amperian force, anti-Amperian force, and directions perpendicular to Amperian force, is proportional to the magnetic pressure around the old spot. The drift angle and velocity of the CS in OMF are simulated. The simulation results show that the drift angle of the CS in OMF has liner relationship with the inclination angle of magnetic field, and it has no obvious relationship with the strength of the applied magnetic field and the amplitude of the arc current, which are in a good agreement with the experimental results. Besides, under the same angle of magnetic field, the velocity of spot motion increases linearly with the strength of OMF. Moreover, the simulation results show that the transverse magnetic field component has a much more predominant influence on the CS velocity than the axial magnetic field component, which are also in agreement with the experimental results. [ABSTRACT FROM AUTHOR]

This paper focuses on the multiobjective design optimization of the permanent magnet synchronous linear motors (PMSLMs), which are applied to a high-precision laser engraving machine. A novel efficient multiobjective design optimization method for a PMSLM is proposed to achieve optimal performances as indicated by high average thrust, low thrust ripple, and low total harmonic distortion at different running speeds. First, based on the finite-element analysis (FEA) data, a regression machine learning algorithm, called an extreme learning machine (ELM), is introduced to solve the calculation modeling problem by mapping out the nonlinear and complex relationship between input structural factors and output motor performances. Comparative simulation experiments conducted using the traditional analytical modeling method and another machine learning modeling method, i.e., support vector machine, confirm the superiority of the ELM. Then, a new bionic intelligent optimization algorithm, called the gray wolf optimizer algorithm, is used to search the best optimization performances and structural parameters by performing iteration optimization calculation for multiobjective functions. Finally, FEA and prototype motor experiments prove the effectiveness and validity of the proposed method. [ABSTRACT FROM AUTHOR]

This paper focuses on the thrust ripple reduction in permanent magnet synchronous linear motors (PMSLMs), which are applied to laser cutting machines. To meet the high-precision performance requirements of laser cutting machines, a novel auxiliary suppression device, tuned viscoelastic damper (TVD), is designed to reduce the thrust ripple of PMSLM. First, TVD is designed with the structure and motion characteristics of PMSLM. The PMSLM with TVD is an integrated structure. Then, the equivalent magnetization method is used to analyze the PMSLM thrust, which is the excitation of TVD. Under the excitation of the PMSLM thrust, the damping force of TVD is expressed by the Kelvin model and validated by finite-element analysis (FEA). Subsequently, the thrust of PMSLM with TVD is obtained by adding the PMSLM thrust and TVD damping force. Finally, the thrust ripple rate is selected as a performance index of TVD in reducing the thrust ripple. Simulation is performed to confirm the theoretical analysis. A prototype of PMSLM with TVD is manufactured and experiments are conducted to validate the effectiveness of the proposed auxiliary suppression device. [ABSTRACT FROM AUTHOR]

The efficiency, threshold characteristics, and the stability of spectral beam combining (SBC) of diode laser array had been studied based on different output couplers (OC). It was found that the lower OC reflectivity, lower internal loss, and shorter cavity-length of emitter were helpful for the realization of high efficiency SBC in an external cavity. However, too low OC reflectivity would also result in an unstable combining with the characteristic of side lobes appeared in far-field and the degraded efficiency. The influence of OC reflectivity on threshold current, lasing spectra, and the beam quality of SBC was investigated and analyzed. [ABSTRACT FROM AUTHOR]

This paper proposes an electromagnetic damping-spring system (ED-SS) to reduce the thrust ripple of permanent magnet synchronous linear motor (PMSLM), which is applied to the laser cutting machine. This approach uses restraining force of ED-SS that offsets the ripple force to decrease the thrust ripple. First, the ED-SS is designed with the structure and motion characteristics of PMSLM. The equivalent magnetization method is used to analyze the PMSLM thrust. Simultaneously, the ripple force is obtained and acted as the excitation of ED-SS. Next, the equivalent surface current method and the virtual work principle are utilized to express the restraining force characteristics and the relationship among the designed parameters of ED-SS. The standard deviation of PMSLM thrust is selected as an index to evaluate the magnitude of thrust ripple. Finally, simulation is performed to verify the validity of the theory analysis. The prototype of PMSLM with ED-SS is manufactured and three prototype experiments are conducted. The experimental results verify the validity of the proposed approach. [ABSTRACT FROM AUTHOR]

The Dick effect is one of the main limitations of short-term frequency stability for most atomic clocks operating in the pulsed mode. Rather than employing better local oscillators with ultralow phase noise, using the interleaving lock technique to eliminate the dead time is a promising approach to suppress the Dick effect. In this paper, we demonstrate the suppression of the Dick effect by the interleaving lock technique in a pulsed Ramsey-coherent population trapping clock with two identical Cs atomic ensembles. The Dick effect is expected to be reduced by a factor of 24 theoretically. The measured short-term Allan deviation is improved from $1.3\times 10^{-11}$ at 1 s to $3.0\times 10^{-12}$ at 1 s. What is even more remarkable is that the Allan deviation curve exhibits ${1/{\tau }}$ slope from 0.01 to 2 s. [ABSTRACT FROM AUTHOR]

The quench protection switch (QPS) is an indispensable component ensuring the safety of the magnet coils of a superconducting Tokamak when a quench happens. In this paper, the second commutation process of a QPS based on artificial current zero is investigated. In this process, the current, which has already transferred from the bypass switch to the main circuit breaker, is forced to commutate from the vacuum circuit breaker (VCB) to the discharge resistor by the countercurrent. An LC oscillating circuit is applied to generate oscillating current to simulate the direct current near its peak which is about 20 kA. The countercurrent with frequencies of 500 and 1000 Hz is provided by a commutation branch. The equivalence of the experimental interrupting process compared with the practical situation is analyzed. Two kinds of vacuum interrupters of the VCB are used in experiments. One kind is equipped with contacts generating transverse magnetic field, and axial magnetic field contacts are used in another one. The experimental results indicate that the initial process of the vacuum arc before injecting the countercurrent has crucial impacts on the interruption performance. The countercurrent with the frequency of 500 Hz is easier to interrupt the current than the case of 1000 Hz. [ABSTRACT FROM AUTHOR]