Shi Zongqian

Analysis of the Carbon Nano-Structures Formation in Liquid Arcing

Graphite electrodes were used for the direct current (DC) arc discharge in water. And high-resolution transmission electron microscopy (HRTEM) was used to investigate the products. Based on the experimental phenomena and nano-structure products, arc plasma characteristics in water were analyzed theoretically. Two growth regions and relevant growth modes were proposed to interpret the formation mechanisms of nano-structures by arc discharge in water. Furthermore, liquid nitrogen and cross magnetic field was applied to change the arcing state respectively, and new carbon nano-structures were obtained. Their formation mechanisms were also analyzed correspondingly.

Influence of Shock Wave on Turbulence in SF6 Puffer Circuit Breaker

Influence of the shock wave on the turbulence in a supersonic nozzle was investigated for a SF6 puffer circuit breaker interruption process. Turbulence is enlarged through the shock wave. Baroclinic generation of vortex causes flow separation and broadening of the arc cross section. V-I characteristics are slightly modified due to the shock waves influence.

Simulation of the Influences of the Pressure Ratio and Cu Vapour on SF6 Arc Characteristics

The inlet and outlet pressure of the SF6 high voltage circuit-breaker nozzle are of importance in determining the thermal interruption capability of a breaker. Besides, electrode evaporation is inevitable during the arcing process, which may affect the SF6 arc behaviour significantly. In this study a numerical investigation on the arc characteristics of a supersonic nozzle is carried out, by considering the influence of the pressure ratio between the inlet and outlet, and the Cu vapour. It is demonstrated that a lower inlet pressure may result in a higher arc temperature, a lower arc voltage and a smaller mach number, and Cu vapour from electrode evaporation may cool the arc significantly.

Modeling and Simulation of Deflected Anode Erosion in Vacuum Arcs

In vacuum switch devices, the connection bus bar out of the vacuum interrupter will generate a transverse magnetic field in the arc column region, and under the influence of this magnetic field, the whole arc column will deflect from the electrode center, thus leading to deflected anode erosion. In this paper, a two-dimensional deflected anode erosion model is established, anode erosions under different deflection distance are simulated and analyzed, and results of anode surface temperature, anode melting and surface evaporation flux are obtained. The simulation results show that the deflected heat flux density will lead to deflected distribution of anode temperature, saturated vapor pressure and vapor flux correspondingly, and the morphology of the anode melting pool has also the same deflection. Moreover, the anode center temperature and its gradient along the y direction decrease with the increase of deflection distance. On the contrary, the temperature of the anode side surface, toward which the heat flux density deflects, increases with increasing deflection distance. Related experiments also verify the correctness of the model and simulation results.

Numerical simulation of high-current vacuum arc with consideration of anode vapor

A high-current vacuum arc (HCVA) with the consideration of anode vapor is modeled and simulated. First, from the HCVA column model, the heat flux density to the anode is obtained, which is put into the anode activity model, and the parameter distributions (such as the vapor temperature and velocity) of anode vapor are obtained from the simulation results of the anode activity model. Then, by iterating and calculating the HCVA column model and anode activity model, the interaction between the HCVA column and the anode vapor is simulated and analyzed. In the simulation, the distribution of the axial magnetic field (AMF) generated by the electrode system is calculated by software ANSYS. The simulation results show that the influence of anode vapor on the parameter distributions in the arc column is significant. The simulation results are also compared with the vacuum arc photograph.

Simulation Research of Magnetic Constriction Effect and Controlling by Axial Magnetic Field of Vacuum Arc

Based on magnetohydrodynamic (MHD) model of vacuum arc, the computer simulation of vacuum arc was carried out in this paper. In the MHD model, mass conservation equation, momentum conservation equations, energy conservation equations, generalized ohms law and Maxwell equation were considered. MHD equations were calculated by numerical method, and the distribution of vacuum arc plasma parameters and current density were obtained. Simulation results showed that the magnetic constriction effect of vacuum arc is primarily caused by the Hall effect. In addition, the inhibition of axial magnetic field (AMF) on constriction of vacuum arc was calculated and analyzed.

Investigation of Vacuum Arc Voltage Characteristics Under Different Axial Magnetic Field Profiles

Characteristics of the arc voltage under different profiles of axial magnetic field were investigated experimentally in a detachable vacuum chamber with five pairs of specially designed electrodes generating both bell-shaped and saddle-shaped magnetic field profile. The arc column and cathode spot images were photographed by a high speed digital camera. The dependence of the arc voltage on arcing evolution is analyzed. It is indicated that the axial magnetic field profile could affect the arc behaviors significantly, and the arc voltage is closely related to the arc light intensity.

Simulation of Vacuum Arc Characteristics at Different Moments Under Power-Frequency Current

In this paper, based on the quasi-stationary magneto-hydrodynamic (MHD) model, vacuum arc characteristics are simulated and analyzed at different moments under power-frequency current. For a vacuum arc with sinusoidal current under a uniform axial magnetic field (AMF), simulation results show that at the moment of peak value current, maximal values appear in the ion number density, axial current density, heat flux density, electron temperature, plasma pressure and azimuthal magnetic field. At the same time, the distributions of these parameters along the radial position are mostly nonuniform as compared with those at other moments. In the first 1/4 cycle, the ion number density, axial current density and plasma pressure increase with time, but the growth rate decreases with time. Simulation results are partially compared with experimental results published in other papers. Simulations and experimental results both show that the arc light intensity near the cathode side is stronger than that near the anode side for diffusing vacuum arcs.

Experimental Investigation on the Influence of Axial Magnetic Field Distribution on Resisting the Constriction of a High-Current Vacuum Arc

Effect of the axial magnetic field (AMF) on resisting the constriction of a high-current vacuum arc is studied in this paper. Two typical AMF distributions were investigated, i.e., the traditional bell-shaped AMF, and the saddle-shaped AMF. Experiments were conducted in a detachable vacuum chamber with a rms arc current in the range of 10 kA to 25 kA. The arc column was photographed by a high-speed digital camera with an exposure time of 2 microseconds. The constriction of the vacuum arc was compared by processing the images of the arc column under the two different field configurations and numerically determining the dimensions of the arc column near the electrodes. It was also confirmed that the AMF distribution had a significant influence on its effectiveness in resisting arc constriction. Furthermore, the AMF strength near the periphery of the arc is more influential than that at the centre of the electrodes in resisting arc constriction.

Influence of Jet Angle and Ion Density of Cathode Side on Low Current Vacuum Arc Characteristics

In this study, the influence of the initial jet angles (IJAs) and ion number densities (INDs) at the cathode side on the low current vacuum arc (LCVA) characteristics is simulated and analysed. The results show that the ion temperature, electron temperature, ion number density, axial current density and plasma pressure all decrease with the increase of the cathode IJAs. It is also shown that LCVA can cause a current constriction for lower cathode IND, and the anode sheath potential is more nonuniform, which is mainly related to the nonuniform distribution of the axial current density at the anode side.