Shenli Jia

Modelling and simulation of anode activity in high-current vacuum arc

Anode activity is critical for the success or failure of vacuum interrupters when the arc current attains a certain limiting value. Anode vapour from anode activity will influence high-current vacuum arc (HCVA) characteristics, and further influence interrupting successfully or not. In order to investigate the interaction between the arc column and anode vapour, a transient two-dimensional anode activity (subjected to HCVA column) model is established in this paper. Based on this model, the anode thermal process under ideal heat flux density and heat flux density from the arc column are simulated, respectively. The simulation results show that for sinusoid current, anode surface temperature first increases rapidly, then decreases slowly. With the increase in the heat flux density to the anode, the anode surface temperature will increase. The maximal value of the anode surface temperature appears near 7 ms (50 Hz current waveform), which is also in agreement with other simulation results. Anode evaporation cools the anode surface, which leads to a more uniform anode surface temperature at the contact centre than that near the contact edge. When the anode is melted, the radial distribution of the anode surface temperature appears as an inflection point. The simulation results are also compared with the experimental results and the results of other researchers. Reasonable agreement is observed. According to the anode activity model, the anode boundary condition of the HCVA model with anode vapour can be defined.

Modeling and simulation of anode melting pool flow under the action of high-current vacuum arc

In this paper, a transient magnetohydrodynamic (MHD) model of an anode melting pool (AMP) flow (AMPF) is established. Mass equation, momentum equations along axial, radial and azimuthal directions, energy equation, and current continuity equations are considered in the model. In the momentum equations, the influence of electromagnetic force, viscosity force and Marangoni force (anode surface shear stress) are included. Joule heating is also included in the energy equations. According to the MHD model of AMPF, the influence of different heat flux densities to melting pool flow velocities (including azimuthal, radial, and axial velocity), anode temperature, fraction of liquid, melting depth, melting radius, and anode vapor flux will be analyzed. In the AMP, the azimuthal velocity is dominant, whose value approximately approaches velocity magnitude, the radial velocity is much smaller than azimuthal velocity, and the axial velocity is the smallest one compared with radial and azimuthal velocity. According to...

Three-dimensional model and simulation of vacuum arcs under axial magnetic fields

In this paper, a three-dimensional (3d) magneto-hydro-dynamic (MHD) model of axial magnetic field vacuum arcs (AMFVAs) is established. Based on this model, AMFVAs are simulated and analyzed. Three-dimensional spatial distributions of many important plasma parameters and electric 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), ion velocities along different directions, electric fields strength along different directions, and so on. Simulation results show that there exist significant spiral-shaped rotational phenomena in the AMFVAs, this kind of rotational phenomenon also can be verified by the many related experiments (AMFVAs photographs, especially for stronger AMF strength). For current simulation results of AMFVAs, the maximal rotational velocity at anode side is about 1100u2009m/s. Radial electric field is increased from arc center to arc edge; axial electric field is ...

Numerical simulation of high-current vacuum arc characteristics under combined action of axial magnetic field and external magnetic field from bus bar

In this paper, the two-dimensional high-current vacuum arc (HCVA) model under the combined action of axial magnetic field (AMF) and external magnetic field from bus bar (EMFBB) is established. Based on this model, the influence of AMF and EMFBB on HCVA characteristics can be simulated and analyzed. Simulation results show that the HCVA column will be deflected by the Lorentz force generated by EMFBB and higher arc current. Moreover, the deflection level will be increased with the increase in external EMFBB strength. For HCVA, due to the smaller axial velocity near cathode side, the deflection of plasma parameters (such as ion number density, ion temperature, electron temperature, plasma pressure, and so on) near cathode side is more significant than that near anode side. The current deflection near cathode side toward direction of Lorentz force is more significant than that near anode side.

3D Numerical simulation of high current vacuum arc in realistic magnetic fields considering anode evaporation

A time-dependent 3D numerical model considering anode evaporation is developed for the high current vacuum arc (VA) under a realistic spatial magnetic field. The simulation work contains steady state 3D numerical simulation of high current VA considering anode evaporation at nine discrete moments of first half wave of 50u2009Hz AC current, transient numerical simulation of anode activity, and realistic spatial magnetic field calculation of commercial cup-shaped electrodes. In the simulation, contact opening and arc diffusion processes are also considered. Due to the effect of electrode slots, the simulation results of magnetic field and temperature of anode plate exhibit six leaves shape (SLS). During 6–8u2009ms, the strong evaporation of anode surface seriously influence the parameter distributions of VA. Ions emitted from anode penetrate into arc column and the axial velocity distribution on the anode side exhibits SLS. The ions emitted from anode surface have the same temperature with anode surface, which cool...

Modeling of the anode surface deformation in high-current vacuum arcs with AMF contacts

A high-current vacuum arc subjected to an axial magnetic field is maintained in a diffuse status. With an increase in arc current, the energy carried by the arc column to the anode becomes larger and finally leads to the anode temperature exceeding the melting point of the anode material. When the anode melting pool is formed, and the rotational plasma of the arc column delivers its momentum to the melting pool, the anode melting pool starts to rotate and also flow outwards along the radial direction, which has been photographed by some researchers using high-speed cameras. In this paper, the anode temperature and melting status is calculated using the melting and solidification model. The swirl flow of the anode melting pool and deformation of the anode is calculated using the magneto-hydrodynamic (MHD) model with the volume of fraction (VOF) method. All the models are transient 2D axial-rotational symmetric models. The influence of the impaction force of the arc plasma, electromagnetic force, viscosity force, and surface tension of the liquid metal are all considered in the model. The heat flux density injected into the anode and the arc pressure are obtained from the 3D numerical simulation of the high-current vacuum arc using the MHD model, which gives more realistic parameters for the anode simulation. Simulation results show that the depth of the anode melting pool increases with an increase in the arc current. Some droplets sputter out from the anode surface, which is caused by the inertial centrifugal force of the rotational melting pool and strong plasma pressure. Compared with the previous anode melting model without consideration of anode deformation, when the deformation and swirl flow of the anode melting pool are considered, the anode temperature is relatively lower, and just a little more than the melting point of Cu. This is because of liquid droplets sputtering out of the anode surface taking much of the energy away from the anode surface. The azimuthal velocity of the anode melting pool for arc current 12.5 kA root-mean-square (rms) is larger than that for 17.5 kA (rms), which is likely to be caused by the thinner liquid layer, and also a smaller melting pool mass of 12.5 kA.

Schlieren imaging investigation of the hydrodynamics of atmospheric helium plasma jets

This work investigates the hydrodynamic characteristics of a coaxial double-ring electrode helium plasma jet by means of a “Z-type” Schlieren imaging system. The Schlieren images and visual optical photographs made show that a transition point from a laminar region to a turbulent region exists for gas flow without plasma when the helium flow rate exceeds a certain value. After plasma ignition, the laminar region shrinks with voltage increases, and the maximum length of the plasma plume is confined to the laminar region. The heat transfer equation and the spectral broadening of the He I 667.8u2009nm were used to estimate the increased gas temperature in the plasma jet, and the change in gas velocity by ionic momentum transfer was found by application of a double sphere collision model. As a result, gas heating is considered to be the dominant factor for the earlier onset of turbulence after plasma ignition, whereas the role of ion momentum transfer to neutral gas molecules is comparatively weak. The hydrodynam...

Vacuum arc behavior and its voltage characteristics in drawing process controlled by composite magnetic fields along axial and transverse directions

In this research, drawing vacuum arc (VA) experiments were conducted using composite contacts under currents ranging from 5u2009kA to 20u2009kA root mean square (rms). The new type of contact comprised an axial magnetic field (AMF) configuration and a transverse magnetic field (TMF) configuration. The TMF plate was in the center, surrounded by the AMF plate. The contact generated both AMFs and TMFs simultaneously. VA appearances and arc voltages were recorded, and the VA was modeled as a conductor for electromagnetic force analysis in ANSYS software. The results showed that the coaxiality of operating mechanisms significantly influenced arc behavior just as the arc was ignited. When arc brightness did not increase after ignition, there was a voltage drop accompanied with diffusion of the VA. As to VA development, when an arc was ignited on an AMF plate, it spread on the plate and rotated. Over time the arc current increased, the constricting arc forms, and the arc column rotated on the TMF plate under the action of Amperes force. With regard to the influence of a magnetic field on a VA at different stages, in the initial drawing arc stage the TMF was dominant, and the arc started to rotate under the action of Amperes force. Afterwards, the AMF was dominant, with a steadily burning arc. As for contact melting, in the initial arcing period, a contracted short arc caused severe melting and erosion of the contact plate. When the ignition spot or root was close to the slot of plate, the electromagnetic force pushed the arc toward slot and contact edge, resulting in local erosion of the slot region.

Plasma backflow phenomenon in high-current vacuum arc

Based on the two-temperature magnetohydrodynamic model, a high-current vacuum arc (HCVA) in vacuum interrupters is simulated and analysed. The phenomenon of plasma backflow in arc column is found, which is ultimately ascribed to the strong magnetic pinch effect of HCVA. Due to plasma backflow, the maximal value of ion density at the cathode side is not located at the centre of the cathode side, but at the paraxial region of the cathode side, that is to say, ion density appears to sag at the centre of the cathode side (arc column seems to be divided into two parts). The sag of light intensity is also found by experiments.

Experimental investigation and numerical simulation of triggered vacuum arc behavior under TMF/RMF-AMF contact

A series of triggering experiments was carried out to investigate the characteristics of vacuum arc controlled by TMF/RMF-AMF contacts. During all the experiments, the current ranged from 5–20 kA (rms) and both the arc appearance and behavior of cathode spots were captured by high-speed camera with corresponding arc current and arc voltage. A 3D steady magnetohydrodynamics (MHD) model was built to simulate and analyze the vacuum arc behavior under TMF/RMF-AMF contacts, and arc plasma parameters were calculated based on the above model. The experimental results showed that arc deflection was visible under both low and high current. Under high current, arc core formed, which meant the arc contracted significantly. In addition, the anode became much more active under high current. The behavior of the cathode spots showed that they split themselves into other new cathode spots. Under high current, the bulk of the spots rotated along a clockwise direction on a transverse magnetic field (TMF) plate, which caused much noise and oscillation in the arc voltage. The simulation results show that ions are likely to gather on the branches of the TMF plate on the anode plane, as a result of the effects between the electromagnetic force and pressure gradient of the arc plasma. The current contracts in the center of the TMF plate on the cathode which was due to the thin connecting rod there. The anode contraction of the current is caused by the Hall effect. Ions move along a clockwise direction on the TMF plate, which is driven by Ampere force. The current contraction resulted in significant melting in the center of the cathode surface while the other region suffered from uniform melting. The melting caused by the anode contraction is more significant than that of the cathode.