Xiao Zhang

Simulation results of influence of constricted arc column on anode deformation and melting pool swirl in vacuum arcs with AMF contacts

In the process of vacuum arc breaking, the energy injected into the anode will cause anode melting, evaporation, and deformation, resulting in the formation of the anode melting pool. The anode activities have great influence on the arc behavior. When the arc current is large enough, even the influence of axial magnetic field is considered, the arc column still is in contraction state, which means the arc burns only on a part of the electrode. In this paper, the model of anode melting pool deformation and rotation is used, and the model includes anode melting and solidification module, magneto-hydro-dynamic module of the anode melting pool, the volume of fraction method, and the current continuity equation. In this paper, the diffuse arc area is selected as 100%, 75%, and 50%, respectively. The anode temperature and deformation, the anode melting layer thickness, and the rotational velocity of the anode melting pool are obtained. The results show that when the current is at 17.5u2009kA (rms) and the diffuse a...

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.

Experimental and simulation of triggered vacuum arc under TMF-AMF contact

A series of triggering experiments were carried out to investigate into the characteristics of vacuum arc controlled by TMF-AMF contacts. During the whole experiments, current ranged from 5kA to 20kA (rms) and both arc appearance and the behavior of cathode spots were captured by high-speed camera with corresponding arc current and arc voltage. A 3D steady MHD model was built to simulate and analyze the vacuum arc behavior under TMF-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 arc contracted itself significantly. The simulation results show that ions are likely to gather on the branches of TMF plate on anode plane, as a result of the effects between electro-magnetic force and pressure gradient of arc plasma.

Modeling of interaction between arc and macroparticle in vacuum trigatron

This work investigates the interaction between high current vacuum arc (HCVA) and the macroparticle (MP) generated from the cathode spots in the small-size vacuum trigatron. Magnetohydrodynamic (MHD) model is used to describe the arc column. MPs are added into the MHD model, which are described by discrete phase model. The control equations of MPs include charging equation, motion equation, and heat transfer equation, in which the evaporation of MPs is also considered. Based on the above model, the effects of the diameter and initial velocity of MPs on the characteristics of them are studied. Simulation results show that MPs leave the interelectrode gap with a deflection angle larger than the initial angle under the influence of plasma. The motion of MPs is similar to that of projectiles. MPs with smaller diameter or slower velocity are influenced by the arc plasma more significantly. MPs can act as a source of the plasma, but these influences are not obvious in HCVA. What may be more harmful to the trigatron is the charging process of MPs during post-arc process.This work investigates the interaction between high current vacuum arc (HCVA) and the macroparticle (MP) generated from the cathode spots in the small-size vacuum trigatron. Magnetohydrodynamic (MHD) model is used to describe the arc column. MPs are added into the MHD model, which are described by discrete phase model. The control equations of MPs include charging equation, motion equation, and heat transfer equation, in which the evaporation of MPs is also considered. Based on the above model, the effects of the diameter and initial velocity of MPs on the characteristics of them are studied. Simulation results show that MPs leave the interelectrode gap with a deflection angle larger than the initial angle under the influence of plasma. The motion of MPs is similar to that of projectiles. MPs with smaller diameter or slower velocity are influenced by the arc plasma more significantly. MPs can act as a source of the plasma, but these influences are not obvious in HCVA. What may be more harmful to the triga...

Simulation of cathode spot crater formation and development on CuCr alloy in vacuum arc

The two-dimensional (2D) rotary axisymmetric model is used to describe the formation and development of a cathode spot on a copper-chromium alloy (CuCr) in a vacuum arc. The model includes hydrodynamic equations and the heat transfer equation. Parameters used in this model come from experiments and other researchers work. The influence of parameters is analyzed, and the simulation results are compared with pure metal simulation results. In simulation, the depth of the cathode crater is from 0.5u2009μm to 1.1u2009μm, the radius of the cathode crater is from 1.6u2009μm to 2.6u2009μm, the maximum velocity of the droplet is from 200 m/s to 600 m/s, and the maximum temperature is from 3500u2009K to 5000u2009K which is located in the area with a radius of 0.5–1.5u2009μm. The simulation results show that a smooth cathode surface is advantageous for reducing ablation, the ablation on the CuCr alloy is smaller than that on the pure metal cathode electrode, and the cathode spot appears on the chromium grain only on CuCr. The simulation results are in good agreement with the experiment.The two-dimensional (2D) rotary axisymmetric model is used to describe the formation and development of a cathode spot on a copper-chromium alloy (CuCr) in a vacuum arc. The model includes hydrodynamic equations and the heat transfer equation. Parameters used in this model come from experiments and other researchers work. The influence of parameters is analyzed, and the simulation results are compared with pure metal simulation results. In simulation, the depth of the cathode crater is from 0.5u2009μm to 1.1u2009μm, the radius of the cathode crater is from 1.6u2009μm to 2.6u2009μm, the maximum velocity of the droplet is from 200 m/s to 600 m/s, and the maximum temperature is from 3500u2009K to 5000u2009K which is located in the area with a radius of 0.5–1.5u2009μm. The simulation results show that a smooth cathode surface is advantageous for reducing ablation, the ablation on the CuCr alloy is smaller than that on the pure metal cathode electrode, and the cathode spot appears on the chromium grain only on CuCr. The simulation resul...

Numerical Simulation of Vacuum Arc Behavior Considering Action of Adjacent Phases in Vacuum Circuit Breakers

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.

Experimental Study on Deflection Behavior of Vacuum Arcs Under the Influence of External Transverse Magnetic Field

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

Numerical simulation of HCVA with considering the micro process of anode vapor

10^{-4}

3D simulation on vacuum arc controlled by external transverse magnetic field

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.

Modeling of cathode spot crater formation and development in vacuum arc

When the arc current is high, the heat flux density injecting into anode will be large and lead to the higher anode temperature, driving the evaporated atoms into arc column. In this paper, the MHD model of vacuum arc considering ionization and recombination of anode vapor is built. The influence of the anode vapor and the micro processes on the arc column is obtained. In the model, the mass, momentum and energy exchange are considered. Additionally, the influence of ionization and recombination process on the electromagnetic process of VA is also considered. In the simulation results, the anode vapor, cathode plasma and VA distribution are all obtained. When the anode temperature is high enough, the anode neutral vapor will enter into arc column, and the strong ionization happens at the interface of anode vapor and cathode plasma. The anode neutral vapor has obviously cooling effect on the arc column. Whether the anode neutral vapor will enter into the arc column or not, is related to the balance between the anode neutral vapor and the cathode plasma.