Dmitry L. Shmelev

Numerical Simulation of a Moving High-Current Vacuum Arc Driven by a Transverse Magnetic Field (TMF)

This paper deals with the numerical simulation of the constricted high-current vacuum arc (>15 kA), driven by a transverse magnetic field (TMF), as found in vacuum circuit breakers applying the TMF arc control. The magnetohydrodynamic approach, together with the detailed heat transfer and evaporation equations for the electrodes, is used to describe the arc behavior self-consistently, restricted to 2-D. A newly developed model describes the cathode attachment of the constricted arc, as a large laterally extended foot points, instead of regular cathode spots. The arc maintains itself when the electrode temperatures are higher than 3400 K on the cathode and 2900 K on the anode. This model leads to the characterization of the physical quantities of the arc plasma and describes the arc motion. A stepwise movement of the arc results due to different instantaneous velocities of the current attachment areas at the cathode and anode.

Numerical simulation of high-current vacuum arcs in external magnetic fields taking into account essential anode evaporation

High-current arcs as found in AMF vacuum interrupters have been numerically simulated taking into account the effect of evaporation of metal vapor from the anode surface. The Magneto-Hydro-Dynamic approach is applied. The physical behavior has been studied and the heat flux to the anode determined. Rise of surface temperature and rate of evaporation has been analyzed for arcing with one half wave of 50Hz-AC-current between Cu contacts. The transition from diffuse to diffuse columnar seems to occur when evaporation rate of metal vapor from the contact surfaces exceeds the emission of plasma produced by the cathode spots.

Mechanism of ion flow generation in vacuum arcs

The ecton model of the cathode spot is used to analyze the main parameters of ion flow in vacuum arcs (ion erosion, mean charge, and velocity). It is shown that the arc plasma is formed as a result of microexplosions at the cathode surface, induced by the Joule heating by the high-density current of explosive electron emission. Ionization processes are localized in a narrow region of the order of a micrometer near the cathode and the ionization composition of the plasma subsequently remains unchanged. Under the action of the electron pressure gradient, ions acquire directional velocities of the order of 106 cm/s even over small distances of the order of several micrometers.

Optical investigations of dynamic vacuum arc mode changes with different axial magnetic field contacts

By using a high-speed charge-coupled device (CCD) video technique, three different axial magnetic field contact systems (i.e., unipolar, bipolar, and quadrupolar systems) are investigated at an arc current of 10 kA. Video recordings were compared to computer simulations of light emission emitted at the side-on of diffuse and diffuse columnar arcs. The computer images reproduced typical trends, such as stronger light intensities in front of the cathode caused by higher-plasma densities in this region. A low-current dc vacuum arc was initiated by contact separation before the high current was injected at a fixed contact distance of 10 mm. Videos were taken from two directions perpendicular to each other to localize the vacuum arc properly. From these investigations, the transient development of vacuum arc under different axial magnetic field profiles can be visualized. The results were interpreted with respect to the behavior of the vacuum arc in the second half cycle after an eventual reignition.

Simulation of a High Current Vacuum Arc in a Transverse Magnetic Field

This paper presents the results of simulations using a model that describes constricted high current (>15 kA) vacuum arcs driven by a transverse magnetic field in a 2-D configuration (parallel rail electrodes). The simulations investigate a number of cases of practical interest for the use of vacuum interrupters. The influence of the electrode gap distance on the arc motion is discussed. It is found that faster arc velocities are obtained for larger gaps. For large gaps (ges5 mm), the Lorentz forces and pressure gradients acting on the plasma jets originating from the hot electrodes strongly affect the arc structure. The arc tends to expand on a longer distance and can efficiently preheat the next area of current attachment. The model also describes the jump of the arc over an electrically nonconductive part of an electrode (slit). This is possible due to the ability of the arc column to expand in the direction of motion and to prepare current attachment at a point beyond the slit. The characteristics of the jump depend on a function of the slit width, electrode gap, and current. Finally, the thermal effect on the electrode surface and the electrode bulk for an arc returning several times to the same position is investigated for a fixed DC current. The results show that the minimum surface temperature increases the first few times the arc returns, before stabilizing at a temperature given by the balance between the arc heat flow and the cooling by metal evaporation and conduction into the electrode.

Modeling of Cathode Plasma Flare Expansion

A kinetic 1-D model of cathode plasma flare expansion to the interelectrode vacuum gap was developed. The kinetic model is a model of 1D3V particle-in-cell and direct simulation Monte Carlo type. The model takes into account the main types of elastic and inelastic collisions of particles in the plasma as well as evaporation and thermofield electron emission from the cathode. The model treats the plasma flare expansion and the electron emission from the outer plasma boundary of the flare self-consistently. The plasma characteristics of the cathode flare obtained with the model are in a reasonable agreement with known experimental results.

Physical Modeling and Numerical Simulation of Constricted High-Current Vacuum Arcs Under the Influence of a Transverse Magnetic Field

This paper deals with the numerical simulation of constricted high-current vacuum arcs (> 15 kA), driven by a transverse magnetic field. The magnetohydrodynamic approach and the radiative transfer equation in the P1 approximation, together with detailed treatment of heat transfer and evaporation at the electrodes, are used to describe the arc behavior self-consistently in a 2-D geometry. The model developed describes the cathode attachment of the constricted arc as a large laterally extended foot point, instead of as regular cathode spots. This model leads to the characterization of the physical quantities of the arc plasma and describes the arc motion. A stepwise movement of the arc results due to different instantaneous velocities of the current attachment areas at the cathode and the anode.

The effect of cathode deuteration on the parameters of vacuum-arc plasma

We propose a model for determining the influence of the relative content of deuterium in a zirconium cathode on the properties of vacuum-arc plasma. It is shown that the occlusion of deuterium in the cathode leads to an additional energy consumption for its ionization and to the related decrease in the average charge of cathode material ions in the discharge plasma. Deuterium in the cathode spot is fully ionized, and the drift velocity of deuterium ions almost coincides with that of ions of the cathode material.

Model of Collective Acceleration of Ions in Spark Stage of Vacuum Discharge

A new mechanism of the collective acceleration of ions at the spark stage of a vacuum discharge is proposed. It has been show n that this acceleration can take place in the presence of a plasma cloud in the electrode gap with strong electronic instability developing in the plasma. The appearance of accelerated ions of the interelectrode plasma is accompanied by a jump in the diode current.

Physical modeling and numerical simulation of constricted high current vacuum arcs under action of transverse magnetic field

This paper deals with the numerical simulation of the constricted high-current vacuum arc (>15 kA), driven by a transverse magnetic field (TMF). The magnetohydrodynamic approach, radiative transfer in P1 approximations, together with the detailed heat transfer and evaporation equations for the electrodes, is used to describe the arc behavior self-consistently in 2D geometry. A model developed describes the cathode attachment of the constricted arc, as a large laterally extended foot point, instead of regular cathode spots. This model leads to the characterization of the physical quantities of the arc plasma and describes the arc motion. A stepwise movement of the arc results due to different instantaneous velocities of the current attachment areas at the cathode and anode.