Vacuum Arc In Axial Magnetic Field Research Articles

Experimental Determination of the Current Constriction Characteristics at the Anode of AMF Vacuum Arcs

Before the formation of the anode spot, the anode current constriction is considered as a result of current constriction on the cathode surface and in the arc column. The objective of this paper is to quantitatively determine the current constriction characteristics by experiments at the anode of vacuum arcs under an axial magnetic field (AMF). In this paper, the radial distribution of the anode current density in a diffused vacuum arc was determined quantitatively by a novel method of four types of split-anode contacts, with various diameters of the central areas. The vacuum arc was in the diffuse arc mode with the arc current ranging from 6-to 14-kA rms. An external AMF was applied at 74 mT. The results indicate that the radial distribution of the anode current density $j_{z}$ is in the form of the three-parameter equation, $j_{z}=aj_{A}e^{(-br\wedge 2)}+c$ , where $j_{A}$ is the average current density on the whole anode surface, $r$ is the radius of the anode contact, and the value of constants $a$ , $b$ , and $c$ depends on the arc current. Moreover, the results reveal the constriction characteristics of the anode current density in high-current vacuum arcs subject to the AMF, which was quite uneven in the radial distribution of the anode current density in the diffuse arc mode. Finally, under various arc currents, the constriction characteristics of the anode current density reveal similar patterns. The current density mainly constricted in the central region, in which the diameter might be only one-third of the whole diameter of the anode contact.

Three-Dimensional Time-Dependent Model and Simulation of High-Current Vacuum Arc in Commercial Axial Magnetic Fields Vacuum Interrupters

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 ( <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$x$</tex></formula> , <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$y$</tex></formula> , and <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$z$</tex></formula> ), 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.

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 1100 m/s. Radial electric field is increased from arc center to arc edge; axial electric field is decreased from cathode side to anode side. Radial electric field at arc edge can be larger than axial electric field. Azimuthal electric field in most regions is much smaller than radial and axial electric field, but it can reach about 1.19 kV/m. Radial magnetic field is the smallest one compared with other components, it reaches to maximum value at the position near to anode, it can influence arc characteristics.

Cathode processes in free burning and stabilized by axial magnetic field vacuum arcs

Collective behavior of the cathode spots (CS) has been investigated in free burning and stabilized by axial magnetic field (AMF) vacuum arcs. Experiments carried out proved previously discovered phenomenon of CS group formation in free burning arc to be a general phenomenon for a short high-current vacuum arc. The dependency of CS group size in the developed are on arc current for different contact materials has been analyzed. Application of AMF with even relatively low intensity strongly affects on cathode processes. In short arcs, it hinders formation of the CS group and consequently reduces thermal stress applied to the electrodes. It has been revealed that high current vacuum arc under the action of AMF can exist only at current densities exceeding certain minimal value that depends on AMF intensity, contact gap, and does not depend on current itself. The dependency of this minimal (or normal) current density on AMF intensity has been studied for short and long vacuum arcs. A qualitative model of the cathode spot dynamics has also been proposed.