Zou Jiyan

A high-capacity triggered vacuum switch with single axial magnetic field electrode

A new type triggered vacuum switch (TVS) is developed. Its cup-like anode can generate a magnetic field parallel to the arc column by flowing current itself. The structure of the TVS, particularly the anode electrode is introduced in detail. Some experimental results are presented. The interactions between the axial magnetic field and the vacuum arc are analyzed. It appears that this axial magnetic field has an important role in stabilizing the arc and improving the current-carrying and charge-transferring capability of TVS.

Electrode erosion under high current vacuum arcs

Electrode erosion was measured under conditions of practical high current and axial magnetic field (AMF). Arc interruptions were made in a demountable vacuum chamber. Electrode erosion was assessed by weighting. It is shown that the rate of electrode erosion with AMF is 39.8 mu g/C and that without AMF it is 1.3 mg/C; the anode gains 15 mu g/C for diffused arcs.<<ETX>>

The theoretical prediction of current chopping ability of vacuum contact materials

Up to now, a theoretical model has not been established which shows the relationship between chopping current and material parameters and has direct significance for materials selection and manufacture. In this paper, based on the heat conduction equation and energy balance principle on the cathode surface, a new criterion, which can predict the current chopping ability and determine the chopping current sequence of different contact materials, is developed and verified by experiment. The new criterion clearly indicates: increasing the electrical resistivity, ionization potential, or decreasing the boiling point, specific heat, work function of material, atom weight, latent heat of fusion, latent heat of evaporation, will make the vacuum materials chopping current low.

Study of mode transition of long gap vacuum arc

By using a self-made CCD optical transient image system, the arc mode transition of long contact gap is studied. The re-ignition initial location at the side of the electrode is found. Adding an axial magnetic field by an additional coil, the high current arc mode becomes diffuse, and the arc voltage is reduced.

The metallurgical research on contact surface deterioration of AgNi, AgW, AgFe, AgCu contact materials

The static welding experiment was done for AgNi, AgW, AgFe, AgCu under the conditions: I=500, t/sub c/=0.1 S, Fc=1 N, Fo=0.8 N, contact size /spl Phi/4, which indicates that the decreasing sequence of contact ability against welding is AgW/spl rarr/AgCu/spl rarr/AgFe/spl rarr/AgNi. Based on this experiment, the surface micro-appearance in the contact welding zone is analysed, the contact areas for different contact materials are compared, and the material compositions distribution are also discussed. The influence of material property and heat power on surface deformation area is studied.

Floating potential of an isolated macroparticle in vacuum arc deposition plasmas

The vacuum arc deposition (VAD) plasma, as a cathode governed plasma, is not in a local thermal equilibrium state in nature, and the ions emitted from the cathode arc spots characterize high directed velocity in excess of their thermal value. Taking this special feature into account, the charging characteristics of an isolated macroparticle immersed in a VAD plasma are analyzed. The floating potentials of the macroparticles as a result of charging are calculated under thin and thick sheath case.

Electrical conductivity of CuCr alloys [for vacuum switches]

Based on the resistance theory of metals, the influence of phase structure on the electrical conductivity of CuCr alloys is analyzed. The electrical conductivity is calculated under different phase structure models. By comparison with measurements, the utility of these models are discussed. Some influencing factors on the conductivity of CuCr are summarized. Several ways to improve the electric conductivity of CuCr alloys for vacuum switch applications are presented.

3-dimensional simulation on electrical conductivity of CuCr contact materials

According to the phenomenal process, a 3-dimensional unit net model for calculation of the electrical conductivity is presented. By this model, the influence of components and its distribution upon conductivity of CuCr alloys is simulated, as well as the gas content in the phase structure. The comparison of the simulation results with typical experimental values approved the utility and effectiveness of this model.

Investigations on magnetic field in the interface regions between plasma armature and rail electrodes in a railgun

The key to controlling rail ablation lies in the interface regions between plasma armature and rails. The distribution of plasma in this region is affected by many factors, the magnetic field being the dominant one. In this paper, we analyze the magnetic field generated by rails and plasma armature in the interface regions, study the pattern and distribution of plasma near the interface and show the affect of magnetic field on plasma distribution and on the energy input to the rails. In order to reduce the initial ablation of the rail, we designed magnetic field coils outside the beginning part of the rails of our railgun. The coils enhance the initial magnetic field and increase the uniformity of the current distribution in the rails. Based on results from experiments and theoretical analysis, we propose a reasonable configuration of magnets and plasma armature.

Metallurgical aspects of arc-remelted CuCr contact materials

The arc-remelting technique is a newly developed process for manufacturing CuCr contact materials for vacuum switches. The quality of arc-remelted materials depends strongly on the operation parameters of the remelting process. In this work the remelting system, especially the designation of the arc plasma torch is introduced in detail. The dependence of the plasma jet current, the gas flow rate, and the cooling effect on the metallurgical aspects of melted CuCr materials is investigated. It is suggested that, in some respects, the increase of arc current, the decrease of gas flow rate, and the increase of cooling effect will result in a fine grain size.