The breakdown field strength E/sub b/(= alpha Vb/d) of gaps made with pure copper and stainless steel depends on the effective area S/sub eff/. It can be expressed by the single experimental equation E/sub b/=K/sub 1/S/sub eff//sup -n/, where K/sub 1/ is a constant, n is about 0.24, S/sub eff/ is the electrode area subjected to more than 90% of maximum field strength, alpha is the shape factor, d is the gap length, and V/sub b/ is the breakdown voltage. The field intensification factor beta /sub l/ obtained through the measurement of prebreakdown current can be expressed by a single experimental equation beta /sub l/=K/sub 2/S/sub eff/n, where K/sub 2/ is a constant. This means that the area of effect of E/sub b/ is represented by the area effect of beta /sub l/ and that the vacuum breakdown may be initiated by field emission. >

Area effect on electric breakdown of copper and stainless steel electrodes in vacuum

In this paper vacuum breakdown phenomena are reviewed in two parts The first considers the development of thought concerning electrical breakdown in vacuum with particular regard to field emission, interaction of cathode emission at the anode, and particle effects, including impurities While Section 1 is basically historical, Section 2 considers these and other topics in the light of recent literature

Electrical Breakdown in Vacuum

The author presents a bibliography covering the field of electrical discharges in vacuum, comprising both electrical breakdown in vacuum and vacuum arcs. A brief section lists some review papers which would be helpful to the novice in this field. The bulk of the presentation consists of bibliographic listings arranged by year of publication and alphabetically by author within each year. An author index refers one to all papers authored or coauthored by a particular person. >

Electrical discharges in vacuum: 1980-90

Using three types of copper electrodes with different surface areas, experiments were performed to investigate the influence of electrode area on the conditioning effect,which is a characteristic of dielectric breakdown in vacuum gaps. The conditioning process varied with electrode area: the smaller the electrode area, the sooner conditioning ended. Breakdown voltages after completion of conditioning also depended on electrode area: the smaller the electrode area, the higher the breakdown voltage. >

Influence of electrode area on the conditioning effect in vacuum

The characteristics of a vacuum arc between CuCr contacts under an axial magnetic field have been investigated Test samples were made of CuCr contacts, and the arcing voltage was measured The arcing voltage of the CuCr contacts under an axial magnetic field is lower than that of pure copper contacts by 10-20 V From the measurement of the post-arc current and interruption test results, it was found that the arc concentrates and a part of the electrode melts at a rather low current, but that the electrode melting does not affect the interrupting capability Also, the insulation characteristics were measured With respect to voltage conditioning, high-current conditioning improved the breakdown voltage by 50 percent for a 20-mm gap and by 100 percent for a 3-mm gap These test results show that CuCr contacts, used with axial magnetic fields, are promising for use in high-voltage and high-power vacuum interrupters

The Investigation of Copper-Chromium Contacts in Vacuum Interrpters Subjected to an Axial Magnetic Field

High voltage impulses were used to investigate various possible factors influencing the prebreakdown current and breakdown in vacuum gaps of sphere-to- sphere and rod-to-plane.

T. Shioiri

Papers

Impulse Voltage Field Emission Characteristics and Breakdown Dependency Upon Field Strength in Vacuum Gaps