The influence of magnetic field shape on dielectric characteristics of vacuum switches

The basic characteristics of vacuum switches are the following: high reliability, mechanical and electric durability, easy maintenance (no requirement for replacing or refilling the media intended for arc quenching, small dimensions and weight, the current being interrupted at the first zero phase without being accompanied by the repeated arc ignition, safety in terms of explosion and fire and zero environment pollution) [1-3]. The phenomenon of electric arc occurs in the course of the switching operation circuit-breaking with current. If this operation breaks the nominal current, the electric arc is wide (the diffuse arc). In case of short-circuit current breaking, the electric arc is narrow. The wide electric arc leads to contacts conditioning and increasing the value of breakdown voltage of the switch with open contacts. The narrow concentrated electric arc leads to considerable topography change of electrode surfaces thereby decreasing the breakdown voltage value of the switch with open contacts [4-7]. The concentrated arc oscillates under the influence of electromagnetic forces along the electrodes’ edge. In modern vacuum switches, the magnetic field in intercontact space is used for quenching the electric arc. The shape of magnetic field is obtained by contact geometry. The most commonly used shape is that of radial or axial magnetic field [8-10]. The aim of this paper is to examine the influence of the magnetic field shape in the inter-contact space in the context of contact degradation during the switching operations of circuit-breaking with current. 2. SWITCHING OPERATIONS OF CIRCUITBREAKING WITH CURRENT