Vacuum interrupter with a radial magnetic field

Abstract

A vacuum interrupter with an enhanced radial magnetic field includes within a vacuum envelope a pair of confronting contacts that are relatively movable between an open circuit and a closed circuit position. The contacts, which can be the spiral-arm type or the slotted-cup type, are surrounded by a tubular metal vapor shield that is electrically isolated from at least one of the contacts in the open circuit position. Each contact is connected in series with a coil energized by the current in the interrupter and positioned proximate the non-confronting face of the contact, and with a current carrying terminal post extending outside the vacuum envelope. The current in the coils produces a radial magnetic field in the intercontact region that encourages a columnar arc between the contacts to move outward and attach to the vapor shield. This helps to promote a transition to a diffuse type of arc and allows for a more compact interrupter with greater interruption capability. The radial magnetic field can also be enhanced by using a contact design having elongated spiral-shaped arms that each extend more than 180.degree. around the contact. The elongated spiral-arm contacts can be used in conjunction with the coil structure or used alone to produce the enhanced radial magnetic field. The vapor shield is fabricated of a thick layer of a Cu--Cr metal mixture, or of a high permeability material.