GB906484A - Improvements in electrical current limiting devices and circuits - Google Patents

Abstract

906,484. Metal vapour discharge apparatus. GENERAL ELECTRIC CO. Dec. 9, 1960 [Dec. 15, 1959], No. 42472/60. Class 39 (1). A current limiting electron discharge device has a non-porous insulator disc 11, Fig. 1, or sphere having one or more capillary apertures extending therethrough and filled from end to end with a vaporizable solid or liquid conductor and rigid terminal members in electrical contact with opposite ends of the conductor are provided, the insulator and terminal members forming a sealed enclosure for the conductor of sufficient rigidity to prevent substantial elastic deformation thereof and oscillatory movement of the conductor within the aperture due to the vaporization of all or a part of the conductor and generetion of high pressure current limiting arcs by currents through the conductor in excess of a predetermined value. The capillaries in ceramic disc 11 may be axial as shown or may radiate outwardly from a disc or sphere. The ceramic disc 11 has capillaries each filled with a conductor of mercury, Ag, Li, Na, K or a eutectic mixture of Na and K. The disc 11 is of polycrystalline ceramic-Al 2 O 3 powder compressed and fired. Reservoirs 14, 15 are filled with the same metal as the capillaries. The envelope is completed by semi-conductive annuli 16, 17 (mixtures of ceramic and metal of matching coefficient of expansion with ceramic disc 11) having plugs 19 with adjustable screws 20. 22, 23 are screw-threaded terminals. The device has a steel housing 10 and steel caps 32, 33. Insulating sleeves 35, 36 are of epoxy resin. Two sets of two ceramic spacer rings 37 have a packing member 38 between them. The terminal members 22, 23 fit tightly within collars 39 which are castellated. The ceramic disc 11 is insulated from the casing by highly pressurized oil. Gauge 43 measures the high pressure and fits within a screwed bore in casing 30. A second screwed bore is closed by a nut 44. Piston 45 compresses Cu sphere 48, the deformation of which is a measure of the pressure. Gaskets 21, 38 are of silicone rubber and O rings of the same material may be under the heads of screws 20. Gaskets 28, 29, 45 are of Cu. An unstable high pressure arc is set up. Use of the device in a 3-phase circuit breaker is described with reference to Fig. 3 (not shown).