GB1231897A - - Google Patents

Abstract

1,231,897. Gas-blast switches. SIEMENS A.G. 11 Dec., 1968 [12 Dec., 1967; 16Feb., 1968], No. 58992/68. Heading H1N. A high voltage on-load isolating switch comprises two fixed contact assemblies 6, 7; a movable bridging contact 8 surrounded by a tubular insulating sheath 30 and a pair of auxiliary contacts 43, 47, the arrangement being such that during interruption when the movable contact is moved in the opening direction (left of Fig. 1) one end 34 of the movable contact separates from the fixed contact 7 to create an arc but contact is maintained at the other end of the movable contact 8 by way of the auxiliary contacts 43, 47; after the arc is extinguished the auxiliary contacts separate to create an isolating gap. The movable contact comprises a plurality of segments 32 embedded internally in the tubular insulating sheath 30; the ends of the segments 32 are curved outwards to provide the contact surfaces. A metal tube 37 has projections 38, 39 engaging the segments and urging them outwards. The projections 38, 39 are placed so that the magnetic forces between the segments have a resultant force acting the increase contact pressure. The auxiliary contact 43 lies within tube 37 and is biased by a spring 50 to the position shown. The tip 48 of auxiliary contact 43 is enlarged and is gripped by the fixed auxiliary contact 47, spring 50 being compressed as the contacts open until its force overcomes the grip of contact 21. The end of tube 37 is closed by an insulating plug 54 which serves as a piston which moves into a cylinder 55 as the contacts open, thus causing an air blast. The cylinder 55 is made of polyoxymethylene, as are all insulating parts of the switch, and under the action of heavy current arcs evolves gas to increase the blast action. Blast gases escape by vents 60. An arcing ring 41 surrounds the movable contact portions 34. The contact segments 32 are of a resilient copper-chromium alloy. The fixed contacts 6, 7 are solid metal members supported from a metal frame 1 by insulators 4. In a modification (Figs. 3-5, not shown), the contacts are simple metal forms embedded in moulded insulating material, this both reducing cost and increasing dielectric strength.