GB423555A - Improvements in and relating to electric switches - Google Patents

Abstract

423,555. Heavy -current switches. BRITISH THOMSON-HOUSTON CO., Ltd., Crown House, Aldwych, London. May 22, 1934, Nos. 15273 and 15274. Convention dates, May 31, 1933. [Class 38 (v)] Contacts; switches, actuating pneumatic actuation; springs, arrangement of.- A switch has a pair of movable contact - carrying parts biassed apart by a spring and operating means for applying a force to either part to act through the resilience of the spring on the other part to close its contact against a cooperating contact. The contacts have surfaces which engage over a substantial area. As applied to a field - reversing switch of a traction motor, movable contacts 14, 15 cooperate with fixed contacts 16 .. 18, which have silver faces and are interconnected by a bar 82 which is welded or brazed to a bar 85 mounted by means of clamps 86 on a frame 60. Contact 14 comprises two silver contact faces 28, 29, welded or brazed to copper blocks 25, 26 which are clamped to seals 32, for springs 34 with intervening tubes 20, which are cold forged over braid 22. The braid 22 is welded to terminal 23 which is clamped at 44, 45 to the frame 60 by means of screws 66, 67. The intermediate contact 17 has silver faces 74, 75 co-operating with, respectively, 29 and a face 52 on contact 15 which contact is similar in construction to 14. Contact 17 has a terminal 72, and is clamped to 60 by clamps 78, insulation 92 separating the several clamps. The contacts 28, 29, &c. are urged apart by springs 34 and the seats 32 have projecting parts 41 on each side engaging in a window 40 in an operating arm 38. The arms of both contacts 14, 15 are riveted at 96 to an insulating cradle 95 which is guided by slots and rollers 103, 107. For reciprocating the cradle, a vertical slot 112 is engaged by a roller 110 on a cam 113 which is rotated through a rack and pinion by the piston 120 of an air engine. In the position shown in Fig. 3, where 110 is below the centre of slot 112, the contacts 14, 16 and 15, 17 are in engagement, and the spring pressure is arranged not only to produce the contact pressure, but also to act back through the drive to hold piston 120 at its lower position, whereby no air pressure is required to maintain the contacts in position. To reverse the contacts, air is admitted to raise the piston and move 110 up to the centre line of 112, so further compressing the contact springs. Further movement moves 95 to the right, relaxing the springs until 14, 15 engage 17, 18, when they are again compressed. When the roller 110 again moves below the centre of 112, the springs relax slightly and serve to maintain piston 120 at its upper position independently of the air supply. The cradle also carries contacts 146 co-operating with further contacts for the interlock circuits of the magnet valves of the air supply.