GB748532A - Improvements in or relating to arrangements for limiting overload currents in direct-current and alternating-current supply systems - Google Patents

Abstract

748,532. Protective cut-out arrangements; electrically-released switches. F. K. G. F. KESSELRING GERATEBAU AKT.- GES. Feb. 10, 1954 [Feb. 10, 1953], No. 3950/54. Class 38(5) An overload protection arrangement enabling the use of current-limiting fuses of relatively-low current-rating, comprises a pair of fuses 3, 4 rated for one-tenth of the normal current, the end caps 5, 6 of which are connected to metal members 8, 9 constituting the fixed contacts of a shunt switch. The centre cap 7 of the fuses is connected at 17 to a movable bridging contact 16 which is normally held closed by a wire 27 having balls 28, 29 engaged in slits 30, 31 of, respectively, the contact 16 and an upwardly-biased leaf spring 19. The wire 27 also passes over an adjustable roller 20 on an arm 21 and is engaged by a knife-edged contact 33 on a leaf spring 32 which is connected by a lead 25 to a terminal 10 conductively connected to end cap 5 by a conductor 15 carrying iron laminations 14. Normally the switch 8, 16, 9 caries most of the current, but when a short-circuit occurs. the inductive effect of parts 14, 15 sends a current through spring 32 and wire 27 sufficient to fuse the latter and release the spring 19 which rapidly opens the switch and diverts the current through the fuse to rupture it. The time between the onset of the overload and the opening of the switch must not exceed 0.5 milliseconds, and the voltage across the fuse must not exceed 15 volts and must be at every instant less than the breakdown voltage of the switch. The latter may be oil or gas-immersed or of the vacuum type. In Fig. 2 a condenser 41, kept constantly charged by an autotransformer 44, discharges across electrodes 47 to fuse the wire 48 when a spark gap 46 is broken down by the discharge of a spark gap 40 energized by a line current transformer 62. In another embodiment (Fig. 3, not shown) the movable bridging contact forms the armature of a magnet which is energized either directly by the line current, or by discharge of a condenser as in Fig. 2. The armature is held in its attracted position by the flux of a permanent magnet forming part of the magnetic circuit, against the action of a bowed leaf spring. The Specification refers also to the automatic connection of a fresh device in circuit after one has operated.