GB164755A - Improvements in automatic maximum-current switches - Google Patents

Abstract

164,755. Siemens - Schuckertwerke Ges. June 15, 1920, [Convention date]. Void [Published under Sect. 91 of the Act]. Automatic circuit-breakers.-Maximum current switches for heavy currents are provided with resistances shunting the main contacts so that when the main circuit is broken, on overload, a sufficient current still passes through the shunt circuit, if the full overload persists, to retain the switch in the open position and prevent its closure either by hand or electromagnetically. In the hand-operated form shown in Fig. 1, the contact member 2 under the action of the spring 4 is maintained in engagement with the contact 1 by the pawl 5, which forms part of the armature 7, engaging with a nose 6 on the pivot part of the contact member. The load current passes through the winding 10 of the electromagnet 9 and, in the event of overload, the armature is attracted and the contact-member released. A shunt circuit through the winding 10 is maintained by way of the shunt resistance 11, and, if the overload persists, the reduced current in the winding is still adequate to hold the armature. Meanwhile, in the opening movement a nose 12 engages behind a spring pawl 13 on an extension of the armature and positively prevents the return of the contact member until the armature is released on removal of the overload. In the form shown in Fig. 2, in which the switch is closed by means of the electromagnet 16, 17 acting through links 15, 14 the local closing circuit includes fixed contacts 21 which are engaged by a bridging contact 22 on the armature only when the armature is in the unattracted position so that the local closing circuit can be closed only when the armature is not attracted, that is, when no overload exists. In this form, the electromagnet has a separate maintaining winding 25 in series with the resistance 11, enabling a smaller maintaining current to be used.