GB420495A - Improvements in and relating to reverse current electromagnetically released electric switches - Google Patents

Abstract

420,495. Electromagnetic switches and automatic circuit-breakers. BRITISH THOMSON - HOUSTON CO., Ltd., Crown House, Aldwych, London. July 2, 1934, No. 19494. Convention date, July 1, 1933. [Class 38 (v)] A reverse current release for a D.C. circuitbreaker comprising a voltage and a current coil mounted on a core to which an armature is attracted during normal conditions and released to open the circuit when the current reverses has a non-inductive resistance connected across the current coil to prevent the armature from being incorrectly retained in the attracted position with rapid current reversals. As shown in Fig. 2, the core 3 carries a voltage winding 4 and a current winding 5, the latter being shunted by a predominantly ohmic resistance 7. The armature 8 is normally attracted to the core 3 holding the switch 1 closed against a spring. With a rapid reversal of current, owing to the inductance of the winding 5, the majority of the current passes through the resistance 5 so ensuring the release of the armature and the opening of the switch 1. The voltage coil circuit including a series resistance 6 is completed at contacts 2 controlled by the switch 1. The resistance 7 (Fig. 3) comprises a pair of socket contact pieces 11 which can be clipped on conductors 12 and are connected by flat pieces 13 of resistance material such as constantan or nickeline. The resistance may be varied by sliding a bridging member 14, which is afterwards clamped in position.