GB250242A - Protective device for electric circuits - Google Patents

Abstract

250,242. British Thomson-Houston Co., Ltd., (Assignees of Compagnie Franþaise pour l' Exploitation des ProcÚdÚs Thomson- Houston). April 1, 1925, [Convention date]. Void [Published under Sect. 91 of the Acts]. Protective arrangements for alternating-current distribution systems employ a transformer having low magnetic leakage between its windings, its primary winding being energized responsively to the current in the protected circuit and its secondary winding being normally short-circuited through an excess current cut-out or other device which is open-circuited so as greatly to increase the inductance of the transformer when an excess current passes through it. The cut-out may be of the fusible or electromagnetic type or may be an electric discharge device such as a vacuum tube. A vacuum tube serves to introduce the high inductance, momentarily, in the event of transient atmospheric disturbances. A circuitbreaker in the secondary winding may be tripped by the closure of a relay energized by current or potential derived from the main circuit. The open-circuiting devices may be associated with means for resetting them with or without a timelag. Instead of open-circuiting the secondary, excess current therein may serve to start up an induction or other motor the resulting backelectromotive-force of which reduces the current in the secondary. The secondary may be connected either to the protected circuit or to earth.