GB665338A - Automatic protective device for an electric apparatus - Google Patents

Abstract

665,338. Protective cut-out arrangement. GRACIARENA, E., and EDERY, F. Nov. 18, 1949. No. 29606/49. Class 38 (v). A device for interrupting the supply to a load in the event of earth leakage, utilises the unbalance produced in the windings of a differentially-wound transformer to operate, via a valve amplifying device, a relay which in turn closes the circuit of the tripping coil of the main circuit-interrupter. For protecting a single-phase A.C. supply, Fig. 1, the unbalance produced in a low resistance differential transformer 22 in the protective interrupter group C, to which the load is connected at 26, is amplified to operate the main interrupter 27 by a group B which is supplied from an auxiliary interrupter group A connected to the supply at 1 such that when the load circuit is open no current flows to the group B. Group A comprises a pair of relays 3, 4 having armatures 6, 14 biassed to the open position. When the load circuit is closed current flows from 1a, through resistance 9, relay coil 10 of low ohmic value, terminal 11a, contacts 40 of interrupter 27, differential transformer winding 25a, the load, differential winding 25, terminal 11, and the supply line 1b. Coil 10 attracts the armature 6 thereby closing a circuit from 1a, through relay contacts 7 and relay coil 12 back to line 1b, and the armature 14 is attracted to close contacts 8, whereby a supply is established to the terminals 13, 13a of the amplifier group B and the resistance 9 is short-circuited. Unbalance from the transformer 22 excites a secondary coil 24 connected through terminals 19 to a "push pull" amplifier 17 supplied by a rectifier valve 18, the unbalance being transmitted through terminals 20 to an operating coil 35 of a relay 30. The armature 33 of relay 30 is also influenced by coils 36, 37 connected in shunt with the valve filament supply through terminals 21 to give the relay 30 greater sensitivity. When the coil 35 is energised it attracts armature 33 and closes contacts 32 to energise coil 31 whereby the armature 41 is moved downwardly and releases a spring biassed arm 42 to open the contacts 40. The contacts 40 are reclosed by pressing a button 39 on the arm 42. For a two or three-phase supply, the interrupter 27 has a corresponding number of contacts 40.