GB224526A - Protective devices for direct current systems - Google Patents

Abstract

224,526. Metropolitan-Vickers Electrical Co., Ltd., (Assignees of Wensley, R. J.). Nov. 5, 1923, [Convention date]. Protective arrangements; automatic circuitbreakers.-A switch for the protection of directcurrent circuits is responsive to sudden changes in current magnitude in one direction only, e.g. to increase of current but not to decreases In the. arrangement, shown in Fig. 1 for the protection of a railroad system, the circuit-breaker 5 has two windings, one connected across the mains 1, 2. and the other energized by the secondary 13 of a transformer of which the primary 4 is in the load circuit. The first winding cannot itself release' the circuit-breaker but, upon a sudden overload, the second winding is also energized to assist it and the circuit is. broken. A sudden decrease in current causes the windings to oppose each other and the circuit-breaker remains closed. The core 14 of the transformer has a gap 15 to prevent magnetic saturation. Fig. 2 shows a modification in which the circuit-breaker has only one winding energized by a transformer 13a, a polarized core or an electrolytic or thermionic rectifier 34 being provided so that the, circuit-breaker responds to increases of current but not to decreases. Fig. 3 shows the invention applied as a flash suppressor for a direct-current generator. The switch 25 has two windings, one connected across the load circuit 29, and the other through a non- inductive high resistance 32 across the series winding 20 of the field magnet. Owing to the inductance of the series winding 20 a sudden overload causes an increase of current in the lastmentioned winding of the switch, and the two windings act together to close the quick-action switch 25 to short-circuit two slip rings 23 connected to the armature winding 22. An ordinary overload circuit-breaker 31 is also included in the load circuit, but this will ordinarily have a certain time lag, so that the flash suppressor will operate first. Reference has been directed by the Comptroller to Specification 154,075 and 195,340.