Patent GB-367872-A (GB)
Title: Improvements in automatic electric cut-outs
IPC: H01H83/14
Filed: 1930-09-27
Abstract: 367,872. Automatic circuit-breakers. SOC. FRANCAISE GARDY and KUNZ, W., 23, Rue de la Voie des Banes Ó Argenteuil, Seine-et-Oise, France. Sept. 27, 1930, No. 28975. [Class 38 (v).] An automatic cut-out is controlled by two opposing electromagnets in circuit respectively with two resistances of different temperature coefficient the two resistance elements being arranged in proximity to one another so that, in addition to the change in resistance of the circuit including one of the coils due to the heating up of the resistance by current therein this circuit will be effected by changes in resistance of this element due to heat engendered in the other resistance element and imparted to it by radiation or conduction. As shown in Fig. 1, the switch members 3, 4 are connected to two parallel circuits including opposing operating and retarding coils 7, 9 in series with resistances 13, 14, the resistance 13 being of high temperature coefficient material such as nickel or iron and being placed in proximity to the resistance 14 which is formed of relatively low temperature-coefficient material such as a nickel-chromium alloy and which acts as a heating coil. In the constructional form of cut-out shown in Figs. 9 and 10 the coils 7, 9 have fixed magnetic cone members 21, 26 and movable magnetic armatures 22, 27 the former of which is secured to a rod 23 and the latter is pressed against the lower side of an enlarged portion 24 of the rod 23 by an adjustable spring 28. The movable cut-out contacts 3 are operated by a pushbutton 34 which rocks a lever 35 connected by a toggle 37 to a crank arm 38 of an operating shaft 39 to which the contacts 3 are secured by arms 50. The cut-out is retained in the closed position against a return spring 57 by a spring-controlled latch 40 engaging a recess in the lever 35. When the operating coil 7 overcomes the retarding coil 9 by a sufficient heating up of the resistance 13 causing a diminution of the current in the retarding coil, the rod 23 rises and the enlargement 24 rocks a tripping member 43 mounted on a shaft 42 causing a member 41 carried by the shaft to break the toggle 37 so that the cut-out can open. During the opening movement the toggle member engages a projection 56 integral with the latch 40, so releasing the latch and pushbutton 34 and enabling the toggle to be reset automatically in readiness for a further closing operation. A heavy shortcircuit causes the operating armature to overcome the action of the spring 28 before the resistance 13 is appreciably heated and so to produce instantaneous tripping of the cut-out. To increase the time lag of operation of the cut-out during normal conditions a heat insulator 15 may be interposed between the resistance elements 14, 13 to cause the latter to be heated up gradually. The elements 13, 14 may be enclosed together within a gas-filled bulb 16, Fig. 8, fitted with plug connectors 19, 20 in its base arranged in the manner of a wireless valve. The bulb may be immersed in oil. The resistance 14 may be arranged in the main circuit and a shunt-connected adjustable resistance may be arranged to vary the action of the cut-out.