GB288326A - Improvements relating to electric circuit breakers - Google Patents

Abstract

288,326. Metropolitan-Vickers Electrical Co., Ltd., (Assignees of Slepian, J.). April 6, 1927, [Convention date]. Arc-rupturing devices of the general character described in Specification 258,234 have in place of the perforated deionizing plates of the earlier Specification a number of solid conducting plates disposed transversely to the arc so as to divide the arc into a series of small parts; the arc is also driven round an endless track over the surfaces of the plates till it is extinguished. The invention is specially applicable to alternating currents, the cool surfaces of the plates preventing re-formation of the arc after the zero of the A.C. cycle has been passed. Fig. 1 shows the invention applied to a circuit-breaker having a main bridging contact 3, auxiliary contacts 15 which open after the main contact, and arcing contacts 8, 14 which open still later. After the main contact 3 has opened current flows through an arm 6 contacts 14, 8 of blow out coil 11 and when the contacts 14, 8 have separated the arc is transferred to the horn plates 22, 23 and is driven upwards by the magnetic field formed between pole pieces 25 of the magnet 11. It then encounters the conducting plates which in the example shown consist of two series 31, 32, of nine plates each, of the shape shown in Fig. 3, placed between three series 62, 63, 64, of plates of the shape shown in Fig. 4. The arc is driven up the V-shaped passage 36 formed by the lower ends of the plates, the effect of the V-shape being to constrict the arc and to raise the current density so as to permit the smooth transference of the are on to the plates themselves. Coils 45, 49, 49, 54 are arranged above the series of short plates 62, 63, 64 and are so connected that, as the arc continues to rise up the plates 31, 32 these coils are placed in circuit with it and produce a magnetic field that is radial to the centres 37 of the plates 31, 32 and drives the arc round and round the dotted lines shown in Fig. 3 till it is extinguished. The theoretical considerations governing the size and number of the plates, their distance apart and the shape of the V passages 36 are discussed, but generally speaking, the plates may conveniently be <1>/16th of an inch thick and <1>/16th of an inch apart and the voltage between adjacent plates should never exceed 300 volts, the voltage required to produce a brush discharge. To secure a uniform distribution of potential along the plates, an electrostatic screen of conducting plates 70 - - 75 surrounds the structure. A practical construction of blow-out is also described (Figs. 5 - - 7 not shown). In this construction, pole pieces attached to the poles 25, extend upwards so as to embrace the arc-chute. Side walls of soapstone are also provided having grooves which prevent the formation of a continuous conducting coating on the soapstone due to condensation of metal vapour from the arc.