Patent GB-485463-A (GB)
Title: Improvements in or relating to electrical circuit breakers
IPC: H01H33/16
Filed: 1936-10-31
Abstract: 485,463. Fluid-blast switches; arcrupturing in switches. BRITISH ELECTRICAL & ALLIED INDUSTRIES RESEARCH ASSOCIATION, WHITNEY, W. B., and WEDMORE. E. B. Oct. 31, 1936, No. 29691. [Class 38 (v)] A circuit-interrupter arranged for a fluid blast to be established across or along the arc-path and to flow through a passage formed with a throat, the wall of which is formed wholly or in part by a fixed arcing electrode which co-operates with a movable arcing electrode withdrawable from the throat in the opposite direction to the blast, has at least one additional electrode located in a blast ontlet passage on the outgoing side of the fixed arcing electrode and away from the wall of that passage so as to be wholly immersed in the blast, and a resistance inserted between the additional, and one of the main, electrodes is connected in circuit with the arc when the are is displaced against the additional electrode by the escaping blast. Fig. 1 shows a gas-blast switch having a hollow fixed segmented contact 2 mounted in a segmental shell 4, which is surrounded by a spring 9 and is secured by laminations 6 and a threaded ring 7 to a coned metal-member 5, which is screwed into a metal cylinder 8 forming the blast outlet. A pair of insulating spiders 12 rigidly connected together, support a hollow truncated cone 14a, or hollow cylinder 14 carrying an arcing electrode 15, which is connected by a lead 16 and resistance R to brushes 73 engaged by the movable contact 1. When the switch is opened, a gas blast admitted at 75 to casing 11 tends to force the arc between contacts 1, 2 up through passage 3 in contact 2 into engagement with electrode 15, which would soon deteriorate if exposed to arcs at currentpeaks. To prevent such displacement while the current is at or near peak-value, the passage 3 is dimensioned so that its walls short-circuit any looping section of the arc. Further, an insulating grid 20, Fig. 3, is provided with slots 22 which only allow the arc to pass through at or near the zero of the cycle. When this occurs, the arc is divided by the electrode 15 into two parts, of which the part between 1, 15 is short-circuited by the resistance R and goes out at current-zero, and the part between 2, 15 is in series with that resistance, and is readily quenched. Contact 1 is then lowered below the brushes 73. Fig. 6 shows the tip of contact 1 modified for use with the grid 20 by being cut away on opposite sides, the original contour being made up with two insulating inserts 23 so as to leave a central tongue 25 exposed at the top and down opposite sides. The longer dimension of the tongue 25 is arranged normal to that of the grid-slots, so further safeguarding electrode 15. The grid may be replaced by a device 26, Fig. 8, formed as an inverted truncated cone with a central passage 27 formed at 'the top as a slot 28, which merges gradually into a circular bottom opening 29 of the same cross-section. In Fig. 10, the passage 3 which is dimensioned so as to prevent movement of the arc at heavy current may have a device 20 or 26, and leads into an outlet 30 in a coned insulating member 31. The electrode 15 is replaced by four hollow, conical metal baffles 32a ... 32d, which are concentrically carried on an insulating spider 33 and connected by leads 35a ... 35d to sections of the resistance R<1> connected to contact 1. Insulation is provided for the baffles at 34. The low-current arc is first blown on to baffle 32b, so forming two arcs as in Fig. 1, the arc between 1, 32b being shunted by a section of resistance. When the arc engages 32a, 32c (as shown), the arc between those two baffles is put out by the shunting-resistance sections, and the arc between 1, 32c has less resistance in parallel whereas resistance is inserted in series with 2, 32a. When the arc engages 32d, the shunt resistance to 1, 32d is a minimum and the series resistance to 2, 32a is a maximum, so both arcs go out. Further baffles may be introduced outside or inside 32b, and the resistance may be connected to contact 2 instead of to contact 1. A magnetic device for confining the are at heavy current comprises a U-shaped pile of laminations fitted to the shell 4, the magnetic force being overcome by the blast at currentzero, Figs. 11, 12 (not shown). In Fig. 13, the fixed contact is divided into two parts 2a by an insulating barrier 43, the parts being interconnected by a resistance R<2>, and the passage 3a tapers upwards to a throat 42 above which are barriers 44 similar to the baffles of Fig. 10. Numerical figures of dimensions and performance are given in the Specification, which refers also to the protection of resistances and sprayer nozzles. The Provisional Specification outlines modifications in detail and refers to Specifications 278,764, [Class 38 (v)], 375,309, and 398,213.