Patent GB-378493-A (GB)
Title: Improvements relating to electric switches or circuit breakers, fusible cut-outs andlightning arresters
IPC: H01H33/96
Filed: 1931-05-09
Abstract: 378,493. High-tension switches, fuses, and lightning arresters. BRITISH ELECTRICAL & ALLIED INDUSTRIES RESEARCH ASSOCIATION, WHITNEY, W. B., WEDMORE, E. B., and CASSIE, A. M., 36, Kingsway, London. May 9, 1931, Nos. 13821/31 and 7054/32. [Class 38 (v).] The arc drawn at a high-tension oil or gas-enclosed circuit-breaker, fuse, or lightning arrester is suppressed by the movement of a differential piston or equivalent bellows pumping device set into action by the gas pressure developed by the arc and serving to compress the oil or gas around the electrodes and force it over and around them. In the construction of circuit-breaker shown in Fig. 1, the fixed contact 16 is supported from an insulator 1 by the conducting sleeve 17 within an oil pot 2 having an insulating covering 3. The pot is immersed in the main oil tank in which the movable contacts 7, 7a are operated. A differential piston 11 with large upper face 12 guided by the wall of the pot and a smaller under face guided by a sleeve 9 is normally maintained in the raised position by a spring 13. In breaking the circuit, the arc drawn as the movable contact leaves the fixed contact develops a gas pressure which acts on both sides of the piston and by differential action depresses it against the action of the spring 13 so as to compress the oil below the piston and force it across the arc. When the piston is depressed below the port 25, the pressure above the piston is relieved and the piston rises under the action of the spring 13. The upper part of the piston has a number of castellations to limit the movement and seep holes 23 may be provided to prevent the trapping of a permanent pocket of gas. The movable eleccrode 7a executes only a small movement in the breaking process ; its movement is stopped while it remains in electrical contact with the cross-bar by an extensible connection in order to reduce the arc energy at the gap as described in Specifications 278,764 and 330,616, [both in Class 38 (v), Electric switches &c.]. In order to prevent knock at the end of the downward stroke of the piston, a dashpot effect is obtained by ports subsidiary to 25, the main port being closed by a flange on the piston before the end of the stroke. Many modifications of the construction shown in Fig. 1 are described. In one, Fig. 3 (not shown), the " fixed " contact 16 is mounted on the piston itself and connected by pig-tail connections. In this case the "fixed" contact follows at a distance the movable contact in the breaking process and the distance between them automatically adjusts itself in dependence on the energy of the arc. To reduce the energy of the parts and to obtain a quicker initial stream of oil at break, the main piston may be provided with a number of light plungers, Fig. 4 (not shown), with large upper surfaces and small under surfaces to act in advance of the main piston. The auxiliary plungers vent into an exhaust manifold at the end of their stroke and then return automatically. In a simplified form, Fig. 6, with gravity return the piston 11 moves upwards under the pressure developed by the arc drawn between the fixed contact 16 and the movable tubular contact 7 which has ports 35. The piston is guided in a depending sleeve 34. In Fig. 7, the fixed contact 16 is mounted on the piston which moves out of the main chamber 2 so as to increase the total length downwards and in this construction an auxiliary piston-like contact under spring action may be employed to provide a selfadjusting subsidiary arc-gap, Fig. 8 (not shown). In Fig. 9 a bellows diaphragm 39 is connected between the piston and the container, which moves as a whole and returns in the breaking process. The piston may carry a number of baffle-plates, Figs. 10 and 12 (not shown), as described in Specification 366,998 to divide up and direct the oil stream, and the arc may be broken up into a number of arcs in series by metal-tipped baffles. A construction employing double bellows in which the upper bellows are vented at the end of the stroke through valves 84 is shown in Fig. 16, and in a modification adapted for the use of hydrogen or helium the working spaces for the fluid each lie between a pair of bellows. In this case the device is self-contained and the contacts completely enclosed so that there is no discharge of gas. A quick initial movement of fluid can be obtained by using conical-shaped bellows or a series of telescoping members equivalent to bellows. Six units of the kind described are required to provide two interruptions per phase in a three-phase system and the exhaust ports are displaced in relation to one another so that the exhaust products have uninterrupted egress. The normal outlet through the fixed contact or through baffle-plates may be furnished with valve members as described in Specification 375,808. Fusible cut-outs.-As applied to a fusible cut-out, the fuse 55, Fig. 13, is mounted renewably in a cartridge 54 within the oil container 2. When the fuse blows, the gas pressure developed by the arc acts through the upper ports 58 on the large upper surface of the telescopic piston 11 and, through the lower ports 58, on the small underside of the piston. The differential action causes the piston to move downwards against the action of the spring 13 compressing the oil in the internal space and forcing it across the arc. At the lower end of the movement the pressure is relieved through ports in the inner casing 53 and the spring restores the piston to its original position ready for renewal of the fuse. Lightning arresters.-As applied to the rupture of the arc at a lightning arrester, Fig. 14, when a discharge takes place between the knob electrodes 63 the gas pressure developed acts differentially on the large upper surface and the smaller lower surface of the piston 11 and depresses it against the action of the spring 66 carrying with it the lower electrode. This compresses the oil within the inner chamber and forces it across the arc until at the bottom of its stroke the pressure is relieved through the port 25 whereupon the piston rises to its original position and the device is ready to deal with another discharge. Specification 378,471 also is referred to.