Patent GB-496860-A (GB)
Title: Improvements in or relating to electric circuit interrupters of the liquid immersed type
IPC: H01H33/92
Filed: 1938-03-18
Abstract: 496,860. Liquid - blast switches. WESTINGHOUSE ELECTRIC & MANUFACTURING CO. March 18, 1938, No. 8443. Convention date, May 28, 1937. [Class 38 (v)] A Circuit-interrupter comprises a casing containing arc - quenching liquid, separable contacts in the liquid and means for operating them to closed and open positions, wherein means are provided responsive to the casing-pressure for assisting the operating means to separate the contacts by transmitting a force to said operating means with substantially no time-lag irrespective of the position of the operating means within predetermined limits. The arrangement is such that the contacts are movable independently of the pressure-responsive means, and enables a smaller spring to be used, with less resistance to the blast. The invenvention is shown applied to the interrupter described in Specification 495,540, in which an oilfilled casing 9 encloses a pair of series-connected arc-quenching units 27, each unit, Fig. 2, comprising a pile of insulating plates cut away to form a narrow arc-chamber 51, a fixed contact 61, and a movable contact 63 which, with a piston 73, is carried on an operating rod 71 common to the two units. Each unit 27 has, further, a vent 119 into the liquid in the casing 9 whereby the chamberpressure due to the arc and piston 73 is communicated to the casing. The rod 71 is extended upwardly into a rod 87 on which acts the accelerating spring 101 which is stressed by the operating linkage 81 during closure. The pressure-compensating means comprises a piston 133 on rod 87 working in the enlarged part 129 of a tubular member 127 carrying a baffle 125, which is slidable in housing 89 and is urged downwards against a hanger plate 25 supporting units 27, by a spring 135 surrounding a further cylinder 131 in which the part 129 is slidable. Positioned in casing 89 immediately above the normal position of baffle 125 is a series of apertures 137 of progressively upwardly-increasing area, whereas cylinder 131 is formed immediately above the normal position of part 129 with circumferential slots 139. When rod 87 is moved downwards to open circuit, liquid is initially drawn through slots 139 into the cylinder 131. When the pressure in casing 9 rises, the piston comprising baffle 125 and part 129 rises, thus closing the slots 139 and compressing the liquid trapped in cylinder 131, which pressure reacts downwardly on piston 133 to assist the opening spring 101 and blast-pistons 73. At the same time, ports 137 are uncovered to relieve the pressure in casing 9. After circuit-opening, spring 135 restores 125, 129 to their original positions, uncovering slots 139 so as not to impede the closing-operation. By proper proportioning of the areas of 125, 129, the reactive pressure may be fully or over-compensated. If pressure-development is delayed, so that the switch is fully opened before the baffle 125 rises and seals ports 139 before uncovering 137, the coincidence of notches 141 on rod 87 with the aperture in top-plate 90 of cylinder 131, allows the pressure in the latter to exhaust into the spring-chamber. If also during closure a high pressure is set up in the arcchamber by an arc, which pressure, by raising baffle 125, covers up ports 139, the coincidence of notches 143 in rod 87 with the aperture in 90 prevents pressure being built up in cylinder 131 which would arrest the closing movement. When the switch is fully closed, the notches 143 are above the plate 90 and cylinder 131 is sealed. In this way, further upward movement of baffle 125 is prevented, and the baffle is at once available if an interrupting operation takes place immediately following closure.