GB278764A - Improvements in or relating to electric circuit-breakers - Google Patents

Abstract

278,764. Whitney, W. B., Wedmore, E. B., and British Electrical & Allied industries Research Association. April 10, 1926. High-potential switches ; arc-rupturing devices. - In A.C. switches in which the arc produced at break is blown out by a stream of gas across the arc bearing surfaces which escapes through a passage formed in one of the contact members, this passage is so dimensioned in relation to the cross-section of the arc at maximum current as to prevent material extension of the arc within the passage for which rurpose the passage dimension should not materially exceed a dimension of twice the diameter of an arc crater or burn formed between contacts during a whole cycle of arcing. The hollow contact member is formed with an extension such as a depending sleeve for guiding the flow of gas, and prevent the arc from spreading. As shown in Fig. 1 the upper contact 12 is formed as a socket member composed of yielding segments pressed together by springs 64 the lower plug contact 10 being carried by a rod 66 secured to the transverse operating bar 67. The contact 12 is secured to a member 13 carried by the insulating cover 18 of the container 14 and formed with a passage which communicates through a tube 26 and valve chamber 32 to a flared outlet 60. The valve 36 controlling the flow of gas through this passage are operated through a toggle 40 connected by a sliding rod 42 to a second toggle 44 which is made and broken by pins 70, 72 on a rod 68 secured to the switch-operating bar 67. The gastight container 14 fitted with a quartz lining 16 is filied with a gas under pressure and when the switch is operated to break the circuit the valves 36 are opened prior to disengagement of the contact members. The gas by escaping through the space between the segments of the fixed contact 12 acquires a considerable velocity before the contacts actually separate. Alternatively corrugations on or passages within the moving electrode 10 may be provided to permit the initial flow of gas. When the contacts separate the gas flow is such as to confine the arc and rapidly extinguish it any attempt of the arc to lengthen materially within the passage 25 by bowing or looping being prevented as the passage is so dimensioned that the arc in creeping within the passage produces a short-circuit of the portion extending therein. The electrodes 12 is formed with means such as a downwardly extending sleeve for guiding the flow of gas and this sleeve may be lined with quartz for a whole or a part of its length to prevent spreading of the arc. The arc should be extinguished during the first or second cycle subsequent to the break so that the contacts need be separated only for a limited distance preferably slightly greater than that sufficient to prevent re-establishment of arcing after the current has passed through a zero point in its cycle, and to further ensure the arc from re-starting a series oil-break switch may be arranged to open subsequently to the gas-break switch. The arc-extinguishing gases employed may be air, hydrogen or an inert gas and where an inflammable gas such as hydrogen is employed a non-return valve in the outlet pipe may be fitted which opens when the pressure in the chamber exceeds a certain limit. The gas is placed under pressure by a pump controlled by the circuit breaker and where a number of breakers are employed they may be fed from a common reservoir. A grid may be inserted in the outlet pipe for preventing the ejection of metal particles and longitudinal partitions may be placed in the passage through the upper electrode for dividing up or restricting this passage and so preventing the entry of the arc therein. The valve chamber may alternatively be placed at the side of, or below, the arcing chamber the chambers either being bolted directly together in the latter case or connected by a U-shaped tube in the former. In a modification described in which the valve chamber is bolted below the arcing chamber (Fig. 2, not shown) a double valve member for controlling the gas supply is carried, on the rod bearing the movable electrode 10.