GB501390A - Improvements in and relating to electric circuit breakers of the oil blast type - Google Patents

Abstract

501,390. Liquid - blast switches; electrically - released switches. BRITISH THOMSON-HOUSTON CO., Ltd. May 26, 1938, No. 16763. Convention date, May 27, 1937. [Class 38 (v)] An oil-blast circuit-breaker comprises a pressure-confining casing having an exhaust passage and containing a quenching liquid, a relatively-movable contact structure adapted to form two breaks in series in the liquid and including a pivoted contact normally biassed towards closed position and located in the exhaust passage to close the same. A relatively-fixed, rigidly-mounted contact is electrically connected to the pivoted contactand a movable rod contact is adapted to engage the fixed contact, opening movement of the rod-contact causing an initial break at the fixed contact for generating arc-pressure for opening the biassed contact and driving a quenching-liquid blast through the passage and the arc at that point. The oil or other liquid-containing fibre cylinder has a pivoted contact 6 urged by a spring 7 against a contact 3, in which position it closes the exhaust passage 13. In opening circuit, an arc is set up initially between a butt contact 8 and a movable contact 10 and when the pressure is adequate, the contact 6 is moved aside by the blast, which quenches the resulting arc at 3, 6. The spring 7 restores the contact 6 subject to the delay-action of dashpot 18, and is adjustable so that contact 6 will only open when the requisite pressure, in the case of small-current arcs, is attained. To prevent undue arc-lengthening with heavy currents, a conducting ring or-sleeve 19 is either connected to the contact 8 or separated from it by a small gap. The resulting heavy-current arc is shown at 19<1>, but small-current arcs strike directly between 8, 10 and are not bowed outwards into contact with 19. The ring 19 may be formed as a squirrel-cage, the spacing between the bars serving, like the vents 20 shown, to relieve gas-pressure which might accelerate the rod 10. A further means for regulating the arc-length with heavy currents comprises a stop 29 provided with two (or more) steps 29<1>, 29<11> which steps are interposed beneath the rod 10 in accordance with the amount of current flowing. The rod 10 is in series with a conducting loop which expands electrodynamically to an extent depending on the current it carries and is fixed to a pair of insulators 24, 25, pivoted together at 26, the insulator 24 being fixed, whereas 25 is linked at 28 to the stop 29 and controlled by a compression spring 30 between it and a fixed guide 31. The steps may be replaced by a wedge-shaped surface to give a uniform variation of the arc-length. Automatic circuit-breakers.-Contact.rod 10 is linked at.34 to an arm 22 carrying the trip armature 33<1>, which is retained by a permanent magnet 33 and released by a trip coil 44 energized from the line. An intermediate pivot for the arm 22 comprises a pin-and-slot connection 41, 42 with a guided cylinder 35, which is provided with a spring buffer 39 co-operating with a roller 40 on a powerclosing device 36 to provide the " wipe '' ordinarily provided at the contacts themselves, this arrangement allowing the contacts 8, 10 to be rotated by spring 32 about the intermediate pivot 41, 42 immediately 22 is released. Resetting is effected by lowering 36 until armature 33<1> is again retained, a spring 43 between the cylinder 35 and a point 43<1> on lever 22 ensuring the centring of the armature on the magnet. The device 36 is then raise to rotate the arm 22 about armature 33<1> and close the breaker from the position shown. Specification 386,283 is referred to.