GB673474A - Improvements in and relating to automatic electric circuit opening devices - Google Patents

Abstract

673,474. Automatic circuit - breakers. BRITISH THOMSON-HOUSTON CO., Ltd. July 29, 1949. [July 31, 1948] No. 19987/49. Class 38 (v). Branch and sub-branch circuit-breakers, suitable for use in the system described in Specification 667,068, comprise a modification of the breaker of Specification 650,509, the release of the holding means being blocked until a predetermined one of a number of current impulses. The blocking means comprises a lever 62, biassed clockwise by gravity, but normally held in the shown position by a latch 65 held in this position by the engagement of its other end with the smooth periphery of a ratchet wheel 95. Full upward movement of the armature 34 is prevented by the engagement of a pin 82, carried by extensions 46 thereof, with the lever 62. The upper ends of the extensions 46 are joined by a plate 48 upon which rests a thrust bearing 59 and a plate 57 frictionally engaging a flywheel 61, the plate 57 also having a slot engaging a fixed screw 56. On upward movement of the armature, the flywheel is raised and on de-energization of magnet 31, it falls slowly due to its rotational inertia. The upward movement of the armature also causes a pin 81 to raise a lever 73 so that a spring-pressed pawl 72 thereon engages and rotates the wheel 95, which is prevented from returning by a pawl 76 on a spring-controlled lever 78 normally held out of engagement with the wheel 95 by a rod 79 held down by the fly-wheel. Thus, due to the slow fall of the flywheel, the pawl 76 is allowed to remain in contact with wheel 95 and subsequent energizations of magnet 31 cause the wheel 95 to be stepped round until the tail of latch 65 engages a V-notch 71 therein, thereby releasing the lever 62 which moves clockwise when the armature drops and allows the armature to rise to its full extent on the next impulse to trip the circuit-breaker. The flywheel eventually returns to its normal position and thereby disengages the pawl 76 by means of rod 79, and resets the lever 62 and latch 65, the wheel 95 being returned to its normal position by a spring 68.