GB765276A - Improvements in or relating to automatic electric circuit breakers - Google Patents

Abstract

765,276. Automatic circuit-breakers. WESTINGHOUSE ELECTRIC INTERNATIONAL CO. Feb. 28, 1955 [March 3, 1954], No. 5818/55. Class 38(5) Ambient temperature compensation for the bimetallic tripping element 45 is provided by securing the element 45 near one of its ends to a portion 70 of a resilient conductor 29, the pressure on which portion may be varied by means of a U-shaped compensating bimetal 81 having a screw 93 screwed into one leg 87 so as to maintain a constant overlap between the latch 67 on the end of bimetal 45 and a carrier 33 pivoted at 41, release of which by the latch 67 on overload trips the breaker. The high expansion part of the compensating bimetal 81 is on the inside of the U so that on a rise in ambient temperature leg 89 and ears 97 will bent towards the left while leg 87 will bent towards the right when resiliency of part 70 of conductor 29 acting through screw 93 and leg 72 of bimetal 45 allows the yoke 85 and leg 87 to move towards the right maintaining ears 97 in contact with shoulders 99 on the switch base. The bending of leg 87 towards the right moves the screw an additional distance towards the right thus permitting further movement to the right of leg 72 and part 70. Since the high expansion side of bimetal 45 is on the outside of the loop at the upper end and to the right of leg 72 the increase of ambient temperature will cause the loop to close thus moving leg toward part 70, which can be further moved to the right by the resiliency of strip 29. The cumulative deflection will thus permit sufficient movement of the part 70 and therefore of pivoting of strip 29 about screw 71 to move the latch towards the left and maintain a constant overlap with carrier 33. An electromagnet having an armature 63 mounted on bimetal 45 and a yoke 65 mounted in recesses 66 in housing 11 and cover 13 for limited movement relevant to armature 63 is provided for immediate tripping on short-circuits or severe overloads, the current through bimetal 45 then energizing' the electromagnet sufficiently for yoke 65 to attract armature 63 thus releasing carrier 33. In another embodiment (Fig. 2, not shown) less temperature compensation may be provided by using the compensating bimetal alone and omitting the loop at the top of the tripping bimetal, while for even less temperature compensation, Fig. 4, the compensating bimetal is omitted and a screw 93 and nut 101 is provided, the former acting directly on the leg 72 of the bimetal 45 and the latter being pressed against shoulders 99 by the resiliency of strip 29. Since the high expansion side is on the outside of the loop an increase in ambient temperature causes leg 72 to bend toward the part 70 and a decrease will cause leg 72 to bend away' from it, thus compensating the bimetal for changes in ambient temperature. The movable contact arm 37 can also be operated manually, a spring 39 imparting a snap action in both directions.