GB901913A - Thermal and magnetic trip device for electric circuit-breakers - Google Patents

Abstract

901,913. Temperature-responsive actuating- elements. SQUARE D CO. Nov. 2, 1959 [Dec. 22, 1958], No. 37052/59. Class 64 (2). [Also in Group XXXVII] A trip device for a circuit-breaker comprises a current-carrying bimetal strip 50 secured at its upper end to an adjustable terminal strip 38 and attached to and partially enclosed by a U-shaped magnetic yoke 51, whose arms 53, 54 are formed with hooked supports 61, 62 in which pivot the upper shoulders 65, 66 of a bimetal strip 64, normally urged clockwise by a spring 71 acting between its lower shoulders 72, 74 and a cup 70 formed on the yoke 51. The movement of strip 64 is limited by the engagement of its lower end 68 in an aperture 69, and its upper end is secured to an ambient temperature compensating bimetal strip 73 whose lower end 73A engages the face 34A of a pivoted spring-urged member 34 to maintain the breaker contacts closed. Fig. 1 (not shown). A moderate short-time overload current deflects the strip 50 anti-clockwise about its upper end, but the heat transfer between the strips 50, 64 is not sufficient to similarly deflect the latter to disengage the members 34, 73. If the overload is sustained, however, the upper end of the strip 64 deflects to assist the strip 50 in tripping the breaker. Tripping is produced on severe overload by the flexure of the strip 50 alone, and on the occurrence of fault current by the attraction of the strip 64 to pole faces 55, 56 of the yoke 51.