Patent GB-1461491-A (GB)
Title: Circuit interrupter and trip device
IPC: H01H71/16
Filed: 1974-03-18
Abstract: 1461491 Automatic circuit breakers WESTINGHOUSE ELECTRIC CORP 18 March 1974 [29 March 1973] 11904/74 Heading H1N An automatic circuit breaker having thermally and electromagnetically responsive overload trip devices operable on to a common trip bar has the armature structure of its electromagnetic trip spring biased towards an unactuated position away from the core in order to establish a gap therebetween with the spring force acting on the armature structure varying inversely with the gap width. Means for increasing the effective adjustment range of the magnetic trip includes an adjusting lever with a resiliently flexible finger engaging the armature structure, the lever being biased so that the finger exerts a reaction force on the armature structure increasing in the gap widening direction in proportion to the degree of flexure. The circuit breaker described, Fig. 1, consists of a known three-pole arrangement with a central manual operating lever 55 for operating a movable contact arm 29 for each pole through a common insulating bar 35 via a toggle link mechanism which is latched by a releasable arm 49 supported at its one end on a pivot pin 173 and co-operating at its other end with a latch member of the latch and trip device 15. The trip device 15, Figs. 3 and 5, has three compartments with a common moulded insulating trip bar 83 rotatably mounted therein and a current conductor 69 in each compartment has a loop 69a to which is attached a bimetal 101 operating to strike a calibration screw 99 for thermal actuation of the trip bar in a known manner and which forms an energizing winding for a magnetic core 105 towards which a pivoted armature structure 111, 119 can be attracted against compression type bias springs 127. An adjusting lever 128 for setting the armature gap comprising a flat plate supported on trunnions 135 for pivotal movement on an axis parallel to that of the armature has fingers 130, 132, 134 of a leaf spring member (which can be integral with lever 128) straddling the lever at its one end, finger 132 being resiliently flexible, whilst at its other end is a calibration screw 131 bearing on a cam surface 139 which is rotatable by an indexed knob 137 and the lever 128 is biased by a tension spring 129 so that the resilient finger 132 is flexed to engage the armature structure with a reaction force in the gap widening direction. The latching mechanism is described with reference to Fig. 4 and includes an arrangement of levers, springs and pivots which latches the common trip bar 83 via a flange 163 of a trip lever 153 which in turn is engaged with a latch lever 155 which engages with the releasable arm 49 when the breaker is in the closed position. An extension 177, Fig. 3, to the trip bar 83 allows external tripping by the insertion of a suitable tool into an aligned opening (179) (Fig. 2, not shown) in the base housing 81 of the trip unit 15 and adjustment of the various calibration screws 99 and 131 can be effected after assembly through access apertures 151 (normally closed with plates 149) in the housing cover 79 of the unit.