GB1431576A - Thermally responsive electrical device - Google Patents

Abstract

1431576 Electrically released switches; thermal relays WESTINGHOUSE ELECTRIC CORP 25 June 1973 [29 June 1972] 30067/73 Heading H1N A polyphase thermal overload and phase unbalance relay 10 having a moulded insulating housing 20 with compartments for the operating parts includes an operating mechanism 50 comprising a latch member 66 biased by a spring 94 for an end 90 to overlie and latch a movable contact arm 68 in the operative position shown in Fig. 4 in which a fixed contact 74 is electrically engaged with a movable contact 76 to complete, for example, the energizing circuit of an adjacent line contactor unit 12 (Fig. 1, not shown). The movable contact arm has forked branches 96, 98 on either side of a guide prong 62 and on being unlatched the arm is driven by a spring 72 to open contacts 74, 76 to close contacts 76, 100, which can complete an alarm circuit, and at the same time to drive a reset rod 70 outwards of the housing 20 to provide indication of the tripped condition (Fig. 5, not shown). The latch member 66 is pivotally supported on a portion 84 of a bracket 64 pivoted at 60, which can be set for operating current value by screw and cam means 86, 88 and the latch is released by actuating means comprising bimetallic members 108 with heating elements 106 (detailed in Fig. 8, not shown) associated with each phase acting on a slide assembly 92, Fig. 7, consisting of two slides 144, 146 disposed and movable parallel with one another. Slide 144 has portions 150, 152, 154 disposed directly adjacent the low expansion sides of the bimetallic elements 108 and slide 146 which carries a pivotal lever 148 mounted on a fixed pivot 168 has portions 156, 158, 160 disposed directly adjacent the high expansion sides. The lever 148 has an extension piece 164 engaged by slide 144 and a nose portion 162 remote from the pivot point which directly engages the end of the latch member 66 remote from the latch. Under balanced overload conditions all bimetallic elements 108 flex equally in the same direction and their free ends 142 engage the portions 150, 152, 154 of slide 144 so that the whole slide assembly including the pivotal lever 148 moves together to act on the latch member 66 to displace it to a position 66a (Fig. 6, not shown) and to unlatch the relay contacts. Under unbalanced load conditions the bimetallic elements will not flex equally and as shown in Fig. 7 the end 142a of one element will retain the slide 146 so that slide 144 moves relative thereto to act on the latch member 66 through the pivotal action of lever 148, the speed of the tripping action being stated to be increased in the ratio of distance "a" to distance "b" as compared with the balanced overload condition. One end of the slide 144 is extended through the side of the housing to provide facilities for manual tripping and the latch member 66 may be of bimetallic material for ambient temperature compensation.