Patent GB-498325-A (GB)
Title: Improvements in, or relating to, automatic circuit breakers and similar electrical switchgear
IPC: H01H71/42
Filed: 1937-07-20
Abstract: 498,325. Protective cut-out arrangements ; thermal switches. CRABTREE & CO., Ltd., J. A. (Schiele Industriewerke) July 20, 1937, Nos. 20009 and 30943. [Class 38 (v)] Polyphase electric switchgear having a thermally-operated tripping device adapted to open the circuit after a time - delay on the occurrence of sustained balanced overloads and without such delay in the event of unbalanced overloads, has the heatsensitive elements anchored on a sliding bar or rotary spindle and operative on a trip bar or the like trip device, which is adapted for disengaging switch contacts or trip mechanism mounted in the release box or casing. In Figs. 2, 3, bimetal strips 2 with heating-coils 4, one for each phase, are mounted on a bar 3 slidable in a groove 1b in the housing, and the free end of each strip is normally engaged between a projection 5 on the housing and a stop 6a on a further bar 6 slidable in a groove 1a. Due to the engagement between 5, 6a, flexure of the strips when heated causes bar 3 to be slid to the left towards an adjustable stop 9 and when it abuts the stop, further flexure causes the free ends to move the bar 6 to the right, so that a lip 7a operates a freehandle trip or opens a switch 8a in the tractivecoil circuit whereby the circuit-breaker opens. On unbalance, one of the strips undistorts, so moving the bar 3 from the Fig. 2 to the Fig. 3 position, the distorted strips thus moving the bar 6 to the tripping position. In Fig. 5, the strips 2 are fixed to a slidable bar 3b and engage fixed stops 5b at one end and at the other end, projections 6b on a bar 6<1> which is urged to the right by spring 8b. When sustained balanced overload occurs, the bar 3b engages stop 9 and further flexure moves 6<1> to the left to release a catch 12. In unbalance conditions, one strip straightens and moves 3b to the left so that the other strips move 6<1> to the left. In Fig. 7, the strips are fixed on a shaft 3c resting on stops 5c and levers 6c on a further shaft 6<2> are held on the strips by spring 8a anchored to a lever 12a. When heated, the strips flex downwards until an ambienttemperature compensating strip 2c engages stop 9, whereupon further fiexure raises levers 6c to free the trip member 12b. On unbalance, one strip remains straight and restrains movement of spindle 3c so that flexure of the others turns spindle 6<2>. In Fig. 8, U-shaped strips 2d straddling heater coils 4d are secured at one end to arms 3<1> on a rotatable shaft 3d which carries a compensating-strip 2<1> co-operating with the stop 9. The rotatable trip-shaft 6<3> carries arms 6d, between which and the stops 5d the other ends of the strips engage. The action is similar to that of the other forms. In Fig. 9 (not shown), the strips 2 are arranged radially about and fixed to a rotatable sleeve, the free ends co-operating, as in Fig. 8, with fixed stops and projections on a rotatable annular member which is concentric with the sleeve and carries a projection operating contacts as in Fig. 2. The Provisional Speciiications refer to Specification 439,242. The first Provisional Specification describes a switch forming the subject of Specification 498,376 and also refers to the provision of internal air spaces and cavities in the walls and partitions of the release-housing to improve its heatinsulating properties.