GB450012A - Improvements in and relating to electric circuit breakers - Google Patents

Abstract

450,012. Automatic circuit-breakers; snap-action switches.. BRITISH THOMSON-HOUSTON CO., Ltd., Crown House, Aldwych, London. Feb. 18, 1936, No. 4924. Convention date, Feb. 18, 1935. [Class 38 (v)] A circuit-breaker of the kind which is manually operable between on and off positions and is automatically opened in response to overload, has an operating mechanism for a movable switch member movable between open and closed position comprising an operating handle having a relatively short radius of movement about a fixed axis between on and off positions, an over-centre spring operatively connected at one end to the switch member, and means including a driving connection between the handle and the opposite end of the over-centre spring for moving the latter through an arc the radius of which is substantially greater than the radius of movement of the handle. The invention is shown applied to a breaker having arc-extinguishing means as described in Specification 420,042. The handle 16 is pivoted at 18 and slotted at 22 to receive a pin 21 which is carried by a pair of links 23, pivoted at 25, and supports one end of the dead-centre springs 19, 20. The other ends are supported on a pin 26 on a member comprising a pair of plates 28 connected by a strap 29 and pivoted at 18, Tn moving from the on position shown in Fig. 1, anticlockwise rotation of handle 16 carries the pin 21 overcentre past the pivot 18, whereupon the pin 26 takes the movable contact 13 to the off position. Just as the overcentre position is reached, the end of a slot 34 in each link 23, 24 engages the pin 26 and positively drives it, and a similar positive drive is imparted in the closing movement. The arrangement is stated to impose only a small strain on the operator, without reducing the closing force on the contacts. On overload, a series bimetal member 32 releases a trip member 30 which is pivoted at 18 and under the action of spring 31, strikes the part 29 to move contact 13 "off", Fig. 4. This action moves the handle to an intermediate position, and to reclose, the handle is moved down to full off position, whereby a part 40 thereon resets the member 30 and tensions spring 31, and is then restored to the Fig. 1 position to effect a rapid movement of the contact 13.