GB694623A - Improvements relating to automatic electric circuit breakers - Google Patents

Abstract

694,623. Automatic circuit-breakers; protective cut-out arrangements. LANDIS & GYR AKT.- GES. Nov. 29, 1951 [Dec. 4, 1950], No. 28063/51. Class 38 (v) In a circuit-breaker having a trip coil 7 for instantaneous tripping on very heavy overcurrents and a thermal trip 8 for tripping on smaller overloads of longer duration, a differential relay 9 causes tripping on the occurrence of a small earth leakage current by closing contacts 12 to energise a heater 13 which causes the thermal trip 8 to trip the circuit-breaker. The relay 9 also acts directly on an armature 15 to produce tripping of the circuit-breaker directly under severe earth-fault conditions. The circuit-breaker has main contacts 5, 6 normally held closed by an overset toggle 21 extending between levers 24, 28, which are pivoted at 23 and 27 and biased by springs 22 and 26 respectively. A bell-crank 19 is normally biased by a spring 17 against a stop 18, but under fault conditions is turned by armature 14 or 15 or the thermal device 8 to collapse the toggle 21. If the fault is a small earth leakage current, this collapsing of the toggle is effected by the unbalance of the currents in the coils 10, 11 of the relay 9 resulting in the movement of a light armature 30 to trip the contacts 12, which close, the heater 13 being energised to render the device 8 effective. On the collapse of the toggle 21, the lever 24 is turned about its axis by the spring 22 to open the contacts 5, 6 and, at the same time, to reset the armature 30 and contacts 12 by means of rods 35, 36. The relaxing of the pressure on the lever 28 by the toggle 21 enables a spring 39 to turn a manual operating member 29 to the off position. The spring 26 is now able to turn the lever 28 sufficiently to reset the toggle 21 so preparing the circuit-breaker for reclosure.